Bruce, you get more information into my head, more efficiently than any other source! I am bookmarking these instructional tutorials as my memory is full.
The principle involved here is called "impedance matching". To get maximum efficiency, you have to match the impedance of the blade (thrust vs drag) to the impedance of the motor (torque vs battery draw). Just like in stereos where you match the impedance (resistance) of the speaker to the impedance of the amp, or like in cars where you match the torque/speed of the tires to the torque/speed of the engine with a "mechanical impedance transformer" - called a transmission!
Excellent video! very educational, enjoyable to watch, kept my attention! answered my questions! You even answered for me my questions on why WW2 aircraft have 4 bladed props, when even those who fly with the actual aircraft could not answer! I just found your videos while searching for prop info for boats! I have watched 6 of your videos, all fantastic. Thank you for posting these excellent videos, please continue!
This is a fascinating subject, I'm glad you're exploring it. I did some of my own trial & error analysis with boats. The variables were mostly the same. However one of the key targets I factored in was the Max Efficiency Amp rating of the motor. A draw value below the figure, let's say 18A meant you were leaving power on the table (not utilized by load) and a drawn value above Max Efficiency meant the motor itself was burning off power as excessive heat. A very challenging subject. I can't wait to see your results. Cheers.
Great video Bruce! I definitely learned a lot from this video and can't wait to see the practical test. Is good to see you back doing more technical videos that we love so much!
There is an additional bonus to multiblade props, and it's one of the reasons that I fly them. Because they produce more thrust, you can fly with less overall blade speed. This makes multiblade props quieter than two blade props, at least in my experience. I would find a hover efficiency test interesting. In theory, some of the inefficiencies due to adding blades, is mitigated by spinning the prop slower. I'd be interested to know how the battery life duration for just hovering would compare between props.
Old post I know, but figured i'd reply anyway in case someone else runs across it. I saw a video of a guy who tested 4 blade, 3 blade and 2 blade (4 blade with 2 blades removed) props on his tiny whoop, and he was gaining roughly 30 seconds more flight time per blade removed So the 2 bladed prop was giving about a minute more flight time than the 4 bladed prop. So the drag reduction of slower prop speed in no way counters the drag increase of having more tips.
His test has flaws. If you want to compare the props, when takling about energi useage, you need to look on the swept area of the props. In his test he is basicly trying to proove that you get better fuel economy If an motor only pulls one car instead of two. I think most of us can tell that with out an test
Thanks for the video Bruce. On my 5" mini quad I've found that the 5x4x4 HQ props are the most efficient, in terms of performance props and my flying style, anyways. 4 minutes of pretty hard flight on a 1300mah lipo. Cornering on 3 or 4 blade props is the biggest selling point to me. All that grip in the corners inspires a lot of confidence.
So I suppose having more propeller blades on an aircraft is a bit like having wider tyres on a vehicle. You get better traction, but also lose more energy through friction.
From rotational Physics, in an ideal world, there is only static friction between the tires and the ground and this friction does no work and thus you don’t lose energy. Rolling resistance is more due to the chemical grip and mechanical grip of the tire literally sinking their rubber molecules into the road and the rolling motion have to pull these molecules out when the tire keeps rolling. That is also how tracks rubbers in--race car tires experiences this so violently that they literally leave part and layers of their tires into the tarmac, and the tarmac now will give more grip and wear the tires less.
These people don’t know what they are talking about Andy, you are right. There is a reason why race cars don’t have ridiculously wide/tall tires, there is a loss of return at some point, just like a propeller.
Please talk Reynolds numbers! And a video about efficiency is needed, as many people have no idea what it actually means. PS RPM comparison in flight on the various props would be very cool, I havent seen anyone do it yet. Holla and ill throw my logger and rpm sensor down to you if needed.
Well done, Bruce! An excellent discussion of propeller basics. For the fixed wing drivers, perhaps a video discussion of the considerations of prop pitch and diameter selection for a given airplane/motor, including going from two to three or four blades.. Cheers!
Do you remember the Voyager project? That first plane doing a non stop around the world? They wanted efficient props for a reason. Some Swiss company promised them experimental miracles built in wood. When blade angle adjusting motors turned out to be toy quality, blades broke off, they finally gave up. Voyager flew around the world with props built (in overtime) by a renowned American propeller company. Find the Voyager story online or in the book.
The real breakthrough in power vs. efficiency will be the development of variable pitch constant speed props for RC/quads. Best of both worlds; Thrust on demand, efficient drag profiles during cruise power settings.
Much more rotational mass in a heavy 4 blade prop. Not tried them yet, but found the 3 blade non bull nose to be perfect for me. Another reason WWII props went multi blade instead of larger... Larger diameter beyond a certain point can make the tips break the speed of sound. Love the discussion, love your work! Thanks as always.
Other reason for late WWII fighters to have propellers with increased number of blades instead of longer ones was to reduce the blade tip speed, as they had then a very high dive speed blade tips had air compressibility issues. Also wider blades have lower tip speed for the same blade area than longer ones. For normal RC planes this doesn't matter because they fly at very low MACH.
It would be nice to see include comparison between a 2 blade prop and a tri-blade of a smaller diameter; keeping the other factors like pitch and bull nose the same.
Bullnose and knife-blade, but there's also Q-tip and Scimitar, as well as some diamond shaped variants. Not sure if those have made it to RC yet along with prop-fans. (More than 6 blades, but not ducted.) Then you also have to keep in mind performance relative to airspeed. A prop that has a lot of bite in a static test might not have the top end aircraft speed of a prop that doesn't work as well in that situation. (So there's probably some choice between punchiness in acceleration and overall top speed.)
