Friday, December 1, 2006
AV - Gift Horse
Mess around with airplanes long enough, you'll get calls from strangers asking for stuff. Hunk of urethane foam. Piece of tubing of a particular diameter & wall-thickness. Quarter sheet of .012 2024-T3. Various tools...
I no longer lend tools since they have a habit of not coming back but if I've got it to spare I usually try to help out with materials, like that twelve-thou aluminum.
So the guy shows up and he's brought his own personal Inspector, one of those Designee-types slightly older than God and equally omnipotent. I go to digging under one of the outside benches where there's a couple sheets of .012 rolled up & sealed and the Great Inspector stands there and gives us a lecture on how I've over-driven the rivets in the structure laying on the table. The shop heads are okay he sez but I've been reverse-setting the things (according to him) and the factory head is all flattened out.
Which isn't too surprising because they happened to AN442's. And are set strictly to spec.
I gave the guy the metal but told him if he needed anything else to leave his idiot 'inspector' at home. I don't have any time for fools.
AN442's are flat head aluminum rivets. Not countersunk rivets; real flat-heads, like you'd find on an old fashioned cow bell or milk pail.
When you get most of your fasteners as new-surplus you're liable to run into just about anything. Nowadays, most homebuilders (and homebuilt 'inspectors') are only familiar with AN470 'Universal Head' rivets and countersunk head rivets having a 100 degree angle (ie, AN426's). But there's a few hundred (!) other types of aluminum rivets out there and if you've got the tools and sets to use them, there's no reason not to. Indeed, you'll see a lot of round head rivets (AN430) on vintage airframes, especially war birds, and it seems only fair to use the same fasteners when making a repair.
You can still buy sets for round-head and brazier-head rivets. When fabricating interior components such as bulkheads or the firewall, where aerodynamic drag isn't a factor, there's no reason not to use AN430's. And if you happen to be making a thermostatically controlled vent for a greenhouse, it's the perfect opportunity to use-up some of those Reynold's 6061 AN442's that have been taking up shelf space since Jonah was a seaman-deuce. But don't let one of them Designees see you doing it or the greenhouse will never get off the ground.