Michael Ash wrote in
:

In rec.aviation.student WingFlaps wrote:
On Apr 27, 6:04?am, wrote:
? ? ? ? Lots of people had the impression you were talking about the
dreaded downwind turn, with all the talk about the energy required
to accelerate to maintain airspeed. The energy required, as pointed
out in a much earlier post with several very good references, is so
tiny that it's not worth fooling with at all.

Perhaps you could put a number on that? Could you try a gliding turn
with stopwatch and altimeter and compare that to a straight glide?

In the optimal 45-degree-banked turn the load factor will be about
1.4. Your best glide speed and min sink speed will increase by the
square root of that, or 20%. The glide angle remains the same if you
increase your airspeed appropriately, so your sink rate will also
increase by 20%. So instead of 650fpm you'll be coming down at 780fpm.
At 78kts (65kts best glide speed from previous post plus 20%) and a 45
degree bank you're making a circle a bit over 500ft across which will
take you 13 seconds to complete half of. The extra sink rate from the
turn will therefore cost you 30 feet over what you would have
experienced in a straight glide for the same amount of time.

You'll also lose about 80 feet to accelerate from 65kts to 78kts. But
you'll gain this back at the end, so as long as the end of your turn
ends at a reasonable height it can be ignored.

The numbers will, of course, vary between aircraft but it would appear
that the extra energy loss due to the turn itself isn't all that
significant. If 30 feet is the difference between making it and not
making it you probably should not be turning around in the first
place.

Did I miss anything?




45 degrees isn't enough unless you have a very nice gliding airplane or
are starting from a good height to begin with.


Bertie