When gliders fail in flight, but pilots manage to land

Thanks (again) Herr Leibacher!! It was indeed July 1994.

KS










On Saturday, June 23, 2018 at 5:56:07 PM UTC-4, son_of_flubber wrote:
Bruno Vassel recalls how the control stick broke off in a glider pilot's hand and how that pilot landed the aircraft safely (using rudder to turn and trim to control speed).
https://www.youtube.com/watch?v=kF0tTzvU8IM&t=411s

Another favorite scenario is 'one spoiler stuck open'... the pilot opened the other spoiler to match and landed promptly.

Spoilers frozen shut... slip to land.

What else breaks and what if anything could be done about it?

On Sat, 23 Jun 2018 14:56:05 -0700 (PDT), son_of_flubber
wrote:

Bruno Vassel recalls how the control stick broke off in a glider pilot's hand and how that pilot landed the aircraft safely (using rudder to turn and trim to control speed).
https://www.youtube.com/watch?v=kF0tTzvU8IM&t=411s

Another favorite scenario is 'one spoiler stuck open'... the pilot opened the other spoiler to match and landed promptly.

Spoilers frozen shut... slip to land.

What else breaks and what if anything could be done about it?


1. L'Hotellier links.

Had one serious incident yesterday:
ASW-20, l'Hotellier of the (inner) wing flap unlocked, causing the
wing flap to go slightly negative after two minutes of aerotow.
According to the pilot he had done a full control check after
assembling the 20.
He needed nearly full aileron to keep the glider level and land it
successfully.


The (inexperienced) pilot made the follwing mistakes:

- Didn't lock the l'Hotellier connection properly (obviously)

- Made the approach and landing with flaps 4 (positive). With the
negative inner flap one one wing this resultetd in a serious
asymmetric lift configuration.

- Pilot approached faster than usual (115 kp/h, 60 kts) with flaps 4.
Aerodynamical forces at this speed pushed the unconnected flap even
further into "negative", increasing the asymmetric lift.


The pilot obvously didn't know how his wing flaps worked - setting
them to 2 or 1 (negative) would have solved the asymmetry and only
needed an additional 7 kts higher approach speed.


2. ASW-24
Elevator trim bowden broke while thermalling and trim was set
significantly tail-heavy. Experienced pilot landed safely, but had to
push the stick forward all the time.


Cheers
Andreas

On Sunday, June 24, 2018 at 2:19:22 PM UTC-7, Andreas Maurer wrote:
On Sat, 23 Jun 2018 14:56:05 -0700 (PDT), son_of_flubber
wrote:

Bruno Vassel recalls how the control stick broke off in a glider pilot's hand and how that pilot landed the aircraft safely (using rudder to turn and trim to control speed).
https://www.youtube.com/watch?v=kF0tTzvU8IM&t=411s

Another favorite scenario is 'one spoiler stuck open'... the pilot opened the other spoiler to match and landed promptly.

Spoilers frozen shut... slip to land.

What else breaks and what if anything could be done about it?


1. L'Hotellier links.

Had one serious incident yesterday:
ASW-20, l'Hotellier of the (inner) wing flap unlocked, causing the
wing flap to go slightly negative after two minutes of aerotow.
According to the pilot he had done a full control check after
assembling the 20.
He needed nearly full aileron to keep the glider level and land it
successfully.


The (inexperienced) pilot made the follwing mistakes:

- Didn't lock the l'Hotellier connection properly (obviously)

- Made the approach and landing with flaps 4 (positive). With the
negative inner flap one one wing this resultetd in a serious
asymmetric lift configuration.

- Pilot approached faster than usual (115 kp/h, 60 kts) with flaps 4.
Aerodynamical forces at this speed pushed the unconnected flap even
further into "negative", increasing the asymmetric lift.


The pilot obvously didn't know how his wing flaps worked - setting
them to 2 or 1 (negative) would have solved the asymmetry and only
needed an additional 7 kts higher approach speed.


2. ASW-24
Elevator trim bowden broke while thermalling and trim was set
significantly tail-heavy. Experienced pilot landed safely, but had to
push the stick forward all the time.


Cheers
Andreas

Another check on controls (lacking help) is to back drive them: Move the aileron on one side and watch the stick and aileron on the other side. Move the elevator and observe the stick move. On some gliders you can pull open the spoiler paddle (once unlocked) and see the other one come up. This demonstrates continuity through the fuselage, and is an indicator that things are connected.

