Turn Radius

[Sycamore SAm]

I can't remember how to do this but how can you calculate turn radius. Is there a rule of thumb?

What would the turn radius be if the aircraft is 150 kts in a 30 degrees bank.

This is driving me nuts.

Thanks.

 

[VNugget]

http://selair.selkirk.bc.ca/aerodynamics1/Lift/Page13.html

 

[gnvav8r]

The figures for turn radius are independent of aircraft type.

Radius = V*V/11.26*tan (bank angle)

where V = TAS

 

[A Squared]

The figures for turn radius are independent of aircraft type.

Radius = V*V/11.26*tan (bank angle)

where V = TAS

I don't know of any rules of thumb which allow for diferent bank angles. There's he explicit equation that gnvav8r posted, but that's not a rule of thumb, and probably requires a calculator unless you can do trig functions in your head.
the only rule of thumb I know is 10% of your groundspeed in knots gives you turn radius in NM for a standard rate turn. Tthe radius computed is actually quite a bit larger than your actual radius. However, it works well for leading a turn to intercept an arc, as the larger estimated radius allows for rolling into and out of the turn. If you want to calculate a more accurate turn radius for various bank angles, grab your calculator and use the equation above.

 

[onthebeach]

Rule of Thumb that works pretty well

The turn diameter when using a standard rate turn is approximately:

(TAS + 10) / 100

Of course turn radius would be half of that.

Example: TAS of 150 knots, (150 + 10) / 100 = diameter of turn approximately 1.6 NM, so radius approximately 0.8 NM.

Remember this requires using a standard rate turn and the bank angle for this of course varies with TAS. If you are locked into wanting something depending on bank angle vs. rate of turn, can't help you there except to do the math as the other guy suggested.

 

[gnvav8r]

Another common Rule of Thumb:

TAS/200 = turn radius (nm)

The question sometime comes up ~ should you use TAS or GS? Remembering that a 20 kt wind will blow you 2000 ft in a minute (I bet Cory Lidle would have loved to have remembered that when he made his fatal turn in NYC... if he'd turned into the wind rather than downwind he might be reading this post...) - - anyhow in the 30 sec it takes you to turn 90 deg a tailwind will have increased your radius by 1000 ft or 1/6th nm. So use whichever.

I use this number all the time in determining when to start the 90 deg GPS intercepts to Final Approach Course.

Pete

 

[BEfly]

......That would've been helpful doing that circling approach the other day!

 

[icefr8dawg]

skip the math and do an Immelman, you'll be going the opposite direction in a few seconds