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humptybump

Well Known Member
I will be retrofitting a pitot mast on my left wing. The plane is finished and painted. The lower wing paint is metallic with clear coat. I do not wish to mount the pitot mast on the inspection cover. I plan to mount the mast one bay outbound of the inspection cover closest to the tie down ring.

I will need to dimple the painted wing skin.

Are there any techniques to help prevent or minimize paint cracking when I dimple the panted aluminum skin ?

The dimpling will need to be performed through one of the large rib access / lightening holes.

Any tricks to getting a good dimple inside the wing ?
 
If you can't get to the hole with a squeezer, I would use Avery this pop rivet dimpler. I would warm the skin with a hair dryer to soften the paint first.

http://www.averytools.com/prodinfo.asp?number=1022

After dimpling, I would try to carefully remove some of the paint so the rivet will sit against the aluminum. If you don't, the rivet will loosen and weep from the vibration of the mast.
Maybe spinning a countersink bit by hand in the dimpled hole would cut just enough paint not to be noticable.
 
Might put a little heat on it before dimpling. Other than that, guessing you'll just have to go for it.
 
You could try some paper painters tape on the outside to cover the paint. Dimple right through it. It might protect the paint well enough.

Alternatively, you could investigate using NAS1097AD3 oops rivets since the 3/23 bodies have heads from 1/16 rivets. You can c'sink the skin (takes about 6 turns by hand with a c'sink cutter).

I assume the strength capability is different because of the small head so a bit of research would be needed before using them in this application. Many people (including me) use them for attaching nutplates to thin sheet.
 
I have an auto body paint collision shop , the paint will probably Crack if dimpled so I would just use SS low domed head screws with a plastic washer under the head of the screw . Four screw heads on the bottom of the wing will not Slow you down ! Mt two cents . :)
 
Thanks for the suggestions. I will practice on some scrap that is sitting in the paint booth. It won't be a totally fair test since the pieces have many layers of old paint but they will be good for testing the "warm air" idea.

The fall back will be using #6 low profile pan head type screws.
 
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