Where to put the Center of gravity

[mymaps]

Hi there!

I have built a modified FT Flyer and now I'm wondering where I should have the CoG, I understood that it should be a bit forward from the Center of Lift, but I don't know where that is in a flat wing.

It is something like this:



That point in the picture was drawn by http://fwcg.3dzone.dk/ (yes, I added the tail with Paint, super professional )

Any experience or book method? It will be a bit difficult to put it in that place ... CoG has been my main problem since the beginning

Thanks in advance!

 

[earthsciteach]

Find the centroid of the wing area and use that as the center of lift. If you don't want to do that peaky math, cut out the shape and find where it balances on your finger. Use that as the center of lift.

 

[mymaps]

Find the centroid of the wing area and use that as the center of lift. If you don't want to do that peaky math, cut out the shape and find where it balances on your finger. Use that as the center of lift.

Oh perfect, so for a flat wing, the centroid of the wing (without tail) can be taken as the Center of Lift, so I should put the CoG a bit more to the leading edge to make it a bit nose heavy, right?


Im searching for some info about glide tests... any luck?

 

[engineer]

I think that site gives a margin to tell you where to put the CG. I'm pretty sure it bases it off the centroid, since there's no profile options.

"Glide Test" has never worked out well for me. Something about stall-speed. I never wanted to really throw my brand-new plane all that hard, which turns out to be worse because it just falls out of the sky on its nose.

 

[earthsciteach]

Oh perfect, so for a flat wing, the centroid of the wing (without tail) can be taken as the Center of Lift, so I should put the CoG a bit more to the leading edge to make it a bit nose heavy, right?


Im searching for some info about glide tests... any luck?

Yes, push the cg toward the leading edge of the wing, ahead of the center of lift. You will likely have to play around with that point a little bit to get it to where it flies to your liking.

I'm with engineer on the glide test. I don't do a glide test unless it is something like a sailplane - very slow flyer and self-stabalizing.

 

[mymaps]

Awful, I had the motor over the leading edge, and initially the battery right behind the motor, turns out it was too nose heavy, 1st crash

Then, I moved the batt to the center, that made the CoG be around the centroid more or less ... too tail heavy, 2nd crash

And the definitive one, that broke the foam along the center junction, had the CoG pushed a bit to the front, I guess that it didn't gain speed enough because it nose dived badly

I'm ordering new motor and batteries, the smallest possible haha, but in the meantime I'm wondering if an scaled up Flyer would do well with my big motor and battery (only the battery is ~170grams/~6 oz)