Vertical Stab offset

Hi guys

I'm in the process of mounting the vertical stabilizer on my Rv6. I built a rv7 tail for my six and was reading the plans which states to mount the VS at a slight offset with a washer at the back.

My RV6 plans say not to worry about it and just mount a trim tab later.

I just wanted to check seeing that I could go either way at this stage.

(need to order a new attach plate if I put it offset but no biggie)

AJ

AJ85WA said:

Hi guys

I'm in the process of mounting the vertical stabilizer on my Rv6. I built a rv7 tail for my six and was reading the plans which states to mount the VS at a slight offset with a washer at the back.

My RV6 plans say not to worry about it and just mount a trim tab later.

I just wanted to check seeing that I could go either way at this stage.

(need to order a new attach plate if I put it offset but no biggie)

Click to expand...

You can do it either way. My short tailed 6 required a tab. Used a taped on piece of wood wedge for a while. Personally, I don't mind the look of tabs at all.

I am building a short tail 6

I fit mine with a 3/16"-1/4" offset but its not flying yet.
I will report back, but I don't know when

Your Choice

Either way works fine. Remember if you offset the vertical, you will need to rework the fairing.
On the other hand, the fairing will probably need rework anyway.
Just something to think about.

1/4" on an RV7A, rudder is feet-off, no trim required. But then again, wheel pants will throw off the yaw trim.

Here's a curve ball question with respect to offset...

Last summer I built and installed an 8 VS and Rudder for my 6 (to add the counterbalance for some added safety margin for racing). When I installed the VS, I placed it with the leading edge in the same spot as the previous VS (minimal offset, if any).

Prior to the mod, coordinated flight required right rudder in climb and at slower speeds, no rudder in normal cruise, and a tad of left rudder at race speeds or relatively high speed descents...what I would consider pretty normal (or the porridge being just about right).

After the mod, I find I need more right rudder than before...in fact, it needs a bit of right rudder even at high speeds now. A bit surprising, given the taller tail and higher aspect ratio rudder (versus the 6 tail). Then again...what do I know?

I figure a trim tab would alleviate this, but I'm considering adding a touch of offset (and suffering the slings and arrows of fairing re-work). That is if its worth the effort to keep drag low (and salvage speed).

Double-checking here, but the direction of offset required is leading edge left (opposite the required rudder input)...correct?

Also, has it ever been shown that offset is less drag than a tab? Just wonderin'!

Currently being baffled by baffles (making an RV-10 baffle kit fit an S-6...good fun!), and will be researching the tail data after that job is done...but thought I'd take the shot and ask the question when I saw this thread! Thanks for any input!

Cheers,
Bob

Some thoughts

Our RV-6A is a short tail version with no offset. Without a tab of some sort it is a right rudder all the time airplane similar to Bob Mills' description of his super 6 after the RV-8 vertical stabilizer and rudder installation. My original solution was the after market plastic wedge. That worked fine but I didn't like the looks of it because of a flaw I induced by filleting the edges with microbaloon and epoxy. It looked great initially but after painting the epoxy seperated from the thin rudder skin around the entire perimeter. I fixed it with a bead of clear silicone sealing the resulting crack in the paint. As I modified the airplane for speed I observed that the wedge was no longer "perfect" for cruise and I had to start having a little right rudder pressure. I often thought about offsetting the leading edge of the vertical stabilizer to the left to build in a little right rudder. Because of some minor damage to the rudder in a ramp incident I had the opportunity to reskin the lower portion of the rudder and add a removable metal tab. Since that mod the ball is once again centered in cruise and it is ground adjustable if needed in the future to compensate for additional speed mods. With that tail configuration with my mod to cover all the access holes in the rudder with small metal plates I suspect the offsetting the leading edge of the vertical stabilizer left to induce a right yaw force might be a little less "draggy" than flying through the air with left tab to force the rudder right to force the tail of the airplane left and produce a feet off the pedals centered ball. It still crosses my mind from time to time like when I see you posting about it. Since I am a little in the "don't fix it if it ain't broke" camp (AKA lazy) I haven't even come close to starting that mod.

You may have read the thread with a similar theme concerning the horizontal stabilizer incidence change - raising the the leading edge to eliminate the cruise flight down elevator trim and its perceived drag effect on the RV-4's cruise speed. The trusted VAF aeronautical observation in that case stated that there would be essentially no effect on speed except some slight drag on the leading edge of the counterbalance horns that could be minimized by rounding them (which also minimizes the dynamic protion of the counterbalance). In a conflict of theory and experimental observation, our friend and current SARL RV Red speed record holder told me a few years ago when I told him I was considering that on our RV-6A, "that was the most effective speed mod I made on my RV-4."

