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.
Replies
Absolutely agree.
Hi Dave,
Two years ago there was a man in India who did exactly that a large gas powered prop in the middle and 4 brushless motors to provide control and he had a great video (you would not want to be around it!)
And while looking for it and failing to find it I found this:
http://imgur.com/MTP3Q5O
and this
https://www.youtube.com/watch?v=jYUuv7i8LOo
And I think this might actually be a video of a newer and much smaller design by the same man:
https://www.youtube.com/watch?v=4r-62t4CoGA
Best regards,
Gary
Max, I'm not a nay-sayer. I'm just trying to bring some reality to the discussion. I'm not saying this cannot be done, I'm just making sure people realize there is a pretty high benchmark which needs to be met. None of those examples shown have been demonstrated to outperform existing systems.
Gary: I do think that if this is going to be possible, that systems like you propose are the only way it will work. Where the gas motor provides primary thrust, directly. And then there's a secondary system of electric motors providing flight control. And all with fixed pitch. It's actually fairly simple, so it maintains the benefit of traditional multicopters.
Hi Rob,
I'm still not sure of the overall efficiency, but that penta rotor hybrid system does work and can provide considerably increased capacity and endurance.
It was interesting to note on that last one https://www.youtube.com/watch?v=4r-62t4CoGA the angle of the brushless motors , clearly to compensate for the primary turning thrust (torque) of the single central rotor, I imagine that's a bit tricky to balance.
The first one I showed http://imgur.com/MTP3Q5O used a dual central prop coaxial system on the gas engine (probably geared) which avoided that problem at the expense of increased mechanical complexity.
Nonetheless, I do think that this "hybrid" concept has potential for real world (commercial) applications and it is entirely possible that a suitably efficient brushless generator could be worked out, hooked to the primary drive engine to provide power to the flight control motors.
A straight engine driven generator providing electric drive for the primary thrust of a hovering vehicle is MUCH less likely to ever prove practical.
Best Regards,
Gary
That "first one" seems really... sub-optimized. Why an Octocopter? Just go quad. And it's got the central props blowing directly on this huge central mass that creates a huge aerodynamic download, probably pretty close to the actual lift being created. Very inefficient.
The way I would do this, is a twin contra-rotating ducted fan center unit, with small electric stability thrusters sticking out the sides.
Still, it's hard to figure how this design is better than just building a simple ducted fan single or coax copter with control vanes, like a Honeywell T-hawk.
Gary
Could the overall efficiency be improved with a model turboprop motor instead of a 2 stroke?
And could a turboprop be converted to a generator by replacing the prob with a generator?
just a thought and it would drive the cost up but its just a theory...
Turbine engines are less fuel efficient than piston engines. The reason they are typically used is power/weight. They are used basically when you want a lot of power at the expense of fuel efficiency.
Actually, though, this might be the key.
The big problem with the concept of a gas-engine-powered drone, is the weight of the gas engine. Consider for example, the Zenoah G320, which has the highest power/weight of any commonly available and reliable single-cylinder gas engine. It's rated at 2400W peak, and weighs 2.3kg.
Next, we need a giant brushless motor as a generator. I'll pick this one, just for arguments sake:
http://www.hobbyking.com/hobbyking/store/__17986__Turnigy_RotoMax_1...
It's rated at 2960W, giving a bit of headroom, though I'm not sure it can actually do that all day long. There's a problem here as this will be generating 50V which is about double that typically used for a large multirotor. But we'll just keep going. The weight is 849g. Then lets add another 500g for a simple method of bolting the motor and generator together and attaching them in the frame. Then we need some electronics to rectify this, we'll also need some large caps... I'll throw 250g at that, not having anything to go by. That's a bit more than a 120A ESC, so not unreasonable. And finally, lets add 1L of gasoline, with a fuel tank is about 900g.
Total system weight is now 4800g, and it can generate a maximum of... well, assuming a 90% conversion efficiency, we'd get 2160W.
Ok, now, consider bolting this power unit into my Tarot X8 1050mm Octocopter. It currently weighs 7200g with camera and gimbal and 2 6S10000 multistar batteries. It draws ~950W in a hover. With those batteries, weighing 2400g, it can fly for about 25 minutes. It's actually fairly efficient for an Octo. Hover throttle is about 50% so it's just nice.
Now, if I remove the weight of those batteries, and add the gas powerplant, total weight goes up to 9600g. Hover power goes up to 1400W, and throttle is at about 65%.
So that's actually not too bad... I'm not sure how long that fuel would last though. It's probably only good for about 20-30 minutes tops. I currently get 25 minutes out of my 800 gasser helicopter with 660cc of gas, at about the same weight. And there's no way this Octocopter is as efficient. The helicopter has 2.8 times the disk area!
If you add another 2400g of weight to the Octocopter, representing maybe a 2L liquid sprayer system, or 3L more gasoline, hover power is now 2200W, and throttle is 81%. So this is the absolute maximum of the system.
That's a lot of effort to carry around 2L of liquid.
Rob,
What if you use the motor/generator setup to dump charge to the batts, instead of only powering the rig, and go for extended flight time?
Now, THAT would be COOL!
Cheers!
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