reverse the last thing you did.

On Jan 26, 5:57*am, mart wrote:






Now the problems started. While putting the airbrakes away the flaps
slipped to negative. *Not very handy at 20 feet and relatively slow.
The glider promptly stalled.

He than did what he was thought by a test pilot." If everything goes
to ****, reverse the last thing you have done."

So contrary to what you would normally do when stalled, which is to
push the nose over , he pulled the brakes again, which in turn pulled
the flaps out again. He said that it saved his bacon. Took out the
undercarriage and hurt his back, but he walked away.




Mart


I am surprised that only one pilot responded to the misconceptions
exibited it the above post! I tried to respond but for some reason my
posts don't seem to get throught...

Anyway, the misconception is that sudden retraction of flaps will
cause a "stall". And in the case above, that a "non-stall recovery",
"recovered the glider from a stall".

Retracting flaps will DECRERASE the effective angle of attack. If the
glider was not already stalled, DECREASING the angle of attack
certainly will not stall it.

What the sudden flap retraction did however, is change the coeffecient
of lift, which resulted in an imbalance of lift, drag and weight,
which in turn resulted in an acceleration, which was partly
DOWNWARD....

The pilot simply redeployed the flaps, returning the original
coeffecient of lift, which arrested the downward acceleration.
A non-stall recovery, for a non stall problem!

The pilot could have also pulled back on the stick, which might have
restored the balance of lift, drag, and weight, and arrested the high
sink rate. This however, WOULD increase the angle of attack, and
might possibly cause an actual stall if the critical angle was
exceeded.

Cookie

On Jan 30, 8:36*am, "
wrote:

The pilot could have also pulled back on the stick, which might have
restored the balance of lift, drag, and weight, and arrested the high
sink rate. *

No way. He'd have gone in (very) hard on the tail.

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of 70 kts to do it. From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

You need to keep in mind that flaps change wing incidence, tail
incidence (relative to wing), and especially max CL. All at once.
This pilot made two mistakes (flaps not locked, too slow too high -
accident would not have happened if he hadn't had to close the
spoilers!) and a very clutch response that saved his ass.

Uncommanded flap changes in close proximity to the ground or other
aircraft are life threatening. You need procedures and control locks
that absolutely prevent this.

My $0.02.

-Evan Ludeman (15m guy)

On Jan 30, 8:35*am, T8 wrote:
On Jan 30, 8:36*am, "

wrote:
The pilot could have also pulled back on the stick, which might have
restored the balance of lift, drag, and weight, and arrested the high
sink rate. *

No way. *He'd have gone in (very) hard on the tail.

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of *70 kts to do it. *From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

You need to keep in mind that flaps change wing incidence, tail
incidence (relative to wing), and especially max CL. *All at once.
This pilot made two mistakes (flaps not locked, too slow too high -
accident would not have happened if he hadn't had to close the
spoilers!) and a very clutch response that saved his ass.

Uncommanded flap changes in close proximity to the ground or other
aircraft are life threatening. *You need procedures and control locks
that absolutely prevent this.

My $0.02.

-Evan Ludeman (15m guy)

I used to rent a C-150. The flap toggle on that airplane was spring
loaded, and if you were not careful, the switch would flip up and
start retracting the flaps after you selected max flap setting. This
happened to me on a short final sometime ago. I had just selected full
flaps, 40 degrees (I think) and had perfect pitch and power for a
touchdown on the numbers. Suddenly it seemed like I was falling out of
the sky.............so I gave more throttle, pitched down a bit more
and then decided I better do a go around. Imagine my surprise when I
noticed the flaps had already retracted!

Brad

"Brad" wrote in message
...
I used to rent a C-150. The flap toggle on that airplane was spring
loaded, and if you were not careful, the switch would flip up and
start retracting the flaps after you selected max flap setting.

Not just C-150's. Most 172's that I rent also have that same flap toggle. What
were they thinking?

Vaughn

On Sat, 30 Jan 2010 08:35:54 -0800 (PST), T8
wrote:

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of 70 kts to do it. From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

Well, I've already seen an ASW-27 land with fully negative flaps aith
a normal approach speed of about 50-55 kts. Impressive nose-up
attitude, but otherwise unproblematic.

On Jan 30, 8:09*pm, Andreas Maurer wrote:
On Sat, 30 Jan 2010 08:35:54 -0800 (PST), T8
wrote:

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of *70 kts to do it. *From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

Well, I've already seen an ASW-27 land with fully negative flaps aith
a normal approach speed of about 50-55 kts. Impressive nose-up
attitude, but otherwise unproblematic.

Sounds a little marginal to me! Glad it was unproblematic.

"70" is just my guess for a safe approach speed in negative flap, with
spoilers out, in a '20 or similar vintage 15m with larger chord
flaps. I've surely never tried this.

