Great discussion. A few items you didn't mention: for prop clearance, pushers often just add blades and reduce diameter in order to gain ground clearance, and to prevent prop strikes during over-rotation. You alluded to frontal profile, but let me expand a bit: With a tractor design, you have a relatively tall engine (particularly if it's a traditional Lycoming/Continental with the induction on the bottom of the engine) which means the cowl must be tall in order to fit it. The pilot then needs to sit high and upright to provide visibility over the cowl. On a pusher with the engine mid-mounted or rear-mounted, the front of the aircraft can be quite slim, both vertically and horizontally. This means the pilot can be seated lower and reclined (like in a Long EZ, or as in my Cozy), which means less overall frontal profile, and less drag. Lastly, one of the big downsides to pushers that you didn't mention is FOD. If you are landing on an unimproved strip or on a runway with loose gravel, stones or any other foreign matter, your nosewheel can (and usually does) kick this up directly into the prop arc. This can cause serious damage to the prop. On a composite prop, smaller nicks can usually be repaired, aluminum props can be dressed if it's not too bad. Otherwise, you're looking at a prop replacement. On a constant speed prop like you are using, this could get extremely expensive in a hurry.
Another difficulty with conventional layout pusher is the lost weight needed to provide the drive shaft and increased structure to support it in torsion and vibration. I think when you are trying for light weight as hard as the DarkAero project that loss in weight efficiency is not trivial.
but you can also completely eliminate the need to reduce prop diameter, by placing the prop as close to the main gear as possible. Airco DH.2, SAAB 21, J7W, XP-55, Cessna O-2, and Long EZ are examples of this. And of course we cannot forget the Wright Flyer with its very large diameter props. But that doesn't alleviate the FOD issue in many pushers. Though not all pushers have the FOD issue either. Seabird Seeker, Aircam, Cessna O-2, and "The Prototype" being but a few examples.
For a student project for a long range aircraft we looked at pusher props because they ingest the boundary layer, reducing the pressure rise and thereby delaying the transition of the flow over the fuselage from laminar to turbulent. I dont remember the exact numbers but they seemed quite favorable. We were a bit worried about the added vibration loads on the blades. Reinforcing them would have reduced the benefits off course. I guess the range of the DarkAero is not enough to make a real difference.
I would add another factor. It seems like FOD prop damage is much more common with pushers. Rocks and debris are often kicked up by wheels, especially on the more civilian airstrips that small planes are commonly used. A pusher has a blade that is much more at risk of FOD. I agree...puller is an appreciably better solution for a civilian small plane.
Prop erosion, and nicks are challenging enough with 12” of clearance in a tractor configuration…. Having a prop with less clearance, will have you rushing the run-up procedure… Having the prop inline with a nose wheel… will lead to lots of dents and scratches on the prop’s leading edge… Props are expensive…. 😃
@@damnsong8675309 mudflaps for the takeoff and landing procedures, basically an added excuse to have an inline flap that doubles as guard for the propeller.
Tractor props are typically considerably quieter than pushers. Pusher blades chopping through the shear created by the wing lift create noise initially, and that also can cause vibration in the blades that tractor props would not be subject to.
Just like how wind turbines have the blade before the tower in a horizontal axis style turbine. If the blades were behind the tower, you wouldn't need a yaw gear, but your blade would flex every time it passes into the wake of the tower. This loading cycle is much worse for a high aspect ratio wing, like a wind turbine blade than for an airplane propeller. The propeller does spin considerably faster, though, so more cycles. Does anyone know whether props fail sooner for pusher configurations?
I have a strong feeling you could design unconventional Propellers to reduce the issue, and arrange the wings in a way it works, perhaps a lifting body aircraft. I may be able to draw something out of this
It was beyond scope here but I'm sure some sort of flow conditioner could be added to make the airflow more laminar and gain both efficiency and quieter props. But that would also add complexity and weight and I'm not sure how well it would work through the speed range.
I think the pusher configuration offers some interesting opportunities in terms of cabin configuration-- for example, you could install a ground-view window that could provide incredible scenic and filming opportunities (which definitely falls well outside the scope of DA1's stated design goals, but could be worth considering for a separate project). I really enjoy seeing just how meticulous everyone at DA has been when tackling these design challenges and walking us through the process, and as always, I'm looking forward to seeing more from your team! Great job, guys!
I think there are other advantages considering how the Learfan was based on this configuration and it was designed by an industry veteran, but it was a different application than this small aircraft. Maybe the propeller efficiency can be increased with some changes, the potential reduction in drag is much higher, the higher crusing speeds justified this design choice, ...
More Cargo Space? In military view, weapons like a cannon or laser can be carried? Radar can be carried like jets. For newer technologies like Active Flow Control, the cargo space can be used to carry the Piston Pump to provide the air to tank like the youtube NASA/DARPA X65...kind of redundant since the flight controls are cable.
While I've long thought that the prop wash from the forward mounted prop would create more drag over the airframe, I'd never considered that the airframe would reduce the efficiency of a rear mounted prop. This was a really interesting and well produced examination of both arrangements.
yup, propellers of all type really want clean air. this is a challenge with helicopters. But not all pushers are equal. some have little to no real interference to the prop disk (e.g. Aircam multiengine)
In my experience with R/C aircraft, which tend to have higher drag, a rear prop gives noticeably better efficiency but a lot more noise due to the disturbed air entering the prop disc.
For beginner RC craft, the pusher prop is much more protected in bad landings and when you hit obstructions like trees and such. Also, some small unmanned aircraft are catapault launched and retrieved by flying into a net. So it is better to keep the prop away from the front of the plane if you are going to "land" by flying into a net.
@@mckenziekeith7434 I like the single engine tractor arrangements found on the Polaris and Seawind, mounted high on the tail away from the fuselage. It isn't as noisy as a pusher as well as still being efficient, especially if there is adequate clearance between prop tips and fuse, however It can cause a downward pitching moment with any rapid throttle increase. Something not discussed is the ability of the traditional "tail dragger" tractor arrangement to reduce takeoff distance. Most high performance STOL aircraft use this arrangement in competitions.
Because smaller rudders required to vercome the p effect of the propeller so one is NOT wasting horse power turning the aircraft in the correct direction. Big advantage, in fact this is the LARGEST advantage compared to all the BS the host brought up, but then I would expect that as he does not know aerodynamics.
@@w8stral Why would a pusher configuration not suffer the same p effect? Because the air that has been moving over the aircraft is moving more in line with the pitch angle of the aircraft instead of the horizon? I am not sure how big that effect is, and I also wonder what happens when you enter a (partial) stall, which then also seriously disrupts the airflow into the propeller. I like pusher configurations, but I would probably mount it on the top of the fin, for minimum air disturbance and biggest ground clearance. But this position pushes the nose down, so you probably need to mount the propeller at an angle to counteract this (like the DC-10)
These guys research their stuff and listen to criticism. The Raptor guy thought he knew it all and got cranky if someone questioned his decisions. So he ended up in the cornfield due to his ego. His latest iteration of the Raptor was seen as a CAD render as an effin biplane several months ago but doesn't seem to have advanced any further!
This was going to be my question since this project started. Canard is much more efficient and safer and I'm sure these guys could out do the DarkAero One.
The "safety" of a canard aircraft comes from the fact that you are so afraid of a main wing stall, which is unrecoverable, that you engineer the canards to stall well before the main wing. This means your aircraft has a higher stall speed than it would have if you put the same wing on a traditional layout. The other issue is that because you've engineered the canard to stall before the main wing, adding flaps to the main wing doesn't reduce your stall speed because your stall speed is based on the canards rather than the main wing. A higher overall stall speed, which you then can't reduce with flaps, means a very fast approach speed (or you need to oversize your wing to give yourself enough lift for a slower stall speed). A fast approach speed means you need a very long runway to land, and you need to engineer your landing gear+brakes to handle higher speeds and more energy dissipation. Oh, and if you ever have to ditch you'll be ditching at higher speeds too. So much for safety. I too was on the "rutan is a genius with his weird looking planes" bandwagon until I read more about the downsides of the canard layout.
@@StephanAhonen You're correct on most of the points you make, I talk about all of those in the video I mentioned in my channel above, the "Why I bought this airplane" video - I go over the pros and cons of canard aircraft, and do go a bit into the weeds talking about aerodynamics. The stall speed is not high because of a "fear" of stalling the main wing, it's because it is impractical to put flaps on a canard (although it can be done - the Beech Starship had flaps, and a complex mechanism to make adjustments to the canard - again, I talk about that in my video). That said, the stall speed is not THAT high. The stall speed of my Cozy is 63 kts, which is pretty close to the 61 kt stall speed of a Lancair (with flaps down), an airplane with a comparable performance envelope. Runway length for canards for landing is not the limitation - it's takeoff. You need enough speed to get the canard to fly before you can rotate the main wing into lifting. That takes some runway. You will land a bit longer than a Cessna, but again - comparable to an equivalently performing aircraft like a Lancair.
@@StephanAhonen the safety of the standard aircraft comes from the fact that you are so afraid of a tail stall, which is unrecoverable, that you engineer the main wing to stall well before the tail.
I have a velocity, one other downfall of the pusher style is anything that comes off the airframe ends up going through the prop. Cowling screws, stones or rocks from a soft field or even a wrench resting on the wing when doing a dry run up……. Ask me how I know. 😂
Interesting discussion. You mentioned balance - with a tractor, you tend to keep the fuel tank and passenger payload close to the CG. With a pusher, you typically need to offset that weight in the back by moving other things forward. That puts limits on how changes in payload and potentially fuel weight affects your CG envelope. The big problem with canards is that flaps cause a large pitching moment when deployed due to the NP being further forward than a rear tail configuration. Most canards land without flaps - and fast. Although in a different class of aircraft, the Piaggio Avanti did a nice job of overcoming both of those compromises with a three-surface design and twin pusher engines behind the wings instead of behind the tail. It is one of the most efficient business class twin turbo prop planes ever built.
Most pushers also simply keep variable payload and fuel near the CG. Seabird Seeker, Aircam, Cessna O-2, SAAB 21, Wright flyer, and many more. Also, look how helicopters handle CG, as they have the same issue with the engines being in the back.
