How to trim the Waiex yaw axis

[Outlaw6]

Been searching for a few days trying to find a better way to trim my Waiex yaw. Right now I have a thin wedge stuck to the rear right edge of the rudder, effectively a trim tab that is less noticeable. It tracks straight but makes the right wing seem heavy, i think this is due to the moment created by the trim tab moving the rudder which moves the ruddervators. So the fuselage wants to go straight but "Y" tail is producing more lift on the left side because the ruddervator is down compared to the left which causes the I think causes the plane to want to slowly roll to the right.
In cruise flight the trim tab gives my left rudder pedal an inch+ forward of the right.
Possible solutions:
1) rig the rudder to have the left trim in with the ruddervators level. I don't like this because I have to use a trim tab.
2) adjust the thrust line by adding washers to the right side engine mounts (it's even now). I like this because in cruise i would go straight when the rudder is straight and have least amount of induced drag.
3) adjust flaps to counteract the roll. Again seems like adding more drag.

I can't find this anywhere on the forum so any advice is welcome.

[GordonTurner]

Not there yet myself, but I would suggest make the easy fix adjust the flaps and the tiny additional drag will go unnoticed. The drag is actually there now, you’re holding the controls for straight flight.

[Outlaw6]

Gordon,
I forgot to mention my Waiex is a nose dragger so the nosewheel is turned to the left in cruise also which creates more drag and more yaw and possibly some roll. So that's four control surfaces (rudder, 2x ruddervators, and a flap) and the nose wheel creating unneeded drag, which may be a noticeable reduction in speed/efficiency.
What you said did make me step back and think that I should first test flight characteristics at cruise speed with the engine at idle to negate P-factor. That should give me a better idea which solution I should choose.

[MichaelFarley56]

I know it can be a little irritating to get everything dialed in perfectly; just like you said, you get one axis all dialed in and it messes up something else! Been there!

Ultimately on my Waiex I added a small trim tab on the stub rudder so the airplane would be in trim at normal cruise power settings and airspeeds, and then adjusted one flap pushrod slightly so the airplane was trimmed in roll axis as well. I wanted to have my airframe all dialed in at cruise power and airspeeds as I figure that's where I'd be spending most of my time.

I also figure that, at 130 mph, the very slight changes in drag isn't going to make any real difference. I know when I'm flying my KingAir 350 it requires regular rudder trim adjustments and I see no change in indicated airspeed when I trim the rudder from 1/2 ball out to perfectly in trim. After I saw that, I wasn't so worried about losing performance in my Waiex; I wanted it to fly straight so I could enjoy the flight more!

Just my two cents of course!

[DCASonex]

As someone pointed out a few years back, the "A:" model Sonex flap linkage is way too flexible. If lever is on the left, right flap will move up in flight making right wing feel heavy. The small angles Sonex provides to close the gap between flaps and sides of fuselage do not act as stops, the ends of the flaps are too flexible, only strength there is due to the small radius bend in the skin. Peter used to offer for sale some nice adjustable stops, I made my own copy of those, but found they contacted the flexible vertical surface of the flaps, so after using them to determine proper location, made my own solid stops from blocks of plastic about 3-4 inches long, two per flap. mounted tight up under upper wing skin inside rear spar, holes drilled to clear existing rivets, and riveted to web of rear spar.These contact the top leading edge of the flaps and make a very positive stop. Makes a big difference in how the plane feels. Set mine so that it is slightly heavy on pilot's side when solo, and on right with passenger. (I also have small trim tab on rudder.) The new Sonex flap operating linkage looks much improved.

David A.

[Area 51%]

How come social convention dictates dropping the flap on a heavy wing (thereby increasing drag) instead of reflexing the flap on the light wing? Is it not possible due to interference between the top of the flap and rear spar?

Speaking of interference...Be careful adjusting the rudder to an off-center position in relation to neutral ruddervators. I had an issue with the bottom forward edge of the ruddervators contacting the rear spar before the rudder got to it's stops. I'm thinking you might introduce that contact on one side with an offset rudder. The only way I was able to overcome that contact was by decreasing the overall down deflection by a degree.

[Outlaw6]

How come social convention dictates dropping the flap on a heavy wing (thereby increasing drag) instead of reflexing the flap on the light wing? Is it not possible due to interference between the top of the flap and rear spar?

Speaking of interference...Be careful adjusting the rudder to an off-center position in relation to neutral ruddervators. I had an issue with the bottom forward edge of the ruddervators contacting the rear spar before the rudder got to it's stops. I'm thinking you might introduce that contact on one side with an offset rudder. The only way I was able to overcome that contact was by decreasing the overall down deflection by a degree.

Both good points. Thanks.

Still hoping someone who has adjusted the thrust line chimes in with how effective that is and how much impact a small change with washers on the engine mount affect yaw. The Aerovee manual mentions adding washers behind the rear bushing to shim the thrust line.

I have the center flap handle. I remember reading the flap stop discussion but don't remember what I concluded lol.

Hope to have the turbo cooling install finished and tested this weekend. Then work on trim.

[DCASonex]

It is entirely possible for the top leading edge of flap to force its way under top wing skin and into rear spar when under load in flight. It did that on one wing of mine and not on the other. very minute difference in hinge placement. Adding the stops kept the flaps where they should have been. The difference in settings of the stops from one side to the other is almost impossible to detect without getting out calipers. Purpose of the stops is not so much to correct for a heavy wing as it is to keep flap from moving up in flight on side opposite the flap lever resulting in loss of lift on that side. To check this, Adjust the flaps down a bit, then have someone hold the flap lever in position while you manually move both flaps and you will see how easy it is to deflect the right side flap..

David A.