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
Nonetheless people love multis. Quite frankly the answer to endurance is by no meas a hybrid, althat is simply excess weight. The only reasonable option is a 100% gas operated multi, with collective (variable pitch) props. This reduces the weight of the electronics, bridge converter, step up step down regulators, motors, and excess wiring. In fact it may not even take a change to the flight controller, as the normal throttle (pwm signal) that would go to the esc, would instead gp to a digital servo. The PIDs would be much different of course, but should be very doable.
Going this route would result in more power, flight time, response, and payload.
In fact, I had a lengthy discus sion on rcgroups many years back where someone made a hybrid multi, and posted it in his personal blog. I can no longer find it, but he 100% accomplished it, with a much larger engine than I would have used!
Sincerely,
Justin
Not quite that simple you need feedback to know rotor rpm. But I'd love to see a weedwacker quad powered by 4 weedeater motors. That would be a hoot! With a 2 hour flight time.
Having 4 gas engines is counter productive, with 4 failure points and slow reaction times.
The craft is simple, with one central engine powering 4 variable pitch rotors via shaft or belt. No need for rpm control, just pitch.
Of course if the rotors were properly designed for positive thrust rather than 3d it would add huge gains to efficiency as well.
I had an idea along the same lines as this - direction from the rotors and lift by gas..
good luck with it!
I'm not willing to prove it but I'm sure you can get fast enough response from a 2-stroke to make it work if you operate in the power band of a specific motor.
Thinking about it a little more you could use small outrunner motors to control the bigger gas motors and even generate enough power to run the on board electronics.
You could develop an algorithm to control the spark advance and timing based on the back emf from the smaller motors and provide a very responsive throttle curve based on data derived from that.
Then you would not even need much of a battery on board to power accessories and more powerful transmitters could be used.
Variable pitch just adds complexity and failure points. A quad like this would be a tank and have very long flight times. Perhaps even 4 hours.
Sounds like a winner! Spark advance FTW!
Open Source 12F1840 CDI
Hummm that is interesting if it can change the timing in real time very fast that might just be good enough!
The only thing I want to start off a project like that is a dynamic balancer. I've seen some software a long time ago that was lost. But I need a dynamic balancer something like the turbine guys use.
All the rotating parts would need perfect balance and I'd use it to get rid of that heavy flywheel/magneto. The engine is externally balanced so that would need to be worked out.
Single piston motors can never be perfectly balanced. There's always a second-order imbalance. 4-cylinder boxers and inline-6 are the only things that can even get close.
And I have some experience with engine management from automotive. Spark advance is employed to stabilize idle, since it's torque reaction is almost instant. However, it has very limited strength Maybe only about 5% total torque. So, idle control is done using a combination of spark advance, and idle-air bypass. You'll never stabilize a copter on spark advance alone.
Again, not saying this can't be done, but it's very hard, and still nobody has explained why this would be better than existing known solutions.
I imagine that if you skipped a spark it would have a pretty significant effect on the torque very quickly.
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