Waiex Yaw correction
Posted: Fri Jun 23, 2023 12:44 am
by 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.
Re: Waiex Yaw correction
Posted: Fri Jun 23, 2023 8:27 am
by 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.
Re: Waiex Yaw correction
Posted: Fri Jun 23, 2023 9:05 pm
by Murray Parr
Bryan Cotton wrote: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.
Re: Waiex Yaw correction
Posted: Sat Jun 24, 2023 10:21 am
by 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 5350 times
Re: Waiex Yaw correction
Posted: Sat Jun 24, 2023 10:46 am
by 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.
Re: Waiex Yaw correction
Posted: Sat Jun 24, 2023 11:15 am
by 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.
Re: Waiex Yaw correction
Posted: Sun Jun 25, 2023 3:54 pm
by Murray Parr
jerryhain wrote: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.
Re: Waiex Yaw correction
Posted: Mon Jun 26, 2023 8:45 am
by 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.
Re: Waiex Yaw correction
Posted: Mon Sep 25, 2023 4:28 pm
by 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.
Re: Waiex Yaw correction
Posted: Tue Sep 26, 2023 9:03 am
by 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
Re: Waiex Yaw correction
Posted: Tue Sep 26, 2023 9:16 am
by Onex107
I don’t know anything about the “V” tail but I’ll throw this in. I presume your rudders are hinged the same as the Onex, on one side. I added a simple gap seal to my rudder and elevators and saw a significant difference in the hands off cruise. Just sayin.
Re: Waiex Yaw correction
Posted: Tue Sep 26, 2023 11:52 am
by Zack
Murray Parr wrote: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.
Please keep us posted. As you point out, it’s possible it’s a Rotax / mount issue, not a waiex design issue.
Re: Waiex Yaw correction
Posted: Wed Sep 27, 2023 3:18 am
by Murray Parr
Onex107 wrote:I don’t know anything about the “V” tail but I’ll throw this in. I presume your rudders are hinged the same as the Onex, on one side. I added a simple gap seal to my rudder and elevators and saw a significant difference in the hands off cruise. Just sayin.
This could be worth a try; do you have any pictures or advice on how you achieved the gap seals?
Re: Waiex Yaw correction
Posted: Wed Sep 27, 2023 3:24 am
by Murray Parr
bvolcko38 wrote: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
Yes, I am probably going to have to add right thrust, down thrust would be harder to achieve. I am thinking of making a new set of bed mounts with the right thrust built in but knowing how much will be the trick as it wouldn’t be adjustable. Another builder suggested to add shims where the engine mount meets the firewall, this would be adjustable and reasonably simple to add. Has anyone else tried this?
I am not sure if any twist in the empennage would be causing the right yaw as it totally goes away if I remove power. I would like to confirm the empennage is true, but I don’t see any measurements in the plans for this.
Re: Waiex Yaw correction
Posted: Wed Sep 27, 2023 8:35 am
by bvolcko38
Yes, I agree, if the yaw goes away when you reduce power, it seems to be an engine thrust problem.
Gap Seals
Posted: Wed Sep 27, 2023 9:51 am
by Onex107
Yes, it was really quite simple to do. I have pictures and can describe the process. I don’t know how to post on the builders site but I can email directly to you.
Re: Waiex Yaw correction
Posted: Thu Sep 28, 2023 2:31 pm
by Outlaw6
I think part of the roll issue can be caused by the ruddervators when using the stub rudder for yaw trim. The rudder trim tab moves the rudder to correct yaw but also moves the ruddervators creating roll in the opposite direction. I have an Aerovee so I trimmed for left rudder to compensate for right P-factor at cruise which gives some right roll tendency from the ruddervators which then needs to be compensated by adjusting lift on one flap (typically lowering the right). I believe the condition is worse on a tri-gear, like mine, because the nose gear turns in the direction of trim also which puts a left turning force below the center line creating some right roll tendency and drag. Plowing the nose gear through air at cruise with 15-20 degrees of left turn burns my OCD.
I brought this up in this thread:
viewtopic.php?f=15&t=4954
I’ve basically lived with it until now. I have the engine off for rebuild so I’m going to look at adjusting the thrust line to compensate for P-factor. Or modify the ventral fin to give me left trim, although I don’t think it has enough surface area to counter the p-factor at cruise.
This is a great first step:
bvolcko38 wrote:Yes, I agree, if the yaw goes away when you reduce power, it seems to be an engine thrust problem.
Trim pitch for cruise speed and go to idle, if it flys straight and level then the issues are from prop induced turning tendencies (p-factor, torque, spiral slipstream).
Re: Waiex Yaw correction
Posted: Wed Oct 04, 2023 1:57 am
by Murray Parr
Good news!
With the help of Cris at Sonex (thanks Cris) who sent me the newer upgraded Barry mount washers and said give these a try, we believe this is the problem (Slightly larger OD than previous which now capture all of the mount rubber instead of a small outer portion of the rubber mount spilling over the edge of the old washers).
I have to admit, I was slightly skeptical that such a small change could make such a difference, however, I installed them and went for another test flight. I noticed immediately upon applying full power and rolling down the runway that the amount of pressure needed to hold right rudder in was way less and on climb out it still felt like I wasn’t having to push anywhere near as hard as before. When I looked down at the rudder pedals, I could see that instead of 2/3 of the way to the floor, the 2 pedals were only about an inch or so apart.
I think it is close enough now that I can start looking at installing a trim tab to hold enough rudder in while at cruise settings.
Thanks for everyone that chimed in here 