Toroidal propeller

[JayMatt]

What do you think of a Toroidal propeller on an airplane? I realize it could be significantly heavier so I would have to be carbon fiber, but would it be worth the noise reduction? Potential speed gains? 

Another interesting tid-bit is that electric planes really aren't much quieter than gas airplanes because most the noise comes from the propeller.  This is what Steve Bertorelli claimed anyway, no personal experience.  

Just a thought provoking conversation for Monday to the builders and creators and engineers out there. 

[carusoam]

Jay,

I saw a pic of the toroidal prop over the weekend…

It got filed in my junk mail folder… 

• weight
• drag
• complexity/cost
• efficiency

 

It looks like boats may be able to use it for a bunch of reasons…

 

As far as sound reduction goes…

Props ARE the noise makers… Bertorelli is good!  But, to prove this for yourself…

Go to the Mooney fly-in… and observe the planes as they depart…

Things to look for…

1) 200hp engine, aluminum prop… turning 2700 rpm (M20J)

2) 280hp engine, aluminum prop… turning 2500 rpm (O1)

3) 310hp engine, aluminum prop… turning 2700 rpm (O3)

4) 305hp engine, MT composite prop… turning 2700 rpm (Rocket)

The Rocket is oddly and noticeably the quieter of the bunch…

No surprise… O3 power doesn’t sneak by you….

 

Compare to the Tesla experience… cruising through the parking lot.  Always watch where you are going…  these things have very little noise coming out of them beyond tire/ground contact noises…

Or the latest hybrid Corvette model… the E-Ray… it has a silent mode for escaping your neighborhood before lighting the fires… 

 

Soooo…. A summary….

Exhaust sounds are large… going electric, removes the exhaust sound…

Prop sounds are gigantic… changing the prop material is an amazing way to reduce this sound…

 

 

Do you have a link to go with that?

Best regards,

-a-

[Pinecone]

Also, I don't see how to make them adjustable pitch/constant speed.  

So the big question for aircraft is whether they are close to as efficient over the whole range of operation.

[Mooneymite]

[carusoam]

Gus,

That will really keep your anchor line/tie downs from getting caught! 

Thanks for posting the pic!

Best regards,

-a-

[carusoam]

Now I remember where I saw it…

welcome to YT!

It may make boats, then drones happier first…

then Cirri…

-a-

 

Edited February 8, 2023 by carusoam

[N201MKTurbo]

A more efficient and heavier fixed pitch prop

[carusoam]

Electric motors may make more sense for the fixed pitch aspect?

-a-

[JayMatt]

Well there are lighter materials out there than aluminum. It's not impossible to make it constant speed either, all it takes is money. 

I found it interesting as it's been used on drones already. It's only a matter of time until one goes on a plane. The question really becomes, How much money for for what gains? If you could put one on a Mooney for 10k and it gained you 5kts... would you do it? Beats a LoPresti cowl...

[N201MKTurbo]

I'm not seeing a way to make it variable pitch. As far as making it lighter, it sure looks that it has twice as many blades as a standard propeller. the smallest configuration would have two loops and each loop has two blades connected at the ends. the only way to lighten it would be to reduce the diameter. I don't think it would give enough thrust at a smaller diameter.

[N201MKTurbo]

There is no use getting excited about this propeller until it has been successfully used in the experimental world for a decade or two. There are no examples of one being used on an airplane yet.

[carusoam]

The interesting part is how quiet does it get…

And drone props will demonstrate how that can work…

If it is good and quiet… there will be a million operating Ukraine…

The video of a boat being quieter was a bit surprising…

I was unaware of prop sound for boats being so strong…  thinking the water/air barrier was going to muffle it…

 

Of course, I didn’t know our props were as loud as they are either…

until somebody went by with an MT… and another plane had their rpm bumped up 200more rpm…. 

 

Best regards,

-a-

[Retrorockit]

The big difference in boats is fuel consumption reduction, and closer to theoretical pitch achieved (less slippage) Less engine load equals less noise.  Less flow lost in the radial plane past the "tips". Less slip might allow higher speed before the tip goes supersonic. There's a lot more to this than noise reduction. Kind of a self ducted prop?

How it will respond to altitude changes IDK?

[A64Pilot]

On 2/8/2023 at 3:22 AM, carusoam said:

Electric motors may make more sense for the fixed pitch aspect?

-a-

Electric could very likely be fixed pitch, a gas motor has to turn up the RPM to make power, electric not so much.

