DEREK PIGGOTT LOW G ARTICLE (loooong)
HOWARD PETRI
consists of two xerox requests and one request to transcribe it to the net.
I'll consider the definition of "overwhelming" met; so here is the article
for those of you who wanted to know but were afraid to ask.
Your Humble Scrivener,
Howard Petri
Pegasus N599JH
STALLING OR LOW G
DEREK PIGGOT
SAILPLANE & GLIDING
APRIL/MAY 1991 pp78,79
That Derek Piggott contends, is the confusion. He was inspired to write
this article after hearing of some low g accidents in Japan.
We are all aware of the sensation of a lift as it starts to descend or
a car going over a humpback bridge. On the ground it only lasts a fraction
of a second but it can last longer and be more severe when we are flying.
Since we live under the influence of normal gravity, ie at 1g for
virtually all our lives, this feeling of anything less is unusual and if
unexpected it can be alarming. Many associate the feeling of reduced
gravity or low g with nightmare dreams of falling.
The majority of us acclimatise to these sensations after a few flights
but those who are particularly sensitive often develop a total abhorrence
of stalling and pitching manoeuvres. Many give up flying but others perhaps
persuade their instructors to avoid pitching manoeuvres and may become a
danger to themselves and others if they fail to overcome their inhibitions.
EARLY FLIGHTS
It is a help if the instructor mentions the sensation of reduced g on
a first flight and links it with the pitching movement so the student
realises it is quite normal. At first almost every beginner is unsure what
is happening when they get unexpected sensations. They are worried about
the reduced g sensation and the feeling of slipping as the aircraft is
banked over into an unruddered turn.
Almost everyone dislikes these sensations which normally remain for a
few flights and then gradually disappear. They occur because the beginner
is unable to interpret what is happening in time to connect it with his
sensations or his control movements.
After a little more experience he learns to recognise what is
happening to the aircraft and an alarm signal is no longer sent to the
brain. For example, after a short time, as the stick is moved forward, he
sees the glider's nose is moving down and his brain expects the sensation
and understands what is happening.
These unpleasant sensations often come as a complete surprise to the
layman. It helps if they are warned that this is quite normal on early
flights, particularly when starting to use the controls. But it is a great
mistake to introduce stalling or pronounced nose down pitching movements in
the very early stages as this may make them more sensitive.
TURBULENCE
If there is reduced g because of flying through turbulence, there is
often no change of attitude and therefore no visual sign of what is causing
the sensation. This is more alarming for the beginner who just gets a
horrible sinking feeling and the impression the aircraft is falling out of
control. So it helps to make the first flights in smooth weather with a
clear horizon and avoid unnecessary pitching movements.
Because of the connection between sensations and vision, the
sensations are greatly amplified if the visibility is poor or if looking in
the cockpit so there is no visual reference to help recognise the exact
movements of the aircraft.
Even experienced pilots get very disturbing sensations if taken into
cloud without the help of instruments. Try being blindfolded for a few
minutes in a two seater while the other pilot makes a few well banked
circles and then straightens up. Besides a vivid impression of a turn in
the other direction, you will feel the effects of reduced g as you stop
turning-something you are quite unaware of in normal flight. Even in clear
air this slight reduction of loading is noticed by the absolute beginner.
To minimise these unpleasant feelings it is best to start any flying
training by emphasising looking ahead and to avoid drawing attention to the
instruments. Later on instructors should make a particular point to
emphasise the need to look ahead during nose down pitching manoeuvres,
such as stall recoveries and recovering from a cable break during a winch
launch.
LOW G SENSITIVITY
Some people are more affected by sub-gravity sensations than others.
They will tend to put their hands out and throw their head back at the
slightest reduction in g.
I have noticed this response on first flights when they are trying
out the elevator. As they move the stick forward a small ammount causing
only a slight reduction in g, their response is almost always to move even
further forward, making the sensation worse. This is totally irrational-
the normal reaction would be to stop doing it or to move the control stick
back in the other direction.
This response to a sensation of falling is a very natural and
fundamental protective instinct. If we are falling our hands go out
automatically to stop us hitting our face.
Our experience in gliders has made us aware of many aspects of low g
sensitivity unnoticed in other types of aircraft. With the much lower stick
forces and higher rates of pitching possible, this instinctive movement of
the hands can result in a sudden steep dive which can be disastrous near
the ground. Accidents and incidents where a glider suddenly and
inexplicably dives into the ground are still occurring all over the world
indicates that some people are flying solo quite unaware of their
vulnerability.
