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Autopilot servo location in RV-6

chriscencula

Active Member
I'm trying to decide how to mount the roll servo in my RV.

I've got both wings with top skins & inboard bottom skins attached.
Trying to decide between putting the servo in the wing VS fuselage...
TruTrak shows the servo mounted in the wing just outboard of the inspection hole (close to the next most outboard rib). The axis of (rotation of) the servo arm is perpendicular to the axis of the the bellcrank to which it attaches...

The Dynon install has the servo under the floor behind the spar...
I wonder in an *actual* installation whether there are likely interference issues with either installation... Dynon: with the servo pushrod and lightening holes, stick bottom and servo rod-end bearing etc? Tru-Trak: interference between mounting bracket and the servo pushrod?

Would be great to hear from others who have completed this installation, particularly if there are good pictures either 1) available -OR- 2) to be taken?
Especially helpful would be the ability to view/inspect any installations in Northern California... May be able to meet at Golden West fly-in if you're 'in the neighborhood' this coming Friday or Saturday?

Some considerations :
1) Access for inspection/maintenance
2) Ease of installation
3) Preferred alignment of servo axis w/bellcrank axis (if mounted near bellcrank)
4) Minimize 'couple' formed by rod-end coupling being off-axis from bellcrank or control stick (to extent possible)


Thanks,
Chris
 
When we added the roll servo to Louise's -6, we put it under the seat, and the only modification required was a slight enlargement to the hole through which the aileron pushrod exits the fuselage (just needed a little notch). Keeping it all in the fuselage made the wiring simple, and access is reasonable - we have removed the servo a couple of times to get at the output arm screw, and it only takes a couple of minutes to get it out.

I haven't done a wing installation yet, so can't give you a direct comparison.

Paul
 
Hi Paul,

Thanks for the reply...
A couple of additional questions:
1) Is the 'floor' in the area 'made' to be removable per Van's standard plans, or is this an 'extra feature' that was added to your plane for access to the servo etc?
2) Were there any other 'very close' clearance issues with moving parts pertaining to the servo installation?

Thanks,
Chris
 
Yes, that portion of the floor is removable - it is basically the seat pan, and how you get at the stick/aileron pushrods.

Placement is important to avoid interference when the stick and servo pushrods move full travel, but it is a no-brainer to find the "right" location. Everything is tight in a small airplane like this, so this is nothing unusual.

Paul
 
Paul, Mel mounted his servo under the right seat, and connected the rod to the base of the stick. Could you draw us a better picture of how you did it? Thanks......... Warren
 
I had mine mounted in my 6.......

under the seat, but moved it to the last bay in the left wing. The way the servo pushrod was angled to the stick under the seat, I felt like it would always be controling roll while biasing the pitch. This would lead to the pitch always seeking. Since moving it to the wing, the roll pushes straight on the aileron bellcrank, with no bias on the pitch. Very eash to get to with left tip off. Works well, your results may vary.
 
seat install second

You can print up the instructions for the under seat install from the Dynon web site. It's well documented with good 3views. My install was uneventfull with just a little triming for clearance.
 
Here's my TruTrak autopilot roll servo installation from last year :D Rosie

Autopilot_roll_01.jpg


Autopilot_roll_02.jpg
 
I should add to the thread.

Put over 3000 hours on yours and see how it looks!
Ha!

Mine was located under the right seat, simply to put as much weight as possible on that side since I fly solo and my airplane is trimmed nuetral. I never found a good way to install the manual aileron trim with the servo connections. Perhaps others have.
For those that say you dont need it with an A/P, I found I flew more without my A/P on than off. There was also a subtle but noticeable adjustment when on A/P and the airplane was not in trim.
 
I put mine

Out in the R wingtip anchored to the last rib, fabbed up the pushrod. Easy to get at to inspect. Why? because I hate to pull the floorboards and it just didn't seem to fit right down there anyway...


.
 
You have to pull them anyway

Out in the R wingtip anchored to the last rib, fabbed up the pushrod. Easy to get at to inspect. Why? because I hate to pull the floorboards and it just didn't seem to fit right down there anyway...


.

at every condition inspection. I have never pulled a wing tip and cant imagine it being easier than floor boards, but hey, to each his own and I have seen both places, as noted, work.
 
Thanks for all the replies, especially the ones with photos :)...

Also just looked at the thread on aileron rigging... Sure wish I had seen some of that info before 'following the plans'... The exit hole for the aileron pushrod on one of my wings is too big... having wrong information on the plans is worse than no information at all!

Hope to hear from some others on their choice of roll servo location & their thoughts on the merits/limitations of the various choices.

Will be at Golden West fly-in Saturday 6/11 (tomorrow), maybe I'll have a chance to talk to some RV-6 builders on this topic?

Thanks,
Chris
 
Thanks for all the replies, especially the ones with photos :)...

