When You Screw up in the Workshop

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.

The lights, a kit option, are not shown on this factory drawing. The landing light has two little stub ribs to hold it in place, and fits between the most outboard two nose ribs in the right wing. Image: Van’s Aircraft.

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.

The RV-12’s left wingtip (shown) has been put to bed. Before we can do the right one, we have to tackle the landing light.

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).

For one brief, shining moment, all was going swimmingly. Like the Red Baron, a photo jinxed us.

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.

  1. 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.
  2. Second, consider your options. For most screwups of this nature that have damaged a part, the options are three:
    1. Use the part as is;
    2. Replace the part;
    3. Repair the part.
  3. 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.

  1. 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.
  2. 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).
  3. 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.

37 thoughts on “When You Screw up in the Workshop

  1. gbob

    So what was the cause of the failure? I’m guessing misaligned mounting holes, fixed nutplates are just that, and floating nutplates don’t float as much as you want them too. The other most likely would be over torqueing, but you don’t strike me as the type. If misalignment is the culprit, don’t feel too bad, it happens to pros often enough. If it was a torque too far, well, that happens too.
    Good call on replacing it though, if it was my plane I would like to pretend I would replace it.
    Also, just because a cleco fits, doesn’t mean it is drilled straight, that’s just a lie we tell ourselves before we try to shoot it together.

    Also again, please keep the plane updates coming, I like seeing your progress.

    1. KevsBlogBrother

      Replacing it is the right call, gbob, thanks for the validation. One thing Hognose did not mention, if we repair and have to dig back in later to replace the lens, it’s going to be a much bigger job, because we will have to drill out a whole lot of rivets. And that carries its own set of challenges and risks.

      When we screw up a plane part, there’s always an “oh shit” pause where we don’t do anything, just because we’re demoralized and have an emotional desire to walk away (or do something stupid and destructive – to our credit, we’ve always chosen to walk away.) But I had a couple of thoughts that I want to share (not only with you but with Hognose, because I know he’s going to read this.)

      1) We can test fit the screws in the nutplates/brackets without the lens being in place and I think we ought to do that.
      2) We might have to replace the brackets which is no biggie, but let’s try to think of a process that will guarantee alignment when we match drill those holes. Not to pass the buck here, but I think having us match drill two components out of three going together (the wing skin, the lens, and the brackets) is not optimal design.
      3) If we have to widen the lens holes a bit (in the replacement lens), I’m comfortable doing that.
      4) I wonder where those plexi bits are?
      5) We can complete at least the first two fuselage steps in the basement.

      1. Gerry Parker

        “there’s always an “oh shit” pause where we don’t do anything, just because we’re demoralized and have an emotional desire to walk away (or do something stupid and destructive”

        Right there with you. As my wife pointed out to me earlier this week- Do the Right Thing. Usually the painful thing, but in the long run it keeps me happy. Otherwise, I obsess about it, so doing things two or three times seems to be the norm.

        Of course, a friend of mine points out, if you put in a wire-nut, when it fails you’ll know what failed…

      2. John M.

        Perhaps finding a good spot at Hog Manor for a punching bag would both provide a good outlet for the destructive impulse in the moment and provide a bit of fodder for Hognose’s regular Friday “Health and Fitness” roundup.

        -John M.

  2. Ti

    A lot of stop drilling cowls on helo’s when I was in Army. Great repair option. I wonder if you could bring temp up in build area and apply a heat gun ‘gently’ while tightening the replacement?

    Loved that shiny alclad shot by the way.

      1. 10x25mm

        Glass transition temperature of PMMA is usually in the vicinity of 110 C (230 F), depending upon the exact copolymers added. A lot of the acrylic intended for lighting lenses has its GTT boosted to improve high temperature strength and stability. Think they boost the GTT of PMMA to 200 C (390 F) or thereabouts for this application. PMMA melts somewhere above 240 C (465 F).

        You have to get above the GTT to significantly improve the flexibility of PMMA and avoid cracking during forming. You don’t achieve much improvement in flexibility by heating PMMA above room temperature, unless you get above the GTT. You should think of PMMA as an organic glass, not as a plastic.

        PMMA can be welded with chemical solvents and this might be an acceptable repair method in your application. Aquarium supply shops may be your best source for these solvents. They do a lot of nice, clear welds, but I am not certain how such welds would heat age in a lighting lens application.

        1. Hognose Post author

          Thanks.

          On the plus side, it’s an LED light so the waste heat is considerably less than in the days of incandescents. And, one hopes, the solid-state LED’s life in an aircraft application will be longer than the too-short lives of incandescents. At least this application is in the wing, and not attached to the cowling, engine mount, or nose gear, all of which lead to early light mortality.

