Saturday, March 12, 2011

Sunglasses for Soaring

A reader asked me about sunglasses. Here's what I know and what I think.
  • Aviator sunglasses are designed to prevent light from coming from a wide range of angles, so they all tend to have a large teardrop shape. They don't change much to follow fashion. I happen to like mine, so I wear them for general use as well, not just for flying. A long time ago, I used to get headaches from bright sunlight, so I tend to wear sunglasses most of the time I'm outdoors or driving.

  • Polarized sunglasses generally should NOT be used for aviation. Two reasons - one pretty obvious, one more subtle:

    Cockpit glass and canopy (or plastics) may have some unintentional polarization, and when combined with polarized sunglasses can show dark spots, distracting color patterns, and even large dark areas which can greatly interfere with vision. Some instrument glass windows, devices such as handheld GPS units and PDA's, and digital watches can also be partly polarized and difficult to read. We need to reduce problems in the cockpit, not create them.

    Polarized sunglasses are designed to cut glare. But sometimes a little glare is a good thing! When we're flying, we're always looking for other air traffic, sometimes at great distances. Depending on light conditions, sometimes a "glint" off a distant aircraft's canopy is all you ever get to see - but that may be enough to catch your eye and distinguish the aircraft from a plain background or from ground clutter. Polarized sunglasses tend to filter out that "glint" and make it harder to see small, distant aircraft. Glare from our own aircraft tends to be not so much of a problem, due to the design and colors of dashboards, cowlings, etc., so I've never felt that losing the polarization caused me any local problems.

  • I started out using American Optical's FG-58 sunglasses. They were advertised as kind of the "standard" aviator sunglasses used by the military. They were OK, but due to the straight and kind of heavy design of the temple, I found them a little uncomfortable. They're pretty rugged. Although I've switched away from them, I still keep them in my gear bag as a backup, or in case I ever have a passenger who needs sunglasses.

  • When I started using a PDA for soaring navigation, I found the AO's to be too dark. I couldn't see my iPAQ's screen. I switched to "gradient" sunglasses in which the lower part is not as dark as the upper part. That way when I glance down I can see the PDA screen, but when I'm looking out the cockpit I get more protection.
All that could apply to any kind of aviation. But for soaring, there's one other feature that I learned to love. Yellow lenses help you see cloud structure better than other colors. It sounds like a trick, but seeing is believing. There's something about the colors of light that water transmits, and the fact that yellow lenses filter out more blue light, that enhances the contrast of clouds, especially the thin wispy parts.
When we're soaring on a day when cumulus clouds exist, we look for clouds that are just starting to form - they have the strongest lift. If you look at the bottom of a "young" CU, it may look flat or slightly concave. That's where the rising moist air cools to the dew point and the cloud forms. But look carefully below the bottom of the cloud. Sometimes you can see that it is not a definite line, you can see wispy trails leading up to the base. You're actually seeing the water vapor starting to condense, and you'll see it more in some places under the cloud than others. Those are the areas of strongest lift. Try this (even from the ground) with and without yellow sunglasses. Huge difference! With lenses of other colors you may not see those wisps at all and with the yellow lenses they pop out at you. Sometimes you can spot the wisps a few minutes before you can see the CU at all - and when you're hunting lift, sometimes that makes all the difference.
So I'm now using Serengeti Aviators Drivers Gradient glasses. I like them a lot. Only two things I would improve about them:
  1. The lenses are not as hard as some other sunglasses. I scratched my first pair after a year or two, right in front of my pupil. I got another pair and am much more careful with them. I always keep them in a semi-rigid case with a soft lining.

  2. The temples are a pretty thin wire. They're strong, that's not a problem. But I have a radio earpiece that I clip on when flying some gliders, and the temple is so narrow the clip slides around a bit. Not a big problem - I much prefer the smaller and lighter temple compared to the AO's.

2 comments:

Larus_p said...

Thanks Roger, very helpful. My application to Evergreen soaring (www.evergreensoaring.com) has been accepted, and they have a full operation planned for Sunday March 20th - I'll be there for my first lesson in 26 years!

Cefn Hoile said...

The use of Stihl yellow contrast safety glasses is a popular choice with paraglider pilots. UV protection, anti-fog, scratch protected and very cheap. With paragliding, it's also worth having eye protection in case of landing in a bush :) Orange ones are slightly darker in case you need the tint, but I haven't tried them.