The UV Index and why your canopy is your friend

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

Guy Byars wrote:
So should open cockpit vintage gliders come with a
health warning then?

No, the gliders with canopies should have the following warning:

WARNING: Do not depend on this canopy for protection against the sun. Even
though you might not receive a sunburn through this canopy, you will still
be exposed to the sun's UVA wavelengths. The UVA wavelengths are a proven
carcinogen. While using this canopy you should still protect yourself with
opaque clothing and broad spectrum sunscreens.

Guy, I am afraid I have to disagree with the notion that sailplane
canopys lack protection from UV. I would like to quote from an artical
written by Friedel Weber (DG Owner) which appeared on the DG websight:
"We also asked Mecaplex about the transmission of UV light through the
canopy. The canopies do not totaly screen out UV but do absorb about
95% of it." Further, during one of my visits to the Aero in
Friedrichshafen several years ago I discussed this at the Mecaplex
stand. We were having some language difficulties at the time so they
offered to send me their catalogue describing their offerings. They
offer different materials. As I recollect, those that I looked at were
polycarbonates all of which absorbed 95% or greater.

What we realy need to be concerned about is all the standing around on
the ground without adequate protection.

Lorry

In message om, Lorry
writes
snip

What we realy need to be concerned about is all the standing around on
the ground without adequate protection.

In fact by the time I've protected myself for all the standing around
helping on the launch line, I've protected myself for flying. One thing
that has caught me is how dehydrated I can get hanging around the
airfield - it has been very hot (for Scotland) this year, but maybe anno
domini is catching up with me as well...

--
Surfer!
Email to: ramwater at uk2 dot net

"Lorry" wrote in message
ps.com...

What we realy need to be concerned about is all the standing around on
the ground without adequate protection.

Lorry

Just right, Lorry
I have heard several Dermatologists say that the first 30 min of exposure
produces the most severe damage. After that, the outer, dead, layer of the
skin becomes more opaque to UV. A good argument for sunscreen before going
out in the sun.

Hartley Falbaum
"KF" USA

In message , HL Falbaum
writes

"Lorry" wrote in message
ups.com...

What we realy need to be concerned about is all the standing around on
the ground without adequate protection.

Lorry

Just right, Lorry
I have heard several Dermatologists say that the first 30 min of exposure
produces the most severe damage. After that, the outer, dead, layer of the
skin becomes more opaque to UV. A good argument for sunscreen before going
out in the sun.

A lot of sunscreens need applying 30 minutes or so before going in the
sun.

--
Surfer!
Email to: ramwater at uk2 dot net

Guy Byars wrote:
I must strongly disagree with Eric's post!!!

He talks about wrinkling and skin damage (sunburn?). Well, if you are only
concerned about sunburn and wrinkling, then go ahead and depend on the
canopy for your protection.

However, nowhere in Eric's post does he mention SKIN CANCER!

The UVA range of the sun's spectrum has a longer wavelength and penetrates
right through your canopy and deeply into your skin. There is a large body
of research which ties UVA exposure to skin cancer.

Your obsession with UV exposure thru canopies makes me laugh. You are
likely getting far more exposure standing out on the ramp waiting for a
tow. How many of you realize how poorly many fabrics protect you
against UV? Not many, based on this collective list of responses. I
remember a story an old physics instructor told me about a checker
board pattern sun burn from wearing plaid shirt while hiking thru the
Italian alps during WWII. Your light colored cotton shirt has only a
SPF of about 10 (or less):

http://tinyurl.com/gzesj

The good news is that there is a laundry product called Sun Guard that
can improve this to around 30:

http://www.sunguardsunprotection.com/

Also, Plexiglas blocks over half of the UVA spectrum, and this is the
shorter wavelength, higher energy half.

Tom Seim
2G
Richland, WA

I never said that canopies lack protection from UV. My point is that it is
in no way complete or sufficient protection against the part of the UV
spectrum that causes skin cancer. Several years ago, I put numerous
Mecaplex canopy samples in a precise spectrophotometer and generated
spectral curves for them. All the curves showed good UVB protection, but
inadequate UVA protection. (Note the spectrophotometer I used for my
research was a very precise research instrument at the University of
Cincinnati.... not a $30 toy)

Although your references claim to have products which block 95% of UV light,
that is not at all a precise measurement of the problem. Perhaps they block
95% of the UVB, but what do they do for the UVA? What % do they block at in
the 280nm-320nm range (UVB)? What % do they block in the 320nm-380nm
range(UVA)?

Again, I reiterate. Canopies will filter out UVB light which will provide
protection against sunburn. Canopies do a very poor job of filtering out
UVA light which causes skin cancer.

Guy Byars


"Lorry" wrote in message
ps.com...

Guy, I am afraid I have to disagree with the notion that sailplane
canopys lack protection from UV. I would like to quote from an artical
written by Friedel Weber (DG Owner) which appeared on the DG websight:
"We also asked Mecaplex about the transmission of UV light through the
canopy. The canopies do not totaly screen out UV but do absorb about
95% of it." Further, during one of my visits to the Aero in
Friedrichshafen several years ago I discussed this at the Mecaplex
stand. We were having some language difficulties at the time so they
offered to send me their catalogue describing their offerings. They
offer different materials. As I recollect, those that I looked at were
polycarbonates all of which absorbed 95% or greater.

What we realy need to be concerned about is all the standing around on
the ground without adequate protection.

Lorry