Possible conversion roll to Yaw trim?

When I built our RV-6A I bought and installed the simple little roll trim accessory kit. It works fine but I keep my fuel burn balanced within 1/2 hour and roll trim is NEVER a problem - I don't even think about it. The little black handle just sits there waiting to add one more task to the removal of the seat pans. Rudder trim does not exist (although I read today in this Forum that it is an option on RV-8s) but it is largely satisfied by the wedge on the left side of the rudder. The amount of right rudder varies quite a bit between takeoff/climb, normal cruise and racing and I would like to fine tune the ball to center all the time. I have been calmly simmering this problem on the back burner for years and this possible solution just bubbled up to the surface. Has anyone disconnected the aileron link and connected it to the rudder cables via cables and pulleys behind the cover panels in the baggage area? If so what were your results?

Bob Axsom

Bob,

I think I've seen some posts on rudder trim that were pretty simple spring biases on the cables, but not in the baggage area. I even seem to remember some pictures.

Louise's -6 (Mikey) has three-axis trim that is pretty neat - it was built with a servo and a tab in the left aileron and the rudder, in addition to the servo and standard tab in the elevator. Three-axis electric trim, and plenty powerful, without any spring forces on the controls. We might try to replicate it on the -3.

Paul

Some ideas...

Haven't done it yet, but ideas for rudder trim are also simmering in my head.

Normally I'd favor aerodynamic trim, i.e. a trim tab. But in the case of the rudder, I'm actually gravitating toward a spring bias system as a way to kill two birds with one stone: 1) adjustable trim capability, and 2) retention -- preventing the rudder cables from ever going slack and potentially snagging on part of the airframe.

I haven't worked out a detailed design yet, but my thinking is along the following lines. Attach an extension spring to each of the lower outboard corners of the rudder pedals (i.e. near where the rudder cables connect) and attach the other end of each spring to a fixed structure forward of the pedal (i.e. near the firewall). So that by itself accomplishes the retention function by pulling both pedals forward with equal force, but not yet adjustable trim.

Now, to add the adjustable trim capability, attach the forward end of one of the two springs to a MAC servo instead of to a fixed structure. The servo should be mounted such that the travel is fore-aft, with the center of travel at the same location (mirror image) as the fixed structure on the other side. So with the servo at center of travel, the spring forces on the two pedals are equal. With the servo away from center, we introduce a bias in one direction.

In its simplest form as described above, this design is quite simple and requires minimal hardware. If there isn't enough room though between the pedals and the firewall, then a pulley system might be necessary (and the servo mounted elsewhere), but I would avoid that mess if at all possible.

Note also that by having one spring fixed and the other on a servo, the rudder pedal tension will be stronger with the trim adjusted to one direction than the other. But with good design (spring selection, geometry) this difference can be kept to a minimum, and I suspect that it will not be noticeable, especially given that yaw characteristics and rudder use in these airplanes is inherently asymmetric in the first place. If one really wanted to make it symmetric still, then one could use two servos (and some electronics to keep them in sync) or one servo and a pulley system, but again I would avoid such complexities if they are not absolutely essential.

More thoughts

I have seen a drawing from Van I believe that has the attachment on the fwd side of the outboard peddles with pulleys and springs and a central bias mechanism. After sleeping on my earlier proposal I realize the attachment point may have to be farther back in the aft fuselage to have a small angle and an unobstructed range of motion. The beauty of converting the existing roll trim system is it is already in the airplane and it is not being used. I saw the bungie cord method in the bay outboard of the passenger seat for right rudder only and that is clever but not the way I want to go. I also do not want to add trim servos, etc. just something that I can use to dial in what I need without adding drag - I am looking for speed as well as the trim function. More thinking required.

Bob Axsom

Thoughts

It would seem to me that if someone were designing a spring-based rudder trim, (or aileron or elevator trim), it would be important to have long springs that had very gradual changes in force as they changed length. And always have two springs opposing each other at neutral.

That way the springs would have minimal force against pilot input on the rudder (aileron, elevator).

All things considered, aerodynamic trim tabs seem superior, although more difficult to build.

I messed around with doing a Bias spring setup on a customers -6, and in the end decided:

1. It wouldn't be hard to make something that works

2. It would be exceeding difficult to make something that works well, and is still simple.

osxuser said:

I messed around with doing a Bias spring setup on a customers -6, and in the end decided:

1. It wouldn't be hard to make something that works

2. It would be exceeding difficult to make something that works well, and is still simple.

Click to expand...

