Hello everyone,
I hope I don't step on any toes here since I am a newbie to the forum.
I have searched the forums and have read a few different discussions regarding this topic so of course I know the idea is not a new one.
There was clearly some good information but it does not sound like anyone has yet succeeded in building a power plant that would work for the purpose.
I believe I have found the components that would be capable of doing the job. At least as far as a producing the raw power for the job.
My goal is to keep the generator package under 10Kg while producing 180 amps@18V continuous and a peak of more than 300 amps. All of this while carrying enough fuel to run for an hour+.

The problems I am running into are more to do with the electronics than the actual power plant.
I believe I have found the required alternator and engine combination to do the job.
But for this to actually work the gross power needs to be rectified and regulated into a form that is usable by the flight control system and the ESC's.
After that there is a motor control circuit required to actually run the generator engine to control the output in relation to load requirements. This system would have to monitor the capacity and charging status of the batteries and the amperage consumed by the drive motors allowing it to determine how much throttle to give the generator.
Finally the flight control module is going to have to know when the generator runs out of fuel to be able to use the batteries for a controlled safe landing.
The assumption is that with a generator on the rig batteries would be required but the amount of batteries required could be reduced by 50 to 75%.

The information I am missing is real world data on how much power is being consumed by a rig that can carry over 10Kg under different flight conditions. For instance I know of a 700mm class rig than can lift in excess of 15Kg running on 4 Turnigy nano-tech 5000mah 6S 65~130C Lipo Packs and 8 Turnigy G60 Brushless Outrunner 500kv motors. what I don't know is what the actual power consumption is for this rig when it is carrying a load while hovering and maneuvering.

I can run the theoretical math of what it could use as a maximum but the goal is not to provide the maximum power but instead to provide something that has a continuous power supply that can hover the rig and a peak that meets the majority of the requirements for maneuvers.

I appreciate any comments or input everyone may have.



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Hello again,

Ok so it seems my initial hopes of doing a package that stays under 10Kg was a bit off. But of course since I am a bit thick in the head with determination and tenacity I have pushed forward on my calculations and research and after talking to manufacturers and doing more research I have been able to come up with a power generation solution that weighs about 15Kg and produces 400+ amps at 28V. From what I can tell with a frame, motors, batteries, electronics, etc. should come in about 8 to 10Kg leaving maybe 3 to 7Kg for camera equipment.

Running time should be 1 to 3 hours.

Even though there is an efficiency loss of up to 40% doing the gas/electric hybrid format I don't see a way for a direct drive gas/mechanical drive option working well.

For starters the mechanical complication of a variable pitch rotor assembly greatly increases the probability of a mechanical failure.  

Secondly what makes a electric multi-rotor work so well is the near instant responsiveness and almost linear torque curve of a brush-less electric motor. This is required for the maneuverability as well as the stability control systems to work effectively. Where as a gas motor has a significantly slower throttle response and narrower torque curve would become an issue.

Finally with the efficiency trade off the possibility of increasing flight times by a factor of 5 or 10 could come in particularly handy under certain applications like search and rescue where stopping to change out batteries every 30 minutes or so can seriously decrease the long-term efficiency of the search.

With a hybrid device that can exceed an hour of continuous flight and simply needs a refill of gas to go back up would be a significant improvement in efficiency.

I have found a manufacturer that can produce the electronics for the application along with the alternator module. The motor being a standard RC aircraft engine is ultra light perfect for the application.

The only real hurdle is cost. The system by no means is cheap. A custom frame with electronics, batteries, motors, props and all is not a trivial expense. The generator pack with fuel cells and motors on a one off production run is likely to cost $15000 or more. Of course in production quantities the cost could be brought down to under $7500.

Am I crazy to think that this should be done? Of course the geek in me wants a toy that can fly for more than 15 or 20 minutes. The engineer in me loves the challenge.

Any thoughts?


I do so love your enthusiasm.  Is this the general idea?

I won't say it is impossible. But I am certain there are serious efficiency issues with it.

Have you seen the Youngblood Stingray?



First of all thank you.

Yes that is close to the general idea. Unfortunately I don't have a readily available way to make a nice diagram like that.

The basic layout would be:

2 150 oz fuel tanks linked to keep the fuel balanced.

