reverse the last thing you did.

On Jan 27, 2:37*am, mart wrote:
Hi All,

Thanks for most responses. I have learned a few things.

About the flaps always being locked, the flap lever moves in a long
slot with on one side the hooks to lock them. They only work in one
direction, to prevent them going forward. That is why the can move out
of lock,backwards, when moving the airbrakes. There is no spring that
pushes them back into the side with the hooks.

I know that this is used by pilots when flying faster then 150km/u or
80 knots with is the point of moving from 0 to -5 flap. *Flying a
90knots you might want to use -1 flap to get best performance. Letting
the flaps float makes that happen.

Coming Saturday I will see if I can do a pratice run doing exactly
what happened , only with a bit of height.

Should have flown today..10k base with 8knot climbs. Work got in the
way.

Cheers,

Mart

In any case, select at least +2 flap before landing;
IIRC this setting will not be pushed further back
when deploying spoilers.
Check it in the cockpit !

Hope this helps,
Best Regards, Dave "YO electric"

mart wrote:
Snip...

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.

You've probably already gleaned 'the obvious' lessons from this
incident, but - hoping to not be beating a dead horse for others who may
not yet have - here's my take. (A 'take' wholly ignorant of how the
LS-6's flap/airbrake system is *supposed* to work, incidentally...but a
take with 2k hours on 3-different flaps-only gliders, meaning each had
differing 'monkey motion' mechanical/hydraulic systems powering the
flaps, & only one ship of which had reflexing flaps...)

In a nutshell, never assume you know everything about how a system - any
system - is supposed to work without spending 'considerable time'
physically examining its realities. Of course, reading about it is good
too...but not wholly sufficient.

Never carry a package by the string...by which I'm suggesting all
mechanical locks should be viewed with a jaundiced eye, whether a gear
downlock, flap detent, or whatever. Locks wear. Some aren't even locks,
but rather 'suspenders' to another 'belt' somewhere. (My current ship's
'apparent' gear downlock falls into that category, according to the
designer.) Don't court failure...but be prepared for it. Use
'suspenders' where you can.
- - - -


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

Excellent advice...if a person has the time/wits to apply it.
- - - -


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.

Even in the absence of being able to deploy spoilers (and - he hoped -
flaps again prior to contacting the ground, i.e. your adviser), my
working conclusion is radically changing fuselage pitch angle (via
radical stick movements) near the ground is generally A Really Bad Thing
To Do. Even if a thoughtful person gets away with it without pranging
something, s/he'll come away with a deeper understanding of what happens
in the short term when one reduces wing angle of attack. Stated another
way, doing this near the ground is a 'good' way to learn that stick
*directly* controls angle of attack, and only indirectly, speed. Guess
which one changes first when you put stick forward close to the deck?

A stall at 20-feet agl is basically unrecoverable via stick input *only*
for the gliders we fly. The only salvation *might* be changing wing
angle of attack via camber change (if an option). In the absence of
complicating flaps, closing spoilers is advisable, too, natch.

Your adviser 'got away with' what would appear to be a rare-enough
situation, to be sure...

Had he not known of the 'reverse what you last did' advice, and instead
attempted to recover via forward stick, my money woulda been placed on
him whacking the ground at a steeper deck angle, harder.

And with the advantage of time and hindsight, had he simply pulled on
flaps (rather than hoping they came back with spoiler activation), it's
*possible* his arrival might have been less abrupt. As always, the devil
is in the details. Only thoughtfully checking your ship can allow you to
most sensibly decide for yourself which approach would have been 'ideal'
in your adviser's situation.
- - - -


I thought I should share it with you just in
case.

cheers,

Mart

VH-NII

Thanks for sharing!!!

Regards,
Bob W.

Bob,

In the spirit of getting to know how things work, could you please
elaborate on "Some aren't even locks, but rather 'suspenders' to
another 'belt' somewhere. (My current ship's 'apparent' gear downlock
falls into that category, according to the designer.)"

Thanks!

-John

On Jan 26, 12:29 pm, Bob Whelan wrote:
In a nutshell, never assume you know everything about how a system - any
system - is supposed to work without spending 'considerable time'
physically examining its realities. Of course, reading about it is good
too...but not wholly sufficient.

Never carry a package by the string...by which I'm suggesting all
mechanical locks should be viewed with a jaundiced eye, whether a gear
downlock, flap detent, or whatever. Locks wear. Some aren't even locks,
but rather 'suspenders' to another 'belt' somewhere. (My current ship's
'apparent' gear downlock falls into that category, according to the
designer.) Don't court failure...but be prepared for it. Use
'suspenders' where you can.

