I unironically re watch your air engine series frequently. Every time there's a new video on one i watch it twice in a row and then in a couple days maybe again. Always a childhood dream of mine, no other entertainer has gotten me to re watch videos on UA-cam. So longer vids with deeper breakdowns are super appreciated :D
It’s because he can break down the whole episode with extra information into an optional long form video so viewers can get behind the scenes and the process of making it
The adverse roll that you described isn’t strictly speaking due to having a vee tail. It’s due to having the control surfaces above the the roll axis. If you rake the tips of the vee downward then the roll will coincide with the yaw. The same holds true for a conventional rudder.
About the bottles - if you are going to revisit gluing/sleeving two of them together, what if you used a balloon on the inside to prevent leaks? Similar to how a bike tube holds the pressure but the tire stops it's expansion, the balloon holds the air (no leak) and the bottles simply stop the balloon from exploding? I imagine the issue then would be shift to making a seal that doesn't rip the balloon - but it would be interesting to see if allows you to shave some weight! You'd also get a really good visual of how much pressure is left in the bottle as you fly as the balloon deflates. Awesome project! keep it up!
@@Araye A small carbon bottle designed for paintball / air rifles would be perfect as it can hold up to 4500 psi. Now I want to try that but I doubt I will have the patience and skills to build it haha
The bit about the propsaver not working as a result of the prop being used as a flywheel - didn't realize it would cause issues, but you explained it really well. Thanks for the deep dive!
The larger sizes of disposable CO2 canisters are more efficient in terms of energy/weight if you ever want to go that route. I also suspect you could also save some weight by switching to a smaller battery, maybe even a non-rechargable battery (two lithium coin cells). Don't need a lot of power for just the servos.
servos..., I tried running 2 servos from a 5v small power bank and the safety always took over and cut the power for a fraction of a second, I didn't think to add 2 small lithium cells in series
I think the profile drag would be much lower, the diameter of the soda bottle is much greater than the CO2 cartridge. I guess it would be difficult to actively regulate the high pressure coming out of the cartridge without adding more weight though.
One more thing regarding Co2. The final conclusion was that it contains half the amount of gas than two 2L pets. But the Co2 much denser than the air so assuming the expanding gas reaches the same velocity it should have 1,5 x momentum. So maybe smaller cylinder would provide the same power therefore less gas exhausted per cycle = longer run
The issue is even with the denser air it depletes around the same weight by design of the engine and the actual amount of air stored is drastically less, such that it would still just be plain worse than the bottles. @@attilaschneider712
@@nathandavis5021 I think the current design has some reduction built in, but even with a new independent reduction valve, it would most likely make up for difference in drag. Not to ment improved "fuel" would almost certainly make up for the extra weight of a pressure reducer.
Excellent video, and I absolutely loved going more in-depth into the topic. Please make more of them, and continue working on the air powered aircraft - it's probably my favourite UA-cam series. Experimenting with multi-engined versions, air tanks in the wings, pusher props might be cool ideas for the future.
I like these "honest" comments, like how it took ages to drill those holes and stuff. In Normal UA-cam-Formats everything can look so easy and fast. But reality is often way more stressful. It brings you back to how things actually work.
Great explanations and so much fun to see, but I think the difference between a CO2 cartridge and the compressed air bottres is smaller because when the motor stops there stil is at least two liter left inside the bottles and the motor does need some pressure to do any work so it is more than that, compared to the very small volume of the CO2 cartridge so very little gas is left unused. Also the CO2 being a liquid compressed should have a more constant pressure output as the bottles with air and the smaller volume create less drag in an airplane. However an engine that runs on compressed air tanks that you can simply pump up yourself so much cooler than an engine that runs on disposable CO2 cartridges.
I haven't done the math, but I think the fact that the CO2 is starting at a much higher pressure means the energy output is much greater. Your engine would need to be designed to operate on 800PSI to take advantage of that; I think a pressure regulator basically burns off the excess energy as heat. (I do agree that being able to use your own air is cooler than buying CO2 though)
This a great directors cut, engineering insights production. Really enjoy seeing this. For the wing leading edge, you might consider using foam cut with a hotwire to make a very thin sheet, or using thing depron. @JuliusPerdana is a RC depron plane crafter. He has many good techniques and videos. eg: "How to bend depron - polyfoam using tape and heat gun", or rolling over a pipe to curve to shape. You could also experiment by increasing rib spacing; particularly behind the spar tube. Another possibility is tacking a strip of paper to the film (with dabs of heat) which could replace the balsa. You'll likely need to apply a heat activated spray adhesive like 3M Super 77 to get the paper to adhere to the ribs. This would allow you to apply the film in the same manor while reducing weight. Hopefully this gives you some alternative ideas.
