A Q on horizontal turns

[Ramapriya]

During a cruise, just pressing on one of the rudders should make an
aircraft turn horizontally in that direction, when no ailerons are
used. Reducing power in the opposite engine should logically accelerate
such a turn.

Makes me wonder why then was it that, in the crash at the end of 2001
just outside of NY, the A300's rear bulkhead came loose when the pilot
used the rudder to correct a yaw induced by probably a wake vortex ?
Ramapriya

[Morgans]

"Ramapriya" > wrote

> Makes me wonder why then was it that, in the crash at the end of 2001
> just outside of NY, the A300's rear bulkhead came loose when the pilot
> used the rudder to correct a yaw induced by probably a wake vortex ?
> Ramapriya
>
>
Google for that discussion, but in short, the rudder was used rapidly going
from full deflection, to other side full deflection. The plane was not
designed for that, and it failed. Part of the fault seems to lie with the
airline, for not properly training its pilots.
--
Jim in NC

[Ramapriya]

Morgans wrote:

> Google for that discussion, but in short, the rudder was used rapidly
going
> from full deflection, to other side full deflection. The plane was
not
> designed for that, and it failed. Part of the fault seems to lie
with the
> airline, for not properly training its pilots.
> --
> Jim in NC

No Jim, I actually know that report, and the statements of both the
airline and Airbus too. The surprise is in knowing that such action,
which I think is natural, isn't automatically built into in the design
of an aircraft. Why do you think that's so? Aren't such boat-turns
normal? Should be, isn't it?

Ramapriya

[Dan Luke]

"Ramapriya" wrote:
> No Jim, I actually know that report, and the statements of both the
> airline and Airbus too. The surprise is in knowing that such action,
> which I think is natural,

Rapid, opposite deflections of the rudder are not "natural,"
particularly in a jet transport aircraft.

> isn't automatically built into in the design
> of an aircraft. Why do you think that's so?

Because designers cannot allow for every conceivable misuse of the
equipment.

> Aren't such boat-turns
> normal?

Not in that kind of airplane--besides, he wasn't just making a rudder
turn, he was wagging the rudder back and forth.

> Should be, isn't it?

Not necessarily. Airplanes are designed for performance that meets a
particular mission. Airliners are not the same as aerobatic aircraft,
for instance.
--
Dan
C172RG at BFM

[tscottme]

"Morgans" > wrote in message
...
>
> "Ramapriya" > wrote
>
> > Makes me wonder why then was it that, in the crash at the end of 2001
> > just outside of NY, the A300's rear bulkhead came loose when the pilot
> > used the rudder to correct a yaw induced by probably a wake vortex ?
> > Ramapriya
> >
> >
> Google for that discussion, but in short, the rudder was used rapidly
going
> from full deflection, to other side full deflection. The plane was not
> designed for that, and it failed. Part of the fault seems to lie with the
> airline, for not properly training its pilots.
> --
> Jim in NC
>
>

And there are many people that fault Airbus for not making this "design
feature" known more widely. I remember reading in Aviation Week shortly
after the crash that Airbus didn't make much effort to notify customers that
full deflection of the rudder could cause a catstrophic accident because
they decided nobody would want to apply full-deflection as it would be
dangerous.

--

Scott

[tscottme]

"Ramapriya" > wrote in message
oups.com...

>
> No Jim, I actually know that report, and the statements of both the
> airline and Airbus too. The surprise is in knowing that such action,
> which I think is natural, isn't automatically built into in the design
> of an aircraft. Why do you think that's so? Aren't such boat-turns
> normal? Should be, isn't it?
>
> Ramapriya
>

Turns in aircraft are most often intended to be what is called
"coordinated." That is the ailerons and rudder are used in conjunction so
that there are *no* purely horizontal forces felt by the passengers. In
airline and corporate flying this is sometimes called "not making the ice
cubes clink." You try to maneuver the aircraft so that the passengers, and
their drinks, are not disturbed.

Making these boat turns would be like filling a station-wagon automobile
with children, accelerating to highway speeds, and then making an abrupt
turn of the steering wheel. The children wuld go sliding all over the car's
cabin.



--

Scott

[Stefan]

tscottme wrote:

> And there are many people that fault Airbus for not making this "design
> feature" known more widely.

