Elm speeds don't spin at 1500+ RPM. The big problem with a single blade propeller is that it needs a countermass to "try" and have balance so it would not shake the aircraft to pieces. The problem is there are two kinds of balance, Static and Dynamic, and without a symmetrical radial and spanwise distribution of mass the two balances are never in the same place and the dynamic balance migrates with RPM. In short it will always vibrate significantly more than a 2+ blade prop. Also fewer blades means larger diameter so the number of blades is usually selected based on the need to reduce the disc diameter of the prop such as to keep it from hitting the ground.
Boeing did a deep study on a single blade windmill back in the late 80s or early 90s don't know what they found , but a have not seen any single blade windmills .
The single blade is more efficient per unit of blade, but the overall windmill has lower efficacy and cost effectiveness. 3 blades is the economic sweet spot of wind turbines with current materials and methods. The economic calculation is quite a bit different from airplane props. Basically each additional blade extracts more energy from the swept disk area but not in full proportion. So (actual numbers for illustration only) 2 blades produces 185% of single blade power, and 3 blades is 260% of a single blade, while 4 bladed is 330%; but the blades costs are fully linear 3 is 150% of 2, the tower costs rise less than linear, and maintenance labor is basically a constant regardless of power output. (Keeping disk diameter fixed and thus tower height and spacing [powerline length] also fixed; but power and force/strength will vary.)
Good video as always thank you It’s all about eccentric loads and resulting vibration, and not just efficiency and structural bending loads. It is possible to balance the mass of a single blade prop, but we can’t forget that the blades are creating a lift force and the centre of lift is an issue. Two or more blades always result in a centre of lift that is coincidental with the centre of rotation, but this is impossible with a single blade. A single blade has a rotating lift vector that is inevitably eccentric to the rotational centre (and centre of mass if it is mass balanced) and so there is an inevitable significant vibration issue due to this even if there is a teetering hub to relieve the structural bending loads. To avoid vibration, the rotational centre, the centre of mass and the centre of lift all have to be coincidental: not just the first two.
The teetering hub doesn't just relieve the structural loads, it moves the centre of lift sideways to the centre of the hub. Obviously this requires a torque, but the torques at each moment of time cancel over a full rotation, so we just need somewhere to store the angular momentum temporarily. Part of the reason the prop is heavy is that it needs to be. It also acts as the angular momentum battery to deal with the eccentric lift. The angular momentum of the prop is not aligned with the spindle at any moment in time, instead constantly being changed by the torque required to keep the force on the spindle down the centre line.
Obviously whoever came up with the idea was a deep thinker and perhaps if they had continued development they would have eventually achieved more success but it was never going to be a slam dunk "oh yea, this is WAY better" thing. The aesthetics alone was a deal breaker for most.
I imagine a single blade would face balance issues not only from the weight, but also from the thrust. With thrust only coming from one side of the hub that would surely have some sort of lever effect on it?
@@LetsGoAviate the hub teetering doesnt change that, at least not how its shown in the video. Maybe its just the explanation thats not quite clear, but making it move freely would cause it to move to the end of travel and exert its bending moment from there. i can think of some bracing to reduce the bending moment, but moving freely enough be moved by hand doesnt seem helpful past changing prop pitch
@@broko336The lever force attempting to bend the blade/drive shaft is nearly completely removed by the teetering hub. If the blade can just bend forward without resistance, than the force trying to bend it forward can't really be transferred to any other part. The blade is allowed to naturally go into a position where it will be balanced by its spinning motion. The blade tilting forward will unbalance the centripetal force and result in there being a net torque to oppose the bending force on the propeller. If you have ever spun something around on a string over your head, the string will get closer and closer to horizontal as you spin it faster, despite gravity attempting to bring the object down. Hypothetically you could achieve the same effect by curving or tilting the blades in the first place, but it would not be able to do so across a wide range of airspeeds and rotational rate, like the teetering propeller can.
I remember in the early days of the program, the ford Aerostar was advertised as having the same superior aerodynamics as the space shuttle. meanwhile, a space shuttle engineer was pointing out the space shuttle had about the same glide path as a pair of pliers.
Props to you. Subscribing .... I once saw an overhead/ceiling fan with a single blade. I knew it wasn't going to be more efficient, but I didn't anticipate how irritating it was to see in operation.
I didn't even know there was single blade propellers, much less that they had a problem. But my guess would be... that it's more unstable? the propellers kinda counter each other's weight.
The non symmetrical forces on a single blade propeller you refer to were used to great effect. An automatic variable pitch propeller was achieved through a simple reliable mechanism. Thus a climb prop on takeoff. A cruise prop in level flight with reduced throttle. I have seen two bladed props with automatic pitch. They also are no longer made. Their mechanism more complex. I would worry about reliability. They have been known to fail where the metal fasteners hold the wood to a metal cup it swivel on the best I recall
If I bring two long fan blades, then two shorter blades behind them, then two shorter blades behind them, is this how I create a high-density air vortex?
ruclips.net/video/aDqLMWi5ZzI/видео.html There were some experiments with single blade wind turbines but they were abandoned for basically the same reasons stated in the video.