Ah yes, #2 is the rub. I'm sure there is an elegent solution and I will develop my version but it is not urgent nor easy so the pot simmers.

Bob Axsom

Been there, done that.

I developed a rudder trim system on my 6 based on spring bias. However the best & most economical one can be found on ML Blueskunk site. For $85.oo machining on it is beautiful & simple. Works well.

chuck beat me to it

Chuck just told me about the site this past weekend. Here's the link: http://www.mlblueskunk.com/Rudder_Trim_System.html

Man! That is the sweetest piece of work I've seen

Man! That is the sweetest piece of work I've seen in a while. I'm buying it. Thanks for the revelation.

Bob Axsom

I bought the system from them last fall...yet to install it, perhaps this weekend, but it is REALLY well done.

Two thumbs up!

for rudder trim..

anybody try a leg press machine? a bicycle? or a bunch of Vx climbs in a Diamond DA20 with a Continental engine..

matt0 said:

anybody try a leg press machine? a bicycle? or a bunch of Vx climbs in a Diamond DA20 with a Continental engine..

Click to expand...

A friend of mine has them....

.....on his -6A which is close to flying. From what I saw, it looks like the springs are a little too soft to overcome the drag of the rudder tubes in the plastic blocks. The arms are about 4" long so there is enough leverage, it seems. I looked at this while the top forward skin had not been rivetted on and it's definitely a fine piece of work.

Regards,

I ordered a set

Good input Pierre. I will install it when it arrives and the schedule permits and report the results. Maybe it isn't necessary to move the inert system but just exert a controlled amount of force in one direction or the other (always right, are you kidding Robert). One task I am not looking forward to is removing the plastic wedge that is riveted to the rudder under an expensive paint job.

Bob Axsom

Bob Axsom said:

Good input Pierre. I will install it when it arrives and the schedule permits and report the results. Maybe it isn't necessary to move the inert system but just exert a controlled amount of force in one direction or the other (always right, are you kidding Robert). One task I am not looking forward to is removing the plastic wedge that is riveted to the rudder under an expensive paint job.

Click to expand...

I don't seem to see the benefit of removing the plastic wedge. As far as I'm concerned, these single engine airplanes are going to have "drag" in one form or another. I've followed the "yaw" question ever since "Duke Fox" proved that you could counteract the drift forces by installing a full length vertical stab pointed downwards in addition to the vertical stab pointing up. He did this with model gas airplanes; as it's not really practical for full scale without being trikes including extra long landing gear. Duke did this experimenting back in the 60's. His main concern was the spiral (helical) prop wash that hits the tail surfaces. As many old timers would know, Duke owned a model airplane engine manufacturing business (Fox) for many years.

Since my 6A has no built in offset on the vertical stab, such as many of the newer models do; I didn't question that a wedge or tab would be required. My now permanent tab which replaced a simple taped on wedge isn't all that large, but it sure offsets a lot of force. I was surprised just how much force the rudder required on my leg when no tab or wedge was present. With those thoughts, I must wonder if the springs included with this rudder trim device would be anywhere in the ball park without a built on tab or wedge.

I also find it interesting over the years, on how many opinions there are in regards to the importance of torque, P-factor, and this spiral slipstream coming off the prop. It appears that so many people claim different priorities of their order. I'll chalk it up to the "unknowns", such as what exactly causes "lift".

In the meantime, if the wedge is removed; won't you just be correcting with rudder anyway; which adds the "drag" right back in? I suppose that if we're coasting downhill, we'd pick up a bit of additional airspeed with the draggy wedge removed, since we're not fighting the slipstream. In this case, it would seem that an airplane with a "0" offset on the tail (such as our 6's) would have an advantage over those with built in offset. I just don't know how the "coasting" advantage would all add up..

The only thing I do know for sure, is that when builders take their first flight and report "straight as an arrow"...............it's only because the engine and tail are both offset to begin with!

L.Adamson --- RV6A

Fox

You say Fox I think 35, old AMA #1967 through the year 1965, Kirkwood Thermaleers . No one else knows what we are talking about and that's probably just as well.

