Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Speed formula

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Old 06-25-2007, 10:00 PM
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skull1971
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Default Speed formula

Hey gang! what was the formula for finding mph over a timed distance? I remember seeing something on here, but can't find it. Got my q-500 up and running, and one of the geezers at the field said he thought it was running in the 130-140mph range, and I want to find out for sure. As far as how fast it was, I don't know, but it was quick.
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Old 06-25-2007, 11:19 PM
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Mike Connor
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Default RE: Speed formula

((5280/feet traveled) x seconds) it took will give you seconds per mile
3600/seconds per mile will give you miles per hour.
Fractions of a second are important, especially on short distances.
Parallax will make it difficult for one person to get an accurate speed.

What kind of engine you got on your Q-500?
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Old 06-26-2007, 08:38 AM
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Default RE: Speed formula

Hers what I use if I have too. Lets say you have a 900ft runway and it takes your plane 6 seconds to fly the distance.

900ft div by 6 sec = 150ft per sec

150 x 60=6000 x 60 =540000

540000 div by 5280 = 102.2 mph.


The 60 x 60 thing is 60 sec in a min and 60 min in an hour
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Old 06-26-2007, 04:49 PM
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Default RE: Speed formula

We have tried timing boats manually and this will be the same case. If your timers both at the entrance and exit are each .25 sec off and you make a 6.5 sec pass then you just went 94mph. That's almost 8mph difference with a human having reaction time of .25 sec. I have not seen anybody yet with that reaction time so your numbers could be outstanding or not worth mentioning. It is a difficult task. If you know a cop or somebody that does, see if they can get him with a radar gun at the field. They usually get a kick out of it.
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Old 06-26-2007, 07:10 PM
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Default RE: Speed formula

Rossi 40 with a little pipe

on a ballpark, GUESS,, 136.36 mph. 600ft runway, about 3 or so seconds.
Go figure,, it's faster than my Shrike 40. I got a Rossi 60 with a pipe, think that'll make it go??

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Old 06-26-2007, 11:17 PM
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Default RE: Speed formula

human having reaction time of .25 sec.
A quarter second reaction time is typical, however it does not apply in this case. When observers are able to anticipate the timing threshold, you would find the error much lower than a ten of second.
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