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Autopilot servo mounting locations

F

Flying Scotsman

Well Known Member
Well, the empennage is completed except for one more leading edge bending (rudder...waiting for a second set of hands to help out, expect to complete it this weekend and put everything together! Woohoo!)...and the wing kit is scheduled to ship next week if Van's holds to their original scheduled date. Can't wait!

But that brings me to the first question we've been pondering re: wings. I intend to put an autopilot in this plane, since I expect to use it for IFR flight. Thus, I need some suggestions on where to mount servos. Our thoughts are to build a kind of "adapter plate" that mounts on the wing spar next to the bellcrank, but I know some people have mounted servos in the fuselage. Any ideas/suggestions/comments, especially since we're planning on choosing/installing avionics as late as possible (and hence, have no specific autopilot picked out yet)?

Thanks for any help...

Steve
 
TruTrak has an installation kit for the -7. It has a bracket that replaces one of the bellcrank brackets in the wing.

Hope this helps.
 
But that brings me to the first question we've been pondering re: wings. I intend to put an autopilot in this plane, since I expect to use it for IFR flight. Thus, I need some suggestions on where to mount servos. Our thoughts are to build a kind of "adapter plate" that mounts on the wing spar next to the bellcrank, but I know some people have mounted servos in the fuselage. Any ideas/suggestions/comments, especially since we're planning on choosing/installing avionics as late as possible (and hence, have no specific autopilot picked out yet)?
Click to expand...

Another option is mounting the servo near the end of the wing where it can be accessed by removing the wingtip. This is a good alternative if you want to wait until you actually need the system before making a purchasing decision.
 
I am nearing completion of my wings and have just started to consider a two axis autopilot (learning heavily towards the Tru Trak ADI II). For it, the wing servo mounts in the right wing and ties directly in with the bellcrack assembly. My main debate with myself is do I go on and get the servo now and mount it, or just make provisions for the wiring and keep my money for a few more months? I do suggest you decide which AP you are going to use and then decide how to mount the associated servos. The TT servos seem pretty easy in the RVs, even if you wait until after you have the wings closed out (provided you have a way to run the wires), but other servos from toehr suppliers may be different.
 
Debate option #2

Jeff R said:
My main debate with myself is do I go on and get the servo now and mount it, or just make provisions for the wiring and keep my money for a few more months?
Click to expand...

Jeff, I'm installing an ADI II and just received the servos and head. My suggestion. (FWIW) Call TruTrak and order just the mounting brackets. They were $50 about 6 months ago when I got mine. They'll deduct the price from your A/P order later when your ready to shell out the big bucks... and you can get the tough stuff installed now while you have good access.
 
Caveman, I did talk to Tru Trak and they said that their distributors often had cheaper prices. I called up Stein Air and, indeed, their total price on buying the servos and the instrument itself was about $50 less. I got the definite impression that Tru Trak prefers people buy through a distributor. Thanks for the suggestion of just buying the bracket - that might be a good compromise.
 
Sam Buchanan said:
Another option is mounting the servo near the end of the wing where it can be accessed by removing the wingtip. This is a good alternative if you want to wait until you actually need the system before making a purchasing decision.
Click to expand...

This sounds like perhaps the best option, as the plan (as any good project manager knows :) ) is to delay any decisions/purchases related to avionics as long as possible (lower prices, more capability and more vendor options as time progresses).

Any gotchas or advice if we choose to go this route?
 
Flying Scotsman said:
This sounds like perhaps the best option, as the plan (as any good project manager knows :) ) is to delay any decisions/purchases related to avionics as long as possible (lower prices, more capability and more vendor options as time progresses).

Any gotchas or advice if we choose to go this route?
Click to expand...

Steve, this really is a straightforward installation and you shouldn't have any problems. There are various ways to mount the servo but the tip rib and spar provide several options for mounting--just go with what you are comfortable with. Here is an example of a wing-tip installation:

http://thervjournal.com/navaid.html

Only gotcha is the same as with any servo installation; make sure the servo arm can't go over center and that there is no way for the aileron bellcrank to get fouled. Some have expressed some concern about a control jam if the pushrod came loose but this would be a problem with any servo. You might consider some sort of simple guide/hanger for the pushrod (maybe located on the next to last rib?) that would keep the rod out of harms way in case of a hardware failure. Make sure you leave sufficient room in your wiring conduit for the servo cable.
 