OK. There's another factor to consider, reduction drives. I found that a prop blade increases power absortion lineally with the increase of pitch, with the square of diameter increase, and with the cube of rpm's. Efficiency increases with diameter, which forces a greater gear ratio to keep tip speed low, which also increases efficiency. Juggling all that I found the best solution for low power engines to be a composite three bladed prop with adjustable pitch. Three blades give you a better equilibrium, too. Six blade, big diameter props gave great take off thrust and very low noise, but are SLOW...
Yeah with reduction drives the propeller spins slower, and so does the blade tips, so diameter can be increased. Used to great effect on some WWII fighters like the F4U Corsair.
@@LetsGoAviate Sadly the F4U also shows the down side of such large props: Increased gyroscopic forces, and thus P-factor. This is a good part of the reason it gained infamy as the 'ensign eliminator'.
Reduction drives are a nightmare for piston prop aircraft engines. The issue is that the prop is also doubling as the flywheel for the engine, and is constantly exchanging far more energy with the engine than the net engine power. For a standard flat plane 4 cylinder engine design, all 4 pistons are moving at full speed at the same time, and are stopped at the same time. The energy to do this is exchanged with the prop twice every rotation. There is also the variation in the torque provided through the stroke. It is workable with enough cylinders and the right design, but unless you design for it the torque variations will shred gearboxes. While they can cope with rapid variations in torque, it is very hard to design something that can cope with rapid reversals in torque.
@@agsystems8220 aircraft engines have included pendulum dampers into their crankshaft since the 50's for this very reason, since it's not exclusive to reduction drives.
I'm guessing it's the air density. Since it's basically auto variable pitch, high air density (cold temps) would make the blade pivot more to in increased lift/thrust, and the friction on the teetering hub needs to be adjusted. But don't quote me, I'm guessing here, I don't know the reasons and I only repeated what the owner of one of these propellers reported.
Wooden propellers absorb moisture, so their mass will change based on conditions. Not usually a problem for a 2 bladed prop (though you want to hanger the prop horizontal to keep things as symmetric as possible), as the change should be pretty even, but for a 1 bladed prop it would be.
Wait, isn't it obvious that a single blade + counterweight will be heavier than two blades, since the moment of inertia has to be the same and the counterweight is shorter?
I might be wrong but if I'm remembering correctly that's how a lot of modern turbo props work. You put the engine at a happy place where its getting the most work out of the fuel then change the prop angle to change thrust
Absolutely magnificent video. It would be really interesting to do an analysis of blade and blade tip shape as well. Lots of interesting theories from the saw toothed serrated trailing edge, to the foward vs rearward sweep, toroidal blades, cycloidal blades etc. Thanks!
Learned a lot, I see you have some videos of some airshows in the past, maybe you know or not, i know ysterplaat still has a museum, not sure if the othes bases has easily accessible museums, would be good to know if/when we go travel
Not many. You've got Swartkop Air Force Museum in Pretoria, which is luckily still open. They also have an open flying day the last weekend of every month I believe, and then the airworthy stuff is flown. I would call and confirm before traveling for the open flying day as it gets cancelled every now and then. There's also the National Museum of Military History in Johannesburg, they have some gems from WWII like a Bf109, FW190 and Me262 etc. Lastly there is the South African Airways museum next to Rand airport in Germiston with some blasts from the past.
@@LetsGoAviate thank you very much, yeah, they now and run the motors of the Shackleton down here but will get cancelled due to weather. Will make sure to reach out and get an idea from them, thanks for the additional recommendations I was only thinking afb initially for some reason
The major limitation of wood is found at prop hub considering the spitfire / Seafire used a wooden prop, they started out as fixed pitch in the prototype then they had aluminum hub to house the pitch mechanism and 3 wood blades, then four, then a six blade counter rotating....then I get sort of fuzzy but I think they may of had like 7 or 8 blade things. The Spitfire went from 800hp to well over 2000hp over its development cycle. They used wood for so long because it dampened vibration and was cheap and easy to shape. In the youtube video link ruclips.net/video/dJ7URD89uBs/видео.html at 0:52 There is a prop strike and from the remainder of the prop you can see how much wood is in a spitfire prop.
I don't think it will be balanced. Since they counter rotate, the 2 single blades will cross over (pass each other) once per revolution, meaning the thrust bending forces adding up instead of cancelling out, potentially making balance worse. I'm not sure if teetering hubs would be possible without the blades crossing over to the other blade's plane of rotation. At a quick glace the complexity seems too high.
It would be a bit of a mess, and there is little reason to do it, but I don't see why it couldn't work. You would need to put significant distance between the blades to avoid the teetering mechanisms causing collisions when manoeuvring (similar to contra rotating helicopters). You would then have a heavy low power prop that could operate at high speed, but is never going to get there because it is low power.
Single blade props were, and still are used in F2A Control line model aircraft racing. Typically the whole crank, prop and spinner are balanced as a single unit, at 40k rpm it needs to done accurately! There's no doubt they are the most effective for that extreme and highly specialised case.
Because single blades rotating at one end are unbalanced, hence the counterweight since you need a counterweight anyway may as well just slap another blade on the same line.