The quickest 1/4 mike car ever offered for public highways has a single fixed gear, the Tesla Plaid.

Musk initially tried a two speed gearbox on the original roadster then found it not to be necessary, the proposed Tesla Semi will have four model 3 gear trains, so even the Semi will be fixed gear.

Only drawback I see is the length of the extension cord for the airplane.

I had a Brunton’s Autoprop on my sailboat, a self pitching prop that adjusted pitch based on RPM and speed through the water, originally designed to get WWII landing craft off the beach, a prop turning backwards is very inefficient and therefore much less thrust, so it spins around and the leading edge stays the leading edge even in reverse, but the deal with a sailboat is when motor sailing, that’s is using both for propulsion a proper prop for just motoring is way underpitched, so you need a way to increase pitch, and the Autoprop did so automatically.

‘There were automatic props for airplanes in the 40’s too.

90% sure back in 1946 this was an option for my C-140

http://www.aeromatic.com

 

[Pinecone]

13 hours ago, A64Pilot said:

Electric could very likely be fixed pitch, a gas motor has to turn up the RPM to make power, electric not so much.

But to change the power without changing the RPM you need to change the load.  Which means variable pitch for an airplane

[A64Pilot]

57 minutes ago, Pinecone said:

But to change the power without changing the RPM you need to change the load.  Which means variable pitch for an airplane

Why would you not want to vary the RPM? Electric motors operate efficiently at very wide RPM bands.

Plus unless there is excess slippage cranking up the torque doesn’t increase RPM just thrust, increase speed increases RPM.

So, here is what you could get with a fixed pitch prop with an electric motor, say 1500 RPM takeoff and 2000 high speed cruise, or whatever  RPM gives the prop its highest efficiency. The Tesla Plaid or any electric car is the perfect example of how electric motors don’t need RPM for huge torque, they accelerate at an incredible rate. Nothing on the street, even high performance motorcycles launch as hard as a Plaid. There is no revving up the motor and dumping the clutch on an EV, it launches at zero motor RPM.

Electric changes the rules we are used to, many no longer apply, granted I don’t think we will see an EV usable airplane anytime soon, but if someone invents a Mr Fusion like Back to the Future it could be a phenomenal performer and exceptionally quiet if desired.

Pipe dream for now.

[Pinecone]

40 minutes ago, A64Pilot said:

Why would you not want to vary the RPM? Electric motors operate efficiently at very wide RPM bands.

Plus unless there is excess slippage cranking up the torque doesn’t increase RPM just thrust, increase speed increases RPM.

So, here is what you could get with a fixed pitch prop with an electric motor, say 1500 RPM takeoff and 2000 high speed cruise, or whatever  RPM gives the prop its highest efficiency. The Tesla Plaid or any electric car is the perfect example of how electric motors don’t need RPM for huge torque, they accelerate at an incredible rate. Nothing on the street, even high performance motorcycles launch as hard as a Plaid. There is no revving up the motor and dumping the clutch on an EV, it launches at zero motor RPM.

Electric changes the rules we are used to, many no longer apply, granted I don’t think we will see an EV usable airplane anytime soon, but if someone invents a Mr Fusion like Back to the Future it could be a phenomenal performer and exceptionally quiet if desired.

Pipe dream for now.

Only if you can increase the load.  With fixed load (fixed pitch) cranking up the torque increases the RPM.  

Electric motors make maximum torque at 0 RPM.  That is why freight trains are diesel electric.  No way, without a massive gear ratio would a IC engine be able to make a train move.   Steam also makes good torque at 0 RPM.

But any fixed pitch prop is going to be a compromise, no matter what powers it.  If you run 1500 for take off and 2000 for cruise, you are giving up massive amounts of take off performance if you are fixed pitch.

[Fly Boomer]

9 hours ago, A64Pilot said:

The Tesla Plaid or any electric car is the perfect example of how electric motors don’t need RPM for huge torque,

Not sure about Tesla motor(s) but some motors produce 100% torque starting at zero RPM.  I seem to remember that the BMW 8 had a zero-RPM motor on each windshield wiper to hold the wiper blade against the glass, with another motor to do the wiping.

Oops.  Just read the post by  @Pinecone.

[A64Pilot]

9 hours ago, Pinecone said:

Only if you can increase the load.  With fixed load (fixed pitch) cranking up the torque increases the RPM.  

