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Old Mar 30, 2013, 06:50 PM
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Gas -electric "twin"

I'm blaming this directly on Kenh3497..His comments on engine powered on board generators flipped that little light bulb on,with an idea.

I fly 1/4 and 1/3 scale models of the old "Golden age classics"...I'd like to turn scale diameter props, but my G-62 is limited to turning a 24" diameter prop (comfortably).

I use belt and gear reductions to rotate 28" diameter props, or outlandishly large engines.

Enter Ken- What about mounting an electric motor to the rear shaft extension, to increase torque?
I see electric models with 24" props on them, and I believe both power sources combined would produce enough torque to turn my "happy prop".

I will make this so easy for you-disregard WEIGHT-forgetaboutit....

-Floor's yours.
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Old Mar 30, 2013, 07:35 PM
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what is going to happen if the gas engine stalls/burbles and the electric motor is trying to turn your large prop and engine all by its self. May only take a split second to realize but I'm uneducatedly guessing a large amp spike.
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Old Mar 30, 2013, 07:44 PM
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-followed by an open circuit breaker, and a dead stick---Noted

continue.
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Old Mar 30, 2013, 08:24 PM
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this is not what your talking about but it should shed some light as the electric motor is able to turn the prop and give enough tourqe to start the engine so with enough power i guess it is achievable
DLE 222 Auto Start System Detail Presentations (2 min 27 sec)
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Old Mar 30, 2013, 08:43 PM
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Originally Posted by miltac View Post
what is going to happen if the gas engine stalls/burbles and the electric motor is trying to turn your large prop and engine all by its self. May only take a split second to realize but I'm uneducatedly guessing a large amp spike.
What do you think miltac?
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Old Mar 30, 2013, 09:50 PM
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Nathan-thanks...I have an electric on -board starter, but through the gear reduction on that drive system, I can only achieve around 1100 rpms..

I'm not interested in a "what -if" failure...I'm curious if under the proper circumstances, it's feasible.

Can an electric motor, and a gas engine work together at 6500 rpms?, directly connected?
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Old Mar 30, 2013, 11:02 PM
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I suppose you could do it like some ships do and the diesel electric locomotives do, by using a gas engine to run a generator that provides the electric power to run the electric motors used to fly the plane with. That would be pretty cool actually. the engine and fuel can be centrally located as well. if the engine quits for some reason, the plane would behave like normal and you can dead stick it in for a landing. Maybe even something for a battery backup could be provided, maybe even something like a hybrid system where the batteries provide extra boost in some cases.
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Old Mar 31, 2013, 12:18 AM
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At the risk of sounding silly.....Why not just eliminate the gas engine completely, and fly electric? There are plenty of reasonably priced motors ESC's and battery packs that can easily turn the biggest prop you could want, for half-an-hour at a time, if you want.
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Old Mar 31, 2013, 12:28 AM
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Using a motor/generator set up like they use on locomotives would be horribly inefficient, and quite heavy. And, you would still have the issue of "what if" the gas engine or diesel decides to quit unexpectedly.

During the 1950's they experimented with carrying a nuclear reactor aboard a modified B-29 Superfortress. The idea was to generate unlimited quantities of electricity with the reactor, and as we all know, nuclear fuel lasts for years before it has to be refueled.
They had planned to turn all four of the bomber's props with huge electric motors. Sadly, once they got the math figured out, and determined the amount of shielding needed to keep from killing the crew....There was the inescapable reality of a possible crash.

The engineers and scientists eventually wrote it off as a very bad idea.
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Old Mar 31, 2013, 02:55 AM
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What do you think miltac?
I think thats a nice drawing, but.I think you would need a really big electric motor just for it to have enough power not to be spun backwards.
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Old Mar 31, 2013, 03:14 AM
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after giving it thought I think it can work as some hybrid cars use both gas and electric. You would need a radio that can be set up with two seperate throttle curves and use a watt meter to dial in the throttle curve, set up somthing so if the gas engine fails the electic stuff wont let out its magic smoke. the question is how big of an electric motor setup you would need to make up the power required for the bigger prop.
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Old Mar 31, 2013, 03:53 AM
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The reason for the existence of electro-Diesel setups (also gas-turbine-electric) in most locomotives, is its ability to produce smooth standing starts and gear-changes, compared to using a huge clutch.
It is also used in seagoing vessels with thrusters.

Those using this setup are willing to put up with the efficiency loss (which compared to our "efficient" two-stroke glow engine, is still incomparable), to gain tractability.

It has no bearing whatsoever on model power units in R/C.
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Old Mar 31, 2013, 05:14 AM
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Quote:
Originally Posted by miltac View Post
I think thats a nice drawing, but.I think you would need a really big electric motor just for it to have enough power not to be spun backwards.
miltec you are unaware of the basic design requirements.
The electrical engine is powered by a reversable 4 quadrants power converter so will rotate backwards too!
1 To start the nitro motor
2 To compensate the rpm of the nitro motor in idle position and 0 airspeed request.

Taurus Flyer
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Old Mar 31, 2013, 05:19 AM
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Originally Posted by Saltmine View Post
At the risk of sounding silly.....Why not just eliminate the gas engine completely, and fly electric? There are plenty of reasonably priced motors ESC's and battery packs that can easily turn the biggest prop you could want, for half-an-hour at a time, if you want.
There's no 'risk' of sounding silly here-.......I want to use an augmented gas engine, and need all the pros and cons.

I can't have a separate throttle for the Electric motor-I'll have no idea how hard it's working, to choose a throttle position.
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Old Mar 31, 2013, 05:25 AM
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Originally Posted by miltac View Post
after giving it thought I think it can work as some hybrid cars use both gas and electric. You would need a radio that can be set up with two seperate throttle curves and use a watt meter to dial in the throttle curve, set up somthing so if the gas engine fails the electic stuff wont let out its magic smoke. the question is how big of an electric motor setup you would need to make up the power required for the bigger prop.
My first thought was to use an electric motor, large enough to turn the 24" x 10" prop 6500 , on it's own merits...Coupled with the G-62 it shouldn't be over-worked to ASSIST in turning the larger prop.
I'm sure there's a 'feedback' system available to keep the electric motor from over-exertion.
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Last edited by epoxyearl; Mar 31, 2013 at 05:34 AM.
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