Hey Tim! Judging by the noise output of your engine, have you thought about a 3 cylinder design for high, medium and low pressure expansion. This had been done on steam engines. Thank you, love the content!
Well done! One thing you might want to modify if you ever give it a go again: "A wing with a chord-wise cut through it tends to behave more like two lower-aspect-ratio wings flying in close formation. The ends of the gap act like wingtips and shed their own tip vortices. If an airplane has significant gaps at the wingroots, it effectively has two low-aspect-ratio wings instead of one higher-aspect-ratio wing. This will cause the wing to have a very low span efficiency and high induced drag. The gap size required to cause this effect is relatively small, and it is much more important to seal chord-wise junction gaps than any other type of gap on an airplane." All the best/Axel
Thanks for sharing your ideas! I wonder which Raynolds number you are calculating lift curves for. In fact I think you should calculate for R=50000 because of low speed and short cord. Then Naca 4412 is not good, see airfoil Tools. A lot drag which increases sink. I would go for Göttingen 269 instead. Compare and see for ncrit=5 and 9!
Dropping the ‘head’ of the engine so a more direct flow out of the bottle might help with gas flow, although would result in an offset crank. PS. Some destructive pressure testing of a few bottles would give you a better idea of what pressures can be achieved.
It is always interesting watching people design and build AC. Your projects are always creative. My two cents worth, I would suggest "stick" framing the tail. It is much stronger, lighter, cheaper, and faster than drilling all those holes. I would suggest using balsa over the entire last panel (from leading to trailing edge) at the wing root and tip. You can get rid of the carbon rods and not have the problem with the warping on the end ribs. You get the bonus of a torsionally stiffer wing root. To save weight, you could also have a half panel instead of a full panel at the root and tip and use half the balsa. Although I love the aesthetic of the V-tail, you are right about the adverse roll when turning. Keep up all the interesting projects and videos. I am really interested to see how your design advances.
A trick I used to avoid the last rib of a wing buckling when tensioning the Monokote is to add a sideways rib to it. This also serves to round off the wingtip and can also add a small angle to it as well as taper the shape.
Bro 4412 is way too thick for such a small and slow plane. Try AG34, AG35, AG36 like on the 2m Allegro. Keep in mind that the 60:1 L/D is the idealized 2D value. Even the best to planes at this scale only get ~20:1 3D L/D Also best way to save weight on the tail is to use the lightest 3m balsa you can find and sand an actual airfoil profIle. You can cut the balsa weight nearly in half while retaining bending stiffness. I can’t tell if you left the LE square but if you did the air is probably immediately separating from the tail which gives lots of drag and reduces control authority. Nice work I really enjoy watching your vids!
Maybe keep the bottles intact & add a hose from rear cap to engine. This might weigh a bit less than the nylon bolt. Also, the rear bottle could face forward.
Just before you released your previous video I had watched your entire air powered engine series almost every day for a week straight. No idea why but I was insanely obsessed with it. You have a great video style.
5:39 hold the pieces up to a light and look for any opacity in the backing. Or Use the same method you did by cutting a small square and stick a tiny piece of masking tape on the side you determine as the correct side (on the larger piece, obviously)
I'm sure you thought about this but an A tail is a great alternative to a v tail as the yaw and roll go in the same direction but there is the same weight saving as a v tail. The main disadvantage is having something dragging below the plane. Would be cool to see something like this on the next rendition.
What about using a larger CO2 cartridge (such as one with double the volume), because it would weigh less due to square cubed law, and it would also have significantly less parasitic and frontal crossectional drag... And you could fit many more of them onto the plane.
The adverse roll on the V tail is probably the main reason you don't see it used much on gliders, where the tail tends to be more slender and wider. An option would be to go to an inverted V tail, but this makes it more vulnerable on landing in the grass.
Tom, I think you'd love to visit next years Icarus Cup held in the UK. Many human powered aircraft competing, great for inspiration for lightweight wing structures.
Could you repurpose the one way valve from a football and fill it with an inflation needle? It looks like you can pick them up cheaply. It would also make filling and disconnecting easier.
