Tuesday, August 31, 2010

ribstitching cord length

The amount of cord you need per rib is the sum of twice the length across the rib, plus twice the maximum width of the rib, plus the distance between stitches, all times the number of stitches in each rib, plus two feet for working cord length.

That is, ((2xCapstrip Width)+(2xMax Airfoil Width)+(Stitch Distance))x(Number of Stitches)+(2 feet working cord length) = string length per rib.

On the aileron cutout ribs, this work out to roughly stretching the string and spool as far apart as my arms will go while unwinding cord five and a half times. On the main ribs, I'm stretching the cord out seven and a half times while unwinding it. The excess will get used for the blind stitches around the aileron control cables.

It's a little excess, but cord is cheap, and having to stop because I ran out of cord before I ran out of rib is really, really, really annoying. Also, I don't trust my splice knots, so I tend to rip all the stitches out on a rib and start over; I'm going to sow this so when it gets recovered in forty years, the knots are still darned good and tight as the fabric around them starts to fail. If I had lower standards, I probably would have been done yesterday instead of Maybe Wednesday - but I refuse to settle for lower standards. This plane may be heavy, but she will be durable, safe, resilient, and capable for every hand upon her yoke.

The next one can be the lightweight bush-class STOL experimental fun machine that you wear as much as you fly - this one will teach people how to fly, and bear them safely through the skies.

Monday, August 30, 2010

PMR-30: even more Squee!

The Keltec PMR-30 prototype has been modified since I last got to play with it in Tennessee - so I was really looking forward to trying it out at Blogorado. This gun is the one and only that changed my mind from a distaste and dislike of handguns to really having fun shooting. It's light enough that I can hold it up for as long as I want to, despite my injuries. Unlike most light guns, including a 38 snubby that I would like to take a plasma arc to, the PMR30 has very little recoil, and even I have no problem firing it. Despite its capacity, the grip is comfortably thin for my small hands, well-textured for grip without cutting into my skin, and I don't have to cut my fingernails off to fire it without hurting myself. This doesn't mean it's just for small-hand people; the people out firing on the Colorado plains included a large rancher who had just as much fun firing it as I did. I intend to carry this gun for self-defense from people; he was contemplating dropping coyotes, snakes, and prairie dogs.

It's now even better - instead of trying to get enough momentum in a damaged shoulder to rack the slide, it now has a half-cock position for the hammer that allows racking it in two motions instead of one, dividing the effort in half. The pistol also locks back on an empty magazine, so you don't have to rack it after a magazine change! This means very little racking the slide, which is awesome - I can go shoot, change the clip, and shoot more without grunting or whimpering, or having to go find somebody else!

I swear they did something to the slide, as well. When I was shooting some really old low-budget ammo and got an incredibly unsurprising failure to fire, pulling the slide back to clear the chamber was as easy as pulling a knife out of a knife block in the kitchen.

In short, I love this little gun. It's the only one I've handled that's both functional and fun for me!

Unfortunately, it's only going to available in limited quantities until they iron out some production issues - see Cheaper Than Dirt's blog post on that. Still, I look forward to getting one for concealed carry!

Saturday, August 28, 2010

Rib Stitching

Here's a nicer, prettier, faster video version of what I'm doing.

Friday, August 27, 2010

Doping the wing

The wing has been covered with Ceconite and ironed taut. Applying dope until it encapsulates the fibers will relieve the tension on the fibers while locking the fabric together, and making a base the silver and color coats can stick to. There are three different dopes for Ceconite - one green, one blue, and one clear. If you look inside an inspection hole and the fabric looks pink instead, it's probably poly-stits instead. The best way to tell is to check the paperwork; the second-best is to look for the stamp on the fabric showing which STC it's under. Some newer systems can use the polyfiber or ceconite fabric for their base, so even the stamp's not a sure thing.

