Hello. I have a couple of questions concerning gas conversions. I am planning to build a Cessna Agwagon that has an 80 inch wingspan and a 55 inch fuselage. The 60 inch span version calls for a .40-.45 engine. I have a Weed Eater 18cc engine that's about 4 years old. I don't know what the final weight range would be for the 80 inch version. My questions are:

1. Will this engine work for a plane that size? If not, what size (cc) do I need?
2. Is this engine even worth converting?
3. Is there a chart/scale that shows (x)cc = (x)ci, as far as power output? (Not a math equation)
4. Is there a chart/scale that matches prop size to cc?


Thanks in advance for all of the info...

DF

An 18cc engine is about 1.10 cubic inches. The conversion formula is: CC's X .0610237= CI. Your 18cc weedeater engine would be pretty heavy for a 40 size plane. I have done a few 16cc engines but not good for much more than a floater plane like a Cub. I have also done some 21cc Echo engines and had them on .60 size planes. A Seagull Models Edge, picture attached. It flew but was lacking for any type of 3-D. Sport flying was fine. There is no chart for props that I know of anyway. Gas engines don't turn RPM like a glow motor but will turn a bigger prop. I try to prop my engines for about 7200 or so and go from there depending on how she flies. Some engines are ported and port timed better than others so they will run better. Echo, Stihl, Husqvarna are easy to get and run very well in my time and experience. Hope this helps.

tim220225, thanks a lot. This really helps me out. I think I'll go ahead and invest in a few props and start testing this engine. Has anyone tried running methanol in these engines for extra power??? I'm sure someone has experimented with it!!! And again thanks...

DF

Df,

I had a 8ft Telemaster made out of foam (used as a paintball target) that weighed about 12lbs and the plane flew OK with the 18cc Weedeater. I later put a 21cc weedeater and it flew a little better. From what I've been reading about electronic ignition, the plane would have flown better if it had EI or as a Gas/Glow conversion. EI would have dopped maybe 6-8oz. and gas/glow would have dropped about 16-18oz. and either would have increased the power. Build it as light as you can and I think it will fly fine.

Ernie S.

I agree. I need to add that I fly all my engines on CH Ignition boxes so they are as light as I can get.

For an 80" Agwagon, I would think ya should be looking in the 25cc range. Those have a pretty good size wing and they're pretty draggy.

Hi,

First… don’t look at the wing span… look at the wing area. And, look to see what the flying weight should be. That should decide what motor you will run. If your model is around 1300 sq in, and over 11 Lbs (just a guess for 80”)… then you will want to go with a GOOD 25cc engine (Toro or an Echo) or bigger. And tim220225’s suggestion is right for the props.

Now for you question on small engines…

Yes… most small (less than 23cc) engines have been known to be low output for their weight. But, I have stumbled on to a few 19.8cc Mitsubishi engines from John Deere weedeaters, and they are absolutely great for their size. They are much lighter than the 23cc engines that are out there, and they can swing a 16x6 at 7600 RPM. (no mods) And, the flywheel is very small and light. (not worth converting to electronic)

Here are a couple pics of one stuffed into a Hanger9 Frenzy 100 (61” span) Just as an FYI… the flying weight is 8Lbs, 7oz.

Dr Honda: Nice job....tell us more how she flys!!! Thanks Capt,n

Yeah, looks and sounds good. But my question is "How about some more info on that mini tuned pipe!?"

AV8TOR

Hi Guys,

Thanks for the kind words… but I don’t want to hijack this thread. So, I’ll start a new one later today.