Safety of winch launch vrs. aero tow?

Robert Ehrlich wrote:

Colin wrote:
...
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.
...

Ok, if you use the lift provided by the fuselage in a slipping turn,
you can devote more of the lift provided by the wings for generating
the centripetal force, by increasing the bank angle, and so the horizontal
component of the wing lift. But you pay this by an increase in drag, i.e.
more height loss. It is not obvious if the gain in time to turn override
the increased rate of sink, but I have some argument that should show that
the answer is no.

The analysis of Dr. Rogers as well as my own one can be used in the case
of a slipping turn can be used if you consider as bank angle not the
geometric bank angle, i.e. the angle between the wing plane and the
horizontal plane, but the aerodynamic bank angle, i.e. the angle between
the total lift vector (wings + fuselage) and the vertical (well as we consider
a glide it is rather total aerodynamic force than lift, but the difference
between both angles can be neglected). In this case our common conclusion
is again that the optimal (aerodynamic) bank angle is 90 degrees, although
the geometric bank angle is higher, and we have to maximize Cl/(Cd^2) in
Dr. Rogers' analysis, minimize Vz*V in my analysis. It is difficult to determine
if you may have a higher max Cl/(Cd^2) with slip, but I have a good argument
that we can't lower Vz*V. Remember in this analysis Vz and V are the horizontal
and vertical speed at zero (aerodynamic) bank angle and the same angle of attack,
i.e. what you find in an usual glider polar. In the case of a slipped turn,
we should use a polar showing Vz versus V for a straight flight with the
same slip angle. I never saw such a polar, but I think it is obvioous that
at any speed V the vertical speed Vz is higher with slip than without it.
i.e. the polar with slip is entirely below the polar without slip. Now the
minimum of Vz*V for the polar without slip is where this polar is tangent
to one of the hyperbolas Vz*V = constant, and except for the point of
contact, the polar is entirely below this hyperbola. So the polar with
slip is also entirely below this hyperbola, and no point of it can
provide a value for Vz*V that is lower or equal to the the value on
the hyperbola, i.e. the minimum of Vz*V obtained without slip cannot
be obtained with slip.

Er, yes ...
But how does the result compare with a large tear-drop flown at normal
glide speed, or for that matter, a smaller tear-drop flown with higher
airspeed and more bank ?
The point is how to complete a rapid 180 without spinning-in, and a
full sideslip with small angle of attack precludes a spin.
The author also encourages us to go out and try it, high up to begin
with of course.
- Colin.

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.

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).

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.

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

Chris OCallaghan wrote:
Eric,

Point of interest: did you let the spin fully develop after the
coordinated turning stall?

No, but there didn't seem to be any need to, as the inner wing dropped
and rotation began.

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.


As Mark points out, the ailerons on the Blanik are significantly
deflected with "down" aileron on the inner wing, which is part of the
reason the inner wing stalls first. They are also deflected this way on
other gliders, but perhaps not as much.

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.

At least, for a straight ahead stall. I don't think this is true for
many gliders in a turn.

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.

We await your report with interest!

In my first reply to Chris, I should've said "as Bruce Hoult points out"
instead of Mark Boyd.

Chris OCallaghan wrote:

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.

"Mark James Boyd" wrote in message
news:3fac007b$1@darkstar...

tell the difference, so I was too scared to do
anything but recover immediately (release the cross-controlled
inputs).

With all due respect ......

That is not a spin recovery, never was and never will be although I'll admit
that in the right circumstances it will occasionally work.

If you are intentionally trying to spin not knowing how to recover properly
then you either have balls the size of footballs or are seriously mentally
challenged.

A STANDARD recovery is

CENTRALISE AILERONS
FULL OPPOSITE RUDDER.
SLIGHT PAUSE
STICK PROGRESSIVELY FORWARD UNTIL THE SPINNING STOPS.
CENTRALISE THE RUDDER.
RECOVER FROM THE RESULTING DIVE.

Very occasionally there may be a 'non standard' method in the POH but they
are few and far between. To be certified a glider should recover reliably
using the standard proceedure.

There is an excellent post by Bill Dean ( and others ) about this in the
archives ( a year ago )
http://groups.google.co.uk/groups?q=...ara.net&rnum=2

Ian

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).
************************************************** ******************************
What really killed them were wings which, by design, are only good for
3.5 g (+50% if the glue holds) when you get into a stall/spin
situation.