• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

trim and stab adjustment

P

pitts12driver

Registered User
San Francisco, CA
When we checked everything on the ground, the overhead trim cranked smoothly from limit to limit. In the air on the first flight, the trim would not move - the cable just slipped.

For the second flight, we increased the spring rate, and the trim moved within a narrow range, but not to the full extent of the travel, and was overwhelmed by air loads at anything over 80 mph. As with the first flight, it ran smoothly on the ground.

It was suggested to us that there might be some difference in alignment on the stab from tensioning the flying wires that is causing the jackscrew to bind in the air. The tension in the flying wires appears extremely consistent, and there does not seem to be a visible skew out of plane on the stab.

All ideas welcomed!
 
Is it a double groove pulley system? If so it surprises me that it would slip.Is it possible to have some slack trapped between the front and rear pulleys that the tensioner can't remove?
 
you do NOT rig it(stabs) level as the rigging instructions say... they assume your plane is all square, as it left the factory 60 or so years ago.. it's probably not

you rig stabs to equal 'slop' on jack screw to yoke.. then it will not bind... and will fly just fine... use your finger on jack screw/yoke to FEEL the slop..
 
Are the two AN3 bolts that hold the tail brace wires to the stabs allowing the clevises to rotate on the bushings? Shouldn't be super tight.
 
adjustment of the flying wires. Stab was slightly misaligned if you felt the jackscrew while the trim was being adjusted. It was only off by a turn laterally and we were good to go
 
PerryB said:
Only one glitch with a new built is pretty good!
Click to expand...

Well, it is the 4th airplane I've built. I asked a lot of talented people to make sure they had their eyes on it and to call out the tiniest of issues. And mostly, we got lucky!!
 
I had the same exact problem on my newly built Javron cub and assumed the spring sent along with the hardware kit was to weak and went with a stronger spring. The spring on mine was not nearly as tight as the certified cub sitting in the hanger with my airplane and the geometry on the whole overhead spring thing is a lot different then a stock cub. I guess I should have posed the question since it appears I may have solved the problem with the wrong solution. I will check that next time I am out but it works well now stop to stop.
 
i am have kind of the same problem ,i can trim nose up but not nose down over 60 mph could you go in to more detail how you found the problem and how you fixed it
 
i am have kind of the same problem ,i can trim nose up but not nose down over 60 mph
Click to expand...

This must be trim season....

We had the same issue as this after the first flight from a rebuild last week. It turned out that we needed to just tweak it until it was free then tighten up the brace wires equal until we were satisfied with the tension. Like what was said above they are all slightly twisted.

We were able to simulate an airload by resisting the leading edge of the stabilizer with our hands. When we could not physically keep it from slipping then we snugged up the wires equally.
 
You must log in or register to reply here.

Similar threads

P
smith cub trimm
Replies
7
Views
3K
Shaun T
S
Tom3holer
185 stab trim/CG question
2
Replies
31
Views
9K
Tom3holer
Tom3holer
irishfield
Trim Screw/Yoke Adjustment J3C-65
Replies
3
Views
2K
irishfield
irishfield
rotto789
Neutral Trim Hedache on my new Bird
Replies
24
Views
11K
CamTom12
CamTom12
Crash Jr.
J-3 Trim problems
Replies
17
Views
5K
Crash Jr.
Crash Jr.
Back
Top