Very good video explaining why 3-blade props could be better or worse than 2-blade props. I'm quite liking the new DYS 5x4x3. They're cheap, well balanced and perform nearly identical to the more expensive HQ5x4x3. With the now popular 2205 motors they rock!. please, test on 4S -that's where speeds get ballistic ;)
this was a great video Bruce , in this hobby we all follow like sheep (new Zealand analogy ) or walk on the backs of giants , but not many ask why am i doing this or that , but something tells me you ask why? alot Bruce and we all stand taller for it ! keep up the good work :) oh and you will not break the DAL props guaranteed :)
essentially... more blades is to pack more blade area in the same diameter. But each added tip is a significant power loss so you loose efficiency. (assuming same blade design) The P-51 used 4 bladed props to keep the tips out of the dirt when taking off and landing.
Part of what I enjoy about flying quads has to do with all the changes and innovations. I fly Airbus A/C on a daily basis for work and I have an M-24 Orion Gyrocopter (2 seater) and aerobatic Acrosport II, Bi-plane, for recreation. Quad flying is cheaper but gives much of the same fun. A lot of the design features in model flying share a heritage in full size aircraft and now that materials are getting lighter and stronger, more cross over will occur. Bruce, I wonder what you see coming up....? Perhaps this idea warrants a short video? "Q-Tip" props i.e. small winglets on blade tips to reduce induced span flow or even variable pitch or constant speed props? (Airbus Neo aircraft have geared engines and have moved from typical winglets to "Sharks"). I would humbly submit, it is the battery tech that we must see where the really important changes need to occur in small and large scale. Thanks so much for your informative and humorous work!
Is there a rule of thumb for upgrading to a 3 or 4 blade prop. I would think i would have to either reduce pitch or diameter in order not to put to much load on my motor. I have a corsair that i put an E-flight power 110 motor with a 110 amp esc . I will be starting off with an 18-8 two blade. I would like to put a scale 4 blade like my previous comment. Any suggestions?
I have the same plane Corsair E-Flite crashed the same reason battery bad solder connection, and I have a 12X8 APC electric propeller , it pulls like crazy on the floor in the house so in the air It maybe OK what size to use 2 blade, and I have a lot of 2 blades in wood 12X6 I'm but afraid of flaps never had them in 15 years of flying so should I even try them ?
Bruce, it might be interesting to measure battery drain after the time trials just to get a real-world measure of the effects of different props on total power draw. I realize that that might require a "calibrated" battery, but it would help with understanding the whole thrust/power/performance/efficiency issue. Just a thought...
7:20 so they had to add more blades bc the engine was too powerful? so a p51-d mustang with only 2 blades or 3, would've been too much engine? so in essence the extra blades created more drag to basically keep the engine tamed from over revving?
great stuff bruce, i'm, just pondering these very questions, could you take a guess at what is the fastest prop for a 2s lowish 'c' rating, (30c) and 6040 knife edges and 5045x3 bullnose's?.. using the jjrc x1 we seem to be getting more punch from 6040s but the 5045x3 BN's have a higher top speed....>scratches head
Hey Bruce , I did my whole degree 8000word dissertation on this topic for my quad copter , I would love to hear your opinion on it, do you want me to email you a copy? Thanks
I would like to see how the 3-blade props compare to the 2-blade props on bench thrust/amperage test, particularly the linearity of the thrust-to-current ratio. Meaning, does the GemFan 3-blade Bullnose give 20% more thrust using 20% more current than the GemFan 2-blade Bullnose (equal thrust gain for equal current increase)? Or would the current draw be a higher percentage gained than the percentage gained in thrust? Or maybe thrust gained is a higher percentage than current draw percentage increase? I think having this data would conclusively show the performance you would gain is higher than the battery life you would lose.
+thechosendude I think it is incorrect to compare 2- and 3-blades props of the same size on the same motor. Because 3-blade prop with the same size and the same pitch will give more thrust on the same rpm, therefore, it will require much more power from the motor. It is always a balance between speed and thrust. If you want higher speed you must sacrifice your thrust. You may select two-blade props of lower size with higher pitch and higher-KV motor. Your model will be slowly accelerating Vice-versa, to obtain higher thrust, you can select 3-blades props, or props of higher size with lower pitch, and need small-KV motors running at lower speed. This makes a model very responsive, but slow. It is may be good for multirotors hovering, because when hovering they are requires only thrust, and no speed (although you cannot get thrust without moving the air) So, direct comparison of just 3- and 2-blades props with all others params are the same - is not informative at all. I think using 3-blades on lower-kv motor on lower rpm will show almost equal thust-to-current curve, but, keep in mind, since rpm is lower, air speed is lower too (Sorry for my English)
AterLux I understand what you mean about drag on more blades and thrust not always equalling speed, but I think it's important to remember most of us "average" flyers aren't doing high-speed racing, we're doing freestyle type flying, where having gobs of instant thrust for punchouts is going to be more favorable than the top speed in a straight line.
Have you seen the miniquadtestbench website? He posts very detailed tests and lets you download his raw data. The raw data is very detailed. The most detailed motor thrust tests on many props I have ever seen.
Very interesting. Can you shed some light on the "scimitar" style bladed prop? What about what is being used on some submarines in what is called a "propulser?" Thank you.
Sorry for venting here. how about constant pitch props? Always wondered why props had that taper to them. I assume its because the speed of the tip is faster than the speed near the hub. Is this correct? More thrust is more torque also right? Hence slowly add power to take off to prevent torque roll. I see pilots constantly not using rudder correctly. I teach fellow pilots use of rudder for Take off, coordinated turns, slipping etc.. There are so many effects with props. Gyroscopic effect and asymmetric effect. Most R/C pilots fly turn and burn only using aileron. Also explain why we have right thrust built into planes. Thanks again for All your great videos. I've learned so much about electrics. I'll be putting up a safety video soon. Unlike a gas or glow motor. Once shut off that's it. Electrics are ALWAYS on. Just got 8 stitches in my arm . Was a dumb thing. especially since I've been flying for over 25 years. Three words. Throttle cut switch....
When do you think the test video will be? I need to order some new props because I use a lot of them.Can't wait too long, Weather is starting to get nice here.
