Waiex Yaw correction

[Murray Parr]

Hello to the group, looking for advice.

My Waiex has a couple of roll and Yaw tendencies. If I put the ball in the centre and let go of the stick it rolls left which I plan on adjusting the flap to make a change. I also need a lot of right rudder (about half way to the stops) under most flight conditions to keep the ball centred, the only time I need less is when descending under low or no power.

Engine is a Rotax with the newer style bed mount and the extra washers installed as per the SB

I took the wheel pants off to see if that makes a change however the next flight was identical tendencies. My next flight will be with wheel pants back on and left flap adjusted 1/2 turn down ( surprisingly half a turn makes 3mm difference in the measurement at the leading edge skin as per plans)

Does anyone have any suggestions or experiences for correcting Yaw in the Waiex models?

If I adjust the stub rudder cables to the left will that be similar to adding a trim tab given that adjustment is independent of the ruddervator adjustments?

Any guidance is much appreciated.

[Bryan Cotton]

Murray,
I would not shorten the cable. Right now you are the trim, and with a shorter cable you will still be the trim. It should be in trim at cruise with your feet on the floor.

The factory supplied trim tab works. I put mine on a couple of months ago. I put it on with aluminum rivets to make it easy to remove and re-bend.

You could also put a spring to pull one of the pedals towards the firewall. Or if you have those tensioning springs installed, make one shorter. I left my tensioning springs out.

[Murray Parr]

Murray,
I would not shorten the cable. Right now you are the trim, and with a shorter cable you will still be the trim. It should be in trim at cruise with your feet on the floor.

The factory supplied trim tab works. I put mine on a couple of months ago. I put it on with aluminum rivets to make it easy to remove and re-bend.

You could also put a spring to pull one of the pedals towards the firewall. Or if you have those tensioning springs installed, make one shorter. I left my tensioning springs out.

Thanks Bryan,

Do you know what plans number the factory supplied trim tab is on? I don't recall seeing anything along the lines of a tab during the build.

My biggest concern is how far the right pedal in pressed to keep the ball centred. I might try to take a picture of it on next flight in case it just feels worse than it is. Was quite tiring after an hours flight holding the right rudder in.

I am going to double check the rigging and incidences and also the thrust line before next flight. In fact, I have never checked the thrust line as that should be set by the engine mount and doesn't appear to be adjustable to the left or right.

Thinking out loud here, the Rotax mount rubbers seem to have a lot of movement on shutdown and I also have some rub marks on the lower left side of the prop shaft opening in the cowl which indicates the engine is pulling itself quite a bit to the left and down a bit.

[Bryan Cotton]

Murray,
I'll have to look. It's really simple and the tab was included in the kit.

rudder trim tab.png (518.77 KiB) Viewed 5506 times

[Bryan Cotton]

I found the bag the trim tab came in and the P/N is SNX-B04-07. That is the aircraft complete page, just after the drawing tree on my legacy plans.

[jerryhain]

My Waiex had one of the ruddervader‘s built with a slight twist. I adjusted them at the 2/3 up from the bottom and it corrected my roll.

[Murray Parr]

My Waiex had one of the ruddervader‘s built with a slight twist. I adjusted them at the 2/3 up from the bottom and it corrected my roll.

Thanks Jerry,

I will check at the 2/3 up from bottom and compare it to the bottom measurement when I start re checking all the rigging, I can see that a slight twist could affect yaw so this will be worth checking out.

[Bryan Cotton]

For what it's worth, I believe my Waiex is built very true and it still needed a trim tab. We nominally have a straight thrust line and that will induce yaw. Before I could find a power setting where I didn't need pedal but it wasn't in cruise! I still need left pedal on climb and right pedal power off.

[Murray Parr]

I am still struggling to find a real solution to the amount of right rudder needed when I apply power. I need a very small amount of left pedal on power off decent (which is about normal I believe) but any amount of power fed in causes a need for quite a bit of right rudder application up to 3/4 on takeoff or climb. Straight and level cruise still needs 2/3 right rudder and to be honest I get a cramp in my foot from holding it so hard for any flight over an hour.

I get that I can put a trim tab on, but the tab would still have to deflect the pedal 2/3 of the available right input for cruise settings.

So far, I have re checked all the rigging and found the left-wing incidence is perfect and the right-wing incidence is 1mm (3/64") less on the plans measurement which in combination of flying left seat solo explains the slight left roll when balanced. I have corrected the slight roll tendency with 1/2 turn flap adjustment.

The wings are level with the fuselage and the measurement between the outer rear wing skin trailing edge and the lower corners of the rear fuselage is 6mm (1/4") greater than target. It is supposed to be 3.6 mm (5/32") greater than the right-wing measurement due to offset caused by wings overlapping each other. I have 9mm (3/8") instead. Not sure what that would cause yet but I will have to give that some further thought.

Checking the engine alignment resulted in 0.7 degrees right thrust and 0.5 degrees down thrust, both of these alignments should improve the yaw condition instead of making it worse.

I set up the ruddervators as per plans (which uses the mixer being centered), I re checked using rudder pedals centered and found the ruddervators and stub rudder weren't centered to each other (the stub rudder was left of center with the pedals centered and the ruddervators were centered). Here is where I thought I found the problem, so I adjusted everything to be centered with each other.

I went for a test flight and found there was no change to the right yaw tendencies or if anything it seems to be slightly worse.

I am now thinking I might have to align the engine with a few degrees of right thrust built in unless anyone else can suggest further adjustments I could try.

[bvolcko38]

Have you ever seen a Ercoupe with the cowling off? Huge amounts of right and down thrust built into the motor mounts. Sounds like you might need some right thrust to counteract some minute amount of twist in your empannage.

JMHO