Safety of winch launch vrs. aero tow?

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).

"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.

On 7 Nov 2003 23:40:26 -0800, (Slingsby)
wrote:

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.


The official conclusion sounds a little different:

The maximum maneuvering load factor limits (in units of gravity or
g's) change with variations in glider speed and flap/airbrake
configuration. From a "flaps up" configuration at Va to the condition
of airbrakes and flaps extended at Vne, the maximum maneuvering load
factor limits decrease from positive 5.3 to a positive 3.5.

In other words: If the pilots had not extended the airbrakes, the
Nimbus would not have disintegrated.

This is what NTSB thinks about what killed them:

The National Transportation Safety Board determines that the probable
cause of this accident was the pilot's excessive use of the elevator
control during recovery from an inadvertently entered spin and/or
spiral dive during which the glider exceeded the maximum permissible
speed, which resulted in the overload failure of the wings at loadings
beyond the structure's ultimate design loads.

Note the term "at loadings beyond the structure's ultimate design
loads".




Bye
Andreas

About the Minden accident on 13 July 1999 to a Nimbus 4DM (LAX99MA251
http://www.ntsb.gov/publictn/2002/AAB0206.htm ).

Note that at the time the NTSB report was published there was discussion
about it on RAS. One of the things reported by posters with experience of
the Nimbus 3/4 models (I have none) was that the airbrakes have been known
to deploy uncommanded by the pilot. So the brakes may have deployed
themselves, and it is possible that this is what killed the pilots.

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


"Andreas Maurer" wrote in message
...


On 7 Nov 2003 23:40:26 -0800, (Slingsby)
wrote:

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.


The official conclusion sounds a little different:

The maximum manoeuvring load factor limits (in units of gravity or
g's) change with variations in glider speed and flap/airbrake
configuration. From a "flaps up" configuration at Va to the condition
of airbrakes and flaps extended at Vne, the maximum manoeuvring load
factor limits decrease from positive 5.3 to a positive 3.5.

In other words: If the pilots had not extended the airbrakes, the
Nimbus would not have disintegrated.

This is what NTSB thinks about what killed them:

The National Transportation Safety Board determines that the probable
cause of this accident was the pilot's excessive use of the elevator
control during recovery from an inadvertently entered spin and/or
spiral dive during which the glider exceeded the maximum permissible
speed, which resulted in the overload failure of the wings at loadings
beyond the structure's ultimate design loads.

Note the term "at loadings beyond the structure's ultimate design
loads".

Bye
Andreas

Andreas Maurer wrote in message . ..
On 7 Nov 2003 23:40:26 -0800, (Slingsby)
wrote:

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.


The official conclusion sounds a little different:

The maximum maneuvering load factor limits (in units of gravity or
g's) change with variations in glider speed and flap/airbrake
configuration. From a "flaps up" configuration at Va to the condition
of airbrakes and flaps extended at Vne, the maximum maneuvering load
factor limits decrease from positive 5.3 to a positive 3.5.

Right. By design they are ONLY good for 3.5 g. Exceed that amount by a paltry 50% and the wings WILL snap off like toothpicks. Guaranteed. They will, and did, snap off together. Both wings were equally weak by design and construction technique AND, they used enough glue.

In other words: If the pilots had not extended the airbrakes, the
Nimbus would not have disintegrated.

This is what NTSB thinks about what killed them:

The National Transportation Safety Board determines that the probable
cause of this accident was the pilot's excessive use of the elevator
control during recovery from an inadvertently entered spin and/or
spiral dive during which the glider exceeded the maximum permissible
speed, which resulted in the overload failure of the wings at loadings
beyond the structure's ultimate design loads.

Remove the word "excessive" and the description becomes more realistic.

Note the term "at loadings beyond the structure's ultimate design
loads".

Bye
Andreas

We're taught (in fact, it's hammered into us) to recover immediately
from the insipient phase of any stall. Hanging in there to allow the
condition to fully develop is an exercise that takes practice, and
probably one that you don't want to get too used to.

Given the confusion of your asi, the next best way to differentiate is
by g load. In a spin, the loading quickly stabilizes to 1.5 to 2g. In
a spiral dive it builds quickly beyond this. Visually, the yaw string
goes right over in a spin, but since a spiral dive needn't be
coordinated, this too can be confusing.

Spinning or spiral diving are both unusual maneuvers. Because of that,
each of us will perceive them a little differently, based on our
personal idiosyncracies. For most of us, a canopy full of mother earth
screams acceleration, overpowering any other cues.

I am reminded of an experience I relive at least once every winter:
the first application of brakes on ice. When I step on the brakes, I
expect the reassurance of weight into my shoulder belt. When that
doesn't happen, I get the oddest feeling that instead of decelerating
I am accelerating, which, of course, makes me want to mash the brake
pedal down even harder. It takes a second or two to break through the
misperception and get my foot back up off the brake. I suspect that we
are all subject to varying degrees of a similar effect when we explore
parts of the envelope we don't often visit. Practice makes perfect,
but why do we need to be perfect unless we're aerobatic pilots.

We should focus instead on the insipient phase. Much more subtle, but
much more valuable in gleaning out every last ounce of performance
when it counts most.




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