Bruce I have a Tarot 650 ironman quad with 4114 320kv motors 16 inch props would it be better to use 3 or 4 blade props for max lift? I know that or atleast I think that flight times will go way down but lifting power will it increase? I was going to switch over to the wooden props? What do you think would provide the most lifting power?
Do you need to reduce the prop size when adding blades if keeping motor and esc the same. I didn't know if the the extra loading would over whelm the electronics and if reducing the prop size would you need a higher kv motor to increase revs.
Is puttung a duct around your propeller, but without the lip to avoid the negative effects of tilting a ducted prop with the lip and then using a bullnose to increase the efficiency (when ducted it should let less air get around the edge) a good idea or am I missing something?
+Damien Van Der Vlist probably not, maybe check your motor specs
8 років тому+4
BTW, you never got to show those 3D printed ducts on a 250 quad :) I know from experience that ducted props increase efficiency, provide some lift in forward flight, hugely increase stability (the darn thing barely wants to move horizontally!) and they act as noise amplifiers even if they cut off the tip vortex, they reverberate all the other noises the motor makes. But all my experience was on a huge 600mm tri... project that I scrapped for a 250mm tri that folds and packs nice in a backpack.
Crazy thought. Why not put a little kick up at the tips of the props to keep the air from sliding off. Would that help with the vortex created and not cause any negative issues?
Hello Bruce, Thanks for this vid! Nice 1!.. Iam very interested in how the efficiency of a coaxial setup might improve with dif props sieze and different pitch. What i believe is that the efficiency improves when a bigger prop is used with lower pitch mounted above and a smaller prop with higher pitch below. (eg used for a y6 setup). I hope i can tempt you doing a video on this. Anyhow thanks for all your support! Gr. Wouter
Another advantage is imparted by how horsepower works, this applies for all rotating machinery NOT JUST RECIPROCATING ENGINES! :) Horsepower is torque multiplied by RPM divided by 5252. By using more blades you trade off needing a small amount of torque at higher RPMs for a greater amount of torque at much lower RPMs. Thus you are decreasing the amount of HP you need to generate the same thrust by a small bit.
very interesting Bruce I assume this is also the reason why hotliners (motorized gliders) use huge two bladed props. This allows for maximum power and efficiency.
Hi Bruce. I was just wondering... What would happen if you've got a really bad balanced prop and instead of adding or removing weight you just cut the tip of the heavy part? It will have a shorter and a longer blade. What will happen to the noise it makes, the tip vortex, the efficency? I can't try that myself as i don't have a rig to test it... Please reply :)
Great video. I was wondering how to choose a prop for flying at high altitude. All the charts are produced at sea level and I will be flying at 7,500 feet.
+Samm Sheperd (SNRS) Q-tip props exist as I'm sure you'll know. But as I understand it they are more commonly used to reduce noise as opposed to increase thrust.
i see some issuses. if the test should really compare the props in effience, you have to pid tune every singel setup. pid and so the energy draw could be completly different
Perhaps you could answer something I've wondered- wouldn't propellers benefit from fences? If spanwise flow hurts a wing, as you mentioned on flying wings, wouldn't the problem be even worse on a propeller, where where is centrifugal force to make it worse?
So, wanting more power, more blades or prop area is one way to go. But what about sticking with 2 blades, non bullnose and spnning the props faster instead? increase KV or cellcount. Granted, the standard 5" gemfans are a bit soft, but assuming a suitable propeller is available.
+Akujiwar Bladefist Spinning faster decreases efficiency. In the worst case a blade hits the turbulence of the blade before it and will not really produce any thrust anymore.
Does anybody know if material makes a difference. In my totally unscientific experience, the glass fiber nylon 5030s react better to my sticks (feel much tighter) than ABS 5030s but they love to shatter if you don't land softly. All in my head?
One thing I've been confused by recently is contra-rotating props. I've read they improve efficiency and are used by planes like the Russian Tu-95. But at the same time miniquads like a Y6 design that have counter rotating props are considered much less efficient due to one prop being in the prop wash of the other. It's strange how depending on the application it's more or less efficient. The only thing I can guess is that the Y6 miniquad has the props too far apart so it doesn't get the benefits like a contra-rotating prop on an airplane. The props are almost touching on a contra-rotating airplane setup.
there is so much more than just efficiency- with some gas engine applications, a difference in just one number on the pitch of a prop can make all of the difference. It sometimes seems that too much air flowing past the tail surfaces gives terrible performance. Experimentation and patience is required to find that one "perfect" prop- once it is found, remember it! Each aircraft is different, even matched aircraft built side by side.
so would a gyrocopter benefit from having 3/ or even 4 bladed props? considering they generate lift due to auto-rotation, would having a bit more drag on the blades make them spin faster, or if not faster, generate more lift at the same RPM? I know this is slightly out of the depth of this vid, but i was really curious. ty
Ok but one thing I just can't quite get any info on is high kv low pitch and small blade vs low kv high pitch big blade. For example, assuming you use say an a2208 motor at 2600 kv and a 5x3 prop, then the same size a2208 motor at 1400kv but with say a 7x7 prop (or whatever gives you the same pitch speed as the 2600kv) what are going to be the similarities and differences? Will the higher kv just be better all around? If so, why even use low kv motors? Why not just use high kv with a lower pitch? In my example, you should have the same speed and power correct? Would one be more efficient?
He mentioned blade pitch vs blade stall speed with the lower pitch maintaining effectiveness at lower speeds. I suspect that the larger the RPM change on a motor, the more power will be required to get to the desired RPM. Thus, the higher speed motors and the heavier props may be more likely to brown out the power rails during wild maneuvers on higher cell-count packs or underrated electronics.
