skoemba

Ok all you Einsteins out there, I have a problem.

I have a odd shaped wing and I would like to calculate the cg. I tried some of the cg calculators I found in the forums but I am not sure if I am correct. I can also not get the exact shape on the calculators. Please help me out here guys (and girls?).

The wing is for a scratch build project.

Here is what the wing looks like. Please note that the dimensions are in millimeters.

DanSavage

My Feedback: (5)

If this is an exact duplicate of the planform, I can find the MAC for the wing.

If it is not an exact duplicate of the planform, then post a pic that shows exactly what it looks like and I'll find the MAC for you.

Dan

Tall Paul

Add the chord dimension at the trailing edge break to the leading edge, and the sweep to this point, then the sweep from there to the tip, and use:
http://perso.wanadoo.fr/scherrer/mat...glish/mce.html

skoemba

Dan,

That picture was drawn on CAD and is the exact shape of the wing. Thanks for the help!

Tall Paul, can you please explain "sweep". Sorry, I'm still new to the terms!

Thanks guys!

Tall Paul

.Sweep is the distance the wingtip is aft of the root leading edge.
The 740 dimension in your drawing.
The program would need two sweep dimensions, as mentioned.. from the root to the leading edge at first break at the notch in the trailing edge, and the dimension from there to the tip.

erbroens

If you want to calculate the CG on your project, just a wing planform drawing is not enough. we should also consider is this is a flying wing, or if it has a horizontal tail, it´s area and distance from the wing. also the fuselage lenght and shape and even the airfoil affects the CG calculations.
Another way to do this by yourself, is building a small flat balsa model of your project and find the CG until you achieve a decent and stable glide rate.

Best regards, Enrique

DanSavage

My Feedback: (5)

Hi Skoemba,

Okay. Here's what I found.

The vertical line is the MAC. The horizontal line is 25% of the MAC.

Dan

marwen1

My Feedback: (6)

I have about 4-5 DELTA wings. 25% of the MAC (virtical center line) is correct, but depending on the weight you have (I assume it is a pusher prop), the CG will come back a tiny bit farther

marwen

skoemba

Thanks a lot guys! I will try the CG Dan and let you know. I guess it's trial and error from hereon!

DanSavage

My Feedback: (5)

You're welcome. Yes, this is only a rough CG that will allow you to fly the model so you can fine-tune the CG.

Good luck and happy landings!

Dan