2 120cc to 150cc gasoline airplane engines linked to 2 5000watt+ alternators

2 200amp+ rectifier regulator units that proved online liPo battery management (similar to a UPS), a feedback circuit to run the throttle servo on the engines, multiple accessory power outputs for things like control electronics, and of course the main power outputs of 200AMP 48V.

2 LiPo batteries (sized to be plenty to safely land the bird in case of fuel/generator failure.

Standard control electronics with GPS

4+ ESC's

4+ Electric motors

I say 4+ because a 6 or 8 rotor does have better redundancy.


Yes there are efficiency issues compared to a purely electric or purely gas design. but the trade off is some efficiency for duration of flight.

Gasoline has roughly 13.68 to 40 times more energy density of a LiPo battery. It is not hard to see how at the proper scale a gasoline based hybrid can have a significantly improved flight duration.


Based on the calculator found at http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en I am confident in the beasts ability to fly with hover ability somewhere close to 50% of available power.


Granted it is all theoretical without someone willing to pay for the build. (to rich for my blood). But I like doing the mental gymnastics. 

I believe there are at least a half dozen different people/groups working on similar concepts. I am sure someone will make it happen.

As for the Youngblood Stingray I have my concerns over a couple of things. When energy is transferred via motion through a ring and pinion (which it appears is happening twice for each rotor) there is a loss of efficiency. (Isn't that why performance car guys always brag on horsepower at the wheels instead of the engine?

In a perfect world or at least my dreams I would be able to find a couple of experienced partners to start a 503c non profit and a kickstarter project to fund it all in hopes of saving lives.

But anyways.... back to reality.


 Unfortunately I don't have a readily available way to make a nice diagram like that.

If you have a PC you do... that was done in Paint.

Paint has been on Microsoft products since Windows 3.1 (looong time ago)

If you are using Linux, Open Office has a drawing program.

Apple -- I am sure there is one with the OS.

The Stingray has a siginificant advantage over your idea so far... it flys.  )don't tell the ring and pinion they are inefficient, they might ask for more money! :) )

Oh, and for homework, read over THIS discussion I found from another DIYD link.


HERE is the DIYD thread from long ago (internet time).



You did that drawing in Paint? Of course I do have access to both Windows and Linux but I can't say when I have seen that kind of drawing come out of Paint.

Yes the Stingray flies but it doesn't seem designed to carry a load.

I read the discussion from the link you posted and they are clearly in the same ballpark.

What is missing is I have actually located a alternator designed for the purpose with the electronics also designed for the purpose with specific weights and output curves.

I also don't think a small (sub 700mm class) will work well because:

1, The output to weight ratio improves as you get larger (at least to a point).

2, To have enough surplus power to carry not only the required full but also the camera gear for tasks like search and rescue.

3, For the craft to be stable enough to fly in less  than perfect weather as in for search and rescue.


I have read several discussions on a few forums about the topic and appreciate any more that around.


I will look back into Paint as a option for drawing diagrams.




If you are interested in the Heavy lift quad idea, there was a kickstarter project last year that seems to have a few of your design elements already included.

I guess the cargo capacity could be used for you alternator system


and the main website (more updates)



Hi Damien,

Yes I came across that one and it looks like a very complicated machine that will likely have yaw issues. 

I am also concerned that they haven't posted an update since October of last year.

A better example of quad-copters capable of handling the kind of weight I am referring to would be the following:



It is quite obvious that producing the required lift is achievable.

The biggest tricks to making a hybrid design work will be balancing the power generation with the output requirements to do it well along with creating a frame design that both supports all of the additional weight in a balanced and flyable manner combined with managing the gyro effect of having several Kg's of mass spinning at up to 8000 rpm's.

I have a good idea of a workable design but of course it will take some time and effort to put it into a cad style diagram. Which I really suck at.


This is kind of what I am thinking about.


I have a good idea of a workable design but of course it will take some time and effort to put it into a cad style diagram. Which I really suck at.

I would not spend a lot of time worrying about CAD. That is mostly for presentation, production, and sales brochures. The engineers that sent men to the moon used slide rules and pencils, calculators when needed.


I need an alternator for 8500 KW power and less than 5 KG weight
would you please introduce me some, if you know any models or companies

I think 8kw from a 5kg power plant might only be available on the Starship Enterprise

But at 55lbs you might be able to get 8kva from a Jakadofsky JetVolt® 230/400V 8/10kVA


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