My thought is the reduction in the need for offsetting the rudder by building in an offset of the vertical stabilizer to the left is more efficient in getting the required yaw force than flying with the rudder offset to the right and the drag in the case of a aerodynamic counterbalanced rudder off set for yaw is higher than a nonaerodynamic counterbalanced rudder off set to achieve the same yaw force. Maybe the fellow in texas that just bought a wind tunnel could run a test on that although at the scale he would have to run the test you might not see the difference.

Bob Axsom

I finished my -6A in 1999 and was mounting the fin in about 96. The user group at that time had a big discussion on offsetting the fin. I did a lot of thought about the issue and decided to do an offset. I took the number from the four or five persons who seemed to be the most knowledgeable (almost all of them had a different opinion) and averaged them. Unfortunately I didn't record the number, but is was something like 3/8 - 1/2".

Since Vans fiberglass parts delivered at that time were not of the best quality (understatement), I already had to rebuild the fairing.

What is amazing is that the ship flies straight with out a trim tab and the ball is dead centered at all airspeeds! However .....

After flying a couple of years, I started looking for more speed. I put a 1/8" shim under the front spar mount on the stab since I was flying with a fair amount of nose down trim at cruise speed with 2 persons and fuel . That gave me about 2-3 knots, an almost neutral trim and no noticeable change in flight characteristic.

I put a piece of tape on the rudder cable next to the pilots seat and measured the position of the rudder in cruise. I was flying with about 7 degrees of rudder. Essentially the rudder was deflecting due to the fin offset and the net result was a no yaw, but a bunch of drag.

I purchased a new fairing in preparation of removing the fin offset. Unfortunately, the story ends there because I got involved as the Crew Chief for Super Sports Air Racer, Bad Intentions. After that was over, we moved and built a new house at Independence Airpark (not completed yet, next month) and purchased a RV-10 kit.

So I can't say what the result would be of going from an offset fin to straight (yet)

Which way was the rudder offset?

I assume the vertical stabilizer (fin) is offset 3/8"-1/2" to the left (please confirm). Which way was the 7 degree rudder offset? I really want to get my head around your initial test results. When you are done we may have the only real comparable data. With your reference tape in place did you return the rudder to the straight alignment with the centerline of the vertical stabilizer? and if so what were the results? Do you have comparable speeds under those two conditions? From how I read your description I understand that the rudder 7 degrees out of alignment with the vertical stabilizer is the natural cruise flight position with no input from you - is that correct? If that is not correct can you give a little more description just to get me on the right track. THIS IS GOOD STUFF!!! One more question, is this a short tail 6 with no counterbalance (like mine - I assume it is because of the build date)?

2-3 kts sigh...

Bob Axsom

Rudder

I installed my 7 vertical stab with no offset, I was looking for more speed and thought this may help. What the offset does, is lets the rudder trail straight behind the stab,if you have no offset, you need to counter act that with more rudder deflection= more rudder to keep ball centered during flight which in turn equals large rudder tab. I am planning to reset my stab with offset and remove the large rudder tab needed to correct this.

Bob Axsom said:

I assume the vertical stabilizer (fin) is offset 3/8"-1/2" to the left (please confirm). Which way was the 7 degree rudder offset? I really want to get my head around your initial test results. When you are done we may have the only real comparable data. With your reference tape in place did you return the rudder to the straight alignment with the centerline of the vertical stabilizer? and if so what were the results? Do you have comparable speeds under those two conditions? From how I read your description I understand that the rudder 7 degrees out of alignment with the vertical stabilizer is the natural cruise flight position with no input from you - is that correct? If that is not correct can you give a little more description just to get me on the right track. THIS IS GOOD STUFF!!! One more question, is this a short tail 6 with no counterbalance (like mine - I assume it is because of the build date)?

2-3 kts sigh...

Bob Axsom

Click to expand...

I guess I don't know how to "Multiquote", but here goes

I am working from memory on a lot of this and it was at least 6 years ago, but I went out to the airplane just now (nice living in an Airpark!) and measured the actual fin offset. I did not remove the fairing so I may be a bit off. Appears to be offset 17/32 to the left as expected. A bit more than I remember, but the measurement could be off by an 1/8 or so.

