Tuning has been a challenge for me on this engine- (first gasser)

Engine: Ryobi 31cc
Prop: Zinger 18X6
Static RPM: 7400 Peak 7500

I'm not sure of the thrust/ib ratio but the model is thrust positive when held nose up

That sounds good for a Ryobi.

I am working on a couple of Ryobi’s now and would be curious about the size and weight of the airplane.

Also when you get it in the air I would be interested in your opinions of props one size up and one size down.

I have flown with this engine several times- Most of these flights have been to check balance and fine tune the engine.

With an 18X8 prop I get about 6900 rpm- not sure of ib/thrust but it feels slightly less than the 18X6 @ 7400 RPM.

I can say this for sure- The plane is fantastic in the air. At 12 pounds its not going to be doing any 3D but It is close to a hover at 100%. Not bad for a $100 engine.

I tried a 16X8 on it and the RPM's were nearing 8800. I think this engine would burn up as the engine unloads in the air. The previous engine was an OS 1.60 FX and its max RPM is 9000 and it also turned the 16X8 @ 8800-9000. The weight penalty of the gas engine is not an issue at all due to the plane requiring allot of extra weight in the nose..

So far so good......