mild hybrid as constant speed/two speed gearbox

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stanislavz

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Kind of Prius-like transmission in aircraft.

Ie. - take an engine with 100 hp, mate it to the prop which is ok for climb/take-off, but won't absorb all power at cruise, add to it 10-20 kw generator, and add motor with same power and propeller for cruise in tail / wing pod etc.. ..

10 kw should be in 10-15 kg total. And you are less in generator/starter on a motor. 20 kw - twice of course = 30 kg.

Could any one more skilled provide kind of main power to addendum motor power graph vs cruise speed ?
 

TiPi

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Hi Stanislavz, I think you have the wrong idea for a "Prius-like" setup. The Prius (and most other hyrid cars) use a smaller than normal engine and augment it with an electric motor for the few times when you need more power than the ICE can deliver (or travel at very low speed with the electric motor only).
In an aircaft set-up with a nominal 100hp engine, that would translate into an 80hp ICE with a 20hp electric motor added during take-off and climb. The problem is that you now need an 80hp engine that is happy to run at something like 90% of its rated power for cruise to get your 75% cruise power.
 

wsimpso1

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Kind of Prius-like transmission in aircraft.

Ie. - take an engine with 100 hp, mate it to the prop which is ok for climb/take-off, but won't absorb all power at cruise, add to it 10-20 kw generator, and add motor with same power and propeller for cruise in tail / wing pod etc.. ..

10 kw should be in 10-15 kg total. And you are less in generator/starter on a motor. 20 kw - twice of course = 30 kg.

Could any one more skilled provide kind of main power to addendum motor power graph vs cruise speed ?
The Toyota, Ford, and Chrysler Hybrid powertrains (I have worked on design of them all at Ford and Chrysler and we bought the Toyota product for use in Ford before we did our own) they are commonly called parallel hybrids, where the engine and one electric motor drive the axle in parallel - one or the other or both can be powering the vehicle - while a second electric motor spins with the output. In particular, this is a very good scheme of an electric CVT. It allows the engine to be run at whatever speed/torque is appropriate (including stopped), enables running at the fuel island (best place on the engine operation range for turning fuel into horsepower), gives instant starts when needed, and enables regen braking. Each of the electric motors and power electronics are about 100 kW or about the power level of the engine in the mix. Mass is not trivial here. It is a great scheme for achieving excellent fuel economy in city driving or at light loads and modest speed on the highway.

The system Stanislav is describing will work, but now you are carrying two props and two generators and the power electronics to run things which is a bit of weight as described, but let's look further...

The big difficulty in the engine connected prop is that a fixed pitch prop becomes an operating compromise - we either pitch it for takeoff and climb and it runs away in cruise keeping us from expressing much power in that mode, or it is pitched for cruise and can not express but a medium fraction of power on takeoff and climb, or it is set somewhere in between. If you are optimized the prop for climb, your parallel scheme would have to move much more than 20% of your engine power through the parallel power path to produce big power for cruise. If you optimized the prop for cruise, the entire output of the engine at reduced rpm is used up in the engine driven prop and there is none left over for the parallel path. Same goes for any in between prop optimization. The only way it will work well is if you run the engine driven prop for take-off and climb speed, and then go to most of your power through the other path for cruise, with a lot more weight in that path than the 20% scheme.

The approach designed almost a century ago that works with a lot less weight is a much simpler CVT - a controllable pitch propellor. With a reliable constant speed governor and a properly sized prop, this scheme allows the engine to make full power and express it through the prop over its entire speed range plus cruise efficiently. There are both electric and hydraulic constant speed props out there that are much lighter and simpler than a couple 70 horsepower electric motors and their power electronics to run them.

Billski
 

stanislavz

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The Toyota, Ford, and Chrysler Hybrid powertrains (I have worked on design of them all at Ford and Chrysler and we bought the Toyota product for use in Ford before we did our own) they are commonly called parallel hybrids
You hade and have a quite impressive portfolio of knowledge :)

Back to topic - yes, if it is more than 20% - hands down, and up to standart variable pith prop.
 

Mad MAC

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The best cheap and dirty hybrid concept and currently probably the most practical, I have seen recently (and is also be retro fit-able to much of the homebuilt fleet) is an Electric Supercharger used for normalisation on hot & high operations (the good old 3 minutes of get out of jail operation).
 

stanislavz

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The best cheap and dirty hybrid concept and currently probably the most practical, I have seen recently (and is also be retro fit-able to much of the homebuilt fleet) is an Electric Supercharger used for normalisation on hot & high operations (the good old 3 minutes of get out of jail operation).
A goodie one... But - why not turbo ? It will also acts like poor man ultra compact silencer.
 

stanislavz

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Just small FYI. For short boosts of power - it is ok to use NOS injection to. 20-30hp shot could be build with smallest tanks in ~2kg region full.