When sufficient dope has been applied, the cloth will turn translucent like a wet t-shirt. Do not apply too much, or you'll get a run on the inside of the fabric, that'll show all the way through the top coat of paint - no way to hide it.

The shininess shows that the dope is still laying on top of the fabric - unlike cotton, polyester will not absorb liquid, so the dope must be brushed til it penetrates the fabric. When you start to feel a resistance to the brush, you're done either way, as the dope has dried too much to really work further.

The more opaque look here shows the dope has penetrated the fibers and encapsulated them.

While waiting for the last of the dope to dry, my IA showed me how to make the cloth patches that secure inspection rings - and yes, that is a coffee can lid. It's the perfect size!

Placing powerful lights under the wing shows the shadow of the ribs like bones in an Xray, making it much, much easier to put the rib reinforcing tape directly on top of the rib, despite the cloth in the way. We had to do it rather quickly, though, so the lights wouldn't heat the underside of the wing.

Spent the rest of today laying out the holes for ribstitching, and poking them in with a needle.

The spacing in the propwash must be no more than 2.5 inches, and 3.5 inches apart outside of the propwash. However, they must be only 1.5 inches apart at the leading and trailing edge, and even though the aileron cove stops far short of the main wing's trailing edge, I still want all the stitches to line up so it looks neat. Neither top nor bottom are flat, and are both different curves - so the bottom is 1 inch shorter than the top at the main ribs, and the aileron cove is also shorter on the bottom than on the top. All holes are to be directly above each other anyway. Confused yet? Fractions and math are involved for optimal layout, as well as a measuring tape, a pencil, string and some tape or clothespins to secure it to be sure it looks right when all the math is done.

By the end of the day, my head hurt, I desperately need to catch up on sleep, and I got the entire wing ready for rib stitching tomorrow.

Wednesday, August 25, 2010

So tired

Back safe from Blogorado. Great food, Awesome people, absolutely awesome time. Review of the upgraded Keltec PMR-30 to come, but now, sleep.

Thursday, August 19, 2010

Wing (and shoulder) are taped!

I am so full of love for my friends. Despite the injured shoulder, the wing was readied for cover yesterday - my friend and wonderful apprentice mechanic set up the night before, came in the next morning, and worked her magic with a rivetgun to make the nutplates appear around the holes I'd drilled. My IA also attached the new better modified butt rib reinforcement that'll relieve the stress of fabric pulling on the bottom when the there's no corresponding fabric pulling on the top. I have so much love and happiness for their help!

Then together, we taped the wing - today I should get the fabric on her before I have to catch a flight! (And double-check my luggage, as somebody with a sense of humor keeps suggesting they fill a small bottle with the aircraft dope, and send it off as 'some of the dope I'm high on.')

The fuselage's annual should start, and work progress, on the wing while I'm taking a very much needed break and seeing my Calmer Half for a few days. I miss my love - I can't wait to see him!

Wednesday, August 18, 2010

Aileron Cable Run

Yesterday, we got the new cables made, and attached to the bellcrank. We cut a thin plastic shim for the surface where the bellcranks rubbed against its housing bracket, but that turns out to throw the securing bolt holes out of whack - so no shim for the bellcrank! I didn't do most of the work on the cable - I did a first crimp wrong, got it off, then on the second try, threw out my shoulder. So the rest of the cables were made by my IA and my friendly fellow apprentice mechanic, and I contributed where one working shoulder and two working hands could.

The old cable run touched the aileron bracket where it crossed -the bracket and cable were protected from each other with a few wraps of friction tape.

I replaced it this time with the thinnest sheet of phenolic I could find, secured by friction tape - it's hard enough the cable can't saw through it, but soft enough it won't abrade the cable, and slick enough that the run slides across like it's greased, without any feel of catching and rubbing.

In two days I leave for a gunblogger gathering, where it reputedly won't be raining. I may cry if it is, because today was the 33rd day in a row of rain. I'm so very tired of it being in the low 60's and drizzling.