Great lesson on the trade offs in aircraft design and iterative process. Since constraints are universal, that’s why air planes end up looking quite similar and innovative designs are few and far in between.
I fly a quicksilver ultralight with a pusher prop that is mid-body. It's really nice not having to look through a prop, plus no possibility of a prop strike even on over-rotate, plus it gives the elevators and rudder huge authority with the prop blasting right onto them.
6:28 Something that some people don't know: The propeller also cools down the pilot. The pilot will often start sweating when the propeller stops spinning. Fr, great vid
There have been several forays into pusher props over the years. The B-36 Peacemaker, the Lear Fan, the Beech Starship, the Piaggio P-166 and the P-180. The B-36 initially had problems with engine cooling. The Lear Fan was only test flown but never went into production. The P-166 was the piston-powered ancestor of the Turboprop P-180. The Starship was considered a loser business deal and Raytheon stopped making parts for it. Pushers sound like a logical idea. They look sleek and sexy. But some of them come with very real issues. On takeoff, if you rotate too quickly, there’s a chance you’re going to get a prop strike. And on landings, you can’t have the nose too high for the same reason. Landings are a real consideration because we typically have a higher nose-up attitude to stall just before touchdown. The Piaggio P-180 is a really sleek looking aircraft and it absolutely is. It’s a head-turner on any ramp even from the jet folks. It’s the fastest production turboprop in the world. But it’s a turboprop. Yes, it uses a variant of the PT-6 engine but it needs all its own parts. If you own a King Air, access to parts is a breeze because King Airs are operated all over the world. The P-180? Not so much. The home-built market has really outpaced the "Big" companies in terms of cost and that has allowed developers to play around more with the pusher concept and there are a couple of companies that make pushers. So overall, pushers are a fascinating idea but they come at a price.
A pusher configuration was used for the Edgley Optica - which provided a good observation platform. But the rear engine configuration and ducted fan was complicated.
when the bd came out the wife said no way no chance now she's long gone and in my shop under construction a carbon fiber BD5 with a zero radar return(the American inventor also invented me ) power ....a m8 Harley Davidson motor twin plug no shake programable in flight ejection, turbo ,and its being rebuilt to about 400 hp.. hey at my age..nursing home suck any way ! @@NeroontheGoon
Love your tutorial videos! Please keep them coming. I'm hoping you guys will expand your planes to include a 4-6-seat plane. Maybe a dual-engine canard-style pusher airplane that is powered by the new Deltahawk? I know some of you will say there is such a plane in the Velocity Twin, but that plane is a dated design made of fiberglass. I'm sure these Darkaero guys would come up with something amazing!
This was an excellent overview of two common propulsion designs! Loved it. I used to live near the final approach of a regional airport. There was a rear-engine style similar to the Gyroflug SC 01 Speed Canard that would sometimes overfly. That thing was incredibly loud and annoying pitch of sound too. I hated the sound, but it did look very cool. The noise was incredibly bad, and it was on final approach at probably 1/2-throttle at most. I hate to be on the other end of this airport where such a craft was taking off at 100% throttle! I would love a follow-up video that describes *twin-engine* modes of puller and pusher propellers. Because my personal fav propeller style planes the twin engine pullers like the classic Cessna 310 series. Given what was stated in the video at 3:55, the twin pullers will have reduced airframe drag since the engine are situated outboard and only cover the thin profiles of the wings. So, a twin-engine pusher would also have outboard motors so may benefit from decreased dirty air and maybe get better thrust and reduced noise too?
Great video. I haven't been around aircraft in over 30 years since school. I never received my A&P, I changed fields. I guess I had a great instructor, because everything came back while you were talking. I even anticipated several potential problems. :)
Just thought of a cool idea. What about keeping the engine up front and run a shaft to the rear for a pusher? That would maintain the cooling challenge and ease of access to the engine. A F86/mig15 look would be awesome!
There's an additional problem aside from added weight and complexity. The P-39 was a midengined tractor aircraft, similar to what you're proposing. The driveshaft had to be lengthened, and the additional forces that came with that length meant that a quick enough power increase would actually break it.
I would guess that for a tractor, the shaft needs to be as short as possible, especially with low blade loading. The 6 cylinders should be close together ( water cooled ) and almost stick into the propeller hub. Then again a modern aluminum engine block isn’t that heavy. Inline six in the front. Two pilots . No fat clutch or gears. Just a “divider” between both pilots. Upright engine, not slant. Might be interesting. Not so great for visibility and collides with the nose gear. No flat firewall.
I would love it if these guys did a thorough analysis of the celera 500l or the long forgotten synergy aircraft. The way they explain complex equations with ball park figures is amazing.
Easygoing, well researched, and it’s evident the presenter really likes the topic. Plus a nod to the cool factor, which surely is what’s really on everyone’s mind. One question-is there a difference in noise between the arrangements?
Excellent analysis and consideration of the multiple tradeoffs. I do like pushers partly because of the better visibility, though as you mentioned, efficiency is about equal overall. People often point to the Cessna 337 as proof of the pusher configuration's higher efficiency, because the climb performance and maybe cruise speed is a little higher with only the rear engine running, versus only the front engine running. But the airframe shape may be directing more air to the rear prop than some other pusher configurations might experience.
I was going to make the same observation. The reason for this behaviour is that air accelerates as it is drawn towards the prop, and accelerating flow is more stable. That might be particularly important for the 337 layout as the rear end is pretty blunt.
The 500l does efficiency to the nth degree. If you're going for full laminar flow pusher is the only option. The way it is implemented on the 500l though, there's no improved visibility lol!
I had to give a chuffing laugh when I saw the Mini-IMP listed on your white board under pushers. After I got my A&P I purchased a set of plans for a Mini-Imp (many years ago when they were still available) and over a three year period got about +-80% done. It actually was a pretty cool design and the cockpit was quite comfortable. If you ever look at the plane, not how the landing gear wheels fit up into the wing (and was part of the air intake system) but folded down and gave pretty good ground clearance. Talking about problems, one of which ended the project: accessing the engine was a nightmare, I had the cog belt reduction system manufactured twice and it wasn't made right either time but the killer was the torsional resonance of the long hollow drive shaft. The tail cone of the design just wasn't stiff enough to handle it. I could have reinforced the tail cone and added (considerable) weight in the nose to get the right CG but then the gross weight was becoming problematic because I'm a big guy and was already at the planes limits. Who wants to go flying with only half a tank of gas to not exceed the weight limit. I tried a 3" diameter drive shaft, then a 3.75 and finally a 4" which aaaaallllmmost tamed the resonance but just not enough to be feeling safe. I stored the plane for years then gave it to a old guy who wanted to try to see what he could do with it. I wasn't rich enough or smart enough to solve the problems. I suspect that's why there aren't more of them flying. PS - I also bought into Jim Bede's fantasy and bought a set of BD-5 plans, even built the wings before the lack of a suitable engine killed that plane (certainly didn't have the money for a turbine like the Coors jet, haha)
Could you expand on the problem with the drive shaft/tailcone please? I would have expected all the propeller torque and any torsional vibration to be isolated from the tail cone via the thrust bearing --was it a case of tailshaft whipping or out of balance and how did it manifest (presumably during ground running --was there any 'ground resonance' via the landing gear springing involved possibly ? ( I just lost a longer post by hitting the wrong button ..#**&# -- I have had a lifelong interest in the tailpusher concept including designing building my own design "Opal" starting in 1975 - worked for Dick Schreder on sailplane design in 1974 and met Molt then (at Oshkosh) ,corresponded and went over to see him in 1990 etc etc -also met EdLesher and Jim Bede then and attended their forums . Maybe 'compare notes' on shaft drive issues etc ? I had thought that the flexidyne was a pretty good damping solution and it worked for Ed Lesher on the Teal and Nomad apparently but admittedly has not led to any significant uptake of the pusher configuration ... curious as to your experience to say the least.. (working on a current roadable using, notionally ,the flexidyne 'solution')
@@rossnolan7283 at the time of my build, flexidyne couplings were restricted because they freaked out that they were being used in aircraft and they thought it would expose them to massive liabilities. So they were only selling to established businesses. I tried going through / ordering from a couple of pump companies to acquire one but there were too many hoops to jump through. So I tried to use Gates cog (toothed) belts in a 1:1 drive to isolate the power pulses. Same 3" wide belt used to drive Roots blowers on race cars, I just used 2 on 6" toothed pulleys. It was a long time ago, late 90's and honesty I've forgotten a lot details of what I tried.
It would be very easy (and understandable) for a set of people so focused on performance and spend so much effort on meticulous engineering to disregard something like "cool factor" out of hand. Very nice that you considered that in your final comparison!
In a tractor configuration are the vibrations on the frame caused by the disturbace of air by the prop, not more ? Does a pusher not give a smoother ride? I was also told that a tractor configuration has more precise steering features ? Your view?
Great video and lots of other good considerations mentioned in the comments, particularly FOD and noise being big problems for pushers. Another important factor that I did not see mentioned was short field performance. Pushers take a lot longer to get off the runway due to the lack of prop wash making the tail surfaces effective at slower speeds. Also, you talked about forward engine placement with long prop shafts to the tail, like the BD-5 or VK-30. An issue here tends to be torsional vibrations in the prop shafts, usually requiring some kind of flex coupling, which adds weight and is another maintenance item.
I am grateful for this excellent explanation and comparison of plane designs. I love the clean drawings and the filtered explanations of many topics. I think both design are relatively close in performance (oddly in model airplanes the pusher seem to be slightly more efficient/ faster) but this plane is well conceived. Also you can design the rear as a T tail pusher to avoid the turbulent air ( I know its not ideal but at least a way around the standard configuration.)
If you wanted max efficiency, you could do like the Sunseeker Duo which puts the engine (actually, motor) at the front of the top of the T-tail empennage where you ingest clean air but don't dump disturbed air over the fuselage, just a portion of the tail. (It's also a sailplane, so the propeller folds in gliding/soaring flight so doesn't even disturb the tail during much of the flight). Sunseeker Duo: ua-cam.com/video/uBA4XeMddMY/v-deo.html
That can have issues in high angle of attack flight in possibly deep stalling with challenging recovery. But, has been done, and possibly airplane parachutes are a good fix for deep stall crew survivability.