Propeller has to have central axis of symmetry - otherwise it's not only inefficient - it's unfeasible. This is obvious the moment you take into account rotating mass and rotating forces. First it would need to have a counterbalance that wouldn't contribute to generated thrust in order to avoid centrifugal vibrations. Second since thrust is generated on a single side of the axle, there will be a massive bending force acting on it, so the axle has to be beefier and much heavier. Third - that bending force is going to constantly change direction leading to massive vibrations in every direction no matter what you do. (other than making a symetrical propeller)
I mean, I covered all that. But yeah, when efficiency considered aerodynamically per blade in isolation, it's the best. Considering everything else, then no, not so much. Definitely not unfeasible though by the dictionary meaning of the word, because it exists and is in use outside of just testing and experimenting.
Don't you just love people saying things that have been demonstrated to work cannot work :P. You are arguing with reality. It does work. You have made a mistake. The important thing to realise is that the angular momentum of the prop is never aligned with the spindle, and is constantly changing. For that to happen there must be a torque. That torque is provided by the misalignment of the centre of lift and the spindle. The teetering mechanism cannot support a bending moment by design, so there is none. The spindle sees no bending moment. The angular momentum of the prop will constantly change to accommodate this, eating all the torque you are worried about. Instantaneously it looks like it makes no sense, but the torques cancel over a rotation and the prop is heavy enough for that not to be a problem. Your three observations are sort of correct. What you miss is that it doesn't manifest as vibration, it manifests as a variation of the angular momentum, and this can be restricted to the prop itself by the teetering mechanism.
You can't just cut one blade off and counterweight it and increase efficiency..... If you get rid of one blade you need to change the design of the single blade to make sure its efficient. We used to race U-control models with one wing and one elevator and even one prop. That was the fastest design around. And around. And around....
Ok I'm less than a minute in and the wake thing should be obviously false. Planes (and their propellers) tend to be moving forward into undisturbed air. I'm predicting the issue is imbalance, not of the propeller mass, but of the thrust force. One blade means the thrust vector passes through the blade itself and not the drive axle. This probably causes a small wobble/vibration Edit: guess I should have expected engineers would have anticipated these issues and the ultimate reason is increased cost for little benefit.
But war planes aren't after efficiency. They are limited by ground clearance and the propellers are trying to make use of all the power available in the very powerful engine
Thank you for a prop-er explanation. The prop-osition of the tittering hub looks like a interesting technology. Reminds me of a guy who build tilt rotor RC vtol, he used similar concept to replace need for complex cyclic mechanism for each necele with similar mechanism.
Brillant exposition of the technical aspects of a single blade propeller. One thing I failed to notice in the imbalance part, sorry if my mistake, is that another imbalance is present due to no balancing the par of force produced by total drag of the blade in the plane of rotation. Thus single blade prop would tend to also rotate orbitally arround the propeller shaft. Even when Center of mass is coincident with the hub, centre of drag par is not.
Just on a purely theoretical standpoint, this doesn't make sense. Having offset center of thrust gives a prop efficiency with a Cosine function, and rotating pivot moment has to be corrected constantly...So it can never be as efficient as a balanced setup.
It is constantly corrected by gyroscopic effects with perfect efficiency. The torque to move the thrust onto the centre line is provided by the constantly changing angular momentum of the prop, which over one rotation sums to zero. At any moment in time the angular momentum of the prop is not aligned with the spindle.
@@agsystems8220 I'm saying any thrust not in line with the center of mass when corrected is no longer a thrust vector parallel with the direction of flight, thus losing efficiency. Instead of f=ma you get a=cosf/m I stand corrected then, I'm versed in rocket propulsion, not propeller aircraft. You have me on the gyro thing, I have no idea. This was just my virgin response on the concept of the video. Thanks for the input, I appreciate it.
@@meusana3681 It isn't thrust in centre line that matters for efficiency, it is thrust in direction of travel. In most circumstances thrust must be in line with the centre of mass to avoid spinning the whole craft out of control, because you would induce a torque on the craft, but here is one of the few cases where that doesn't quite apply. The torque is still created, but averages over time to zero, and the angular momentum variation is soaked up by the propeller itself rather than passed on to the aircraft. The propeller's angular momentum is never quite aligned with the axis of rotation, and the torque that is continuously changing the angular momentum is also continuously transferring the thrust to the aircraft centreline. Spinning stuff is often counterintuitive. This isn't quite on the level of a gyroscope sitting sideways on a string, but it is that sort of effect.
Makes no sense because you'll still need a counterweight to balance the single prop, might as well just use another prop to do so. Also anyone who thinks air around a moving prop is undisturbed should try standing near a running one. 5$ if you can find the undisturbed air lol.
You're thinking of just taking a two-bladed propeller, removing one blade and counterweighting it but that's not how the argument for for single-blade propellers goes. What you would do is have a blade that is much larger and longer than on the single bladed propeller than the blades on a two-blade propeller so the engine is loaded down the same. You're trying to get the efficiency gains of a longer, wider airfoil on the same engine and the hope is that this increase in aerodynamic efficiency outweighs the cost of the counterweight. Like going from a biplane with two smaller wings to a monoplane with one larger wing.
I wonder if things could be different with electric propulsion, like for a drone. The countermass could be battery, so it's not dead weight. And a weird trick is that a single motor could be used for both propulsion and steering. You alternate between spinning the prop for thrust, and holding it steady to steer. Or maybe you don't have a countermass at all. The prop is on the end of the tail boom, and you simply accept that the boom will nutate in a tight cone in reaction to the blade. The drone doesn't need any tail surfaces other than the prop blade.