Well, I've since researched this much more and all I can really conclude is theres so many friggin variables that its not worth it to even factor these in, best to just get your speed however you can\cheapest way you can. Ive found thinking of kv as a customization to match your equipment is much better than trying to figure out what's going to be the most perfectly efficient. I like high kv because you can get more power from a cheaper motor, that's really the biggest concern of mine, power vs cost.
And more thrust* before anyone throws a "ya but" at me explaining power doesn't necessarily translate into thrust :), which is true but pretty much every example I can find you'll get more thrust from a higher kv motor with all else equal. Low kv is good sometimes too, you can go with an oversized motor with a low kv to get pretty crazy thrust from minimum watt draw with a large prop, so you're paying more for motor and more for prop but they'll run on cheaper electronics. Oh and also theres the partial throttle effects, I guess low kv is much more efficient partial throttle, I tend to fly full throttle a lot so that doesn't affect me much.High kv will use a much smaller lighter prop, and low kv uses very large heavy props, so I suspect it takes about the same amount of power to get each setup up to rpm, but the smaller prop will be less efficient, which is another factor.
I'm mostly thinking triple blades offer the best ratio, especially to avoid ring-State and I was wondering if you're use a 3d printed clover prop with integrated circular duct if it would give you some benefit :-?
love my DAL probs have not fully broken one yet chiped tips of the a fair bit but that is not noticeable un like the gemfans i started with were if i poked a wall to hard they exploded
to share a story about larger props and larger engines. My stepfather put his favourite engine into his favourite airplane. the result was a 300 horse motor on his navion and a prop that just cleared the ground. of course mods to regular aircraft need approval. he was told how the rule was with a deflated nose oleo the prop had to clear one foot. so he photographed himself with his boot under the prop with oleo deflated - one foot of clearance! they let him get away with it.
I would love to see those inefficient props compared to 6" two bladed props. In my opinion it is crazy to use them only to spare 1". I am very happy with my 6" props!
The Kingkong props are do completely unbreakable. With learning I have had some horrible crashes and have yet to break a prop. So as a learner I brought heaps of then and the only reason I change them as they are too bent to fly right. I do not know how good they are as props and would love to see the thrust tests. Thanks.
Bruce are you saying that a 5040x3 has more thrust per rpm than a 5040x2? I always thought the "40" represented the inches of air moved per 1 rev for the entire prop, and not a single blade, or am I mistaken?
+Jon Keller The number denotes how far a prop would "screw" through the air within one revolution. If you'd cut a prop down to one blade or you've got ten blades of the same pitch, it would still be the same distance every time.
+Jon Keller 2 blades, 3 blades, pitch remains the same. More blades = more thrust. Imagine the propeller moving through a solid material. Like a screw through wood. Pitch would determine how far in the screw, or propeller, would move for each revolution. Now, adding more blades, it would not move further per revolution, but if you were to attempt to pull it out, more blades would make that more difficult, as its got more grip.
I guess I've never thought of it as moving through a solid, but rather moving air. Makes sense. Most of the acro guys I've spoken to will tell you that they use tri's because of the added stability though, and not more thrusts.
For the only planes.. They also can't spin the props past the speed of sound without dropping in efficiency so they needed more blades to transfer the power
Hello, nice intro to multi props! How about equations? Electric ducted fans get as much as ten bladed props. They are known for poor thrust and high current draw so what : when does the drag induced by the amount of blades counterbalance the increase in thrust? Or should we just fit as many blades as we can in the prop wake , until it becomes one big disk:) ? When is motor max load reached? I am not equiped with Kv and motor equations well enough, you could enlighten me, BR
Bruce, you get more information into my head, more efficiently than any other source! I am bookmarking these instructional tutorials as my memory is full.
The principle involved here is called "impedance matching". To get maximum efficiency, you have to match the impedance of the blade (thrust vs drag) to the impedance of the motor (torque vs battery draw). Just like in stereos where you match the impedance (resistance) of the speaker to the impedance of the amp, or like in cars where you match the torque/speed of the tires to the torque/speed of the engine with a "mechanical impedance transformer" - called a transmission!
Greg Collins thank fuck someone mentioned this, i was going insane
So then we need a transmission propeller. Is that why they made jet engine?
..paused, watched videos about ducting propeller systems ..and back to this one. Great stuff!!
Excellent video! very educational, enjoyable to watch, kept my attention! answered my questions! You even answered for me my questions on why WW2 aircraft have 4 bladed props, when even those who fly with the actual aircraft could not answer! I just found your videos while searching for prop info for boats! I have watched 6 of your videos, all fantastic. Thank you for posting these excellent videos, please continue!
This is a fascinating subject, I'm glad you're exploring it. I did some of my own trial & error analysis with boats. The variables were mostly the same. However one of the key targets I factored in was the Max Efficiency Amp rating of the motor. A draw value below the figure, let's say 18A meant you were leaving power on the table (not utilized by load) and a drawn value above Max Efficiency meant the motor itself was burning off power as excessive heat. A very challenging subject. I can't wait to see your results. Cheers.
Looking forward to the testing. Great episode.
If you have any 3+ bladed props that you want to convert to 2 bladed props, send them to me and I will fly them for 5 minutes
41Extremo i can do it in 3 minutes and i can do them 4 at a time... :p
LOL
I have a 5-bladed propeller. Can you convert it into 2-blades?
IRFZ44 I can convert it to one 3b and one 2b !
George Tsiros How?
Great video Bruce! I definitely learned a lot from this video and can't wait to see the practical test. Is good to see you back doing more technical videos that we love so much!
Bruce, excellent, in true form. Keep up the great work!
There is an additional bonus to multiblade props, and it's one of the reasons that I fly them. Because they produce more thrust, you can fly with less overall blade speed. This makes multiblade props quieter than two blade props, at least in my experience.
I would find a hover efficiency test interesting. In theory, some of the inefficiencies due to adding blades, is mitigated by spinning the prop slower. I'd be interested to know how the battery life duration for just hovering would compare between props.
