Charlie, it sounds like you had a
interesting chief pilot! I'm sure a 747 can be safely flown through an 'approach
to stall' and recovered. However, I'm not so sure 'in the pattern' is
the best place for this phase of flight? I've never flown into Miami but I'm
thinking that's probably populated [built up] area as well? [Never mind the fact
that it was done down low!]
The thing about human nature is we can justify pretty much anything to
ourselves. It's if/when we can justify it to our peers and the general
population which makes it 'ok'.
Jarrett Johnson
235/320 55%[and holding]
On Sat, 05 Jan 2013 14:54:49 -0500, Charlie Kohler
<charliekohler@yahoo.com> wrote:
I remember the day,
Way back when, our chief pilot was suspended by the FAA for doing an approach to
stall (shaker) - in a 747- in the pattern at Miami international. He was
confident it was perfectly safe.--- I was not on board.
Charlie K.
See me on the web at
From:Matt Hapgood <mehapgood@gmail.com>
To:lml@lancaironline.net
Sent: Saturday, January 5, 2013
2:33 PM
Subject: [LML] Re: stalls
Johnson,
I apologize for the lack of clarity. The data collection that I
referred to was for the purposes of simulating the aircraft, not certifying it.
I appreciate your clarification.
Matt
Matt your saying you don't think the likes of a DC-9 or an MD-80, any model
of Lear [or any jet w/ rear engines above the wings or T-Tails] hasn't been
stalled to validate that turbulent airflow doesn't impact the engine performance
or blanket the horizontal tail prior to being certified by the FAA for
production?? I would agree that the simulator manufactures don't model
flight in their simulators past the point of stall as there are too many
variables to do so accurately giving repeatable and consistent results, but that
doesn't mean that certified airframes [Jet or any other type] aren't tested for
stall and behavior while stalled.
Sites like
http://en.wikipedia.org/wiki/1963_BAC_One-Eleven_test_crash would lead me
to believe they do in fact flight test aircraft to these levels during flight
testing of new commercial aircraft. I've found other sites that talk about the
deep stall problems with and early Gloster jet as well as Canadair, 727 and
DC-9. The 727 incident caused Boeing [according to this site] to swear never to
build another T-tail aircraft. I believe 'Stick Pushers' were brought about due
to testing of Dc-9's and their resultant like for deep stalls.
Something that seems to keep getting missed in this whole discussion is the
terminology of "Stall". Maybe this is where the confusion comes from
various people who [possibly] see things similarly but are
describing them differently. There are different levels of a stall. An "Approach
to Stall" is a much different thing that an full on "Aerodynamic Stall", a "Deep
Stall" or an "Accelerated Stall".
The definition of a Stall [or Aerodynamic Stall] is " a reduction in
the lift coefficient
generated by a foil as angle of attack
increases. This occurs when the critical
angle of attack of the foil is exceeded. The critical angle of attack is
typically about 15 degrees, but it may vary significantly depending on the
fluid, foil, and Reynolds number."
[according to Wiki. ]
Another definition [Wiki again] is "stalls in fixed-wing flight are often
experienced as a sudden reduction in lift as the pilot increases angle of attack
and exceeds the critical angle of attack"
A Deep stall is generally defined as pushing the aircraft past the point of
stall and/or holding it in a stalled condition such that the horizontal tail
also becomes 'stalled'. It can be construed as causing the stalled/turbulent
wake from the wing to blank the horizontal stabilizer. Another description
is to dynamically stall the aircraft via maneuvering [think a "tail slide" type
maneuver]. It is generally described as reached/developed when the elevator is
no longer effective, either by blanking of the horizontal tail or loss of
airflow over the tail. Typically deep stalls are pitch stable with a extremely
high rate of decent and are [in the case of blanked H-tails]
un-recoverable.
Rather than re-write it, I've cut and pasted an excerpt from the FAA pilots
"Airplane Handbook" [Found here]
http://www.faa.gov/library/manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf on
the topic of approach to stall.