Well, most drone applications that I can think of are going to want a nice, steady camera of some form, so having the airframe nutating around is definitely undesirable. There might be some possibility in the cheap toy drone catagory, where the novelty of a single propeller that also steers the vehicle might drive sales, assuming of course that you don't end up with excessive wear from the unbalanced blade with cheap materials. You wouldn't be able to control roll with the propeller, similar to a helicopter needing a tail rotor, but maybe if you gave the drone symmetrical wings like the fins on a rocket, you could just let it spin at it flys, with the onboard microcontroller keeping track of orientation so that the controls stay in sync with the direction of the ground.
4 Biggest Propeller Myths Explored : ruclips.net/video/Vgj3Bbwqtjs/видео.html The Effects of a Propeller on an Aircraft : ruclips.net/video/WnJxrHmtT_c/видео.html One Video To understand Propellers : ruclips.net/video/hvboi6w1Z9A/видео.html
I understand the Physics, but it's crap. If single was better we wouldn't be adding a 5 Blade to the New Super Kingair! Which is better? A 4 blade EDF or a 12 Blade EDF! 12 runs smoother and faster, draws more current. Which is Quiter? I know
Only if the bearings are engineered for the hell they have to deal with. Only if the driver doesn't have to feel changes in his rocky journey. Sick of these youtube "engineers" reinventing the wheel and coming out with squares.
What did I "reinvent" mate? I gave a technical overview of something interesting someone else invented. If it makes you so sick stop watching it and go do something else.
It really is not that simple as "more blades is clearly better". It depends on the factors I mentioned to get optimal power absorption without sacrificing a lot of efficiency. The Germans stuck with 3 blade props almost religiously, even on the 2,000+hp FW190 Dora, while the Americans quickly switched to 4 blades even on lower powered planes like the P-51 Mustang (compared to Corsair, P-47 etc.). It's about power absorption vs efficiency. The higher the power output the more blades will be required, as there is a finite amount of power absorption possible per blade, and even less if efficiency isn't to be greatly sacrificed. I made a video on 2 vs 3 blade props if you are interested in the subject.
Single blades are unnatural. They're surely evil in some way, perfect for a Halloweencopter
They are natural, maple seeds.
Zipline drones use 2 1/2 blades.
They were looking for a quieter propeller, and ended up with one that's a little more efficient too.
I’m sure they are also perfect for VTOLs as they can naturally feather down the airstream in cruise flight.
Ever see a pine tree seed when it falls out of a pinecone?😉
Elm speeds don't spin at 1500+ RPM. The big problem with a single blade propeller is that it needs a countermass to "try" and have balance so it would not shake the aircraft to pieces. The problem is there are two kinds of balance, Static and Dynamic, and without a symmetrical radial and spanwise distribution of mass the two balances are never in the same place and the dynamic balance migrates with RPM. In short it will always vibrate significantly more than a 2+ blade prop. Also fewer blades means larger diameter so the number of blades is usually selected based on the need to reduce the disc diameter of the prop such as to keep it from hitting the ground.
Who's to say a two blade prop isn't actually a single blade with a cleverly designed counterweight?
Can't argue with that 😆
@@LetsGoAviateI can.... Which one is the counterweight? The service and inspection intervals will be different for each.
@@christopherleveck6835 the counterweight has a counterweight
@@ckogsh2585blade-ception!
@@warmstrong5612 the props are illusions, there are only counterweights 🤣
why stop at 1 blade? my 0 blade propeller design has a higher rpm and lower weight than any other, also no instability and can never crash!
Лучший комментарий!
you 0 blade prop is shi, try my -1 prop instead
It's called bladeless and I think Dyson already invented it. 😂
It also makes the plane start at its final destination so it is extremely efficient!
@@ckogsh2585lol was just about to say -1 and chose to say -2 instead😂😂
Boeing did a deep study on a single blade windmill back in the late 80s or early 90s don't know what they found , but a have not seen any single blade windmills .
The single blade is more efficient per unit of blade, but the overall windmill has lower efficacy and cost effectiveness. 3 blades is the economic sweet spot of wind turbines with current materials and methods. The economic calculation is quite a bit different from airplane props.
Basically each additional blade extracts more energy from the swept disk area but not in full proportion. So (actual numbers for illustration only) 2 blades produces 185% of single blade power, and 3 blades is 260% of a single blade, while 4 bladed is 330%; but the blades costs are fully linear 3 is 150% of 2, the tower costs rise less than linear, and maintenance labor is basically a constant regardless of power output. (Keeping disk diameter fixed and thus tower height and spacing [powerline length] also fixed; but power and force/strength will vary.)
Good video as always thank you
It’s all about eccentric loads and resulting vibration, and not just efficiency and structural bending loads.
It is possible to balance the mass of a single blade prop, but we can’t forget that the blades are creating a lift force and the centre of lift is an issue. Two or more blades always result in a centre of lift that is coincidental with the centre of rotation, but this is impossible with a single blade.
A single blade has a rotating lift vector that is inevitably eccentric to the rotational centre (and centre of mass if it is mass balanced) and so there is an inevitable significant vibration issue due to this even if there is a teetering hub to relieve the structural bending loads.
To avoid vibration, the rotational centre, the centre of mass and the centre of lift all have to be coincidental: not just the first two.
