How to set the CG of a plane
 

Hello, would love to know the right way to set the CG of my plane. The plane is a high wing trainer that I have had to do some mods to repair a leaking tank and loose servo board.
This said plane also had a three blade prop that is now gone along with the flywheel.

The CG is 2" 3/4 to 3" from the leading edge of the wing. The plane instructions do not say if the fuel tank should be full or empty. This is my first post and I thank everyone for help.

Flying cootie.

RE: How to set the CG of a plane
 

The tank should be completely empty when checking the CG.

On the bottom of the wing make a short line out from the fusealage at 2- 3/4 inches and another at 3 inches. Do this on both sides.

Now face the plane at the front and using your index fingers ,one under each wing, put them in the middle of the marks you made and lift. The plane should be sitting level on your finger or slightly nose down. If it is tail down then add nose weight, if it is way nose down try moving your fingers to the 2-3/4 inch mark and see if it now sits level or slightly nose down. If it is still way nose down, then add weight out near the tail

You can also try moving the reciever battery in the plane either towards the frnt if your tail heavy or closer to the tail if nose heavy. Adding dead weight (stick on lead weights) increses the overall weight of the plane, but if moving the battery brings it into the CG range then you have not added dead weight. Instead you have moved the useful weight.

See this link.

http://www.krcs748.com/introduction.htm

When checing a high wing plane, you pick it up on the bottom of the wing (gear facing down or also right side up), on a low wing you check it on the top of the wing (gear facing up or up side down)

RE: How to set the CG of a plane
 

Empty tank because if you used a full tank the plane would become more tail heavy as you flew, not what you want. The saying goes, "a nose heavy plane may not fly well, but a tail heavy plane only flys once". (Or words to that effect.)

Follow Bill's advice on balancing.

Welcome to RCU by the way.
Dennis-

RE: How to set the CG of a plane
 

Welcome to RCU Cootie!

Dennis, I believe the expression is "A nose heavy plane won't fly well, and a tail heavy plane won't fly long."

Anyway, for a trainer, Mark the location of the CG under the wing as Bubbagates suggested, then simply put one finger on each mark and lift the plane up. It should sit level, or SLIGHTY nose down.

But remember, this is a starting point. Now fly the plane. If it's good, leave it alone. If it's sluggish or tends to land fast, try shifting some weight back. If it's a bit too sensitive to elevator controls, you could lessen the elevator throw, or shift weight forward.

It's basically a balancing act. Once it is set to the recommended CG, that means it's safe to fly. Now it's up to you to make it fly the way YOU want it to.

RE: How to set the CG of a plane
 

Thank you to all the people that have posted to this question.
The plane is nose heavy a little bit with a empty tank.
I am using a "homemade" stand made out of a 4x4 and two pencels eracer side up.

How about "port" and "starboard" balance? I have read that this could be off also.
How would this be checked?

Thanks to all, Herb.

RE: How to set the CG of a plane
 

To do "lateral" balance (port and starboard or side to side) can be done several ways but to do it by yourself:

Keeping the plane right side up, set the very tip of the bottom of the tail (not the elevator but either the rudder, if you can or the tip of the fuselage at the tail) on the edge of a table, paint can or whatever, then making sure that the engine is not on the compression stroke, hold the front of the plane by the spinner, prop bolt (NOT THE PROP ITSELF) while holding onto a wing making sure to keep wing and the plane level, now let the wing go and see which wing drops, the wing that drops is the heavy wing. Do this several times and if each time the plane drops to a certain side, then you need to add weight to the opposite wing which is the light wing. If the plane randomly drops a wing, meaning it drops one way then the other and equal amount of times, then the balance is close enough, if it drops more times to one side then the other then again that is the heavy wing.

Having 2 people makes this job easier since one can hold the front and the other can hold the back.

Get some stick on lead weight from the LHS, set them on the top of the light wing at the tip until you get the balance right, then tape the weight to the bottom of the wing at the tip with good strong nylon or fiberglass reinforced tape. You can also cut into the covering and glue the lead inside if you do not want to see the weight on the outside which is my perferred way but you need to reseal the covering with a piece of tape or iron on a patch of covering.

RE: How to set the CG of a plane
 

Thanks, this should help me and alot of other people who are getting back to the hobbie or people just starting off.

Sorry about the port-starboard thing, ex-navy guy that I am, I can't get rid of thinking that way.

Thanks, Herb.

RE: How to set the CG of a plane
 

No problem, most everyone here probably new what you meant