It seems there are two distinct causes of these accidents:
1. Mistaking the low g sensation for a stall.
2. Reacting instinctively to reduced g by moving the stick forward and
being overcome by the increased sensation of the even lower g caused by
moving the stick even further forward.
STALL VERSUS REDUCED G
One survivor from a "dive in" accident confirmed he knew it was
useless to try to pull out of the dive while he could feel the glider was
still stalled. This gave us the clue that some students were learning to
think of the feeling of low g as an indication the glider was stalled. If
they do this, they may respond wrongly to any pitching or sharp descent. In
making a normal stall recovery when the aircraft is not stalled, any
movement forward will increase the pitching and produce a more vivid
sensation making these pilots think the aircraft isn't recovering or is
more stalled. this is a sure recipe for panic and is fatal unless there is
plenty of height.
I once had a student who responded with a stall recovery when the
glider hit some turbulence on the final approach. The glider dived almost
vertically and I was just in time to pull back on the stick so that we hit
the ground in a level attitude, miraculously without damage.
Certainly several fatalities seem to have been caused in similar
incidents, although this cannot be proven.
Since then instruction on stalls and recoveries has been modified to
emphasise from the start there is no sensation of stalling, only symptoms.
It is also prudent to teach the student to "ease forward" or "to relax the
backward pressure" to unstall the aircraft rather than use the terms
"stick forward", "push forward", or "stick hard forward" which can result
in a violent movement of the hand if a stall occurs unexpectedly.
During the early flights, any feeling of low g or even turbulence
needs explaining. Also when trying out controls and lowering the nose the
instructor should draw attention to the sensation and explain it is caused
whenever the nose is lowered.
After the first gentle straight stalls we should demonstrate that even
a small movement forward results in the reduced g feeling. We should take
good care to emphasise that this sensation, is not a symptom of stalling
and can occur when flying normally and, in some cases when flying through
turbulence. Only a very slight ammount of reduced g occurs during normal
stalls and it only lasts a brief moment and wouldn't be felt by anyone
other than a beginner or the oversensitive. Any large ammount of reduced g
sensation is caused by making far too much movement forward during the
recovery.
SENSITIVITY AND INSTINCTIVE REACTIONS
A common sign of still being rather sensitive to reduced g is for the
pilot to repeatedly overdo the forward movement during stall recovery, in
spite of being reminded to ease forward gently. At a later stage he will
often insist on thermalling with excess speed and repeatedly poke the stick
forward a little at the slightest gust.
Apprehension about stalling is always a sign of under-training and
usually a lack of understanding about the causes of stalling and spinning
and of the behavior of the aircraft. The cure is better ground instruction
and very careful stall practice on every flight. Even if the rest of your
flying is perfect, it isn't safe to fly solo if you are still disturbed
by stalls or low g.
Pilots who dislike stalling will seldom explore any new solo aircraft
they are flying. Then if an unintentional stall occurs their responses and
recovery action will be impaired and may lead to an accident.
THOSE MOST AT RISK
It is often the young, above average student who is most at risk.
They learn very quickly and often make stall recoveries from the very
beginning so they don't experience any significant reduction in g.
Pleased with their progress, the instructor is liable to move on
quickly to incipient and full spins which don't normally involve low g
sensations. As a result they have far less training and experience than
the average beginner. They may have learnt to associate stalling with the
slight ammount of reduced g they experience on recovery without this being
obvious to the instructor.
Suddenly experiencing low g because of flying into turbulence on the
base leg of a circuit, their response will be a stall recovery; but since
the glider is flying normally any forward stick movement will reduce the g
still further. This will make them think the aircraft isn't responding
normally and they will move still further forward on the stick with
disastrous results.
It is remarkably easy for someone affected by low g to slip through
to solo without this fact being noticed. Some will manage to avoid stalling
exercises by diverting the instructor's attention to other aspects of their
flying and occasionally they have been known to make sure they get a poor
winch launch when they have been briefed to do more stalling.
A persistent fear of stalling must be the result of being misinformed
and of not understanding what an aircraft will and won't do if stalled.
An intensive dislike of the sensation can only be overcome by a proper
understanding of its cause, ie pitching not stalling, and by gradual
acclimatisation and training. However, it is difficult for the instructor
to persist with stalling exercises when they are upsetting the student so
much.