I don't know the exact payoff in speed (drag) but the wedge is not adequate for all flight regimes in my airplane. If the trim system works as I believe it will I can trim yaw in flight to center the ball. That will satisfy my personal preference and it cannot make the plane go from point A to Point B slower than the wedge that must often be supplemented. Thanks for the input though - I wish I could convince myself that I don't have to take the wedge off. That will come after I take the wedge off and tests show that I wasted my time and have to repair the paint on the rudder.

Bob Axsom

Bob Axsom said:

You say Fox I think 35, old AMA #1967 through the year 1965, Kirkwood Thermaleers . No one else knows what we are talking about and that's probably just as well.

I don't know the exact payoff in speed (drag) but the wedge is not adequate for all flight regimes in my airplane. If the trim system works as I believe it will I can trim yaw in flight to center the ball. That will satisfy my personal preference and it cannot make the plane go from point A to Point B slower than the wedge that must often be supplemented. Thanks for the input though - I wish I could convince myself that I don't have to take the wedge off. That will come after I take the wedge off and tests show that I wasted my time and have to repair the paint on the rudder.

Click to expand...

I figured, that in all this time.............you forgot just how much force that tab nullifies. And you're probably right about Fox..

BTW--- I wouldn't mind an adjustable tab on my 6A too; when you consider the range of cruising speeds.

L.Adamson --- RV6A

6 of one, a half-dozen of the other?

Bob Axsom said:

I don't know the exact payoff in speed (drag) but the wedge is not adequate for all flight regimes in my airplane. If the trim system works as I believe it will I can trim yaw in flight to center the ball. That will satisfy my personal preference and it cannot make the plane go from point A to Point B slower than the wedge that must often be supplemented. Thanks for the input though - I wish I could convince myself that I don't have to take the wedge off. That will come after I take the wedge off and tests show that I wasted my time and have to repair the paint on the rudder.

Bob Axsom

Click to expand...

Bob, PMFJI, and I am sure you know WAAAY more that I do about drag, but wouldn't all or a very high percentage of the added drag come from the deflection of the rudder? The wedge is just a fixed tab, which at one airspeed/power combination is "just right". The purpose of an adjustable rudder trim, (either a moving tab, or an adjustable spring) is to be able to trim out the rudder forces at ANY AND ALL airspeed/power combinations. By removing the wedge, you may need "stronger" springs, which will still deflect the rudder the same amount. Rudder deflected the same=drag the same?????

I vote for taking data before you remove the wedge, decide later.

Another thought: As you are a racer, wouldn't you want to have the vertical stab offset such that there is no rudder deflection at your top racing speed?? i.e.: min drag at top speed??

Just thinking out loud, so to speak I'm sure someone who knows more about aerodynamic will jump in and straighten me out...........

Thanks for the input

I guess the bottom line is I want the wedge off of the rudder - there I've admitted it - so it is going to come off. If I had installed the vertical stabilizer with some offset of the leading edge to the left that would accomplish the same thing as the right rudder application but again, it is a fixed offset suitable for some flight conditions but not all. To offset it now would require alterations of the fuselage/empennage fairing. The rudder trim should allow me to dial in the exact correction I need with internal spring force rather than aerodynamic wedge force. The difference in speed caused by the opposing forces of the wedge and the rudder may not be measurable but I can't ignore the effect. If I leave it on I am dragging an unnecessary static wedge through the air. I flew the plane without the wedge during the test phase and I know the right rudder demand was pronounced. In fact I recognize the possible need to reinstall a wedge in the future but as the sign on our dynamic test lab wall used to say "one test is worth a thousand expert opinions" and I have to know the answer.

Bob Axsom

PCHunt said:

Another thought: As you are a racer, wouldn't you want to have the vertical stab offset such that there is no rudder deflection at your top racing speed?? i.e.: min drag at top speed??

Click to expand...

I'm willing to bet, that a vertical stab offset in the front, is just as much drag as a rudder deflection in the back. It just makes pilots think the plane is flying straight and true without always pounding on the rudder (with no tab/wedge to start with). I'm quite sure that the rudder deflection provided by my built in fixed rudder tab, is no worse on drag than a "9" with built in offset. Either way, it's still a necessary compromise that's required for single engine prop planes.

Now, if someone were to measure the "speed gains" when heading downhill without a built in offset and engine at low power. It would seem that the "non" offset stab would be faster due to less drag. Props or settings would need to be the same also.

As to tabs hanging off my flight surfaces; my plane has a military look. Therefor, they are okay.... in my mind...

