Electric and Counter Rotation

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

RonL

Well-Known Member
HBA Supporter
Joined
Jan 9, 2007
Messages
502
Location
Texas
To bring this back to the fact of what's real and in front of our eyes, I have some questions


upload_2019-4-7_17-2-55.png

Are wind conditions in and around the small mountains near Quartzite Arizona, ever calm enough to fly something of this design. As a hobby prospector this would satisfy a need to hop rugged terrain and settle down in tight spots, but I feel it is a little like a butterfly in the wind.
I have never been to Arizona, but I think there are some here that can confirm if conditions might ever be suitable.

Any input ? Thanks.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
6,722
Location
Saline Michigan
The propeller is heavier than the rest of the rotational mass?
Mass moment of Inertia is the integral of dm*r^2. Props have a lot more r on most of their mass, and generally make for a lot more MMOI than the crankshaft or starter gear or any other items in the system.

Get into rotary engines like were common a century ago, with the whole engine spinning, and that greatly pumps up the engine side MMOI. All we have spinning is the crank, starter ring, camshaft at 1/2 speed and thus 1/4 effect, and accessoriy cores.

Billski
 
Last edited:

RonL

Well-Known Member
HBA Supporter
Joined
Jan 9, 2007
Messages
502
Location
Texas
Mass moment of Inertia is the integral of dm*r^2. Props have a lot more r on most of their mass, and generally make for a lot more MMOI than the crankshaft or starter gear or any other items in the system.

Get into rotary engines like we're common a century ago, with the whole engine spinning, and that greatly pumps up the engine side MMOI. All we have spinning is the crank, starter ring, camshaft at 1/2 speed and thus 1/4 effect, and accessoriy cores.

Billski
It's that large amount of MMOI that I think can contribute to the generating of power if you have the components in motion and make use of a fast cycle switching from motor to generating. Generator output can be several times greater than motor draw. A hypothetical example might be 3 seconds power draw and 1 second generator output.

Consider if the nine cylinders were to be electric motors instead, the forward speed of a plane would instantly become the driving force that continues to turn the mass of (now) generators and prop. Fast electronic switching can reduce the cycle to a non-detectable event to our physical senses.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,085
Location
97FL, Florida, USA
It's that large amount of MMOI that I think can contribute to the generating of power if you have the components in motion and make use of a fast cycle switching from motor to generating. Generator output can be several times greater than motor draw. A hypothetical example might be 3 seconds power draw and 1 second generator output.

Consider if the nine cylinders were to be electric motors instead, the forward speed of a plane would instantly become the driving force that continues to turn the mass of (now) generators and prop. Fast electronic switching can reduce the cycle to a non-detectable event to our physical senses.
No.


BJC
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
6,722
Location
Saline Michigan
It's that large amount of MMOI that I think can contribute to the generating of power if you have the components in motion and make use of a fast cycle switching from motor to generating. Generator output can be several times greater than motor draw. A hypothetical example might be 3 seconds power draw and 1 second generator output.

Consider if the nine cylinders were to be electric motors instead, the forward speed of a plane would instantly become the driving force that continues to turn the mass of (now) generators and prop. Fast electronic switching can reduce the cycle to a non-detectable event to our physical senses.
RonL,

What you are proposing is a perpetual motion machine, which can not work. People have tried...

Let's take this case - to make propulsive power 3/4 of the time, then coast for 1/4 of the time, then repeat. Let's follow this through. We have a generator capable of absorbing all of the engine's power at its level flight cruise speed. We have an airplane flying at one power setting, in level flight, with the speed steady.

Then we turn on the generator for a full second. At the start of that second, the prop is at full speed, fully absorbing the power of the engine AND the generator supplies a similar decelerating torque to the engine. The engine is making its full load, while the prop and generator are making twice that much in the declerating direction, and the engine is now slowing down.

During this one second that the prop is slowing down, the thrust from the prop is reduced and the airplane is decelerating. With a big inertia on the engine, the engine only slows down a little, but it does slow down. So does the airplane.

Then we turn off the generator, and now we have to accelerate the engine back up to speed so that it can accelerate the airplane back up to speed. The acceleration takes some energy, so we do not get fully back to the speed we were at before we started this process. If we had low MMOI, it would slow quickly. If we had big MMOI, it would not slow as much, but it would still slow. When the generator turns off, the engine has some extra torque over what the prop is turning to thrust and accelerates the prop back towards its steady state speed. With a big MMOI, this might take the whole 3 seconds, with a small MMOI, it might be back up to speed quicker. The airplane does a similar accel-decel-accel cycle...

Eventually the airplanes settles down to oscillating about the speed a little below the speed it would go if you simply ran the engine at 3/4 of the power you were running. You will actually be slightly slower than that 3/4 power steady state speed for a couple reasons:
  • The steady state total energy is slightly less than the total of the drag from oscillation. Energy goes with speed cubed, so the extra energy for the period above the average speed is bigger than the energy not spent when slower than the average speed;
  • The second reason is that while the prop is trying to accelerate the airplane, until the prop is fully back up to speed, some of the power is consumed in accelerating the MMOI and the mass of the airplane...