SUPER SENSITIVE PEOPLE
Perhaps most interesting and most dangerous are the small minority
who are chronically affected. Fortunately most of them dislike it so much
they avoid flying again, but to a few overcoming their fear of flying
becomes a challenge. In some forty years of full time gliding instruction
I have come across about a dozen students severely affected.
They look as though they are having an epileptic fit with the
slightest lowering of the glider's nose or the most gentle stall. They
become quite unconscious of what they are doing for a few seconds, and
yet many may still insist they want to learn to fly. If not spotted early
in their training they become a menace to themselves and their instructors.
These are the students who really do freeze on the controls, and with
the stick pushed and held firmly forward, the instructor has to be quick
and strong to prevent an accident. With very gradual familiarisation
training spread over many months some have been completely cured.
NEGATIVE G
It is very unusual to experience negative g in gliders except by
flying upside-down or by pitching violently nose down at high speeds.
Even zero g where the dust leaves the cockpit floor is unusual except when
making a violent nose down recovery from a very steep attitude on a fast
winch launch. Zero g is particularly unpleasant for almost every pilot
and very alarming if it occurs for the first time when a pilot is solo.
For this reason it should be demonstrated at least once towards the end
of pre-solo training.
Prolonged and pronounced low g is a sure sign that the aircraft is
not stalled. At very low speeds and when the aircraft is sinking, the
accelerations are very small and do not continue for more than a few
seconds. It is also important to realise that low g in any steep diving
attitude indicates the aircraft is unstalled and can normally be levelled
out of the dive by easing back.
There are other situations involving reduced g which can be
incapacitating. Reports about light aircraft landing accidents often say
the aircraft bounced or ballooned, pitched nose down and then flew into
the runway in a series of worsening crashes, smashing the nose gear and
engine. Certainly a low g sensitive person is liable to become completely
incapable of further thought once the aircraft pitches nose down the
first time and invariably show the basic response of pushing forward on the
stick and keeping it there.
The same kind of accident used to be common with gliders and the
pilots could never remember anything after the first bounce. They have
become less common since fully held-off landings have been taught. With
these it is likely a student will experience ballooning a number of times
in training and will have learned how to avoid automatically moving forward
on the stick. Those scared of ballooning will nearly always fly the
aircraft on to the ground instead of making properly held off landings.
TESTING THE STUDENT PILOT
Gliding instructors must be aware of the problems and watch for them
in their students. We should test every student before solo to make quite
sure they are not seriously affected by reduced g. This doesn't mean always
pitching violently to get weightlessness or negative g but introducing
small ammounts of reduced g.
The student can be asked to pitch nose down gently from level flight
and from diving and climbing attitudes. Those who are still sensitive are
incapable of doing this exercise and their reactions are obvious. They
should have more training until there are no bad reactions.
Then it is sensible to give them some experience in recovering from
unusual attitudes to see if they remain unaffected. This must be done at a
safe height, first explaining what will happen. A slow, steep, slipping
turn; a very nose high wing down position so that a full stall is
unavoidable; a steep diving position and an incipient spin after a low g
position are possible situations to try. They also have a confidence
raising effect because the student finds he can make safe recoveries from
attitudes far steeper than he is likely to get into by error.
Perhaps this kind of test should be used for every pilot regardless
of the aircraft they are learning on.
SUMMARY
If you dislike stalling and the sensations of low g persist with your
training. Make sure your CFI understands your problem and get him to
explain it.
Instructors should:
1. Explain to beginners the sensations involved in flying.
2. Avoid any pronounced pitching manoeuvres and particularly stalling on
early flights while the student is still sensitive to these movements.
3. Emphasise visual clues on early flights. Introduce the ASI later.
4. Explain low g on the same flight as stalling is introduced, emphasising
that the low g sensation is not a symptom of a stall.
5. Avoid the terms "stick forward" etc for recoveries from cable breaks
and stalls. Teach them to lower the nose to a certain attitude instead.
6. Practise a few recoveries from unusual positions with every student.
7. If you have a student who is upset badly by low g or stalling, make
sure he understands his problem and that your other instructors know
about it too.
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Chris Rollings, national coach comments:
All of the above is very good. However anyone reading it casually
might be mislead into thinking that if he experiences reduced g then he
cannot be stalled, which is of course not the case. The humpback-bridge
sensation is familiar to all of us in a steep stall. What Derek is saying
is that the reduced g sensation does not necessarily mean we are stalled.
It can and does frequently have other causes. Anyone who doubts this
should go and compare stalls and unstalled reduced g situations in a glider
with an accelerometer.