trim screw (again)

[gilligansae]

All,

Getting a bit of difficulty during my annual- trim play is about .350". IA references FAA advisory cirlular section 4-36 on flutter, stating that if the trim tab length is more than 35% of the length of the surface, then you are allowed trim play (vertical) of 1% of the total cord length of the surface.
His calculation is that the trim play needs to be ~ 0.090".

So, we took some play out of the link at the tab itself, now I am going to go and tackle the other linkages.... but, I think the most play is in the leadscrew.

Anyone have any data on the leadscrew?
what kind of thread is it?
Can it be produced w/ a Die and a new barrel w/ a tap?

I fear that I will have to make new parts (cut fabric off etc....)
He is taking a stand on it...
I have read all the forum posts on trim and it appears that lots of folks have trim play in the .250"- .500" range... don't tell your IA!!!!! (not if he uses the FAA Advisory Circlular as light bedtime reading!!)

Anyone got any advice? Anyone got a barrel and leadscrew I can purchase?
thanks,
Jeff

[Guest]

Re: trim screw (again)

Someone had made them up at a machine shop.

Use the search function and you may find it.

I am thinking it was DJVEGH.

Dave

[Guest]

Re: trim screw (again)

check this out

http://vb.taylorcraft.org/showthread.php?9725-elevator-trim-part-B12-406

[gilligansae]

Re: trim screw (again)

yeah, seen all the posts. Just dont know the specs for the thread.
if someone knows the thread specification (size, pitch, threads per inch, left vs right hand)
can it be made w/ a die and a tap?
does anyone have one for sale?
thanks

[M Towsley]

Re: trim screw (again)

All of my play is in the linkage from the jackscrew to the tab, not the jackscrew. Play at the tab is a common thing on these planes, my first BC-12 was the same. It has been discussed here, before.

Rob Lees made a new one, hopefully he will jump on.

[Robert Lees]

Re: trim screw (again)

... Rob Lees made a new one, hopefully he will jump on.

I made several. Unfortunately I have none left. They are not cheap to make (you need to make the screw and barrel at the same time. Because these are made from unobtanium, you could make these under "Owner Produced Parts" regulations, using your old ones as the "Approved Data".

You need to do fabric surgery to get at them in situ. I don't know what the thread form is, but it is RH and a standard thread, to my recollection.

If you end up going the surgery route, there is a bellcrank inside the port elevator that you can work on to get rid of some slop there.











Note that the second photo above shows the lubrication hole. I have seen so many Taylorcraft with this hole not opened up after re-covering the fabric. Even mine was the same! (Photo below after I opened it up):



Here's the bellcrank surgery I did: scroll down the page.

Hope that helps.

Rob

[shipljl]

Re: trim screw (again)

The thread is 1/2-13 UNC. I made a new one (the inside threaded part) on a lathe. I cut the threads with a bottoming tap chucked into the tail stock of the lathe and turned the lathe head by hand. Probably could have done it with a free tap but I wanted perfect threads so it wouldn't wobble.

It really helped reduce the play.

[astjp2]

Re: trim screw (again)

What did you use to make the knurling? I am working on getting the tooling to make custom parts, I have a mill now and trying to buy a lathe. Is it brass or sintered bronze? What about lubing with grease instead of oil? Just pondering on how to improve, we could also goto acme threads...

[M Towsley]

Re: trim screw (again)

I think mine was lubed with grease at one time. Flying in cold weather stiffens the trim up appreciably. Fine in the summer, though. It would have to be something that is not affected by cold.