Mart et al:
Having probably 800 hours in LS-6, I never had the flaps jump toward
negative when they were positive.
This will however happen in a flapped Schempp glider if you have
allowed the flap selector track to wear and not replaced it. It does
not happen if the track is as new. This happened to me on short final
in a N3. Don't panic, fly the glider, everything is fine. Replace the
track.
The best possibility I can think of for the LS-6 is that something
(certainly not winter clothing at Narromine, this time of year) was
pushing outward on the flap handle to prevent it from latching into
the ratchet track. Did the pilot in the story keep a water bottle or
any other supplies on the left side of the cockpit? Was he overweight
or overdressed? If so, that is likely the "POS" that some would,
having no experience in LS flapped ships, blame the glider for.
The one place I found the airbrake/flap interconnect in LS- 6 (LS-3
works the same) to be a problem was in wave. You can not use much
airbrake to prevent yourself from climbing above 17,999' or you'll go
over flap operating speed in a hurry. It becomes a legal problem,
which is usually preferred to a mechanical problem.
Jim

The best possibility I can think of for the LS-6 is that something
(certainly not winter clothing at Narromine, this time of year) was
pushing outward on the flap handle to prevent it from latching into
the ratchet track.

I once experienced strange behavior during take off in a glider I had a few
hundred hours in. The trim lever was caught and moved to its back stop by
the band of my wrist watch. I felt something tear on my wrist, a little
later during take off I realized that the trim was completely wrong, but it
took me some time to understand what really happened ...

Michael

jcarlyle wrote:
Bob,

In the spirit of getting to know how things work, could you please
elaborate on "Some aren't even locks, but rather 'suspenders' to
another 'belt' somewhere. (My current ship's 'apparent' gear downlock
falls into that category, according to the designer.)"

Thanks!

-John


I was referring to my Zuni I's (S/N 3) gear downlock system.

For years I believed the primary downlock was 'an LS-like' gas strut in
the system, (probably) backed up by the over-centering action of the
wheel-support structure steel tubing. (It's a *strong* strut.)

Eventually, if I've understood George Applebay (the designer) correctly,
I was informed I had things backward in the sense the gas strut was
intended primarily to help raise the gear, though residual pressure in
up/down positions *does* assist in keeping the geometry unchanging.
There *is* a mechanical uplock, while the downlock was intended to be
the gear geometry in conjunction with braking action.

Because it does me good to believe my primary downlock is still the gas
strut, I treat the gear system as if it is.

Regards,
Bob W.

I understand completely, now - thank you, Bob!

-John

Bob Whelan wrote:
I was referring to my Zuni I's (S/N 3) gear downlock system.

For years I believed the primary downlock was 'an LS-like' gas strut in
the system, (probably) backed up by the over-centering action of the
wheel-support structure steel tubing. (It's a *strong* strut.)

Eventually, if I've understood George Applebay (the designer) correctly,
I was informed I had things backward in the sense the gas strut was
intended primarily to help raise the gear, though residual pressure in
up/down positions *does* assist in keeping the geometry unchanging.
There *is* a mechanical uplock, while the downlock was intended to be
the gear geometry in conjunction with braking action.

Because it does me good to believe my primary downlock is still the gas
strut, I treat the gear system as if it is.

mart wrote:
I had an interesting talk in Narromine last week with a local
instructor about my LS6. I bought it because I thought it to have few
vices.

He knew one.One that almost killed him.

Coming back after a racing task he selected +10 flaps, plenty enough
to land with, especially when it's a bit windy.
On final he pulled full airbrakes after gong through some lift on
base. This causes the flaps to come along, out +10 towards Landing
flap. This happens automatically. It only doesn't lock automatically
in that case. When about 20 feet of the deck he put half his airbrakes
away for a smooth landing.

So far, that is what I do as well.

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.
The glider did not stall, because the stall attitude with negative flaps
is _very_ nose high; instead, it sank because the lift was reduced when
the flaps went to negative. Had he applied back stick, he would have
decreased the sink rate and, perhaps, hit the ground more slowly.
"Perhaps", because the nose high attitude would cause the tail to hit
first, and that _might_ cause the glider to hit hard on the main gear.
If he'd been 5 feet off the ground instead of 20 feet, that would have
worked fine, especially if he closed the spoilers as a pilot usually
does when the sink rate increases.

Putting the nose forward, then back, might have worked. Hard to say with
out knowing and running the numbers, or trying it!

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

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)