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[70.61.86.226]) by mx.google.com with ESMTPS id q4sm51963458anp.18.2013.01.05.08.29.51 (version=TLSv1/SSLv3 cipher=OTHER); Sat, 05 Jan 2013 08:29:52 -0800 (PST) References: Mime-Version: 1.0 (1.0) In-Reply-To: Content-Type: multipart/alternative; boundary=Apple-Mail-2EE1EFE0-79EE-4994-B2BD-44115374DC15 Content-Transfer-Encoding: 7bit X-Original-Message-Id: <0C480C27-8BE8-40D8-B30B-4435B6046856@gmail.com> X-Original-Cc: "hjjohnson@sasktel.net" X-Mailer: iPad Mail (10A8426) From: Matt Hapgood Subject: Re: [LML] Re: stalls X-Original-Date: Sat, 5 Jan 2013 11:29:51 -0500 X-Original-To: Lancair Mailing List --Apple-Mail-2EE1EFE0-79EE-4994-B2BD-44115374DC15 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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 appr= eciate your clarification. =20 Matt On Jan 5, 2013, at 11:19 AM, "Jarrett Johnson" wrote= : > Matt your saying you don't think the likes of a DC-9 or an MD-80, any mode= l of Lear [or any jet w/ rear engines above the wings or T-Tails] hasn't bee= n stalled to validate that turbulent airflow doesn't impact the engine perfo= rmance or blanket the horizontal tail prior to being certified by the FAA fo= r production?? I would agree that the simulator manufactures don't model fl= ight in their simulators past the point of stall as there are too many varia= bles to do so accurately giving repeatable and consistent results, but that d= oesn't mean that certified airframes [Jet or any other type] aren't tested f= or stall and behavior while stalled. > =20 > Sites like http://en.wikipedia.org/wiki/1963_BAC_One-Eleven_test_crash wou= ld lead me to believe they do in fact flight test aircraft to these levels d= uring 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 Ca= nadair, 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 de= ep stalls. > =20 > Something that seems to keep getting missed in this whole discussion is th= e terminology of "Stall". Maybe this is where the confusion comes from vario= us people who [possibly] see things similarly but are describing them differ= ently. There are different levels of a stall. An "Approach to Stall" is a mu= ch different thing that an full on "Aerodynamic Stall", a "Deep Stall" or an= "Accelerated Stall". > =20 > The definition of a Stall [or Aerodynamic Stall] is " a reduction in the l= ift coefficient generated by a foil as angle of attack increases. This occur= s when the critical angle of attack of the foil is exceeded. The critical an= gle of attack is typically about 15 degrees, but it may vary significantly d= epending on the fluid, foil, and Reynolds number." [according to Wiki. ] > =20 > Another definition [Wiki again] is "stalls in fixed-wing flight are often e= xperienced as a sudden reduction in lift as the pilot increases angle of att= ack and exceeds the critical angle of attack" > =20 > A Deep stall is generally defined as pushing the aircraft past the point o= f stall and/or holding it in a stalled condition such that the horizontal ta= il also becomes 'stalled'. It can be construed as causing the stalled/turbul= ent wake from the wing to blank the horizontal stabilizer. Another descripti= on is to dynamically stall the aircraft via maneuvering [think a "tail slide= " type maneuver]. It is generally described as reached/developed when the el= evator is no longer effective, either by blanking of the horizontal tail or l= oss of airflow over the tail. Typically deep stalls are pitch stable with a e= xtremely high rate of decent and are [in the case of blanked H-tails] un-rec= overable. > =20 > Rather than re-write it, I've cut and pasted an excerpt from the FAA pilot= s "Airplane Handbook" [Found here] http://www.faa.gov/library/manuals/aircr= aft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf on the topic of approach t= o stall. > =20 > _____________________________________________________________________ > =20 > APPROACHES TO STALLS (IMMINENT STALLS)=E2=80=94POWER-ON OR POWER-OFF > An imminent stall is one in which the airplane is approaching a stall but i= s not allowed to completely stall. This stall maneuver is primarily for prac= tice in retaining (or regaining) full control of the airplane immediately up= on recognizing that it is almost in a stall or that a stall is likely to occ= ur if timely preventive action is not taken. The practice of these stalls is= of particular value in developing the pilot=E2=80=99s sense of feel for exe= cuting maneuvers in which maximum airplane performance is required. These ma= neuvers require flight with the airplane approaching a stall, and recovery