Stalling and spinning generally

This somehow was posted in another thread but deserves a thread of its
own, I think.

In article , Dave Martin
writes

snip

it must be realised that the pilot caused the inadvertent
stall in the first place by inappropriate use of the
controls. He is unlikely to start making skilful or
precise movements now. Do not attempt to use the secondary
effect of the rudder to restore the wings to the level
position. This would introduce yaw which could result
in the glider spinning. The priority must be to unstall
the glider by moving the stick forward.'

I agree 100% with the above and some years ago had a short article
published in the BGA magazine Sailplane and Gliding on this precise
subject. I repeat this article at the end as it is still relevant.
Timeless, even.

Question: What is the use of lots of rudder near the stall likely to
induce?

No prize for the answer!

The answer is the same whether the use of rudder was well-intentioned or
not.

In the 1950s I was taught to "pick a wing up near the stall by using
rudder", but this often led to a low speed situation being converted
into the first stages of a spin, and sometimes a fully-developed spin
with a tragic conclusion if near the ground.

By the time I became an instructor in the UK Royal Air Force (1965),
instruction had changed to "in an inadvertent slow speed situation,
first reduce angle of attack using forward stick. When at a normal
flying speed, level the wings by gentle use of aileron". Incidentally,
at this time in the RAF, spinning was no covered pre-solo, only stalling
and recovery from inadvertent slow-speed situations. Fully-developed
spinning was covered at about the 30-hour stage as part of training for
aerobatics. Food for thought in the gliding world? There have been
quite a few glider spinning accidents during spinning training. I used
to be a Canberra (US B-57) flying instructor and we killed more people
in training for engine failures than were killed by engine failures
themselves. There is training and there is training, and when the
training itself becomes lethal we need to analyse carefully what we are
doing it for.

Anyway, here is the old S&G article, a bit long but it has many
significant points:

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From Sailplane and Gliding, October 1989 edition, page 221

SPINNING TRAINING - A CAUTIONARY NOTE

My basic point is very simple - The automatic application of large
amounts of opposite rudder in slow-speed "wing-drop" situations will,
for most gliders and powered aircraft, make the situation worse. This is
particularly important near the ground, where rudder applied
unnecessarily at slow speed can actually cause a crash.

I know of several accidents where this occurred, in each case the
machine being written off and the pilots badly injured.

1. In one case a stall was being deliberately practised and a
mild wing-drop occurred. Full rudder was applied and the machine quickly
entered a spin from which the pilot was unable to recover before the
ground intervened.

2. A similar case was where an inadvertent wing-drop at low
speed was turned into a full spin by coarse use of rudder, the machine
also crashing into the ground.

3. Another case that I witnessed happened at the launch point
and was even more ironic; a wing-drop occurred at about 200ft on the
approach which the pilot diagnosed as due to a stall but almost
certainly was simply due to turbulence. He had been taught to apply
opposite rudder in this situation, he duly did and the glider crashed
into the ground with its wings almost vertical.

The instinctive reaction to detecting an inadvertent low speed situation
should be to move the stick rapidly forward by an amount proportional to
the severity of the situation and then away from the dropped wing (if
there is a wing-drop). But please be very careful with the rudder until
a fully developed spin is diagnosed. It is a powerful control at the
stall and must not be abused.

I well recall gliders with horrendous stalling characteristics where a
stall was virtually an incipient spin. They would not nowadays be
granted a C of A by the National Regulatory Bodies (CAA/BGA in the UK,
FAA in the USA, LBA in Germany). I vividly remember stalling the Kite 2
(most were spun in) and Geoffrey Stephenson's Gull 1 (also eventually
spun in). A large wing-drop was usually implicit even in an attempted
"straight stall. Fortunately, stalling characteristics have improved
considerably since those days and automatic application of large amounts
of rudder to correct a wing-drop is no longer necessary, if indeed it
ever was.

Having also flown over 50 types of powered aircraft I can assure you
that, at the wing-drop stage, using forward stick for recovery followed
by normal control actions to level the wings, works equally well in a
Harvard (the 1930s piston version, not the Harvard 2 turboprop of
today), Hawk, Hunter, Canberra, Nimrod, Provost/Jet Provost, Vampire and
indeed all aircraft and gliders I have stalled except perhaps the said
Kite 2 and Gull 1 which, unfortunately, are not now available for
experiment.

