Close, but not exactly. The tips are tapered on the trailing edge. I
have a Royal Rudder Bug and the plans somewhere. I'll take a look.
BTW, there are two Rudder Bugs, the Walt Good one and the Royal
version. The Royal version is a little smaller than Walt's.
You could goto the Yahoo Group VRCS (Vintage Radio Control Society)
and ask the question. Several fellows there would know.
Dan, I know that tip shape effects stability and tip stall but nowhere have I
ever read or heard of it effecting the CG. Now if you have a flying stab..
that would change things alittle.. general rule of thumb is balance between 28%
and 33% of the wing area...
I agree with your thumb. However, I just put down the Berkley, Royal
Rudder Bug plans which has the 62 inch wing. The wing cord at the
fuselage is 10 inches and they show the CG at 2 inches from the LE.
This is a 20% location. Boy, that blows my mind. It is shown as a
rudder only, but all the rudder only planes I flew in the 60's had the
CG real aft, like tail heavy. I have the plane and have not flown it
as yet. I don't think I will balance mine at 20%. I like your figures
Like I said, if it has a full flying stab that would make a difference and also
make some sense since the flying stab would move the CG forward.. I thinks????
But a Goldberg skylane does have a flying stab and the CG still falls within
the 28-33% range.
Wing shape, including tip profiles, DO affect CG location. If the
trailing edge only is tapered, the centre of lift (C/L) of the airfoil
moves forward along with the forward-swept TE. If the CG isn't
adjusted to accomodate the more forward C/L, the airplane will be tail
Any tapered or elliptical wing, or any swept wing, for that
matter, will present more hassle in determining CG location. Swept
wings especially can be difficult, since the centre of lift moves
outward at higher cruise speeds (due to smaller tip vortices) and
therefore back somewhat, making the airplane act noseheavy. Airliners,
since they have swept wings, have to be carefuly monitored when flying
at max cruise because the C/L moves back far enough that the
stabilizer may not be able to raise the nose if the speed got any
higher, especially if the airplane is loaded with the CG near the
forward limit. They call this speed range "coffin corner," for obvious
Most models have rectangular wings, with no sweep, to make things
easy to build and to balance. The 25-33% CG rule works ok for these.
Like full-scale, though, if a guy wants to get more efficient or go
faster, the rectangular wing isn't going to cut it.