Dihedral Question

[Robin G]

My mod 3 wants to roll to starboard. We have checked and rechecked the rigging and the only thing we can find is a difference in the dihedral of the starboard and port wings. The port wing has an angle of 2.2 degrees and the stbd is 1.5 degrees. In the opinion of anyone more informed than myself, is that sufficient to induce the roll? Also does anybody with a 3 know the recommended dihedral for the wings. By the way, the washout is almost identical on both wings.

Thanks in advance for any input.

robin g

[SkyPirate]

generally if your dehidral is more on one wing the plane will try to center itself raising the lower wing if the wash out is the same unless your holding the stick in the center position then yes it will roll towards starboard,..I'm not sure on the right dehidral angle ,..but they should both be the same regardless ,.. I'd say no more then 2 on each wing which would give you 4 degrees total,..less dehidral ,..less natural stability,.more dehidral ..more natural stability...

I'd level my two front wing mounts left to right on the fuselage by jacking and supporting the airframe with tail level too ,,then set the wing dehidral,..doing it while setting on tires alone can be misleading sometimes,..only 1/2 a lb difference of air in the tires can change the planes stance.

then I'd check the flaperons to see if they are nuetral ,,meaning at the same angle of attack with stick in center position
hope this helps

Chase

[SkyPirate]

if the wash out is correct on both wing's, lengthening the aft strut connect point alone on one side will change the wash out making the less wash out angled wing ( the opposite of the one that was changed) stall first when approaching a stall which could induce a dropped wing at first ( the lesser wash out angled wing) then snapping back the other way into a spin,..the advantage of flaperons will help prevent this to a point if counter inputs are applied prior to fully stalled atitude,.. if the stall isn't recovered before that point ..it will snap roll to the opposite side.

Keep the wash out the same on both wings.

Chase

[SkyPirate]

Robin ..just curious ..but is your wing sewn or just glued,..if it is just glued ..the wing that is raising ..have you checked to see if there is seperation from the fabric to the ribs? ,.in flight it will increase the camber creating more lift in turn raising the wing that has fabric seperation,..
not being able to see the wing ,..I'm just trying to think of all things that might cause your problem.

Chase

[Robin G]

Thanks everybody. The wings are stitched. This weekend I will push up the low wing from 1.5 degrees to 2.0 and pull down the high wing from 2.4 to 2.0. I suppose those long heavy cambered wings could be reacting to the difference.
I have fooled around with the washout and nothing has had any impact. So the dihedral might be the issue.

rg

[t j]

Robin, just a heads up. Be sure to check the witness hole in the strut rod ends when you push up that low wing. I don't have the measurements on a model 3 to calculate how much that 0.5 degree will screw the rod ends out but seems it may be quite a bit and not have much holding after the adjustment.

For what its worth my classic 4 has a slow roll to the right if I fly it hands and feet off. It takes a nat's eyebrow of pressure on the left rudder to fly straight and level hands off. I attribute the right roll to spiraling slip streem from the left hand prop. If you tried adjusting the washout with no success A fixed trim tab on the rudder may be an easy fix if you run out of adjustment on the wing struts.

A small wedge of wood glued to the top of the trailing edge of the flaperon has been used to correct a heavy wing too. Paint it to match and no one will notice. You can duck tape one on to test for size needed.

[SkyPirate]

C5 ..I was talking aerodynamically,.. the kitfox's wing design,..luckily gives you a truck load of forgiveness,..not so in all wing designs,..
I'd prefer to get the dehidral and washout right first ,..then if tweaking needs to be done,..so be it ,..
don't get complacent with what you "think" will happen ..be ready for the worst.

Chase

[JimS]

Lowell,
Your right about the vertical stab not being offset on the KF 4 on account of the plane being able to be equiped with a 582 or a 912. When I swapped out my 582 to the 912 the trim tab came off one side of the rudder and went on the other side. ( for those that don't know, the engines turn the prop opposite directions)

JimS

[SkyPirate]

I don't believe any of the model's of kitfoxs have an off set on the vertical stab. unless someone modified it after it left the factory.

Chase

[Robin G]

Here's the latest on my heavy winged 3. I put 2 turns in the washout with no apparent results, still wanted to roll smartly to the right. Then I taped a trim tab on the heavy side flaperon to push it down and the wing up. Again, little to no results. So I moved the trim tab to the underside of the other flaperon and "bingo", there was a notable improvement. It was not a complete fix so I added another couple of inches of tab which added even more correction. I need to adjust the location and size of the tabs as they are adding some drag, but the machine will finally fly straight.

Thanks to you all for your input.

robin g