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Rudder trim

Marvin

Active Member
After 9 years of flying the -8A we have decided to install the rear rudder peddles. No problem with the instalation as it is straight forward. What I am looking for is the builder who some how, some way, used the system and made a adujstable rudder trim. When parked he then use the system as a guss lock for the rudder. I saw this in Arlington and wondering if he would share how he did it. I think it would also help dampen the dutch roll at high speed in rough air.

I wasn't dreaming I saw it with my own eyes.

Dick Johnson
 
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8A Rudder Trim

Dick

I have installed an adjustable rudder trim system similar to what you described.
Very simple but effective for both trim & as a gust lock. I have the ground-adjustable pedals but it would be easy enough to modify the setup for the standard pedals. I have a few photos I can send plus a list of parts - from memory about $20 for parts & an afternoons work. Pls advise your address so I can send the info.

cheers

John Moody
Melbourne
VH-MKX
 
Why not share

It would be great if you would be willing to share the pictures and info here so that many others can view and learn about it. Also, it will remain in the system for others to see in the future.
 
Is anybody out there?

Dick

I have installed an adjustable rudder trim system similar to what you described.
Very simple but effective for both trim & as a gust lock. I have the ground-adjustable pedals but it would be easy enough to modify the setup for the standard pedals. I have a few photos I can send plus a list of parts - from memory about $20 for parts & an afternoons work. Pls advise your address so I can send the info.

cheers

John Moody
Melbourne
VH-MKX

John
I would greatly appreciate a copy of your rudder trim info. I sent you a private message nearly a month ago, which you have not viewed. You have your email access via the site turned off, so I could not contact you that way. Please check your private messages.
Charlie
 
8A Rudder Trim

Sorry - I missed Dick's post & the follow-up queries until today.

I have sent a couple of photos to Dick & will get some more & the parts list in the next couple of days. No problem about sharing - just not competent to post images etc.

John Moody
 
John Moody's RV-8A rudder trim system

John contacted me via email and sent me details of his system. Per his request, I am publishing that info here. This is the total of two emails he sent to me.
Charlie

Attached are a couple of photos showing the general setup - not taken to show this system but I will get some detailed photos of the parts & parts list in the next couple of days.

If you think this stuff is of any value, please post on the VAF site - I see that there were others interested.

Unfortunately I destroyed the aircraft in a crash about 12 months ago, but am fairly advanced on the rebuild & will be reusing the same trim system.
Happy to provide any assistance requested.
regards

John Moody

Photo 1 - the LHS trim spring shown below - comprises a 6 in x 1/4-20 threaded rod drilled at one end to take the tension spring loop. The fwd end of the spring is sandwiched between 2 x 1/16 thk triangular shaped plates bolted to the rudder pedal track.
The spring tension is adjusted by adjusting the nuts on the threaded rod which is connected to the rudder cables by a fabricated angle ex 1 x 1-1/2 x 1/8.
The spring was selected to have the required extension & load capacity. I will dig out the McMaster-Carr part nos. I tried 3 different springs to get the combination that worked best.

imgp2278r.jpg


Photo 2 - you can (sort of) see both trim springs. The RHS setup is the same as the LHS except that it has a thumbscrew (obscured by the seat) on the threaded rod so that the RHS spring can be adjusted to set the trim.

imgp2293r.jpg


I've taken a few photos of the rudder trim components, as shown below, &
extracted the parts list. As you can see the parts do not require modification
of any of the stock parts nor do they interfere with the rudder cables, pedals etc.

The spring lengths were selected to have some pretension with the rudder
pedal at maximum travel forward, without exceeding the extension limits of the springs with the pedal at maximum travel aft.

Photo 1 - the top item is the LHS bracket & spring - non-adjustable. The
bottom item is the RHS adjustable spring with the thumb nut. Note that the RHS spring is larger diameter/ thicker wire than the LHS - I found that this provided more RH trim force & worked better for me.

imgp2550r.jpg


Photo 2 - RHS adjustable trim - inverted L bkt ex 1 x 1-1/2 x 1/8 angle 1 in wide,
6in ss threaded rod 1/4-20, ss thumb nut, 1 in spacer, Oilite washer, 1/4-20 Nylock. The thick washer riveted to the L is not required - I thought that the threaded rod might rotate with the thumb nut so I allowed to be able to file a flat on the rod & use a set screw in the thick washer to stop the rotation. However with the Oilite washer there is not enough friction to rotate the rod. A 4 in long rod would probably be long enough here as well. The spacer is required to provide finger clearance from the swinging arm.

