It comes from the certification standard CS23 (or FAR
23), quote:
"CS 23.3 Aeroplane categories
(a) The normal category is limited to nonaerobatic
operations. Non-aerobatic operations
include –
(1) Any manoeuvre incident to normal
flying;
(2) Stalls (except whip stalls); and
(3) Lazy eights, chandelles and steep turns
or similar manoeuvres, in which the angle of bank
is not more than 60°.
(b) The utility category is limited to any of the
operations covered under sub-paragraph (a); plus –
(1) Spins (if approved for the particular
type of aeroplane); and
(2) Lazy eights, chandelles, and steep
turns, or similar manoeuvres in which the angle of
bank is more than 60° but not more than 90°."
A true max rate turn involves flying to the edge of the manouever envelope, and could therefore risk ecxeeding the load factor limit if entered at a speed above Va. Perhaps another reason for leaving it to aerobatic cat aeroplanes which have a g meter fitted and a higher limit load factor. The military teach them in UAS/EFTS but they have the luxury of using aerobatic aeroplanes for ab initio training.
Of course there is a difference between the maximum instantaneous turn rate when entered aggresivly from cruising speed as an emergency avoiding manoeuver, and the maximum sustainable level turn rate once the speed has decayed. The latter depends on engine power and for a low powered aircraft the maximum sustainable bank angle may be less than 60 deg anyway. For a Cessna 172 at sea level with max power this bank angle turns out to be 56 deg and speed 85 kts, loading 1.8g. In this case it would be possible to demonstrate a maximum sustainable turn while remaining within the normal cat limits.
Last edited by Rivet gun; 21st Mar 2006 at 21:22.