_____________________________________________________________________
APPROACHES TO STALLS (IMMINENT STALLS)—POWER-ON OR
POWER-OFF
An
imminent stall is one in which the airplane is approaching a stall but is not
allowed to completely stall. This stall maneuver is primarily for practice in
retaining (or regaining) full control of the airplane
immediately upon recognizing that it is almost in a stall or that a stall is
likely to occur if timely preventive action is not taken. The practice of these
stalls is of particular value in developing the pilot’s sense of feel for
executing maneuvers in which maximum airplane performance is required. These
maneuvers require flight with the airplane approaching a stall, and recovery
initiated before a stall occurs. As in all maneuvers that
involve
significant changes in altitude or direction, the pilot must
ensure that the area is clear of other air traffic before executing the
maneuver.
These stalls may be entered and performed in the attitudes and
with the same configuration of the basic full stalls or other maneuvers
described in this chapter. However, instead of allowing a complete stall,
when
the first buffeting or decay of control effectiveness is noted,
the angle of attack must be reduced immediately by releasing the back-elevator
pressure and applying whatever additional power is necessary. Since the
airplane will not be completely stalled, the pitch attitude
needs to be decreased only to a point where minimum controllable airspeed is
attained or until adequate control effectiveness is regained. The pilot must
promptly recognize the indication of a stall and take timely, positive control
action to prevent a full stall. Performance is unsatisfactory if a full stall
occurs, if an excessively low pitch attitude is attained, or if the pilot fails
to take timely action to avoid excessive airspeed, excessive loss of altitude,
or a spin.
_______________________________________________________________
Therefore when I say that I've had to demonstrate approach to stall and
recovery in the turbo-prop twin that I fly, I mean.. reduce speed to the first
sign of stall [horn and buffet in my case] and then recover. However, in doing
this maneuver everything is dynamic, at flight idle with full flaps I'm
losing several knots per second so, while I may get confirmation of the
approach to stall and initiate recover [hold the pitch angle and increase power]
the time required to react and the engines to respond, allows the aircraft to
get past the 'initial' state of the stall and reach some form of a stalled
condition [as noted by the several hundred fpm decent that occurs while I'm
pitched at +10deg deck angle]. I'm pretty sure this is typical of anyone doing
training of this sort per discussion with my check pilot. In this
airframe [C425] it's a non-event as it behaves very well in this phase of
flight.
The same applies to simulators, I was just in one [a full motion
simulator] like 1.5yrs ago and we did approach to stalls in it as well,
that isn't to say that we 'stalled the aircraft' or that I'm saying a simulator
will 'simulate' the aerodynamics of a full stall or a deep stall, simply that
the simulator can 'simulate accurately' the effects of an approach to stall such
that the pilot can effectively recognise and take appropriate action to
avoid/(recover from) the stall [in the bigger 'stuff' this is identified at
'stick shaker']. In my comment [as you've clipped below] I didn't differentiate
the 'approach to stall' as it pertains to simulators clearly, I guess I need to
proof-read my writing better LOL.
Being able to fly in these scenarios has another advantage, for those who
flying w/ TWAS systems. In our aircraft/company the procedure when a TWAS alert
is issued, the procedure is to "pitch to stick shaker", increase to max
torque, verify speed reduction to Vx and hold this pitch angle/airspeedfor
climb or until the emergency is resolved". If you don't know at what speed
that is [due to not flight testing your airframe to those speeds], how are you
going to "fly" to it? How would you even practice this maneuver w/out
knowing your speeds or having the proper alerting systems [a properly calibrated
stall warning [AOA] system, bitching Betty etc].
Fwiw
Jarrett Johnson
235/320 55% [and holding]
Off-topic technical comment. I'm no expert, but I have taken
an airplane (a twin turbo-prop) through the data collection process for stall
buffets and taken a simulator through FAA approval (high level, full motion).
The aircraft was definitely not stalled, nor does the simulator simulate a
stall.
Years ago I asked the sim experts (aero engineers) why they didn't
model the stall phase. Their short and simple explanation when something
like this: If you make a reasonably good paper airplane and throw it in
the air, you can reasonably model it's flight. Now try throwing an
unfolded sheet of paper in the air. Got any idea where it's gonna go or
what it's gonna do? That's what it would be like trying to model a
stall.
Matt
--- 4-The thought that Jets aren't tested in slow flight [and slower]
is false as well, all of these jets are fully tested before being signed off an
'released' for production. All pilots in training then fly these maneuvers while
doing type training [in simulators which duplicate the tested results]. If you
think that once you get your Airline Transport License your done w/
stall/approach to stall training for the rest of your flying career, your
mistaken.
www.innovention-tech.com
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