Gas Hybrid Quad Rotor UAV?

While trying to think of a way to increase the payload capacity, size and flight time of a quad rotor aircraft I had an idea, which may or may not be novel and was wondering if anyone else has entertained it.

Could a combustion engine powered auxiliary power unit (APU) be installed on a quad rotor aircraft that is light and powerful enough to maintain a charge of the main battery that is used to power the motors and avionics?  In other words, could a small engine powering a generator keep up with the electrical demands of the aircraft that would have to carry it and the fuel?  

Here is a link to a company that produces generators for conventional RC aircraft:

Food for thought at least.

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    • And yet, I have a gas powered helicopter, that can fly for 1 hour, using off the shelf components, is very reliable, and only costs about $2-3000 depending on how you outfit it.

  • IMO no this won't work...yet. You would need over 1kW of generating power and it is simply too heavy for rotary wing applications because generators dont have the power:weight ratio needed. :-(

  • A combustion engine is complex, but more important weight a lot.

    Also compustion -> battery -> engine has 2 passages, and so you have 2 point of loss of efficiency; combustion -> engine (and then maybe some big capacitator to keep up and some system of feeedback from eletric engine power request to combution engine "accelertaion" is needed)

    You may use directy the combustion engine, but rapid change of speed are not good; so you keep constant speed (so you can aslo use ONE engine for all rotor) and then use a dinamic pitch like a elicopter. A lot of complexity and cost.

  • Hello!

    Have a look on this:

    for one time you have to speak (read) French ;-)

    The ONERA ( ~ French NASA) work on micro electro-generator gas turbine, 20cc for 100W, or 600Wh/kg

    Here, the same but in English :

    More impressive ,heavy and not really new, the Jakadofsky JetVolt

  • I believe the original train of thought was developing multi rotor flight lasting much longer than the current 25 minutes or so. So the benefit objective of adding the gas engine was long flight. Same concept for using a fuel cell.
    • Max, yes, we get that.  But it's like saying "I am building the most efficient skateboard that I can. It will have unobtanium bearings, special polymer wheels, carbon fiber honeycomb sandwhich deck, and magnetic levitating suspension."

      Why are you worrying about efficient skateboards?

      "So I can commute to work on my skateboard."

      Well, wouldn't a bicycle be more efficient than a skateboard?  And you can just go buy one?

      "I bicycle is so complicated.  You have a crank, and a chain, and gear, and this complicated frame, wheels with spokes."

      Yes, but they've been making bicycles for 100 years.  It's gotten to the point where they are very reliable, and very cheap.  It may have all those parts, but you never have to think about them.  Every once in a while, you have to lube the chain, and if anything does go wrong, just take it to a repair shop, there's one on every street corner.

      "But a skateboard has only 4 moving parts.  It will be more reliable, I just need to work on the efficiency. 5 years, and $100,000 of R&D, I think I can do it."

      • im new here. how i can give a +1 to your comment?

  • The essence of a multirotor is the simplicity of fixed pitch props. Once you go to variable pitch props you may as well go for a standard helicopter.

    How about about one central petrol motor with a fixed pitch prop which does the heavy lifting, surrounded electric motors with fixed pitch props which are used for balancing?

    • There is no simplicity when you bring in a gas engine.... I think that is the biggest point everyone is trying to make. Even if it was a single gas engine powering a prop and either magneto's or a generator pumping power into the electrical system, it is ridiculously complicated....

      Doing ANY type of gas quad, whether it be with 4 engines, a single engine, or a hybrid gas/electric, the simplicity of a multi rotor goes out the window. There is zero advantage. The only reason to do it, is to say you did it.

      People seem to enjoy adding electrical components and further complicating algorithms etc, which all naturally have bugs, rather than learning how to adjust a single, or a couple small linkages. A linkage is simple, and once set it is RELIABLE.

      • Actually, as I've begun to operate a gas powered heli, what strikes me is how EASY it is.  I fill it up with fuel, pull the cord, and it's running.  No batteries to charge, keep balanced, worry about over-discharging, worry about overcharging, worry about running a generator at the field to charge....  no AC/DC power supply, etc. etc. etc.

        Fill the gas, pull the cord, and go.  How much longer will it fly?  Well, how much fuel is in the tank.

        Nitro is an entirely different animal, and I'm not talking about that.  A Zenoah, once properly tuned, will run forever and day as long as you use good fuel and oil.  It's a commercial engine, not a hobby engine.

        So it's not the gas engine that kills simplicity.  It's a gas engine in combination with multiple propellers.  That is what requires you to use a either complicated mechanical power distribution, or a complicated hybrid-electric drivetrain.

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