Interesting, as a layman I've always wondered why we don't see pushers with a heat exhaust ducted similar to a center-mounted cannon in WW2 fighters to keep the turbulences on the blades to a minimum.
That's why I like the Cessna 337, you don't have to decide, it has both a pusher engine , and a puller prop in a centerline thrust configuration, and the weight of the engines at both ends makes the CG equation easier. The added bonus is you have a second engine if one fails. Only downside is two engine maintenance and fuel burn rates.
*The German 'Dornier Do 335 Pfeil' PULLER and PUSHER had an experimental design element that connected the front and rear proppeller with a long drive shaft. It could take off with the front prop only and during flight a clutch could transfer all the power to the rear prop. The rear prop folded flat until it was engaged and the props opened up.*
I was wondering what putting a rear prop did to the directional stability of the plane. If I pull a suitcase on wheels behind me, it follows and corrects any deviation; but if I push it, it's unstable and tends to go off to the side, or even fall over, and requires constant correction. On the other hand, shopping trolleys/carts can be pushed from the back without problems.
Great vid - I'm tossing around a canard concept with a forward-swept wing with the trailing edge 2' forward of the first disc of a contra-rotating setup. NACA research says sufficient separation smooths out the airflow for the prop. It means the engine is ahead of the wing, but I'm using a liquid-cooled engine for it. I need to build a wind tunnel to test the design.
This was a really cool video. I know its a fictional plane, but the Sanka mk b has made me obsessed with pusher props for the last 10 or so years. The canard and wing design along with the contra rotating propellers just look awesome to me
Isn't the flow disturbance argument valid for ship hulls as well? Then wouldn't putting the propeller in front of the ship a more efficient option than the conventional pusher?????????
Inspired by the Dornier fighter, how about a plane with TWO props, one pusher and one puller. Front mounted engine drives both props. Rear prop spins opposite the front (due to an offset gear). Stable since torque is balanced out. Cooling is normal. Only thing is to have an engine with enough horsepower to power both props. Maybe if the rear prop is up high it would avoid some of the turbulence and at the same time some of the tail clearance issues.
Anyone seriously interested in this should be buying Raymer’s “Aircraft Design - A conceptual approach”, if you want a brief introduction his “Simplified airfield design for Homebuilders”. But actually having this theory to application example worked out and explained by the Dark Aero team is immensely helpful in understanding it all.
Hi, DarkAero. Thank you for an informative video. clear and concise and easy to understand. Much appreciated. I'm no aeronautics engineer, 'justa pore, dumm bulldozer op'rator', but I do have some 'kwestyuns' if you wouldn't mind answering them. 1. The Pilatus Porter - when they switched over to a turbo-prop engine, they had to lengthen the nose by quite a bit to maintain trim due the lighter engine but it also resulted in a longer, sleeker nose - which leaves me wondering if placing the engine a little further back and running a drive shaft to a puller prop could also give a more streamlined shape, maybe with vents to trap cooling air for the engine? Again, it would likely need some modifications to cater for trim. 2. I am wondering if there is any real advantage - or disadvantage - to placing the engine and propeller on a pylon above and behind the cockpit in either a puller or pusher configuration? I suspect that this might mean some changes to other aspects of the aircraft, including the landing gear and I seem to remember seeing small aircraft with this configuration so I am really just wondering about the pros and cons of it. 3. There was some talk a couple of years ago of 'unstallable' wings that were made up of multiple aerofoil shaped 'mini-wings' placed in banks layered backwards from front to rear at varying pitches. You can find videos of them here on You Tube - I would post the links but You Tube doesn't seem to like that any more. Have you had anything to do with them and, if so, what is your take on them? Thanks again. Just my 0.02. You have a wonderful day. Best wishes. Deas Plant.
An additional affect not mentioned is the wing lift generated by a puller, which may offset some percentage of the drag. The angle of attack of the outboard wing can be slightly lower. On the other hand, another possibility is to have a twin boom with T tail for the pusher.
A pusher like the Aircam or Seabird Seeker is a really good design. all payload, fuel, and engine is right near the wing. Ground clearance not an issue. helicopter visibility. And can even have trigear or tailwheel. Even still get airflow over the tail for low speed tail authority, but no fuselage nor wing drag. But a twin like the Aircam can have minimal drop in prop efficiency since not all of the airflow is disturbed, much remains laminar. But a twin tractor also has the benefits of much reduced airframe drag due to propwash, while giving additional lift to the wings, while still getting improved visibility, ground clearance, ease of access to teh engines, etc. lots of tradeoffs.
very interesting! regarding airframe efficiency, what was the reason for choosing a conventional tail and not a T-tail used by very high performance gliders? this would also decrease prop wash on the elevator for the pull configuration.
As an engineer I like to see how your thought process is, I like that you compare different options. I guess that the only way to know for sure whether the pusher or the puller configuration is the most efficient in your case is to try both, fluid dynamics is one of the most contra intuitive fields of physics and can yield some unexpected results.
10:00 you can also shift the main landing gear closer to the prop, so that the point of rotation is so close to the prop it never really changes height over the ground, completely eliminating the issue. And you can do this with more designs than just canards or flying wings too.
The tradeoff is that this increases the length of runway needed for takeoff. The rear landing gear is usually located just aft of the aircraft CG in worst-case loading to allow easy rotation, producing a significant angle of attack increase, finally increasing lift at a lower takeoff speed.
@@tomthoe placement of the main landing gear has little to do with takeoff distance, unless you screwed up the design. But you can screw up the design of any configuration in the same way. there is no significant angle of attack increase. For a given design, the stalling speed AOA does not change due to the location of the landing gear. The issue here, is you don't understand aircraft design well enough to understand my comment, nor how to design an airplane properly to do as I described. The example you're trying to give is a garbage design, and also lacks creativity. I claimed, accurately and truthfully, that it can be done if designed properly (in more than one way and configuration as well). You tried badly to refute that by citing a terrible design, as if that refutes my claims about a proper design.
@@SoloRenegade Interesting. Can you help me understand what mechanism you would use to increase lift to reduce the required takeoff roll for the minimum weight penalty?
@@tomthoe no need to increase the takeoff roll at all. Explain why you believe the takeoff roll need to increase? And then I can tell you how to fix it. Why do you need to increase lift? there is no weight penalty for a properly designed airplane. Explain where the extra weight came from in your crappy design.
@@SoloRenegade I see that you did not fully read my comment and that you see no negative consequences with shifting the rear wheels away from the CG. Can you help me understand why all pusher prop designs have the rear wheels located just aft of the CG?
Hello. A bit off topic to this latest video, however: You May wish to consider a fore and aft jig system, where you can rotate the aircraft for most efficient mechanical work / painting / installation, etc. There are automotive engine rotating stands… you guys can figure it out. Thanks for your videos! You give many of us enthusiasm for your continued successes 👍.
With prop efficiency decreasing due to airflow issues forward or aft of the aircraft, would you just need to consider propeller length and pitch to regain your efficiency ?
Is that a 6 cylinder I/O Lycoming powerplant? I used to work on those things. What's the displacement? 540? 560? Exhaust and baffling...hated every minute trying to take that stuff off. Every stud holding the exhaust to the cylinder was rusted to the core and the baffling... I needed a special Philips screw bit to get enough grip to back the screws out. Normal Philips screwdrivers/bits would just start rounding out the screw heads. Other than that, they were great to take apart. I don't think the big 6 cylinders had this problem but the smaller 4 bangers had a problem with the oil sump gasket getting pulled inward during start-up. It would happen at the back of the sump, right in the middle (where the case halves came together). Owners would put these little "dimples" or tiny shallow holes (I guess, I'm not describing it too good). What this would do is add grip to the metal by raising the metal around the tiny holes by something like ten thousandths of an inch (the sump only, they wouldn't do the same to the case halves). 4-5 holes to the left of center and the same for right of center. Talk to your engine mechanic, he might be able to describe (maybe even show you an example) better what I'm trying to convey thru text.
I would have a view from building a fairly light weight single engine plane. My thinking is to put a pusher prop up on a "pod" above the fuselage, or at the top of the (reinforced) rudder. An idea also just came to me to make this engine electric. However, it would be powered a typical engine running a (small/compact) generator. This arrangement gives flexibility to where the weight of the propulsion system is located. Particularly the prop, which could be placed in clear air above the (rear of the) fuselage. The motor/generator combination could be placed in the nose to make maintenance easier. The electrical wiring to the electric propeller motor would be easy to route, unlike a pusher prop driven by some long drive shaft.
The SAAB J-21 pusher prop fighter, the only one ever mass produced and in prolonged service, was less maneuverable than nose driven types, despitd a larger wing and lower wing loading.
Another consideration is safety in a crash scenario. With the engine and prop in front, the mass of the engine absorbs some of the impact forces, whereas with it at the rear, the tendency is that you will need to insure that the engine cannot come loose and move forward in the event of a crash. In event of a crash with the engine at the rear, there is a greater likelihood that fuel lines will be severed, and increased risk of fire inside the cabin, in my opinion.
"In event of a crash with the engine at the rear, there is a greater likelihood that fuel lines will be severed, and increased risk of fire inside the cabin," this is baseless. it is wholly dependent upon where the fuel is located, even in a tractor, and where the fuel lines are run. If the engine never impacts the ground, how exactly are the fuel lines magically severed? Also, even helicopters like the OH-6/MD-500 are famously crash resistant with the engine in the rear. Airlines and corporate jets also do well as pushers. how does the Aircam result in fuel in the cockpit, or engine hitting the pilot? A great many ultralights have been pushers, and rarely are pilots killed by the engine/prop specifically upon crashing.
Formula 1 race cars crash into brick walls at over 200mph with the engine in the rear, and the engine has never come through the cockpit. engines are TERRIBLE crumple zones.
@@SoloRenegade F1 cars also don't have to worry about not getting off the runway because they burned too much weight budget making the driver tub. And of course they don't crash into brick walls, but energy dissipation walls and the relative speed between the car and the wall is more like 40 mph because of the angles. Maybe we should compare hydrofoil boats to airplanes next.