I love the behind-the-scenes review, please continue them! A "fun" note - if you were flying this in the States, you'd need a RemoteID tag before takeoff. Include that in your preflight checks 😂
Hej Tim, great video as always, your air-engine series is great :) I am wondering about one thing : the CO2 cartridge isn't as as bad as originally presented. It has a smaller potential air capacity, but also considerably lower drag compared to the bottles. Do you think that lowering drag could outweight a smaller total output? You could even build a flying wing, integrate everything.
Maybe someone mentioned it but given the weight of the compressed air, the CG would shift rearwards as the air runs out. Surely that could have a huge influence on the flight characteristics?
added problem with the co2 canisters is that they cool down the co2 considerably as it comes out (adiabatic cooling). this would probably cool down the seals and make the engine not run as well. It also expands less as it is cooler. CO2 is also denser than normal air ~2kg/m3 vs 1,3kg/m3 air but i have no idea what that would do to the engine.
with some smart engineering I think you could optimise the bottles further, as you said with the splicing but also just one wrap of carbon or glass fibre sheet, a little resin and I wouldn't be surprised if you can get upwards of 200psi in them.
Just a Idea I got while watching. Have you thought about using the space in the wings as air storage, maybe using 3 layers of plastic film to make a seal and using a hole in the carbon rods as "fuel lines".
One last thing - I think you should get better efficiency out of your engine at higher loads and lower RPM, as in such a plastic build, friction builds up really fast. You should get yourself a few basic plastic propellers with various pitches, see what works best, and then buy a fancy carbon one at the right size.
Awsum !!! I didn't see your previous video (yet) , maybe you could call this a re-debrief video as this is where more learning / ideas are created / realized...... good on you !!!!!! 😉😎
37:23 so how an altitude sensor works it makes sense as submarines increase pressure deeper your go you decrease that same stored pressure the higher you go as well as stored fuel temperature vs air temperature that's why your flight characteristics change via altitude (context) reference the combined 2 liter bottles having forces around it acting on it
Have you considered adding a tuned expansion chamber to the exhaust outlet? It works wonders for 2-stroke engines in terms of increased power output over a narrow rev range. I wonder if it might improve the efficiency of an air-engine too? 🤔
I built most of the fuselage and the main wing's spar of a Cozy MK IV from plans I bought back in 1998. It's the 4-seat version of the famous Long EZ by the God of aeronautics himself, Burt Rutan. The first chapters of all his plans are the bible of composite construction. Hot-wire foam cutting done right, is hard to beat. Most flying surfaces of composite experimental aircraft is built that way. The next best thing, would be a CNC mill. If you hot wired two pieces, a leading edge portion to glue to the front of the spar, and the trailing part to the back of the spar, would give the closest construction to the real plane. No need to glass a skin. Just sand and paint to protect the foam against UV.
I'm wondering if car engine piston rings can be used in your air engine. There are pistons designed with holes in the oil scraper ring seat. You can print a piston with 2 rubber ring seals (for example you can use rubber O-rings or print them as you did it for the current model) and add a bunch of tiny L-shape holes from the top of the piston to the space between O-rings. In that case, you technically should get better compression and fewer leaks at the bottom dead point and the top dead point when your current rubber seal shrinks. Also, you can change the shape of the intake and exhaust to a conical shape with more rounded edges like it is done in 4 throttle intakes on motorbikes so the engine chamber can be filled with air faster and the air leaves the chamber faster. Another thing I'd try is using a T-shaped or V-shaped valve instead of a ball so the combination of the inlet channel and the engine chamber together act like a compression chamber of a turbojet engine. And the last thing I wanted to ask is - why don't you try to wind up a clock spring with an air piston and then use it to rotate the propeller of the aircraft?
Could you take some weight out of the piston skirt too? Is it possible to print a bottle with isogrid ribs to hold extra pressure and streamline it? Or even take the c02 canisters as it will drastically reduce frontal area?
Hi Tom, Mark here, thanks for the deep dive. Love it. BTW, I still have one of those Air Hogs planes which I got as an adult 30 years ago. Hanging in the garage with my RC gliders. I saw that DLG on the original video, obviously, and wondered about it so I looked it up. Sadly the website is pretty sparse. Can you provide some details? Like where is this made, etc.
When doing the maths, do you take into account that there will be 4 litres of air that will go unused, since at 1atm inside and 1atm outside, it has no willingness to move through the engine ? There will obviously be an amount of CO2 in the canisters that will also stay inside the canister, but the volume is so much smaller, so less will go unused?