Actually, they did. There was that letter which Airbus, Boeing and the
FAA (yes, all three, together, in one letter!) wrote to the operator
pointing out exactly this and asking for a change in pilot training. But
of course, "many people" in the USA welcome any rumour which could be
used against Airbus.

Stefan

[Ramapriya]

tscottme wrote:

> Making these boat turns would be like filling a station-wagon
automobile
> with children, accelerating to highway speeds, and then making an
abrupt
> turn of the steering wheel. The children wuld go sliding all over
the car's
> cabin.

Scott,
Not having been in an aircraft boat-turn before, I find your example a
wee addling. The kids would get hurled across the seats because the
station wagon is trying to turn horizontally about its axis while being
restricted in its lateral movement by the tires that are grounded. In
an aircraft, there's just thin air outside, so I'd presume it'll mildly
keep sliding sidewards too (in the opposite direction) while turning
about its axis. It might just feel like in a briskish whirligig.
Or does it? :)

Ramapriya
ayirpamar@gmail

[G.R. Patterson III]

Ramapriya wrote:
>
> In
> an aircraft, there's just thin air outside, so I'd presume it'll mildly
> keep sliding sidewards too (in the opposite direction) while turning
> about its axis. It might just feel like in a briskish whirligig.

I've never been in a briskish whirligig, so I don't know, but, when you make a
rudder turn, momentum attempts to have the contents continue in a straight line.
In some areas of a large aircraft, unsecured cargo would slide sideways in such
a turn. In a coordinated turn, the forces of momentum and gravity balance out.

As far as passengers are concerned, uncoordinated maneuvers tend to make them
nauseous. This effect is stronger the further away from the center of the wing
they sit.

George Patterson
The desire for safety stands against every great and noble enterprise.

[Dudley Henriques]

"Stefan" > wrote in message
...
> tscottme wrote:
>
>> And there are many people that fault Airbus for not making this
>> "design
>> feature" known more widely.
>
> Actually, they did. There was that letter which Airbus, Boeing and the
> FAA (yes, all three, together, in one letter!) wrote to the operator
> pointing out exactly this and asking for a change in pilot training.
> But of course, "many people" in the USA welcome any rumour which could
> be used against Airbus.
>
> Stefan

I'm not all that familiar with this accident, but if I recall correctly,
a checklist item before takeoff on the airplane was to select the yaw
damper to "ON" which would have limited the rudder deflection. This
wasn't done, and if not, would have been a direct contributor in this
accident.
I believe Airbus properly supplied the operator with a valid checklist
that included the yaw damper select. The crew missed it, or ignored
it...either way, the damper was selected "OFF" when the investigators
found the sub panel .When that rudder was deflected as they entered the
turbulence from the departing aircraft ahead of them, instead of
applying a damped rudder throw as would have been the case had the
damper been properly selected to "ON", the pilot flying the aircraft at
the time applied and was given full rudder command. This, and the
inertia forces encountered in both the initial throw and the reverse,
coupled with the turbulence, was too much for the vertical stabilizer.
Had the damper been selected properly as called for by the checklist,
this accident might not have happened.
Keep in mind, I haven't even read the report. I'm just going on what was
relayed to me by an associate friend of mine with the FAA.
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/CFI Retired
for private email; make necessary changes between ( )
dhenriques(at)(delete all this)earthlink(dot)net

[Peter Duniho]

"Ramapriya" > wrote in message
oups.com...
> Not having been in an aircraft boat-turn before, I find your example a
> wee addling. The kids would get hurled across the seats because the
> station wagon is trying to turn horizontally about its axis while being
> restricted in its lateral movement by the tires that are grounded. In
> an aircraft, there's just thin air outside, so I'd presume it'll mildly
> keep sliding sidewards too (in the opposite direction) while turning
> about its axis.

It's a little of both. It won't be as bad as the aforementioned station
wagon, because the rudder isn't capable of producing as much of a turn. In
fact, this is why it's so important to use aileron to bank the plane too for
a turn. But a turn does still happen to a lesser degree, and the passengers
would still feel the apparent force pushing them to the outside of the turn.