Actually the MOST efficient is to have both pusher and tractor pulling propellers together. Better known as centerline thrust. A great example of this concept was Nazi Germany's Dornier Do 335 Pfiel (Arrow) aircraft, which was Germany's fastest piston powered fighter plane of WWII. The concept is also utilized in the Cessna 337 Skymaster and the militarized Cessna 02 Skymaster. The idea actually cancels out propeller torque, thus increasing efficency. Its been proven to work quite well. Its possible to have one engine power both propellers utilizing driveshafts and gearboxes.
Yes the dornier was an awesome designs super fast but they had problems with the engine over heating on the rear engine and also needed super tall landing gear to have clearance for that huge rear prop. I also found the skymaster very interesting but apparently it wasn't quite as fast as a standard twin setup probably due to the wing configuration . The maintenance was more expensive, and had a noisier cockpit. But the cool Factor outweighs it's deficiencies.
I thought of this too. One engine driving both props. I guess if that's too much load you could reduce prop pitch or surface area so the engine isn't overloaded. The main advantage would be the balanced torque. Another might be to reverse the pitch of the rear prop on landing so the thing would stop on a dime.
I learned something today. That is a good day. Thank you! What about the engine above the cabin or midway the fuselage? The center of gravity, drag and prop efficiency would be optimized?
What is it about the design of UAVs that makes the pusher configuration much preferred? Is it just a simple matter of wanting to remove obstructions from the front mounted camera and sensors?
Just from a few model airplanes in my childhood - If the prop is at the back, it would be more agile, but energy would be wasted in level flight maintaining attitude. If the prop pulls the fuselage along, it's slower to respond, but with much better control.
Another thing to consider safety for people around the airplane, most people are used to the idea of a prop being at the front, if you put one at the rear that's going against that convention, which I can see as perhaps being more hazardous, since people are used to approaching from the sides and rear of the plane.
I like the approach of your team into the development of this project, I have a feeling that behind your project there is someone with a very very mature work ethic and state of mind, no hurries at all but a firm and steady pase. Congratulations you will go far!!
A nice thorough analysis, but I'd add another factor against the pusjher; the prop shaft. It adds weight, although I sippose a carbon-fibre tube might not weigh much. In addition, it has to be very carefully balanced and not have any flexibility or resonance frequencies with anything in the airframe. Generally solvable problems, but potential unnecessary development effort.
This was very insightful. I'm curious how propeller position influences handling - does one have better responsiveness / manoeuvrability? The analogy with cars is that rear wheel driving cars have more traction during acceleration, sharper steering feel, and more balanced handling. While front wheel drive cars have a numb steering feel but are less prone to oversteer (safer).
so well explained. im sure there must be more to it but it feels like ive really learned something lol. what do you think about planes that have both pusher and puller proppellers like the do 335? id love to hear your thoughts on that!
This is very interesting. Your airflow disturbance visual got me thinking about jet intakes, which I know are not relevant with this specific aircraft by DA. However, how would you go about estimating the lift lost due to dual intakes placed on the bottom of a wing? Wouldn't the effective area of the wing creating lift be decreased by the sections where the intakes are placed?
How would a pod (tractor or pusher) above the fuselage change efficiency and drag? It would seem like you could reduce drag with a smaller nose section and get smoother air flow over the wings. Dual (smaller) pushers on the wing would also seem a good alternative and maybe add to safety.
Excellent video. My comment is outside of the scope of your discussion, and is not criticism. I prefer tractors. This is one of the reasons: Using your two example planes, the length of the fuselage would have to change for the pusher. You would have to lengthen the fuselage forward of the wing to regain proper CG. This shortens the relative distance between the wing and the tail. This, in turn, reduces the effectiveness (Moment arm/leverage) of the elevator and rudder, and can make the aircraft less stable in pitch and yaw. A larger tail would be required. An extreme example of this is the modern fighter with a long nose and the tail very close to the wing. These are incapable of maintaining stability without computers flying the aircraft for you. (Also notice how large the tails are on these aircraft)
So taking what I just learned, the best arrangement would be twin puller motors located at the wingtips. Clean air makes for high efficiency and considerably less airframe is exposed to prop wash minimizing drag. I suppose there "might" be some other factors involved. :)
Nice Video, comments below. 1 Ducted Fans and Propellers are more efficient and easily accomplished with a pusher. 2 Integrated Tail Control Surface/ Ducted Fan / Stator Blades work best in front of the Propeller. 3 Using Engine Cooling to deliver more Waste Heat Thrust is easier to accomplish with a pusher.
Probably impossible to figure but which configuration does better when 1) engine shuts down, meaning the glide capability, 2) survivability of the passengers in a crash, 3) and closely related, which config does better in a water landing, meaning when ditching the aircraft à la Sullenberger?
My understanding, from before watching the video, is that pushing can cause a feedback loop of nose up/down, where as the front propeller is a negative feedback loop, dampening the pitch.
hey there i dont know s... about engendering that go in airplanes but a question if you have " problems with visibility on a tractor configuration can you have one -3 cameras in the nose to mitigate the lack of visibility ...am assuming you have a display in cokpit this days you can use for that
Look at the 2023 race results at Oshkosh. In the respective engine category, canards blew everyone else, followed by a Whitman tailwind (70 year old design) and then the RV's.
This is a very good analysis and summary of the important points. But the 'conclusion' is almost all based on the reduced efficiency of the pusher in the disturbed air of the airframe. Would have liked to see some discussion on when the reduced prop efficiency is less than the reduced airframe efficiency ... AR, speed, parasitic fuselage drag etc
I have questions on the number of blades and drag. If you have a smaller diameter prop with more blades does that reduce the amount of wing exposed to disturbed air? Would this have a benefit to drag, or would the more frequent pulses of disturbed air increase drag?
On the "Dark-Air-One" -- _or any other "puller-prop" style airplane_ -- Could the wing portion closest to the fuselage, and in the direct wake of the propeller, be "skeletonized" to reduce the effects? The airplane might look ridiculous, but the loss of lift from "skeletonizing" that portion of the wing, might be outweighed by the lost of turbulent drag.
Is there any chance DarkAero can be flown first as a remote-control aircraft, before putting a pilot in it? You've got the actuators for autopilot, are those good enough to take off and land? Spin recovery?
Propeller efficiency is decreased by a pusher arrangement sure but the net thrust of a pusher would arguably be higher? A a portion of the airflow behind the propeller for a puller encounters the nose of the fuselage pushing back against the airflow decreasing thrust efficiency. A pusher configuration does not encounter this issue, did you take that into consideration when you say "propeller efficiency"? I'm busy designing a flying wing and this was one of the reasons i went with a pusher design, i think the main reason people go with a pulling design it is much easier to balance the CG rather than the prop efficiency and i'm sure that was more important in your decision?
If the airframe was designed to create a high pressure zone around the prop (in a rear prop design) would the increased engagement with the air (able to push off it more if there's more of it) positively counteract the negative effects of turbulence? Suppose (more unreasonably) you had a design that increased air pressure while maintaining laminar flow (does that apply to gas? I know it does to liquid...) then I'm sure the mentioned effect would be observed, but as you vary the disturbance and pressure you should be able to reach a point where efficiency benefits from the effects of the air on rear prop placement. The real question is whether these modifications would increase weight too much or be too impractical to implement and cause it all to be inconsequential.
Do pullers have an advantage during low speed as it forces more air over the body (even if it is unstable air)? How do landing, take off, or near stall behavior differ between the two models.
A lot of comments about noise, which is important. Not that its a huge general aviation problem, but a pusher would reduce the likelihood if flicker vertigo (not looking through the propeller). I haven't seen anyone discuss in the comments, so I thought I'd bring it up.
How about a design with the engine on top of the airframe behind the canapé with a push prop? The same idea as with these old flying boats. The airframe can have a double tail. Interesting vid guys! Keep on going the good stuff.
Great discussion. A few items you didn't mention: for prop clearance, pushers often just add blades and reduce diameter in order to gain ground clearance, and to prevent prop strikes during over-rotation.
You alluded to frontal profile, but let me expand a bit: With a tractor design, you have a relatively tall engine (particularly if it's a traditional Lycoming/Continental with the induction on the bottom of the engine) which means the cowl must be tall in order to fit it. The pilot then needs to sit high and upright to provide visibility over the cowl. On a pusher with the engine mid-mounted or rear-mounted, the front of the aircraft can be quite slim, both vertically and horizontally. This means the pilot can be seated lower and reclined (like in a Long EZ, or as in my Cozy), which means less overall frontal profile, and less drag.
Lastly, one of the big downsides to pushers that you didn't mention is FOD. If you are landing on an unimproved strip or on a runway with loose gravel, stones or any other foreign matter, your nosewheel can (and usually does) kick this up directly into the prop arc. This can cause serious damage to the prop. On a composite prop, smaller nicks can usually be repaired, aluminum props can be dressed if it's not too bad. Otherwise, you're looking at a prop replacement. On a constant speed prop like you are using, this could get extremely expensive in a hurry.
The tradeoff with decreasing diameter is decreased prop efficiency, but your other points are excellent reasons to consider both options.
Another difficulty with conventional layout pusher is the lost weight needed to provide the drive shaft and increased structure to support it in torsion and vibration. I think when you are trying for light weight as hard as the DarkAero project that loss in weight efficiency is not trivial.
but you can also completely eliminate the need to reduce prop diameter, by placing the prop as close to the main gear as possible. Airco DH.2, SAAB 21, J7W, XP-55, Cessna O-2, and Long EZ are examples of this. And of course we cannot forget the Wright Flyer with its very large diameter props.
But that doesn't alleviate the FOD issue in many pushers. Though not all pushers have the FOD issue either. Seabird Seeker, Aircam, Cessna O-2, and "The Prototype" being but a few examples.
And of course, a lot of this changes when you look at twin-engine canards.
For a student project for a long range aircraft we looked at pusher props because they ingest the boundary layer, reducing the pressure rise and thereby delaying the transition of the flow over the fuselage from laminar to turbulent. I dont remember the exact numbers but they seemed quite favorable. We were a bit worried about the added vibration loads on the blades. Reinforcing them would have reduced the benefits off course.
