The UV Index and why your canopy is your friend

Some older ones do, some don't. That's what we found by testing a
variety of gliders at our gliderport. So, I wouldn't suggest resting
easy until you've tested your own canopy.

Greg Arnold wrote:
Do older canopies also protect against UV, or is it only the newer ones?
Maybe you could do this test on some of older canopies at your
gliderport?


Eric Greenwell wrote:
I recently bought an Oregon Scientific UV888 Personal UV Monitor (~$30).
Among other things, it measures the UV flux and computes the UV Index
(UVI), then determines a "safe exposure time" based on your input of
skin type and the SPF of the sunscreen you are using.

Naturally, I made a measurement in the sun (UVI = 8), then another one
inside the cockpit (UVI = 0), indicating the canopy provides quite a bit
of protection. Testing other kinds of plastic, like baggies, plastic
wrap, Lexan, etc., gave readings from 0 to 7, so not every kind of
plastic is protective.


Looking at an "erythemal dose rate" chart, you can see almost all (99%)
of the dosage in the direct sun occurs below about 330 nm. Since our
canopies block UV below about 360-370 nm, they provide essentially
complete protection from damaging rays. The fraction of the UVA that
comes through will still give you some tanning, and some fabrics will
fade slowly, but your skin is protected from the UVB. This is very good
news, that the canopy affords even more protection than I first thought.

wrote:
Greg Arnold wrote:
Do older canopies also protect against UV, or is it only the newer ones?

I haven't tested a variety of canopies, but based on the data sheets
from acrylic manufacturers, and comments by canopy and sailplane
manufacturers, I'd expect even older canopies (mine is 12 years old) to
offer plenty of protection. Acrylic that transmits UVB is more expensive
than the ordinary kind, so there would be little reason to use it.

Maybe you could do this test on some of older canopies at your
gliderport?

Some older ones do, some don't. That's what we found by testing a
variety of gliders at our gliderport.

Do you recall which gliders didn't offer as much protection, and how you
tested the canopies?

So, I wouldn't suggest resting
easy until you've tested your own canopy.

And at $30 or less for a UV Index meter, it'd be a cheap purchase for a
club to make. You only need to check each canopy once! And, if anyone
finds canopies that _don't_ pass the test, please tell us about it.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Someone brought one of those UV meters out to the field a month or two
ago, probably the same one you have. As best as I recall, it was
reading 12 (extreme) outside. When put under a newish DG800, older
DG200, and very old Kestrel, it read 0. Put under a 20 y.o. LS-6 it
read 3 or 4, indicating only around 75% was being absorbed (still
better than nothing).

wrote:
Someone brought one of those UV meters out to the field a month or two
ago, probably the same one you have. As best as I recall, it was
reading 12 (extreme) outside. When put under a newish DG800, older
DG200, and very old Kestrel, it read 0. Put under a 20 y.o. LS-6 it
read 3 or 4, indicating only around 75% was being absorbed (still
better than nothing).

Very interesting. It's going to be a while before I'm near a collection
of gliders, so I hope others will buy or borrow a meter and check the
gliders in their club, and report the results.

Do you know if the LS-6 had the original factory canopy or a replacement?

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

I think it's the factory canopy but I'm not sure.

Eric Greenwell wrote:
wrote:
Someone brought one of those UV meters out to the field a month or two
ago, probably the same one you have. As best as I recall, it was
reading 12 (extreme) outside. When put under a newish DG800, older
DG200, and very old Kestrel, it read 0. Put under a 20 y.o. LS-6 it
read 3 or 4, indicating only around 75% was being absorbed (still
better than nothing).

Very interesting. It's going to be a while before I'm near a collection
of gliders, so I hope others will buy or borrow a meter and check the
gliders in their club, and report the results.

Do you know if the LS-6 had the original factory canopy or a replacement?

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Are most glider canopies made of approximately the same thickness
material?

Chip Bearden
ASW 24 "JB"

wrote:
Are most glider canopies made of approximately the same thickness
material?

All the ones I've looked seem to be about 0.60". Typical acrylic's
cutoff is steep and deep (1% transmission below the cutoff), so even
twice the thickness makes little difference. The acrylics designed to
pass UV (at least from the Cyro company) have a more gradual "tail".

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Earlier, Eric Greenwell wrote:

All the ones I've looked seem to be about 0.60"...

Now wait a minute, Eric, I think you might have slipped a decimal
point.

A thickness of 0.60" is about 5/8" or about 15mm. I have seen aircraft
transparencies that thick, but only on transport and jet fighter
windshields. In polycarbonate, thicknesses like that might be
considered "Bullet Resistant" (I don't like the term "bulletproof").

The canopies for the early HPs are usually made from 1/16" thick
material; that's about 0.063" or just over 1.5mm. That's pretty typical
for small transparencies such as you'd find in older sailplanes with
two-piece canopies. It makes for a transparency that is perfectly
adequate for most sailplane flight loads, but with less than inspiring
stiffness; especially for limber plastics like polycarbonate. For a
while I had a 1/16" Lexan forward canopy on my HP-11, and I remember
once when I was pressing back to Truckee through hail that the whole
forward canopy shimmered like a soap bubble with each hailstone strike
- and they were not much bigger than peas.

More typical sailplane canopies, such as the HP-24 transparencies I've
been ordering, are made from 1/8" material; that's 0.125" or just over
3mm. Most of the broken European sailplane canopies I've seen seem to
be about 3mm thick.

Here's the thing, though: The minimum thickness of a canopy is often
substantially less than that of the original sheet of material. Since
most canopies are either free-blown or stretch-formed from flat
material, the finished canopy has more surface area than the original
pre-formed material. That extra area doesn't come from nowhere; it
comes from stretching the acrylic while it is hot and rubbery. Since
(for our purposes at least) acrylic is incomressible, it has to get
thinner where it is stretched, and gets thinnest where it is stretched
the most.

It's hard to say how much thinning is typical, but I have seen pieces
of a broken canopy made from 1/8" material where the minimum thickness
at the crown was about 0.090".

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

Bob Kuykendall wrote:
Earlier, Eric Greenwell wrote:

All the ones I've looked seem to be about 0.60"...

Now wait a minute, Eric, I think you might have slipped a decimal
point.

It's the "beanie" option offered by all the manufacturers to pilots that
like to fly with the hats that have the little button in the center. It
hurts like heck when turbulence throws you against the canopy, but it
doesn't crack the plastic!


More typical sailplane canopies, such as the HP-24 transparencies I've
been ordering, are made from 1/8" material; that's 0.125" or just over
3mm. Most of the broken European sailplane canopies I've seen seem to
be about 3mm thick.

All this time I've been flying gliders, and I've never measured one
until tonight. So, here it is: 0.096"! Lots thicker than I thought.
That's at the vent window opening on my ASH 26 E, the only convenient
point to put a caliper (I hope I never get the chance to measure it
elsewhere).

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org