Old post I know, but figured i'd reply anyway in case someone else runs across it. I saw a video of a guy who tested 4 blade, 3 blade and 2 blade (4 blade with 2 blades removed) props on his tiny whoop, and he was gaining roughly 30 seconds more flight time per blade removed So the 2 bladed prop was giving about a minute more flight time than the 4 bladed prop. So the drag reduction of slower prop speed in no way counters the drag increase of having more tips.
His test has flaws. If you want to compare the props, when takling about energi useage, you need to look on the swept area of the props.
In his test he is basicly trying to proove that you get better fuel economy If an motor only pulls one car instead of two. I think most of us can tell that with out an test
Great video and really anxious to see various props efficiency video. As always, your videos keep us coming back and watching. 2 👍👍 thumbs up Bruce.
Thanks for the video Bruce. On my 5" mini quad I've found that the 5x4x4 HQ props are the most efficient, in terms of performance props and my flying style, anyways. 4 minutes of pretty hard flight on a 1300mah lipo. Cornering on 3 or 4 blade props is the biggest selling point to me. All that grip in the corners inspires a lot of confidence.
Finally, I've always wondered about the science of blade count/dimensions xD
So I suppose having more propeller blades on an aircraft is a bit like having wider tyres on a vehicle. You get better traction, but also lose more energy through friction.
that is not a true statement. as more tier less pounds on each square inch of tire. and in mud and snow tires will ride up not sink in to grip
The majority of drag on cars, trucks, etc is from aerodynamic force, not from the tires
From rotational Physics, in an ideal world, there is only static friction between the tires and the ground and this friction does no work and thus you don’t lose energy. Rolling resistance is more due to the chemical grip and mechanical grip of the tire literally sinking their rubber molecules into the road and the rolling motion have to pull these molecules out when the tire keeps rolling. That is also how tracks rubbers in--race car tires experiences this so violently that they literally leave part and layers of their tires into the tarmac, and the tarmac now will give more grip and wear the tires less.
These people don’t know what they are talking about Andy, you are right. There is a reason why race cars don’t have ridiculously wide/tall tires, there is a loss of return at some point, just like a propeller.
Please talk Reynolds numbers! And a video about efficiency is needed, as many people have no idea what it actually means. PS RPM comparison in flight on the various props would be very cool, I havent seen anyone do it yet. Holla and ill throw my logger and rpm sensor down to you if needed.
so zero blades would be the most efficient, but produce the least lift. got it.
thanks i sprayed milk out of my nose
😄
Dennis Haupt Lol.
Lol
no zeros blades is infinitely inefficient
Well done, Bruce! An excellent discussion of propeller basics. For the fixed wing drivers, perhaps a video discussion of the considerations of prop pitch and diameter selection for a given airplane/motor, including going from two to three or four blades..
Cheers!
Great work sir👍. You are a great teacher.
Excellent video, great explanations. Thank you.
As always, very good explanation of the topic at hand :-)
Do you remember the Voyager project? That first plane doing a non stop around the world? They wanted efficient props for a reason. Some Swiss company promised them experimental miracles built in wood. When blade angle adjusting motors turned out to be toy quality, blades broke off, they finally gave up. Voyager flew around the world with props built (in overtime) by a renowned American propeller company. Find the Voyager story online or in the book.
The real breakthrough in power vs. efficiency will be the development of variable pitch constant speed props for RC/quads. Best of both worlds; Thrust on demand, efficient drag profiles during cruise power settings.
@@WilliamHelstad any helicopter
@@WilliamHelstad im not sure about the efficiency since they are not as well shaped as a fixed pitch prop. But they are multi pitch constant rpm
Much more rotational mass in a heavy 4 blade prop. Not tried them yet, but found the 3 blade non bull nose to be perfect for me. Another reason WWII props went multi blade instead of larger... Larger diameter beyond a certain point can make the tips break the speed of sound. Love the discussion, love your work! Thanks as always.
Very well explained, thank you! 👍
Other reason for late WWII fighters to have propellers with increased number of blades instead of longer ones was to reduce the blade tip speed, as they had then a very high dive speed blade tips had air compressibility issues. Also wider blades have lower tip speed for the same blade area than longer ones. For normal RC planes this doesn't matter because they fly at very low MACH.
Good point
It would be nice to see include comparison between a 2 blade prop and a tri-blade of a smaller diameter; keeping the other factors like pitch and bull nose the same.
Bullnose and knife-blade, but there's also Q-tip and Scimitar, as well as some diamond shaped variants. Not sure if those have made it to RC yet along with prop-fans. (More than 6 blades, but not ducted.)
Then you also have to keep in mind performance relative to airspeed. A prop that has a lot of bite in a static test might not have the top end aircraft speed of a prop that doesn't work as well in that situation. (So there's probably some choice between punchiness in acceleration and overall top speed.)
Thanks for doing this. Do you have like a visual chart with pros and cons of each blade type?
Very good video explaining why 3-blade props could be better or worse than 2-blade props. I'm quite liking the new DYS 5x4x3. They're cheap, well balanced and perform nearly identical to the more expensive HQ5x4x3. With the now popular 2205 motors they rock!. please, test on 4S -that's where speeds get ballistic ;)
I would love to see the announced real life test of these props. Any idea when you will be able to test them?
this was a great video Bruce , in this hobby we all follow like sheep (new Zealand analogy ) or walk on the backs of giants , but not many ask why am i doing this or that , but something tells me you ask why? alot Bruce and we all stand taller for it ! keep up the good work :) oh and you will not break the DAL props guaranteed :)
great as always! Balance between the diffrent props should be intresting to know.
essentially... more blades is to pack more blade area in the same diameter.
But each added tip is a significant power loss so you loose efficiency. (assuming same blade design)
The P-51 used 4 bladed props to keep the tips out of the dirt when taking off and landing.
It will be amazing test Bruce! Awesome!
