Hello there. First of alI, I apologize for my poor written English skills. Over the past couple of days I 've been trying to get my mind around this interesting project I accidentally came across while researching gas/electric powered multirotor platforms. 

Apparently ,these guys are working with the Border Patrol on replacing RC helicopters. This thing is a 4 stroke. It is said that the machine will fly 65 minutes without any batteries onboard with a 4lb payload. I guess this was the test machine and their now going into production on two different models. This machine and one with 10lbs payload and 120 minutes flight times. This is all the information I managed to find.

First thing that comes to my mind when comparing this to HYBRIX for example  http://www.quaternium.com/portfolio/hybrix-uav/   is that this is much quieter then hybrix which uses a 2stroke engine.  

Since this is the only picture could find online , I was wondering if we could get a discussion going as to what motor is best suited for this 4stroke engine to generate electricity. It is a honda gx25. All the specs on it are online.

Would, lets say. T-motor U12 motors do the job of generating enough power for this thing to be airborne more then an hour like the company claims.

KV......................................................................................90

Configu-ration...............................................................36N40P
Shaft Diameter...............................................................15mm
Motor Dimension(Dia.*Len).....................................Φ107×37mm
Weight(g).........................................................................794g
ldle current(10)@10v(A)......................................................1.2A
No.of Cells(Lipo)..............................................................6-12S
Max Continuous current(A)180S..........................................50A
Max Continuous Power(W)180S.......................................2500W
internal resistance............................................................47mΩ
Also, it would be great if someone  knew more about the company and is willing to share. 
Thank you!

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I don't have very much to offer except that from my very basic research you will get approximately 50% efficiency at best from the conversion, so for example if your gas engine is 2hp you should expect 1hp in electrical output.

In regards to the U12 motor for the generator, you want to figure out the best operating RPMs for your gas engine.  Once you find this optimum RPM then you can decide which KV you need to get the right voltage output.  For instance if you want 12S voltage (~45v) output from the 90kv U12 motor, then you need to spin it at 4,050 RPM.

Can't this be done with a weed wacker motor (23CC) a generator and a charger controller? Maybe a solar charge controller? If the input power can exceed the MAH usage I assume the battery would stay topped off and then when the gas runs out you RTL

This type setup but small as possible?

I had not seen this. I find it strange that the GX25 engine pulls enough power to keep that multirotor in flight, but I would like to know more about this project.

Mr N.: Do you know something about this company?

I'm also interested in the Honda 4-strokes, but also believed they don't make a lot of power.  The factory power rating I think is only about 1hp.  But I'm not sure what it can do with some tuning.  These engines are popular with university projects like the Hypermile competitions.

Rob, 

For me GX25 or GX35 are too far from required performance.

A modern 4t engine should do 5hp with 35cc @ 10000rpm (with the same BMEP than a CRF250 or similar), but it is multiply x5 the current Honda engines performance.

I see there are people working on it, increasing compression ratio, bigger carburetor and a simple pipe as exhaust they get about 1.6 or 1.8hp, but it is not enough and next modifications are more difficult

I would love to work on this but right now I see it difficult

Yes, too bad.  It's fairly trivial to get 100 hp/L out of a modern 4 stroke, which would mean this thing should be making 3.5hp.  Up to 200 hp/L is possible for a high performance engine, which would return 7hp here.

1.3hp is just really low.  37 hp/L is really bad.  That's actually less than my old Land Rover.

My viewpoint:

The Honda GX25 and GX35 can't be used in hybrid multirotor, we have tried it, the power is not enough, GX25 is 1hp and GX35 is 1kw, and now the most efficient multirotor lift power ratio is about 8~10, so even the efficiency from engine power to electric power is 100%, it only lift maximum 10kg, most  current quadcopter empty weight is about 13kg, so as a result, this type hybrid multirotor cann't fly away from ground.

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