The teetering hub doesn't just relieve the structural loads, it moves the centre of lift sideways to the centre of the hub. Obviously this requires a torque, but the torques at each moment of time cancel over a full rotation, so we just need somewhere to store the angular momentum temporarily. Part of the reason the prop is heavy is that it needs to be. It also acts as the angular momentum battery to deal with the eccentric lift. The angular momentum of the prop is not aligned with the spindle at any moment in time, instead constantly being changed by the torque required to keep the force on the spindle down the centre line.
Obviously whoever came up with the idea was a deep thinker and perhaps if they had continued development they would have eventually achieved more success but it was never going to be a slam dunk "oh yea, this is WAY better" thing. The aesthetics alone was a deal breaker for most.
I wish there are more videos such as this on YT. Zero click bait, 100% information.
I imagine a single blade would face balance issues not only from the weight, but also from the thrust. With thrust only coming from one side of the hub that would surely have some sort of lever effect on it?
Absolutely yes, as mentioned in the video. The teetering hub helps with that though.
@@LetsGoAviate the hub teetering doesnt change that, at least not how its shown in the video. Maybe its just the explanation thats not quite clear, but making it move freely would cause it to move to the end of travel and exert its bending moment from there.
i can think of some bracing to reduce the bending moment, but moving freely enough be moved by hand doesnt seem helpful past changing prop pitch
@@broko336The lever force attempting to bend the blade/drive shaft is nearly completely removed by the teetering hub. If the blade can just bend forward without resistance, than the force trying to bend it forward can't really be transferred to any other part. The blade is allowed to naturally go into a position where it will be balanced by its spinning motion. The blade tilting forward will unbalance the centripetal force and result in there being a net torque to oppose the bending force on the propeller.
If you have ever spun something around on a string over your head, the string will get closer and closer to horizontal as you spin it faster, despite gravity attempting to bring the object down.
Hypothetically you could achieve the same effect by curving or tilting the blades in the first place, but it would not be able to do so across a wide range of airspeeds and rotational rate, like the teetering propeller can.
@@markjacobson4248 thanks, i didnt consider inertia forces when spinning when thinking about it
I've only seen single blade props on rubber power models, and yes the airplane absolutely did wobble.
This propels my knowledge about propellers to new heights.
Not that i need to know anything about them, but i did watch the video voluntarily, so...
i've seen a sail plane with short chubby wings. the space shuttles. awful glide slope though
I remember in the early days of the program, the ford Aerostar was advertised as having the same superior aerodynamics as the space shuttle. meanwhile, a space shuttle engineer was pointing out the space shuttle had about the same glide path as a pair of pliers.
amazing
@@kenbrown2808 That's exactly something an engineer would say. 😂
@@TurboHappyCar a good engineer would, anyway. bad engineers don't know how to translate into terms the average layman can comprehend.
Props to you. Subscribing ....
I once saw an overhead/ceiling fan with a single blade. I knew it wasn't going to be more efficient, but I didn't anticipate how irritating it was to see in operation.
I didn't even know there was single blade propellers, much less that they had a problem. But my guess would be... that it's more unstable? the propellers kinda counter each other's weight.
The non symmetrical forces on a single blade propeller you refer to were used to great effect. An automatic variable pitch propeller was achieved through a simple reliable mechanism. Thus a climb prop on takeoff. A cruise prop in level flight with reduced throttle. I have seen two bladed props with automatic pitch. They also are no longer made. Their mechanism more complex. I would worry about reliability. They have been known to fail where the metal fasteners hold the wood to a metal cup it swivel on the best I recall
The p-factor would go crazy there
So turns out it was actually exactly why I thought
Still a great video!
props for props of using prop as a prop
Wow, simple and great explanation. :)
If I bring two long fan blades, then two shorter blades behind them, then two shorter blades behind them, is this how I create a high-density air vortex?
Off topic, but has anyone ever seen a single blade windmill? Just curious.
There was GROWIAN, an experimental wind turbine in Germany in the last millennium that was single bladed...
ruclips.net/video/aDqLMWi5ZzI/видео.html
There were some experiments with single blade wind turbines but they were abandoned for basically the same reasons stated in the video.
@@emily36130 Thanks.
Saw one at Redstone Arsenault (Huntsville AL) back in the 70s.
OK. There's another factor to consider, reduction drives. I found that a prop blade increases power absortion lineally with the increase of pitch, with the square of diameter increase, and with the cube of rpm's. Efficiency increases with diameter, which forces a greater gear ratio to keep tip speed low, which also increases efficiency. Juggling all that I found the best solution for low power engines to be a composite three bladed prop with adjustable pitch. Three blades give you a better equilibrium, too. Six blade, big diameter props gave great take off thrust and very low noise, but are SLOW...
Yeah with reduction drives the propeller spins slower, and so does the blade tips, so diameter can be increased. Used to great effect on some WWII fighters like the F4U Corsair.
Issue with large props spinning slowly is that they great very annoying bass noises at high volume.
@@LetsGoAviate Sadly the F4U also shows the down side of such large props: Increased gyroscopic forces, and thus P-factor. This is a good part of the reason it gained infamy as the 'ensign eliminator'.
