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On 23/03/2014 15:55, harryagain wrote:
"Nightjar" wrote in message
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On 23/03/2014 06:34, harryagain wrote:
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I have never flown an aircraft in which side-slipping was recommended
for
cooling - what type are you thinking of?


Pawnee ex-crop duster, used for glider towing.
This was the manufacturers advice.


It isn't in the owner's manual.

Colin Bignell

It was never intended/designed to use it towing gliders.
Lots of take offs and landings/descents from around 3000'.
Our grouse was that the front cylinders wore out before the rear.
Even though the air is ducted.


Interesting - I've towed with a Pawnee 235 and, once the post-release 10
seconds had been dealt with (and the CHT was below 200, I think) then
there was no need or recommendation to do anything other than fly it. I
can't recall the descent power settings or speed but the aim, as with all
towing, was to get back ASAP while controlling the rate of cooling with
power/speed, going no faster than Va (a bit of loading helps) and keeping
eyes out. The ROD was "adequate" without sideslip.

The view in the landing attitude was unusual, but very good compared to
some tailwheel types, so no unnatural actions are needed.

If you close the throttle and dive at the ground after glider release (as
some of our nutters did), the barrels are overcooled. The pistons of course
are at their hottest as the tow has been at full throttle.
So the piston/barrels clearances are reduced. I heard of one siezed up,
apparently it had a recent overhaul and clearances were already small.
Worst effect is in cold weather ofcourse.

There is no means of controlling the air.
So either sideslipping or a more gradual descent reduces engine wear.
It was apparently even worse years ago when oils were less good.
So we are talking about sideslipping all the way down, nothing to do with
the landing.

Cylinder head temperature is no guide, it lags far behind what is actually
going on.

Gliding clubs are full of nutters as I expect you know.
It was nomal at our place for the tug to find a thermal and circle in it
with the glider on tow.
When the glider released, some tug pilots rolled into a vertical bank wich
became a near vertical dive. At least intiially.