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Changing to manual trim?

A

alpinelakespilot2000

Well Known Member
I've already built my -9 empennage with electric trim. After visiting Van's last week to pick up my fuse. kit, I had a chance to sit in the -9 with manual trim and kind of like it.

I can't remember, but have I already made a choice that has committed me to electric (like did I not drill a hole somewhere in a spar or rib or the HS or left elevator somewhere that I needed to for manual trim) or would it be not too much effort to install a manual trim in my completed emp? I have not yet started the fuse. so there would be no issue there. I really like "simplicity," so that is driving my decision. It's not a "performance" issue of electric vs. manual.

I'm thinking I could sell my electric trim and not come out at too much of a loss.

Thanks for your thoughts,
Steve
 
I've also been seriously re-thinking my choice of electric trim after sketching out the wiring needed. If one of the coolie hat wires in the stick accidentally shorts to ground, the trim will travel uncommanded right to the stop. Not good. You can't beat manual for simplicity and safety. It's accessible from both seats, doesn't need wiring, and is cheaper.

On a -7 one would need to drill a couple of holes in the HS (which most people with electric do anyway to run wiring) and I think change out the access panel on the elevator for the manual variety. Not sure if that applies to the -9 as well.
 
What about the counterbalance weight... is that a factor? Just food for thought, I don't know.
 
manual trim

The manual trim is simple, responsive and easy to use. If you are still building all you need is the holes drilled for routing the cable, the cable and one fitting for the access plate. The locations are called out on the plans, can't remember the number. I have an extra fitting. I don't even know how I ended up with two. If you decide to go manual and need the fitting (probably under $7 bucks) you can have my extra one for free. Jack

p.s. - counterbalance weight is no factor.
 
Im thinking of manual trim also. Can someone tell me does the trim knob have any position indicator on/in it? or is it just a matter of checking the tab on pre-flight ?
 
Build9A said:
If you are still building all you need is the holes drilled for routing the cable, the cable and one fitting for the access plate. .
Click to expand...
Thanks Jack, I guess that's what I'm asking. I did not drill any extra holes in my HS or elevator. Did I need to if I want to use manual trim? If so, where? I'll go back through my instructions or plans tonight to try to figure it out, but was just curious if anyone had in fact done this retrofit.

Thanks again.
 
I'm also debating Electronic Trim vs Manual Trim and the question for me is: When you install an autopilot does it/can it use the Electronic Trim's servos or do you have to install new servos either way?

If you have to install new servos for an autopilot regardless, there's certainly no reason to go with the electric trim!
 
Last edited:
ccrawford said:
I'm also debating Electronic Trim vs Manual Trim and the question for me is: When you install an autopilot does it/can it use the Electronic Trim's servos or do you have to install new servos either way?
Click to expand...

The autopilot needs its own servos.
 
Trim & A/P

ccrawford said:
I'm also debating Electronic Trim vs Manual Trim and the question for me is: When you install an autopilot does it/can it use the Electronic Trim's servos or do you have to install new servos either way?

If you have to install new servos for an autopilot regardless, there's certainly no reason to go with the manual trim!
Click to expand...

The autopilot servos act directly on the control horn in the fuselage - no trim involved. In fact you have to keep the a/c in trim to keep the elevator force below the breakaway force in the a/p servo clutch. You can (for more $$) get the a/p to tell you when re-trimming is needed.

Dennis Glaeser
7A Wings (I'm using electric trim)
 
Steve....

I recall there being a factory hole in the front spar of the HS that you need to enlarge to a specific size for using the manual trim. It is on the HS drawing. I know you can go back anytime and drill it out, because I haven't drilled mine out yet (and I have planned for manual trim from day one). It calls for an odd sized hole, and out of my hundreds of drill bits I didn't have that specific size. Therefore, I just figured I would drill it later.

From my interpretation of the -9 drawings, it shouldn't be an issue at all. Check the drawing that deals with the HS (sorry, I don't have the exact dwg number handy).

Take care,
 
DGlaeser said:
The autopilot servos act directly on the control horn in the fuselage - no trim involved. In fact you have to keep the a/c in trim to keep the elevator force below the breakaway force in the a/p servo clutch. You can (for more $$) get the a/p to tell you when re-trimming is needed.
Click to expand...

