CG help needed! Sportster Bipe.
 

https://cimg4.ibsrv.net/gimg/www.rcu...81065b6d6.jpeg
My Plans.
https://cimg8.ibsrv.net/gimg/www.rcu...e71b86b7ef.png
Outerzone plans.
Hi friends
I have a Great planes Sportster Bipe which I built two years ago.
Im having CG issues.
The plans that came with mine show a different CG location than the plans on outerzone.
when I attempted to balance mine according to my plans I had to add ungodly amounts of lead to the nose to get it balanced.
I’m using an OS SF .45 ( yes-it’s a .45) for power.
When I attempted to fly it the plane was so nose heavy that the slightest bump in the grass would flip it upside down nomatter how much up-elevator I gave it.
I never could get it airborne.
Others have said that they used the same engine to balance theirs without adding weight so my plans must be incorrect.
I’m posting a picture of the CG on my plans as well as the plan from outerzone.
Has anybody had this issue?
If you are currently flying a Sportster Bipe can you please give me the CG measurement that you have?

I’ve never built a Bi-Plane. Here is an article that may help. Calculate CG per the article then compare to what you have. Good luck.

https://www.modelairplanenews.com/balancing-biplanes/

I would balance as per the outerzone plans. The GP plans looks way forward to me.

I just checked my plans from the GP sportster kit (which I flew for many years until some idiot tried to drag it through a corn field). Anyway, the CG on the kit plans is 1" from the center of the CG to the front of the lower wing spar. It looks pretty close to the picture above. I suspect you are balancing your plane wrong. Make a mark on top of the bottom wing 1" in front of the spar about 12" - 18" out from the fuse side right over a wing rib. Now flip the plane over and put a finger over each mark and see how it balances. Mine balanced fine with a Fox .45. No nose weight required.

Carl

Thanks for the help!
when I’m done rebuilding it I’ll give it a try.