And for same 912 rotax - turbo kits do exists with 120 hp output..
 

wsimpso1

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Let's put some numbers on things. An airplane with the prop pitched for 75% power in cruise will only run 80-85% of max rpm during take-off and initial climb - let's call it 83% rpm. Fixed pitch propellors make torque based upon rpm squared and express power based upon rpm cubed. That prop at 83% of max rpm is making 69% of max torque and 58% of max power. To make full rpm for a period of time, the engine boost you are talking about would have to multiply engine torque by 1/ 0.69 = 1.45 and multiply power by 1/0.58 = 1.72.

You would have to take that 100 hp Rotax to 172 hp to do that. Taking a 100 hp Rotax to 120 hp? Cube root of 1.2 is 1.06, so instead of 83% rpm, you are now at 88% rpm, 77% torque and 68% power (instead of 58%). Would you notice the difference? Is it enough to operate your airplane safely? Maybe. You get to evaluate if that is enough to operate safely with accelerate-stop distances within your field lengths and climb gradients to clear terrain...

Most current airplane engines do not even have that 20% reserve in their mechanicals and ability to cool the engine, much less 72% boost. This is possible in some engines running big turbochargers, big intercoolers, mixture enrichment, spark retard, etcetra and severely reducing engine life to do it. If you selected an engine/psru with capability to run at those power levels with good reliability, then you would need to carry around the extra equipment and drag all of the time to have it for only a couple minutes a flight...

Variable pitch prop and boost equipment for normalizing power with altitude sound like a much better deal to me.

Billski
 

stanislavz

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An airplane with the prop pitched for 75% power in cruise will only run 80-85% of max rpm during take-off and initial climb - let's call it 83% rpm. Fixed pitch propellors make torque based upon rpm squared and express power based upon rpm cubed. That prop at 83% of max rpm is making 69% of max torque and 58% of max power. To make full rpm for a period of time, the engine boost you are talking about would have to multiply engine torque by 1/ 0.69 = 1.45 and multiply power by 1/0.58 = 1.72.
Super.

No, turbo kit is only for rotax 912 80hp to 120 hp. And they still get an 1500 tbo oficially. 100hp is kind of stroker and bigger bore kit, but same bottom end . So no turbo for 100hp. But for 80 hp using same bottom end - 20% of more stress.

+- ok....
 

vhhjr

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Truth in advertising: I have not flown a CVT system, but I do have some data from a rolling test stand up to about 40 mph. I used a single cylinder 12 hp engine driving a fixed pitch prop through a Comet CVT with the springs and weights adjusted to keep the engine running at 3600 rpm no matter what prop I put on it.

The interesting part was that the CVT changed the drive ratio as the forward speed increased. See the file below of Blue Machine Graphs.

If one used a more sophisticated snowmobile CVT one would get even better load compensation. Current snowmobiles regularly have over 150 hp engines in them and will run all season on a drive belt. Snowmobile CVTs are heavier than a fixed ratio belt drive and similar in weight to a geared PSRU.Snapshot 1 (2-8-2012 9-06 PM).png
 

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vhhjr

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I have almost finished replacing the propeller with an 11" ducted fan unit. The CVT provides a reduction ratio between .9 and 2.5 and there's a final drive to the DF of 1:1.6. In theory the engine running at 3600 rpm will drive the DF at some speed between 2300 and 14400 rpm. The actual operating rpm will be the point where the torque required by the DF and the drive system losses equal the torque output of the engine. I have run the unit for a couple minutes and will report back when I have some data.

I also have a 17" DF in the works and a 35 HP 2si engine to replace the 12 HP Harbor freight engine now on the test stand.

The rotor for the 11" unit is made from 15 blades from the compressor section of a Rolls-Royce Avon jet engine. The 17" unit has 12 blades from an unknown Russian jet engine compressor section.

The fun never ceases!

Vince Homer
 

pictsidhe

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The prius transmission uses planetary gearing to mix engine and electric power to the wheels. As it is in a car, it needs to provide a very large speed range. An aircraft version would need to provide a much lower speed range. If that was +/-10%, the electric portion would only be 10%. This is starting to look a little attractive. I think that it will probably still lose out to a variable pitch prop in both weight and complexity. But, if you had a battery in the system, you can now add some temporary takeoff power and the hybrid starts to make sense.