L.Adamson --- RV6A

Some more thoughts...

I'm no aerodynamics expert, but my intuition says that the VS+rudder will generate the minimum amount of drag for a given coordinated flight condition when they are in-trail with each other (and of course, no tab, no wedge). But I could imagine reasons why that might not be the case. Can any of you aerodynamics gurus comment on that?

Anyway, IF that's true, then a racer would want to ideally offset the VS such that the rudder will be in trail with the VS in the flight condition in which he expects to spend most of the race. And any trim mechanism should be internal, as in spring bias, not aerodynamic, so that it too does not induce any added drag.

Now, for me personally, I'm not a racer, so my motivations are different. My interest in an adjustable rudder trim system is such that the plane can be kept in proper trim in all 3 axes under any flight condition. This reduces pilot fatigue when hand-flying the airplane, and facilitates hands-off (actually feet-off) coordinated flight when a 2-axis autopilot is engaged.

roee said:

Anyway, IF that's true, then a racer would want to ideally offset the VS such that the rudder will be in trail with the VS in the flight condition in which he expects to spend most of the race. And any trim mechanism should be internal, as in spring bias, not aerodynamic, so that it too does not induce any added drag.

Click to expand...

The offset vertical stabilizer will induce drag just like an offset rudder would. The rudder will no longer be in perfect trail of an offset stab....... hopefully.

Since the rudder is farther back & therefore has a bit more leverage; which induces the most drag to keep the airplane on the straight and narrow................ the rudder with tab/wedge, or the offset vertical stab?
I'd bet on the rudder as being the least in drag.

L.Adamson

L.Adamson said:

The offset vertical stabilizer will induce drag just like an offset rudder would. The rudder will no longer be in perfect trail of an offset stab....... hopefully.

Since the rudder is farther back & therefore has a bit more leverage; which induces the most drag to keep the airplane on the straight and narrow................ the rudder with tab/wedge, or the offset vertical stab?
I'd bet on the rudder as being the least in drag.

L.Adamson

Click to expand...

I see your point about the rudder being further aft, and therefore having a greater moment for the same amount of force ("sideways lift"). True. But on the other hand, I'm looking at the VS + rudder as a system, a single "sideways lift"-generating surface. So two of the factors we care about are 1) how much "sideways lift" does the VS+rudder system generate, and 2) indeed, how far aft is the VS+rudder system's center of lift. And then one more factor the racer especially cares about is 3) what is the VS+rudder system's total drag contribution. The optimum configuration would give us a combination of (1) and (2) that provides the correct moment while minimizing (3).

All the above factors will be affected by the effective camber and angle of attack of the VS+rudder system. The effective camber is affected by the rudder deflection relative to the VS. The effective angle of attack is affected by VS offset, rudder deflection, and any asymmetry in the airflow in that region due to spiraling slipstream, etc.

Indeed, it may very well be that the optimum configuration is not necessarily an offset VS with rudder perfectly in trail with it. It may be that a different VS offset and the rudder at some other deflection angle produces a more efficient camber / AoA combination. But in a broader sense, it's whatever that optimum configuration is that the racer should seek.

HI Bob,
You and Pierre hit on something that I wanted to clarify. In most cases the trim system will NOT move the rudder while static. It works like Bob said. It puts tension on the rudder system to keep the aircraft trimmed. It works best when you center the ball with your foot and trim the system to hold what you have. I have tested several springs in length and how much they will pull per inch of stretch. I have also found that no two airplanes are the same. If the rudder tube bushings are too tight, it does not trim as easy or work as good for obvious reasons. I have had cases where two springs were required on the pulling side to trim the aircraft. The good thing is that you don't notice the springs when using the rudders. I have found that in 200 hours of flying this system, the trim needed adjustment only a few times if flying the same cruise speed. The system works well if set up and operated correctly. I thank everyone for the interest in our systems. Please let me know if I can be of help. Steve www.mlblueskunk.com

roee said:

... my intuition says that the VS+rudder will generate the minimum amount of drag for a given coordinated flight condition when they are in-trail with each other (and of course, no tab, no wedge). But I could imagine reasons why that might not be the case. (snip)

Click to expand...

Roee, your intuition is *probably* correct. For a trimmed flight condition such as cruise, we have relatively light yaw axis trim force requirements along with high airspeeds. The VS/Rudder doesn't need to operate at a high "lift" coefficient under these conditions, so the faired VS/Rudder will work pretty efficiently. Remember, our tail surfaces have zero camber when everything's lined up.

