Hello , Im flying a ultra sport 40 arf , And its coupling pretty badly in knife edge away from
the canopy ( nose down ) , Im not sure if its an incidence problem or the aileron rigging .
If so How can I alter incidence with an arf like this ? How much adjustment might be needed ?
Which direction do I need to go ? I cant leave a gap in the wing saddle , Is my problem
somthing else all together ? Im lost [sm=drowning.gif] Any help would be great !
Thanks
NATHAN

It's more likely pitch caused by the rudder than by incidence.
You could work with incidence with shims, with the idea that you don't want a permanent installation.
How to shim is a situation based on how the wing is mounted.
A small amount of shim under the trailing edge, if the wing has dowels at the leading edge and bolts at the trailing edge isn't impossible, but I think essentially it's a situation where the inertial axes of the plane are such... vertical surface relative to the actual rotational axes is the culprit.
I'm betting that hard rudder in level flight results in a roll-pitch down in the direction of the rudder deflection. A couple of my planes can be depended on to do this.

This is not too unusual, and not always easy to get rid of. The first thing to try, is to (1) make SURE you have the plane trimmed for hands off level flight, as any pitch in level flight will be magnified in knife-edge, then (2) try a stretch of knife-edge using ONLY enough rudder to hold it in position. A well-trimmed pattern plane that will knife edge all day long can be made to pitch and/or roll with a huge amount of rudder application.

If this doesn't help, then moving the CG so that you are a little more nose-heavy may help. This will require a touch of up elevator to fly level, and that may be enough to straighten out the KE flight.

I am not big on moving the ailerons either way of a true center, as it messes up your airfoil, with undercamber one way, and reflex when inverted, or vice-versa.

There is some other "black-magic" approaches that I won't go into, as they mess up other maneuvers. The best way in this modern era, is a computer radio with some mixing capabilities which will allow you to correct any such problems in just two or three flights.

Clair

Something I notice flying today is the plane has alot of DOWN trim for hands off
level flight , Its very noticeable while sitting on the groud , Could this be an indicator
of the problem ? I think that may be the problem once knife edge ? But the cg
is right in the middle of its range , The book says 3 5/8 to 4 3/8 from leading edge,
Im at 4 1/8 dry , that puts me pretty nose heavy for quite awhile durring my flight .
The plane is already kinda hard to slow down , moving the cg forward
will only make it harder . Any ideas ?
THANKS AGAIN
NATHAN

You'll probably have to get the trim sorted out before fancifying the KE requirements.
There's pattern ship trimming procedures available which detail the methods for nulling out unwanted airplane problems.

I have a hunch that you are going to find it's not an incidence problem. It's more the relative position of the wing and horizontal stab to each other on the plane of the fuselage. The horizontal stab height in the fuselage may need to be raised or lowered relative to the wing, and not change the incidence angles.

I think you might have hit upon your KE problems with the down elevator trim. You need to get this level in order to better straighten out the KE flight. Suggest checking the engine thrust line, as it might need to go down a degree or two. This should bring that elevator back to neutral, and hopefully straighten out the KE.

Yes , another member suggested the thrust angle also , so im going to try that
the get back to you guys ! Thanks for all your help !