Safety of winch launch vrs. aero tow?

I still fly at dunstable and can say that there can still be a problem on
very still days off the Winch where you have too much height to land
straight ahead but not enough to turn safely. This is especially true for
abinitios/early solos. Unfortunately Dunstable is still far from flat and
still has a horrendous dip to the downs side over half the field with the
aver half having being filled in with spoil from the M1 making diagonal
landings in that direction difficult/impossible unless you want to do a
lemming act off the cliff edge that bisects part of the field but at least
the hedge has been partially removed on part of the southern edge leaving
the option of running on into a ploughed field. While I have never seen an
outfield landing following a winch break I could see it happening a calm
days with certain glider types.
Areotowing in Strong Easterly winds out towards the downs - that is best
confined to the horror vault. The wind coming across the top of the downs
produces a very violent wave pattern across the field and just as you are
getting to the roughest part where it feels like the wind is almost vertical
and trying to slam you back into the field the tug has to execute a sharp
right turn at V low altitude. There are parts of the field where the wave
effect produces a complete wind shadow.
As for being pulled off at 200ft - I wish. One of JJs (who probably taught
the previous poster) last acts before retiring for the winter was to pull me
off over the sw hedge - luckily we have a dip a bit further on that gives
another 40 ft and somehow I got it down back on the field after a 270. When
I asked him later if it was circa 150ft I was given the laconic comment -
"Not as much as that - remember each wing is only 30ft so you dont need a
lot providing you remember you already have flying speed and fly the turn
precisely". I never did have the courage to ask him exactly how high we
were.


"W.J. (Bill) Dean (U.K.)." wrote in message
...
Not always.

I learnt to fly at the London Gliding Club, Dunstable Downs some 40 years
ago, entirely on the winch, and on the T21b.

There was one run for which I was taught that the correct procedure for a
launch failure at a certain height was to land beyond the airfield
boundary
in the farmer's field.

The point surely is that before the launch starts the pilot should have in
mind all the possible options to cope with any launch failure; this may
include an off-airfield landing for either a wire or an aerotow launch.

Incidentally, the London Club now has more land, and outlandings after a
winch launch failure are not now required.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.


"Bill Daniels" wrote in message
nk.net...

snip

My original point was that with airtow stuff happens and sometimes you
aren't in position for a return to the runway. In winch launching, you
are.

Bill Daniels

Yes, JJ was one of my two instructors at Dunstable 40 years ago (John
Jeffries, not to be confused with some young whippersnapper from Nevada who
has hijacked these initials).

I remember the way he used to fly, and it is obvious that some things don't
change.

My other instructor was Mike Till, I flew with him mostly, I see he is on
the current roster.

As to launch failures generally, aerotow failures will often involve
outlandings, fortunately such failures are rare compared with wire launch
failures.

There has been considerable discussion as to how aerotow failures should be
taught, since it is important that the pupil should not assume that the
airfield can always be reached. It maybe that JJ could get back, but this
does not mean that you can when it happens for real. Instructors are apt
to pull a simulated failure when it is still possible to get back, though
only just with JJ. There is a lot to be said for using a motor-glider for
teaching aerotow landing options, though JJ won't like this idea!

In real life some aerotow operations are carried out where an aerotow
failure may result at best in a controlled crash. Remember that if the tug
has an engine problem it may operate at low power before failing, so you
will be slower and lower than on a normal tow before you abandon the tow or
it abandons you.

As to wire launch failures at Dunstable, yes there is often a very narrow
gap between being too low to turn and too high to get in straight ahead.
It is certainly a good idea to have fields outside the airfield in mind when
reviewing the options while doing the launch failure bit of "eventualities"
before starting the launch. Often the field is partly blocked by gliders
awaiting retrieve, and tractors on their way to do the retrieve. If you do
not think of an option when reviewing options before starting, you are
unlikely to think of it when conducting a very high pressure recovery which
is by definition not expected (though it must be thought about).

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.


"Stephen Haley" wrote in message
...

