Would anyone like to have the FAI 100 meter timing distance to calculate you airspeed? FAI rules state the timing must be done over a 100 meter straight course (328.2 feet)

If you have a buddy with a very accurate thumb, plus an instant "on" flashlight, or better yet a strobe flash with a dump button, you can get a pretty accurate speed in MPH with an athletic stop watch.

This is the average speed over the course and not just a peak speed using GPS or the speed recorded for an instant such as a radar speed gun.

It pretty long to type out the numbers, but if there are some who would like to have an accurate table to work from, I can pound them out sometime and post it.

Blue Skyy

This is what I use.
We have a 700ft runway but you can use any length. If i fly our 700ft runway in 5 seconds, it looks like this.

700ft divided by 5 sec = 140ftper sec.
140 x 60= 8400 x 60=504000
504000 divided by 5280= 95.45mph.

About the same way I do it, but use a table to find the speed. That way I don't have to use a calculator at the field. I also add one tenth of a second to make up the lag in pressing the stop watch from the entry point on the run. My runs were consistantly too fast due to that lag in starting the stop watch.

Actually your way is much better... No table to lose!

Blue Skyy

Is to use 2 stop watches. The first on is clicked when the plane passes it, and left running. The second one is clicked when the plane passes it and left running. Then both watches are brought to one person who stops them both. Time of the second watch is subtracted from the time of the first watch. That is the time thru the trap.

No flashlights, signals, nothing. And having one person stop both watches is pretty close to instantaneous.

And I'm not out to set a new FAI 10cc record, so I can use a course longer than 358 ft or whatever...the longer time makes the effect of clock error much lower.

[QUOTE]Originally posted by ChuckAuger
[B]Is to use 2 stop watches. The first on is clicked when the plane passes it, and left running. The second one is clicked when the plane passes it and left running. Then both watches are brought to one person who stops them both. Time of the second watch is subtracted from the time of the first watch. That is the time thru the trap.



I am trying to picture this but I need slides!

It's a pretty radical concept.

Chuck;
Sounds like a great idea. I'll try it next week when
it warms up again.
Then I'll have three ways to measure the speed...

Syd

at a display we set two markers on the flight line at a set distance, i then sat in the car park a couple hundre feet away while the pilots flew right over the markers, i then timed it. the closer they flew to the markers the better the result, but by the end of the slot i could give them a failry close average speed. good enough for joe public watching them

Interesting ways to check the speed of our planes. I really liked the 2 stop watch method. I must try that one!

Blue Skyy