Combat math

[Darwin Ulledahl]

Had a blast test flying me Winder. This thing really moves  . Been 45 yrs since my last one. Need help calculating MPH. What is the speed (mph) if the radius is 63 ft, trust line to shoulder. (2.3) sec for one lap?

[Richard Entwhistle 823412]

117.234 mph

[Tim Wescott]

117.234 mph

You didn't show your work.

[Gordan Delaney]

That sounds a bit to fast for a ST 35. Just my thought.

Gordy

[Mike Haverly]

http://www.flycl.co.uk/control_line_speed_calculator.htm 

Here is my work.   112.38 according to this.  That is still pretty quick for Tigre.

[Tim Wescott]

http://www.flycl.co.uk/control_line_speed_calculator.htm 

Here is my work.   112.38 according to this.  That is still pretty quick for Tigre.

That's the same number I got working from first principles -- but Howard's an engineer, so I didn't want to argue with him.

From first principles:

(63 feet) * (2 * pi) / (2.3 sec) = 172.1ft/sec

(172.1 ft/sec) * (3600 sec/hour) / (5280 ft/mile) = 117.34 mi/hr

(Note that I rounded while showing my work, but carried over intermediate results -- which is absurd, because for that last .04 mph to mean anything you'd need to have measured the line length to 63 feet +/- 1/4 inch, and you'd have had to measure to less than 1/1000th of a second -- 117 mph is probably more honest).

[Paul Smith]

It would be a lot easier if you used the standard 60' line length.  Then you could use the common formula:  1800/seconds per half mile.

By that formula, it works out to 111.8 MPH, disregarding the fact that you penalized yourself with over-long lines.

[Darwin Ulledahl]

Thanks guy's, that's what I came up with using my high school math 117 mph. Using 60ft lines my 63ft radius length was measured from thrust line to  my shoulder as the pivot point.

Darwin

[Motorman]

If you're going that fast you better get a better prop on it.

MM

[Brent Williams]

I'm sure you were scootin' along, but the pertinent question to ask is 2.3 seconds at what altitude?  

There is a big difference between 2.3 seconds at 5 feet off the deck vs 2.3 seconds at 30+ft off of the deck.

We fly in a hemisphere, the higher you go, the smaller the circle.

[Tim Wescott]

Thanks guy's, that's what I came up with using my high school math 117 mph. Using 60ft lines my 63ft radius length was measured from thrust line to  my shoulder as the pivot point.

Darwin

If your lines are 60' from handle center to fuselage center, the way the rules say, then you've got an awfully long arm.