Let's not forget the time it takes to complete the turn or the distance
covered over the ground.

Without getting into the math, I can comfortably say that, using a 30 deg
bank will take longer to complete the turn and leave you further from the
runway. Likewise, at higher elevation airports your sink speed will be
higher (think true airspeed) so height loss will be greater than at sea
level.

wrote in message
...
On Wednesday, May 7, 2014 6:24:23 PM UTC-7, Bruce Hoult wrote:

No matter what your stall speed or L/D, it turns out the optimum to
minimise loss of height in a turn is to bank at 54.7 degrees.

Feel free to play.

Thanks Bruce - I did play with this a bit. Always helpful to do the math.

Several observations pop out from the numbers:

1) The 25-30' height loss for a 180 is small compared to the 200' I always
use as the minimum safe altitude to make this maneuver. Not that I'm
recommending a smaller margin - there are considerations of sink and wind
and clearance for the bottom wingtip in the bank.

2) Speaking of the bottom wingtip in the bank, if you subtract that height
difference for each different bank angle you get a height loss for a 180
measured at the bottom wingtip that is actually minimal at a lower bank
angle than 54.7 degrees. Obviously this would be most likely to apply at the
end of the maneuver, not the beginning, unless there is unusual terrain.

3) Whether you include the wingtip clearance in the calculation or not, the
total height loss doesn't vary all that much between 30 and 60 degrees of
bank - about 6 feet of difference for the center of the aircraft and only a
foot or two of difference at the lower wingtip.

The conclusion this draws me to is that the most important consideration in
PTT is to make a smooth, coordinated, deliberate turn that you can manage
easily - and to make sure not to dig the bottom wing into the ground. Within
a pretty broad range, there isn't much percentage in optimizing the bank
angle.

9B