Help Needed Badly - Gasoline Engine Quad (Variable Pitch)


This is my first post ever over here. I'll be honest I'm not a lot into making quads or anything of this sort but my professor asked me if I could do it and I said yes, as I need this project to graduate.

So now I'm stuck with poor knowledge about quads.

The task that I'm stuck on is that there are four engines that my professor ordered. They're JC120 EVO, 12.5hp gas engines. I want make/order a variable pitch propeller for it. Can you help me find exact dimensions and where should I order it from?

The JC120 EVO detailed specifications can be seen here.

Also the quad is being designed to carry a load of at least a 100lb. Does the assembly of the variable pitch and the propellers have to do anything with the weight? Do they have to be stronger than the usual? He asked me to machine it. But honestly I think doing it in 2 weeks will be not be easy for me.

Any help will be greatly appreciated!! I can not graduate until I complete this task =(.

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I gotta see this! Keep us posted.

Sorry if I sound negative, but I'd say you have little chance to get this to work.

You need two props to spin the opposite way than the others for a start, so those two would need additional gearing.

As multi-rotors are so unstable, they need very quick speed changes to each prop as demanded from the flight controller to fly.

The thrust from the prop is one factor, but the torque is also needed for yaw, and stay straight. Variable pitch (with constant speed) only addresses one of these requirements, so you'd need custom firmware to control each throttle individually also for yaw, and compensating the pitch as it does. Or, if you forget variable pitch and try to use the conventional motor/ESC control to each engine, the throttle response is simply not fast enough.

Another factor is safety. Quads and Hex's have no redundancy - any failure of a motor / prop / flight controller etc and they fall uncontrollably from the sky, usually in an unpredictable way at great speed. I've just re-built my hex following a crash caused by a compass issue (I think), and the horizontal impact speed was 45mph according to the logs. The weight of that (a few kg) is enough to cause serious damage, a quad with 4 engines, gearboxes, frame etc etc out of control would easily kill someone.

Personally I can't see how this will work, and if it does, ever be safe.

A better bet might be to use one engine to drive a (small) alternator, to re-charge a small battery pack, to power conventional ESCs / motors. I'd suggest an Octo, for lift and redundancy, and design in a big enough battery to keep it flying for a few minutes if the engine stops so you can land in a controller manner. That way you can get extended flight times (just add fuel) and lifting capacity, with a safety margin.

Or... forget trying to re-invent the wheel and build a traditional RC helicopter!

This could be done as a tricopter. A Tri uses a servo on the tail for yaw rather than motor torque. This doesn't address the safety issue which is a huge concern. These copters fall out of the sky all the time.

I've got to agree with Alan here...

Safety issues aside, this sounds at first like an amazingly cool project, but after a moment or two consideration I realize that it would be extremely difficult to realize under any timeframe or budget.

Even before dealing with flight control, just getting the 4 engines to start together and synchronize their power output alone would be a daunting task, then you need to take into account the drivetrain loss in reversing two of the four engines.

Then you need to consider the complexity (and strength requirements) of mechanism that could handle pitch adjustment of a fairly huge propeller with 12hp + of power. and multiply that complexity X 4.

The easiest way I could imagine attempting this in a limited time period (and this is a bit of a stretch of the imagination already) might be gearing the engines together to drive a giant set of fixed pitch, counter-rotating propellers for lift, + a generator to power a surrounding, traditional, electric quad/hex/octo configuration.

This would use the the gas engines for sheer lifting power, and rely on the electric system for directional control (developing the software to control this would be another story entirely though).

Regardless of approach - The inherent danger of such a beast is daunting to say the least.

Hope you can turn something out, i know it's been done before:

Before someone calls 'shenanigans', I would be very curious as to who your professor is and what university you're studying at?  I'm also curious as to why gas engines over electric and why the 100lb payload requirement. 

Guys, keep in mind you CAN control ya with pitch as well... you COULD essentially have one engine powering all motors, via a geared or belt drivetrain. Or you could simply use 4 separate motors with a governor keeping constant RPM.

Most FC's can be adapted to control pitch on collective pitch rotor set ups. Pitch can both control vertical thrust and applied torque. It (as in Constant speed quads) has been done several times.

Hi Shehryar,

Either your professor has a really sick sense of humor or hes a sadist or he has no idea at all what he is asking you to do.

From my own experiences with professors it's most likely to be the middle one.

It is extremely difficult to get this to work at all satisfactorily with 4 independent gasoline engines, keeping stabilization actions working in a timely manner is unlikely (with fixed props)

As you seem to be heading towards variable pitch that probably is at least possible because you can over power the motors and use the pitch for control, but I think variable pitch props in this size either don't exist or would not be in your budget if they did.

Machining sufficiently functional variable pitch hubs may be possible, but it is a considerably major project by itself.

And the time frame you have mentioned is ludicrous, a small team experienced in multicopters working on this for a full semester (or year) maybe (although I would prefer to stand a considerable distance from the test flight.)

I have some beginner level design information on my quadcoptersarefun,com site:

And the DIYDrones wiki has a little too:

But basically I think you need to go back and talk with your professor about the magnitude of this project and the impractical aspects of implementing it.

If he laughs, you will know my estimate of his character was correct.

A quadcopter using a single gas engine with direct drive of all 4 variable pitch propellers was completed (more or less successfully) in a California University over a school year by a good sized team of undergraduate students.

The single engine quad with fixed pitch linked to by Spencer is a Curtis Youngblood project, a championship level Traditional heli flyer who put together a single motor variable pitch electric quadcopter he sells that is absolutely amazing.

And he did the gas one as a proof of concept.

He has spent years working on this stuff and is Totally skilled in all aspects of it.

The project you are engaged in is not something I am pretty sure that no one who actually understood what was involved would undertake, certainly not without a lot of time and a lot of money.

Best Regards,


You selected one of the worst engine choices possible, likely to obtain the least expensive product.  I am an SME with regards to two stroke gas engines and I can only wish you all the luck you can hope for with your project,  Whatever else you do, the engine will let you down.

OK, I'll say it.....if it looks like a duck and quacks like a duck....and it's yellow and it has webbed feet and it floats on water and it swims...and it's name is Donald..But let's assume for a second this is legit..

Counter rotation - you may actually be able to change the timing so that the engine can run in the opposite direction - or, you may be able to mount two of the motors upside down (does that work?) or - servos for yaw.

Problem 2 - What risk assessment would let you start the last motor with the spinning propellers of death right next to you - electric starter? wires, entanglement?  Nah.

Vibration - hard to know how you would even approach isolating the IMU from frequencies and amplitudes associated with these engines - mount it on 5kgs of vibration damped steel?

Constant speed - IF you could have two of the motors in counter rotation, and IF you could come up with a variable pitch prop, you could achieve yaw. However, this would rely on fine, fast response control of RPM. not sure how you do that on a petrol engine.

The other option would be to have a single engine driving four variable pitch props with two geared for counter rotation. OR, you could have one big engine driving one big prop with individual variable pitch blades (for pitch and roll) with a smaller variable pitch prop controlling yaw. 

That appears to be a hybrid, as I suggested?

Hello  Shehryar Niazi

Please tell your professor that his demand is pure Science Fiction...

O yes it can be done, but if you can achieve that I suggest you go directly to DARPA..

4 years  and still not finished, maybe your professor can help them...

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