It is raining today with low clouds or else I would go up and redo the flight measurements. It is very simple. I think the rudder was deflected to the right in trail. (does that make sense?? The more I think about it, the more I get confused!) I did return the rudder to neutral and it did take a lot of force and put the ball in the corner. Don't remember the change in airspeed, but it must have been significiant. I remember being shocked at how much rudder deflection I was flying with.

The kit was started in '95 and it is the original fin/rudder with no counterbalance.

The test is very easy to do and takes about 5 minutes to prep and a couple minutes once in the air. Just wrap a piece of tape around the rudder cable on the pilots side of the bulkhead at the spar. Make sure it is well attached (oil/grease may be on the cable). Have someone hold the rudder in neutral and measure the distance from the edge of the tape to the bulkhead. measure in the air (just put a touch of pressure on both rudder pedals to avoid any slack), then force the rudder back to neutral and check airspeed and ball.

On the ground have someone hold the rudder while you move it to inflight, trail position and measure deflection.

Exactly what you find on your airplane is critical

I understood the tape marker test method immediately when you mentioned it but I would probably never thought of it - very good method. I just got home from the hangar where I was working on the annual. I'm fixing some tomato soup and toasted cheese for dinner - got to watch the Gifted Man on TV then I'm going to get back on this. Thank you so much for the additional information.

Bob Axsom

bpattonsoa said:

I guess I don't know how to "Multiquote", but here goes

I am working from memory on a lot of this and it was at least 6 years ago, but I went out to the airplane just now (nice living in an Airpark!) and measured the actual fin offset. I did not remove the fairing so I may be a bit off. Appears to be offset 17/32 to the left as expected. A bit more than I remember, but the measurement could be off by an 1/8 or so.


It is raining today with low clouds or else I would go up and redo the flight measurements. It is very simple. I think the rudder was deflected to the right in trail. (does that make sense?? I don't knowThe more I think about it, the more I get confused!) I did return the rudder to neutral and it did take a lot of force and put the ball in the corner. Don't remember the change in airspeed, but it must have been significiant. I remember being shocked at how much rudder deflection I was flying with.

The kit was started in '95 and it is the original fin/rudder with no counterbalance.
The test is very easy to do and takes about 5 minutes to prep and a couple minutes once in the air. Just wrap a piece of tape around the rudder cable on the pilots side of the bulkhead at the spar. Make sure it is well attached (oil/grease may be on the cable). Have someone hold the rudder in neutral and measure the distance from the edge of the tape to the bulkhead. measure in the air (just put a touch of pressure on both rudder pedals to avoid any slack), then force the rudder back to neutral and check airspeed and ball.

On the ground have someone hold the rudder while you move it to inflight, trail position and measure deflection.

Click to expand...

My first rationalization for this was wrong - I have to think on it some more - interesting.


Bob Axsom

Bob Axsom said:

I understood the tape marker test method immediately when you mentioned it but I would probably never thought of it - very good method. I just got home from the hangar where I was working on the annual. I'm fixing some tomato soup and toasted cheese for dinner - got to watch the Gifted Man on TV then I'm going to get back on this. Thank you so much for the additional information.

Bob Axsom

Click to expand...

Hey Bob...when you toast your cheese, doesn't it gum up your toaster sump'n fierce?

OK, back to the great discussion! I also thought the tape on cable method to be pretty clever. Might even put another tape mark on the sidewall stiffener to make viewing/measuring it easier. Silly me, I've been looking in my mirrors to see how much counterbalance horn I see on each side (I need to mark those a different color too! ).

That counterbalance may be part of what slowed me down a couple knots when switching from the 6 tail to the 8 tail. It is sticking out a bit from what I can tell from the cockpit. I'm planning a glass cap height reduction experiment as well. It will be interesting to see if reducing the height of the tail will change the rudder-required characteristics in flight (if I can feel changes that small...it is somewhat subjective). Once that is done, then I may play with offset (so I can test one change at a time).

Bruce, that amount of offset sounds like a lot (but I don't know what I don't know on this topic). I've been contemplating trying with 1/4" to start and testing incremental changes to try to find that magic spot where its feet off in normal to near high speed cruise (as before) and looking for small speed increases hiding within. Fairing work for multiple small changes might be painful, but making a bit of room for the offset and covering it with speed tape may be the answer there.

What type of offset is called for (or used) by 8 drivers or 7 drivers reading this (and how are the results)?

