Bumper yaw string

A comment to Bumper's worries about tape residue:

I could only imagine that the tape on my 14-year old LAK-17a was
original to the ship and it was with great trepidation that I undertook
to replace it with a MKIV. As it turned out, the plastic part of the
tape simply popped off as easily as though it would have on its own on
the next flight leaving a huge mess of adhesive. With great care I
touched it with a finger nail and, to my delight, it simply flaked off.
It only took a minute or two of gentle scratching with my fingernail and
it was all gone! Then a bit of spit and a gentle rub with a microfiber
cloth and the canopy was pristine and ready for my new upgrade.
Couldn't be happier!

On 11/30/2015 10:28 PM, bumper wrote:
I received a private email asking why the MKIV is better than taped yarn and what improvements occurred between the various MK's. I'd like to share my response:


Were to start?!

Firstly I wanted to get rid of the tape. When tape residue hardens, it can be extremely difficult to remove. Clear tape is the absolute worst. UV degrades the plastic part and the underlying adhesive is like concrete. The plastic won't peel off but stays intact enough to "protect" the adhesive from any solvent one is brave enough to use on the acrylic. Denatured alcohol, applied briefly is about as brave as I can get. I've spent almost an hour removing one of those on one of *redacted - a famous supporter of soaring* ships. No thanks.

So there were two primary goals. Get rid of the tape and make sure that what replaced it would come off cleanly when that time arrived. Also the base should be completely clear. And shaped to help minimize static yarn static cling and keep it clear of the canopy in flight (no touching so no yarn "wipe mark" from fine scratches).

Initial change from MKI to MKII was shape only. The MKI was shaped like a baseball diamond, pointy end forward. The MKII is 3/4" long and pie shaped in a sense, it being cut from a 3/4 inch circle rather than a 1 1/2" circle (which would make it a real pie shape).

MKII to MKIII was an overlay plastic material change. But sill using semi-rigid plastics with a mechanically pressed yarn channel.

MKIII to MKIV changed to a softer plastic overlay (edit - less tendency to lift up off canopy at the edges), with a thermoformed yarn channel.

Subsequent improvements did not result in a MK number change, but included injecting a polymer into the base yarn after final assembly to help prevent yarn pull-outs. Not a common problem, but there were a few. There were a number of lesser improvements relating to assembly methods, mostly for quality, consistency, and for ease of assembly.

Included index dot (some use them to mark center line inside canopy) has changed from paper to plastic and finally to "white" reflective tape. Light color so it doesn't fool the peripheral vision into thinking it's another aircraft. Size has changed too, and is now 5 mm.

A recent change to a corner rounding punch to cut the rear radius was a complete flop. Could not make it do as nice a job trimming the clear double sided adhesive as doing it the old way by hand using scissors. It looked so good going in and I spent hours trying to get it to work. Can't win them all.

The shape, like one section of zig-zag tape, creates two tiny vortices to help keep the yarn "alive", while the .038" base thickness and yarn tunnel keeps the yarn from touching the canopy in flight.

There are some 30 steps in manufacturing each MKIV, along with a dozen primary jigs and fixtures and a number of custom made tools as well. All to make the job go a bit smoother and to insure perfect alignment of center yarn hole, yarn, base, adhesive, and a bubble free clear laminate. All resulting in a small thing that looks befitting of the ship it goes on.

all the best,

bumper


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Dan, 5J