Rigging - Type III

I've completed all the repairs from the 2 towing accidents and completed all the rigging, fllaperons included, one question remains. What should the dihedral be? Each wing measures 1 1/4 degree for a total of 2 1/2 degrees. That seems a little high, but she flies fine. In an attempt to even up the wings when folded, I lengthened both struts on one side and shortened both on the other, but later decided that that was affecting the dihedral. So the question now remains, what should the dihedral be?

Thanks,

On my SS it is 1 degree on each wing.

I guess then 2 1/2 total is not too out of reason. I notice in pictures of other KF's that they appear to be rigged pretty flat, maybe a degree overall.

Dihedral is not a big thing other than it provides lateral stability, which is a good thing.

Thanks for the reply.

Chuck,

I'd try stick pretty close to what the manual calls for - or call Skystar if it's not in there.

To much dihedral angle or dihedral effect can cause yaw-roll coupling tendencies (dutch roll) - not always with a good outcome.

Good Luck,
Greg

When I was building my first Model IV I had ordered the Speedster elevator with trim. When I got close to rigging the wings I toyed with the idea of rigging with the flatter dihedral of the Speedster and called the factory to question differences and reasons. I was told that the dihedral was not that critical. Move up ten years or so and my buddy always complained about his dihedral made his IV look like a diving pidgeon. Consensus flatter dihedral from two of us at least - flatter is prettier.

Also two or three years ago there was an article in Kitplanes on dihedral. The jist - on a low wing airplane - important. On high wing - not important. Aerodynamically on a low wing when pressing the right rudder pedal the airplane skids into the dihedral of the left wing and that results in bank. On a high wing it is the skidding forcing air against the fuselage that raises the left wing.

Lowell,

Quote:

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Also two or three years ago there was an article in Kitplanes on dihedral. The jist - on a low wing airplane - important. On high wing - not important. Aerodynamically on a low wing when pressing the right rudder pedal the airplane skids into the dihedral of the left wing and that results in bank. On a high wing it is the skidding forcing air against the fuselage that raises the left wing.

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That's partially the "jist", the point of the article was - the inherent interference of the fuselage on a high wing aircraft has a "similar" effect as positive dihedral, so a high wing aircraft needs less positive dihedral built in to have the same effect as a low wing aircraft that has to have more positive dihedral built in.

It is still important to have the correct dihedral dialed in, to minimize adverse aircraft handling. The positive dihedral required on a low wing aircraft is greater than it needs to be on a high wing aircraft, it's still important though.

Greg

Thanks everybody for a good discussion on the subject. I'll contact the Mc Bean's in the morning and get their view.

John McBean's reply:

Chuck,
I cannot find a dihedral measurement… I have reviewed the manual and could not find the info directly relating to the dihedral.
We use a 1 degree today.. but seem to recall it being greater than that on the earlier models. Fact is I do not remember a degree.. I seem to recall an inches of dihedral… something like 1.5 inches..


Fly Safe !!
John McBean
Ph 208.337.5111
www.kitfoxaircraft.com
"The Sky is not the Limit... It's a Playground"

I think I found the answer to my question in Service Letter #25. A 4 foot level beneath the front spar should read between 1.1 and 1.4 inches. The Tangent of 1.3/48=0.0270. The angle whose tangent is 0.0270 is 1.1 degrees. That's for each wing. Mine measures 1.25 degrees. I think I shall go work on something that needs to be fixed. This is apparently close enough.

Cheers,