[spitfirefan]

I just finished building a GP Super Skybolt. Went to balance the place and it's taking 29 oz of nose weight to balance it. According to the plans the balance point is 2 3/4 inches from the leading edge measured at T7 which is where the interplance struts attach so it's impossible to put the c of g balancer there......I measured and moved the balancer to T6.

Anybody tell me is this is normal for this plane to use that kind of weight??

I'm using a ST75 as an engine.......

[aceplant00]

Is the engine mounted when you are balancing. Everything else fuel tank installed servos, batteries etc.

[kwm]

Check the manual online and it said the CG is 4 5/8 from leading edge of top wing if this is the 60 size ARF.

[E Smith]

I have just finished building the kit. The balance point is shown on the plan at 5" back from the top wing at the centre line. Project that point out to wherever you will support it. Nearly two pounds of weight sounds excessive.

Ed S

[AJCoholic]

FWIW I flew one of those built from a kit, with a ST 91 and slimline pitts muffler and if I remember correctly, very little weight was needed up front to balance.

That much needed weight in a relatively small airframe is a sign something is not correct... double check your CG

AJC

[spitfirefan]

Yes the plane is in ready to fly condition. Plane weighs in at 8lbs 13oz. I've got a couple of ideas to play with both with my CofG balancer and with the plane. Was looking for a couple of other opinions that this was an unusual situation before I went too crazy!!

Thnx guys!!!

[E Smith]

Check the manual online and it said the CG is 4 5/8 from leading edge of top wing if this is the 60 size ARF.

The top wing is swept back. At what point on the span is the 4 5/8?

Ed s

[Gary Maker]

Building from a kit!

Specifications

Wing span: 57" Length: 52" Weight: 8.5-9.5lbs

Wing area: 930 sq in Airfoil: symmetrical

CG: 2¾" aft of top wing leading edge at rib T7(@ strut), ±3/8"

THROWS: Ele: 7/8" low 1-3/8" hi Dihedral: top wing 0°

Rud: 1½" low MAX hi bottom 2°/panel

Ail: 5/16" low ½" hi (¾" @ last rib)


This above was taken directly from the website for the kit model. Yet for the ARF model is says to place the C of G at 4 3/4" aft of the leading edge of the top wing.

Why would the kit model balance any differently than the ARF model? Something seems very strange with Great Planes own instructions.

Seeing that a plane that is less than 9lbs is requireing almost 2lbs of dead weight to balance, tells me that the balance point suggested for the kit is very wrong. I would go with the 4 3/4" specs which should make a world of difference. Man, there is nothing worse in my opinion than having to add dead weight to any plane.

Have you tried moving the balance point aft as others here have suggested? If so, how did it balance with the change?

[Cricklewood]

On another thread I frequent they talk about the CG of a biplane being 28-30% of the mean cord back from the leading edge of the top wing. The mean cord is determined by placing the plane in it's normal flying position and then measuring from the leading edge of the top wing to the trailing edge of the bottom wing. From what I have read this is a good starting position. It may also help give you a better idea of which of the distances, 2 3/4" OR 4 3/4", mentioned above is correct.

Chris

[Terry Gauvin]

Originally Posted by Cricklewood

The mean cord is determined by placing the plane in it's normal flying position and then measuring from the leading edge of the top wing to the trailing edge of the bottom wing.

Assuming span, taper and sweepback of both wings are identical.