I put the *probably* asterisks in there to answer this question because we have other coordinated flight situations where the faired VS/Rudder might not be the most aerodynamically efficient shape. In that vein, another case to consider would be a prolonged climb to altitude.

In the climb case, we have much larger trim forces required, and lower speeds. (I'm aware of the propeller-induced velocities on the tail, but those will not increase local flow speeds as much as you'd see during cruise. And the "P-factor" additives are worse while climbing) Under these conditions, we're asking the VS/Rudder system to operate at a larger lift coefficient. Adding camber to an airfoil has the effect of shifting the minimum drag point to correspond with a higher lift coefficient. Ultimately, we'd like to see C_l(required) correspond with C_d(min) to get min drag.

With the higher C_l requirement in climb, its likely that having some camber (ie, some rudder deflection) in the vertical tail would be optimum for the least drag. But, we wouldn't know that without any analysis and/or testing.

The vertical stab can be mounted with its leading edge offset to trim the airplane for one flight condition. I offset the VS in my RV4 1/2" left of centerline. This value was based on measured rudder deflection for cruise with the VS on the centerline, then calculating rudder deflection that would have the same effect. This offset was spot-on for my 4; we'll see what my 8 requires after it flies...

Rudder Trim System

I purchased and installed the M L Skunk Works Rudder Trim System and tested it. The first installation would not hold the ball centered in level flight after I centered the ball with my feet and cranked the trim system hard right. I advised Steve of the results and he was very helpful in supplying many additional springs of various sizes and suggestions for such things as parallel installation of springs on the right rudder. I installed the most powerful springs of the set and test flew again. The system again would not retain the ball centered in level flight. I followed the directions for increasing the drag in the system and it just retained the ball in the center when cranked hard right. I observer that under these conditions the right offset rudder was inducing a left roll. Basically it appears to work if you are willing to install and carefully adjust the system but I removed it after the test flight today - I just didn't like the feel.

Bob Axsom

for what its worth

I have adjusted both my HS and VS to try to achieve a minimum of trim input at cruise speed. The vert stab adjustment made little difference in speed but the adjustment on the HS made a large difference in speed. I would think that eliminating the trib tab on any surface would reduce drag and any controlsurface that is not deflected would be less drag.

cm

That was my thought as well

My horizontal stab seems right with the design shim in place. The CG came out right on the money although the weight is high. Early in the test phase of my short tail six I determined that it was not too sensitive to rudder inputs. I did tape the wedge and when the full size part was found to work well I installed it permanently. The spring trim was an approach I took to get rid of the wedge. My experience indicates that it has to work much harder with the uncounterbalanced small rudder. I doubt that the later large counterbalanced tail sixes would have as much difficulty. I decided after my third test just to stop work on it for now move on to some other way to get more speed. One of these days I'm going to have to bite the bullet and get a new prop. I will have the wedge on at the Tennessee Valley Air Race.

Bob Axsom

Christopher Murphy said:

I have adjusted both my HS and VS to try to achieve a minimum of trim input at cruise speed. The vert stab adjustment made little difference in speed but the adjustment on the HS made a large difference in speed. I would think that eliminating the trib tab on any surface would reduce drag and any controlsurface that is not deflected would be less drag.

Click to expand...

When it comes to an offset vertical stab versus a rudder wedge/trim tab; I doubt there is much difference (if any) speed wise. My 6A with a tab is fast, compared to several RV's around here. IMO, all the offset vertical stab is good for...............is to say that the RV flew hands off without trim, on the first flight! In my mind, any built in offset is still drag.

But...................I'd like some real proof, one way or another...

L.Adamson --- RV6A

Well you won't get it from me obviously

It seemed to me that a wedge exerting a force one way to deflect the rudder the opposite way would result in more drag than just off setting the the rudder with internal forces. Off setting the leading edge of the fin or vertical stabilizer seems like the equivalent straight streamlined way to do the same thing. I appreciate Chris' effort to try the mod and test it and report the results. I had thought about it but there is no way that I'm going to mess with the nice fitting fairing since he already says it isn't worth the effort - I didn't know what the results would be but I know Chris and his findings are good enough for me. I'm sticking with the ugly wedge for now. Recently I was looking through my race photos and I saw the ground adjustable trailing metal tab on the rudder of Bruce Hammer's screaming fast Glasair I TD. Just thinking for now - tinker time is pretty much over for this year and I will have to race what I have.