imgp2551r.jpg


Photo3 -LHS non-adjustable trim - same inverted L bkt as RHS, 4 in ss rod,
Oilite washer, 1/4-20 Nylock & hex nuts. Note lighter spring than RHS

imgp2552r.jpg


Photo4 - Spring anchor brackets ex 1/16 sheet approx 2 in bolts ctrs
- 2 no. each side bolted through rudder track, spring sandwiched between
& held with AN3 bolt.

imgp2553r.jpg


Purchased parts list ex McMaster-Carr
1) 1 no. aluminium spacer 1/2od x 1/4id x 1 p/n 92510A769 ($1.71)
2) 1 no. light spring 7/16 in dia p/n 9654K144 (comes in pkg of 3 unfortunately $8.44)
3) 1 no. heavy spring 37/64 in dia p/n 9654K448 (ditto $10.24)
4) 1 no. 4 in ss threaded rod 1/4-20 p/n 90575A563 ($1.32)
5) 1 no. 6 in ss threaded rod 1/4-20 p/n 90575A570 ($1.98)
6) 1 no. ss thumbnut 3/4 in x 1/4-20 p/n 91833A138 ($6.35)
7) 2 no. Oilite washers p/n 2879T1 ($0.76 ea.)
Additional parts - 1/4-20 Nylock & hex nuts, AN3 bolts nuts & washers as required

Please advise if you need any clarification or info.

I found that once I had the trim set for feet-off-the-pedals at about 160 kt cruise, only very light pressure was required at other speeds so I rarely changed the trim. The springs work very effectively to stop the rudder being blown around on the ground so I didn't use a rudder lock in any wind conditions. Hope all this helps.
regards
John Moody
 
Glad Someone Asked

came up with a system that's so simple I'm worried about it being wrong some how.

I bought about 10-12 feet of 1/8" bungee cord, I fed one end thru the main spar on the left and the other end thru the main spar on the right. Then installed snap bushing (black plastic grommets) in the seat floor ribs, near and about parallel to the rudder cable all the way back to near the rear battery. The ends are clamped to the rudder cable, the clamps are positioned midway between bulkheads so there is no chance of the clamps hitting a bulkhead as the rudders pedals are pushed.

I don't have everything fully installed, but, anticipate the system will allow me to slightly tension the bungee by reaching down to the front of the main spar, sliding it to tension that side of the rudder. I also expect it will always keep some light tension on the cables to keep the rudder from swinging in the breeze.

I'll upload photos if this is too confusing.

View looking at the front of the main spar. The bungee is blue:
21bky6r.jpg
[/IMG]

View of the blue bungee coming aft thru the main spar, and thru the seat bulkheads:
2r3uohl.jpg
[/IMG]

Fuzzy picture of the clamp (Home Depot) attached to the bungee and the rudder cable:
1zufmg.jpg
[/IMG]
 
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Pics Please!

I came up with a system that's so simple I'm worried about it being wrong some how.

I bought about 10-12 feet of 1/8" bungee cord, I fed one end thru the main spar on the left and the other end thru the main spar on the right. Then installed snap bushing (black plastic grommets) in the seat floor ribs, near and about parallel to the rudder cable all the way back to near the rear battery. The ends are clamped to the rudder cable, the clamps are positioned midway between bulkheads so there is no chance of the clamps hitting a bulkhead as the rudders pedals are pushed.

I don't have everything fully installed, but, anticipate the system will allow me to slightly tension the bungee by reaching down to the front of the main spar, sliding it to tension that side of the rudder. I also expect it will always keep some light tension on the cables to keep the rudder from swinging in the breeze.

I'll upload photos if this is too confusing.

I'd love to see pics of your solution if you wouldn't mind posting. If you don't want to post, could you send me a PM with pics? thanks.
 
Rudder Trim

Hey guys,

I am looking to get info on this. Seems like all the photos are gone/no longer online. Can we get a re-post on these systems with photos please?

Thanks!

Wingnut
 
Added the photos again

Thanks for asking, I have the bungie held on the top of the main spar with one of those 3M plastic hooks on adhesive tape. It goes up and over the stick, reach down and pull on the left or right bungie that puts the same pressure on the cable you'd be holding with your foot to keep trim. This thing is so simple, don't feel anything in the pedals.

Thanks for asking.
 
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