Part of what I enjoy about flying quads has to do with all the changes and innovations. I fly Airbus A/C on a daily basis for work and I have an M-24 Orion Gyrocopter (2 seater) and aerobatic Acrosport II, Bi-plane, for recreation. Quad flying is cheaper but gives much of the same fun. A lot of the design features in model flying share a heritage in full size aircraft and now that materials are getting lighter and stronger, more cross over will occur. Bruce, I wonder what you see coming up....? Perhaps this idea warrants a short video? "Q-Tip" props i.e. small winglets on blade tips to reduce induced span flow or even variable pitch or constant speed props? (Airbus Neo aircraft have geared engines and have moved from typical winglets to "Sharks"). I would humbly submit, it is the battery tech that we must see where the really important changes need to occur in small and large scale. Thanks so much for your informative and humorous work!
+flytelaw1 Yes, I already posted a video on the q-tip props a while back, very interesting indeed.
+xjet Thanks...will have a look for it...Cheers, Chris
Is there a rule of thumb for upgrading to a 3 or 4 blade prop. I would think i would have to either reduce pitch or diameter in order not to put to much load on my motor. I have a corsair that i put an E-flight power 110 motor with a 110 amp esc . I will be starting off with an 18-8 two blade. I would like to put a scale 4 blade like my previous comment. Any suggestions?
Hi. I am new to this channel. This was good info for me. However I could not find the flight testing video. Can someone share the link please. Thanks
I have the same plane Corsair E-Flite crashed the same reason battery bad solder connection, and I have a 12X8 APC electric propeller , it pulls like crazy on the floor in the house so in the air It maybe OK what size to use 2 blade, and I have a lot of 2 blades in wood 12X6 I'm but afraid of flaps never had them in 15 years of flying so should I even try them ?
Bruce, it might be interesting to measure battery drain after the time trials just to get a real-world measure of the effects of different props on total power draw. I realize that that might require a "calibrated" battery, but it would help with understanding the whole thrust/power/performance/efficiency issue. Just a thought...
7:20 so they had to add more blades bc the engine was too powerful? so a p51-d mustang with only 2 blades or 3, would've been too much engine? so in essence the extra blades created more drag to basically keep the engine tamed from over revving?
great stuff bruce, i'm, just pondering these very questions, could you take a guess at what is the fastest prop for a 2s lowish 'c' rating, (30c) and 6040 knife edges and 5045x3 bullnose's?.. using the jjrc x1 we seem to be getting more punch from 6040s but the 5045x3 BN's have a higher top speed....>scratches head
Hey Bruce , I did my whole degree 8000word dissertation on this topic for my quad copter , I would love to hear your opinion on it, do you want me to email you a copy? Thanks
I would like to see how the 3-blade props compare to the 2-blade props on bench thrust/amperage test, particularly the linearity of the thrust-to-current ratio. Meaning, does the GemFan 3-blade Bullnose give 20% more thrust using 20% more current than the GemFan 2-blade Bullnose (equal thrust gain for equal current increase)? Or would the current draw be a higher percentage gained than the percentage gained in thrust? Or maybe thrust gained is a higher percentage than current draw percentage increase? I think having this data would conclusively show the performance you would gain is higher than the battery life you would lose.
+thechosendude
I think it is incorrect to compare 2- and 3-blades props of the same size on the same motor.
Because 3-blade prop with the same size and the same pitch will give more thrust on the same rpm, therefore, it will require much more power from the motor.
It is always a balance between speed and thrust. If you want higher speed you must sacrifice your thrust. You may select two-blade props of lower size with higher pitch and higher-KV motor. Your model will be slowly accelerating
Vice-versa, to obtain higher thrust, you can select 3-blades props, or props of higher size with lower pitch, and need small-KV motors running at lower speed. This makes a model very responsive, but slow. It is may be good for multirotors hovering, because when hovering they are requires only thrust, and no speed (although you cannot get thrust without moving the air)
So, direct comparison of just 3- and 2-blades props with all others params are the same - is not informative at all.
I think using 3-blades on lower-kv motor on lower rpm will show almost equal thust-to-current curve, but, keep in mind, since rpm is lower, air speed is lower too
(Sorry for my English)
AterLux I understand what you mean about drag on more blades and thrust not always equalling speed, but I think it's important to remember most of us "average" flyers aren't doing high-speed racing, we're doing freestyle type flying, where having gobs of instant thrust for punchouts is going to be more favorable than the top speed in a straight line.
Have you seen the miniquadtestbench website? He posts very detailed tests and lets you download his raw data. The raw data is very detailed. The most detailed motor thrust tests on many props I have ever seen.
Very interesting. Can you shed some light on the "scimitar" style bladed prop? What about what is being used on some submarines in what is called a "propulser?" Thank you.
Im looking to make a 1:16 Mooney bravo rc plane I’m looking for a 3 blade prop to go on. I’m asking for my friend!
Sorry for venting here. how about constant pitch props? Always wondered why props had that taper to them. I assume its because the speed of the tip is faster than the speed near the hub. Is this correct? More thrust is more torque also right? Hence slowly add power to take off to prevent torque roll. I see pilots constantly not using rudder correctly. I teach fellow pilots use of rudder for Take off, coordinated turns, slipping etc.. There are so many effects with props. Gyroscopic effect and asymmetric effect. Most R/C pilots fly turn and burn only using aileron. Also explain why we have right thrust built into planes. Thanks again for All your great videos. I've learned so much about electrics. I'll be putting up a safety video soon. Unlike a gas or glow motor. Once shut off that's it. Electrics are ALWAYS on. Just got 8 stitches in my arm . Was a dumb thing. especially since I've been flying for over 25 years. Three words. Throttle cut switch....
When do you think the test video will be? I need to order some new props because I use a lot of them.Can't wait too long, Weather is starting to get nice here.
Bruce I have a Tarot 650 ironman quad with 4114 320kv motors 16 inch props would it be better to use 3 or 4 blade props for max lift? I know that or atleast I think that flight times will go way down but lifting power will it increase? I was going to switch over to the wooden props? What do you think would provide the most lifting power?