Electric motors make maximum torque at 0 RPM.  That is why freight trains are diesel electric.  No way, without a massive gear ratio would a IC engine be able to make a train move.   Steam also makes good torque at 0 RPM.

But any fixed pitch prop is going to be a compromise, no matter what powers it.  If you run 1500 for take off and 2000 for cruise, you are giving up massive amounts of take off performance if you are fixed pitch.

You may or may not give up a little due to prop efficiency, but it’s not going to be much. A 200HP electric motor will produce 200 HP across a wide RPM range.

The same reason why a train doesn’t need a transmission is why an electric airplane motor wouldn’t need a constant speed prop.

The ONLY reason an ICE airplane needs one is to allow the engine to turn up RPM to its max power.

‘As an example the PT6-34Ag motor makes 750 SHP at 58.7 lbs torque at 2200 RPM, and at 64.5 lbs torque at 2000 RPM, being a free turbine you can slow the prop 200  RPM and have the same performance, you could slow it even more except the torque would exceed the gearbox limit.

Torque x RPM = power, that’s why an electric motor makes its highest torque at 0 RPM, as RPM increases torque decreases because HP is relatively constant, power does slightly decrease with RPM due to drag, but it’s not significant.

[Pinecone]

But you are missing the fact that when you slow the PT-6 to 200 RPM you are greatly increasing the pitch of blades, thus the load.

A fixed pitch prop cannot make take off HP at 200 RPM no matter what the motor.

We don't use torque and HP to fly airplanes, we use THRUST.

[A64Pilot]

7 hours ago, Pinecone said:

But you are missing the fact that when you slow the PT-6 to 200 RPM you are greatly increasing the pitch of blades, thus the load.

A fixed pitch prop cannot make take off HP at 200 RPM no matter what the motor.

We don't use torque and HP to fly airplanes, we use THRUST.

A prop can certainly absorb T/O power at low RPM if it’s long enough, to start with props don’t make power, the engine does.

Torque x RPM is power and of course we use power, that’s where the thrust comes from, we takeoff at redline RPM not for the prop, but because that’s the engines max power

You’re failing to understand why we run the prop RPM that we do, it’s not because of the prop, it’s because of the engine. It’s relatively difficult to make an engine make good power at a usable by the prop RPM, most engines want to turn much higher RPM, but the prop loses efficiency at high RPM due to tip speed and becomes noisy, so some motors have been geared, which adds complexity, cost and weight.

If we could make power at much lower than 2700 RPM, then we could run much more efficient props and make much less noise. High RPM decreases prop efficiency, not increases it, within limits of course you couldn’t run our props at 200 RPM, but if you removed the requirement of having to turn 2700 a much more efficient prop could be built for our aircraft.

We need constant speed props because our motors can only make power at a very narrow RPM band, not for the prop.

You know for instance turbo fans are fixed pitch, and yet they make T/O thrust and can operate at very high speeds at very high altitudes, they do so by varying RPM not by changing pitch, because the way a free turbine works doesn’t couple it’s power to output shaft RPM nearly as much as a piston engine does.

 

[RoundTwo]

43 minutes ago, A64Pilot said:

You know for instance turbo fans are fixed pitch, and yet they make T/O thrust and can operate at very high speeds at very high altitudes, they do so by varying RPM not by changing pitch, because the way a free turbine works doesn’t couple it’s power to output shaft RPM nearly as much as a piston engine does.

 

The rotors are fixed, but the stators are variable and that changes the AOA on the downstream rotors.

[Pinecone]

16 hours ago, A64Pilot said:

A prop can certainly absorb T/O power at low RPM if it’s long enough, to start with props don’t make power, the engine does.

Torque x RPM is power and of course we use power, that’s where the thrust comes from, we takeoff at redline RPM not for the prop, but because that’s the engines max power

You’re failing to understand why we run the prop RPM that we do, it’s not because of the prop, it’s because of the engine. It’s relatively difficult to make an engine make good power at a usable by the prop RPM, most engines want to turn much higher RPM, but the prop loses efficiency at high RPM due to tip speed and becomes noisy, so some motors have been geared, which adds complexity, cost and weight.

If we could make power at much lower than 2700 RPM, then we could run much more efficient props and make much less noise. High RPM decreases prop efficiency, not increases it, within limits of course you couldn’t run our props at 200 RPM, but if you removed the requirement of having to turn 2700 a much more efficient prop could be built for our aircraft.

We need constant speed props because our motors can only make power at a very narrow RPM band, not for the prop.