I guess the range of the DarkAero is not enough to make a real difference.
I would add another factor. It seems like FOD prop damage is much more common with pushers. Rocks and debris are often kicked up by wheels, especially on the more civilian airstrips that small planes are commonly used. A pusher has a blade that is much more at risk of FOD. I agree...puller is an appreciably better solution for a civilian small plane.
Prop erosion, and nicks are challenging enough with 12” of clearance in a tractor configuration….
Having a prop with less clearance, will have you rushing the run-up procedure…
Having the prop inline with a nose wheel… will lead to lots of dents and scratches on the prop’s leading edge…
Props are expensive…. 😃
Not all pushers have the FOD issue though either. Seabird Seeker, Aircam, Cessna O-2, and "The Prototype" being but a few examples.
Just add some mud flaps with metal silhouettes of naked ladies! Style AND functionality!
@@damnsong8675309 mudflaps for the takeoff and landing procedures, basically an added excuse to have an inline flap that doubles as guard for the propeller.
You can build a extendable shield to protect the prop during take off and landing
Tractor props are typically considerably quieter than pushers. Pusher blades chopping through the shear created by the wing lift create noise initially, and that also can cause vibration in the blades that tractor props would not be subject to.
Just like how wind turbines have the blade before the tower in a horizontal axis style turbine. If the blades were behind the tower, you wouldn't need a yaw gear, but your blade would flex every time it passes into the wake of the tower. This loading cycle is much worse for a high aspect ratio wing, like a wind turbine blade than for an airplane propeller. The propeller does spin considerably faster, though, so more cycles. Does anyone know whether props fail sooner for pusher configurations?
The twin beam Bayraktar TB2 drone is a good example of a pusher with a non interfering tail and Rotax 912.
I have a strong feeling you could design unconventional Propellers to reduce the issue, and arrange the wings in a way it works, perhaps a lifting body aircraft. I may be able to draw something out of this
It was beyond scope here but I'm sure some sort of flow conditioner could be added to make the airflow more laminar and gain both efficiency and quieter props. But that would also add complexity and weight and I'm not sure how well it would work through the speed range.
Prop at the front also gives you more stick authority and lower stall speed. The air goes over the wings and control sufaces.
a huge factor
Seabird Seeker
Chinook PLUS 2
Challanger II
Sky Arrow 600
Cessna O-2
.....
All have airflow over the tail.
I think the pusher configuration offers some interesting opportunities in terms of cabin configuration-- for example, you could install a ground-view window that could provide incredible scenic and filming opportunities (which definitely falls well outside the scope of DA1's stated design goals, but could be worth considering for a separate project). I really enjoy seeing just how meticulous everyone at DA has been when tackling these design challenges and walking us through the process, and as always, I'm looking forward to seeing more from your team! Great job, guys!
I think there are other advantages considering how the Learfan was based on this configuration and it was designed by an industry veteran, but it was a different application than this small aircraft. Maybe the propeller efficiency can be increased with some changes, the potential reduction in drag is much higher, the higher crusing speeds justified this design choice, ...
This is fantastic idea.
More Cargo Space? In military view, weapons like a cannon or laser can be carried? Radar can be carried like jets. For newer technologies like Active Flow Control, the cargo space can be used to carry the Piston Pump to provide the air to tank like the youtube NASA/DARPA X65...kind of redundant since the flight controls are cable.
While I've long thought that the prop wash from the forward mounted prop would create more drag over the airframe, I'd never considered that the airframe would reduce the efficiency of a rear mounted prop. This was a really interesting and well produced examination of both arrangements.
yup, propellers of all type really want clean air. this is a challenge with helicopters. But not all pushers are equal. some have little to no real interference to the prop disk (e.g. Aircam multiengine)
In my experience with R/C aircraft, which tend to have higher drag, a rear prop gives noticeably better efficiency but a lot more noise due to the disturbed air entering the prop disc.
For beginner RC craft, the pusher prop is much more protected in bad landings and when you hit obstructions like trees and such. Also, some small unmanned aircraft are catapault launched and retrieved by flying into a net. So it is better to keep the prop away from the front of the plane if you are going to "land" by flying into a net.
@@mckenziekeith7434 I like the single engine tractor arrangements found on the Polaris and Seawind, mounted high on the tail away from the fuselage. It isn't as noisy as a pusher as well as still being efficient, especially if there is adequate clearance between prop tips and fuse, however It can cause a downward pitching moment with any rapid throttle increase.
Something not discussed is the ability of the traditional "tail dragger" tractor arrangement to reduce takeoff distance. Most high performance STOL aircraft use this arrangement in competitions.
Noise is synonymous of power loss, as noise is a result of energy loss.
Because smaller rudders required to vercome the p effect of the propeller so one is NOT wasting horse power turning the aircraft in the correct direction. Big advantage, in fact this is the LARGEST advantage compared to all the BS the host brought up, but then I would expect that as he does not know aerodynamics.
@@w8stral Why would a pusher configuration not suffer the same p effect? Because the air that has been moving over the aircraft is moving more in line with the pitch angle of the aircraft instead of the horizon? I am not sure how big that effect is, and I also wonder what happens when you enter a (partial) stall, which then also seriously disrupts the airflow into the propeller.
I like pusher configurations, but I would probably mount it on the top of the fin, for minimum air disturbance and biggest ground clearance. But this position pushes the nose down, so you probably need to mount the propeller at an angle to counteract this (like the DC-10)
This channel is everything that the Raptor development channel wasn’t.
Probably this plana will fly
@@bernhardjordan9200 The Raptor flew...
@@flexairz "The Raptor flew..."
Into that cornfield.
I used to like the guy’s enthusiasm until he lost it…
These guys research their stuff and listen to criticism. The Raptor guy thought he knew it all and got cranky if someone questioned his decisions. So he ended up in the cornfield due to his ego. His latest iteration of the Raptor was seen as a CAD render as an effin biplane several months ago but doesn't seem to have advanced any further!
A video about canards and the reasons you chose not to use one would be very interesting.
Have a look at my channel, I have a video about canards and why I DID choose one (both pros and cons).
This was going to be my question since this project started. Canard is much more efficient and safer and I'm sure these guys could out do the DarkAero One.
The "safety" of a canard aircraft comes from the fact that you are so afraid of a main wing stall, which is unrecoverable, that you engineer the canards to stall well before the main wing. This means your aircraft has a higher stall speed than it would have if you put the same wing on a traditional layout.
The other issue is that because you've engineered the canard to stall before the main wing, adding flaps to the main wing doesn't reduce your stall speed because your stall speed is based on the canards rather than the main wing.
A higher overall stall speed, which you then can't reduce with flaps, means a very fast approach speed (or you need to oversize your wing to give yourself enough lift for a slower stall speed). A fast approach speed means you need a very long runway to land, and you need to engineer your landing gear+brakes to handle higher speeds and more energy dissipation. Oh, and if you ever have to ditch you'll be ditching at higher speeds too. So much for safety.
I too was on the "rutan is a genius with his weird looking planes" bandwagon until I read more about the downsides of the canard layout.
@@StephanAhonen You're correct on most of the points you make, I talk about all of those in the video I mentioned in my channel above, the "Why I bought this airplane" video - I go over the pros and cons of canard aircraft, and do go a bit into the weeds talking about aerodynamics.
The stall speed is not high because of a "fear" of stalling the main wing, it's because it is impractical to put flaps on a canard (although it can be done - the Beech Starship had flaps, and a complex mechanism to make adjustments to the canard - again, I talk about that in my video).
That said, the stall speed is not THAT high. The stall speed of my Cozy is 63 kts, which is pretty close to the 61 kt stall speed of a Lancair (with flaps down), an airplane with a comparable performance envelope.
Runway length for canards for landing is not the limitation - it's takeoff. You need enough speed to get the canard to fly before you can rotate the main wing into lifting. That takes some runway. You will land a bit longer than a Cessna, but again - comparable to an equivalently performing aircraft like a Lancair.
@@StephanAhonen the safety of the standard aircraft comes from the fact that you are so afraid of a tail stall, which is unrecoverable, that you engineer the main wing to stall well before the tail.
I have a velocity, one other downfall of the pusher style is anything that comes off the airframe ends up going through the prop. Cowling screws, stones or rocks from a soft field or even a wrench resting on the wing when doing a dry run up……. Ask me how I know. 😂
just like helicopter tail rotors
Interesting discussion. You mentioned balance - with a tractor, you tend to keep the fuel tank and passenger payload close to the CG. With a pusher, you typically need to offset that weight in the back by moving other things forward. That puts limits on how changes in payload and potentially fuel weight affects your CG envelope. The big problem with canards is that flaps cause a large pitching moment when deployed due to the NP being further forward than a rear tail configuration. Most canards land without flaps - and fast. Although in a different class of aircraft, the Piaggio Avanti did a nice job of overcoming both of those compromises with a three-surface design and twin pusher engines behind the wings instead of behind the tail. It is one of the most efficient business class twin turbo prop planes ever built.
Most pushers also simply keep variable payload and fuel near the CG.
Seabird Seeker, Aircam, Cessna O-2, SAAB 21, Wright flyer, and many more.
Also, look how helicopters handle CG, as they have the same issue with the engines being in the back.
I like both.
An electric and gas.
One of the front the other in the back.
Best of both worlds.
@@jtjames79 battery weight and drag penalty is going to be huge.
Great lesson on the trade offs in aircraft design and iterative process. Since constraints are universal, that’s why air planes end up looking quite similar and innovative designs are few and far in between.
I fly a quicksilver ultralight with a pusher prop that is mid-body. It's really nice not having to look through a prop, plus no possibility of a prop strike even on over-rotate, plus it gives the elevators and rudder huge authority with the prop blasting right onto them.
6:28 Something that some people don't know: The propeller also cools down the pilot. The pilot will often start sweating when the propeller stops spinning.
