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General control line discussion => Open Forum => Topic started by: Darwin Ulledahl on May 07, 2016, 05:09:41 PM

Title: Combat math
Post by: Darwin Ulledahl on May 07, 2016, 05:09:41 PM

Had a blast test flying me Winder. This thing really moves  :o. 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?

Title: Re: Combat math
Post by: Richard Entwhistle 823412 on May 07, 2016, 05:15:35 PM

117.234 mph

Title: Re: Combat math
Post by: Tim Wescott on May 07, 2016, 05:21:04 PM

Quote from: Richard Entwhistle 823412 on May 07, 2016, 05:15:35 PM

117.234 mph

You didn't show your work.

Title: Re: Combat math
Post by: Gordan Delaney on May 07, 2016, 05:29:14 PM

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

Gordy

Title: Re: Combat math
Post by: Mike Haverly on May 07, 2016, 05:43:50 PM

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.

Title: Re: Combat math
Post by: Tim Wescott on May 07, 2016, 07:56:46 PM

Quote from: Mike Haverly on May 07, 2016, 05:43:50 PM

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).

Title: Re: Combat math
Post by: Paul Smith on May 07, 2016, 08:23:20 PM

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.

Title: Re: Combat math
Post by: Darwin Ulledahl on May 07, 2016, 09:02:31 PM

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

Title: Re: Combat math
Post by: Motorman on May 08, 2016, 12:57:44 PM

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

MM

Title: Re: Combat math
Post by: Brent Williams on May 08, 2016, 08:58:13 PM

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.

Title: Re: Combat math
Post by: Tim Wescott on May 08, 2016, 09:03:25 PM

Quote from: Darwin Ulledahl on May 07, 2016, 09:02:31 PM

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.