Safety of winch launch vrs. aero tow?

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.

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?

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.)

Ian Forbes wrote:

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


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

I used to think this, but I soon discovered our club Blanik would
happily spin from a coordinated turn by using a shallow bank and simply
reducing the airspeed. Since then, I've done this with other gliders.

A coordinated turn doesn't prevent the inner wing from flying at a
higher angle of attack than the outer wing, which is why it stalls
first, and a spin can begin. I haven't experimented with it enough to be
certain, but I suspect a slipping turn would reduce the tendency for the
inner wing to stall first.

Eric,

Point of interest: did you let the spin fully develop after the
coordinated turning stall? There is an aerodynamic tipping point --
that is the self-righting tendency of the tail that would typically
favor a spiral over a spin assuming that the only deflected control
surface was the elevator. Of course a wing drops when in a turning
stall, but without aileron deflection generating drag my guess would
be that designed yaw stability would prevent spin development.

There is a significant difference in the assymetric drag profile with
and without aileron deflection. Remember that most modern aircraft
begin their stall at the root. That means less torque and less
disposition to overpower yaw stability and enter a spin. Slapping an
aileron down to pick up the low wing adds significat drag at the tip.
Add some rudder (cross-controls), and now you have a greater
disposition to get the aircraft spinning rather than spiralling.

I'll give this a try over the weekend -- that is, making no recovery
to a coordinated turning stall to see how it develops. My Ventus spins
happily if aggrevated. It should prove a good test bed.

Eric Greenwell wrote in message ...
Ian Forbes wrote:

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


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

I used to think this, but I soon discovered our club Blanik would
happily spin from a coordinated turn by using a shallow bank and simply
reducing the airspeed. Since then, I've done this with other gliders.

A coordinated turn doesn't prevent the inner wing from flying at a
higher angle of attack than the outer wing, which is why it stalls
first, and a spin can begin. I haven't experimented with it enough to be
certain, but I suspect a slipping turn would reduce the tendency for the
inner wing to stall first.

A clarification...

When I ask did you let the spin fully develop, I mean through one or
more full turns, ie, to the point where it is easily differentiated
from a spiral. The initial turning stall very often self-recovers
within a quarter turn (yaw stability). If the stick is not moved
forward, the glider will continue to turn in a steepening bank and
accelerate. Most pilots instinctively recover long before they can
tell the difference between a stall -- recovery -- spiral dive
scenario and a stall -- spin. This often causes confusion about which
is which. I'm quibbling a little here, but there is a difference in
recovery times and altitude loss between the two. Your underlying
message, "Don't trust the yaw string alone to prevent a spin" is a
good one. Airspeed/AOA is the primary concern. A straight yaw string a
close second.

There is some value in understanding that a straight yaw string helps
a sailplane resist spinning. If we can be certain of this, low
altitude stalls can be more confidently addressed with greater control
and less loss of altitude. I'm thinking principally of wind shear
while turning base to low final. If the pilot doesn't detect the loss
of airspeed, he will certainly notice that the nose pitches down
(position of the elevator will try to return the glider to the lower
angle of attack) and may respond, initially, by trying to raise the
nose, aggrevating the situation. If a stall develops a quick glance
at the yaw string can help determine appropriate action, that is,
release back pressure and raise the lower wing using coordinated stick
and rudder, versus ailerons neutral, stick aggressively forward and
hard-over opposite rudder, then recovery from the ensuing dive.



(Chris OCallaghan) wrote in message . com...
Eric,

Point of interest: did you let the spin fully develop after the
coordinated turning stall? There is an aerodynamic tipping point --
that is the self-righting tendency of the tail that would typically
favor a spiral over a spin assuming that the only deflected control
surface was the elevator. Of course a wing drops when in a turning
stall, but without aileron deflection generating drag my guess would
be that designed yaw stability would prevent spin development.