I still fly at Dunstable and can say that there can still be a problem on
very still days off the winch where you have too much height to land
straight ahead but not enough to turn safely. This is especially true
for abinitios/early solos. Unfortunately Dunstable is still far from
flat and still has a horrendous dip to the downs side over half the field
with the other half having being filled in with spoil from the M1 making
diagonal landings in that direction difficult/impossible unless you want
to do a lemming act off the cliff edge that bisects part of the field but
at least the hedge has been partially removed on part of the southern edge
leaving the option of running on into a ploughed field. While I have
never seen an outfield landing following a winch break I could see it
happening a calm days with certain glider types.

Aerotowing in strong easterly winds out towards the downs - that is best
confined to the horror vault. The wind coming across the top of the
downs produces a very violent wave pattern across the field and just as
you are getting to the roughest part where it feels like the wind is
almost vertical and trying to slam you back into the field the tug has to
execute a sharp right turn at v low altitude. There are parts of the
field where the wave effect produces a complete wind shadow.

As for being pulled off at 200ft - I wish. One of JJs (who probably
taught the previous poster) last acts before retiring for the winter was
to pull me off over the sw hedge - luckily we have a dip a bit further on
that gives another 40 ft and somehow I got it down back on the field after
a 270. When I asked him later if it was circa 150ft I was given the
laconic comment - "Not as much as that - remember each wing is only 30ft
so you dont need a lot providing you remember you already have flying
speed and fly the turn precisely". I never did have the courage to ask
him exactly how high we were.


"W.J. (Bill) Dean (U.K.)." wrote in message
...

Not always.

I learnt to fly at the London Gliding Club, Dunstable Downs some 40
years ago, entirely on the winch, and on the T21b.

There was one run for which I was taught that the correct procedure for
a launch failure at a certain height was to land beyond the airfield
boundary in the farmer's field.

The point surely is that before the launch starts the pilot should have
in mind all the possible options to cope with any launch failure; this
may include an off-airfield landing for either a wire or an aerotow
launch.

Incidentally, the London Club now has more land, and outlandings after a
winch launch failure are not now required.

W.J. (Bill) Dean (U.K.).


"Bill Daniels" wrote in message
nk.net...

snip

My original point was that with airtow stuff happens and sometimes you
aren't in position for a return to the runway. In winch launching,
you are.

Bill Daniels

"W.J. (Bill) Dean (U.K.)." wrote:
...
There is a lot to be said for using a motor-glider for
teaching aerotow landing options, though JJ won't like this idea!


I agree with JJ's opinion. My computation identified the minumum of
Vz*V as an important factor in the possibility of turning back, and
this values is usually much higher in a motor-glider, due to higher
wing loading and worse aerodynamic.

...
As to wire launch failures at Dunstable, yes there is often a very narrow
gap between being too low to turn and too high to get in straight ahead.

I don't understand clearly what is the problem at Dunstable. What is the
length of runway ahead of you when you reach 150m?

...
Often the field is partly blocked by gliders
awaiting retrieve, and tractors on their way to do the retrieve.

In this case, if they don't allow a sufficient free space to land
in case of a cable break, you should delay the start.

Teaching aerotow launch failure options with a motor glider.

JJ has always disliked the idea of using a motor glider for any purpose
whatever, and he has the same opinion of turbo and self-launching gliders
(unless old age is getting to him and he has changed his opinion recently).
His opinion is purist, aesthetic and emotional, and I can remember him
admitting this. Dunstable never used a motor glider for training while he
was running things, they got one after he retired from the club management.
It is a matter of what is most fun, flying with JJ has always been fun
(unlike some instructors I could name).

It is now a BGA requirement that glider pilots get a "Cross-Country
Endorsement" to their Gliding Certificate before deliberately flying
cross-country. See "Laws and Rules for Glider Pilots" edition 14 (BGA),
page 44 section 17.12. In the section on Field Landings it states: "The
candidate must make a minimum of two successful approaches, selected by
himself in a motor glider. .....". The motor glider is used of course so
that an approach can be made without actually landing.