Interesting. In the Cessna 172SPs I fly it seems like the autopilot uses the trim? Whenever the the autopilot adjusts the elevator to maintain altitude or to a stop a decent/ascent you can watch the manual trim wheel turn as it adjusts. The 172s also have electric trim but I think that's only for roll.

Maybe this is a special setup with the KAP-140 AP in a Cessna; since I've never flown anything else I don't have much to compare against. :D
 
txaviator said:
I recall there being a factory hole in the front spar of the HS that you need to enlarge to a specific size for using the manual trim. It is on the HS drawing. I know you can go back anytime and drill it out, because I haven't drilled mine out yet (and I have planned for manual trim from day one). It calls for an odd sized hole, and out of my hundreds of drill bits I didn't have that specific size. Therefore, I just figured I would drill it later.

From my interpretation of the -9 drawings, it shouldn't be an issue at all. Check the drawing that deals with the HS (sorry, I don't have the exact dwg number handy).

Take care,
Click to expand...

Thanks Gary. I seem to remember that same hole, but last night looked in my preview plans for that hole and didn't see it. Maybe it's only on the full size plans? I'll go back and dig out the full size ones and take a look tonight. I assume the hole would have to be on the rear spar somewhere if it is "easy" to drill out later? BTW--got a few good pictures of Van's 9 last week. Have you seen it yet? Pretty cool. And simple.
 
Steve,

It is on the full-size plans for sure. I just checked it out. Look on DWG 3, detail A-A (upper left section of the print. You drill out the spar doubler to a 5/8" hole. You can still get to the spar doubler of course, very easily at this point. Hope this helps?

Also, yes, I have seen the -9 at Van's on a number of different occasions. You are right, it is fairly simplistic, and very nice! I can't wait to be at that point! My building is about to go full steam ahead, once this degree is completed. It is killing me having SB wings sitting here in crates, and I haven't done a thing with them in 3-4 months!
 
Trim position indicator - NOT NECESSARY

Jamie Aust said:
Im thinking of manual trim also. Can someone tell me does the trim knob have any position indicator on/in it? or is it just a matter of checking the tab on pre-flight ?
Click to expand...
The first time I tookoff I set the elevator trim tab at zero (flat - level) and adjusted the pitch trim to take the control pressure off as I climbed out (more nose up was needed). Now when I land I crank in the nose up required for a nice stable approach at about 85 kts then as I approach the flare I dial in a little more nose up on short final so the flare is a soft stick movement to hold the nose off and make a soft touch down on the mains that is easy to balance without musscle-ing through the transition. This leaves the elevator trim about where it needs to be for takeoff - I usually dial out a little of the nose up trim after takeoff to get it climbing at 85-90 kts without any control pressure from me. It has the feel of dialing a micrometer - it is sweet indeed.

Bob Axsom RV-6A
 
Trim tab control cable connection.

No one in this thread mentioned the different shape of the two angles riveted to the trim tab where the control cable clevis attaches. It has a different shape for the trim servo compared to the point it attaches for the trim cable. You can see a picture of the clevis connected to the trim tab at the bottom of the page using this link to my web site:

http://www.n2prise.org/rv9a127.htm#May16

Jerry K. Thorne
East Ridge, TN
RV-9A 90622
N2PZ 124.6 Hobbs hours
www.n2prise.org
 
n2prise said:
No one in this thread mentioned the different shape of the two angles riveted to the trim tab where the control cable clevis attaches. It has a different shape for the trim servo compared to the point it attaches for the trim cable. You can see a picture of the clevis connected to the trim tab at the bottom of the page using this link to my web site:
Click to expand...

Good point, Jerry. I did in fact think of it and have thought about a couple different methods for solving that issue short of building another trim tab:

1. attach an extension onto the existing trim control horn that mimics the original trim attach horn attach point.

2. Just drill out the rivets on the existing horns and use pulled rivets to attach the new horns.

I'm leaning heavily toward number 2--a couple of pulled rivets on the bottom of my trim tab don't bother me a bit.

Any other potential solutions?

Anyway, I'm committed now as my electric trim is sold and I'll be ordering my manual trim parts with my next order from Van's.

Thanks again.
 
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