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]

 

 

 

On Fri, 04 Jan 2013 15:38:44 -0500, Matt Hapgood <matt.hapgood@alumni.duke.edu> wrote:

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

From: Jarrett Johnson <hjjohnson@sasktel.net>
Reply-To: Lancair List <lml@lancaironline.net>
Date: Friday, January 4, 2013 2:01 PM
To: Lancair List <lml@lancaironline.net>
Subject: [LML] Re: stalls

--- 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.