The basic turn performance equation is. .
radius = V^2 / (g * tan(bank angle))
which can be massaged (by getting rid of the constants) into
radius = KTAS^2 / (68637 * tan(bank angle))
for radius in nm, bank angle in degrees, and speed in kt.
If some more work is done on the first equation, we can arrive at
rate of turn = (g * tan(bank angle)) / V
which can be massaged into
rate of turn = 1092 * tan(bank angle) / KTAS
for rate of turn in degrees/second, bank angle in degrees, and speed in kt.
Both of these equations you can rearrange to suit your requirements and they suit normal calculator sums just fine. If you are really, really keen and into mental self abuse you can even use your Jepp or Dalton nav computer to confuse you with the answer ...
You may find equations elsewhere which have the multiplying factors differing to the above by a very small amount ... this just reflects the specific constant values used and calculator round off errors.
Alternatively, you may find equations in a different form, eg it is quite common to find the rate of turn equation expressed in terms of load factor, which is not a great deal of use for a civil pilot .. in any case, that sort of presentation reduces to the above equation with just a modicum of trigonometric massaging.
The basic derivation of these equations is quite straightforward and, should you have a boring need to know it, is shown in just about every basic undergrad aerodynamics or flight mechanics textbook ... one of which should be available in your local library.
Likewise, if you want a nice, easy to use graph, I can email you one I drew up for a local IFR training school some years ago.
The workaround described in the first post is a bit rough and ready, giving reasonable answers only for the normal sort of letdown procedural speeds ....
. .For practical considerations in civil IFR operations, I really can't see much use in worrying too much about this stuff .. except for the very occasional base turn letdown where the procedure designer faces a problem (or makes a mistake) which results in too tight a turn radius, 20 to 30 degrees of bank (depending on the aircraft's speed) works fine provided appropriate allowance is made for a sensible lead procedure to acquire the next track.
[ 14 February 2002: Message edited by: john_tullamarine ]</p>