I'm putting together my first bi plane (a .25 size ARF). It's very nicely constructed, but the directions are minimal. It says the CG is 81mm from the leading edge at the center of the upper wing. Should I straight edge across the wing to find the spot at the wing tips to hold to see if it's balanced? I've tried it and the location turns out to be about 1 1/2 inches from the leading edge at the tips since the wings are swept back some. My other planes all have straight wings, so this has never been an issue.

Also, does it matter where you put the connecting rods for the upper and lower wing airlerons? Should they be centered on the airlerons? Put behind the wing supports? (which in this case are about 2/3's of the way out from the fuselage). The airlerons run all the way out to the wing tips, and have just one servo in the lower wing.

Thanks in advance for any help.

Brian

Ps. I'm assuming I've been balancing my planes correctly, by having a friend and I put our finger under the "CG" at the wing tips and holding the plane up, and adding weight where necessary to have it slightly nose down. If I'm wrong, please let me know.....

Usually, you balance a model at the fuselage. On your biplane, since it says to balance on the upper wing, just project the fuselage sides up to where the projection intersects the bottom of the upper wings. Balance there.

Don't balance at the tips because any dihedral will add an error and make the model look more balanced that it may actually be.

As far as the ailerons are concerned, where do the instructions have you mount the servo and pushrods? That would be the first determining factor. Where are the horn mounts located? Where is the servo or servos to be mounted? And so on. An ARF kit should give you some guidance about control system installation.

Servo in the lower wing.. horns at the trailing edge of the surfaces, pushrod between

Well, I'll be.....looks like I have been balancing my planes incorrectly. I never knew that it's to be done at the fuselage. Thanks so much for that info.

As far as the ailerons, there is only one servo for them. It is located at the center of the bottom wing and is encapsulated in the fuselage along with the pushrods when the wing is attached, so, it essentially just operates the bottom wing's ailerons. The directions call for control horns to be attached to all four ailerons, with a connecting rod between them (these are totally seperate and not connected in any way to the servo itself, or how it operates the movement of the aileron pushrods for the bottom wing). So essentially, the one servo will move both wings, but it does not specify where to put the control horns along the length of the ailerons. I'm guessing that just centering them will be best.

This plane was made in China and the directions have minimal script, using mainly pictures (and not great ones at that).

The picture attached to the one reply looks like a seperate servo for both bottom wing ailerons, so putting the control horn and connecting rod for the upper wing directly above it would make sense.

Many thanks for the replies......

Balancing is done where where the kit manufacturer states, if they make such a statement, otherwise at the fuselage.

I once had a kit that dictated that it be balanced part-way out from the root and at a certain distance aft of the leading edge. This was on a 12' wing glider, and that balance point was used because if you balance at the fuselage, the long wings with their large amount of dihedral put a lot of weight above the model, so it would tend to rotate on over. If you balanced at the wingtips, there was enough flex in the wings that the model would always seem to balance.

Bshin - the good thing is that you are now an advanced flyer having balanced all your planes tail heavy!!!

I have a biplane that was given to me slightly damaged and don't know what it is. Is there an acceptable way to determine its CG.

If the wings are both the same size, balance 25% back from the leading edge of the most forward wing to the trainling edge of the aft most wing. Just pretend that you have an overhead lamp and balance 25% back from the leading edge of the shadow. If the wings do not have equal area, the guess is a little more complicated.