Also just looked at the thread on aileron rigging... Sure wish I had seen some of that info before 'following the plans'... The exit hole for the aileron pushrod on one of my wings is too big... having wrong information on the plans is worse than no information at all!

Hope to hear from some others on their choice of roll servo location & their thoughts on the merits/limitations of the various choices.

Will be at Golden West fly-in Saturday 6/11 (tomorrow), maybe I'll have a chance to talk to some RV-6 builders on this topic?

Thanks,
Chris

Some thoughts that would apply to any brand of servo:

http://thervjournal.com/navaid.html
 
Aileron Servo

I would say you are commited to install the servo in the fuselage as your access to install it in the wing is really limited with the skin installed.
It would be more accessable in the fuselage and you could use both hands as the wing mount is a one handed operation through the insp. opening
Walt RV-6A
IO-320 waiting on final insp.
 
Hello 'Rusty screw'... I have not yet installed the lower outboard wing skin, so still have decent access to the bay where the bellcrank is...
Does that change your response?

Thanks,
Chris
 
Hello 'Rusty screw'... I have not yet installed the lower outboard wing skin, so still have decent access to the bay where the bellcrank is...
Does that change your response?

Thanks,
Chris

I installed the servo mid-wing in my RV-6 before the bottom skin was installed. I had to remove the servo for adjustments after the plane was flying and it barely fit through the inspection hole. That location is so tight I would not install a servo there in an RV-6 because future access is difficult. I suggest either a cockpit or wingtip installation in an RV-6(A).
 
Hi Sam,

Thanks for the feedback... That's one more vote against putting it near the aileron bellcrank...

Anyone else?

Thanks,
Chris
 
Sam's thread looks like a simple and easily maintained system, way out there in the wing tip! Will you look at pitch control as well? Would that be located close to the elevator bellcrank in the mid fuselage?

Patrick
 
Sam's thread looks like a simple and easily maintained system, way out there in the wing tip! Will you look at pitch control as well? Would that be located close to the elevator bellcrank in the mid fuselage?

My 6A's pitch (TruTrak) servo is located behind the baggage bulkhead near the elevator bellcrank, where so many others are installed. It was added after the airplane was built. I also have a Trio A/P servo in the wingtip, as it was installed after the wings were complete.

L.Adamson --- RV6A
 
Thanks for the other replies on servo mounting...
I've been out of reach for a while due to work obligations...

Sounds like quite a few have put servos @ the wingtip location...
I really like the access in the wing tip, but don't like the addition of a long pushrod (in addition to the one connected to the pilot's controls).

Look forward to more feedback (and checking the pictures of those recently posted... can't check pictures well at the moment).

Thanks,
Chris
 
Thanks for the other replies on servo mounting...
I've been out of reach for a while due to work obligations...

Sounds like quite a few have put servos @ the wingtip location...
I really like the access in the wing tip, but don't like the addition of a long pushrod (in addition to the one connected to the pilot's controls).

Look forward to more feedback (and checking the pictures of those recently posted... can't check pictures well at the moment).

Thanks,
Chris

No downside to the "long pushrod" has been found in the wingtip installations. The servo works perfectly in this location.

Some builders have added a support for the pushrod so it can't interfere with the bellcrank if the connection at the servo comes undone. But this should be the case with any servo installation.
 
Chris,

Sorry to take so long to jump in...been running a bit and wanted to take another picture. I put my Dynon SV-32 roll servo in the fuselage...outer left bay, as Paul did in Mikey. No reason at that time other than it was per the Dynon instructions. I'm sure Sam's and others' wing installs are fine, but I'll pass some of the things I learned along the way, when installing into a bought-flying aircraft, with lotsa stuff in that bay to work around.

I would try to get the servo as far aft in the bay towards the spar as possible...or at the very least, make sure you test the space between the aileron push tube and servo rod end (at the servo arm) in the bracket position you want...before you drill the bracket holes in the fuselage. The closest point of approach between the two happens at full fwd, full left stick, as shown in this picture (its close to full throw in this pic anyway):

rollservo1.jpg


Due to the plastic snap bushing where the wires penetrate to the left of the pic, I needed to trim the bracket a bit (you can see the left side of the bracket curves around the bushing). As it turned out, I have good clearance from the push tube, but without the wires and the bushing, I could have gone aft another 1/4", and the clearance would be just a bit better. Not sure if there is any coupling due to the slight forward angle of the servo push rod as was mentioned earler. I've had pitch oscillations at times, but it does not correspond to a roll input (that I can tell). Pitch issues are intermittant, and seem more associated with the AP chasing than the roll servo coupling (IMHO). Roll has been pretty nice...as long as my ailerons are in trim! ;)

At the other end of the aileron throw, the same rod-end was contacting the side skin at the aileron push-tube hole edge, so I also cut a little notch in the hole edge to allow for clearance. Not sure if its the same as Paul did, but it's as shown here:

rollservo2.jpg


The fore-aft orientation of the bolt in the rod end bearing was necessary to clear the aileron push rod at the other end of the throw, so the nut had to go on the back, which made the notch necessary. On the pitch servo, the bolt is the other way around, so the shoulder of the bolt is riding in the servo arm (it was the other way 'round, til Dan H and Mike S pointed that out in a post after the install two summers ago). Couldn't do that on the roll servo, due to the geometry, but (as Dan and Mike also said), its a small enough bolt and small enough forces that the stress on the servo arm bolt should be minimal.

