Peter Ashwood-Smith C-GZRO wrote:
Andrew, do you compensate for density altitude when you define your gates?

An interesting fact, which is not obvious to many folks, including
some aerobatic pilots (judging by the number of loop into the ground
accidents) is that the radius of any turn, up, down, sideways or
whatever, is a function of the square of TRUE airspeed, which is of
course a function of density altitude and calibrated airspeed.
So, if the density altitude increases your true airspeed by 5mph,
you get a 5mph^2 impact on your radius. This kind of change in radius
can ruin your day if you are playing down near the dirt.
This velocity^2 thing is also why the reverse cuban or loop down is
a real killer. If you start the pull with X knots too many, you will
use X^2 more radius for the 1/2 loop, throw in an increase in TAS of
say Y due to density altitude and you are into (X+Y)^2 more radius ...
not good. If you have not left margin either in terms of available G
or altitude you are either gonna high speed stall on the way down (and
hit the ground) or hit it on the arc.
This sort of question is on the ICAS exam now if I'm not mistaken.
Peter

Hence the reason I asked the question.
Thank you, Andrew and Peter.
The original ICAS/FAA ACE proposal required a PhD in Aeronautics and
computational fluid dynamics software to answer the questions.
Fortunatly, the program was changed and common sense prevailed.
Sadly, there are still many acro pilots out there who have no
understanding of how density altitude affects their flight and refuse to
be educated.