  3. James

    Ah,as a carpenter/shade tree mechanic/ ect. I do understand the “ooops syndrome”!I after a lot of cussing(Unless in customer occupied home),breathe/clean a bit job site/tools/whatever,then,repair/replace and along the way with repair/ replace learn what the F$%K I did wrong.Many mistakes in carpentry many times reusable stock,I many times do longest first cuts and can still make it work if error,sometimes,I just screwed meself and a trip to the lumber yard ect.

  4. TRX

    If you can’t get the cover off without drilling rivets, how are you going to replace the lights?

    1. CJ

      They look like LEDs to me – it’ll be a heckuva long time before those need to be replaced. It’s good to see aircraft parts starting to catch up to the 21st century, although I’m guessing that may have more to do with the flexibility of a homebuilt “experimental” aircraft. Swapping out an incandescent position light on a Cessna 152 for a LED would be a bajillion dollar STC, I’m sure.

      1. KevsBlogBrother

        If we ever have to replace the landing light once the wing is buttoned up, yeah, it’ll be tough. But since it is an LED, and the landing light doesn’t get used that often (we’re not building a 747 here), it will probably not burn out in our lifetimes. It might fail for some other reason!

        And you’re right on the money about the cost of doing anything to a certified airplane such as a 152. Experimental aircraft have been driving the innovation train for decades for precisely that reason.

  5. Chris Novatny

    If you like building airplanes, check out a little project that my Dad & I have been volunteering on for the past year.

    http://www.champaignaviationmuseum.org/

    We are 11 years into the project.
    The best part is that almost every Saturday, we have our 3 WWII Vets at the museum, Art, Red & George.

    1. KevsBlogBrother

      Wow, Chris! If Hognose and I ever get N603NH finished, we’ll definitely come out. It would be an honor and a privilege to put some rivets in that Fort.

    2. CJ

      Wow! I had no idea there was a B-17 resto going on at Urbana Grimes! I’ve been to the USAF Museum countless times and saw the Memphis Belle before they started the work on her. My dad and I used to fly out of I74 all the time; Dad did some instructing there too. I’ll have to stop by the next time we’re visiting family.

      1. Hognose Post author

        If you read the stuff that Chris linked, it started out to be a restoration, but it turned into more of a scratchbuild. From Boeing plans, from the Smithsonian.

      2. Ti

        Very neat project. Reading the blog comments here from everyone shows how that human spirit to build something is in the DNA and with the freedom to do it, makes this the greatest place on earth! I’m sorry, I’ll go back to something boring now…

  6. John D

    I’d be sure the mounting holes are large enough that there is no interference of the screws, and then use thin plastic or fiber washers under the screw heads-

    Stuff happens- I’m not even going to discuss how I snapped a 150 yr old shotgun hammer in two this week….

    Sigh.

  7. Cap'n Mike

    “1. First, Stop. ”

    Thats some great advise right there.
    How many times have I made a mistake worse on the 1988 Mustang I restored/am restoring (Its never really done) by not just stopping after the first screw up.

  8. Keith

    On a road trip down the eastern side of the Rockies many years ago with my parents there was us and semi a couple of miles ahead and nobody else on the highway. On the straight stretches the driver would light up the highway for miles ahead with a cab mounted aircraft landing light. This was many years before LED’s so who knows how much the driver paid for it.

    My father had a Tripacer many years ago. He and help redid the fabric on the fuselage. I’m sure there were many ‘oh crap’ moments in doing that. As a side line he used to work on small boat outboard engines and I know there such moments in that because I witnessed them.

    Then there was the time (10 or so) we were pulling a boat up hill from the landing. I was riding in the back of the truck pulling it and watched the trailer come unlatched and go rolling back towards the lake…

    It was stopped by the tongue of another persons loaded trailer, about 3-4 feet from the water.

    Keep your powder dry and your faith in God.

  9. raven

    Just drop a flare if it’s dark. ….

    This sort of thing drives me mad. Who thinks up these convoluted methods?

    It looks like the lens is trapped between the brackets and skin? How hard is it to remove? Did I read this correctly- the light has to come out to get at the lens? And the wing rivets have to come out to get to the light?

    why acrylic- is that brittle stuff still the best we have?

    Why put the lens inside the aluminum? Would it not make more sense to wrap it over the wing leading edge, externally?

    Or- is the choice of acrylic , presumably for long life under UV exposure, directly related to the placement of the lens, IE, “it’s hard to get to, so make sure it does not yellow?”

    Is the lens sealed to the wing skin?- is there a water infiltration potential?

