Back in about 1970, I decided to see how high I could climb in a University of London Air Squadron Chipmunk....
Off from White Waltham, 'Twyford Outbound', turn at Mapledurham and route to the west of Reading, then start the climb when clear of Green One.
Eventually I reached something over 13500 ft, but was getting very cold and rather bored.
But getting down again without the engine getting too cold was far more difficult. A loop with the engine at idle lost some height, but my oxygen depleted condition meant I saw stars over the top....the youthful hangover from the previous night's bar session probably didn't help either
So then I went into a descending spiral at around 75º with about 1800 rpm set until I eventually got down to a suitable height to re-enter the free lane at Woodley.
The engineers couldn't understand why the fuel tank fillers were so cold though....