This is a plane story, just because our latest screwup was in fabricating a landing light, but it could definitely be a gunsmithing story, so we’re going to run with it.
After several weeks stalled by finicky wiring issues, the Blogbrother and Your Humble Blogger finally had the wiring to our second and last wing completed. First, a little stage-setting. Both wings have tip strobe/position lights, with several wires that have to be connected just so using archaic Molex connectors. Each wing has one extra challenge: the stall warning system on the left side, and the landing light on the right. The stall warning side is done, so completing the tip light wiring and connectors, and completing and installing the landing light parts, were the last hold-ups.
Working with the smallest size Molex pins and connectors is finicky, mentally demanding work, and you have to be fresh to do it. At last the tip light wiring was done, and the landing light assembly was ready for its moment in the spotlight. The wiring and Molexes all went swimmingly — over several days, because the necessity of turning words on a page into wire positions in the connectors was brain-frying. Small Dog MkII could detect the stress, and he went off and hid in our messy office, and ate something that turned his muzzle black. (Inkjet printer cartridge is the odds-on favorite. He also ate the lower half of the book jacket of The Bay of Pigs and part of a package that OTR used to send us some info). It’s not like he goes unfed, the toothy little thing.
The landing light itself bolts, with bolts you absolutely, positively cannot reach once the wing is closed out, to two small ribs, and so adjusting the angle is important as you really only get one chance. Then the ribs are riveted in place. With much imprecation and a blasphemy or two we got the assembly into place and clecoed in.
Then the lens goes in, held by eight screws that go, four each, through the acrylic lens, into a pair of brackets that took too long to fabricate themselves. (Each bracket has a rivnut that is held on with two flush rivets. People think of flush rivets as something used on an aircraft’s exterior for aerodynamic reasons, but they’re often used internally when a fastener head must not interfere with part fit, especially on 110-knot airplanes where it isn’t the rivet heads standing between you and the speed of sound). It was clear that the lens could not be put in without a hand in the back holding it.
You know, right where the light assembly and sub ribs were.
So out came the ribs, the light assembly (now wired in place) was lain down, and a hand snaked through to put the lens and Cleco it in place… which meant going to get smaller Clecos, as the ones we used with the Nº 30 holes in the sheet metal were too small to go through the threaded part of the rivnut. (Fortunately, the right Clecos were available downstairs in the gun, etc, shop’s toolboxes, not requiring a wait until Fastenal opens in the morning).
If we had not already cut the hole in the leading edge of the wing, we’d have thrown the light somewhere out in the trackless snow, to puzzle us in spring, and resolved to fly in daylight only.
But we worked through it, got everything Clecoed into place, and when Blogbro arrived for the night’s work, we had cunningly arranged it so that all that needed to be done was screw in 8 screws in place of the small Clecos, start up the compressor, rivet 10 rivets to permanently install the landing light, and then, rivet the wingtip skins in place, leaving the wing complete except for a fiberglass wingtip strobe/position light fairing (glass work awaits warmer weather).
Ten minutes later, tightening the brass screws that hold the landing light lens in place, we heard a soft crack. Reacting to our emotions, probably, rather than the sound, Small Dog alerted.
Yep, the lens had cracked.
We now faced a decision, and that’s what makes this story of airplane building germane to anyone who smites guns, or, really, builds anything out of anything: what do you do when you screw up?
Fortunately, screwing up is not a novel experience (we are the Rong Brothers after all, because we’re two brothers building a plane, and we’re not the Wright Brothers). And we have a drill for when we bugger a part.
- First, Stop. This is something that has to be considered dispassionately. You’re never dispassionate right after you have blown something, as the color of your language attests.
- Second, consider your options. For most screwups of this nature that have damaged a part, the options are three:
- Use the part as is;
- Replace the part;
- Repair the part.
- Understand why you damaged the part so that if you are working with a repaired or replaced part, you don’t do the exact same thing.
This is a pretty generic, top-level troubleshooting menu that will work for anything. Sometimes only one of the three corrective strategies works. In this case, we could have used any of the three.
- A cracked lens is not a safety of flight item. We could have made a command decision to sign off on it and live with it. Since a crack in acrylic will propagate until it stops (usually at the opposite edge of the part) this did not seem like an optimal solution.
- Replacing the part would have the factory ship us a strip of properly curved acrylic from which we would cut, drill, countersink, and generally fabricate a replacement part. It’s probably the right answer for a part on a new airplane. “I’ll order the part in the morning,” Blogbro sighed (it was his turn). “But I’m not going to pay a fortune for next day air, like you do. It comes when it comes. We can work on the fuselage.” (That’s easy for him to say, it doesn’t cost him another stall in the garage to work on wings and fuse simultaneously).
- There is an approved repair for acrylic cracks in low-speed aircraft, and if you look closely at older small planes you will often see it. This consists of drilling a hole at the very end of the crack to stop further propagation of the crack, and reinstalling the part (this is called, logically enough, “stop-drilling”). Stop-drilling is used for cracks in acrylic, and non-structural fiberglass or aluminum parts like fairings, every day. But we already know that we will not do this. We are not trying to make the best RV-12 ever built, but we’ve seen a lot of builders’ handiwork and we are trying, and so far, succeeding, in building a very good one.
You will always have these choices. Repair, replace, let be.
Here’s a concrete example: in the past six months we’ve received not one, not two, but four firearms with inoperable or frozen safeties, three of them collector pieces. “Replace” is of little interest in rare collector firearms, and may not be possible in a product that was discontinued 50 or 70 or 90 years ago; although one could always fabricate a replacement part. (Someone, once, built it. Therefore, you can rebuild it. Whether that is cost-effective or wise is another question entirely). “Use as is” obviously was satisfactory for the last owners, because, let’s face it, most collector firearms never see a round and most dealers disclaim any idea of their safety or suitability for firing. But being unable to apply a safety bugs us, so we’re going to fix three of the four. (The fourth was bycatch in an auction lot, and is a junker not worth fixing. We will disclose the safety problem when we dump it, unlike the large auction house that sold it to us).
Yes, we’ll definitely choose repair as our fix for those safeties. As soon as we get the %#^#^!! landing light and wingtip done.