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I just finished installing a Trio 2 axis on a flying rv-6. It was very easy, Safeair1 makes an install kit for the wingtip install (a little different than Sam's mount), and I also purchased the harness from Stein. It was a breeze.

I would wait until needed, just make sure you provide a conduit out to the wingtip for the wiring.
 
buz said:
I just finished installing a Trio 2 axis on a flying rv-6. It was very easy, Safeair1 makes an install kit for the wingtip install (a little different than Sam's mount), and I also purchased the harness from Stein. It was a breeze.
Click to expand...

The mount in my article was sorta a prototype since we had never seen a wingtip installation before. There are several ways to mount the servo on either the tip rib or the end of the spar just inside the rib. As long as the servo is secure and can't jam anything it should be a safe installation.

Glad to hear Safeair is offering a wingtip mount. I still think this is a great place to put a Navaid or Trio servo since they are lightweight.
 
Question About Trio Servo Mounting

I kind of had the same question about the Trio A/P servo. I tried (unsuccessfully) elsewhere to get a response to this question:

Does anyone see a problem with mounting the Trio A/P servo to the web of the wing spar using nutplates installed on the forward face of the web?

This would be an installation in the bay just outboard of where the aileron belcrank is located. I have verified that I could remove the servo should it require service.

I personally don't see an issue unless there is a metal fatigue factor to consider. I just dont see the rib as being an ideal location even when reinforced. There are two ligtening holes in the bay outboard of my proposed location and the reinforcement fork for the main wing spar does extend to my proposed location.

The A/P servo istelf looks like it has #6 screws so there would be 4 holes plus the additional 8 - #40 holes for the nutplates. That is a total of 12 holes in the spar web.

I was pretty disappointed with the response from Van's as they pretty much avoided answering the question altogether and kept telling me about the TruTrak installation.

I'm not trying to hijack the thread, I figured this would have been the right one to ask it in.
 
ShookieRV7A said:
I kind of had the same question about the Trio A/P servo. I tried (unsuccessfully) elsewhere to get a response to this question:

Does anyone see a problem with mounting the Trio A/P servo to the web of the wing spar using nutplates installed on the forward face of the web?

This would be an installation in the bay just outboard of where the aileron belcrank is located. I have verified that I could remove the servo should it require service.
Click to expand...

I've seen the servo mounted to the web at the wing tip but not at midwing. Even though I wouldn't hesitate to use the web at the outboard end of the wing, and drilling into the web at midwing shouldn't create structural issues, like Vans I'd be reluctant to do that on my plane. Why not put the servo at the tip of the wing?
 
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Clear as mud... :)

Thanks for the response. In my limited experience, I would have thought that the rib mounted option I have seen pictures of would be less structurally sound than mounting it on the spar web.

I figured the thicker material on the spar web would have been a better option. I have looked at the rib mounted SafeAir1 kit. Again, another rib mounted installation, only this one makes use of a much longer control rod.

I am utterly confused. Rib mounting over using the spar goes against what I had thought would have been a convention of - mount it to the thicker material.
 
ShookieRV7A said:
Thanks for the response. In my limited experience, I would have thought that the rib mounted option I have seen pictures of would be less structurally sound than mounting it on the spar web.

I figured the thicker material on the spar web would have been a better option. I have looked at the rib mounted SafeAir1 kit. Again, another rib mounted installation, only this one makes use of a much longer control rod.

I am utterly confused. Rib mounting over using the spar goes against what I had thought would have been a convention of - mount it to the thicker material.
Click to expand...

Scott, the SafeAir kit provides plenty of rigidity, and the pushrod is plenty stiff/strong.

The wingtip location works great. :)

Many servos in years past were mounted under the seat and attached to........a rib!

Keep in mind the servo is only going to be moving the trailing edge of the aileron less than 1/4". The servo control movements on an RV are miniscule for proper control in cruise. When the autopilot is disengaged, and control movements might be larger, rigidity is a non-issue since the servo isn't being driven by the pushrod. The Trio servo completely disengages the geartrain when unactivated.
 
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