My own plans for takeoff power is water injection for the octane boost effect and cooling I'll need. With an engine that can run 75% power without water at a higher than normal CR, I can get higher power while there is water in the tank. Water is fairly easy to find for refills...
 

dino

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A little alcohol in the injection cocktail would help.
 

pictsidhe

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A little alcohol in the injection cocktail would help.
It does, but not something to be relied on, harder to find than water... It also messes with the mixture. Alcohol screenwash is pretty good and a good idea in winter.
 

Bill-Higdon

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Truth in advertising: I have not flown a CVT system, but I do have some data from a rolling test stand up to about 40 mph. I used a single cylinder 12 hp engine driving a fixed pitch prop through a Comet CVT with the springs and weights adjusted to keep the engine running at 3600 rpm no matter what prop I put on it.

The interesting part was that the CVT changed the drive ratio as the forward speed increased. See the file below of Blue Machine Graphs.

If one used a more sophisticated snowmobile CVT one would get even better load compensation. Current snowmobiles regularly have over 150 hp engines in them and will run all season on a drive belt. Snowmobile CVTs are heavier than a fixed ratio belt drive and similar in weight to a geared PSRU.View attachment 90941
I can't wait to see Vince try something like this upload_2019-12-29_10-56-21.png
 

Dan Thomas

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Truth in advertising: I have not flown a CVT system, but I do have some data from a rolling test stand up to about 40 mph. I used a single cylinder 12 hp engine driving a fixed pitch prop through a Comet CVT with the springs and weights adjusted to keep the engine running at 3600 rpm no matter what prop I put on it.

The interesting part was that the CVT changed the drive ratio as the forward speed increased. See the file below of Blue Machine Graphs.

If one used a more sophisticated snowmobile CVT one would get even better load compensation. Current snowmobiles regularly have over 150 hp engines in them and will run all season on a drive belt. Snowmobile CVTs are heavier than a fixed ratio belt drive and similar in weight to a geared PSRU.
This idea was tried in the first iteration of the BD-5, and it didn't pan out. Bede abandoned it. The propeller has a really narrow useful operating range, and it's near an RPM that puts the propeller tips at Mach 0.8 or thereabouts. You can see the effect; if your airplane has an RPM redline of 2700, half that will get you nothing more than a fast taxi. It will take off and climb at 2400 or 2500 on a fixed-pitch prop, only about 1100 RPM more than the fast taxi. Reduce the RPM by 100 or so and it might stop climbing. At half the fast taxi RPM it won't want to move much at all. Not even a slow taxi with some airplanes.

So the only real solution is a constant-speed prop, or at least a controllable-pitch. That has been known for a long, long time, and many experimenters have found that anything else is mostly a waste of time and money.
 

vhhjr

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Trying to make a fixed pitch prop behave like a controllable-pitch one is not the object of this latest experiment with the Blue Machine. I am very early on the learning curve with this ducted fan and having the CVT saves me from needing a bunch of pulleys and belts. In todays test the CVT settled at a reduction ratio of 1.27:1 meaning the DF was absorbing all the torque produced by the engine at that speed. The engine was running at 4080 rpm and the CVT output was 3210. The final pulley ratio is 1:1.6 making the fan run at a bit over 5000 rpm. Id I want the fan to run faster I need more horsepower or I need to modify the fan. As the DF wasn't making much thrust, just mostly stirring the air, the next step is to change the pitch of fan blades. Back to the machine shop to make a new hub and blade mount system. I'll also clean up and paint the DF mounting structure an get the thrust and torque instrumentation back in working order. More later.

Vince Homer
 

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Dan Thomas

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The pitch on those blades looks far too steep. I'd say they are fully stalled. Are they compressor guide vanes instead of compressor blades?
 

vhhjr

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It is my understanding they are late stage compressor blades. Early 60's Rolls Royce Avaon vintage. Some of the blades still have a QC date stamp on them. We knew they are the wrong pitch and I am building a new hub that will allow the equivalent of ground adjustable blades.

In spite of being almost flat the DF did develop a little thrust. The blades are so flat they are mostly just stirring the air. With corrected pitch we are targeting about 25 - 30 lbs of thrust with the current single cylinder engine. With a standard prop I was getting around 70 lbs of thrust. There's a bit more system drag with the DF because of the second belt drive.

Vince Homer
 
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