Big inertia or small inertia and many short intervals, or few large ones, or continuous modest running all result in the same thing - the energy applied to propulsion is what makes the bird go. Make less to drive the bird, and it will slow down.

Billski
 

RonL

Well-Known Member
HBA Supporter
Joined
Jan 9, 2007
Messages
502
Location
Texas
Billski, What I said is not as clear as I had intended :(. thanks for your answer. :)
My intent is an all-electric power system and could look almost identical to the Gnome engine in the video, nine motors all geared to a main ring gear, the whole setup, and prop turns like the Gnome engine.
I'm pretty sure that electric motors have a much better recovery time than an Internal Combustion Engine, I agree with you in general about the loss of speed of the airplane when power is cut, but did you intend to dismiss the windmill effect of air against the prop as the plane's speed drops off? To me, this is a very momentary power source and an assist to Rpm recovery.
Primarily I'm thinking 1% or 2% fluxation in speed and Rpm (cycle times in microseconds)
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,533
Location
NJ
The electric cars have regeneration brake system and can be more efficient that way. However probably on the runway when landing or going down hill at approach to the airport will you see an advantage. Otherwise we are back to perpetual motion and a net loss from friction.
 

RonL

Well-Known Member
HBA Supporter
Joined
Jan 9, 2007
Messages
502
Location
Texas
The electric cars have regeneration brake system and can be more efficient that way. However probably on the runway when landing or going down hill at approach to the airport will you see an advantage. Otherwise we are back to perpetual motion and a net loss from friction.
No PM, but closer to the first law than most people try to go.
I'm going to have to try to put down in words on paper, then come back to the thread with a description that might make sense.
The loading and unloading of a prop at speed might be the breakdown area of my thoughts.

For anyone to think about while I'm preparing a better post.

Consider the prime mover the nine motor configuration (like the Gnome) spinning at 3,000 Rpm
Forward speed 250mph into a 30mph headwind,
What would be the dynamics of airflow in front of and behind the propeller in the short time cycle of say 0-3 seconds?

I believe for the evaluation of regeneration of electrical energy, the drag friction can be disregarded.
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,533
Location
NJ
not drag friction,....system regeneration at less than 100 % , line loss, etc....extra weight, with no net gain. Perhaps you are looking at the 80% prop efficiency vs higher efficiency of the "mass moment of inertia regeneration system".......and you think longer battery life would result....Well the math should be fairly straight forward for someone with time on their hands, the hardware/engine design should be interesting, after you prove it with the calculations.......
 
Last edited:

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
6,722
Location
Saline Michigan
Billski, What I said is not as clear as I had intended :(. thanks for your answer. :)
My intent is an all-electric power system and could look almost identical to the Gnome engine in the video, nine motors all geared to a main ring gear, the whole setup, and prop turns like the Gnome engine.
I'm pretty sure that electric motors have a much better recovery time than an Internal Combustion Engine, I agree with you in general about the loss of speed of the airplane when power is cut, but did you intend to dismiss the windmill effect of air against the prop as the plane's speed drops off? To me, this is a very momentary power source and an assist to Rpm recovery.
Primarily I'm thinking 1% or 2% fluxation in speed and Rpm (cycle times in microseconds)
No way around it. If you reduce the ON time, you reduce the total work done in a period. If you make power from the windmilling prop, that extracts power from the kinetic energy of the airplane, adds to the deceleration of the airplane, and increases the energy that must be put back in when the engine is making power that turns the prop.

Perpetual motion machines do not exist. You are proposing a perpetual motion machine. Done...

Billski
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,533
Location
NJ
Perpetual motion machines do not exist. You are proposing a perpetual motion machine. Done...

Billski
Well the decay time of the Earth around the Sun for all practical purposes .......pretty close.
 

Toobuilder

Well-Known Member
Log Member
Joined
Jan 19, 2010
Messages
4,727
Location
Mojave, Ca
I think some people can't quite get their head around the duty cycle of a typical GA airplane. Some apparently believe that once airborne, the airplane throttles way back and just coasts along like a car on the freeway. Not the case. The airplane is like a fully loaded car, pulling a trailer up a steep grade. It takes all available power to "keep up with traffic", and letting off the throttle even for an instant results in instant deceleration which takes time to recover.

Airplanes fly up against the drag wall at all times. If you want to compare the mission to a hybrid car, load that Prius up with 5 adults, bury your foot to the floor and climb the Rockies. You might be amazed at the poor fuel economy this tech brings you when mismatched to the mission.
 

RonL

Well-Known Member
HBA Supporter
Joined
Jan 9, 2007
Messages
502
Location
Texas
Some apparently believe that once airborne, the airplane throttles way back and just coasts along like a car on the freeway. Not the case.
That's kinda odd :) 50 years ago when I was solo flying 150, 172, and 182 Cesna planes, that's pretty much what I remember being taught....full throttle on takeoff and at altitude cut back to about 80%. Wasn't able to see it through to a PPL.
Being as most seem bent on going to perpetual motion not being possible, I'll stop before things keep going downhill.

I do think a nine motor Gnome power unit sounds kinda cool :cool:
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
7,427
Location
North Carolina
But perpetual motion is all downhill! Unlike school, which is as we all remember, is uphill going in and coming home ;)
 
2
Top