Straying from the build plans, question about CG

[OrangutangSurfer]

From what I understand if I increase or decrease the the plans lets say 125% or 80% the CG should be on the same mark. (shouldn't it).

but what if I change the wing design, not the shape just the design. like use a different airfoil on the delta, or switch the versa wing to a KF airfoil. I considered trying to make a thin Armin style airfoil for the F22 mostly just to increase the wing strength and prevent the flex problem i'm having (pic below). I was going to take the versa design and just reshape to match the wings of the F22. I know the F22 is supposed to be a simple build, but I'd be willing to put the time in for a more durable plane (for flying not crashing). If not the Armin airfoil can I get away with dual layering the wing portion of the design?


IF I can change the airfoil. how will this effect the CG, considering the fact I've changed the planes means to create lift, does this make a difference?

I'm still a noob and this might be more advance plane stuff but take a look at my F22 below. the nose is trashed and that's my fault, but the the flex in the wing is from flying (10-15 mph winds). I probably have 10 flights on it.

-Jes

 

[andybenton]

Scaling the planes up will indeed move the cg.
Changing the angle of a delta will also change the cg, as for the airfoil changing the cg? No clue sir

 

[makattack]

If I deviate from the FT plans, I would check the CG with some glide tests with everything mounted (including battery). Isn't the general rule of thumb that the CG should be 25% back from the leading edge of a wing? I thought I recall that from the flitetest podcasts on designing your own plane.

Just found a published article that should be useful for you:
http://flitetest.com/articles/easy-aircraft-design

 

[OrangutangSurfer]

I'll probably start simple and just make some "cosmetic changes" to the F22 I enjoy the way it flies, its been my favorite plane so far, (though with just one flight on the spitfire it's a close second). I'll try to double up on the wing for strength but going to do my best not to create too much of an airfoil, maybe i'll just round it off with an iron and tape it off with packaging tape, I read a post elsewhere, somebody added a KF step to the F22, i don't remember the specifics but there were problems. I considered adding a spar between the 2 layers also but I've never even seen one so I'm not sure how much more ridged they are, I'll have to go check the local hobby shop. I want to do my best to keep from slowing it down much.

I've only flown it in the wind, once i get it out on a low wind day I intend to have some fun. in the 10-15 mph wind this morning it didn't turn to well when I came from across the wind and turned into the wind it almost "drifted" like a car in a turn. I put so much stress on the wing today it was unflyable by the end of the 2nd 1500mah battery

-Jes

 

[rcspaceflight]

If I deviate from the FT plans, I would check the CG with some glide tests with everything mounted (including battery). Isn't the general rule of thumb that the CG should be 25% back from the leading edge of a wing? I thought I recall that from the flitetest podcasts on designing your own plane.

Just found a published article that should be useful for you:
http://flitetest.com/articles/easy-aircraft-design

I think the rule of thumb is 33% of the wing chord from the leading edge, but that only applies to traditional plane designs. I made a Star Wars X-Wing and the CG ended up directly on the leading edge of the wing.

But to answer the OP, I don't think changing the airfoil will change the CG. It would probably change the center of lift, but I'm unsure of the difference and how those two relate to each other. I say glide test it with the CG where Flite Test says it should be. That should at least be a really good starting point.