Hypothetical Scenario #2 - Urgent Action required

This is a voluntary pop quiz.

You're circling in a 30 degree left bank at 3000 AGL.

You hear a sudden change in the relative wind. Both rudder pedals go to the floor. The yaw string is not straight.

Sub-scenarios:

2A The yaw string points to the right pedal (adverse yaw to the left)

2B The yaw string points to the left pedal (adverse yaw to the right)

What do you do next? What just happened?

To derive the full benefit of this exercise, you might respond to this thread with your answer before looking at any of the other replies.

My hypothetical solution is found as a comment below.

You hear a sudden change in the relative wind. Both rudder pedals go to the floor. The yaw string is not straight.

This may not be right, but fair is fair and so I will stick out my neck. If it happened in the air, I would have to do something NOW without consulting any experts.

Explanation the adverse yaw:
A rudder cable breaks and my foot pressure pushes the pedals to the floor. The cable that I need to restore the rudder to neutral is broken. The rudder centering spring is not strong enough to neutralize the rudder and wind keeps the rudder "locked over".

Sub-scenarios:

2A The yaw string points to the right pedal (adverse yaw to the left)

There is an immediate danger of spinning and I have no rudder to recover from spin. Immediately drop the nose to avoid spin. Try right aileron to level wings. If that does not work, prepare to bailout. Let go of the stick, open the spoilers, and see whether the glider stabilizes itself. If glider enters spin or spiral dive, immediately bail out.

2B The yaw string points to the left pedal (adverse yaw to the right)

My lucky day! Glider has entered a turning slip and it is losing altitude fast. Drop nose to avoid stall. Level wings with right aileron to reduce rate of descent. Be very careful to not bank to the right.

Evaluate my ability to fly more or less straight and turn left without rudder control. Can I get where I need to be without turning right? (A right turn with full right rudder would dangerously skid and possibly spin.)

Consider the possibility of a "slip to land" LEFT hand pattern. It might be possible to fly in slight leftward turning arcs if it is not possible to fly absolutely straight.

Decide whether to attempt a landing or bail out.

If bailing out, consider where the glider might land on it's own and if possible keep it away from human settlements. If flying over a densely populated area, consider piloting and ditching the glider where it won't hurt anyone (except me the pilot)... possibly in a big lake? Or into the trees? Open spoilers and try to put the glider into a benign spiral.

If trying to land... fly a "slip to land" pattern. It might be better to land off-airport where there are less things to run into on the ground. If there is a crosswind, choose a runway where it is a left crosswind (since the left wing is dropped). I'm going to touchdown with adverse yaw and probably ground loop. If possible adjust pattern to avoid obstacles that might be hit by a ground loop. At touch down apply full airbrake, full wheel brake and full forward stick in order to push nose into ground and thereby minimize the energy of a highly probable ground loop. This is safer and it is easier to repair noses than wings and broken tail booms.

So - I will bite.

If both pedals go to the floor you have a disconnected rudder - probably
due to a snapped rudder cable OR a failed tensioner.

In either case you have to use secondary aileron effects to obtain yaw
control - with the initial attitude (In a left bank of 30 degrees),
speed and relative degree of adverse yaw determining how successful you
will be.

Scenarios then:
2A Yaw to Left, string to the right - The rudder disconnects and
centres freely, but you were holding the stick to the left (pro-turn) -
adverse yaw on the upward wing caused a yaw to the right. The rudder may
have locked over setting up a high descent rate slip. The yaw will tend
to cause the right wing to drop as it slows.
2.A.1 First lower the nose to avert possible spin entry.
2.A.2 the dropping outer wing should be allowed to continue till level -
then attempt to stabilise with small aileron movements.
2.A.3 if the yaw string returns to centre then the rudder is free and
the use of adverse yaw _ moderate aileron (Secondary and primary effect
of ailerons in unison) technique to head for a safe landing area.

2.B If the string is pointing to the left pedal you have a skid into the
turn.If left unchecked this will result in a spiral dive as the wings
autorotate and the nose drops. Correction would be to:
2.B.1 Momentarily reverse the ailerons to stop the skid (big aileron
deflection without rudder to balance generally results in yaw first then
roll.)
2.B.2 Correct attitude excursion with elevator to maintain safe speed.
2.B.3 Centralise aileron and use small deflections to level the wings.
2.B.4 Continue to use the "early open class" technique of big opposite
aileron to start a yaw, then moderate pro-turn aileron to turn.
2.B.5 if you get it wrong the crossed control aileron reversal can cause
a spin entry...