17:52 There's probably a deep rabbit hole of power train optimisation on your air engine - how would you even characterise efficiency here? Thrust per psi, thrust per volume of air entering the piston chamber? If you do manage to figure out the engine efficiency and torque curves, matching the best propeller becomes possible for the design operating point if you can get the prop performance curves, either from published prop test data or estimated using a performance calculator. Probably too dense and boring to put into a UA-cam video but interesting engineering wise to think about. Good work!
A thought that struck me with the piston. If it was rectangular instead of square, the piston maybe could "keel over" in one direction at the bottom or top to change the width and thereby let the air by on the compression stroke. Come to think of it: your idea with the channels sounds simpler :)
A major efficiency gain could be had by adding some kind of cover for the inner wingtips, to eliminate those wingtip vortices, or am I missing something?
I wonder if LW-ASA might be better instead of the ABS? It'd save off some weight, but it might still have the issue of being too weak. Regardless, ASA would likely still be a better option over ABS, given the better UV resistance.
What if you made the wings into pressure chambers? That could increase their rigidity, counteract the contour between the spars, and improve the efficiency of the vehicle. But I'm no engineer.
Did you make any calculations on air drag of the bottle vs the CO2 cardridge? The drag should scale linearly with crossectional area, so a 2 times reduction in "tank" radius should reduce the dragforce by a factor of 4. Don't exactly know how this will relate to flight time as velocity might also increase, but might be worth a test anyway.
Well, the first time I flew mine I got totally convinced of it somehow having a spirit of some sort. I had already had a bad experience misusing and underwinding a professional rubber band balsa plane and I didn't expect this plane to do any better so...I somehow thought it would be OK to fly it close to a bunch of trees. It somehow dodged them all...but the last one :) but it got every neuron of my brain amazed by the power and roaring sound :D I miss it...
Would it be a possibility to put dry cubes into the bottle. If it's not too hot( which it isn't in UK) there should be a gradual evaporation, creating CO2 gas...just a thought
Just mention, the co to canister are better because the drink bottle is large era the co canister has smaller erea the drag from dink bottle do not outweigh the volume to erea
![[UA] Eternal Fire проти NAVI | EPL Season 20 Malta](http://i.ytimg.com/vi/chvlsDygrZM/mqdefault.jpg)
I unironically re watch your air engine series frequently. Every time there's a new video on one i watch it twice in a row and then in a couple days maybe again. Always a childhood dream of mine, no other entertainer has gotten me to re watch videos on UA-cam.
So longer vids with deeper breakdowns are super appreciated :D
Man saw reaction channels taking off and decided to react to his own contact lol
Love this format. Please keep doing this. 👍🏻
Meta as heck!
He can call it an In Depth Review and avoid the reaction stigma altogether
It’s because he can break down the whole episode with extra information into an optional long form video so viewers can get behind the scenes and the process of making it
The fact he snubbed his own sponsor bit made it even better
The adverse roll that you described isn’t strictly speaking due to having a vee tail. It’s due to having the control surfaces above the the roll axis. If you rake the tips of the vee downward then the roll will coincide with the yaw. The same holds true for a conventional rudder.
Liking it so he sees
I loved this format! Please do more like this in future!
I agree with this.
Agreed. Fun format.
About the bottles - if you are going to revisit gluing/sleeving two of them together, what if you used a balloon on the inside to prevent leaks? Similar to how a bike tube holds the pressure but the tire stops it's expansion, the balloon holds the air (no leak) and the bottles simply stop the balloon from exploding?
I imagine the issue then would be shift to making a seal that doesn't rip the balloon - but it would be interesting to see if allows you to shave some weight! You'd also get a really good visual of how much pressure is left in the bottle as you fly as the balloon deflates.
Awesome project! keep it up!
additionally, he could build a much more streamlined fuselage with cartridges, reducing drag as compared to flying 2 liter bottles around.
@@Araye A small carbon bottle designed for paintball / air rifles would be perfect as it can hold up to 4500 psi. Now I want to try that but I doubt I will have the patience and skills to build it haha
@@jean-micheldupont1150 if one person can do it, so can you. all you need is the desire. with desire, all things can be overcome.
The bit about the propsaver not working as a result of the prop being used as a flywheel - didn't realize it would cause issues, but you explained it really well. Thanks for the deep dive!
The larger sizes of disposable CO2 canisters are more efficient in terms of energy/weight if you ever want to go that route. I also suspect you could also save some weight by switching to a smaller battery, maybe even a non-rechargable battery (two lithium coin cells). Don't need a lot of power for just the servos.
servos..., I tried running 2 servos from a 5v small power bank and the safety always took over and cut the power for a fraction of a second, I didn't think to add 2 small lithium cells in series
I think the profile drag would be much lower, the diameter of the soda bottle is much greater than the CO2 cartridge. I guess it would be difficult to actively regulate the high pressure coming out of the cartridge without adding more weight though.
One more thing regarding Co2. The final conclusion was that it contains half the amount of gas than two 2L pets. But the Co2 much denser than the air so assuming the expanding gas reaches the same velocity it should have 1,5 x momentum. So maybe smaller cylinder would provide the same power therefore less gas exhausted per cycle = longer run
The issue is even with the denser air it depletes around the same weight by design of the engine and the actual amount of air stored is drastically less, such that it would still just be plain worse than the bottles. @@attilaschneider712
@@nathandavis5021 I think the current design has some reduction built in, but even with a new independent reduction valve, it would most likely make up for difference in drag. Not to ment improved "fuel" would almost certainly make up for the extra weight of a pressure reducer.
The air-powered plane series has been a fascinating watch and this commentary augments it well.
Excellent video, and I absolutely loved going more in-depth into the topic. Please make more of them, and continue working on the air powered aircraft - it's probably my favourite UA-cam series. Experimenting with multi-engined versions, air tanks in the wings, pusher props might be cool ideas for the future.
Thank you Tom, I really enjoyed the director's cut it answered all my questions.
These additional videos are great Tom! Thanks for taking the time!
I like these "honest" comments, like how it took ages to drill those holes and stuff. In Normal UA-cam-Formats everything can look so easy and fast. But reality is often way more stressful. It brings you back to how things actually work.
Great explanations and so much fun to see, but I think the difference between a CO2 cartridge and the compressed air bottres is smaller because when the motor stops there stil is at least two liter left inside the bottles and the motor does need some pressure to do any work so it is more than that, compared to the very small volume of the CO2 cartridge so very little gas is left unused. Also the CO2 being a liquid compressed should have a more constant pressure output as the bottles with air and the smaller volume create less drag in an airplane.
However an engine that runs on compressed air tanks that you can simply pump up yourself so much cooler than an engine that runs on disposable CO2 cartridges.
I haven't done the math, but I think the fact that the CO2 is starting at a much higher pressure means the energy output is much greater.
Your engine would need to be designed to operate on 800PSI to take advantage of that; I think a pressure regulator basically burns off the excess energy as heat.
(I do agree that being able to use your own air is cooler than buying CO2 though)
This a great directors cut, engineering insights production. Really enjoy seeing this.
For the wing leading edge, you might consider using foam cut with a hotwire to make a very thin sheet, or using thing depron. @JuliusPerdana is a RC depron plane crafter. He has many good techniques and videos. eg: "How to bend depron - polyfoam using tape and heat gun", or rolling over a pipe to curve to shape.
You could also experiment by increasing rib spacing; particularly behind the spar tube.
Another possibility is tacking a strip of paper to the film (with dabs of heat) which could replace the balsa. You'll likely need to apply a heat activated spray adhesive like 3M Super 77 to get the paper to adhere to the ribs. This would allow you to apply the film in the same manor while reducing weight. Hopefully this gives you some alternative ideas.
I definitely loved the extra technical insights, wouldn't object to having the extra detail directly in the main video to be honest.
Hey Tim!
Judging by the noise output of your engine, have you thought about a 3 cylinder design for high, medium and low pressure expansion. This had been done on steam engines.
Thank you, love the content!
it’s been awesome to see this project progress through the years and all your innovations👍
Well done!
One thing you might want to modify if you ever give it a go again:
"A wing with a chord-wise cut through it tends to behave more like two lower-aspect-ratio wings flying in close formation. The ends of the gap act like wingtips and shed their own tip vortices. If an airplane has significant gaps at the wingroots, it effectively has two low-aspect-ratio wings instead of one higher-aspect-ratio wing. This will cause the wing to have a very low span efficiency and high induced drag. The gap size required to cause this effect is relatively small, and it is much more important to seal chord-wise junction gaps than any other type of gap on an airplane."
All the best/Axel
Absolutely right. The Performance will increase signifikant. Lets say other 30 Seconds..
Thanks for sharing your ideas! I wonder which Raynolds number you are calculating lift curves for. In fact I think you should calculate for R=50000 because of low speed and short cord. Then Naca 4412 is not good, see airfoil Tools. A lot drag which increases sink. I would go for Göttingen 269 instead. Compare and see for ncrit=5 and 9!
I really like this more detailled sort of reaction video. Would love to see more in the future.
Dropping the ‘head’ of the engine so a more direct flow out of the bottle might help with gas flow, although would result in an offset crank. PS. Some destructive pressure testing of a few bottles would give you a better idea of what pressures can be achieved.
Should be in slow motion to see the condensation forming and leaving
It is always interesting watching people design and build AC. Your projects are always creative. My two cents worth, I would suggest "stick" framing the tail. It is much stronger, lighter, cheaper, and faster than drilling all those holes.
I would suggest using balsa over the entire last panel (from leading to trailing edge) at the wing root and tip. You can get rid of the carbon rods and not have the problem with the warping on the end ribs. You get the bonus of a torsionally stiffer wing root. To save weight, you could also have a half panel instead of a full panel at the root and tip and use half the balsa.
Although I love the aesthetic of the V-tail, you are right about the adverse roll when turning.
Keep up all the interesting projects and videos. I am really interested to see how your design advances.
This is like a directors commentary I love it
A trick I used to avoid the last rib of a wing buckling when tensioning the Monokote is to add a sideways rib to it. This also serves to round off the wingtip and can also add a small angle to it as well as taper the shape.
Great format ! Keep it going
Bro 4412 is way too thick for such a small and slow plane. Try AG34, AG35, AG36 like on the 2m Allegro. Keep in mind that the 60:1 L/D is the idealized 2D value. Even the best to planes at this scale only get ~20:1 3D L/D
Also best way to save weight on the tail is to use the lightest 3m balsa you can find and sand an actual airfoil profIle. You can cut the balsa weight nearly in half while retaining bending stiffness. I can’t tell if you left the LE square but if you did the air is probably immediately separating from the tail which gives lots of drag and reduces control authority.
Nice work I really enjoy watching your vids!
This is where the "Tim Station" norm was born and I'm very proud to say that i was there!
Maybe keep the bottles intact & add a hose from rear cap to engine. This might weigh a bit less than the nylon bolt. Also, the rear bottle could face forward.
In the US, you can sometimes find 3 liter soda bottles like that. Maybe something to look for.
Just before you released your previous video I had watched your entire air powered engine series almost every day for a week straight. No idea why but I was insanely obsessed with it. You have a great video style.
yeah i agree with the idea that i would not go so much for weight but starting to focus on a more aerodynamic fuselage
5:39 hold the pieces up to a light and look for any opacity in the backing.
Or
Use the same method you did by cutting a small square and stick a tiny piece of masking tape on the side you determine as the correct side (on the larger piece, obviously)
Really enjoyed watching this to get some of the thinking behind things - definitely good to see more of these :-)
I'm sure you thought about this but an A tail is a great alternative to a v tail as the yaw and roll go in the same direction but there is the same weight saving as a v tail. The main disadvantage is having something dragging below the plane. Would be cool to see something like this on the next rendition.
A tail? Ive never heard of that one
Love it, please do more, your video on your main channel are too short for me, I love more details and anecdotes !
What about using a larger CO2 cartridge (such as one with double the volume), because it would weigh less due to square cubed law, and it would also have significantly less parasitic and frontal crossectional drag... And you could fit many more of them onto the plane.
The adverse roll on the V tail is probably the main reason you don't see it used much on gliders, where the tail tends to be more slender and wider. An option would be to go to an inverted V tail, but this makes it more vulnerable on landing in the grass.
I wish Tim Station could do the director's commentary on everything
You can melt acryl with acetone to make good glue for plastic.
I think your air engine videos are my favourite, seeing the itteration is facinating!
Tom, I think you'd love to visit next years Icarus Cup held in the UK. Many human powered aircraft competing, great for inspiration for lightweight wing structures.
25:53 drilling holes and adding covering film might add sort of craters on its surface, which might form turbulent air and adding drag
Could you repurpose the one way valve from a football and fill it with an inflation needle? It looks like you can pick them up cheaply. It would also make filling and disconnecting easier.
I love the original video and this reaction with background info is chef's kit ❤.
Appreciate the breakdown
I love the behind-the-scenes review, please continue them! A "fun" note - if you were flying this in the States, you'd need a RemoteID tag before takeoff. Include that in your preflight checks 😂
Hej Tim, great video as always, your air-engine series is great :) I am wondering about one thing : the CO2 cartridge isn't as as bad as originally presented. It has a smaller potential air capacity, but also considerably lower drag compared to the bottles. Do you think that lowering drag could outweight a smaller total output? You could even build a flying wing, integrate everything.
