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Fastest way to lose height

One UK CAA examiner, ex RAF, told me they practiced high speed descents, all the way down low, because that gives you the best options if descending through IMC and getting visual say 300ft AGL. They did it in the PC12 too.

You end up 2-dimensional whether you hit at 100kt or 200kt so may as well go for 200kt and have more options, is what he said, basically

Administrator
Shoreham EGKA, United Kingdom

Was that for safe decent trough IMC? Or when looking to decend ASAP?

When I did fly gliders in short IMC (BGA/RAF call it cloud flying), I got completly opposite advice during training.

Say you run out of battery for eletric turn indicator (what you need to do legal IMC in UK) or you suspect water in the pitot/static, you just trim it at roughly 1.3×Vso (fixed trim position not wtr to ASI) open full airbreaks and let go everyting while watching your altimeter, you end up with a “stable spiral dive”…

I try it many time in VMC tests/IMC descents trough clouds, it works on most sailplanes with airbraks/trim and I don’t see why it should not work for aeroplanes with flaps/trim while the engine is off?

Paris/Essex, France/UK, United Kingdom

I don’t see why it should not work for aeroplanes with flaps/trim while the engine is off?

I think, on any “IFR tourer”, you would go through Vne in 10-20 seconds, counting from when the roll angle goes through about 30 degrees. Disintegration due to aerodynamic forces some 10-20 seconds later, depending on build quality and how “tight” it is controls-wise (flutter etc).

Administrator
Shoreham EGKA, United Kingdom

Ibra wrote:

I try it many time in VMC tests/IMC descents trough clouds, it works on most sailplanes with airbraks/trim and I don’t see why it should not work for aeroplanes with flaps/trim while the engine is off?

Having flown both gliders and powered aircraft, I would say it won’t work because airbrakes on gliders are different things entirely compared to flaps when it comes to drag. Some gliders can even be flown straight down with airbrakes extended without exceeding Vne.

What Peter writes would happen in gliders, too, if it were not for the airbrakes.

Last Edited by Airborne_Again at 18 Apr 05:43
ESKC (Uppsala/Sundbro), Sweden

You would need to be careful doing anything with large control deflections, e.g. side slips if you are going above manoeuvring speed. It would turn into a worse situation with structural failure.

Darley Moor, Gamston (UK)

The difference is that speedbrakes/airbrakes add drag with no lift. Flaps add both. Not what you want when trying to lose altitude whole going fast.

Last Edited by JasonC at 18 Apr 09:16
EGTK Oxford

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

They are designed to cruise fast with high fuel efficiency, so probably that will compromise on roll/spiral stability or short field performance.

In some gliders (high performance ones) you need those airbraks openned early as well to contain speed.

Peter’s scenario goes along this:



Paris/Essex, France/UK, United Kingdom

JasonC wrote:

The difference is that speedbrakes/airbrakes add drag with no lift. Flaps add both. Not what you want when trying to lose altitude whole going fast.

Very true, that solves the puzzle !

Paris/Essex, France/UK, United Kingdom

You have to be very careful when recovering from an intentional or unintentional spiral dive. Some aircraft have a natural tendency to start a spiral dive if the controls are left alone. The Bonanza is one of them. A wing will drop and the nose will drop. Since the nose dropped, IAS increases. With the increase in speed comes the increase in lift generated. Since the lift vector is not straight up but canted left or right, the G’s start building up.
When the pilot realizes his predicament, his instinctive reaction is to level the wings and pull on the yoke to reduce the rate of descent.
If the aircraft was in level flight before and trimmed for say 150 Kts, after ending up in a spiral dive, after having the wings leveled, the airspeed may be far above trimspeed. This means that the aircraft will try to pitch up by itself. The trained pilot will know that at this moment, he must push quite hard on the yoke, not pull, to counteract the pitch-up force generated by the out-of-trim airspeed.
Spiral dive recovery is taught in the BPPP Bonanza program and is an eye-opener for those doing it the first time (at safe speeds and under supervision).

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

EBKT

Don’t remember exact number, but I think it was around 6 to 8k fpm when I practiced this procedure.

LPFR, Poland
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