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Fastest way to lose height

In the recent SouthWest engine catastrophic failure I understand the Captain (lady, ex Navy pilot) may not have deployed the spoilers due to concern about structural weakness following damage from the engine. The crew seem to have dealt with the emergency with great professionalism.

Oxford (EGTK), United Kingdom

I think it was around 6 to 8k fpm

It was 8000fpm when I did it in a TBM850

may not have deployed the spoilers due to concern about structural weakness following damage from the engine

Very smart! This is off topic but applying the same reasoning would have made this somewhat reckless.

That TBM accident report is horrible.

Administrator
Shoreham EGKA, United Kingdom

dirkdj wrote:

Here is an accident report of a TBM 700 due to a botched spiral dive recovery:TBM 700 accident report

I can’t believe most of these guys survived the spin down from 20,000 feet!

Wonder what their quality of life is now.

Ibra wrote:

I guess in most touring aircraft full flaps are not powerful enough to prevent overspeeding.

I would think there are no powered aircraft — touring or not — where the flaps add enough drag to prevent overspeed unless they were specifically designed to also work as airbrakes (e.g. 90° deflection) and most likely not even then. Also consider that the maximum speed with flaps extended will be much lower than with flaps retracted.

ESKC (Uppsala/Sundbro), Sweden

I just noticed 8000 fpm decent is 80kts along the vertical, not bad compared to the max speed of human body in a free fall (100kts)

You are right Airborn_Again, putting a side structural failures, opening air-breaks (90° deflection) does increases both frontal area and drag coefficient unlike flaps (30° deflection) which tend to act on drag coefficient only without much noticeable effect on frontal area

I did some calculations, square of max speed from a free fall is mass divided by frontal area * drag coefficient, in a C152 this gives around 400kts clean and 330kts with flaps at max AoA (ISA conditions and free fall = no-lift) which is way beyond 150kts VNE
- Formula: https://en.wikipedia.org/wiki/Terminal_velocity
- Drag coef: http://www.aerospaceweb.org/question/aerodynamics/q0184.shtml

I think the huge increase in frontal area + low mass is what probably prevent speed build-up in gliders compared to aeroplanes

Last Edited by Ibra at 18 Apr 23:00
Paris/Essex, France/UK, United Kingdom

Speed limiting glider airbrakes are also more strongly fixed. Some powered aircraft have airbrakes but no flaps. The DR1050 airbrakes are quite flimsy aluminium sheet, and their limit speed is 81 knots.

Maoraigh
EGPE, United Kingdom

Maoraigh wrote:

The DR1050 airbrakes are quite flimsy aluminium sheet, and their limit speed is 81 knots.

Still a rare ship that can do well in IMC

Paris/Essex, France/UK, United Kingdom

In my V35A Bonanza, I get 6000 FPM with the gear down, prop max, power off, descend at gear speed. With the later Bonanzas with the approach flap detent, the emergency descent is with approach flaps, gear down, prop full, power off, fly at max gear speed. My Bonanza has a gear speed of 144 Kts and the next year ups that to 154 Kts.

KUZA, United States

Some aircraft have a natural tendency to start a spiral dive if the controls are left alone.

I would think all common types are unstable in roll i.e. they will all enter a spiral dive. To be stable in roll you need some kind of a massive dihedral on the wings, and a dihedral wastes lift.

The DR1050 airbrakes are quite flimsy aluminium sheet, and their limit speed is 81 knots.

That means you cannot use them in any out of control situation, and you have to slow down using other means to 81kt (which is a really very slow speed) before you can use them. And 81kt is very sub-optimal for a rapid descent, which needs a high speed (on the TBM case above the 8000fpm is achieved with a TAS which is initially – at say FL250 – over 400kt!).

Administrator
Shoreham EGKA, United Kingdom
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