Do you need to reduce the prop size when adding blades if keeping motor and esc the same. I didn't know if the the extra loading would over whelm the electronics and if reducing the prop size would you need a higher kv motor to increase revs.
At 5:55 you show a black 4 blade. That's a nice scale prop. I'm working on a corsair. Who makes it? As always. Another great informative video.
How is the correlation between more blades and Amp drawn? Is there a nice curve?
OK so what about 5 or 6 blades like the piper m500 & m600 some have 4,5,6 blades ??
Is puttung a duct around your propeller, but without the lip to avoid the negative effects of tilting a ducted prop with the lip and then using a bullnose to increase the efficiency (when ducted it should let less air get around the edge) a good idea or am I missing something?
Why don't they fence (winglet) the tips to prevent lift wrap over the tip?
excellent exposition
what is more powerful a polished plastic prop like with armoural on it or a satin finished prop ??
so if I wanted to go to 3 bladed props would I need to upgrade from 12amp esc? I have 2204 2300kv motors on 3s
+Damien Van Der Vlist probably not, maybe check your motor specs
BTW, you never got to show those 3D printed ducts on a 250 quad :)
I know from experience that ducted props increase efficiency, provide some lift in forward flight, hugely increase stability (the darn thing barely wants to move horizontally!) and they act as noise amplifiers even if they cut off the tip vortex, they reverberate all the other noises the motor makes. But all my experience was on a huge 600mm tri... project that I scrapped for a 250mm tri that folds and packs nice in a backpack.
Crazy thought. Why not put a little kick up at the tips of the props to keep the air from sliding off. Would that help with the vortex created and not cause any negative issues?
Hello Bruce,
Thanks for this vid!
Nice 1!.. Iam very interested in how the efficiency of a coaxial setup might improve with dif props sieze and different pitch.
What i believe is that the efficiency improves when a bigger prop is used with lower pitch mounted above and a smaller prop with higher pitch below. (eg used for a y6 setup).
I hope i can tempt you doing a video on this.
Anyhow thanks for all your support!
Gr. Wouter
Another advantage is imparted by how horsepower works, this applies for all rotating machinery NOT JUST RECIPROCATING ENGINES! :)
Horsepower is torque multiplied by RPM divided by 5252. By using more blades you trade off needing a small amount of torque at higher RPMs for a greater amount of torque at much lower RPMs. Thus you are decreasing the amount of HP you need to generate the same thrust by a small bit.
Bruce what would happen if have props with wing tips like on high efficiency airliners like 737-900 lr
What about the high pitch props? like the 5050 tri blades from gemfan. Would a 5050 2 blade prop be the way forward over more blades/bullenose ?
very interesting Bruce
I assume this is also the reason why hotliners (motorized gliders) use huge two bladed props. This allows for maximum power and efficiency.
Hi Bruce. I was just wondering... What would happen if you've got a really bad balanced prop and instead of adding or removing weight you just cut the tip of the heavy part? It will have a shorter and a longer blade. What will happen to the noise it makes, the tip vortex, the efficency? I can't try that myself as i don't have a rig to test it... Please reply :)
I have a question, If you want to run a 5x4x3 on a 15 amp ESC do you run the chance of burning out the esc? lets say on a RS2205 -2300KV motor?
Great video. I was wondering how to choose a prop for flying at high altitude. All the charts are produced at sea level and I will be flying at 7,500 feet.
Wonder how long until we see a props with winglets to increase efficiency.
+sqwert that would be cool
+sqwert 2 blade with winglets came with my tidewater stock
+sqwert would be great to see, but the centrifugal forces would be huge.
They exist, but the compromise often isn't worth the trouble
+Samm Sheperd (SNRS) Q-tip props exist as I'm sure you'll know. But as I understand it they are more commonly used to reduce noise as opposed to increase thrust.
Hello, have you done any testing on folding propellers?
i see some issuses. if the test should really compare the props in effience, you have to pid tune every singel setup. pid and so the energy draw could be completly different
Please do explain offset thrust!
Perhaps you could answer something I've wondered- wouldn't propellers benefit from fences? If spanwise flow hurts a wing, as you mentioned on flying wings, wouldn't the problem be even worse on a propeller, where where is centrifugal force to make it worse?
So, wanting more power, more blades or prop area is one way to go. But what about sticking with 2 blades, non bullnose and spnning the props faster instead? increase KV or cellcount. Granted, the standard 5" gemfans are a bit soft, but assuming a suitable propeller is available.
+Akujiwar Bladefist
Spinning faster decreases efficiency. In the worst case a blade hits the turbulence of the blade before it and will not really produce any thrust anymore.
Does anybody know if material makes a difference. In my totally unscientific experience, the glass fiber nylon 5030s react better to my sticks (feel much tighter) than ABS 5030s but they love to shatter if you don't land softly. All in my head?
what does the curve look like, as # of propeller blades increases vs efficiency?
One thing I've been confused by recently is contra-rotating props. I've read they improve efficiency and are used by planes like the Russian Tu-95. But at the same time miniquads like a Y6 design that have counter rotating props are considered much less efficient due to one prop being in the prop wash of the other. It's strange how depending on the application it's more or less efficient. The only thing I can guess is that the Y6 miniquad has the props too far apart so it doesn't get the benefits like a contra-rotating prop on an airplane. The props are almost touching on a contra-rotating airplane setup.
single blade props are the most effeciant.
but hard to balance
Teleportation is even more efficient.
