PPRuNe Forums - View Single Post - John Farley's thoughts on forced approaches
Old 28th Nov 2019, 06:26
  #34 (permalink)  
chevvron
 
Join Date: Nov 2005
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Originally Posted by LOMCEVAK
Chevvron,
If I may make a few technical corrections to what you have said (and lightningmate was a good friend and colleague of mine): The normal gliding speed in the Hunter with undercarriage and flaps up was (and still is!) 210 KIAS which gave a range of 2nm/1000 ft altitude loss (4.7 deg glide angle). For practise, 2 notches of flap (23 deg) was lowered and 5500 RPM set (in a T Mk7) to simulate windmilling engine drag. When the '1 in 1' slope was intercepted (1nm/1000 ft, 9.34 deg glide angle) the undercarriage was lowered and 210 KIAS maintained by lowering the nose. Airspeed was then varied between 180 and 240 KIAS to maintain the '1 in 1' slope. At a visually judged point (typically between 500 and 1000 ft above touchdown) the flaps were lowered fully to reduce speed to 170 KIAS for commencing the flare. If it was a practise the power would be reduced at the flare to 4500 RPM (to protect the engine surge margins for the tough-and-go or go-around and maintain a short engine spool up time).

This pattern worked because of the drag characteristics of the Hunter with the undercarriage down at 210 KIAS. It was initially used also in the Hawk T1 when it entered service and it worked with idling thrust but would not with windmilling drag, and hence the radar forced landing pattern was developed. This pattern will work with any drag polar so can be used on most types.

Returning to where this thread started, if a high drag aircraft is gliding with a steep angle then a given angular change of glide angle will equate to a smaller distance over the ground than for a low drag aircraft with a shallower glide angle. Therefore, it is easier to judge the touchdown point in a high drag aircraft. However, the probability of not having sufficient energy to make an airfield following an engine failure is greater with high drag.
Thanks for correcting me; my excuse is it happened 40 years ago and a few minutes earlier I had experienced my first 'grey out' as we piulled through a loop at 5.5g and I hadn't got a g-suit!!
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