Not sure everyone understands how the rudder control system in most of our ships, works. Typically, a cable on each side from the rudder to the pedal with a spring at each pedal (to keep the pedal erect). If a cable breaks or becomes disconnected, the pedal on that side will be pulled forward by its spring........ends up flat on the floor! Meanwhile, the spring on the other rudder pedal will pull in uncommander rudder! Sensing this, the pilot tries to correct with opposite rudder, but that puppy is flat on the floor! Next, the pilot applies opposite aileron before the uncommanded rudder gets out of hand. This works, but the ship is now flying in a full slip!
This is exactly what happened to two pilots flying an ASH-25, a few years back and they were on the ridge! The PIC flew away from the rocks, in a full left slip and made a radio call giving his location, situation and intentions (bail out). Hearing his call, I thought for a few seconds, then asked if the rudder pedals in the other seat were working? Anxious seconds later, a much relieved voice reported that, in fact the front seat rudder pedals were working normally. They headed for the nearest airport with the front seat pilot holding enough right rudder pedal to keep the rudder near neutral.
Something to add to your bag of tricks,
JJ

Karl H. Striedieck: Attitude Problems (from No Elevator Control), Jul, 1994, pages 43-44 [Safety; Patterns and Landings; Instruction; Equipment\Hotellier Fittings]

Yes, John, that's the one! I don't know why I didn't see it in the search results last night. Excellent, must-read article by KS about what to do if....

Chip Bearden

The ASH25 incident JJ recounts brings this to mind:
In 2-seater situations where the second pilot is essentially a "ride", is there consideration of the second (if qualified) pilot taking control?
Jim

Broken rudder cable in a Puchacz. Used ailerons to sideslip it all
the way to landing and full airbrakes that reduced rudder
effectiveness by about half. Interesting approach and landing
across the field.

Loose gapseal in LS4 in spiraldive on aileron. Unable to roll out
until combination of opposite aileron, rudder and full airbrakes
slowly overcame it.

Broken rudder cable in a Puchacz. Used ailerons to sideslip it all
the way to landing and full airbrakes that reduced rudder
effectiveness by about half. Interesting approach and landing
across the field.

Loose gapseal in LS4 in spiraldive on aileron. Unable to roll out
until combination of opposite aileron, rudder and full airbrakes
slowly overcame it.

I believe there is a similar article by Richard Johnson. Remember stick problem - either no forward travel or stick limited to keeping glider in high angle of attack - put glider in turn where that stick configuration is required, buy some time to make a more thought out decision.

Mark

On 6/23/2018 3:56 PM, son_of_flubber wrote:
Bruno Vassel recalls how the control stick broke off in a glider pilot's
hand and how that pilot landed the aircraft safely (using rudder to turn
and trim to control speed).
https://www.youtube.com/watch?v=kF0tTzvU8IM&t=411s

Another favorite scenario is 'one spoiler stuck open'... the pilot opened
the other spoiler to match and landed promptly.

Spoilers frozen shut... slip to land.

What else breaks and what if anything could be done about it?

Progressive failure of a weldment inter-connecting rudder cables to pushrod
actuating rudder (Zuni S/N 3). Initial symptom was isolated (intermittent,
uncommanded) yaw-"pulses" at thermalling/low speed (weak, barely sustainable,
day). After 2nd occurrence, eventually concluded "something" wasn't right in
rudder control system; determined to precautionarily land from a pattern
sufficiently large to not require rudder. Symptom increased to intermittent
(downwind/final), low-frequency (several cycles/sec?), large amplitude (nose
motion vs. "buzz") rudder flutter. Otherwise uneventful pattern/landing.

Unable to diagnose problem at field; ultimately diagnosed at home. Removal of
weldment and subsequent eyeball/microscopic inspection led me (and George
Applebay - ship designer/builder) to conclude an imperfect weld connecting
"fishmouthed" pushrod connection arm to weldment's vertical tube left behind a
small hole/stress riser. Fracture path showed surface rust at/within hole and
bright metal along subsequent fracture path. Pushrod-connecting arm remained
(barely) attached to central mounting shaft, with pre-disassembly/post-landing
position of all rudder actuation controls essentially as-designed.

New part made/installed.

Bob W.

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