The use of motor gliders for glider pilot training generally has always been
controversial in he U.K., the strongest advocate was always Derek Piggott.
However whenever a club has got used to using a motor glider for teaching
the cross country skills of Navigation, Field Selection and Field Landings
it has always been accepted as being valuable, and its use for teaching
Field Landings is now mandatory.

In the case of aerotow launch failures the training I had in mind was for
the cases where turning back to the airfield is not a safe option. This
then becomes an exercise like any field landing, except that the decision to
land is immediate and unexpected, but should be into a field already known
about.

As for the case where it is possible to turn back to the airfield, if it is
not possible in a motor glider with a very experienced instructor
supervising, and the exercise known about in advance; would it be sensible
for a rather inexperienced pilot solo and taken by surprise?

The type of motor glider almost invariably used for this area of training in
the U.K. is one of the Falke series.

Winch launching at Dunstable.

I flew 917 launches at Dunstable as instructor between 1992 and 1994, almost
all of them by winch, most in the K21 the remainder in the K13. I did many
launch failure exercises (we all did) and none of them finished in a field.

The field is fairly small, and roughly rectangular in shape so all the winch
runs are short. I recall that 1,200ft was a good launch, and sometimes on
some runs we got 800ft or less. 150m or 450ft would be far too high to
land ahead unless the wind was strong, on a no wind day such a height would
be considered easy for a short circuit.

As for congestion on the airfield, of course one would not launch if there
were nowhere to land, it is simply that one seldom had the whole area
available.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.


"Robert Ehrlich" wrote in message
...


"W.J. (Bill) Dean (U.K.)." wrote:
...
There is a lot to be said for using a motor-glider for
teaching aerotow landing options, though JJ won't like this idea!


I agree with JJ's opinion. My computation identified the minimum of
Vz*V as an important factor in the possibility of turning back, and
this values is usually much higher in a motor-glider, due to higher
wing loading and worse aerodynamic.

...
As to wire launch failures at Dunstable, yes there is often a very
narrow gap between being too low to turn and too high to get in straight
ahead.


I don't understand clearly what is the problem at Dunstable. What is the
length of runway ahead of you when you reach 150m?

...
Often the field is partly blocked by gliders
awaiting retrieve, and tractors on their way to do the retrieve.


In this case, if they don't allow a sufficient free space to land
in case of a cable break, you should delay the start.

I don't understand clearly what is the problem at Dunstable. What is the
length of runway ahead of you when you reach 150m?

Simple answer is not really enough when launching in flat calm conditions
which aggravate matters in 2 ways
1) Lack of wind reduces the overall height gained by upto 30% which means
you will be substantially further down the field @ 150ft.
2) Lack of headwind means that the landing will be longer.
10kts of wind changes everything and produces a reasonable overlap.

The ordinance survey shows the field at about 1k in length
As for runway we are a grass field which is far from level.

"Robert Ehrlich" wrote in message
...
"W.J. (Bill) Dean (U.K.)." wrote:
...
There is a lot to be said for using a motor-glider for
teaching aerotow landing options, though JJ won't like this idea!


I agree with JJ's opinion. My computation identified the minumum of
Vz*V as an important factor in the possibility of turning back, and
this values is usually much higher in a motor-glider, due to higher
wing loading and worse aerodynamic.

...
As to wire launch failures at Dunstable, yes there is often a very
narrow
gap between being too low to turn and too high to get in straight ahead.

I don't understand clearly what is the problem at Dunstable. What is the
length of runway ahead of you when you reach 150m?

...
Often the field is partly blocked by gliders
awaiting retrieve, and tractors on their way to do the retrieve.

In this case, if they don't allow a sufficient free space to land
in case of a cable break, you should delay the start.