Pete

[Ron Garret]

In article >,
"Peter Duniho" > wrote:

> "Ramapriya" > wrote in message
> oups.com...
> > Not having been in an aircraft boat-turn before, I find your example a
> > wee addling. The kids would get hurled across the seats because the
> > station wagon is trying to turn horizontally about its axis while being
> > restricted in its lateral movement by the tires that are grounded. In
> > an aircraft, there's just thin air outside, so I'd presume it'll mildly
> > keep sliding sidewards too (in the opposite direction) while turning
> > about its axis.
>
> It's a little of both. It won't be as bad as the aforementioned station
> wagon, because the rudder isn't capable of producing as much of a turn. In
> fact, this is why it's so important to use aileron to bank the plane too for
> a turn. But a turn does still happen to a lesser degree, and the passengers
> would still feel the apparent force pushing them to the outside of the turn.

There's another thing that happens when you stomp on the rudder: while
the plane is yawing about its vertical axis, one wing is moving faster
than the other through the air and therefore generates more lift,
causing the plane to bank even without any aileron input. But the plane
yaws first and banks afterwards, so the effect is that the wing makes
this sort of circular stirring motion. It can be quite disconcerting if
you're not used to it.

BTW, Ramapriya, where do you live? Pilots are a generous lot, and you
can probably find someone to take you up so you can experience all this
firsthand.

rg

[Ramapriya]

Ron Garret wrote:

> BTW, Ramapriya, where do you live? Pilots are a generous lot, and
you
> can probably find someone to take you up so you can experience all
this
> firsthand.

I normally live and work in Dubai, United Arab Emirates. For about a
month or so more, I'll be in Khartoum (Sudan). Just yesterday, I've
lined up someone who knows the owner and pilot of a YAK-40. I'll go
check out his patience one of these days :))

I also have my eyes on a long-disused YAK-40 lying within the airport
premises. I hear the owner might pay if someone takes it, so... :))
Ramapriya

[David CL Francis]

On Thu, 6 Jan 2005 at 09:35:46 in message
>, Peter Duniho
> wrote:

>It's a little of both. It won't be as bad as the aforementioned station
>wagon, because the rudder isn't capable of producing as much of a turn. In
>fact, this is why it's so important to use aileron to bank the plane too for
>a turn. But a turn does still happen to a lesser degree, and the passengers
>would still feel the apparent force pushing them to the outside of the turn.

I have no special theory abut the sad crash - I just don't know enough
about it - but the comments about why the loading cases are 'not as high
as they should be' caused me to start writing.

I don't know how much steady yaw 'g' can be generated by an airliner. I
do know that there are smaller high powered aircraft that can fly 'knife
edge' and must therefore be capable of generating a steady one 'g' yaw
'acceleration'. I have doubts as to whether a station wagon can generate
much more than one 'g' in a turn.

But my point is this. Higher loads and angles of yaw can be generated by
control inputs that are in phase with the natural yaw frequency. A
single application of full rudder will generate a deflection in yaw
which may overshoot the final steady state yaw deflection which will
then be damped out. However if control inputs are added so as to
increase the yaw rate as the aircraft oscillates from one side to the
other then it is theoretically possible to generate very large loads
indeed. The maximum will be generated dependent on the amount of yaw
damping present and the energy inputs. An operating yaw damper does the
opposite; it operates so as to reduce the amplitude of yaw oscillations.

The same sort of thing can occur in pitch but conventional aircraft are
likely to have much better damping in pitch than yaw. The classic
phugoid oscillation in pitch is not often mentioned, the ones I am
referring to here are the short period stability oscillations.

I believe this driving up of the deflections might be described as
'pilot induced oscillations'.

I have not the data to answer the questions posed by this but the
possibility may be there. The fact that yaw dampers are often fitted to
assist the pilot (human or auto) seems to suggest that at some parts of
the flight envelope large deflections of yaw angle need to be reduced.
('Yaw dampers' may also be part of a system to produce automatic
balanced turns but that is not the effect I am alluding to.

Why can flutter be so destructive? Because at certain speeds the input
of aerodynamic forces changes in such a way as to drive the structure to
deflect beyond its limits in an oscillatory way.

Divergence means that a single structural defection will increase the
load on the structure so much that it bends enough to reinforce the
aerodynamic force and this can lead to catastrophic failure. It is
however rare in aircraft!

Peter:- believe me it was only after I had written this that I realise I
had entered quoting your post. Several posts before that made me want to
react. I am not reacting directly because of your post. I am not
following you about - honest!
--
David CL Francis

[Peter Duniho]

"David CL Francis" > wrote in message
...
> [...] I am not following you about - honest!

That's alright...I was just getting over my previous persecution complex. I
needed something new to obsess about. :)