A weighty problem

As much as it takes. A tail heavy plane only flies once.

Move all the radio stuff as far rearward as you can, even going as far as putting servos near the tail surfaces.

Don

Oops, I was thinking it was nose heavy.....so, take the servos out of the tail (LOL) and move everything as far forward as possible.

Don

Build a box to mount on the firewall, to mount the engine on. Don't add that much weight. It will become a dog.

-- Jim in NC

Is a bigger engine out of the question? If you're gonna add weight, you may as well add power too.......

How did it become so tail heavy in the first place? Did it start out that way (possibly why it crashed already), or is it from the repairs you've made?

MrBonk

Be careful with a gas engine to keep all the electrical stuff (including batteries) away from the engine; most folks say 12" distance if possible. Gassers' ignition systems can cause interference.

Wow Ed, your bipe is about the same size as mine, and mine only weighs

18lbs. I don't think adding 4 lbs would be much problem for my engine, but your G38 probably won't be able to fly a 24lb draggy bipe. Would it be possible to move the engine further forward by building a box? How did you figure where the CG should be, is it possible you made a mistake?

Another engine is definitely out of the question.

This plane was a wreck when I got it and I spent the entire summer and way too much money fixing it and the the engine. It could very well be why it was crashed in the first place but I have no way of knowing.

>

OK I screwed up!! When I measeured off the 4 inches from the leading edge, I measured in the center of the wing instead of at the mean aerodynamic chord (swept wing), so I was 2 inches too far forward, I'll bet when I reassemble this puppy tomorrow the balance will be close !!!

Ed

Kewl, you gonna fly it this weekend?

A CG 7-8 inches from the firewall is one thing. But, the CG location relies on the wing planform. How does this 7-8 inches relate to the wings?

FWIW, my Balsa USA Citabria Pro has a CG roughly 9 inches from the firewall. So a bipe with 1500 squares could easily have a similar distance. Especially IIRC the Pitts has staggered wings.

Better compute the proper CG for the beast and then check it. You may find it's pretty close to being on.

I am curious as to how you determined the CG, especially since it is an unknown aircraft. Somehow, out of balance by 1/4 of the aircraft weight has to be incorrect.

Ed I probably don't need to tell you this, but lately, I have seen two gas powered planes crash on their first flight because it wasn't done; Be sure to range check the plane WITH THE ENGINE RUNNING! Later Bill

Your right. I used the method I saw in a magazine for determining the balance point of a biplane, it accounts for the stagger and sweep of the wings. Basically you find the mean aerodynamic chord, take 25% or 30% based on whose advice you are following and that is how far back from the leading edge is the balance point. I measured both 25 and 30% and plan to balance in between My error was after computing the 4 and 4.8 inches, I erroneously marked it off in the center of the wing instead of at the MAC. Looks to be very close now that I am doing it correctly.

Ed

w4jle wrote:

Glad to here your problems were just pencil marks, they are the easiest to cure! ;>)

I think he was using that measurement to indicate the moment arm for the weight, not the actual CG of the wing.

Exactly right Mathew.

Ed

Mathew Kirsch wrote:

Nothing works better for me than actually _seeing_ the balance point.

If you find my meager web site at

can make off with a copy of Jim Archer's "Vanessa CG Machine".

It lets you hang any size model and has a plumb bob to indicate where the physical balance point is.

Costs next to nothin' to build.

Cheers, Fred McClellan the dash plumber at mindspring dot com