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Speed,Combat,Scale,Racing => Speed Talk => Topic started by: Dick Tyndall on June 18, 2021, 07:17:43 PM

Well, since I don't have an old rule book with the speed chart in it, I don't quite understand how to calculate the planes speed from the rules on AMA's website. Can someone please explain how this calculation is done? I didn't listen enough in math class in school.........I will be timing some combat planes on 60 foot lines.
Dick Tyndall

7 laps on 60' lines is 1/2 mile. so the math is fairly simple
(7 * 2* pi *60 = 2639 feet, 1 mile = 5280' so 1/2 mile = 2640', close enough :) )
A bit more math and you get that speed in mph = 1/2 * 3600/ time for 7 laps = 1800 / time for 7 laps.
Notable numbers for combat models:
24 sec = 75 mph
22.5 sec = 80 mph
20 sec = 90 mph
18 sec = 100 mph
15 sec = 120 mph
(Same numbers work for 8 laps on 52.25' lines)

Here's what I have and keep in my flight box sometimes. It's rather old school from the March 1960 issue of Aero Modeller Magazine. I used this whiz wheel, and also a calculator and the above formulas, and compared the results. The whiz wheel is right on the dot. I have since changed out the tack to a low profile thumbtack. I have a lot of grommet sets, so I should eventually change it from pin to grommet, but I just never get around to it.
Mark
(https://i.postimg.cc/zXVMYxpZ/Speedcalculator.jpg) (https://postimages.org/)
(https://2img.net/h/i32.photobucket.com/albums/d26/batjac/DSCN3082_zpsba11ae2a.jpg) (https://2img.net/i/fa/pbucket.gif)
(https://2img.net/h/i32.photobucket.com/albums/d26/batjac/0bcaaf0b2fdb49708fce569bc79910be_zps6ce2dadf.jpg) (https://2img.net/i/fa/pbucket.gif)
(https://2img.net/h/i32.photobucket.com/albums/d26/batjac/DSCN3090_zpse1d66440.jpg) (https://2img.net/i/fa/pbucket.gif)

Thanks Pat and Mark for the info. Don Stoneman and I went out Saturday to fly the "Toothpick" that he built but I didn't get any lap times that day. Need to get some more time on the engine. I figured we were going about 105 MPH on 10% nitro fuel. It was the first time I had seen one of these fly in over 40 years! We'll be stepping things up and using your calculations the next few times out to see where we are speed wise. Thanks again!
Dick Tyndall

Just a tip, when you're timing a plane from outside the circle, you can get better readings if you start and stop the watch while the plane's on the opposite side of the circle.
Motorman 8)
Always did. Used a tree, a telephone pole, any stationary object on the other side of the circle. You can even use the pilot if he's not walking around too much in the circle flying the airplane.......