Help Me Identify: Need CGHelp
 

Hello,
I'm new to all this but my neighbor has been doing this for a while and he tells me that we need to figure out the CG. Can you guys help me figure out what this plane is and if somebody has or knows where the CG is it would most appreciated. What I know about the plane. We think it's a .40 size. We put a ThunderTiger .46 engine.

RE: Help Me Identify: Need CGHelp
 

The first thing you need to do is to find the Mean Aerodynamic Chord (MAC)

To do this, follow the diagram below.

Once you have established the MAC, figure approximately 25 - 30% of the MAC for CG. This will give you a good starting place where a good pilot should be able to fly the plane.

Once flown, you can determine if you want to move the CG forward or back for your specific flying style.

RE: Help Me Identify: Need CGHelp
 

How would this apply to a bipe with a swept wing on top? I'm restoring an old Super Baby Great Lakes and need to figure out the CG.

Steve

RE: Help Me Identify: Need CGHelp
 

For Bipes it's basically the same, but you need to find the CG of both wings and average it out.

But I have a simpler method

I just lift the plane from behind the top wing. With your fingers completely under the wing, it should sit slightly nose down. Then fly it and adjust as necessary.

RE: Help Me Identify: Need CGHelp
 

Oooo...ya simpler, and considerly more dangerous. Just measure the wing/stab/moments and crank out the CG. You don't even need to unerstand the theory or math with the online CG culators.

RE: Help Me Identify: Need CGHelp
 

Could you be a bit more specific about how to do that?

RE: Help Me Identify: Need CGHelp
 

I'll make this short and sweet. That plane is a Tornado,cant remembet the manufacturee but i do know the CG location on it. I have one, the CG is measured 1/2'' back from the leading edge at the WING TIPS! If you make marks on each tip at these points and draw a straight line from one tip to the other,you get the CG location at the fuse.

They fly great to.

That should help you out with the Tornado,as to the bipe,all you need to do is take the measurement of the wings cords ( from leading edge to trailing edge) and take 30 to 33% of the cords as you starting points.

Example == top wing measure 8 inches , 33% of 8 is roughly 3 inches.
bottom wing measured the same way

Now measure the distance the top wing is in front of the bottom wing from both wings trailing edges. You can then cut that measurement in half ( if 1 inch,use 1/2 inch as starting point)

With that measurement you can now safely set you CG by the 33% figure of the bottom wing by moving it ahead 1/2 inch.



This formula will give you a safty margen for you CG as it will make the plane a bit nose heavey i have found using this method over the years. You can adjust the CG to your comfort level of flying as you get used to the plane.

Hope this info helps you out!

Good luck flying, Art

RE: Help Me Identify: Need CGHelp
 

Hey Thanks so much will try it out and let you know. We had the CG measured out at about 4 1/2" from leading edge and it wasnt flying right at all. My budy almost crashed it a couple of times. That should make a big diffrence.

RE: Help Me Identify: Need CGHelp
 

Glad i could be of some help to you! Enjoy the Tornado,i do mine!


Art

RE: Help Me Identify: Need CGHelp
 

It really is easy. Measure the airplane with a yardstick. Plug the numbers into the online application. Choose a Static Margin of 15% and click the COMPUTE button:

http://www.geistware.com/rcmodeling/cg_super_calc.htm

What are the measurements? They're listed in the application's input box and shown on the diagram beside it.

Do you actually need to go to all that trouble (5 minutes with a yardstick is trouble?) just for a model airplane? Actually no. With an average model like you've shown, you don't even need to find a MAC and the 25% point. That effort "is good enough" but with the picture you've posted of your airplane, that sucker is so average, just balance on or in front of the spar and that "is probably good enough."

You've actually got 3 choices.........
"is probably good enough"
"is good enough"
"will be reliably accurate no matter what planform the model has"

RE: Help Me Identify: Need CGHelp
 

Thanks again just so I understand I put the wing on and then from the leading edge on both sides of the wing tip measure 1/2" down and then at the intersecting point on the fusealage that's my CG?

RE: Help Me Identify: Need CGHelp
 

Yes,you measure 1/2 inch back ( toward trailing edge) from the very Tip of the wing. The draw or use a piece of string taped across the wing from these marks. Where the string crosses the fuse is your CG POSITION AT THE FUSE ON THE WING.


Art