In both cases, turns have to be wide and gentle and made with enough
speed for safety. If the string stays deflected then you have a locked
over rudder and have little choice about directing the side slip, you
can make it a forward slip and steer to some degree, but landing choices
are limited by the high descent rate. If not facing a suitable landing
area in the limited range available, consider baling out.


Debate?

On 2014/02/08 9:05 PM, OneTango wrote:
This is a voluntary pop quiz.

You're circling in a 30 degree left bank at 3000 AGL.

You hear a sudden change in the relative wind. Both rudder pedals go to the floor. The yaw string is not straight.

Sub-scenarios:

2A The yaw string points to the right pedal (adverse yaw to the left)

2B The yaw string points to the left pedal (adverse yaw to the right)

What do you do next? What just happened?

To derive the full benefit of this exercise, you might respond to this thread with your answer before looking at any of the other replies.

My hypothetical solution is found as a comment below.


--
Bruce Greeff
T59D #1771

On Sat, 08 Feb 2014 11:05:21 -0800, OneTango wrote:

This is a voluntary pop quiz.

You're circling in a 30 degree left bank at 3000 AGL.

You hear a sudden change in the relative wind. Both rudder pedals go to
the floor. The yaw string is not straight.

One of the rudder cables has broken.

Sub-scenarios:

2A The yaw string points to the right pedal (adverse yaw to the left)

The left cable broke, giving full right rudder. With the stick centred,
the glider should skid right, causing the left tip to rise and, if
uncorrected, the glider should eventually start a skidding right turn. It
may be possible to fly straight with judicious use of left aileron. If
straight flight is possible and a suitable field is in gliding range,
than by thinking well ahead and using the ailerons carefully, it should
be possible to fly a wide pattern and land in the field. If straight
flight is impossible, which may be the case if the glider has a powerful
rudder and you didn't loose more than 2-300 ft finding out, jump out.

2B The yaw string points to the left pedal (adverse yaw to the right)

The right cable broke, applying full left rudder. It may be possible to
straighten out with stick centred or a small amount of right aileron - be
careful or adverse yaw may merely tighten the turn. If the turn shows
signs of tightening, jump out before height loss becomes significant or
speed and G forces build up.

------

If my right foot comes off the pedal in an aircraft with a raising panel,
e.g. an ASK21, I won't get it back on the pedal. In consequence I have
practised rudderless turns, with an instructor, in an ASK-21 and am
confident I can line up for an into-wind landing in a glider with similar
rudder power and stability. As a consequence I will not fly an ASK-21
solo.

I have no such problems in my Libelle, the club's G.103, Juniors or
Puchacz. I think there's a reasonable chance of flying straight with full
rudder in the Libelle, Junior, G103 or ASK-21 but not in the Puchacz
unless its huge rudder would tend to blow straight.

AFAIK none of the gliders I usually fly and have listed above have
springs that would hold the rudder hard over if the cable broke, so
another approach would be to hold your feet clear of the pedals
(difficult in some gliders, plant your heels on the pedal pivots or slide
the pedals right forward. If this works, then you can fly wide,
rudderless turns provided you didn't spin the glider in the mean time.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Sat, 08 Feb 2014 11:44:09 -0800, OneTango wrote:

You hear a sudden change in the relative wind. Both rudder pedals go
to the floor. The yaw string is not straight.

This may not be right, but fair is fair and so I will stick out my neck.
If it happened in the air, I would have to do something NOW without
consulting any experts.

With all due respect, I think you've got the rudder direction vs yaw
string reversed. In a skid the end of the yaw string is in the same side
of the glider as the TE of the rudder and has got there in this scenario
because the opposite rudder cable has broken.

Left cable breaking gives right rudder. The glider skids to the left
while yawing right and causing the string to point right.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Hmm, Adverse Yaw is caused by differential drag during aileron usage. Un-commanded yaw would be the correct term here.

Mike

I think you should carry a pistol and shoot yourself. I know that's what I feel like doing when I see this kind of thread.

Boggs

On 2/8/2014 9:38 PM, Waveguru wrote:
I think you should carry a pistol and shoot yourself. I know that's what I
feel like doing when I see this kind of thread.

Boggs


Ha ha ha!

Gary, Gary, Gary...for the good of soaring, please don't follow your own
advice as I imagine most U.S. soaring pilots would hate to lose a commercial
operator in this manner before his time.

Bob - had a rudder control failing/fluttering in flight once - W.

Go fast. Less adverse yaw at higher airspeed.

Check cell phone, if a good signal, call insurance agent and add hull coverage with minimum deductible.

bumper