Reduction drives are a nightmare for piston prop aircraft engines. The issue is that the prop is also doubling as the flywheel for the engine, and is constantly exchanging far more energy with the engine than the net engine power. For a standard flat plane 4 cylinder engine design, all 4 pistons are moving at full speed at the same time, and are stopped at the same time. The energy to do this is exchanged with the prop twice every rotation. There is also the variation in the torque provided through the stroke. It is workable with enough cylinders and the right design, but unless you design for it the torque variations will shred gearboxes. While they can cope with rapid variations in torque, it is very hard to design something that can cope with rapid reversals in torque.
@@agsystems8220 aircraft engines have included pendulum dampers into their crankshaft since the 50's for this very reason, since it's not exclusive to reduction drives.
mandatory thunder screech 'mach 1.0' comment
All very interesting.
I wish the part where temperature was effecting the propeller had been explained in a bit more detail.
I'm guessing it's the air density. Since it's basically auto variable pitch, high air density (cold temps) would make the blade pivot more to in increased lift/thrust, and the friction on the teetering hub needs to be adjusted. But don't quote me, I'm guessing here, I don't know the reasons and I only repeated what the owner of one of these propellers reported.
Wooden propellers absorb moisture, so their mass will change based on conditions. Not usually a problem for a 2 bladed prop (though you want to hanger the prop horizontal to keep things as symmetric as possible), as the change should be pretty even, but for a 1 bladed prop it would be.
I didn't know single blade propellers were a thing. How do they avoid excessive vibration from being out of balance?
They use a counterweight on the other side
Is there any special prop profile for >mach1 like for wings?
Wait, isn't it obvious that a single blade + counterweight will be heavier than two blades, since the moment of inertia has to be the same and the counterweight is shorter?
Would you please give your opinion on the zipline blade design and if it would cause the same stresses as a single blade?
What happens when you have a gearbox attached to change prop speed to whatever you want. Say something like a tiltrotor. What happens to efficientcy.
Already done that, lot of ww2 plane have variable pitch propeller
I might be wrong but if I'm remembering correctly that's how a lot of modern turbo props work. You put the engine at a happy place where its getting the most work out of the fuel then change the prop angle to change thrust
I can get 2 aesthetically pleasing blades for less than one? Great, I'll take 10,000; war is coming.
Two blades, one on each counter rotating shaft, and
Absolutely magnificent video. It would be really interesting to do an analysis of blade and blade tip shape as well. Lots of interesting theories from the saw toothed serrated trailing edge, to the foward vs rearward sweep, toroidal blades, cycloidal blades etc. Thanks!
Learned a lot, I see you have some videos of some airshows in the past, maybe you know or not, i know ysterplaat still has a museum, not sure if the othes bases has easily accessible museums, would be good to know if/when we go travel
Not many. You've got Swartkop Air Force Museum in Pretoria, which is luckily still open. They also have an open flying day the last weekend of every month I believe, and then the airworthy stuff is flown. I would call and confirm before traveling for the open flying day as it gets cancelled every now and then.
There's also the National Museum of Military History in Johannesburg, they have some gems from WWII like a Bf109, FW190 and Me262 etc.
Lastly there is the South African Airways museum next to Rand airport in Germiston with some blasts from the past.
@@LetsGoAviate thank you very much, yeah, they now and run the motors of the Shackleton down here but will get cancelled due to weather. Will make sure to reach out and get an idea from them, thanks for the additional recommendations I was only thinking afb initially for some reason
The major limitation of wood is found at prop hub considering the spitfire / Seafire used a wooden prop, they started out as fixed pitch in the prototype then they had aluminum hub to house the pitch mechanism and 3 wood blades, then four, then a six blade counter rotating....then I get sort of fuzzy but I think they may of had like 7 or 8 blade things. The Spitfire went from 800hp to well over 2000hp over its development cycle. They used wood for so long because it dampened vibration and was cheap and easy to shape.
In the youtube video link ruclips.net/video/dJ7URD89uBs/видео.html at 0:52 There is a prop strike and from the remainder of the prop you can see how much wood is in a spitfire prop.
What if you have a single blade eith contra rotation? Then what?
I don't think it will be balanced. Since they counter rotate, the 2 single blades will cross over (pass each other) once per revolution, meaning the thrust bending forces adding up instead of cancelling out, potentially making balance worse.
I'm not sure if teetering hubs would be possible without the blades crossing over to the other blade's plane of rotation. At a quick glace the complexity seems too high.
It would be a bit of a mess, and there is little reason to do it, but I don't see why it couldn't work. You would need to put significant distance between the blades to avoid the teetering mechanisms causing collisions when manoeuvring (similar to contra rotating helicopters). You would then have a heavy low power prop that could operate at high speed, but is never going to get there because it is low power.
Good video! Thank you!
It should be simpler and lighter and cheaper to make an adjustable pitch single blade propeller. Always wanted to do it. Maybe now.
oof simplifications all over, but still reasonably accurate. well done.
it was the exact thing I was thinking it would be
What is the motivation behind a single propeller?
Stupidity or geek factor, I guess.
Great video ! We love your channel and all your videos. Thank you for your amazing job and for sharing !!!
Thanks!
Single blade props were, and still are used in F2A Control line model aircraft racing. Typically the whole crank, prop and spinner are balanced as a single unit, at 40k rpm it needs to done accurately! There's no doubt they are the most effective for that extreme and highly specialised case.
