OK, I'm using an OS46VF on a pipe on the new plane. I'd like some input on a prop to use. This is a Tom Lay prepped engine that I got from a friend. I started off with an Eather 12x4 3 blade. Clearly not enough pitch and the engine was laboring; probably too much prop. Went to a Bolly 11.75 x 4.25 2 blade and it was better, still not enough pitch though (somehow 5.6 second laps doesn't do it with this plane). Ground RPM with the Bolly was about 10,500 and this got me a very rich 2 stoke in level flight with a couple of breaks to a fast 4 stroke per lap. Pipe length is 17.75 inches. Fuel is 10/23 Wildcat. The plane is 765 square inches (about) and about 67oz (was 63, but 4 oz. of nose weight was a killer).

I was concerned about the weight but even diving right at the ground with a hard turn it just seems to "flick" through turn with no discernible "sink" and it's going to need some more tip weight.  I don't care much for seeing the top of the plane on inside turns and the bottom on outsides, but that's trim talk and this is the engine forum.

So, any ideas for prop sizes to try? Does the 11.75 Bolly just need more pitch maybe?

Another issue. I've got the weirdest tank problem. The fuel siphons out sitting on the ground through uniflow vent. The vent enters the fuselage about mid tank height, goes up above the tank (with plane sitting on the gear) and back down to plug into the tank. The uniflow and overflow vents are attached to the plane and plug into the tank with silicon tubing, so I can move the vents around if needed. It seems that it may even lose fuel in flight through this vent. I put in 5 oz last weekend (it's a 6.25 oz tank) and capped the uniflow vent until I started the plane. Took off, flew for about a minute and a half. While flight testing, I dove right a the ground and pulled up suddenly (just testing the turn) and the engine shut off. Landed and set the plane in the pits and noticed fuel siphoned out. Not sure how much dripped out, but based on the small puddle, probably a half ounce. When I drew out the remainder of the fuel, there was still about 2.25 ounces in the tank. I've had both a .265 and a .275 venturi in it without appreciable difference in this problem.

Any idea? I suspect I need to move the uniflow vent to exit entirely above the tank, but there may be other issues.

Hi Randy

The  11 3\4 x 4 1\4  works  but the  best  2  props we  found  were the  12.2 x 4.2 2 blade or the  12 x 4.25  3 blade

pitch  these to 4 1\4 at the ten or 11 inch station, I did several 100  of these  motors  and  many people  used this setup  .275 venturie  10%  18.5 inch pipe lenght

Regards
Randy

Howard,

May have solved the tank problem. Man, I checked that tank before I put it in, but checking it last night revealed that I had two leaks. Took a bit of pressure in the the tank to find, but I had bubbles coming out the joint where the uniflow vent exits the tank and more at the pickup tube exit. Just pin holes, but enough. So, a bit of solder work and it seems tight now. I'll check it again after it's flown and if they show back up, the tank goes in the can to be replaced by a new and improved model.