You know for instance turbo fans are fixed pitch, and yet they make T/O thrust and can operate at very high speeds at very high altitudes, they do so by varying RPM not by changing pitch, because the way a free turbine works doesn’t couple it’s power to output shaft RPM nearly as much as a piston engine does.

 

Go back and read what you wrote.

YOU stated with electric you could take off and 1500 RPM and cruise at 2000 RPM with a FIXED PITCH.

NO WAY, NO HOW.

You even refute your own post talking about a turbo fan and how higher RPM is higher power.

We have had geared engines (not typically in GA).  If what you are saying is completely correct, why did they not run their props at 500 RPM?

[Austintatious]

I am not convinced these Toroidal props for air purposes are any good at all.   For boats they make sense... The geometry is actually quite different, about as different as water and air.

The Toroidal props for air looks horrendously bad to my eye.  And so far, all the people on Youtube that have tried them say they are silly and do little to reduce noise.

[Austintatious]

20 hours ago, A64Pilot said:

You’re failing to understand why we run the prop RPM that we do, it’s not because of the prop, it’s because of the engine. It’s relatively difficult to make an engine make good power at a usable by the prop RPM, most engines want to turn much higher RPM, but the prop loses efficiency at high RPM due to tip speed and becomes noisy, so some motors have been geared, which adds complexity, cost and weight.

If we could make power at much lower than 2700 RPM, then we could run much more efficient props and make much less noise. High RPM decreases prop efficiency, not increases it, within limits of course you couldn’t run our props at 200 RPM, but if you removed the requirement of having to turn 2700 a much more efficient prop could be built for our aircraft.

We need constant speed props because our motors can only make power at a very narrow RPM band, not for the prop.

You know for instance turbo fans are fixed pitch, and yet they make T/O thrust and can operate at very high speeds at very high altitudes, they do so by varying RPM not by changing pitch, because the way a free turbine works doesn’t couple it’s power to output shaft RPM nearly as much as a piston engine does.

 

I disagree with the idea we need CS props because of narrow power bands. 

We don't need constant speed props because of engine power bands.  We have them to allow us to fly more quietly and efficiently in cruise while still allowing maximum power at takeoff.  The very fact that there are fixed pitch aircraft using the exact same engines as other aircraft with constant speed proves that we dont NEED CS props for power band reasons.  It is about having options to optimize for multiple operational regimes.

The RPM we run for a given prop size is all to do with Tip speeds.  This is why Bigger props turn slower... Take it to the extreme and think helicopter blade.  You want to keep the tips subsonic as the drag at the tips goes up very rapidly with tip speed, thus the higher the RPM, the more power lost to simply moving the tips through the air.  This is why lower RPM props are more efficient.  We just do not care about efficiency during T/O.

We could run lower RPMs and get max thrust, but that means longer blades.  Those effect other design considerations, for instance my rocket only has about 8 inches of clearance between the prop and ground.

Jets are a bit different , For t/o and cruise operation we are full power and anything less and we lose efficiency (BSFC).   You cant really compare them to prop aircraft and their engines because of the fact that if you try to reduce RPM with a fixed pitch prop You can only change it so much on account of the air flow eventually windmilling the propeller.  This does happen in a turbojet/turbofan, but not at the lower speeds of a piston Fixed propeller.   While different, the underlying mechanics are the same in the jet engine vs FP piston and until a Fixed pitch propeller is being driven by the air and not the engine, these two setups operate the same... reduce engine power, reduce RPM and reduce thrust.  However once past the 0 thrust threshold in a Fixed prop setup, the prop begins to create massive amounts of drag and the RPM is kept high (way above idle).  In a jet the drag does not increase much and the RPM's of the fan/core are able to drop to very low RPM.     The only difference with a CS prop is that instead of reducing RPM, we reduce torque.  Once again, after the 0 thrust point is hit, the propeller begins to create a lot of drag.  

Electric motors even with their VERY wide power band, would not make  CS prop obsolete, in fact they would make them even more desirable.  You would still want to be able to reduce/adjust the RPM/pitch for cruise flight and for T/O you would want the highest RPM possible without driving the tips too close to supersonic or getting past the max power output RPM of the electric motor.  This need/desire for an adjustable prop grows the faster the aircraft is capable of flying, even though the electric motor can produce max power over a wide RPM range.

This all again refutes the assertion that we have constant speed props because of a narrow power band.

Edited March 2, 2023 by Austintatious