The proper name for a propeller is an 'air screw'. This says it all regarding the helical path.
Helicopter. Pronounced "he-lick-o-tear".
Because single blades rotating at one end are unbalanced, hence the counterweight since you need a counterweight anyway may as well just slap another blade on the same line.
Good luck getting a stc for it. :)
Propeller thrust is generated by blade lift, not drag.
Propeller has to have central axis of symmetry - otherwise it's not only inefficient - it's unfeasible. This is obvious the moment you take into account rotating mass and rotating forces.
First it would need to have a counterbalance that wouldn't contribute to generated thrust in order to avoid centrifugal vibrations. Second since thrust is generated on a single side of the axle, there will be a massive bending force acting on it, so the axle has to be beefier and much heavier.
Third - that bending force is going to constantly change direction leading to massive vibrations in every direction no matter what you do. (other than making a symetrical propeller)
I mean, I covered all that. But yeah, when efficiency considered aerodynamically per blade in isolation, it's the best. Considering everything else, then no, not so much. Definitely not unfeasible though by the dictionary meaning of the word, because it exists and is in use outside of just testing and experimenting.
Don't you just love people saying things that have been demonstrated to work cannot work :P. You are arguing with reality. It does work. You have made a mistake.
The important thing to realise is that the angular momentum of the prop is never aligned with the spindle, and is constantly changing. For that to happen there must be a torque. That torque is provided by the misalignment of the centre of lift and the spindle. The teetering mechanism cannot support a bending moment by design, so there is none. The spindle sees no bending moment. The angular momentum of the prop will constantly change to accommodate this, eating all the torque you are worried about. Instantaneously it looks like it makes no sense, but the torques cancel over a rotation and the prop is heavy enough for that not to be a problem.
Your three observations are sort of correct. What you miss is that it doesn't manifest as vibration, it manifests as a variation of the angular momentum, and this can be restricted to the prop itself by the teetering mechanism.
You can't just cut one blade off and counterweight it and increase efficiency.....
If you get rid of one blade you need to change the design of the single blade to make sure its efficient.
We used to race U-control models with one wing and one elevator and even one prop.
That was the fastest design around. And around. And around....
So if the plane isn't moving it spin through its wake. But if it moving no issue
Have I ever seen a glider with short and wide wings? Yes, the Space Shuttle orbiter!
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Yes. Props for prop props! 😂
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Drag racing boats have been using single blade props for decades.
It just seems like unbalanced propulsion
7:00 double blade is not heavier than single blade, because single have counterweight to balance propeller.
ok 7:47 you explained ;)
🙂
Ok I'm less than a minute in and the wake thing should be obviously false. Planes (and their propellers) tend to be moving forward into undisturbed air.
I'm predicting the issue is imbalance, not of the propeller mass, but of the thrust force. One blade means the thrust vector passes through the blade itself and not the drive axle. This probably causes a small wobble/vibration
Edit: guess I should have expected engineers would have anticipated these issues and the ultimate reason is increased cost for little benefit.
Adding a second blade is in most cases less efficient because two blades have double the tip drag
Single blades have inherently worse dynamic balance and thus higher vibration.
No it does not double the tip drag, they are different tips on a different aspect ratio airfoil with different loading.
.... I converted my full scale piper cub to work on rubber band s with a single blade folding prop.....
@@allangibson8494And the downward-advancing single blade will do some pretty horrifying things…
Huge bending moment on the axle due to unbalanced thrust.
Most propellers of WWII did not have 2 but 3, 4 or even more blades. Only some of huge wind turbines used single blade.
But war planes aren't after efficiency. They are limited by ground clearance and the propellers are trying to make use of all the power available in the very powerful engine
Can't imagine a single blade running on a plane.
Must be unbalanced af. 😬
Next video: why a one wing plane is better
Thank you for a prop-er explanation. The prop-osition of the tittering hub looks like a interesting technology.
Reminds me of a guy who build tilt rotor RC vtol, he used similar concept to replace need for complex cyclic mechanism for each necele with similar mechanism.
Upvoted for the expression on your face after your corny props for the prop prop joke.😅😊
And I thought that single blade props were for control line modles or even Howard huges single blade helicopter
This reminds me of the ceiling fan Will Smith had in i,Robot.
Props for useing a prop as a prop ? To quote doctor Maturin ‘ he who would pun would. Pick a pocket sir ‘
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7:00 and single blade has counterweight as well. else it wouldn't work for long
I'm gonna comment before watching. I think it's going to be because of unbalanced force from thrust
Seen on rubber powered models.
More blades, more better. Just look at how many blades turbofans have,
Brillant exposition of the technical aspects of a single blade propeller. One thing I failed to notice in the imbalance part, sorry if my mistake, is that another imbalance is present due to no balancing the par of force produced by total drag of the blade in the plane of rotation. Thus single blade prop would tend to also rotate orbitally arround the propeller shaft. Even when Center of mass is coincident with the hub, centre of drag par is not.
Balance ? Loosing one rotor blade on a helicopter turns people into jelly.
Just on a purely theoretical standpoint, this doesn't make sense. Having offset center of thrust gives a prop efficiency with a Cosine function, and rotating pivot moment has to be corrected constantly...So it can never be as efficient as a balanced setup.