There is a significant difference in the assymetric drag profile with
and without aileron deflection. Remember that most modern aircraft
begin their stall at the root. That means less torque and less
disposition to overpower yaw stability and enter a spin. Slapping an
aileron down to pick up the low wing adds significat drag at the tip.
Add some rudder (cross-controls), and now you have a greater
disposition to get the aircraft spinning rather than spiralling.

I'll give this a try over the weekend -- that is, making no recovery
to a coordinated turning stall to see how it develops. My Ventus spins
happily if aggrevated. It should prove a good test bed.

Eric Greenwell wrote in message ...
Ian Forbes wrote:

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


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

I used to think this, but I soon discovered our club Blanik would
happily spin from a coordinated turn by using a shallow bank and simply
reducing the airspeed. Since then, I've done this with other gliders.

A coordinated turn doesn't prevent the inner wing from flying at a
higher angle of attack than the outer wing, which is why it stalls
first, and a spin can begin. I haven't experimented with it enough to be
certain, but I suspect a slipping turn would reduce the tendency for the
inner wing to stall first.

Most pilots instinctively recover long before they can
tell the difference between a stall -- recovery -- spiral dive
scenario and a stall -- spin. This often causes confusion about which
is which.

I personally intentionally tried a spin entry once in a glass
glider and got a surprise and made an immediate spin recovery.

It seems the airspeed indicator rotates all the way around, so
80 knots indicated is the same as 20 knots indicated.

Imagine my surprise when the glider stalls, the nose drops,
and the ASI wobbles and then indicates ???
I tried it a few more times and by god could never
tell the difference, so I was too scared to do
anything but recover immediately (release the cross-controlled
inputs). Whichever it was, the glider sure picked up
speed like lightning when nose down.

I still wonder if this killed the Nimbus4DM pilots in Reno.
Imagine looking at the ASI and not knowing if
you should be doing a spin recovery or a spiral recovery
(two very different things).

In article ,
(Chris OCallaghan) wrote:

Point of interest: did you let the spin fully develop after the
coordinated turning stall? There is an aerodynamic tipping point --
that is the self-righting tendency of the tail that would typically
favor a spiral over a spin assuming that the only deflected control
surface was the elevator. Of course a wing drops when in a turning
stall, but without aileron deflection generating drag my guess would
be that designed yaw stability would prevent spin development.

Even with the string in the middle, the elevator will *not* be the only
deflected control surface.

The Blanik makes this very obvious. As you slow down in a shallow turn
(10 degrees, say) you need more and more out of turn aileron in order to
prevent the turn from steepening, and you need more and more into turn
rudder to keep the string in the middle. Both controls can get a
significant way towards their limits in what seems like a perfectly
normal turn. When the inner wing eventually stalls everything is
perfectly set up for a rapid departure and spin.

-- Bruce

You've just described a cross-control stall. I think Eric's point was
that the additional drag at the wingtip wasn't necessary to initiate
auto rotation. The control inputs you've described are counter
intuitive. Is this a peculiarity of the Blanik? I only have a couple
of flights in them.

Typically, shallow banked turns like to roll level, especially if
there is any tendency to slip (dihedral). In most of the models I've
flown, overbanking doesn't become noticeable until you reach 30+
degrees.

Bruce Hoult wrote in message ...
In article ,
(Chris OCallaghan) wrote:

Point of interest: did you let the spin fully develop after the
coordinated turning stall? There is an aerodynamic tipping point --
that is the self-righting tendency of the tail that would typically
favor a spiral over a spin assuming that the only deflected control
surface was the elevator. Of course a wing drops when in a turning
stall, but without aileron deflection generating drag my guess would
be that designed yaw stability would prevent spin development.

Even with the string in the middle, the elevator will *not* be the only
deflected control surface.

The Blanik makes this very obvious. As you slow down in a shallow turn
(10 degrees, say) you need more and more out of turn aileron in order to
prevent the turn from steepening, and you need more and more into turn
rudder to keep the string in the middle. Both controls can get a
significant way towards their limits in what seems like a perfectly
normal turn. When the inner wing eventually stalls everything is
perfectly set up for a rapid departure and spin.

-- Bruce