Gas+electric hybrid multi-copters ...


Hi All,


We have recently discovered a way to build hybrid gas/electric-powered multi-copters and would like to share it with you.


The main advantages are:

1) Heavy lift - due to gas engine power

2) Long endurance - due to high gas fuel power density

3) Safety - power source redundancy for safe landing


For the full description of the idea please have a look at:

We are also looking for partners to help us with prototyping and commercializing the idea.

You comments in the blog are welcome ...


Best Regards,

The team

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  • Internal combustion engine with 4 variable pitch prop assemblys is likely to have the features you are looking for. Kind of like how Kurtis Youngbloods Stingray works.

  • for multicopter ?? no, but a gas powered fixed wind plane that co generates electricity is the ideal solution

  • Uh, thanks for the laugh? An IC engine running a peak efficiency (100% load and whatever rpm maximizes efficiency) is exactly what a generator is, and is exactly what is being proposed here. No one is saying that you're throttling, so you're never "not providing power". You're providing constant power at the peak engine efficiency, and skipping the dynamo losses.

    As for the "provider the same current to spin the props," look up rotational inertia frames... It's just like a car on a train - the car is moving faster relative to the ground than the train. The top of the motor is spinning relative to the bottom of the motor, and the bottom of the motor is spinning relative to the frame. Therefore, the top of the motor is spinning faster, relative to the frame. No extra losses required (except when not adding electric, you need to "brake" the motors). That's not to say it's a good design, but that fundamentally it functions as he describes.

    As for the slip rings, there are high power, high speed versions, but, as I said, they're expensive and add weight.

    I'm imagining that a planetary gearset (like the Hybrid Synergy Drive in a Prius) would be a good solution for a hybrid UAV though.

  • Moderator
    Go back to engineering school , the IC engine is less efficient than a generator as it is running at a higher rpm, it produces heat while not providing power= more losses. If you are spinning the motor cases the you still have to provider he same current to spin the props+ slip ring = more losses. Slip rungs brushes do not work at high speed
  • I'm not sure, but I get the impression that some of you are misunderstanding the design. The idea is to run an engine into a drive system that spins the bottoms of the (presumably small, weak) electric motors, and then use the battery packs to add some power to whichever props need it. Because the engine is not throttling up and down, you can continuously run it at its peak efficiency point.

    The gas engine system of this is actually more efficient than a generator. A generator is a gas engine, running at its peak efficiency point, turning a shaft that turns a dynamo. By skipping the dynamo and using a gear box (consistently more efficient that dynamo), your overall energy efficiency is higher.

    That said, however, there are a few issues that I don't see mentioned here (though it sounds like Dan gets it). The first is that to be able to spin the bottom of the motors while also providing power to the top requires concentric slip rings, which are expensive and add weight and power loss. The second is that gearboxes and drive shafts are very heavy by quadcopter standards, and the added weight will push up the thrust requirements and then the power requirements and any efficiency savings may be lost. Finally, you'll have some serious losses in maneuverability if you can't go below a baseline thrust.

    I'm not going to run the numbers for the system right now, but I suspect that Dan is correct. If you remove the electric motors, gear boxes, drive shafts and just do a gas ducted fan/helicopter system, the weight savings will outweigh the benefits of this quad setup. You may, however, want to explore using this "hybrid" design on a helicopter system. That one is definitely worth doing the concept level calculations for, in my opinion.

  • I think the separate generator 'pod' is the way to go. It could be attached to a normal large copter when extra endurance is required. I think our normal brushless motors could be run as a generator from an IC engine with a rectifier/regulator system. A loosely hung system shouldn't transmit vibrations to the copter.

    Its on my long list of things to try, somewhere near the bottom.

  • Did a engineering study myself 2 years ago, conclusion..... waste of time.*

    If your going to use gas, it is better just to stick with a T-Hawk type design. The extra weight added to air frame doesn't justify the limited extra stability you get from a quad design.

    If you looking for down range, regular Heli design works better as well.


    Lets face it, the IMU code is working very well, so all this effort isn't worth it :)


    *Test used RC gas twin motor, direct coupled to brushless RC motor as generator, using modified ESC as regulator (needed the FET array). Power output vs weight vs stability gain vs endurance was the bases for my conclusions.



  • To backup what others said:

    - electric motors are more efficient, and a simplier mechanical design (only one moving part each).

    - building an engine as a generator is more efficient that trying to use it as a variable rate torque engine.


    If I was a millionaire, that's what I would build; lightweight "aloominum" block generator and electric drive.

  • I've been looking into this sort of concept myself and planning a build along the same lines. One thing that concerns me is that aren't drone now suppose to be more friendly to the environment, having an IC engine on a near static vehicle will result in a lot of pollutants in to the environment. One way you could get around this and what I've been researching into is having a IC engine run on hydrogen with a hydrogen generator on board and small compressed tanks of hydrogen and an electric generator or small motor with a planetary gear box to spin up a bit more efficiency out of the engine. There are loads of possible routes down to a solution but there is a lot of engineering involved to do this kind of project and your number crunching will have to be spot on to make it be a stable craft.  

  • I've thought about it, and even at some point in past crunched some numbers - all were not so positive. Take it from an engineer with over ~15 years of experience in related fields. Each of your bevel gears will have approximately 80% efficiency transferr, platetaries similarly! The IC engine has relatively high torque and your driving shafts will have some mass = rotary inertia" some of which will be lost in your transmission chain, but You need to account for that sizing up the motors. Maybe You should use platetaries at each prop - and electric motors at the orbit / planet gear this way when the electric motor is stopped the prop spins with speed = IC engine, to stop it you will need to match the IC engine speed. This could make for fewer gears but would increase complexity in manufacturing. In the end looks like cool learning project but in my opinion outcome is easy to predict - sorry for being blunt, but crunch the numbers first.
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