-Evan Ludeman / T8

On Jan 30, 11:35*am, T8 wrote:
On Jan 30, 8:36*am, "

wrote:
The pilot could have also pulled back on the stick, which might have
restored the balance of lift, drag, and weight, and arrested the high
sink rate. *

No way. *He'd have gone in (very) hard on the tail.

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of *70 kts to do it. *From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

You need to keep in mind that flaps change wing incidence, tail
incidence (relative to wing), and especially max CL. *All at once.
This pilot made two mistakes (flaps not locked, too slow too high -
accident would not have happened if he hadn't had to close the
spoilers!) and a very clutch response that saved his ass.

Uncommanded flap changes in close proximity to the ground or other
aircraft are life threatening. *You need procedures and control locks
that absolutely prevent this.

My $0.02.

-Evan Ludeman (15m guy)

Evan,

I did not mean to imply that pulling back on the stick was the
solution to the problem. Note I used the word "might". I agree with
you that at a relitively slow speed, and neg flaps, that there would
not be enough up elevator authority to completely arrest the high sink
rate. You would reduce the sink but probably not enough.

But, you picked up on the minor point of my post, not the major point
which is the fact that the original post contains the misconception
that the retraction of the flaps caused the glider to "stall", and
that a redeploying the flaps caused a "stall recovery"..........

BTW, landing tail first is not necessarily a bad thing, but landing
tail first with a high sink rate is a bad thing.

I did witness a PIK 20 make a succesful landing with it flaps stuck in
the full neg position...(no spoilers on this model). The approach
speed was relatively fast, but no super fast. The landing took up
quite a bit of runway, but really was uneventful! (this was not a
"sudden" retraction of the flaps however).


Cookie

On Jan 31, 7:23*am, "
wrote:
On Jan 30, 11:35*am, T8 wrote:



On Jan 30, 8:36*am, "

wrote:
The pilot could have also pulled back on the stick, which might have
restored the balance of lift, drag, and weight, and arrested the high
sink rate. *

No way. *He'd have gone in (very) hard on the tail.

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of *70 kts to do it. *From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

You need to keep in mind that flaps change wing incidence, tail
incidence (relative to wing), and especially max CL. *All at once.
This pilot made two mistakes (flaps not locked, too slow too high -
accident would not have happened if he hadn't had to close the
spoilers!) and a very clutch response that saved his ass.

Uncommanded flap changes in close proximity to the ground or other
aircraft are life threatening. *You need procedures and control locks
that absolutely prevent this.

My $0.02.

-Evan Ludeman (15m guy)

Evan,

I did not mean to imply that pulling back on the stick was the
solution to the problem. *Note I used the word "might". *I agree with
you that at a relitively slow speed, and neg flaps, that there would
not be enough up elevator authority to completely arrest the high sink
rate. *You would reduce the sink but probably not enough.

But, you picked up on the minor point of my post, not the major point
which is the fact that the original post contains the misconception
that the retraction of the flaps caused the glider to "stall", and
that a redeploying the flaps caused a "stall recovery"..........

BTW, landing tail first is not necessarily a bad thing, but landing
tail first with a high sink rate is a bad thing.

I did witness a PIK 20 make a succesful landing with it flaps stuck in
the full neg position...(no spoilers on this model). *The approach
speed was relatively fast, but no super fast. *The landing took up
quite a bit of runway, but really was uneventful! *(this was not a
"sudden" retraction of the flaps however).

Cookie

I agree on tail first landings -- that's my norm on grass -- and that
the LS-6 didn't stall. My point was that the -6 pilot didn't have
enough airspeed to flare in neg. flap.

Some numbers: max Cl for the 62-K131

On Jan 31, 7:23*am, "
wrote:
On Jan 30, 11:35*am, T8 wrote:



On Jan 30, 8:36*am, "

wrote:
The pilot could have also pulled back on the stick, which might have
restored the balance of lift, drag, and weight, and arrested the high
sink rate. *

No way. *He'd have gone in (very) hard on the tail.

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of *70 kts to do it. *From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

You need to keep in mind that flaps change wing incidence, tail
incidence (relative to wing), and especially max CL. *All at once.
This pilot made two mistakes (flaps not locked, too slow too high -
accident would not have happened if he hadn't had to close the
spoilers!) and a very clutch response that saved his ass.

Uncommanded flap changes in close proximity to the ground or other
aircraft are life threatening. *You need procedures and control locks
that absolutely prevent this.

My $0.02.

-Evan Ludeman (15m guy)

Evan,

I did not mean to imply that pulling back on the stick was the
solution to the problem. *Note I used the word "might". *I agree with
you that at a relitively slow speed, and neg flaps, that there would
not be enough up elevator authority to completely arrest the high sink
rate. *You would reduce the sink but probably not enough.

But, you picked up on the minor point of my post, not the major point
which is the fact that the original post contains the misconception
that the retraction of the flaps caused the glider to "stall", and
that a redeploying the flaps caused a "stall recovery"..........

