measuring airstrip lengths

[zero.one.victor]

An old Alaska pilot I know told me about a good way to measure out the length of that uncharted airstrip or sandy stretch of beach that you're thinking about landing on. It's an old trick,but some of you might not have heard of it.
At 60 knots (70 mph) groundspeed, you cover 100 feet every second. Just slow down to a steady 60 knots,time your flight along the strip,and do the math. If you're on the way somewhere & see an inviting place but don't want to take the time to slow down & stabilize at 60 knots, use 90 knots (105 mph) instead. That works out to 150 feet per second. Takes some of the guesswork out of the land/no-land decision. A GPS comes in handy to check the indicated airspeed for a given groundspeed.
I remembered hearing about this trick when I was given a digital stop-watch like alot of guys use for IFR. I couldn't remember the speeds involved but it was easy to work the math out. I've tried it out,and it works pretty slick. Gives me a good reason to pack the stopwatch around anyway.

Eric

[n3437d]

All well and good if one is flying along said runway at a reasonable minimum safe altitude (for terrain). How about taking into account "slant angle?" The higher one is and the more acute the angle is the more error one injects into the "rule of thumb"

[zero.one.victor]

I never claimed it was rocket science-- just a method that's a bit more accurate than just squinting at the strip & comparing it to your thumb.
I find that by using the intersection of my v-strut ( I fly a ragwing) as a bombsight, I can be reasonably accurate as to when I'm overhead the beginning & end of the strip.
If you're not pretty much right over the strip & at a reasonably low altitude, all the bets are off.

Eric

[mit]

All well and good if one is flying along said runway at a reasonable minimum safe altitude (for terrain). How about taking into account "slant angle?" The higher one is and the more acute the angle is the more error one injects into the "rule of thumb"

You have your ass right down on it cause your looking for stumps and holes and moose and bears and big rocks.... oh I forgot we weren't talking about landing on a sand bar. And the timeing thing may be on the third pass.