Hello Everyone,

Just to share some pics of my Weed Trimmer engine conversion plane.

Its kind of a self designed Long John with the wings of an U-CAN-DO 3d 60.

The engine is a converted Mitsubishi TL 33cc with nothing more than baffles taken out of the muffler, its original 10.5 mm Mikuni carb and a prop hub.

I have fly it with different props with the following results

- Master Airscrew 16x8 wood @ 7,400 RPM
- APC 17x6 @ 8,000 RPM

Even though it seems to have a better performance with a 17 inch prop it flies better with the 16 one, maybe I´ll try a 15x10....any comments will be apperciated.

Your performance numbers are a little low. The carb size is close to being ok, so I wouldn't worry about that for the moment. But you say it is 10.5mm. Where are you measuring it? A carb size is determined by it's smallest diameter in the venturi. What your engine needs is an 11.1 mm venturi carb. The Walbro carbs also have a number cast into them near the choke. The number you want is "28".

The next thing you need to do is add either one large or two somewhat smaller exit tubes to the muffler. If you use two they should be around 11mm i.d. One large tube would also work, and it should be around 19mm i.d.

These changes will help a lot!

By the way, your plane looks very nice. Good job!

Good luck,
AV8TOR

You should have 7400 rpm with a 18 X 8 as a reference point?

Thanks both very much for your comments.

Actually I do have the 2 tubes out of the muffler and and extra hole in it to free the exhaust.,,I already bought a 13.5 mm Walbro Carb but Im still trying to figure out how to mount the throttle.

I forgot to mention that I fly in México city at an altitude of 2,240 metres (7,350 ft)

Considering this altitude numbers, do you think I would need to use a smaller prop to get the optimal power out of this engine? It flies well with the 17x6 and the 16x8 but no doubt it could greatly benefit from a better vertical performace

In my experience with glow engines, here in México City we cannot use similar prop sizes like the ones used by the guys living closer to the sea level, we do really experience a shortage in power given the altitude which we try to complensate with smaller props to gain some RPM´s.

Once again thanks a lot and please any advice will be very much appreciated.

Oh yes, the altitude makes a huge difference. You lose about 25% power at your altitude, and possibly more if it is hot out. See how the carb does, and use whatever prop that flies the plane how you like it. If there is any way to increase the compression ratio, (lower the cylinder), that helps, especially at higher altitudes.

AV8TOR