As an example, the piston Harvard usually has a nasty wing-drop at the
stall, and a "classic" full spin, losing about 60Oft per turn. Many have
been "spun in", with fatal results at low level. In this context I quote
the current Boscombe Down Pilots' Notes (Boscombe Down is the UK
equivalent of Edwards and Eglin AFB in the USA, and used the Harvard for
slow speed photo-chase): "At the stall, the nose and either wing may
drop. With flaps up, the wing drops more rapidly than with flaps down.
If the stick is held back, the aircraft will spin. To recover from the
stall with minimum loss of height, apply power and simultaneously move
the control column sufficiently far forward to unstall the aircraft.
Ailerons then become effective and wing-drop should be corrected with
lateral stick. Ease out of the dive into a gentle climb ..."

Note the absence of any instruction to use rudder (that comes later in
the recovery drill for a fully developed spin), and the emphasis on
smooth handling with no automatic use of coarse or full control
deflections - "Sufficiently far forward", "Ease out", "Gentle climb".

In gliding, what we need is instruction which clearly distinguishes
between a fully developed spin, which should now be very rare except for
deliberate training at a safe height, and the earlier stages such as
wing-drop at a stall which are better recovered by quickly reducing the
angle of attack and then levelling the wings in the normal way, and not
by inducing autorotation the other way by unfeeling boots of rudder.

Stalling and spinning characteristics also vary with the C of G
position. At forward C of G all aircraft tend to be very stable in pitch
and some may not spin at all, just exhibiting a sideslipping spiral dive
in response to full pro-spin control. But as C of G moves aft, pitch
stability reduces and the tendency for a wing-drop at the stall, and to
enter a full spin, increases.

Light pilots, beware!

The Janus is an example, which I had to test for the UK Military (the
Air Cadets, anyway). It will only exhibit a true spin at fully aft C of
G, at all other C of Gs it enters a rather horrendous sideslip in
response to boots of rudder. It has very low directional stability and
is unstable in sideslip below about 55kt. Perhaps this has something to
do with some other Janus accidents (see S&G 1998 page 97). It is also
extremely twitchy in pitch control at fully aft C of G, which shows up
particularly on an aerotow in turbulent conditions and indeed sets the
aft C of G limit. These considerations should be borne in mind when, for
instance, stalling or spinning two-seaters when solo, where C of G will
generally be further aft than when dual.

Instructors have their uses, even if only as ballast!

Wind Gradient.

Stalling and spinning training is carried out at a safe height, whereas
the "worst case" inadvertent slow speed situation is probably the final
turn in a field landing in conditions of turbulence and wind gradient.
Airfields are generally flat (there are some notable exceptions) whereas
the topography around fields may not be, and wind gradient will
therefore be more severe. A slow speed situation could easily get
out-of-control (due to the lower wing being in a lower wind speed, and a
glider with benign characteristics when practising stalls at height
might bite you if you are less than careful near the ground.

There are two rather pessimistic "old adages" which may, on field
landings, be relevant -

1. "If you are going to crash, crash with your wings level".
Particularly relevant in the case of asymmetric thrust on aircraft such
as Camberra/B57, Boeing 707 etc. But also applicable to a glider on an
awkward approach to a field.

and

2. "Always hit the far hedge rather than the near hedge".

Think about it!

I am sorry this article is so long, but my overall conclusion is that we
want more practice in slow-speed situations which we may meet
inadvertently, such as a slow, badly flown turn with thermalling or
landing flap, rather than over-concentration on the deep stall or the
full spin.

And we should practise a recovery technique which is both
straightforward and that will not get us into more trouble.

Lots of us do not have either the regular flying practice of the
professional pilot, or the intuitive handling ability of a Chuck Yeager,
Neil Armstrong, John Farley or Brian Trubshaw (the latter two are
distinguished Brit test pilots, on Harrier and Concorde respectively,
Brian departing to the great test flying "cloud in the sky" a couple of
years ago).

Glider stalling characteristics will, of course, vary with type, flap
position, C of G an even wing condition (bugs, rain etc). Practise
recoveries regularly at a safe height to optimise your technique. But
generally, short of a fully developed spin, the best technique will be
to rapidly move the stick centrally forward to unstall the wings (just
enough to do this, not mechanically fully forward), and then recover
from the ensuing attitude by normal use of controls. Beware the
unnecessary use of coarse control, particularly rudder and particularly
near the ground!

IAN STRACHAN
Lasham Gliding Society

Ian is a qualified Service test pilot and an A1 category RAF flying
instructor as well as being a glider and motor glider instructor. It is
understood that Bill Scull, BGA director of operations, and Bernie
Morris, chairman of the BGA Instructors' Committee, are in agreement
with the main points of this letter.

------- end of quote from S&G ---------

--
Ian Strachan
Lasham Gliding Society, UK

Bentworth Hall West
Tel: +44 1420 564 195 Bentworth, Alton
Fax: +44 1420 563 140 Hampshire GU34 5LA, ENGLAND