Don Johnstone[_4_]
October 14th 13, 02:15 AM
I have started a new thread on this because it is an important subject.
I have read the article at
https://dl.dropboxusercontent.com/u/79580374/Acceleration.pdf
The first thing to understand is that the wing drop is a symptom of a
problem that has already occurred, it is not the primary cause of the
problem. The problem, or rather the serious consequences, were almost
unknown prior to the introduction of powerful winches with rapid
acceleration. With less powerful winches wing drop did occur but this did
not result in the airborne cartwheel which occurs off a powerful winch. The
lack of acceleration gave the pilot plenty of time to react and release.
The assertion that the accidents are caused by slow acceleration is
incorrect, in fact the opposite is true.
For many years I flew with the Air Cadet organisation and accidents of this
type are almost unknown, certainly there has never been one where there has
been death or injury. I suggest the reason for this is the strict limits
put on the operation and the manpower available to move gliders around at
the launch point. Air Cadet Gliding Squadrons employ staff cadets who do
most of this work. I suggest the basic reason why there are fewer
incidents, and the Air Cadet movement does as many winch launches in a year
as the BGA clubs, is for the following reasons.
1. The Air Cadets operate to strict weather minima especially crosswind
limits.
2. Gliders are always taken to cables, cables are never taken to aircraft.
3. If you are pulling out 6 cables at a time you have to keep them very
straight. the MVG winch has 6 drums.
4. Of all the winches I have flown the MVG winch has the smoothest and most
rapid acceleration, typically in a 15knot wind the glider (Grob103) would
be airborne in it's own length.
This operation reduces the factors which can contribute to yaw. The only
incident I witnessed was caused by the pilot starting the launch with
rudder applied anticipating yaw from a crosswind. The wing obligingly
dropped as a result of the yaw produced. The glider was released before the
wing struck the ground.
With early low powered Eagle winches the procedure was to adopt a gentle
climb to a safe height before entering the full climb. The procedure
changed following the introduction of the MVG winch which had a very large
diesel engine (8 litres if my memory serves) driving through a true torque
converter so that if the gentle climb scenario was carried out or over done
the speed increased very rapidly. The recommended procedure was to enter
the the full climb provided that the glider was above the minimum speed and
accelerating. This was the procedure I used in the 10 years I flew off the
MVG winch. It was never ever suggested that the elevator should be anywhere
other than at neutral prior to the launch.
From what I have read in accident/incident reports the accidents have all
occurred very rapidly and the acceleration is part of the problem in that
it exacerbates the yaw/roll condition.
One of the symptoms is wing drop. In most cases aileron is applied to try
and level the wings, in the case of the accidents this is invariably
unsuccessful. During a winch launch we are approaching the stall from the
"Other" direction, we are accelerating through the stalled condition.If we
think about what we tell people not to do with a glider which has a high
angle of attack with yaw/roll and pitch present, aka spinning this might be
a clue. Well tell them to keep the ailerons neutral, we tell them NOT to
try and pick up the wing with aileron.
Because the ground is so close once the yaw/roll has started the glider is
irrecoverable and the only option is to release to lessen the impact, not
to prevent it, it is already too late for that, but to try and prevent the
glider from becoming airborne. Given the rapid acceleration of modern
winches the time allowed to pull the release is very very short and that is
the reason why my hand is always on the release ready to pull it if at any
time there is roll over which I have no control. I cannot stress the
importance of holding that release, it can be a lifesaver.
My feeling is that the primary culprit in these cases is yaw, I am
convinced that the roll is a symptom of this yaw.
I have read the article at
https://dl.dropboxusercontent.com/u/79580374/Acceleration.pdf
The first thing to understand is that the wing drop is a symptom of a
problem that has already occurred, it is not the primary cause of the
problem. The problem, or rather the serious consequences, were almost
unknown prior to the introduction of powerful winches with rapid
acceleration. With less powerful winches wing drop did occur but this did
not result in the airborne cartwheel which occurs off a powerful winch. The
lack of acceleration gave the pilot plenty of time to react and release.
The assertion that the accidents are caused by slow acceleration is
incorrect, in fact the opposite is true.
For many years I flew with the Air Cadet organisation and accidents of this
type are almost unknown, certainly there has never been one where there has
been death or injury. I suggest the reason for this is the strict limits
put on the operation and the manpower available to move gliders around at
the launch point. Air Cadet Gliding Squadrons employ staff cadets who do
most of this work. I suggest the basic reason why there are fewer
incidents, and the Air Cadet movement does as many winch launches in a year
as the BGA clubs, is for the following reasons.
1. The Air Cadets operate to strict weather minima especially crosswind
limits.
2. Gliders are always taken to cables, cables are never taken to aircraft.
3. If you are pulling out 6 cables at a time you have to keep them very
straight. the MVG winch has 6 drums.
4. Of all the winches I have flown the MVG winch has the smoothest and most
rapid acceleration, typically in a 15knot wind the glider (Grob103) would
be airborne in it's own length.
This operation reduces the factors which can contribute to yaw. The only
incident I witnessed was caused by the pilot starting the launch with
rudder applied anticipating yaw from a crosswind. The wing obligingly
dropped as a result of the yaw produced. The glider was released before the
wing struck the ground.
With early low powered Eagle winches the procedure was to adopt a gentle
climb to a safe height before entering the full climb. The procedure
changed following the introduction of the MVG winch which had a very large
diesel engine (8 litres if my memory serves) driving through a true torque
converter so that if the gentle climb scenario was carried out or over done
the speed increased very rapidly. The recommended procedure was to enter
the the full climb provided that the glider was above the minimum speed and
accelerating. This was the procedure I used in the 10 years I flew off the
MVG winch. It was never ever suggested that the elevator should be anywhere
other than at neutral prior to the launch.
From what I have read in accident/incident reports the accidents have all
occurred very rapidly and the acceleration is part of the problem in that
it exacerbates the yaw/roll condition.
One of the symptoms is wing drop. In most cases aileron is applied to try
and level the wings, in the case of the accidents this is invariably
unsuccessful. During a winch launch we are approaching the stall from the
"Other" direction, we are accelerating through the stalled condition.If we
think about what we tell people not to do with a glider which has a high
angle of attack with yaw/roll and pitch present, aka spinning this might be
a clue. Well tell them to keep the ailerons neutral, we tell them NOT to
try and pick up the wing with aileron.
Because the ground is so close once the yaw/roll has started the glider is
irrecoverable and the only option is to release to lessen the impact, not
to prevent it, it is already too late for that, but to try and prevent the
glider from becoming airborne. Given the rapid acceleration of modern
winches the time allowed to pull the release is very very short and that is
the reason why my hand is always on the release ready to pull it if at any
time there is roll over which I have no control. I cannot stress the
importance of holding that release, it can be a lifesaver.
My feeling is that the primary culprit in these cases is yaw, I am
convinced that the roll is a symptom of this yaw.