Sunday, November 15, 2009

Still working on the spar box

With the spar box all clecoed together, the next steps involve fitting, drilling, and generally massaging the powder-coated steel parts into place. These parts are relatively hefty when compared to the light aluminum of the spar box itself and require more substantial hardware to attach.

The control arms get clecoed in first. There are two of them: a top and a bottom. These are the arms that the cables used to control the horizontal stab in flight. The plans said to cleco them in place and then final drill with a #12 size bit. The problem I had was that the holes were too small to take a cleco, so I had to drill them out with a #30 bit first.

Just to the left of the top control arm is the socket/bracket that will hold the big steel counter-balance arm. It gets clecoed in place turned 90 degrees to its final orientation. This provides access to the holes that will be drilled through the arm for an attaching bolt to pass through:

You can see the two open holes at the top of the counter-balance arm brackets; those will be covered when the bracket gets permanently installed and is turned back 90 degrees. It was clever of the Van's designers to make enough of the holes common in location after the 90 degree turn to allow the bracket to be clecoed in either position. That allowed for easier access to drill the holes for the attach bolt. Always thinking, those guys.

Here it is looking at it from the front of the spar box:

This is the back side. The control arm is pushed in from the front until the back edge is flush with the back edge of the support bracket:

The directions have you match drill with the #30 bit, then final drill with a #12. They then have you push a bolt through, ostensibly to make sure the arm doesn't turn while you're drilling the hole on the other side of the spar box:

You do pretty much the same thing with the control arms:

Drilling through the steel takes a little more effort than drilling through aluminum!

Once all of those holes are drilled, all of the steel parts get removed for deburring. While they're out of the way, some doublers get installed on one of the spars:

These doublers will end up having nutplates installed on them, and those will eventually support the hinges that the stab will pivot on. There will be quite a bit of force applied to those hinges, hence the need for doublers.

The bolts that hold the control arms to the spar box will also be screwed into nutplates. The installation of these particular nutplates was somewhat unique (so far, anyway) for the RV-12 in that the holes for the rivets were not drilled for us by the factory. Instead we had to do what builders of "real" RV airplanes do: use a bolt screwed lightly into the nutplate to hold it in place while the first rivet hole is drilled by using the nutplate as a template. A cleco then uses that hole to hold the nutplate in position while the second hole is drilled:

All of this drilling results in parts that will be happier and line up better if they are returned to the exact same position after removal for duburring, so everything gets marked so it can be returned to the same location:

I couldn't write legibly enough on the tiny tabs the of the nutplates, so I used symbols.

To cleco everything back together after deburring, I found it easier to use one cleco down through the top of every piece, then flip the spar over and cleco from the other side:

Here's everything all clecoed in and ready to be riveted:

Can you find the nutplate that I got oriented incorrectly? Here's hoping that doesn't make any difference!

The riveting will have to wait for another day. There were plenty of pre-winter preparation chores to be done and the oil change on the RV-6 still hadn't been done. The cowls are still broken, but that's no reason for not finishing the oil change. I was able (and this is very rare indeed!) to get the old oil filter off of the engine and the new one on without spilling a single drop of oil. Not bad for a routine oil change that has been anything but routine.

1 comment:

Ted said...

The nutplate orientation makes no difference at all. You are good!

Post a Comment