physics question about pull ups

On Apr 21, 8:41*am, Chris Reed wrote:
A pilot flying at the UK Juniors a few years ago described a racing
finish in a K8, producing no more than a 200 ft climb from a 90kt
pull-up. He said that a K8 in this mode was the ultimate efficient
machine "for converting height into noise".

Disregarding drag, the formula to convert speed in knots to the height
in feet with equivalent energy is speed squared, divided by 22.57. It
will take this much height, plus a bit more, to accelerate to that
speed, and on slowing down you will get that much height, less a bit.

For 90 knots this is 359 ft.
At, say, 50 knots, it is 111 feet.

So you'd expect only 248 ft gain even with no drag at all.

I don't have time right now to run the numbers, but am interested and
will probably do that this evening... But looking at the Nimbus vs.
K8 examples, The sink rates need to be factored in. If they both
start 50 feet above the ground, and initiate the same degree pull up,
as the speed bleeds off they gain potential energy. If they start at
100 kts and the K8 sink rate at 100 kts is 900 fpm, and the nimbus is
600 fpm(not the actual numbers, just for an idea) then during that
time at 100 kts the nimbus loss is less than the K8. So, for that
moment when both are at 90 kts, if the K8 is losing 850 fpm and the
Nimbus 500 fpm, the K8 is still losing more. factor this in with the
theoretical no drag equations and you should be able to see the
difference. If from 100 kts they should reach 1000 ft, then you
subtract whatever you get from integrating the sink rates, the nimbus
might have lost 250 ft leaving it at 800 ft agl while the K8 might
lose 600 ft and ending its pull up at 450 ft. The polars need to be
integrated into the equation in order to get the actual differences.
The same would go for a given sailplane wet vs. dry. As the polar is
shifted to the right when wet, the sink rate changes. The wet
sialplane, through the speeds in the range of the pull up would be
losing less than the same sailplane dry over the same speed range.