Design > Stunt design
Vertical CG
Ken Culbertson:
As I am nearing completion of an inline twin version of my Endgame design I am getting increasingly concerned that I may have gotten the vertical CG way off. I simply forgot the tricycle landing gear and the extra ESC. The fuselage area including the rudder is pretty balanced with a small edge going to the top but it is all light molded balsa. The motor and battery are both on the centerline, a mistake that I cannot correct with an odd shaped battery. The timer and both ESC's along with most all of the wiring ended up below the center line. Nothing can be moved in the vertical plane without building a new fuselage. Right now, fully assembled "ready to fly" without covering it appears to hang fairly straight by the leadouts so I may be wasting my time worrying about it, but, if initial flights show outboard wing up in both directions, what do I do?
In my experience only changing the asymmetry of the wing area can fix this. What if adding raw weight to the top would help? It would probably take 2-3 ounces to balance 2 ESC's and the wheels. This is my first electric inline twin canard, next time ( LL~) I will spend a little more time on the plans!
Ken
I was thinking relative to the fuselage when I wrote that. When you read it not knowing what I was thinking you get a giant "Huhh"? Sorry, relative to the flight plane the outboard tip would be Up in Level and Down inverted. Relative to the fuselage both would be the same direction - towards the top. My bad.
BillLee:
--- Quote from: Ken Culbertson on January 04, 2025, 12:18:10 PM ---.....out it, but, if initial flights show outboard wing up in both directions, what do I do?....
--- End quote ---
Maybe I don't understand, but why would vertical cg offset result in "wing up in both directions"?
Bill
Massimo Rimoldi:
Move the leadout exit point vertically to bring it to the same height as the CG.
Massimo
Brett Buck:
--- Quote from: BillLee on January 04, 2025, 12:36:59 PM ---Maybe I don't understand, but why would vertical cg offset result in "wing up in both directions"?
--- End quote ---
It doesn't. I am not sure where the strange obsession over vertical CG has come from, unless you do something way off the track, it's very hard to get it far enough off that other trim problems won't completely swamp it.
If that is the issue, it needs more tip weight.
Brett
Brett Buck:
--- Quote from: Ken Culbertson on January 04, 2025, 12:18:10 PM --- Right now, fully assembled "ready to fly" without covering it appears to hang fairly straight by the leadouts so I may be wasting my time worrying about it, but, if initial flights show outboard wing up in both directions, what do I do?
--- End quote ---
Add tip weight, this is not a vertical CG problem. Add tip weight until the wings are level, if it is rolled in one way and rolled out the other way, tweak the flaps until it is the same. Then you can start trimming normally.
I sincerely doubt that your vertical CG is off far enough to notice, even if it was 2" low or high, which it isn't, it would have a very minimal effect on the performance and it certainly would not result in a constant inboard roll in both directions, it causes inboard one way and outboard the other way.
I would disregard the issue, unless you have other unresolvable trim issues after every other adjustment has proven inadequate (in this case, an infinitesimal tweak beyond that required to compensate for the other misalignments and warps).
Brett
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