Robert Ehrlich wrote:

Colin wrote:

Many years ago a highly respected aerobatic pilot in UK (still working
today) wrote an article in our Pilot magazine on this subject. He
reminded us that three things were required:
1. A rapid 180 degree change of heading.
2. Minimum loss of height.
3. Normal airspeed at the end of the manoever.
Controversially, he maintained that a highly banked slipping turn
satisfies all three criteria. The rate of decent is very high during
the turn, but the duration is so short that it results in less height
loss than either of the two alternatives (eg:slow and gentle or fast
and furious), and the airspeed is normal throughout.
Just don't forget to keep loads of top rudder on.

- Colin


I don't see why the turn should be a slipping one, you certainly will
loose more height in a slipping turn than in a normal one. And height
loss is what make the turn possible or not.

1. A slipping turn can be made at a high bank angle and low airspeed.
2. Rate of turn is dependent on angle of bank and airspeed, such that
the highest rate of turn is achieved with a high bank angle and a low
airspeed.
Brian illustrated this by inviting us to compare the rate of turn
achieved by a C150 and a jet fighter at the same angle of bank.
It has to be a slipping turn or we would stall, so the maximum bank
which can be used is dependent on the amount of top rudder available.

- Colin

Colin wrote:


I don't see why the turn should be a slipping one, you certainly will
loose more height in a slipping turn than in a normal one. And height
loss is what make the turn possible or not.


1. A slipping turn can be made at a high bank angle and low airspeed.

I don't understand this: at any given bank angle, how can you achieve a
lower airspeed when you are slipping? Doesn't that require more elevator
power? How would a slipping turn enable that?

Stephen Haley wrote:

I don't understand clearly what is the problem at Dunstable. What is the
length of runway ahead of you when you reach 150m?

Simple answer is not really enough when launching in flat calm conditions
which aggravate matters in 2 ways
1) Lack of wind reduces the overall height gained by upto 30% which means
you will be substantially further down the field @ 150ft.
2) Lack of headwind means that the landing will be longer.
10kts of wind changes everything and produces a reasonable overlap.

The ordinance survey shows the field at about 1k in length

I was talking of 150m, not 150ft. If your 1k length is also in feet,
this is pretty short (~ 300m), i.e. the winch is probably far beyond the
landable area, which is unusual. If it is 1km, even if you had a very
poor climb and you are at mid field (500m) at 150m, 500m seems highly
sufficient in any condition of wind for a landing straight ahead.

Robert Ehrlich wrote:
...
In this case our common conclusion
is again that the optimal (aerodynamic) bank angle is 90 degrees,
...

Corrcting myself: should be 45 degrees.

On Thu, 06 Nov 2003 00:02:30 +0000, Colin wrote:

1. A slipping turn can be made at a high bank angle and low airspeed.

I believe in (and teach) a few basic principles when flying close to the
ground.

- Stall/spin accidents kill more pilots than any other single cause.

- Stalls occur when you fly too slowly.

- Spins occur when you stall and the glider is not "co-ordinated" ie
either slipping or skidding.

Therefore if you are flying close to the ground, keep the airspeed
comfortably above stalling speed. And if you can't do that, keep the
aircraft co-ordinated.

(When instructing, close to the ground, if the student can't maintain a
steady airspeed, I take over control at the first sign of loss of
co-ordination).

Using a low airspeed slipping turn to turn 180 deg when less than 200 ft
above the ground sounds like the advice that a legendary grandmother is
once said to have given "now son, be careful when you go flying, don't fly
to high and don't fly too fast!"

Maybe some aerobatic super pilot can prove me wrong, but if you have to
resort to these measures to get back to the field then I think you would
probably be better off taking your chances going in straight ahead.


Ian

(I have seen gliders “land� in some unusual places and get away with
relatively minor damage and no injuries. Provided the glider is flown in a
controlled manner to the point of touch down, and the landing is done with
lowest possible energy - full flaps, into wind, air brakes closed - damage
is often minor. On the other hand I have seen two crashes where the glider
went in wing tip first and cartwheeled. Both were right-offs with serious
injuries.)