Jea but they are heavy due to counter balance so 2 blade seems to be the best
Wrong, single blade ducted fan for the win! :)
TheRattleSnake3145 balance?
there is so much more than just efficiency- with some gas engine applications, a difference in just one number on the pitch of a prop can make all of the difference. It sometimes seems that too much air flowing past the tail surfaces gives terrible performance. Experimentation and patience is required to find that one "perfect" prop- once it is found, remember it! Each aircraft is different, even matched aircraft built side by side.
so would a gyrocopter benefit from having 3/ or even 4 bladed props? considering they generate lift due to auto-rotation, would having a bit more drag on the blades make them spin faster, or if not faster, generate more lift at the same RPM?
I know this is slightly out of the depth of this vid, but i was really curious. ty
Is a contra ducted fan bwtter than a regular ducted fan? Thanks!
I would love to know how a 5inch tri/quad compares to a 6inch 2 blade as far as thrust.
Use the ball of sting to measure the height. No latency. Tie the ground end of the string to a mug. When the mug lists off stop the watch
Ok but one thing I just can't quite get any info on is high kv low pitch and small blade vs low kv high pitch big blade. For example, assuming you use say an a2208 motor at 2600 kv and a 5x3 prop, then the same size a2208 motor at 1400kv but with say a 7x7 prop (or whatever gives you the same pitch speed as the 2600kv) what are going to be the similarities and differences? Will the higher kv just be better all around? If so, why even use low kv motors? Why not just use high kv with a lower pitch? In my example, you should have the same speed and power correct? Would one be more efficient?
He mentioned blade pitch vs blade stall speed with the lower pitch maintaining effectiveness at lower speeds. I suspect that the larger the RPM change on a motor, the more power will be required to get to the desired RPM. Thus, the higher speed motors and the heavier props may be more likely to brown out the power rails during wild maneuvers on higher cell-count packs or underrated electronics.
Well, I've since researched this much more and all I can really conclude is theres so many friggin variables that its not worth it to even factor these in, best to just get your speed however you can\cheapest way you can. Ive found thinking of kv as a customization to match your equipment is much better than trying to figure out what's going to be the most perfectly efficient. I like high kv because you can get more power from a cheaper motor, that's really the biggest concern of mine, power vs cost.
And more thrust* before anyone throws a "ya but" at me explaining power doesn't necessarily translate into thrust :), which is true but pretty much every example I can find you'll get more thrust from a higher kv motor with all else equal. Low kv is good sometimes too, you can go with an oversized motor with a low kv to get pretty crazy thrust from minimum watt draw with a large prop, so you're paying more for motor and more for prop but they'll run on cheaper electronics. Oh and also theres the partial throttle effects, I guess low kv is much more efficient partial throttle, I tend to fly full throttle a lot so that doesn't affect me much.High kv will use a much smaller lighter prop, and low kv uses very large heavy props, so I suspect it takes about the same amount of power to get each setup up to rpm, but the smaller prop will be less efficient, which is another factor.
I suppose the old car argument "Torque vs Horsepower" comes into play here somewhere. I've still got a lot to learn. :)
Yea it kinda does, that ones way simpler though, horsepower all the way as long as you have adequate torque ;)
servus ,what happens if we have a prop that has more than 4or5 blades but lowerrpm and with efficientending
Will you also test these props on your bench and test and measure then how much lift they generate and how much amps they use?
I'm mostly thinking triple blades offer the best ratio, especially to avoid ring-State and I was wondering if you're use a 3d printed clover prop with integrated circular duct if it would give you some benefit :-?
love my DAL probs have not fully broken one yet chiped tips of the a fair bit but that is not noticeable un like the gemfans i started with were if i poked a wall to hard they exploded
to share a story about larger props and larger engines. My stepfather put his favourite engine into his favourite airplane. the result was a 300 horse motor on his navion and a prop that just cleared the ground. of course mods to regular aircraft need approval. he was told how the rule was with a deflated nose oleo the prop had to clear one foot. so he photographed himself with his boot under the prop with oleo deflated - one foot of clearance! they let him get away with it.
I would love to see those inefficient props compared to 6" two bladed props. In my opinion it is crazy to use them only to spare 1". I am very happy with my 6" props!
The Kingkong props are do completely unbreakable. With learning I have had some horrible crashes and have yet to break a prop. So as a learner I brought heaps of then and the only reason I change them as they are too bent to fly right. I do not know how good they are as props and would love to see the thrust tests. Thanks.
Bruce are you saying that a 5040x3 has more thrust per rpm than a 5040x2? I always thought the "40" represented the inches of air moved per 1 rev for the entire prop, and not a single blade, or am I mistaken?
+Jon Keller
The number denotes how far a prop would "screw" through the air within one revolution. If you'd cut a prop down to one blade or you've got ten blades of the same pitch, it would still be the same distance every time.
+Jon Keller 2 blades, 3 blades, pitch remains the same. More blades = more thrust. Imagine the propeller moving through a solid material. Like a screw through wood. Pitch would determine how far in the screw, or propeller, would move for each revolution. Now, adding more blades, it would not move further per revolution, but if you were to attempt to pull it out, more blades would make that more difficult, as its got more grip.
I guess I've never thought of it as moving through a solid, but rather moving air. Makes sense. Most of the acro guys I've spoken to will tell you that they use tri's because of the added stability though, and not more thrusts.
winglets on the bullnose perhaps?
Did you not make the prop test video or did I miss it between your other videos?
if your loading more then would it give less rpm at a certain point and give less thrust? a point of diminishing returns.
For the only planes.. They also can't spin the props past the speed of sound without dropping in efficiency so they needed more blades to transfer the power
Are you going to test the new six-bladed props too?
Why are there no hanglider style wings on a helicopter?
So with a ducted bullnose we should have the best of both worlds?
Great. Can not wait for next video ;)
Hello, nice intro to multi props!
How about equations?
Electric ducted fans get as much as ten bladed props. They are known for poor thrust and high current draw so what : when does the drag induced by the amount of blades counterbalance the increase in thrust? Or should we just fit as many blades as we can in the prop wake , until it becomes one big disk:) ? When is motor max load reached?
I am not equiped with Kv and motor equations well enough, you could enlighten me, BR