Fr, great vid
There have been several forays into pusher props over the years. The B-36 Peacemaker, the Lear Fan, the Beech Starship, the Piaggio P-166 and the P-180. The B-36 initially had problems with engine cooling. The Lear Fan was only test flown but never went into production. The P-166 was the piston-powered ancestor of the Turboprop P-180. The Starship was considered a loser business deal and Raytheon stopped making parts for it. Pushers sound like a logical idea. They look sleek and sexy. But some of them come with very real issues. On takeoff, if you rotate too quickly, there’s a chance you’re going to get a prop strike. And on landings, you can’t have the nose too high for the same reason. Landings are a real consideration because we typically have a higher nose-up attitude to stall just before touchdown. The Piaggio P-180 is a really sleek looking aircraft and it absolutely is. It’s a head-turner on any ramp even from the jet folks. It’s the fastest production turboprop in the world. But it’s a turboprop. Yes, it uses a variant of the PT-6 engine but it needs all its own parts. If you own a King Air, access to parts is a breeze because King Airs are operated all over the world. The P-180? Not so much. The home-built market has really outpaced the "Big" companies in terms of cost and that has allowed developers to play around more with the pusher concept and there are a couple of companies that make pushers. So overall, pushers are a fascinating idea but they come at a price.
A pusher configuration was used for the Edgley Optica - which provided a good observation platform. But the rear engine configuration and ducted fan was complicated.
My grandfather was one of the few people who actually built and finished his BD-5. I used to sit in it and pretend I was a fighter pilot.
You’re lucky you didn’t die just being around that POS!
Wow that is so not even a little interesting, this isn't about you
@@slowery43 Just glad you survived…😂😂😂😂
when the bd came out the wife said no way no chance
now she's long gone and in my shop under construction a carbon fiber BD5
with a zero radar return(the American inventor also invented me )
power ....a m8 Harley Davidson motor twin plug no shake programable in flight ejection, turbo ,and its being rebuilt to about 400 hp..
hey at my age..nursing home suck any way !
@@NeroontheGoon
@@reysayre Carbon fiber fiber BD5, the horror continues.
Love your tutorial videos! Please keep them coming. I'm hoping you guys will expand your planes to include a 4-6-seat plane. Maybe a dual-engine canard-style pusher airplane that is powered by the new Deltahawk? I know some of you will say there is such a plane in the Velocity Twin, but that plane is a dated design made of fiberglass. I'm sure these Darkaero guys would come up with something amazing!
This was an excellent overview of two common propulsion designs! Loved it.
I used to live near the final approach of a regional airport. There was a rear-engine style similar to the Gyroflug SC 01 Speed Canard that would sometimes overfly. That thing was incredibly loud and annoying pitch of sound too. I hated the sound, but it did look very cool. The noise was incredibly bad, and it was on final approach at probably 1/2-throttle at most. I hate to be on the other end of this airport where such a craft was taking off at 100% throttle!
I would love a follow-up video that describes *twin-engine* modes of puller and pusher propellers.
Because my personal fav propeller style planes the twin engine pullers like the classic Cessna 310 series. Given what was stated in the video at 3:55, the twin pullers will have reduced airframe drag since the engine are situated outboard and only cover the thin profiles of the wings. So, a twin-engine pusher would also have outboard motors so may benefit from decreased dirty air and maybe get better thrust and reduced noise too?
Great video. I haven't been around aircraft in over 30 years since school. I never received my A&P, I changed fields. I guess I had a great instructor, because everything came back while you were talking. I even anticipated several potential problems. :)
Keep going! Great content as always. Proud reservation holder!
Just thought of a cool idea. What about keeping the engine up front and run a shaft to the rear for a pusher? That would maintain the cooling challenge and ease of access to the engine. A F86/mig15 look would be awesome!
That would require a significant increase in weight and reduced interior space. Depends on your requirements I guess.
There's an additional problem aside from added weight and complexity. The P-39 was a midengined tractor aircraft, similar to what you're proposing. The driveshaft had to be lengthened, and the additional forces that came with that length meant that a quick enough power increase would actually break it.
@@HikariKobayashiuse a high RPM, low torque engine ( V8 automotive). Torque tube from Corvette 6 . Planetary gear at the rear. Fast 5 blade prop.
I would guess that for a tractor, the shaft needs to be as short as possible, especially with low blade loading. The 6 cylinders should be close together ( water cooled ) and almost stick into the propeller hub.
Then again a modern aluminum engine block isn’t that heavy.
Inline six in the front. Two pilots . No fat clutch or gears. Just a “divider” between both pilots. Upright engine, not slant. Might be interesting. Not so great for visibility and collides with the nose gear. No flat firewall.
I would love it if these guys did a thorough analysis of the celera 500l or the long forgotten synergy aircraft. The way they explain complex equations with ball park figures is amazing.
Easygoing, well researched, and it’s evident the presenter really likes the topic. Plus a nod to the cool factor, which surely is what’s really on everyone’s mind. One question-is there a difference in noise between the arrangements?
Excellent analysis and consideration of the multiple tradeoffs. I do like pushers partly because of the better visibility, though as you mentioned, efficiency is about equal overall. People often point to the Cessna 337 as proof of the pusher configuration's higher efficiency, because the climb performance and maybe cruise speed is a little higher with only the rear engine running, versus only the front engine running. But the airframe shape may be directing more air to the rear prop than some other pusher configurations might experience.
I was going to make the same observation. The reason for this behaviour is that air accelerates as it is drawn towards the prop, and accelerating flow is more stable. That might be particularly important for the 337 layout as the rear end is pretty blunt.
The 500l does efficiency to the nth degree. If you're going for full laminar flow pusher is the only option. The way it is implemented on the 500l though, there's no improved visibility lol!
Based in this analysis it might be interesting to evaluate wingtip prop configuration, especially on the tail wings
I had to give a chuffing laugh when I saw the Mini-IMP listed on your white board under pushers. After I got my A&P I purchased a set of plans for a Mini-Imp (many years ago when they were still available) and over a three year period got about +-80% done. It actually was a pretty cool design and the cockpit was quite comfortable. If you ever look at the plane, not how the landing gear wheels fit up into the wing (and was part of the air intake system) but folded down and gave pretty good ground clearance.
Talking about problems, one of which ended the project: accessing the engine was a nightmare, I had the cog belt reduction system manufactured twice and it wasn't made right either time but the killer was the torsional resonance of the long hollow drive shaft. The tail cone of the design just wasn't stiff enough to handle it. I could have reinforced the tail cone and added (considerable) weight in the nose to get the right CG but then the gross weight was becoming problematic because I'm a big guy and was already at the planes limits. Who wants to go flying with only half a tank of gas to not exceed the weight limit.
I tried a 3" diameter drive shaft, then a 3.75 and finally a 4" which aaaaallllmmost tamed the resonance but just not enough to be feeling safe.
I stored the plane for years then gave it to a old guy who wanted to try to see what he could do with it. I wasn't rich enough or smart enough to solve the problems. I suspect that's why there aren't more of them flying.
PS - I also bought into Jim Bede's fantasy and bought a set of BD-5 plans, even built the wings before the lack of a suitable engine killed that plane (certainly didn't have the money for a turbine like the Coors jet, haha)
Could you expand on the problem with the drive shaft/tailcone please? I would have expected all the propeller torque and any torsional vibration to be isolated from the tail cone via the thrust bearing --was it a case of tailshaft whipping or out of balance and how did it manifest (presumably during ground running --was there any 'ground resonance' via the landing gear springing involved possibly ? ( I just lost a longer post by hitting the wrong button ..#**&# -- I have had a lifelong interest in the tailpusher concept including designing building my own design "Opal" starting in 1975 - worked for Dick Schreder on sailplane design in 1974 and met Molt then (at Oshkosh) ,corresponded and went over to see him in 1990 etc etc -also met EdLesher and Jim Bede then and attended their forums . Maybe 'compare notes' on shaft drive issues etc ? I had thought that the flexidyne was a pretty good damping solution and it worked for Ed Lesher on the Teal and Nomad apparently but admittedly has not led to any significant uptake of the pusher configuration ... curious as to your experience to say the least.. (working on a current roadable using, notionally ,the flexidyne 'solution')
Apologies fot the 'crossing out' it is a quirk of my very old laptop and only happens intermittently and shows up after sending .
@@rossnolan7283 at the time of my build, flexidyne couplings were restricted because they freaked out that they were being used in aircraft and they thought it would expose them to massive liabilities. So they were only selling to established businesses. I tried going through / ordering from a couple of pump companies to acquire one but there were too many hoops to jump through. So I tried to use Gates cog (toothed) belts in a 1:1 drive to isolate the power pulses. Same 3" wide belt used to drive Roots blowers on race cars, I just used 2 on 6" toothed pulleys.
It was a long time ago, late 90's and honesty I've forgotten a lot details of what I tried.
It would be very easy (and understandable) for a set of people so focused on performance and spend so much effort on meticulous engineering to disregard something like "cool factor" out of hand. Very nice that you considered that in your final comparison!
- just like the tailfin rake of "later model" Cessnas - if it looks fast on the ground it sells better (Pilatus never cared).
In a tractor configuration are the vibrations on the frame caused by the disturbace of air by the prop, not more ?
Does a pusher not give a smoother ride?
I was also told that a tractor configuration has more precise steering features ?
Your view?
Great video and lots of other good considerations mentioned in the comments, particularly FOD and noise being big problems for pushers. Another important factor that I did not see mentioned was short field performance. Pushers take a lot longer to get off the runway due to the lack of prop wash making the tail surfaces effective at slower speeds. Also, you talked about forward engine placement with long prop shafts to the tail, like the BD-5 or VK-30. An issue here tends to be torsional vibrations in the prop shafts, usually requiring some kind of flex coupling, which adds weight and is another maintenance item.
I am grateful for this excellent explanation and comparison of plane designs. I love the clean drawings and the filtered explanations of many topics. I think both design are relatively close in performance (oddly in model airplanes the pusher seem to be slightly more efficient/ faster) but this plane is well conceived. Also you can design the rear as a T tail pusher to avoid the turbulent air ( I know its not ideal but at least a way around the standard configuration.)