I need to go put my arm up carefully and get healing rest - I've got to heal enough to shoot some wonderful toys later this week, and hug lots of people!

Sunday, August 15, 2010

Today's task list

Started the day by trying to clean last winter's grime out of the cockpit, then worked on the left wing.

Still to go: redo plumbing out of wing tank, re-install wing tank and drag wires through wing tank, add reinforcements for metal tank covers. Make new cables, fabricate new spacers for the bellcrank, install the control cable & bellcrank assembly, cover the wing. The list is getting short!

progress pictures - leading edge

The wingtip is composed of six separate pieces of metal, filed and shaped together to fit. Originally, there were five pieces, but when my IA made the decision to extend the leading edge to the top of the spar all down the length, I had already made the wingtip pieces to match the original, and fabricated a patch to cover the gap.

The patch only covers two rib bays because one rib was placed a quarter-inch outboard from the old spar; I didn't catch this until after it was nailed in place on the front and rear. Thus, the one-bay-wide panel that covers the decreased width and increased angle from the standard leading edge toward the wingtip was made full-length on the second time 'round. Yes, this means none of the other pieces fit as meant either, and had to be hand-trimmed, shaped and filed to fit.

View from the underside of the last two pieces outboard.

This has been one of the most aggravating parts so far - I expected it to take two days, and it took almost two weeks. Also, I am a rank beginner when it comes to sheetmetal - I can't help but compare my work to the gleaming polished sides of a T-6 on the field, and feel frustrated. Fortunately, it'll all be hidden under tape and cloth, and if I did not show my shame here, you would never know it.

Wednesday, August 11, 2010

More important than mechanical minutae

Terry was a good man, and a good pilot, and never hassled me about my progress on my plane out of anything other than friendly humor.

Wild Bill was a good man, good pilot, sharp mind and keen business sense combined with a love of aviation and pride in his planes (He never minded me taking a break to ogle his beauties, and would proudly point out the little oddities and engineering marvels not obvious at the first glance.)

Aaron Malone I only met a few times, but I remember him as loud and fun-loving.

It's a small world, and when we're talking airplanes, we don't often cover family, or profession, or other topics - I never realized until he was gone that Aaron was the brother-in-law of one of my friends... or that his wife iswas Terry's daughter.

If you have the time, inclination, and attention to spare, please say a small prayer for her and her family.

I know not a day goes by you don't hear of multiple car wrecks in the rush hour report, but there's the psychological buffer that you don't expect to know the person involved. Three crashes in three weeks, and hunting season has just started... be careful out there.

Sunday, August 8, 2010

You Can't Ignore These Begging Eyes...

(Cartoon drawn by and shared courtesy of Emily Willemse)

Tuesday, August 3, 2010

Taylorcraft aileron cove

Pre-war Taylorcraft aileron cove looks kinda like swiss cheese. In order to get the fabric covering of the aircraft to stay on the metal, lots of holes were drilled in the aileron cove, and a peice of fabric was laid on the inside (back of the peice) and doped. When the fabric was wrapped over the aileron well while covering the wing, the dope on the surface fabric would bond to the fabric strip on the inside, and despite the extreme concave surface, the fabric would not snap away from the metal.

I wanted to avoid making all these holes, and to use the post-war solution of screwing a small thin strip of metal down the length of the cove in the middle of the curve, then laying a fabric patch over it. However, when I got the aileron cove fitted and attached, I discovered a small problem: insufficient clearance. There is very little space between the aileron cove and aileron - in fact, it will be about an eighth of an inch when the fabric, dope, and color coat have been put on. This is definitely on plane that doesn't need gap seals.

It does, however, need the fabric on the back of the cove. I am not going to try to move the aileron himges and control surfaces out; I'm just going to put the battery back on the charger after depleting it making holes with the step drill. At least it's starting to look like an airplane! (The yellow on top of the wing is the aileron - I got tired of carting it across the shop and back every time I wanted to check clearance.)