Bruce, I would be very interested to see the results if you decide to take out some or all of that offset. Since its been there from the start, its hard to tell what its doing, and how it interacts with overall airframe "true-ness" (small differential horizontal stab or wing twist, control surface alignment, etc.) though it sounds like its working pretty well for cruising. Love to hear about it if you change it!

Very interesting topic of discussion! Thanks!

Cheers,
Bob

Well this has really got me hooked

Bruce, how was the 7 degree rudder deflection measured? I didn't get back to the hangar last night but when I get out there today I will measure the chord of the vertical stabilizer (VS) at the base and calculate its offset in degrees from the 17/32" measurement. I should measure the chord at the top of the VS, its height (front & rear) and the same four dimensions of the rudder and the length of the control horns.

Some questions:

(1) When you offset the leading edge of the VS to the left (the airplanes left) 17/32" the rudder I assume that the rudder hinge point is unchanged with respect to the fuselage. Is that correct? If not, please describe.

(2) If you re-fly the test at top speed cruise, could you determine the length of travel of the left rudder cable from ground neutral to flight neutral?

(3) If you re-fly the test at top speed cruise, could you determine the direction of travel of the left rudder cable from ground neutral to flight neutral?

(4) If you re-fly the test at top speed cruise, which rudder pedal has to be pressed to return the rudder to the ground neutral position?

In return as soon as I get our airplane annual finished I can fly the same test and provide you the information for an identical tailed RV-6A where there is no VS offset.

Bob Axsom

P.S. Bob Mills - It used to but Jeanine taught me to use the electric skillet.

rvmills said:

........What type of offset is called for (or used) by 8 drivers or 7 drivers reading this (and how are the results)?
.......Very interesting topic of discussion! Thanks!...

Click to expand...

Bob M, Aurora has the big -7 tail and is offset 1/4" per the plans.
Normal cruise 175kts TAS my feet can be on the floor. 178kts or so I can rest my left foot on the pedal to keep the ball centered. 180kts or so I put just a tiny pressure to keep things centered. and above 182kts, I have to watch the ball a little closer to ensure I have things dialed in. If I make make changes to pick up enough to put me over 190kts consistently I may look at installing rudder trim, as I think I let it wander a little.

Bob A, tomato soup and grilled cheese is one of my favorite winter lunches. I knew we had something in common.

rvmills said:

Bruce, that amount of offset sounds like a lot (but I don't know what I don't know on this topic). I've been contemplating trying with 1/4" to start and testing incremental changes to try to find that magic spot where its feet off in normal to near high speed cruise (as before) and looking for small speed increases hiding within. Fairing work for multiple small changes might be painful, but making a bit of room for the offset and covering it with speed tape may be the answer there.

What type of offset is called for (or used) by 8 drivers or 7 drivers reading this (and how are the results)?

Bruce, I would be very interested to see the results if you decide to take out some or all of that offset. Since its been there from the start, its hard to tell what its doing, and how it interacts with overall airframe "true-ness" (small differential horizontal stab or wing twist, control surface alignment, etc.) though it sounds like its working pretty well for cruising. Love to hear about it if you change it!

Very interesting topic of discussion! Thanks!

Cheers,
Bob

Click to expand...

I know the offset seems like a lot. It could be less because I didn't take off the fairing to measure it.

I was planning to do a test flight without the fairing to get a new baseline airspeed and see if it had any other bad effects. That way I could do a test flight at the new fin position and decide if I wanted to change it again. There probably is an offset the would produce the best cruise speed. Changing the offset is a matter of just changing one part, although it has a bunch of 1/8" rivets. I suspect flying without the tail fairing would be no issue.

I may remove the offset in the future, but for now we are moving into a house we have almost completed at the Independence airpark and have a new RV-10 kit in the new house/hanger waiting to get started.

My initial plan was to go back to no offset at all. Without a counterweighted rudder, the drag increase of a small trim tab would be small. I know for sure, based some on my experience with the Super Sports air racer that getting the trim tabs off of the aircraft (or at least neutral at high speed) is good for speed. There is potentially a major problem with this, however it does not apply to the rudder and ailerons.

If you adjust the incidence of the elevator it is only effective at producing zero trim forces at one combination of weight, C.G. and speed. Since all of those are constantly changing, the incidence is set at a compromise. I messed with my stab. incidence only after determining that I had a lot of trim in the same direction at several loadings.

Bob: The rudder hinge point is unchanged. Today is low clouds and rain, again, so data flight is put off again. I measured my in trail deflection by repositioning the cable to the flight position and then measuring. I am quoting the number from my memory, so it could be off some.