Bob Axsom

Interesting discussion

The force required to hold the ball in the center at a given cruise condition is the same regardless of how it is applied. The rudder does not have more leverage than the VS. That's because the VS and Rudder work as a single aerodynamic unit. Moving the rudder from the streamlined position changes the camber of the VS/Rudder airfoil form zero camber to +/- camber therefore changing its coefficient of lift. This will cause horizontal lift to effect the yaw of the aircraft. The yawing force is centered at the aerodynamic center of lift for the HS/Rudder.

If you offset the VS, and have perfect trim at your desired curise speed with the rudder in trail, without a tab, its because the offset angle of attack of the VS/Rudder is providing the same force at zero camber. There is no free lunch!

If you like to do aerobatics, then the best set up is to have everything at zero incidence like a Pitts or Eagle. Then the aircraft will fly the same at positive or negative G.

The wedge tab may be ugly, but it is so KISS. I would love to have a movable tab on the Doll, but I decided it is not worth the trouble. I would bet that the drag caused by the wedge is not measurable in knots.

I Do not agree but your view is good to get out there

I know you meant VS rather than HS and based on that understanding I still think your conclusion is not correct. If the position of the vertical stabilizer is such that it is inducing a yaw force then the rudder position has to account for that as well as the the other yaw forces of the moment. And, yaw force requirements should not be equated to drag; different yaw force application methods can result in different levels of drag. Well, you get the picture. Chris Murphy's work with the angle of the horizontal stabilizer is a very clear example of this. With the change in angle the margin of stability is changed but the elevator deflection required to maintain level flight is reduced - the drag is reduced and the speed is increased. His findings with the vertical stabilizer indicate that its yaw angle is pretty close to being right for cruise flight. The beauty of the wedge or the tab is that the resulting force changes relative to speed where the internal spring force is constant across all speed and must be adjusted with a control or overcome by the pilot with a change in speed. With a system of this sort it is important to have enough force to accommodate maximum yaw requirements, enough friction to hold it and an indicator to inform the user where relative to the full range of spring force travel the system is currently set. It would be very easy for a distracted pilot to be turned by the loaded rudder during taxi operations.

Anyway this is not a simple subject that should be dismissed by a rationalization that all approaches are equal in the end - they are not.

Bob Axsom

I have designed a rudder trim system for my HR-II that can be easily adapted to any RV. It uses bias springs, but is mounted aft of the baggage bulkhead, so it puts no force on the pedals, just the cables.

It uses a RAC servo for control.

I am also considering making a servo driver that will automatically bias the rudder trim depending on angle of attack and airspeed, but that will be a winter project.

In the meantime, I am assuming that there will be a fixed rudder tab for neutral trim in cruise, and the bias trim will accomodate changes due to airspeed and attitude. This allows lighter springs which should not affect ground handling much.

I promise that I will publish photos soon of the still-in-development setup, for those who are interested.

Vern

Good luck with the Rocket

I looked at a photo of Mark Manda's HR II I took at Taylor a couple of years ago to see if it has a balance rudder but it is out of the frame so I don't know. I suspect it will be an easier task if it is not a simple "flapper" back there.

Bob Axsom

vlittle said:

I have designed a rudder trim system for my HR-II that can be easily adapted to any RV. It uses bias springs, but is mounted aft of the baggage bulkhead, so it puts no force on the pedals, just the cables.

It uses a RAC servo for control.

I am also considering making a servo driver that will automatically bias the rudder trim depending on angle of attack and airspeed, but that will be a winter project.

In the meantime, I am assuming that there will be a fixed rudder tab for neutral trim in cruise, and the bias trim will accomodate changes due to airspeed and attitude. This allows lighter springs which should not affect ground handling much.

I promise that I will publish photos soon of the still-in-development setup, for those who are interested.

Vern

Click to expand...

Here are the pics. The right side has a fixed bias spring (no servo). Sorry for the poor quality. My Canon died right after these were shot. The cushion clamps have been replaced with cable clamps in the final installation.

Adjustment to spring tension is made by changing the position of the cable clamps.

No wedgie or electric rudder trim on Dave Anders RV4. All done with horizontal offset @ leading edge.