empennage fairing screw question

trib · #1 02-11-2006, 07:02 PM

I'm installing the empennage fairing, which fits very well, but have a question about the mounting screws. The plans call for using AN509 8R8s, which are countersunk, flat head screws. The fiberglass on the fairing is way too thin to countersink to fit the screws. It seems more suitable for non-countersunk round head screws, but these of course would add parasitic drag. Does the fiberglass need to be built up? Looking at the construction video and other sites, I haven't seen any mention of this or using other than the screws called out in the plans. Any suggestions?

Tim Ribble
7th year building a 6A

kevinh · #2 02-11-2006, 08:34 PM

On my RV7 they called for AN509 6R8. This worked quite well.

Eventually the aft screw on one of the sides pulled through - because I must have installed it with a bit too much tension when I mated the fiberglass. That was solved by adding a tinnerman washer for that one screw. If anyone asks about it I'll make up some story about P-factor, slip stream and asymetric loading of the tail surfaces requiring that washer.

Quote:

Originally Posted by trib

I'm installing the empennage fairing, which fits very well, but have a question about the mounting screws. The plans call for using AN509 8R8s, which are countersunk, flat head screws. The fiberglass on the fairing is way too thin to countersink to fit the screws. It seems more suitable for non-countersunk round head screws, but these of course would add parasitic drag. Does the fiberglass need to be built up? Looking at the construction video and other sites, I haven't seen any mention of this or using other than the screws called out in the plans. Any suggestions?

Kyle Boatright · #3 02-11-2006, 08:38 PM

I used #6 screws with tinnerman washers under them. If your fairing fits well, you probably don't need all of the screws called out in the plans. A well fitting fairing could probably be installed with 6-10 screws.

KB

godspeed · #4 02-11-2006, 09:07 PM

I used tinnerman washers on all the screws and they sit very flat ,I think it looks better and will have much easier time with inspections ect , they will be painted anyway..
some may not like it, but I think it looks hardy and will last much better in the long run..

Danny..

dan · #5 02-11-2006, 10:13 PM

Quote:

Originally Posted by godspeed

some may not like it, but I think it looks hardy and will last much better in the long run..

I used tinnerman washers as well on my emp fairing, wheel pants, wing tip lenses, cowling screws, etc. They distribute the force quite nicely.

One trick I used on the #8 screw holes in my wheel pants, which you might consider, is to glass the tinnerman washers right in. You can theoretically paint right over it and you won't see 'em, but you still benefit from them being there.

See: (nope, you can't see 'em cuz they're in there)

Take this with a grain of salt, though, because I haven't painted my plane -- just primed over those glassed-in tinnermans. I figure...if they ever "surface" over time, then I'll peel 'em out and just use exposed tinnermans.

)_( Dan
RV-7 N714D
http://www.rvproject.com

mark manda · #6 02-12-2006, 08:55 AM

another little detail trick which I tried on my emp fairing was--

I like the look of tinnerman washers but #6 is huge. So I drilled out #4 washers for the #6.

Then an advisor/friend said the scres were sitting up a bit. He pulled the tinnermans, dimpled them and the #6 screw looks great in a #4 tinnerman.

nice look dan. (I beat the heck out of my paint on the nose gear when I didn't torque the big nut enough.) 8hrs.

FWIW, mark

mark manda · #7 02-12-2006, 08:59 AM

Quote:

Originally Posted by mark manda

another little detail trick which I tried on my emp fairing was--

I like the look of tinnerman washers but #6 is huge. So I drilled out #4 washers for the #6.

Then an advisor/friend said the scres were sitting up a bit. He pulled the tinnermans, dimpled them and the #6 screw looks great in a #4 tinnerman.

nice look dan. (I beat the heck out of my paint on the nose gear when I didn't torque the big nut enough.) 8hrs.

FWIW, mark

edit-- you don't have to counter sink too much. I have the thin FAiring etc. and not problems. i'm concerned about the wheel pants more.

kevinh · #8 02-12-2006, 11:42 AM

Quote:

Originally Posted by mark manda

I like the look of tinnerman washers but #6 is huge. So I drilled out #4 washers for the #6.

Then an advisor/friend said the scres were sitting up a bit. He pulled the tinnermans, dimpled them and the #6 screw looks great in a #4 tinnerman.

Smart! This is definitely going in the bag of tricks.

randylervold · #9 02-13-2006, 11:23 AM

On my RV-8 for all the fairings, wheel pants, and prop spinner, I used #8 stainless steel truss head screws with thin nylon washers under them. I think they look nice and they are less visually intrusive than those large tinnerman washers. If you're not familiar with a truss head screw, it has a wider and flatter head than a conventional screw and thus provides more clamping surface. The thin nylon washers prevent them from marring the paint. This is a pic of the #8 flavor holding my light switch console in...

Of course the countersunk screws by themselves look the best, especially in stainless steel, but I too worry about the strength over time. I am in the finishing stages of my RV-3B and will need to choose fasteners for the same things here soon. I think I'll go the truss head screw route again even though they do stick up just a bit but use #6 instead of #8 for the emp fairing.
BTW, a great source for them is McMaster-Carr...
http://www.mcmaster.com/