I agree, wrapping your mind around what the offset fin does to the rudder is mind warping. Are there any aerodynamic types out there following this thread with an idea? We could start a Poll!

Weather was better today so I reflew the test. Amazing how well the mind sometimes remembers some things and forgets others.

The rudder in trail was offset 6 degrees to the right, step on the left pedal to return to neutral. When doing so, the ball moved 3/4 to the right. Lost about 4 knots in speed.

The distance to my mark on the left rudder cable was 2 7/8" in neutral, 3 3/16" in trail with ball in center.

I think this means I have too much rudder offset. If I were to make a SWAG it would be offset the rudder about what the -7 has you do, or 1/4" and make it up with a trim tab.

Would be very interesting if others could do the test and report results.

I ran a test today also

I marked a piece of tape with long marks (1 inch) and short marks (1/4 inch) and attached it to the passenger side wall below the rudder cable so I could see it and I wrapped black electrical tape around the rudder cable with the leading edge in line with one of the 1 inch marks when the rudder was in line with the center line of my vertical stabilizer (VS). When in level cruise flight the tape was forward 1/4 inch from the brfore flight reference point (in line with the VS). When I went to max RPM (2710 today) the tape was another 1/4 inch forward (1/2" total). Our airplane has no VS offset (I rigged it carefully when we built it).

I also observed that there was no down elevator in cruise but in race configuration (which it is now) the wing span is 1.5 ft shorter than stock and the 3 inch tips are stream lined so the lifting wing span is effectively 2 ft shorter than a stock RV-6 wing. I was rushed by the fading daylight so the speed results are just what I got at 6000 ft pressure altitude - I don't know what the density altitude was - the speed was down to 181.8 kts (2 kts slower) even though I removed the tie down rings before the flight.

When I got back to the hangar I made some rough measurements but I haven't done anything with them yet. At the hinge line the VS is ~35" tall and the rudder is 53." The rudder width at the horn is 3.6" wide and the control horn cable attach point is 1.6" outboard of the rudder skin so the distance from the pivot point to the cable pull point is 3.4." The point where the cable attaches to the control horn is ~1.8" aft of the rudder hinge line (pivot point). The rudder chord is 11.5 " after the VS skin edge (some overlap) at the top and 21" at the bottom. The VS chord is 12" at the top and 27" at the bottom.

DARN! I didn't think to measure the trim tab - I'll go back to the airport and measure it now and report when I get back.

Bob Axsom

OK I'm back

The functional part of the trim tab (the part sticking out in the wind) is 7" tall and 1 3/8" wide. It is located 6 1/2" up from the bottom of the rudder and it is bent 3/8" to the left of the plane of the left side rudder skin (I couldn't come up with an accurate way to measure the deflection from the rudder center line tonight).

Bob Axsom

So in reading the last few posts, it looks like there are some commonalities (in a sense).

Observations:

Bob, your rudder cable travel was 1/4 to 1/2 inch from (ground neutral, or a ground-faired rudder).

Bruce, your travel from ground-faired was 5/16".

Bruce measured 6 degrees of rudder deflection in coordinated flight.

We don't yet have that deflection number for Bob.

Bob, if you can have someone measure the deflection of the rudder while you hold the rudder pedals in the various positions while on the ground, it would give a comparative angle of rudder deflection between you and Bruce (him with VS offset, you without, but with a tab).

To make the comparison a bit more valid, you guys should pick an airspeed that is as fast as possible, but one that you can both fly (Bob's is mighty fast!) and fly the test at similar speed and DA conditions.

I think the real comparison is how much rudder deflection is required for coordinated flight, with and without offset.

If there is a difference of a few degrees of rudder deflection with and without VS offset, then I'd like to ask guys like Steve Smith if they can comment on how much drag those few degrees might represent. I'd also like to ask about the drag tradeoffs between offsetting the VS 1/4" (or so), versus having to stick out the rudder 6 or so degrees. Then add to that last part, the drag penalty of adding a wedge or tab to hold that six degrees for you.

1/4" offset vs 6 degrees of unfaired rudder vs unfaired rudder plus trim tab...

Seems like small changes, but could they be a larger speed impact than those small dimensions might lead one to believe.

Then testing the theory by actually changing the offset and re-flying to test for rudder deflection requirements and top speed would be interesting to see.

I'm all apart for winter mods and repairs, or I'd join in. I need to decide whether to add some offset before I put 'er all back together, or to wait so I can do before and after tests.

