Bill Malvey wrote:
>It would be interesting to replicate these claims on the ground. Have a
>helper hold the plane at a measured distance and see what you can see. 4700
>feet is nearly .9 miles, which is a pretty good distance. At that distance a
>120 inch span plane is only subtending 0.12 degrees of your visual field.
>That's a VERY small target for your eye.
Here's another way to look at this. The 20/20 line on the eye chart in your eye doctor's office has letters that subtend one minute of arc each, and since there are 60 minutes of arc in one degree, the 20/20 letter is about 0.017 degrees "tall". (I just measured the 20/20 E in my exam room and it is about 6mm high, and is about 15 feet from the exam chair. Yes, its a slow afternoon here.) So, assuming Bill's calculations above are correct, the sky is clear, the plane is dark against the bright sky, the wing chord is reasonably thick, and the pilot has 20/20 vision, the sailplane should be visible at that altitude. Just don't look away from it or you might not see it again! I lost my 4 meter Discus a few weeks ago in Visalia at a much lower altitude because the sky was very hazy, the wings were white, and I looked away for just an instant. Expensive lesson!
Stan Sadorf
[EMAIL PROTECTED]