The servo looks a little cocked in these photos, but its the angle of the pics...it's in line with the ribs.

After the install, I decided to make a little viewing/inspection panel so I could check that it was staying together well and maintaning the clearances. Probably more of a distrust of my work...the panel/AP was my first big project on the plane. I just cut a small rectangle out of the floor, made a plexi overlay, and used four of the existing floor nutplates to mount screws and tinnerman washers to hold it in place (the two left screws are hidden under my velcro-in side panels):

servowindow.jpg


Probably overkill, but I can always make a quick check from time to time. Of course, I do pull the floor up on condition inspections...and I've had the floor up more than I care to admit, due to radio and antenna work.

Speaking of antennae...you'll see that I have a comm antenna in the bay just to the right of the servo. During the panel upgrade, I moved it there from the center of the fuse at the same station line. I then put a TED antenna in the middle for my Monroy, then put comm 2 on the opposite side, in the same bay (second from right). Turns out that puts the comm 1 & 2 only 27" apart (rather than the 36" recommendation) and I have bleed over into comm 1 from my comm 2 or my APRS when I run them on that comm 2 antenna. I only described this, so you can plan around that. Your antennas may be in different locations already, but if you were thinking about doing them in those bays, I just wanted to pass along my results, likely from being too close together.

Overall, its easy to get to (floor pan screws notwithstanding), a bit tight to get in and out, but not bad really, and the wiring was perhaps made simpler by being in the cockpit. I don't feel qualified to recommend one location over the other, but just wanted to pass on a few tidbits to add to your database! :)

Have fun and good luck!!

Cheers,
Bob
 
Last edited:
Fuselage Instalation

My TruTrak roll servo is located under the seat pan on the left side very similar to Bob Mills' installation. I have full access and it is completely visible during annual condition inspection. I lubricate all of the control rod end bearings and visually inspect this each year. I installed the system after I had been flying the plane for over a year and it functions perfectly. Replacement, removal and service would be easy. It is so near the aircraft center line that there is no noticeable effect on roll from the off center weight placement.

Bob Axsom
 
Thank you to both 'Bobs', especially the one with the pictures!
I'm waiting to catch a flight right now back to California (Via ORD).

Maybe I can check out Bob Mills install some time when I'm in Reno/Sparks?

I haven't been 'over there' in quite a few months and owe a visit to the 'parental units'... Maybe I can check out your plane while there?

Thanks,
Chris
 
Servo Installation

Recently completed a Trio installation with the roll servo in the right wing, last outboard rib. Working thru the removable fiberglass wing tip was very easy and there are some excellant instructions and photos in the Trio installation manual. There are no clearance issues and the simple bell crank attachment was no problem. This was my first auto-pilot install and the installation and set up was a piece of cake. Auto-pilot works flawlessly, Bob.
 
Thank you to both 'Bobs', especially the one with the pictures!
I'm waiting to catch a flight right now back to California (Via ORD).

Maybe I can check out Bob Mills install some time when I'm in Reno/Sparks?

I haven't been 'over there' in quite a few months and owe a visit to the 'parental units'... Maybe I can check out your plane while there?

Thanks,
Chris

Chris, just saw this post. You're absolutely welcome any time! PM me or call 7755443511 if you're ever headed this way or are in town!

Cheers,
Bob
 
I retrofitted a servo in the aileron bellcrank area in the wing of my completed RV-6. It was a little bit of a pain to do but certainly doable, and it works great there. Would be an easy install if the bottom skins are not yet riveted.

No long pushrod...easy access...no possibility of elevator coupling, and no interference issues with manual trim.
 
Hi Bob (Mills),

Sorry I didn't check this site while just over in Spanish Springs...
Was over there this past weekend to visit with relatives (one that drove from the Midwest!)...

I'll try to remember to get in touch with you next time I'm coming your way...

I'm sure my dad would also enjoy seeing your plane... They live not too far from Spanish Springs airport where I *think* there at least a couple of RVs...
Was going to drop over there this morning before returning to CA, but decided to just head straight back to beat the weekend return flow (traffic... wouldn't be an issue with the RV6A finished!)

