Thursday, October 22, 2009

Installing nut plates

No, nut plates aren't those little trays you set out for guests to snack on when they come over on Superbowl Sunday. Nut plates are used to provide a replacement for a nut & bolt arrangement where the back of the piece being attached won't be accessible. Consider the parts that I've been working on for a week now. If you remember, I'm working on the back part of the tail fin to which the rudder will eventually be attached:

Once the skin is riveted to the frame of the tail fin, it will be impossible to get at a nut in there while the rudder hinge is bolted on. So instead of using a nut, we use a nut plate. The nut plate is permanently riveted in place, in this case by using small solid rivets. The smaller #3 rivets are much easier to squeeze than the larger #4 rivets that were used to build the rudder hinge assemblies, but to offset that they have the added complexity of being flush rivets. That means they sit flush against the surface that they are being riveted to. If you remember, they are able to do that because we used the countersink tool to clear away some material around the hole. Note that they aren't quite so easy that I didn't end up having to drill one out. It slipped up in the hole as I was squeezing it and didn't end up flush at all. Quite the opposite.

Here's what the flush rivets look like from the outside (when you do it right):

On the other side, deep under the skin, they look like this:

See how that works? Pretty cool, eh?

Here's how it will look when the rudder hinge thingy gets bolted on:

That will be years from now. I think it's one of the last things you do.

That's it for tonight. The next step involves rounding radii on some of the ribs that give the tail fin its aerodynamic shape, and once that's done they need to be fluted. I'll describe fluting when we get to it, but the point is that I'm going to wait until Saturday when the Certified Fluting Expert that I keep on retainer can make a shop visit.