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Bumper
Products by John Morgan
Overview
John Morgan makes some very nice, simple, inexpensive products for
sailplanes. For fun he flies a Schleicher ASH 26 and an Aviat Husky
A1-B.
Click on the images above to view larger
versions.
Notes from Bumper on Synthetic vs. Natural
Wool Yaw String
Natural wool is reputed to be kinder to canopy plastic in terms of not
scratching. However, natural wool doesn't last as long as synthetic yarn
with lot's of UV exposure. In practice, since the clear base of the MKIV
raises the yarn slightly, on most gliders the yarn doesn't touch the canopy
in flight. Thus, scratching has not been an issue with synthetic yarn.
Another plus, the synthetic yarn is shinier and thickness is more
consistent.
I've seen gliders tied out on the ramp with an arc of scratching under the
yaw string. This is caused by dust and dirt and probably would occur with
any string or yarn material given enough time, wind, exposure, and abrasive
dirt.
Natural wool is reputed to be kinder to canopies, and so this was the string
material I first used for the MKI some 11 years ago.
The natural wool works well, but in a few cases, such as with the Civil Air
Patrol gliders being stored on the Minden ramp with no canopy cover in windy
conditions, the natural wool fades and weathers quickly, and within a year
of so will start going away. Sometimes leaving just a stub of yarn.
In my testing of the MKII, I determined that during flight the string
doesn't touch the canopy! (This also assumes an anti-static plastic polish
or cleaner (like Plexus) is used on the canopy - always a wise idea to help
keep abrasive dirt from clinging to the canopy.) This test was done
with a piece of plexi with a MKII mounted and held out my truck window.
Pretty much all angles of attack, not stalled, the string flows back
parallel and just above the boundary layer. This is as intended and part of
the reason for the MKIV's .038 thick "turbulator" base.
Over a year ago I started offering synthetic yarn, mostly for the improved
durability. It also has advantages in having a more consistent thickness and
sheen for better appearance. It has been popular, accounting for over half
of sales. Natural wool remains popular too.
How to Order
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