No. The gas pressure is too high and it cools as it releases.
Oh man, watched that other video earlier and was thirsting for MOAR. Now here ya are!
Maybe someone mentioned it but given the weight of the compressed air, the CG would shift rearwards as the air runs out. Surely that could have a huge influence on the flight characteristics?
added problem with the co2 canisters is that they cool down the co2 considerably as it comes out (adiabatic cooling). this would probably cool down the seals and make the engine not run as well. It also expands less as it is cooler. CO2 is also denser than normal air ~2kg/m3 vs 1,3kg/m3 air but i have no idea what that would do to the engine.
When you mention the 60 L/D, you're surely talking about the airfoil, right?
60 L/D for the wing seems like a very high value even at stall.
This was great, Tom. Please keep doing these.
An inverted V tail would couple the yaw and roll moments, just roll 180's degrees and you should be good to go :-)
Also, DEFINITELY do these videos again!
Hi Tim, You should buy carbon Archery arrow shafts - they have all of the specs written on the sides - - wall thickness grams per inch etc..
with some smart engineering I think you could optimise the bottles further, as you said with the splicing but also just one wrap of carbon or glass fibre sheet, a little resin and I wouldn't be surprised if you can get upwards of 200psi in them.
Just a Idea I got while watching. Have you thought about using the space in the wings as air storage, maybe using 3 layers of plastic film to make a seal and using a hole in the carbon rods as "fuel lines".
You could try wrapping a foam wing in foil for drag reduction
I liked this video better than the original. Both are good, but I just like this better.
This kind of projects should give bamboo stripes more try. easy manufacturing, No 3D mumbo jumbo.
You should really try a pump that pumps both-ways. (on the up stroke as well as the down stroke)
Enjoy very much listening to your detail explanation.
Love flying objects, especially VTOL.
Thank you Tom 🙏🙏
One last thing - I think you should get better efficiency out of your engine at higher loads and lower RPM, as in such a plastic build, friction builds up really fast. You should get yourself a few basic plastic propellers with various pitches, see what works best, and then buy a fancy carbon one at the right size.
with the co2 cartridge, would the reduced drag aid in enough way to compensate for the lower gas contained to weight ratio?
You should buy a lase cutter, you will save a lot of time if you are going to cut wood and other things!
Awsum !!! I didn't see your previous video (yet) , maybe you could call this a re-debrief video as this is where more learning / ideas are created / realized...... good on you !!!!!! 😉😎
37:23 so how an altitude sensor works it makes sense as submarines increase pressure deeper your go you decrease that same stored pressure the higher you go as well as stored fuel temperature vs air temperature that's why your flight characteristics change via altitude (context) reference the combined 2 liter bottles having forces around it acting on it
Have you considered adding a tuned expansion chamber to the exhaust outlet? It works wonders for 2-stroke engines in terms of increased power output over a narrow rev range. I wonder if it might improve the efficiency of an air-engine too? 🤔
Crazy thought. Carbon fiber 4000psi paintball tank. Inline reg
I built most of the fuselage and the main wing's spar of a Cozy MK IV from plans I bought back in 1998.
It's the 4-seat version of the famous Long EZ by the God of aeronautics himself, Burt Rutan. The first chapters of all his plans are the bible of composite construction.
Hot-wire foam cutting done right, is hard to beat. Most flying surfaces of composite experimental aircraft is built that way. The next best thing, would be a CNC mill.
If you hot wired two pieces, a leading edge portion to glue to the front of the spar, and the trailing part to the back of the spar, would give the closest construction to the real plane.
No need to glass a skin. Just sand and paint to protect the foam against UV.
I'm wondering if car engine piston rings can be used in your air engine. There are pistons designed with holes in the oil scraper ring seat. You can print a piston with 2 rubber ring seals (for example you can use rubber O-rings or print them as you did it for the current model) and add a bunch of tiny L-shape holes from the top of the piston to the space between O-rings. In that case, you technically should get better compression and fewer leaks at the bottom dead point and the top dead point when your current rubber seal shrinks. Also, you can change the shape of the intake and exhaust to a conical shape with more rounded edges like it is done in 4 throttle intakes on motorbikes so the engine chamber can be filled with air faster and the air leaves the chamber faster. Another thing I'd try is using a T-shaped or V-shaped valve instead of a ball so the combination of the inlet channel and the engine chamber together act like a compression chamber of a turbojet engine. And the last thing I wanted to ask is - why don't you try to wind up a clock spring with an air piston and then use it to rotate the propeller of the aircraft?
