Hi; I have a hobbico superstar with an OS 40 LA engine installed on it and I want to install a Super Tigre GS-46 in its place. The OS is about 12 1/2 oz and the ST 46 is about 15 oz. Does this mean that I have to add 2 1/2 oz of lead weight to the tail to balance it out ? Thanks

You should be able to move the battery, receiver around to offset the weight difference.

It does mean you will have to add weight.

However, since the tail is much farther from the CG than the nose, you'll wind up adding a lot less weight. You could calculate how much weight, it's weight * distance from CG, but I'd just mount the engine and add as little weight as far back on the fuse as you can get it.

A general rule of thumb, it takes 3 ounces in the nose to offset 1 in the tail. Therefore, it would take 1 in the tail to offset 3 in the nose. Just a starting point.

NO, even if you don't do anything, the extra weight will not hurt you.
You will just need more elevator to fly.

Whoo Hoo another Supertigre fan! I just put a GS-40 in my Avistar. Are you sure about the weights? The GS-40 is around 19 oz with muffler. The LA 40 is a VERY light engine for its size. As stated before, try and move stuff around first, adding weight is the last resort. Your receiver battery is the heaviest thing in the airplane, move it where you need it but for God's sakes make sure it's SECURE wherever you put it! Does you no good from a balance standpoint if it's sliding around! I wound up moving battery back about 6" or so, it's balanced perfectly, no weight required.
And if you haven't run it yet, you'll be amazed at the difference in pull between the LA and the S-T. I havene't had a chance to fly mine yet.... hopefully this weekend.

Best of Luck!

Andy

Thanks for the info guy's !!!