Trim Actuator

[Flybyjim]

I am very frustrated with adjusting the trim actuator and trying to get this to work. I have searched past posts and found John P. post from 2014 but my situation and his resolve do not seem to match.
My actuator stroke is 4 inches, with the rod end all the way in at full stroke I have 3/4 inch between tubes. If I turn the rod end out (you can not turn the actuator rod to try to lengthen the rod end even if you remove the jam nut) to get the 7/16" called for in the instructions my rod end is only turned in 6 turns leaving 12 turns out of the actuator, this can not be correct. What am I doing wrong? Is 4 inches correct for the stroke of the piston.

Jim

[Flybyjim]

Anyone out there with advice?

[jiott]

With the 7/16" called for in the book, when I started to fly I found that I didn't have near enough nose-up trim to operate with full flaps. I also found that I had more than enough nose-down trim. So I ended up screwing the rod end farther into the actuator rod (I can't remember how many turns) to get more nose-up and of course less nose-down. The sweet spot for me ended up with the stabilizer front tube almost touching the bottom of the slots in the covers with full nose-up trim. This still requires a little back-pressure on the stick when approaching to land with full flaps, but that is OK. Still have never found a situation where I needed full nose-down trim. This was my experience on my SS7. Don't be afraid to experiment with this, you can be quite a ways off in proper trim and still compensate for it easily with stick pressure (I have been known to forget to set the trim for T/O and leave it in the nose-up landing position-quite a surprise but easily overcome with forward stick).

[PapuaPilot]

I have found the same thing to be true as Jim did. You want the stabilizer leading edge to go down as far as possible.

Rigging this is not hard. The jack screw goes up or down until it gets to its internal stops. The stroke is ~4" and it is not adjustable. To rig the trim run the jackscrew either to the top or bottom of its travel. DO NOT turn the jackscrew by hand. Now all you need to do is adjust the length of the rod end (without spinning the jackscrew). I would do it like Jim said, get leading edge tube of the stabilizer as close as you can to the bottom of the slots in the panels.

FYI for your first flight I would put the trim in the middle of its travel and then figure out where it needs to be for subsequent takeoffs.

[Flybyjim]

Okay, I can go with this but what about the number of threads that should be the minimum into the actuator?

Thanks

[jiott]

As Phil says, trim in the middle for first flights and you will be fine. My sweet spot for T/O (after rod end adjustments as described earlier) ended up being about 3/4 of the way to full nose-down. This feels good on T/O with half flaps and then after pulling off the flaps I hardly need to adjust trim for straight cruise flight, sometimes just a quick stab on the nose-down switch.

I wish I had, but didn't install a trim position indicator. Now I don't need it because I can easily adjust trim for T/O without having to look at the stabilizer. I just hold the trim switch until it reaches full nose-down (you can see when the stick quits moving) then I press nose-up for 2 seconds (count one thousand one, one thousand two) and its in perfect T/O position.

[jiott]

If you adjust it somewhere near like Phil and I suggest, I believe you will have more than enough threads engaged. You are correct though, there is a proper minimum number of thread engagement, maybe someone knows this number. I know on a female rod end there is a little hole that you can use to see if the male end is in far enough.

[jiott]

I just found it on the Aurora (they make most rod ends) website: Minimum thread engagement, unless otherwise stated, is 1.5 times the major thread diameter will support the advertised max load.

[PapuaPilot]

Good job Jim, I didn't have any idea how to answer that question.

[Flybyjim]

Good info to know. So if I understand this: If the dia. of the threaded rod end is 1/2 inch then the minimum length you need to thread the shaft into the socket is
1/2 plus 1/4 equals 3/4 inch of thread.
You fellows are of great help, much experience in this group.