It is constantly corrected by gyroscopic effects with perfect efficiency. The torque to move the thrust onto the centre line is provided by the constantly changing angular momentum of the prop, which over one rotation sums to zero. At any moment in time the angular momentum of the prop is not aligned with the spindle.
@@agsystems8220 I'm saying any thrust not in line with the center of mass when corrected is no longer a thrust vector parallel with the direction of flight, thus losing efficiency.
Instead of f=ma you get a=cosf/m
I stand corrected then, I'm versed in rocket propulsion, not propeller aircraft. You have me on the gyro thing, I have no idea. This was just my virgin response on the concept of the video.
Thanks for the input, I appreciate it.
@@meusana3681 It isn't thrust in centre line that matters for efficiency, it is thrust in direction of travel. In most circumstances thrust must be in line with the centre of mass to avoid spinning the whole craft out of control, because you would induce a torque on the craft, but here is one of the few cases where that doesn't quite apply. The torque is still created, but averages over time to zero, and the angular momentum variation is soaked up by the propeller itself rather than passed on to the aircraft. The propeller's angular momentum is never quite aligned with the axis of rotation, and the torque that is continuously changing the angular momentum is also continuously transferring the thrust to the aircraft centreline.
Spinning stuff is often counterintuitive. This isn't quite on the level of a gyroscope sitting sideways on a string, but it is that sort of effect.
Makes no sense because you'll still need a counterweight to balance the single prop, might as well just use another prop to do so. Also anyone who thinks air around a moving prop is undisturbed should try standing near a running one. 5$ if you can find the undisturbed air lol.
You're thinking of just taking a two-bladed propeller, removing one blade and counterweighting it but that's not how the argument for for single-blade propellers goes. What you would do is have a blade that is much larger and longer than on the single bladed propeller than the blades on a two-blade propeller so the engine is loaded down the same. You're trying to get the efficiency gains of a longer, wider airfoil on the same engine and the hope is that this increase in aerodynamic efficiency outweighs the cost of the counterweight. Like going from a biplane with two smaller wings to a monoplane with one larger wing.
Good analysis. Now, please tell the Europeans to stop calling "Spoilers" 'air brakes' on gliders.
Ever seen a ceiling fan from iRobot?
Er . . . balance?
God damn old people couldn’t ever science bro
I can't tell your accent 😂
And im fine with that
wow
Worked for Cahill and Korda both Wakefield winners.
Haha. Good jokes.
Great points! Very smart 👍
I wonder if things could be different with electric propulsion, like for a drone. The countermass could be battery, so it's not dead weight.
And a weird trick is that a single motor could be used for both propulsion and steering. You alternate between spinning the prop for thrust, and holding it steady to steer.
Or maybe you don't have a countermass at all. The prop is on the end of the tail boom, and you simply accept that the boom will nutate in a tight cone in reaction to the blade. The drone doesn't need any tail surfaces other than the prop blade.
Well, most drone applications that I can think of are going to want a nice, steady camera of some form, so having the airframe nutating around is definitely undesirable. There might be some possibility in the cheap toy drone catagory, where the novelty of a single propeller that also steers the vehicle might drive sales, assuming of course that you don't end up with excessive wear from the unbalanced blade with cheap materials.
You wouldn't be able to control roll with the propeller, similar to a helicopter needing a tail rotor, but maybe if you gave the drone symmetrical wings like the fins on a rocket, you could just let it spin at it flys, with the onboard microcontroller keeping track of orientation so that the controls stay in sync with the direction of the ground.
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4 Biggest Propeller Myths Explored : ruclips.net/video/Vgj3Bbwqtjs/видео.html
The Effects of a Propeller on an Aircraft : ruclips.net/video/WnJxrHmtT_c/видео.html
One Video To understand Propellers : ruclips.net/video/hvboi6w1Z9A/видео.html
I understand the Physics, but it's crap. If single was better we wouldn't be adding a 5 Blade to the New Super Kingair! Which is better? A 4 blade EDF or a 12 Blade EDF! 12 runs smoother and faster, draws more current. Which is Quiter? I know
Watch the video, everything is explained. Except the Re-number.
Very informative thanks. Nothing like organising and sorting out requirements of design
Only if the bearings are engineered for the hell they have to deal with. Only if the driver doesn't have to feel changes in his rocky journey. Sick of these youtube "engineers" reinventing the wheel and coming out with squares.
What did I "reinvent" mate? I gave a technical overview of something interesting someone else invented. If it makes you so sick stop watching it and go do something else.
Single blades are out of balance.
🙂
Clearly more blades are better otherwise 3 blade props in WWII wouldn't have been replaced by 4 blade props.
It really is not that simple as "more blades is clearly better". It depends on the factors I mentioned to get optimal power absorption without sacrificing a lot of efficiency. The Germans stuck with 3 blade props almost religiously, even on the 2,000+hp FW190 Dora, while the Americans quickly switched to 4 blades even on lower powered planes like the P-51 Mustang (compared to Corsair, P-47 etc.).
It's about power absorption vs efficiency. The higher the power output the more blades will be required, as there is a finite amount of power absorption possible per blade, and even less if efficiency isn't to be greatly sacrificed.
I made a video on 2 vs 3 blade props if you are interested in the subject.
Single blade is unballanced