I had an idea about building a gas powered quad.  It would be powered by some of the new small 4-stroke engines like the honda gx-35.

I know what you're thinking... gas engines don't respond fast enough.  But, everyone bases this on using the throttle and carb to control the power output.  My idea is that in addition to the throttle you could use a microprocessor controlled CDI ignition to control the power.

With a microprocessor ignition you could immediately cut or reduce power output by skipping a spark for super quick power reduction and you could also retard the spark for a smoother, but still quick reduction.

At say 3000 RPM (typical) you could reduce power within 1/3000 of a sec by skipping a spark, or every other spark for a quarter sec or something of that nature.  The throttle could also participate, but the spark control would be immediate.

I'm curious how a gas quad like this would perform.  A Honda GX-35 puts out about 1.5 hp, and many sources say it easily turns a 20x8 prop at around 3000 RPM.  

Would that be too large for practical use in typical applications?  Each engine would be about 1.5 hp @ around 8 pounds (very lightly modified).  That would be 6 hp @ ~32 pounds.  I've also read that when the flywheel/magneto (using CDI) and clutch are stripped they can come in under 6 lbs.  That would be ~6 hp @ 24 lbs.

I'd like to know if this is new territory or if someone has already tried this and what their results are.  I haven't been able to find anything of the sort, so maybe it's a truly new idea.

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Somebody has to be the Nervous Nellie, it may as well be me this time!

Be careful with the 20 inch blades, so you don't end up like this guy... we certainly don't want to lose you!

http://www.abc.net.au/news/2011-08-03/nz-man-decapitated-by-homemad...

How can you be decapitated by a hovercraft?  The blades are underneath the whole structure and protected by the floor and a large rubber skirt.

I can see losing a hand, but decapitated?  He might be a candidate for a Darwin award.

I've got no other knowledge of the case, but I'm guessing it may have been the forward motion propeller.  You could imagine a home-brew unit not having a cowling.

You don't need specific phase rectifiers, just use 2 standard full wave bridge rectifiers and ignore 1 of the AC side inputs and obviously connect the two dc sides together.

You can get a full wave , high voltage or amperage heatsinked full wave bridge block at Radioshack. Again, each block has 2 AC inputs and then the DC + and -. 3 wires, 4 ac inputs, ignore one of the inputs.

I'm working on getting a CDI design going with the sophisticated capabilities discussed above...

http://www.rcuniverse.com/forum/m_11163300/tm.htm

A two-stroke engine running at 6000 RPM should provide control opportunities at 100hz.  A 4-stroke would only have 50hz, but given an air-frame that was designed to be naturally stable (lower CG) it might also work.

Why not include a couple of extra propless electric worker motors whose only purpose is to recharge the battery. They could operate by storing energy into an on board capacitor (like a manual flash camera). That could create the needed power to maintain the charge in the battery for longer flight. They would draw power from the battery just as the prop motors do, but their main purpose is only for recharging the battery. I think of my rechargeable crank operated flashlight. The flashlight does not need to be turned off to recharge, and is easily charged while still running. The same could happen here as well. 

This may not solve the issue of energy reclamation from the prop motors. Reading some posts, a gas engine/electric hybrid would create too much weight and become less practical. Bigger props to lift the weight would need more energy unless this could be miniaturized on an RC scale. Then you would still have the issue of on board fuel storage. Solar power would be a nice back up system to what I mentioned above for overcast days.

Just my thoughts

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