  10. Badger

    Really love these updates on the build; fascinating stuff from you both. And appreciate your ticking off “the drill” – the equivalent (probably with similar verbal blasphemy as well) as to working on something electronic and one realizes they just “let the magic smoke out.”

    Also love that you’re going with aluminum. (Evokes pre-War Air Corps livery.)
    :)

  11. James In Australia

    Chloroform will fix acrylic cracks. A drop applied by brush on the outside will fill the crack by capillary action for an almost invisible repair.
    Of course replacement is the best option, but if you have no choice…..

    1. Hognose Post author

      Hey that’s a great tip. We’re anal enough that we’re going to get a replacement part. Tomorrow I’m going to ask my glass shop if they can replicate the curve.

      1. James In Australia

        They may be able to bend glass, but you would need a toughened laminated piece of glass. That involves more processes in a set order, normally out of the capabilities of a domestic glass bender.

        If it were me I’d just get some polycarb sheet and bend it myself. I did a series of impact tests on various plastics for a work project. I’ve shot polycarb and a 4mm sheet will withstand a .22 on a slight angle with only a smear as a witness. It takes .17 Hmr to penetrate and that just leaves a hole without spreading as does .308 etc. Much better than acrylic which shatters with just a .22.

  12. Steve M.

    KevsBlogBrother, Gerry Parker, and James

    I couldn’t agree more with your responses! KevsBlogBro captures that demoralizing sensation I know all too well.

    As Gerry Parker mentioned, my wife has helped in the resolution department more times than I can count. From preventing further loss and destruction,
    “Honey, take a break, walk away”,
    to guiding me to a proper response,
    “It is fixable and it will drive you nuts if you leave it that way so do what you need to do to make it right”,
    finally to actually making the repair. Good woman. She’s been a great help.

    Like James mentioned cleaning up the work area always seems to be a help. I find it easier to concentrate on fixing my screw up after the area is decluttered, cleaned, organized, etc.

    The father in law is working on building a Bleriot XI. Plans were sourced from a friend within a very well known aviation museum. The fuselage frame is largely complete. Whether or not it ever flies is anyone’s guess.

    1. John Distai

      Steve – Please count yourself extremely lucky and give your wife some extra kindness.

      My spouse would say “Oh, you shot a hole through the gas line with the nail gun? That sounds bad. Is that what I smelled in the other room? You should call someone to get that fixed. In the meantime, I think you should open some windows so the rest of us don’t get a headache. Can we please discuss this year’s vacation plans after dinner tonight? By the way, I’m leaving to take the children to [ some activity ]. See you in a few hours! Call me if you need me!”

  13. Judd Fancher

    I must confess, I’m a daily Weaponsman reader. As an avid shooter I find the information, humor and prose to be highly enjoyable. Harrumph!

    I am also building and RV-8. Not as far along as you both, just finished the empennage, waiting for the QB wings+fuse to be delivered. I am following your build progress with great interest. Please keep the great blog posts coming! Any and all posts on the airplane are enjoyed as well!

    1. Hognose Post author

      Judd, thanks for reading and commenting!

      Quite a lot tougher than a -12, the RV-8. But you’ll be rewarded with amazing performance.

      One great thing about RVs is that they are the AR of airplanes. Everybody’s got one! When we thought our wingtips were going to be ugly in detail, we were able to go a few miles and look at a factory SLSA RV-12 and, behold, the same details on his wingtips are ugly — it’s the design, not the execution. We also were able to see an RV-10 in progress. The RV-10 guy convinced us to keep the project moving through the winter by using a high-end automotive rattle can primer on parts instead of the much-more-work Stewart System we used on the wings and empennage. Stewart’s Eko system is definitely more economical, if you don’t count the two turbine sprayers we bought (I bought a used commercial one and when it went paws up, couldn’t get parts from Graco; he then bought a new one).

      This is the first coat on some of the parts for the first step in fuselage/center section production, Step 20 in the plane. Setup and cleanup time is essentially nil with the cans.

      1. Judd Fancher

        Thanks! I tried both the Stewart Systems Eko-Poxy primer (two part water based) and Eko-Prime primer (one part water based). I like the one part Eko Prime much better, and the Eko-Etch does a good job with preparation. I went cheap and bought $50 LVLP spray gun for primer. It seems to spray the primer just fine.

        I’ve seen all sorts of homebuilt quality levels. Hopefully I will be up higher on the quality end. I want passengers to feel confident when they get in the plane, not that they are stepping into a rattling disaster. But I’m so early in the process that I cannot boast about my craftsmanship yet. I have too much to go, ask me in a year or two.

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