oversize engine

first problem will be the extra wing loading next you will have to add weight to counter the nose heavyness from the larger engine, hence more wing loading... It will be powerful but most likely to fly like a PIG, I would not go over a 50 if you want extra power.

I put a Saito .91 on that plane.

Problem encountered: It wouldn't fly through trees worth a damn. A friend took the fuselage, rebuilt it, attached two Avistar wings to it, and is still flying it. I'm sure he's got it overpowered, but I don't know by how much.

Yes.

Where are you in upstate? I'm in Buffalo.

Marty

I did some searching on the GP Ultimate and most say it was a rather heavy beast that would benefit from some extra oomph. Your wing loading will increase, and you might wind up nose heavy, but that can be corrected by putting the battery, and the elevator and rudder servos in the tail. Just make sure you beef up the battery compartment so it won't go tearing through the fuselage if you make an unintended landing. Try to build it light as you can, but go for the .61.

Morris

LOL. I live in Fulton, which is about halfway between Syracuse and Oswego. I don't think I'll go as much as that as this is my second plane and I still haven't learned to fly the first one, even through trees. I just finished building a PT-40 with a .46 on it.

If you're ever up here in Buffalo, we can ask Erol to fly his Ultimate Avistar for you. ;o)

Marty

A lot of nonsense answers! A 46 will under power the plane. A 61 will make it go fast in a straight away. A Tower 75? is just a bored out 61 but a lot faster (and lighter). You really want an OS 91 FS for that plane, then you can do whatever you want, whenever you want to. :)

When you balance it hang it by a string from the ceiling. With a 91FS it balanced perfect. Don't forget to add a brace where the CG is before you cover it:) -- so you can screw a small eyelet in to hold the string. OH, and don't put a smoke systen in it. The engine doesn't get hot enough.

The biggest thing you want to do when using an "oversize" engine is to make the plane balance properly without having to add tail weight. If you mount the engine as far back on the mount as possible and mount the servos as far back as possible, you might be able to avoid needing tail weight. Something that is more work, but cures nose heaviness when using bigger engines, is to chop the nose off and install a new firewall farther back. I have a Sundancer that I bought with an ST 91. I wanted to use an OS 1.20 twin, so I shortened the nose about two inches. It balances properly with the heavier engine, but the only weight I added was the extra weight of the engine which changes the wing loading very little. It flies great.

There are .50 size engines available with nearly the power of a .60 and weigh less than most .40's. That way you can have extra power without all that extra weight.

-- Bob