PDA

View Full Version : Need another way to set diehedral.



BobMo
02-23-2012, 07:11 AM
IF:
I level my inner and outer wings.
measurer 56 5/16" from the attach point/pivot out the bottom of the outer wing.
Raise the outer wing 4" at that point.

Will my wing have 4 degrees dihedral?

bsdunek
02-23-2012, 07:25 AM
arcsin 4/56.3 = 4 deg. so you will have 4 deg per wing, or 8 deg total. This is of the outer wings. Not knowing what you're building and the length of inner and outer wings, I don't know what the average diehedral would be.

Eric Witherspoon
02-23-2012, 05:00 PM
Another way to do this, so you aren't hunting around at that 56 inch point wondering what exactly 4" of lift looks like, is to cut a board at the 4 degree angle - maybe make it half of the 56.3" measurement and 2" high on the short side. Put that angled board on the wing panel to be lifted. Put a high-precision level on top of that. Then just shim up the outer wing panel until the level shows - level.

Neil
02-24-2012, 05:27 PM
Another way to measure 4 degrees is to use the sine of 4 deg. which is .06975" and multiply that by the length of a long level, say 48" and that comes out to 3.348 or really close to 3 and 11/32. Make a shim to go under the end of the level and it will measure 4 degrees all day. I generally measure dihedral with the wings leveled to zero degrees of incidence. On my biplane (which has 2 deg. dihedral and 1.5 deg. of incidence) that means the fuselage is propped up to 1.5 deg. tail high. This really matters a lot with a swept wing.

Got no idea what you are building but with any design measurement accuracy suffers if you don't start with a zero deg X Y base line.

A degree board as Mr. Witherspoon describes works well too. You just have to know how to get the 4 degrees and know all other plains are at zero.

Back to your original question, 56 5/16" or 56.3125" x .06975=3.9147 or about .085"(less than 3/32") short of 4". Probably close enough as long as the rise measurment is taken from the same plain as the attach point.

Tom Downey
02-24-2012, 07:11 PM
get one of these
http://www.amazon.com/Magnetic-Angle-Cube-While-Supplies/dp/B0035MIQ6U

BobMo
02-25-2012, 10:25 AM
Thank for the tips. I had not found my digital level and I remembered the 56 5/16" = one degree for every one inch rise. Plus, I just wanted another way to double check my digital levels accuracy. I'll try them all before I drill my attach plates.

Thanks,
Bob