If you wanted max efficiency, you could do like the Sunseeker Duo which puts the engine (actually, motor) at the front of the top of the T-tail empennage where you ingest clean air but don't dump disturbed air over the fuselage, just a portion of the tail. (It's also a sailplane, so the propeller folds in gliding/soaring flight so doesn't even disturb the tail during much of the flight). Sunseeker Duo: ua-cam.com/video/uBA4XeMddMY/v-deo.html
That can have issues in high angle of attack flight in possibly deep stalling with challenging recovery. But, has been done, and possibly airplane parachutes are a good fix for deep stall crew survivability.
Well it helps with sailplanes that don't need a motor to maintain stable flight.@@Georgewilliamherbert
You also have higher trim drag with this arrangement
We have advanced very far since first looking at birds and desire to fly.
Appreciate the summary table.
Interesting, as a layman I've always wondered why we don't see pushers with a heat exhaust ducted similar to a center-mounted cannon in WW2 fighters to keep the turbulences on the blades to a minimum.
That's why I like the Cessna 337, you don't have to decide, it has both a pusher engine , and a puller prop in a centerline thrust configuration, and the weight of the engines at both ends makes the CG equation easier. The added bonus is you have a second engine if one fails. Only downside is two engine maintenance and fuel burn rates.
*The German 'Dornier Do 335 Pfeil' PULLER and PUSHER had an experimental design element that connected the front and rear proppeller with a long drive shaft. It could take off with the front prop only and during flight a clutch could transfer all the power to the rear prop. The rear prop folded flat until it was engaged and the props opened up.*
Hey can you make video about contra rotating props
I was wondering what putting a rear prop did to the directional stability of the plane. If I pull a suitcase on wheels behind me, it follows and corrects any deviation; but if I push it, it's unstable and tends to go off to the side, or even fall over, and requires constant correction. On the other hand, shopping trolleys/carts can be pushed from the back without problems.
Great vid - I'm tossing around a canard concept with a forward-swept wing with the trailing edge 2' forward of the first disc of a contra-rotating setup. NACA research says sufficient separation smooths out the airflow for the prop. It means the engine is ahead of the wing, but I'm using a liquid-cooled engine for it. I need to build a wind tunnel to test the design.
This was a really cool video. I know its a fictional plane, but the Sanka mk b has made me obsessed with pusher props for the last 10 or so years. The canard and wing design along with the contra rotating propellers just look awesome to me
the drawings are great and I also particularly like that you break out some percentages and equations
Wouldn't the disturbed air over the wings from the tractor prop harm lift thus requiring a higher AOA resulting in even more drag?
Isn't the flow disturbance argument valid for ship hulls as well? Then wouldn't putting the propeller in front of the ship a more efficient option than the conventional pusher?????????
Inspired by the Dornier fighter, how about a plane with TWO props, one pusher and one puller. Front mounted engine drives both props. Rear prop spins opposite the front (due to an offset gear). Stable since torque is balanced out. Cooling is normal. Only thing is to have an engine with enough horsepower to power both props. Maybe if the rear prop is up high it would avoid some of the turbulence and at the same time some of the tail clearance issues.
Anyone seriously interested in this should be buying Raymer’s “Aircraft Design - A conceptual approach”, if you want a brief introduction his “Simplified airfield design for Homebuilders”.
But actually having this theory to application example worked out and explained by the Dark Aero team is immensely helpful in understanding it all.
Are stall characteristics irrelevant when considering pusher vs pull? Would a heavy engine mounted forward offer better stall/spin behavior? Or worse?
no differences because in all case is the gravity center the same vs lift center
Love these explanations videos, thanks, loving following your project
I just love your design process walk-throughs. Great work!
Hi, DarkAero.
Thank you for an informative video. clear and concise and easy to understand. Much appreciated.
I'm no aeronautics engineer, 'justa pore, dumm bulldozer op'rator', but I do have some 'kwestyuns' if you wouldn't mind answering them.
1. The Pilatus Porter - when they switched over to a turbo-prop engine, they had to lengthen the nose by quite a bit to maintain trim due the lighter engine but it also resulted in a longer, sleeker nose - which leaves me wondering if placing the engine a little further back and running a drive shaft to a puller prop could also give a more streamlined shape, maybe with vents to trap cooling air for the engine? Again, it would likely need some modifications to cater for trim.
2. I am wondering if there is any real advantage - or disadvantage - to placing the engine and propeller on a pylon above and behind the cockpit in either a puller or pusher configuration? I suspect that this might mean some changes to other aspects of the aircraft, including the landing gear and I seem to remember seeing small aircraft with this configuration so I am really just wondering about the pros and cons of it.
3. There was some talk a couple of years ago of 'unstallable' wings that were made up of multiple aerofoil shaped 'mini-wings' placed in banks layered backwards from front to rear at varying pitches. You can find videos of them here on You Tube - I would post the links but You Tube doesn't seem to like that any more. Have you had anything to do with them and, if so, what is your take on them?
Thanks again.
Just my 0.02.
You have a wonderful day. Best wishes. Deas Plant.
An additional affect not mentioned is the wing lift generated by a puller, which may offset some percentage of the drag. The angle of attack of the outboard wing can be slightly lower. On the other hand, another possibility is to have a twin boom with T tail for the pusher.
How about the efficiency of the pusher right behind the wing near the center of gravity?
A pusher like the Aircam or Seabird Seeker is a really good design. all payload, fuel, and engine is right near the wing.
Ground clearance not an issue. helicopter visibility. And can even have trigear or tailwheel. Even still get airflow over the tail for low speed tail authority, but no fuselage nor wing drag.
But a twin like the Aircam can have minimal drop in prop efficiency since not all of the airflow is disturbed, much remains laminar.
But a twin tractor also has the benefits of much reduced airframe drag due to propwash, while giving additional lift to the wings, while still getting improved visibility, ground clearance, ease of access to teh engines, etc.
lots of tradeoffs.
Thank you, @@SoloRenegade !
Anyone else impressed with the white board game! My sketches would not be this neat! JS!
very interesting! regarding airframe efficiency, what was the reason for choosing a conventional tail and not a T-tail used by very high performance gliders? this would also decrease prop wash on the elevator for the pull configuration.
As an engineer I like to see how your thought process is, I like that you compare different options. I guess that the only way to know for sure whether the pusher or the puller configuration is the most efficient in your case is to try both, fluid dynamics is one of the most contra intuitive fields of physics and can yield some unexpected results.
Thinking more of the center of mass being moved back might cause some problems with stability.
Brilliantly straightforward video...Thank you for making these.
Subbed!
10:00 you can also shift the main landing gear closer to the prop, so that the point of rotation is so close to the prop it never really changes height over the ground, completely eliminating the issue. And you can do this with more designs than just canards or flying wings too.
The tradeoff is that this increases the length of runway needed for takeoff. The rear landing gear is usually located just aft of the aircraft CG in worst-case loading to allow easy rotation, producing a significant angle of attack increase, finally increasing lift at a lower takeoff speed.
@@tomthoe placement of the main landing gear has little to do with takeoff distance, unless you screwed up the design. But you can screw up the design of any configuration in the same way.
there is no significant angle of attack increase. For a given design, the stalling speed AOA does not change due to the location of the landing gear.
The issue here, is you don't understand aircraft design well enough to understand my comment, nor how to design an airplane properly to do as I described. The example you're trying to give is a garbage design, and also lacks creativity.
I claimed, accurately and truthfully, that it can be done if designed properly (in more than one way and configuration as well). You tried badly to refute that by citing a terrible design, as if that refutes my claims about a proper design.
@@SoloRenegade Interesting. Can you help me understand what mechanism you would use to increase lift to reduce the required takeoff roll for the minimum weight penalty?
@@tomthoe no need to increase the takeoff roll at all.
Explain why you believe the takeoff roll need to increase? And then I can tell you how to fix it.
Why do you need to increase lift? there is no weight penalty for a properly designed airplane. Explain where the extra weight came from in your crappy design.
@@SoloRenegade I see that you did not fully read my comment and that you see no negative consequences with shifting the rear wheels away from the CG. Can you help me understand why all pusher prop designs have the rear wheels located just aft of the CG?
Hello. A bit off topic to this latest video, however: You May wish to consider a fore and aft jig system, where you can rotate the aircraft for most efficient mechanical work / painting / installation, etc. There are automotive engine rotating stands… you guys can figure it out. Thanks for your videos! You give many of us enthusiasm for your continued successes 👍.
Nice drawings! Somebody there is pretty handy with a whiteboard marker
With prop efficiency decreasing due to airflow issues forward or aft of the aircraft, would you just need to consider propeller length and pitch to regain your efficiency ?
Is that a 6 cylinder I/O Lycoming powerplant? I used to work on those things. What's the displacement? 540? 560?
Exhaust and baffling...hated every minute trying to take that stuff off. Every stud holding the exhaust to the cylinder was rusted to the core and the baffling... I needed a special Philips screw bit to get enough grip to back the screws out. Normal Philips screwdrivers/bits would just start rounding out the screw heads. Other than that, they were great to take apart.
I don't think the big 6 cylinders had this problem but the smaller 4 bangers had a problem with the oil sump gasket getting pulled inward during start-up. It would happen at the back of the sump, right in the middle (where the case halves came together). Owners would put these little "dimples" or tiny shallow holes (I guess, I'm not describing it too good). What this would do is add grip to the metal by raising the metal around the tiny holes by something like ten thousandths of an inch (the sump only, they wouldn't do the same to the case halves). 4-5 holes to the left of center and the same for right of center. Talk to your engine mechanic, he might be able to describe (maybe even show you an example) better what I'm trying to convey thru text.
What about if you have a pusher arrangement that is above or just behind the front wing. That could fix some problems like the ground clearance.
I would have a view from building a fairly light weight single engine plane. My thinking is to put a pusher prop up on a "pod" above the fuselage, or at the top of the (reinforced) rudder. An idea also just came to me to make this engine electric. However, it would be powered a typical engine running a (small/compact) generator. This arrangement gives flexibility to where the weight of the propulsion system is located. Particularly the prop, which could be placed in clear air above the (rear of the) fuselage. The motor/generator combination could be placed in the nose to make maintenance easier. The electrical wiring to the electric propeller motor would be easy to route, unlike a pusher prop driven by some long drive shaft.