Thanks for doing these tests...its neat information!

Cheers,
Bob

That is why I got the dimensions

We can calculate the deflection knowing the geometry of the system but I have an appointment in 50 minutes and I'm still in my pajamas. Got to run no breakfast today. I will do the calculations later.

One thing we don't know is, how elastic is the system?

Bob Axsom

At my kitchen table the rudder offset on straight VS

The rudder offset appears to be a little less than 7.5 degrees or 2.75 inches at the end of the widest point on the rudder. I will verify that when I get to the hangar a little later today.

Bob Axsom

Strange, the same in trail deflection as mine, yet no fin offset.

I will contact Steve Smith (have known him for a long time) and try to get him involved in this.

Confirmed

I went to the hangar and verified rudder deflection as stated earlier.

Bob Axsom

Don't confuse pressure and deflection

Hi all,

Bruce's idea to measure the rudder deflection in flight is a good one.

Be careful not to confuse the need for rudder pressure and rudder deflection.
It may well be that there is some pedal pressure required to hold the rudder at zero deflection, because it is at a slight angle of attack from prop swirl.

So, just because you need some pressure doesn't automatically mean you have drag.
If you do find that you have right rudder deflection, then you can probably reduce the drag a little bit by offsetting the fin leading edge to the left. A rough rule of thumb is that the needed incidence of the whole surface is about 1/3 of the equivalent rudder or elevator deflection. So, for example if your fin is rigged perfectly on airplane centerline, and you find that you are cruising with 6 degrees of rudder deflection, then you can probably zero that out by offsetting the fin 2 degrees to the left. This is a pretty rough wag, but it usually works pretty well.
Remember to reset your tape marks when you do this, because "in-trail" rudder will now also be 2 degrees deflection with respect to the fuselage.

With no counterweight, I would not have expected much drag change. But 7 degrees as you guys are talking about is a fair bit of deflection, so there may be some drag reduction to be had.

If you measure left rudder deflection in flight (relative to "in-trail", it means you have too much fin offset.

hope that helps a little.

BTW, my -8 is rigged with no offset, and flies pretty straight with only just light pressure on the right pedal at cruise. Slight left pedal needed during high-speed descending. I tried a wedge on the rudder, about 1 1/4 wide by 6" long. Then I cut it in half. Then I took it off. I guess it depends on how straight you really are trying to fly. My Horizon instrument with a ball is mounted at a very slight angle in the instrument panel, so sitting on the ground, the ball is not quite centered. Or maybe one gear leg is a hair longer than the other. Not much point in trying to center it when it doesn't center on the ground. I suppose I should fix that by leveling the wingtips on the ground and then getting the ball to center.

In My Case

I did not know what to expect before I ran my test. Thinking about it afterwards and having seen what took place it is easy to rationalize everything. I set up the tapes before flight and was careful to avoid parallax. I was up and cruising in level flight in the 170s with no rudder pressure and i looked at the tape and saw that it indicated the right rudder pedal had been moved forward 1/4" and the ball was centered with no feeling of pressure on either foot. Then I ran a three leg speed test, still with wide open throttle but the prop was pushed all the way in and yielded 2710 rpm. The speed leveled out at 185 kts GPS GS. As I am recording speeds every 20 sec. I checked the ball and it is still centered but the right rudder cable has now mover 1/2 " total in the right rudder direction and I still felt no rudder pressure.

Bob Axsom

rvmills said:

So in reading the last few posts, it looks like there are some commonalities (in a sense).

Observations:

Bob, your rudder cable travel was 1/4 to 1/2 inch from (ground neutral, or a ground-faired rudder).

Cheers,
Bob

Click to expand...

I put the piece of tan colored masking tape with 1/4" and 1" reference marks on the pasenger side wall then I got out and aligned the rudder with the centerline of the VS, then I got in and added a black piece of tape to the cable in line with the center inch marker in the 4" span of masking tape as viewed from the normal sitting position for me to avoid paralax errors, then I got out and verified that the rudder was still aligned with the centerline of the VS. (there is an army of 1 here you see)

The inflight observations shouldn't have been a surprise but they were. One should expect a right rudder deflection if you have a trim tab on the rudder offset to the left. I observed the cable position changed from the 1/4" cable travel in cruise from ground neutral to 1/2" from the same ground neutral position at top speed. Maybe what is not so intuitive is the increase in deflection at higher speed with the ball remaining centered with no sensory feedback to the pilot that the rudder deflection had increased. Pretty smooth.

Bob Axsom