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Meticulous vs Ridiculous

B

BigD

Well Known Member
Tailkit is finished to the point of mounting the elevators, HS, VS and rudder and doing the fairings, which I decided to go ahead and fit now rather than wait til much later, particularly as I have another 3 weeks until the wing kit arrives. I'll admit I am still learning when it's worth 'fixing' something and when you're better off deciding something is a blemish but acceptable (and not making things worse...). In getting the left elevator attached, after reading some good tips about how to get the bolt/nut/washers on and through the hole (i ended up using a magnet to good effect for the nut) I find that it has the correct travel up and down but the gap between the horn and the HS starts at 1/8 inch near the pivot point and narrows to a little more than 1/16 inch at the tip. I should probably just be glad it works as is but, maybe because I'm spending too much time thinking about it have a couple of questions. The plans say to adjust, if necessary the rod end bearings for fit, but is the ultimate goal that they both be the same distance from the rear spar? Is it possible (or even desirable) to straighten the gap out by turning the outer rod end bearing out some (but then having the two not 'parallel' with the rear spar? and this assumes that the horn is actually perpendicular to the leading edge of the elevator, which I guess I'm going to check. Will the travel/horn clearance change any after tightening the attachment bolts?
I also learned the hard way that the HS needs to dangle off the table a little more than the picture, or at least, more than I allowed for, to give full travel to the elevator horn. After unscrewing it and moving it, besides having a little more finger or tool room to make the attachment (duh!) I started wondering why it is screwed down in the first place, other than to be very stable for the drilling operation. It seems like the more I think about it the less certain I feel, hence the questions...

==dave==
 
Dave-

You don't provide which model you are building, but on the issue of the counterbalance arm not being parallel to the HS, this could be a reflection of the counterbalance not being square to the rest of the elevator. If this is the case, drill out a few of the counterbalance rib and skin rivets in the location where it meets the body of the elevator (on both the top and bottom sides), straighten it out so that it is perpendicular, re-drill (perhaps up to #30), then re-rivet (perhaps using a few pulled rivets). This happened to me and this solution from Van's worked well.

On the issue of when to rework and when to just move on, I recommend delaying those decisions as long as possible (e.g. until you need to permanently mount that questionable part onto another expensive part). Once you get farther into the build and gain more experience you'll be better able to judge whether an attempt to fix will improve the situation or make it worse.

Good luck.
 
Yes, it's a 10, sorry if I didn't make that clear. It maybe sounds like I'm driving myself crazy, which isn't the case - I'll be fooling around with it to learn the hard way anyway, but you don't know what you don't know.

==dave==
 
After setting the rod end bearing dimension to the spar make sure the leading edge of the elevators does not rub the aft spar of the horizontal before drilling horn.

Not your question but a common mistake.

Pat
 
In addition to Steve's suggestion, realize that a run of 1/16" on the counterbalance is about 1/64" adjustment on the rod bearing (due to the longer dimension). That's like a half turn and I doubt you'd really notice it.
 
Rod End Bearings

When doing this myself I had questions about getting the full range of motion up and down on the elevators. The following is an excerpt from my build log specifically about the rod end bearings. You don't want to back them out too far. I know some people have even bought longer rod end bearings to do this job:

One thing I had to do was figure out how many turns the bearings could be backed out and still be safe. I found out that they need to be fully engaged to the nut-plate that they screw into. That means that all the threads have to be in play, so to speak. I found this position by counting threads. There are 6 full revolutions of threads in the nut plate. This means that after 6 full revolutions of the bearing, all threads are in play. This is the point at which the bearing can?t be backed out any further. I then turned them in and counted the turns until the starting spot as indicated by the plans were reached. I counted 1.5 turns. To get the elevator to swing freely over the full range prescribed in the plans (30 degrees up and 25 degrees down) we pretty much had to back all but one of the bearings out that 1.5 turns.

from: http://airplane.athomeinthewilburness.com/2011/08/05/assembly-2/
​
 
Talked to Van's this morning - 1/16 is probably a little close, going to try a half- turn adjustment on the rod end bearing. Failing that, probably file some metal down, after looking at the perpindicularity (just made that up). The critical part is the trailing edge, and as already mentioned, the rod end bearings staying within the distance tolerance. HS screwed to table for drilling. Gonna fool with it tonight.

==dave==
 
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