Mathematically Challenged

[jlfernan]

I'm installing a Gretz Aero pitot mast on my 9A. I'm having a heck of a time calculating the correct length rivet to use. It has to go thru the skin, the spar, and the mounting bracket. Anyone out there who has already done this and wants to save me a headache, your help will be greatly appreciated.

[Jamie]

Just use a rivet gauge, like this one:

(avery tools sells them).

You simply insert the a rivet in the hole and set the gauge on it. The numbers on the gauge refer to the rivet diameter, so you would use the '3' for AN3 rivets. If the rivet is equal to or longer than the cutout in the gauge, you're good to go. No need to do any math.

[fehdxl]

If you have numerous lengths, just trial and error fit them until you have 1-1/2 times the diameter of the rivet showing past the mounting bracket.

For example,
for a -4 rivet -> 4/32 * 1.5 = 6/32 or 3/16" sticking out
for a -3 rivet -? 3/32 * 1.5 = 4.5/32 or 9/64 sticking out

Or of you want to cheat like I do, get a gage from Fred at Clear Air Tools -- takes all of the brainwork out of the process. Direct link to the Rivet Reader


Hope this helps.

-Jim

[captainron]

If you know the thicknesses of the layers you're riveting, you can do the math.
Examples:
Skin= .020
Spar= .040
Bracket= .032
Total= .092
For a 1/8th rivet,you will need an additional .180 for a total of .272
Rivets are measured (length) in 1/16ths or .0625"
Divide .272 by .0625 for a total of 4.35 sixteenths for a 4-4.5 rivet.

For a 3/32nd, or "3" rivet you will need an extra .140 length after all the thicknesses. So .092+.140=.232
.232 divided by .0625=3.712 sixteenths for a 3-3.5 or possibly a 3-4 rivet.