[efwd]

One thing concerning me here. If you have not flown your aircraft yet, then you might consider the words in the manual. It is suggested that the 7/16inch is established as a safe place to initiate first flight as this is purposefully establishing a slight nose heavy situation as apposed to a nose high on lift off and possible stall. You can make adjustments after first flight to improve trim. Everyones Wt. & Balance will be different.
Eddie

[jiott]

Good point Eddie. It can't hurt to go by the book to start with, even knowing you will probably change it later.

[Flybyjim]

Eddie,
I am a long way away from flight, just setting the stab on for the first time and setting up the actuator. In a couple of other builds the minimum of turns into a receiver for an end rod was stated as 10 turns so when I could only have 6 turns for the 7/16 distance I became concerned and wondered how others set up. Thanks for your reply.

[jtpitkin06]

I am very frustrated with adjusting the trim actuator and trying to get this to work. I have searched past posts and found John P. post from 2014 but my situation and his resolve do not seem to match.
My actuator stroke is 4 inches, with the rod end all the way in at full stroke I have 3/4 inch between tubes. If I turn the rod end out (you can not turn the actuator rod to try to lengthen the rod end even if you remove the jam nut) to get the 7/16" called for in the instructions my rod end is only turned in 6 turns leaving 12 turns out of the actuator, this can not be correct. What am I doing wrong? Is 4 inches correct for the stroke of the piston.

Jim

Jim,
I'm going back to your original question.

Let's suppose you elect to use the recommended 1.5 times the diameter for thread engagement. The rod end ( ball joint, Heim joint... Whatever you call it), is AN3 threads; or, if you like, call it a 3/16-32 screw.

So 1.5 times 3/16 is 9/32 or 9 turns.

Now, you say you get only 6 turns engagement when the starting clearance of the stab is set to 7/16. Remember that dimension is plus or minus 1/16. To be comfortable turn the rod end in another 3 turns and you are only off by 1/32 in the nose up direction.

Also note that most pilots are opting for a little more nose up trim which would screw your rod end inward even more.

I'd say your trim actuator is not a sleep loss item. The important part is the horizontal stab does not hit the fuselage in either the full up or full down position.

To answer your other question, the travel of the actuator is 4 inches and is not adjustable. Only the total length is adjustable by turning the rod end in or out.

John Pitkin
Greenville, TX

[Maverick]

Hello. I have a question about the trim actuator that doesn't necessarily go along with this message string but I didn't see another string that would be more appropriate so, I'm going to add it here.

I have a series 5 kit. The actuator that I have can be seen in the diagram below. The instructions call for there to be a bearing (P/N-93027.000). To put that in you are instructed to ream out the housing. Then you are to use a bushing, (P/N-11002.00). It seems to me if you ream out the housing it weakens the part. And, the bushing fits nicely in the housing so, what is the need to put in the bearing? It seems that the load will be on the AN3 bolt and the bushing. And, the amount of rotation on the bolt is really very limited so is the bearing really necessary. What do you think about this? Ream with bearing and bushing? Or no ream and bushing only?

Thanks.

[David47]

This configuration of bearing-bushing-bolt is common practice. The whole point is to have the bearing a snug fit so that it doesn’t rotate. The bushing does the rotating. I wouldn’t just put the bushing in with no bearing and allow that to rotate in the actuator. You’ll oversize the hole over time. Reaming of the hole to get the bearing in has already been considered by the designer when determining the strength.

[jrevens]

David’s right. Even though the arc of rotation is very small on this assembly, it is poor practice in general to use the surface of a bolt as a rotating bearing surface. The enlargement of the hole for insertion of the “bearing” is also relatively minor in this instance.

[jrevens]

David’s right. Even though the arc of rotation is very small on this assembly, it is poor practice in general to use the surface of a bolt as a rotating bearing surface. The enlargement of the hole for insertion of the “bearing” is also relatively minor in this instance.

Hey Maverick,

I just re-read what you posted, and my reply didn’t really address what you were asking about... sorry about that. I must have been tired! David’s reply is more accurately to the point.