cg placement on delta wing

akimbo

Active member
I am in the process of building and designing a plane based on the Lippisch p.15 concept and i am not sure where the cg should be. I tried doing a glide test with the cg about 25% down the wing and it did not seem to be right. is cg different for these types of planes?
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mastermalpass

Master member
My experience with designing deltas is to just glide test and move the ballast until it feels about right. With your wing mostly in the centre of the fuselage, I'd try having the CG nearer the centre of the wing root and work from there.
 

dap35

Elite member
The 25% rule only works for rectangular wings. There are a number of on-line CG calculators. It is way less destructive to calcuate it than to guess and throw your plane.
 

mastermalpass

Master member
The 25% rule only works for rectangular wings. There are a number of on-line CG calculators. It is way less destructive to calcuate it than to guess and throw your plane.

Yeah I should mention my glide test, move ballast, repeat trial was done on a cardboard concept model.
 

Merv

Site Moderator
Staff member
Here is a FT article that explains the process of finding the MAC, mean aerodynamic cord, of a tapered wing. Set the CG at 25% of the MAC. With a rectangular wing, the MAC and the cord are the same.

 

akimbo

Active member
Here is a FT article that explains the process of finding the MAC, mean aerodynamic cord, of a tapered wing. Set the CG at 25% of the MAC. With a rectangular wing, the MAC and the cord are the same.

Thank you, that article really helped. I am definitely going to use this knowledge for future projects.
 

Merv

Site Moderator
Staff member
Thank you, that article really helped. I am definitely going to use this knowledge for future projects.
I use a CAD program to find the MAC Make a diagram of the wing as you would look at the wing from above. Then follow the instructions in the article. You can also just measure the area of the wing, then set the CG at 25% of the area. Draw a line, then measure the are of each side of the line. Keep moving the line until you get the CG where you want it.

I will find the CG for 25% and 30%. When flying a new plane, I start at 25% to get the plane trimmed out. Then move the CG aft until it flys the way I want it to. The CG at 25% is a very stable plane. I prefer a bit of instability, which allows easier flips and twists.

On my Versa, it flies the way I want it to with the CG at 30%. It turns into an uncontrollable flying squirrel at 31%. Flying wings are very sensitive to CG, if you are going to experiment, move it aft slowly.
 
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