BTW, landing tail first is not necessarily a bad thing, but landing
tail first with a high sink rate is a bad thing.

I did witness a PIK 20 make a succesful landing with it flaps stuck in
the full neg position...(no spoilers on this model). *The approach
speed was relatively fast, but no super fast. *The landing took up
quite a bit of runway, but really was uneventful! *(this was not a
"sudden" retraction of the flaps however).

Cookie

I agree that the LS-6 didn't stall. I like tail first landings also.

My point was that the -6 was likely slow enough that it simply
couldn't fly in negative flap and certainly couldn't flare. Looking
up some old charts and extrapolating a bit, I can guesstimate that a
reasonable Cl max with flaps down would be 1.3 - 1.4 and perhaps as
much as 0.9 with flaps negative (by extrapolation -- the chart doesn't
go there because it's not normally of interest!). That's a big
difference. Means -- roughly -- that the minimum flying speed with
flaps up is 22% higher than with flaps down. If you are somewhere in
that speed range and the flaps retract, you sink, regardless of what
you do with the stick. That's consistent with what th LS-6 pilot
reported. A stabilized approach in negative flap is obviously
different - you approach faster because you must to keep flying.

Now if I take my 22% number -- for whatever good that might be -- and
adjust a 52 kt approach speed I get 63 knots. Fair enough. That
makes sense with your observation of the PIK, fast, but not blazingly
so. 70 may be overkill.

regards,
Evan Ludeman / T8

On Jan 31, 12:14*pm, T8 wrote:
On Jan 31, 7:23*am, "





wrote:
On Jan 30, 11:35*am, T8 wrote:

On Jan 30, 8:36*am, "

wrote:
The pilot could have also pulled back on the stick, which might have
restored the balance of lift, drag, and weight, and arrested the high
sink rate. *

No way. *He'd have gone in (very) hard on the tail.

It's probably possible to land a 15m glider in negative flap, but
you'd need a final approach speed of *70 kts to do it. *From the
description of this incident, it sounds like the pilot was closer to
50 kts and certainly under 55.

You need to keep in mind that flaps change wing incidence, tail
incidence (relative to wing), and especially max CL. *All at once.
This pilot made two mistakes (flaps not locked, too slow too high -
accident would not have happened if he hadn't had to close the
spoilers!) and a very clutch response that saved his ass.

Uncommanded flap changes in close proximity to the ground or other
aircraft are life threatening. *You need procedures and control locks
that absolutely prevent this.

My $0.02.

-Evan Ludeman (15m guy)

Evan,

I did not mean to imply that pulling back on the stick was the
solution to the problem. *Note I used the word "might". *I agree with
you that at a relitively slow speed, and neg flaps, that there would
not be enough up elevator authority to completely arrest the high sink
rate. *You would reduce the sink but probably not enough.

But, you picked up on the minor point of my post, not the major point
which is the fact that the original post contains the misconception
that the retraction of the flaps caused the glider to "stall", and
that a redeploying the flaps caused a "stall recovery"..........

BTW, landing tail first is not necessarily a bad thing, but landing
tail first with a high sink rate is a bad thing.

I did witness a PIK 20 make a succesful landing with it flaps stuck in
the full neg position...(no spoilers on this model). *The approach
speed was relatively fast, but no super fast. *The landing took up
quite a bit of runway, but really was uneventful! *(this was not a
"sudden" retraction of the flaps however).

Cookie

I agree that the LS-6 didn't stall. *I like tail first landings also.

My point was that the -6 was likely slow enough that it simply
couldn't fly in negative flap and certainly couldn't flare. *Looking
up some old charts and extrapolating a bit, I can guesstimate that a
reasonable Cl max with flaps down would be 1.3 - 1.4 and perhaps as
much as 0.9 with flaps negative (by extrapolation -- the chart doesn't
go there because it's not normally of interest!). *That's a big
difference. *Means -- roughly -- that the minimum flying speed with
flaps up is 22% higher than with flaps down. *If you are somewhere in
that speed range and the flaps retract, you sink, regardless of what
you do with the stick. *That's consistent with what th LS-6 pilot
reported. *A stabilized approach in negative flap is obviously
different - you approach faster because you must to keep flying.

Now if I take my 22% number -- for whatever good that might be -- and
adjust a 52 kt approach speed I get 63 knots. *Fair enough. *That
makes sense with your observation of the PIK, fast, but not blazingly
so. *70 may be overkill.

regards,
Evan Ludeman / T8- Hide quoted text -

- Show quoted text -


OK.....I'm with you now. Back to the original post and original
problem......it's like the guy who goes to the doctor and says, "Doc
it hurts when I do this." So the doc says, "Don't do that!"

"My LS-6 crashes when I retract the flaps at low
altitude"......."Don't retract the flaps at low altitude!"


Cookie