Turnbacks
Joined: Jun 2003
Posts: 8
Likes: 0
From: London
I once fiddled around with a spreadsheet to investigate this scenario. I concluded from a straight-out departure, you need several thousand feet of runway beyond the rotation point. Otherwise, after the height loss in the turn, any expected glide ratio is insufficient to carry you back to the point of rotation.
Assume
Best climb of 60 kts = 1 NM / min = 6000 ft per min.
Climb rate: 600 fpm
Height lost in 180 deg turn: 300ft
(According to current wealth of experimental data: Thanks chaps!)
Glide ratio 10:1
1 Minute after Rotation
Dist = 6,000ft, Height = 600ft, Hgt after turn 300ft => gliding distance 3,000ft
2 Minutes after Rotation
Dist = 12,000ft, Height = 1,200ft, Hgt after turn 900ft => gliding distance 9,000ft
In each case the gliding distance is insufficient to backtrack distance covered – need another 3,000ft of runway beyond the point of rotation.
Neither light tail winds (10Kts), nor the trigonometry of 5 deg climb slopes materially affect the outcome.
...all rather academic, but stresses how difficult it is to make it back safely!
Assume
Best climb of 60 kts = 1 NM / min = 6000 ft per min.
Climb rate: 600 fpm
Height lost in 180 deg turn: 300ft
(According to current wealth of experimental data: Thanks chaps!)
Glide ratio 10:1
1 Minute after Rotation
Dist = 6,000ft, Height = 600ft, Hgt after turn 300ft => gliding distance 3,000ft
2 Minutes after Rotation
Dist = 12,000ft, Height = 1,200ft, Hgt after turn 900ft => gliding distance 9,000ft
In each case the gliding distance is insufficient to backtrack distance covered – need another 3,000ft of runway beyond the point of rotation.
Neither light tail winds (10Kts), nor the trigonometry of 5 deg climb slopes materially affect the outcome.
...all rather academic, but stresses how difficult it is to make it back safely!
Joined: Jan 2003
Posts: 811
Likes: 0
From: The Heart
If you want to know the right answer, ask a glider pilot.
As one has already replied that they always have a plan of action which changes with height, I'd like to expand a little.
I case of an engine failure what you need is a decent flat bit of land. What you've just left was a very small 'licenced' area of what is in most cases a very much larger area of very suitable land which a rescue crew, can probably get to within three minutes or less. See the difference it made at Sioux City!
The plan you devize for your departure field may not require a 180. Maybe just a 90 degree turn to a cross runway. Perhaps a gentle 270.
Just as long as you maintain flying speed; and this is the big killer in GA, stall/spin accidents whilst making a forced landing.
As one has already replied that they always have a plan of action which changes with height, I'd like to expand a little.
I case of an engine failure what you need is a decent flat bit of land. What you've just left was a very small 'licenced' area of what is in most cases a very much larger area of very suitable land which a rescue crew, can probably get to within three minutes or less. See the difference it made at Sioux City!
The plan you devize for your departure field may not require a 180. Maybe just a 90 degree turn to a cross runway. Perhaps a gentle 270.
Just as long as you maintain flying speed; and this is the big killer in GA, stall/spin accidents whilst making a forced landing.
Joined: Mar 2002
Posts: 349
Likes: 0
From: Biggleswade
Turnbacks are not a good idea for the inexperienced or the faint hearted. Here's why:
I read a Boscombe Down report a few years (about 20) ago that implied that the minimum height loss in a glide occurs at between 55 and 60 degrees of bank. Now, with 60 degrees of bank, the load factor is 2, which means you're flying with 2 G on the aircraft. At 2 G the stall speed is increased by a factor of just over 1.4. So, if you're gliding at 1.3 VS, you'll stall, flick, spin, crash and burn before you've even started turning.
Trying to turn back at any other angle of bank will lead to too great a height loss, so again, it's a lost cause.
Turnbacks have been carried out successfully, I've even done one myself - I may even talk about it publicly one day, but not just yet! But, far better to plan the takeoff and climbout to use available fields in the forward sector in the event of engine failure. If there's no such field available, you shouldn't be operating single engine there in the first place.
A
I read a Boscombe Down report a few years (about 20) ago that implied that the minimum height loss in a glide occurs at between 55 and 60 degrees of bank. Now, with 60 degrees of bank, the load factor is 2, which means you're flying with 2 G on the aircraft. At 2 G the stall speed is increased by a factor of just over 1.4. So, if you're gliding at 1.3 VS, you'll stall, flick, spin, crash and burn before you've even started turning.
Trying to turn back at any other angle of bank will lead to too great a height loss, so again, it's a lost cause.
Turnbacks have been carried out successfully, I've even done one myself - I may even talk about it publicly one day, but not just yet! But, far better to plan the takeoff and climbout to use available fields in the forward sector in the event of engine failure. If there's no such field available, you shouldn't be operating single engine there in the first place.
A