Best regards,
Chris Cencula
 
Hi Bob (Japundza),

I took advantage of the help I had in the form of a visit to by my parents over the holiday weekend and finished the install of the bottom outboard skins on both wings... In the sake of 'progress at present' I decided to close the wings... Hope I don't regret that later... Probably not, since there seem to be at least two (and three, by your example) remaining alternatives.

Can you describe how you installed the servo (and what type) in a completed RV6 wing? How about pictures? If you did anything 'custom' (as opposed to per Dynon/Truetrak recommendations), would it be possible to get some pictures or other details?

Thanks,
Chris
 
Chris,

Any time. Sorry we missed each other. I had the floor up for maintenance till Saturday too. I live in Sparks/Spanish Springs, just a few miles from N86 (Sp Spgs AP). Not sure how many RVs (if any) are there...might be, and I know Max the AP manager there, but its still dirt, so I'm up at Stead...and there are loads of RVs there. Happy to have you and/or your Dad visit any time!

Cheers,
Bob

Hi Bob (Mills),

Sorry I didn't check this site while just over in Spanish Springs...
Was over there this past weekend to visit with relatives (one that drove from the Midwest!)...

I'll try to remember to get in touch with you next time I'm coming your way...

I'm sure my dad would also enjoy seeing your plane... They live not too far from Spanish Springs airport where I *think* there at least a couple of RVs...
Was going to drop over there this morning before returning to CA, but decided to just head straight back to beat the weekend return flow (traffic... wouldn't be an issue with the RV6A finished!)

Best regards,
Chris Cencula
 
RV-6 Roll Servo Installation Questions

I am preparing to install GRT roll and pitch servo's, and GRT does not supply any installation guidance. I looked at the Trutrak installation drawings and have a couple questions for those who have installed the roll servo in the fuselage under the seat....


Did you install a strengthening plate on the bottom (under) side of the fuselage belly skin like shown in the Trutrak drawings?


Also, I test fit the roll servo bracket in the fuse, and it lays right on top of the rib flange and rivets. Should I put a spacer sheet between the roll servo bracket and the belly skin to raise the roll servo bracket up off of the rib flange?


Thank you!
 
Jim, I just finished a a Trutrak install, wth the roll servo under the left seat. Pretty easy to get to and to inspect on annual. My ribs were a tad closer together that spec so I installed an 032 AL shim under the servo bracket to level things out - sounds like same issue you have. Trutrak supplies a doubler plate for the outside of the belly skin.

All fits well, no interference with manual aileron trim, and first two flights have gone well. Be careful with setback from front spar to servo bracket, if too far forward servo arm bolt will contact aileron pushrod at full forward stick, too far aft and servo pushrod contacts aft edge of rib lightening hole. Just measure carefully :)
 
Jim

I installed min a couple of months ago. Due to some preexisting antennas I mounted mine on the copilot side, in the last "bay" as far back as I could get it. It fit between the ribs flat on the belly skin. I did install the provided plate on the outside of the skin as directed. It will likely oil can too much without it.

I did have to relieve the holes in the ribs slightly to prevent fouling of the control arm. I'll look and see if I have any pics.
 
Thank you,

Jim, I just finished a a Trutrak install, wth the roll servo under the left seat. Pretty easy to get to and to inspect on annual. My ribs were a tad closer together that spec so I installed an 032 AL shim under the servo bracket to level things out - sounds like same issue you have. Trutrak supplies a doubler plate for the outside of the belly skin.

All fits well, no interference with manual aileron trim, and first two flights have gone well. Be careful with setback from front spar to servo bracket, if too far forward servo arm bolt will contact aileron pushrod at full forward stick, too far aft and servo pushrod contacts aft edge of rib lightening hole. Just measure carefully :)

Thanks for the replies!

Yes, I believe my ribs must be a bit closer than spec as well. I think I will plan to use a shim underneath just like you did. My servos came from GRT, and they did not supply a doubler plate for the belly skin. I am thinking a hunk of .040 AL should work. Does that sound about right?

Thank you
 
Jim, .040 sounds about right for that exterior doubler. As mentioned, for the shim inside, to bring the mounting surface up level with the rib flange, I think I used .032 (whatever the rib material thickness is, I know I easily found some scrap in the bin of the same thickness).
 
Trutrak servos come with installation diagrams for the -6 which puts the servo under the seat. The install according to their diagrams is straight forward. Move the servo as far forward as it will naturally go without interfering with the pushrod. The pictures above look like my installation.
There is a reinforcing plate that I used under the servo.
 
RV-6 roll pilot roll servo location.

Bear in mind that the RV-6 aileron bellcrank is mounted on a wing rib and not on the spar as in later RV?s. The rib location is not as strong. Early -6?s experienced some cracking of the wing skin where there is a stiffener connecting the rib with the bellcrank to the upper wing skin. The same is true of the RV-4 I built. I mounted the servo under the seat.
 
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