Radius of turn

[Bell427]

Hay!

I need some help. My instructor gave me a task, to find out, from where the rule of thumb equation for radius of standard turn ( r(nm)= TAS(kt)/200) is derived from. The more precise equation is: r(NM)= TAS(kt)/189,4, for rate R=3°/s turn.

I know that full equation for radius of turn in NM is:
r= TAS(kt)/ rate of turn(1,2,3,)x60x3,14(pi)

thanks for answer!

[Nightrider]

Just had a chat with some little schoolboys.....Their answer was:

180 Kts means 180 NM per hour....
divided by 60 minutes gives 3 NM / min
multiplied by 2 min (as in "standard turn") gives 6 NM which is the complete circle.
This divided by 3.1415 gives 1.9099 NM as the diameter
This divided by 2 gives 0.9549 as the radius....

The rule of thumb divides 180 by 200 which equals 0.9......

Now...where was the problem???:sad:

[Capt Casper]

Geometry.
Circumference (c) = 2 x pi x radius (r)
or r = c / 2 pi
Rate 1 turn = 2 minutes
@ 100Kt, 2 minutes = (100 x 2 / 60) nm = c (approximately)
so r = (100 x 2 / 60) / 2 x 3.1428
on your calculator = 0.5303 or approximately 0.5
So at 100kts r = 0.5nm or 0.5% IAS
For mental arithmetic purposes assume TAS = IAS and use the formulae radius of turn at rate one = 1/2 % IAS :ok: