Hi,

( Firstly )  - please excuse what might be a really stupid  question - but, since I'm new to all of this... I cant help thinking....

Isn't there some way ( even on a very small scale ) to use a combination of a small 2 stroke powered motor ( or a typical RC gas powered engine ) to spin a small generator and thus create power to assist in "trickle charging "  - or even powering a quad?

I understand there is a weight issue, but I'm thinking the right combination of ESC and motors ( electric ) and prop size could possibly provide enough grunt to lift the thing.

If this were possible, then using a real liquid fuel would ONLY make the drone progressively lighter  compared to the total weight at the start  as it consumes its supply of fuel - in the meantime,

While I'm at it - what about using DC to AC inverter technology some how to an advantage in power output?

 - Just asking.. lol!

[ there are no stupid questions -  the only time a question is stupid, is when you should have asked - but you didn't.]

Cheers!

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Okay, that is impressive.   So not impossible, just damn difficult.

May have to sit down and work on this...   With a CNC machine at my disposal and a spare modified 25HP engine, what could go wrong?

I think we can all agree that we have been there before.

Every engineer wishes he could start out with more before he has to start making compromises.  My personal methodology is to try to innovate before I compromise.

The thread lives!

No way you could use that engine to fly a quad.  I would be surprised if it makes more than 1-200 Watts.

Yea, that engine wont get you anywhere, but the flying rag is a fun and old idea.

Its alive!!!

Interesting stuff.  Incredible to see those seemingly bright guys putting themselves in a virtual gladiator ring with that beast.  Nowhere to run if it goes wrong.

I'm also not sure how re-purposing a bunch of commercial RC Helicopter parts is a senior engineering project?

Anyway, I'd like to see the thing flying.  I've seen a number of these contraptions, but I have yet to see them do more than just hover.

I have two favorite quotes,

"The true sign of intelligence is not knowledge but imagination" ~ Albert Einstein

"Knowledge is knowing that we cannot know" ~ Ralph Waldo Emerson

Yep, seen them before.

On the first one... it's funny that I'm looking to replace the tail drive with a dedicated tail motor, to eliminate the complicated and unreliable tail drivetrain on my heli.  And here somebody is adding 4 of the systems to a quad which previously ran perfectly well with 4 motors. ;)

I'd also like to see video of these things actually *flying*.  The problem is, with variable pitch props, the "simple thruster" model that is being employed so well with Arducopter falls apart with a little airspeed.  All of a sudden, you need much more advanced control.

Now, it has to be said, my opposition to this idea of gasoline powered quads should hardly be considered "violent".  I'm just extremely skeptical.  Consider me the devil's advocate.  You are GOING to have to solve the problems I bring up.  You can do it in the initial design stages and save yourself some time and money, or ignore my points, and solve them after a few iterations.

I enjoyed reading Brad's proposed power system in the other post he just linked to.  I forgot about that.  There's a few things that might make his assumptions quite a bit worse than where he ended up with, showing a 3:1 power density benefit on the side of gasoline.

1) I think he did not include the weight of the motor-generator bracketry, nor the motor-frame bracketry.

2) Needs to include weight, and power loss due to cooling system.  I think you could probably expect to use at least a 1/2hp on a fan just to cool the motor.  It doesn't help that it's an airplane motor, with small cooling fins.  I realize that in a "clean sheet" design, you'd fix this.  But just something else to think about.

3) The energy density of gasoline being used, is that accounting for the reduced energy density of E10 fuels which are common?  Remember, the alcohol in them is pre-burnt, as they have oxygen in them already. ;)

4) I think the assumption of 10% conversion efficiency might be optimistic for engines of this scale.  There is a pretty simple law at work here, where the maximum theoretical efficiency of an engine scales with the volume of the combustion chamber.  We're not talking about a case where small hobby engines are cheaply made, I'm talking about a *something-eth* law of thermodynamics.  Smaller volumes have a higher combustion chamber surface to volume ratio, resulting in more energy going into the engine materials.  Then you also have incredibly poor carburetion efficiency and scavenging.

These are all the problems I see with this concept of having a gasoline engine driving a genset to make electricity for an electric propelled quad.

Not to say that these CANNOT be overcome with a maximum effort, clean sheet design.  I'm sure they can.  I just look at the economics of it.  You'd have to spend an aweful lot of money to develop a system to chase this theoretical 3-5X energy density improvement.  The resultant system would be pretty expensive.  And at the end of the day, you'd be competing with a battery that costs a couple hundred dollars.

Don't get me wrong, I completely understand that gasoline has a much higher energy density than LiPos, and this is the answer to long range flight.  I just think that using electricity as an intermediary power distribution system is a really tough road to go down.  Mechanical distribution is just that much simpler, and lighter weight.

The problem with mechanical distribution is that, at least using off-the-shelf hobby parts, it is extremely unreliable.  Both belts and shafts create a lot of vibration.  Belts are like flying Van de Graaf generators.  Shafts strip gears every time you touch a prop.  They're all unreliable.  I've been flying these things for a long time.  I've NEVER had an in-flight motor or ESC failure on a heli or quad.  I've had many tail drive systems failures.  And you want to put 4 of them on a quad?

Gotta cut this short, but I think that a gasoline powered  tandem rotor helicopter presents a pretty strong case of mechanical complexity vs. efficiency.

The level of complexity will undoubtedly be on the high side of things however the efficiency is something that can be improved with more experimenting.

What I am thinking about doing is to chain drive everything and use servos to control the variable pitch.   The only real catch that makes this slightly awesome, I have a spare GXV50 in my garage and the means to machine my own parts.  Right now I would like to figure out what more needs to be done to run oxyhydrogen on it...

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