negative flaps--what speeds?

"Dave Martin" wrote in message
...

The exercise I described is one of the BGA stall reinforcement
exercises. The common cause following a winch launch
failure, pushing hard forward, then as the attitude
looks correct and as the glider is in a reduced G situation
starting a turn. (Without getting the books out that
is as simple as I can describe it) This has caused
several accidents in the UK some of them fatal.

The danger also exists when pulling up sharply in to
a thermal and pushing over hard at the top of the pull
up then starting a turn in reduced G.

Fingers crossed as yet I have never entered a spin
pulling up into thermals. But as an instructor at
a winch launch site, it something you need to be able
to demonstrate.

But we are getting away from the thread...........

Regards


Dave

These are fun maneuvers. I find a Blanik L-23 to be a prefect trainer for
them - it spins easily, recovers easily with little altitude loss or
airspeed gain.

My winch stall maneuver is done at a safe altitude (of course). First, I
ask the student to dive then zoom up at 45 - 50 degrees, then when the
airspeed drops to about 55Kts, I yell "wire break" and expect the student to
push over smartly in a simulated wire break recovery. (This gets the
student used to the attitude and feel of a wire break and the control inputs
needed for a recovery before trying it for real on the winch.)

If the student doesn't screw it up on his own, I will demonstrate a botched
recovery by doing nothing until the nose falls on its own then stopping the
pitch-down at the normal gliding attitude. This results in the airspeed at
about 15 knots with the glider held level with near full-up elevator. The
L-23 will usually oblige with a quick flip into a spin even if no turn is
attempted - try a turn and it will spin for sure. No student observing this
has failed to appreciate that the wings should be level and the nose needs
to be well below the normal glide attitude and held there until a safe
airspeed is achieved.

The thermal entry stall/spin only requires that the pilot hold into-the-turn
rudder a second or two longer than needed while trying to reduce airspeed
still further. In most cases, this is a full cross-controlled accelerated
stall from a 45 degree bank - wheee! (I've caught some high time pilots
with this one.)

Bill Daniels

"Bill Daniels" wrote in message

The thermal entry stall/spin only requires that the pilot hold into-the-turn
rudder a second or two longer than needed while trying to reduce airspeed
still further. In most cases, this is a full cross-controlled accelerated
stall from a 45 degree bank - wheee! (I've caught some high time pilots
with this one.)

Bill Daniels

Interesting exercise. Also sounds like a good way to teach
low-G/low-AOA affects on stall speeds. I can see how it would work
well in something like a Blanik, with a huge elevator. How do
competition ships with small elevators react? I'll have to try with
my LS6, but I have the feeling that the elevator is not powerful
enough to keep the nose from falling through and causing a stall/spin.

On the other hand, in the same nose high/close to stall speed
situation, the LS6 (and any other glider, I'm sure) reacts perfectly
well to an unloaded (low-G) roll in the direction of the intended
turn, followed by an easy nose down acceleration to a safe speed
before pulling on the G necessary for the turn. Not a recommended
normal thermal entry by any means, but a way to recover from a
botched, overenthusiastic zoom-in.

The obvious key is the G (or AOA) versus airspeed relationship.
Trying to turn when the airspeed is down in the teens would show that
the pilot has a certain lack of situational awareness!

Kirk
66

"Kirk Stant" wrote in message
om...
"Bill Daniels" wrote in message

The thermal entry stall/spin only requires that the pilot hold
into-the-turn
rudder a second or two longer than needed while trying to reduce
airspeed
still further. In most cases, this is a full cross-controlled
accelerated
stall from a 45 degree bank - wheee! (I've caught some high time pilots
with this one.)

Bill Daniels

Interesting exercise. Also sounds like a good way to teach
low-G/low-AOA affects on stall speeds. I can see how it would work
well in something like a Blanik, with a huge elevator. How do
competition ships with small elevators react? I'll have to try with
my LS6, but I have the feeling that the elevator is not powerful
enough to keep the nose from falling through and causing a stall/spin.

On the other hand, in the same nose high/close to stall speed
situation, the LS6 (and any other glider, I'm sure) reacts perfectly
well to an unloaded (low-G) roll in the direction of the intended
turn, followed by an easy nose down acceleration to a safe speed
before pulling on the G necessary for the turn. Not a recommended
normal thermal entry by any means, but a way to recover from a
botched, overenthusiastic zoom-in.

The obvious key is the G (or AOA) versus airspeed relationship.
Trying to turn when the airspeed is down in the teens would show that
the pilot has a certain lack of situational awareness!

Kirk
66

A stall occurs only when the AOA exceeds about 16 degrees for most airfoils.
Low G, by itself, isn't dangerous and, in fact, reduces the stall speed
since the wing isn't loaded. The stalling AOA comes in at the transition
from low G to one G.

Most competition ships fly with the CG well aft so, even with small
elevators, they have plenty of elevator authority for some interesting
stalls. I do worry that many competition pilots get very close to a
stall/spin departure without realizing it during an aggressive thermal
entry. This is particularly dangerous when down low (I've GOT to center
this thermal or land out.) Desperately and aggressively trying to center a
small core when under the stress of a pending outlanding is a bad
combination - there have been a more than a few bad outcomes to this
situation.

Bill Daniels