d&tm writes:

I should add that this calulation assumes all the lift is coming from the
wing , but that theory would imply that an aircraft cant hold altitude in a
90 degree bank, and of course we have all seen aerobatic aircraft do this.

No, you haven't. It's impossible to hold altitude in a 90° bank. In
fact, it's impossible to execute a coordinated turn with a 90° bank.
A 90° bank requires infinite speed, because the acceleration vector
would have to be perpendicular to gravity, which is never possible as
long as gravity is non-zero. With both vertical and horizontal
non-zero components, the net acceleration vector can never be
completely horizontal or vertical. You can eliminate the non-zero
horizontal component in level flight, but you cannot eliminate the
force of gravity, so a 0° "bank" (i.e., level flight) is perfectly
possible, but a 90° bank is not.

You can come infinitely close to 90°, but you can never reach it, in
any type of aircraft. In an aircraft that can withstand 9 Gs, you can
reach slightly less than an 84° bank, but no more.

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