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.
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.
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.
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.
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
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.
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