Next: Variable Pitch Propeller
Could you take some weight out of the piston skirt too?
Is it possible to print a bottle with isogrid ribs to hold extra pressure and streamline it?
Or even take the c02 canisters as it will drastically reduce frontal area?
Hi Tom, Mark here, thanks for the deep dive. Love it.
BTW, I still have one of those Air Hogs planes which I got as an adult 30 years ago. Hanging in the garage with my RC gliders.
I saw that DLG on the original video, obviously, and wondered about it so I looked it up. Sadly the website is pretty sparse. Can you provide some details? Like where is this made, etc.
When doing the maths, do you take into account that there will be 4 litres of air that will go unused, since at 1atm inside and 1atm outside, it has no willingness to move through the engine ?
There will obviously be an amount of CO2 in the canisters that will also stay inside the canister, but the volume is so much smaller, so less will go unused?
17:52 There's probably a deep rabbit hole of power train optimisation on your air engine - how would you even characterise efficiency here? Thrust per psi, thrust per volume of air entering the piston chamber?
If you do manage to figure out the engine efficiency and torque curves, matching the best propeller becomes possible for the design operating point if you can get the prop performance curves, either from published prop test data or estimated using a performance calculator.
Probably too dense and boring to put into a UA-cam video but interesting engineering wise to think about. Good work!
such a cool series. thanks for the additional insights!
villain origin sotry: "lost toy plane on a school roof" xD perfect
One way to counter the V tail phenomena is to make it a Λ (lambda) tail instead. Unfortunately it makes the tail more fragile when landing.
Wouldn't it still roll? Why would that change things?
Fill in the space between your wings. You're doubling your tip losses by having that gap there!!
A thought that struck me with the piston.
If it was rectangular instead of square, the piston maybe could "keel over" in one direction at the bottom or top to change the width and thereby let the air by on the compression stroke.
Come to think of it: your idea with the channels sounds simpler :)
A major efficiency gain could be had by adding some kind of cover for the inner wingtips, to eliminate those wingtip vortices, or am I missing something?
About bike valves, the large ones are Schrader valves and those SUCK. Try Presta valves found in road bikes, they are screw on and work waaay better.
Have you looked at the S1223 airfoil? It might have higher drag overall, but it has super high L/D.
Very cool moves
Love the deep dive. 👍
should make a machine that throws the dlg glider in the background
I wonder if LW-ASA might be better instead of the ABS? It'd save off some weight, but it might still have the issue of being too weak. Regardless, ASA would likely still be a better option over ABS, given the better UV resistance.
What if you made the wings into pressure chambers? That could increase their rigidity, counteract the contour between the spars, and improve the efficiency of the vehicle. But I'm no engineer.
Yep this was awesome & very enjoyable. Cheers
Invert the V-tail and you will get coordinated turns .
the CO2 cartridge thing could be something to look into because you'd have less drag than the 2litre bottle frontal area?
Did you make any calculations on air drag of the bottle vs the CO2 cardridge? The drag should scale linearly with crossectional area, so a 2 times reduction in "tank" radius should reduce the dragforce by a factor of 4. Don't exactly know how this will relate to flight time as velocity might also increase, but might be worth a test anyway.
Those carbon stringers should have been more ridged. Could test the rigidity of different shapes of carbon?
i really appreciate these videos that help explain things in more detail so thanks :)
can you use a toroidal propeller in this build?? , why or why not
Well, the first time I flew mine I got totally convinced of it somehow having a spirit of some sort.
I had already had a bad experience misusing and underwinding a professional rubber band balsa plane and I didn't expect this plane to do any better so...I somehow thought it would be OK to fly it close to a bunch of trees.
It somehow dodged them all...but the last one :) but it got every neuron of my brain amazed by the power and roaring sound :D
I miss it...
Would it be a possibility to put dry cubes into the bottle. If it's not too hot( which it isn't in UK) there should be a gradual evaporation, creating CO2 gas...just a thought
I have seen 3 liter bottles years ago. So, maybe you could source some of those.
Just mention, the co to canister are better because the drink bottle is large era the co canister has smaller erea the drag from dink bottle do not outweigh the volume to erea