Hi. I just finished assembling an Avistar with a Super Tigre GS-45 engine. In the engine manual, it says that the engine should be aligned so that the fuel tank centerline is in line with the high-speed needle or up to 3/8" lower. With the Avistar, it is considerably lower (like 1.5 inches). Am I doing something wrong?

Thanks,
Steve

Steve,
The engine manual is correct. If you can repostion the tank to get that setup.

Cheers.

I don't think I can move the tank much. I can probably get it .25" higher if I started cutting and filing. The only other option would be to move the whole tank backwards where there's more room and extend the tubing.
BTW, it looks like the needle valve on the OS 40 is at about the same height as the Super Tigre; the OS 40 is the "recommended" engine for the Avistar.

Has anyone used a Super Tigre with an Avistar?

Thanks,
Steve

I had an O.S. 46FX in mine, worked just fine despite the tank being low, though I don't remember exactly by how much. The FX and GS45 look similar. I'm not sure why the tank is so low in the first place, but remember this is a trainer and you won't be doing much inverted flying at first, so the Avistar tank position shouldn't make much difference. The ST recommendation is for general flying, ie some inverted. Besides as you pointed out there isn't much room to correct this on the Avistar (assuming you mounted the engine correctly). So, give it a try, have an experienced guy start it up rich for you, do a nose high test and check things out. My bet is that it will be just fine, when it starts becoming a problem, because of all of the aerobatics you will be doing, it will be probably easier to step up to your next plane, and not affected the resale value of the trainer. Good luck!

BTW, I think the Avistar is best as a trainer with a lighter 40. More power and weight of the 45/46 will get it in aerobatic mode, but note that I've stripped the gear of the aileron servo a few times, remember you still have rudder and stressed the airframe so much that the wood holding the dowels gave out. The latter only happened once, ie crash

I fly an Avistar with the ST 45 but I installed a hatch over the fuel tank and the fuel tank is a little higher than stock now but it flew fine with the tank at the stock location before the forced rebuild.
FEB

Fly it as-is. You won't have any trouble if you tune the engine with the tank 1/4 full, then refill & go flying.

I fly mine with a TT.46 that is still breaking-in (and thus slobbering rich) and can easily fly for 10 min @ 1/2 throttle without using more than 1/4 to 1/3 of a tank. Unless you're flying a marathon at full throttle, I can't see a normal flight using a full tank. I haven't had any problems related to fuel/ tank height with the stock configuration.