The SAAB J-21 pusher prop fighter, the only one ever mass produced and in prolonged service, was less maneuverable than nose driven types, despitd a larger wing and lower wing loading.
Another consideration is safety in a crash scenario. With the engine and prop in front, the mass of the engine absorbs some of the impact forces, whereas with it at the rear, the tendency is that you will need to insure that the engine cannot come loose and move forward in the event of a crash. In event of a crash with the engine at the rear, there is a greater likelihood that fuel lines will be severed, and increased risk of fire inside the cabin, in my opinion.
Yes, and that's why mid-engined Porsche Boxsters and Caymans have a cable, or wire rope, to restrain the engine in case of frontal collision.
Is there anyone named Lindberg in your family?
"In event of a crash with the engine at the rear, there is a greater likelihood that fuel lines will be severed, and increased risk of fire inside the cabin,"
this is baseless.
it is wholly dependent upon where the fuel is located, even in a tractor, and where the fuel lines are run. If the engine never impacts the ground, how exactly are the fuel lines magically severed?
Also, even helicopters like the OH-6/MD-500 are famously crash resistant with the engine in the rear.
Airlines and corporate jets also do well as pushers.
how does the Aircam result in fuel in the cockpit, or engine hitting the pilot?
A great many ultralights have been pushers, and rarely are pilots killed by the engine/prop specifically upon crashing.
Formula 1 race cars crash into brick walls at over 200mph with the engine in the rear, and the engine has never come through the cockpit. engines are TERRIBLE crumple zones.
@@SoloRenegade F1 cars also don't have to worry about not getting off the runway because they burned too much weight budget making the driver tub. And of course they don't crash into brick walls, but energy dissipation walls and the relative speed between the car and the wall is more like 40 mph because of the angles. Maybe we should compare hydrofoil boats to airplanes next.
Actually the MOST efficient is to have both pusher and tractor pulling propellers together. Better known as centerline thrust. A great example of this concept was Nazi Germany's Dornier Do 335 Pfiel (Arrow) aircraft, which was Germany's fastest piston powered fighter plane of WWII. The concept is also utilized in the Cessna 337 Skymaster and the militarized Cessna 02 Skymaster. The idea actually cancels out propeller torque, thus increasing efficency. Its been proven to work quite well. Its possible to have one engine power both propellers utilizing driveshafts and gearboxes.
Yes the dornier was an awesome designs super fast but they had problems with the engine over heating on the rear engine and also needed super tall landing gear to have clearance for that huge rear prop. I also found the skymaster very interesting but apparently it wasn't quite as fast as a standard twin setup probably due to the wing configuration . The maintenance was more expensive, and had a noisier cockpit. But the cool Factor outweighs it's deficiencies.
I thought of this too. One engine driving both props. I guess if that's too much load you could reduce prop pitch or surface area so the engine isn't overloaded. The main advantage would be the balanced torque. Another might be to reverse the pitch of the rear prop on landing so the thing would stop on a dime.
I learned something today. That is a good day. Thank you! What about the engine above the cabin or midway the fuselage? The center of gravity, drag and prop efficiency would be optimized?
What is it about the design of UAVs that makes the pusher configuration much preferred? Is it just a simple matter of wanting to remove obstructions from the front mounted camera and sensors?
Just from a few model airplanes in my childhood - If the prop is at the back, it would be more agile, but energy would be wasted in level flight maintaining attitude. If the prop pulls the fuselage along, it's slower to respond, but with much better control.
Another thing to consider safety for people around the airplane, most people are used to the idea of a prop being at the front, if you put one at the rear that's going against that convention, which I can see as perhaps being more hazardous, since people are used to approaching from the sides and rear of the plane.
A very interesting video, and comments section. Worth a watch and a read. Cheers all!
I like the approach of your team into the development of this project, I have a feeling that behind your project there is someone with a very very mature work ethic and state of mind, no hurries at all but a firm and steady pase. Congratulations you will go far!!
A nice thorough analysis, but I'd add another factor against the pusjher; the prop shaft.
It adds weight, although I sippose a carbon-fibre tube might not weigh much. In addition, it has to be very carefully balanced and not have any flexibility or resonance frequencies with anything in the airframe. Generally solvable problems, but potential unnecessary development effort.
Could you please tell me what equipment do you use to record your videos?
They have excellent audio and visual presentation.
Thank you,
Franklin
This was very insightful. I'm curious how propeller position influences handling - does one have better responsiveness / manoeuvrability? The analogy with cars is that rear wheel driving cars have more traction during acceleration, sharper steering feel, and more balanced handling. While front wheel drive cars have a numb steering feel but are less prone to oversteer (safer).
so well explained. im sure there must be more to it but it feels like ive really learned something lol. what do you think about planes that have both pusher and puller proppellers like the do 335? id love to hear your thoughts on that!
This is very interesting. Your airflow disturbance visual got me thinking about jet intakes, which I know are not relevant with this specific aircraft by DA. However, how would you go about estimating the lift lost due to dual intakes placed on the bottom of a wing? Wouldn't the effective area of the wing creating lift be decreased by the sections where the intakes are placed?
How would a pod (tractor or pusher) above the fuselage change efficiency and drag? It would seem like you could reduce drag with a smaller nose section and get smoother air flow over the wings. Dual (smaller) pushers on the wing would also seem a good alternative and maybe add to safety.
Excellent video. My comment is outside of the scope of your discussion, and is not criticism.
I prefer tractors. This is one of the reasons:
Using your two example planes, the length of the fuselage would have to change for the pusher. You would have to lengthen the fuselage forward of the wing to regain proper CG. This shortens the relative distance between the wing and the tail. This, in turn, reduces the effectiveness (Moment arm/leverage) of the elevator and rudder, and can make the aircraft less stable in pitch and yaw. A larger tail would be required.
An extreme example of this is the modern fighter with a long nose and the tail very close to the wing. These are incapable of maintaining stability without computers flying the aircraft for you. (Also notice how large the tails are on these aircraft)
So taking what I just learned, the best arrangement would be twin puller motors located at the wingtips. Clean air makes for high efficiency and considerably less airframe is exposed to prop wash minimizing drag. I suppose there "might" be some other factors involved. :)
Nice Video, comments below.
1 Ducted Fans and Propellers are more efficient and easily accomplished with a pusher.
2 Integrated Tail Control Surface/ Ducted Fan / Stator Blades work best in front of the Propeller.
3 Using Engine Cooling to deliver more Waste Heat Thrust is easier to accomplish with a pusher.
Probably impossible to figure but which configuration does better when 1) engine shuts down, meaning the glide capability, 2) survivability of the passengers in a crash, 3) and closely related, which config does better in a water landing, meaning when ditching the aircraft à la Sullenberger?
My understanding, from before watching the video, is that pushing can cause a feedback loop of nose up/down, where as the front propeller is a negative feedback loop, dampening the pitch.
Aesthetics are underrated. Tractor config looking familiar and understandable means a lot.
hey there i dont know s... about engendering that go in airplanes but a question if you have " problems with visibility on a tractor configuration can you have one -3 cameras in the nose to mitigate the lack of visibility ...am assuming you have a display in cokpit this days you can use for that
What about having the propeller elevated above the body like you see on some motor sail planes.
Would a canard design pusher be more efficient overall?
Look at the 2023 race results at Oshkosh.
In the respective engine category, canards blew everyone else, followed by a Whitman tailwind (70 year old design) and then the RV's.
This is a very good analysis and summary of the important points. But the 'conclusion' is almost all based on the reduced efficiency of the pusher in the disturbed air of the airframe. Would have liked to see some discussion on when the reduced prop efficiency is less than the reduced airframe efficiency ... AR, speed, parasitic fuselage drag etc
I have questions on the number of blades and drag. If you have a smaller diameter prop with more blades does that reduce the amount of wing exposed to disturbed air? Would this have a benefit to drag, or would the more frequent pulses of disturbed air increase drag?
On the "Dark-Air-One" -- _or any other "puller-prop" style airplane_ -- Could the wing portion closest to the fuselage, and in the direct wake of the propeller, be "skeletonized" to reduce the effects? The airplane might look ridiculous, but the loss of lift from "skeletonizing" that portion of the wing, might be outweighed by the lost of turbulent drag.
Is there any chance DarkAero can be flown first as a remote-control aircraft, before putting a pilot in it? You've got the actuators for autopilot, are those good enough to take off and land? Spin recovery?
Propeller efficiency is decreased by a pusher arrangement sure but the net thrust of a pusher would arguably be higher? A a portion of the airflow behind the propeller for a puller encounters the nose of the fuselage pushing back against the airflow decreasing thrust efficiency. A pusher configuration does not encounter this issue, did you take that into consideration when you say "propeller efficiency"? I'm busy designing a flying wing and this was one of the reasons i went with a pusher design, i think the main reason people go with a pulling design it is much easier to balance the CG rather than the prop efficiency and i'm sure that was more important in your decision?
If the airframe was designed to create a high pressure zone around the prop (in a rear prop design) would the increased engagement with the air (able to push off it more if there's more of it) positively counteract the negative effects of turbulence? Suppose (more unreasonably) you had a design that increased air pressure while maintaining laminar flow (does that apply to gas? I know it does to liquid...) then I'm sure the mentioned effect would be observed, but as you vary the disturbance and pressure you should be able to reach a point where efficiency benefits from the effects of the air on rear prop placement. The real question is whether these modifications would increase weight too much or be too impractical to implement and cause it all to be inconsequential.
Great job and thank you sooo much for the education. You guys are amazing and I wish you the very best!
Incredible sharing of knowledge and design :) Just outstanding
Do pullers have an advantage during low speed as it forces more air over the body (even if it is unstable air)? How do landing, take off, or near stall behavior differ between the two models.
A lot of comments about noise, which is important. Not that its a huge general aviation problem, but a pusher would reduce the likelihood if flicker vertigo (not looking through the propeller). I haven't seen anyone discuss in the comments, so I thought I'd bring it up.
Amazing video. Great explanation, just earned a subscriber.
How about a design with the engine on top of the airframe behind the canapé with a push prop? The same idea as with these old flying boats. The airframe can have a double tail. Interesting vid guys! Keep on going the good stuff.