What is the simplest way to find the CG? I have a GWS PT-17 and i am having a tough time getting it balanced any advice would be greatly appreciated.

Use the top wing; Balancing using the lower wing should be done with the plane upside down.
I expect the distance to the c.g is mentioned relative to the upper wing, per the Tiger Moth from the same manufacturer.

[link=http://www.rcuniverse.com/forum/CG_Calculator/m_2212144/tm.htm]http://www.rcuniverse.com/forum/CG_Calculator/m_2212144/tm.htm[/link]

Check that out =) Calculate it in 10 seconds

Whohoo, my first post on RCU. Somebody alert the media.

The simplest way to "find" the CG is to put it where it was designed in the first place. On most planes, this is at the main spar location. A good rule of thumb is 25-30% of the wing chord distance aft of the leading edge.

Hope this helps.

-- John

I think he's looking for a technique to actually balance the airplane, not figure out where the CG is. On a "thick-wing" GWS, the CG points should be molded right in the bottom of the wing. They are on my Estarter.

If the balance points aren't molded in, my modus operandi is to take the measurements from the instructions and mark the CG location on each side of the wing, near the fuselage. I then put my index fingers on these points and lift straight up. If the plane tips forward, it's nose heavy and needs to have the weight shifted back. Conversely, if it tips back, it's tail heavy and needs weight shifted forward.

You always balance an airplane with the bulk of the plane's mass below the balance point. A high-wing plane like an EStarter would be balanced upright. A low wing plane like a Spitfire would be balanced upside down. A biplane like the Stearman could be balanced either way, but the instructions usually refer to a specific wing for the CG point. Most biplanes are balanced upright, hanging from the top wing.

Balancing the plane at the specified CG is critical, but not so critical that it has to be within a hair's width. It's close enough when it balances on your fingertips.

thanks for all the info. the instructions said 10mm of the leading edge of the bottom wing, i didn't even think about turning the plane upside down to balance. daaaaaa!