Spacewalker - Dehideral Angle
07-16-2004, 07:42 PM
#1
Spacewalker - Dehideral Angle
Hello all, I'm going to build a 1/2A Spacewalker. The dehidreal angle on most of the larger planes I've looked at is around 6 degrees. This seem's like a bit too much, but as I really don't know what I'm talkin about I'm looking for some advice. Can I decrease the angle to around 2 or 3 degrees? I'm thinking this will make for a more stable and predictable plane during inverted flight. Is there somthing I'm missing here and is the 6 degree angle important for this type of low wing aircraft?
Thanks in advance for you input.
Rrragman
Thanks in advance for you input.
Rrragman
07-16-2004, 09:43 PM
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RE: Spacewalker - Dihedral Angle
Darren:
The lowered dihedral will indeed make inverted flight a lot easier, and so long as you have aileron control there's no reason not to flatten the wing somewhat. If you go too far you'll find the plane is more stable inverted than upright. The ideal point will be with the center of lift at the same height as the center of gravity.
Bill.
The lowered dihedral will indeed make inverted flight a lot easier, and so long as you have aileron control there's no reason not to flatten the wing somewhat. If you go too far you'll find the plane is more stable inverted than upright. The ideal point will be with the center of lift at the same height as the center of gravity.
Bill.
07-16-2004, 10:22 PM
#3
RE: Spacewalker - Dihedral Angle
Bill, Thank you that's good information. How is it that you determine what the center of lift is? Then once you've figured that out, do you then dink with the CG post build and try to match the two?
Darren
Darren
07-16-2004, 11:15 PM
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RE: Spacewalker - Dihedral Angle
Darren:
There's no really easy way to figure the center of lift, but for all practical purposes it can be considered the same as the geometric center of the wing. Figure it for each panel separately, then consider a spot 1/2 way between the upper and lower surfaces of the wing to be the center of lift. But with our quick and dirty method, use that spot on the top surface. Now a line drawn between the spots on the tops of the two wings should pass through the vertical center of gravity. The true cg will be somewhat forward of that point, but at the same height.
Now the reason we used the upper surface, The wing still has some dihedral, and that's going to add stability while upright, and decrease stability inverted. So we want the center of lift still a little below the vertical cg. If you get it just right the plane will be neutral both upright and inverted. Getting the cg and lift aligned is easiest with a mid wing, that's why the better aerobatic planes are mid winged.
Back to yours. Figuring the vertical cg can also be a pain, so lets just use "TLAR" design. or "That Looks About Right." And that's another way to say "SWAG" design. But it's not really a "Simple Wild A***d Guess," as we have some experience to base it on. Make your center of lift line pass through the fuselage at about 35 to 40% of the fuselage height. You'll be pretty close.
Everybody knows about setting the cg fore and aft, very few bother with vertical cg. After you have the plane flying you can move the heavy items up and down to adjust the upright/inverted flight characteristics. Not a lot, but some.
Have fun.
Bill.
There's no really easy way to figure the center of lift, but for all practical purposes it can be considered the same as the geometric center of the wing. Figure it for each panel separately, then consider a spot 1/2 way between the upper and lower surfaces of the wing to be the center of lift. But with our quick and dirty method, use that spot on the top surface. Now a line drawn between the spots on the tops of the two wings should pass through the vertical center of gravity. The true cg will be somewhat forward of that point, but at the same height.
Now the reason we used the upper surface, The wing still has some dihedral, and that's going to add stability while upright, and decrease stability inverted. So we want the center of lift still a little below the vertical cg. If you get it just right the plane will be neutral both upright and inverted. Getting the cg and lift aligned is easiest with a mid wing, that's why the better aerobatic planes are mid winged.
Back to yours. Figuring the vertical cg can also be a pain, so lets just use "TLAR" design. or "That Looks About Right." And that's another way to say "SWAG" design. But it's not really a "Simple Wild A***d Guess," as we have some experience to base it on. Make your center of lift line pass through the fuselage at about 35 to 40% of the fuselage height. You'll be pretty close.
Everybody knows about setting the cg fore and aft, very few bother with vertical cg. After you have the plane flying you can move the heavy items up and down to adjust the upright/inverted flight characteristics. Not a lot, but some.
Have fun.
Bill.