i= nitiated before a stall occurs. As in all maneuvers that involve > significant changes in altitude or direction, the pilot must ensure that t= he area is clear of other air traffic before executing the maneuver. > =EF=BB=BF > These stalls may be entered and performed in the attitudes and with the sa= me configuration of the basic full stalls or other maneuvers described in th= is chapter. However, instead of allowing a complete stall, when > the first buffeting or decay of control effectiveness is noted, the angle o= f 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 de= creased only to a point where minimum controllable airspeed is attained or u= ntil adequate control effectiveness is regained. The pilot must promptly rec= ognize 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 t= ake timely action to avoid excessive airspeed, excessive loss of altitude, o= r a spin. > =EF=BB=BF > =EF=BB=BF_______________________________________________________________ > =20 > Therefore when I say that I've had to demonstrate approach to stall and re= covery 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 do= ing this maneuver everything is dynamic, at flight idle with full flaps I'm l= osing several knots per second so, while I may get confirmation of the appro= ach to stall and initiate recover [hold the pitch angle and increase power] t= he 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 c= ondition [as noted by the several hundred fpm decent that occurs while I'm p= itched at +10deg deck angle]. I'm pretty sure this is typical of anyone doin= g 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. > =20 > 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 'sim= ulate' the aerodynamics of a full stall or a deep stall, simply that the sim= ulator can 'simulate accurately' the effects of an approach to stall such th= at 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 th= e 'approach to stall' as it pertains to simulators clearly, I guess I need t= o proof-read my writing better LOL. > =20 > Being able to fly in these scenarios has another advantage, for those who f= lying w/ TWAS systems. In our aircraft/company the procedure when a TWAS ale= rt is issued, the procedure is to "pitch to stick shaker", increase to max t= orque, verify speed reduction to Vx and hold this pitch angle/airspeedfor cl= imb or until the emergency is resolved". If you don't know at what speed th= at 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 know= ing your speeds or having the proper alerting systems [a properly calibrated= stall warning [AOA] system, bitching Betty etc]. > =20 > Fwiw > =20 > Jarrett Johnson > 235/320 55% [and holding] > =20 > =20 > =20 > On Fri, 04 Jan 2013 15:38:44 -0500, Matt Hapgood 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 airc= raft was definitely not stalled, nor does the simulator simulate a stall. =20= >=20 > Years ago I asked the sim experts (aero engineers) why they didn't model t= he 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 pa= per in the air. Got any idea where it's gonna go or what it's gonna do? Th= at's what it would be like trying to model a stall. >=20 > Matt >=20 > From: Jarrett Johnson > Reply-To: Lancair List > Date: Friday, January 4, 2013 2:01 PM > To: Lancair List > Subject: [LML] Re: stalls >=20 > --- 4-The thought that Jets aren't tested in slow flight [and slower] is f= alse 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 wh= ile doing type training [in simulators which duplicate the tested results]. I= f you think that once you get your Airline Transport License your done w/ st= all/approach to stall training for the rest of your flying career, your mist= aken. > =20 >=20 > =20 >=20 --Apple-Mail-2EE1EFE0-79EE-4994-B2BD-44115374DC15 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Johnson,

I ap= ologize for the lack of clarity.  The data collection that I referred t= o was for the purposes of simulating the aircraft, not certifying it.  = I appreciate your clarification.  

Matt

On J= an 5, 2013, at 11:19 AM, "Jarrett Johnson" <hjjohnson@sasktel.net> wrote:

Matt your saying y= ou don't think the likes of a DC-9 or an MD-80, any model of Lear [or any jet w/ rear engines a= bove 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 t= o 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 a= nd consistent results, but that doesn't mean that certified airframes [Jet or a= ny other type] aren't tested for stall and behavior while stalled.

 

Sites like http://en.wikipedia.org/wiki/1963_BAC_One-Eleven_test_crash&nb= sp;would lead me to believe they do in fact flight test aircraft to these levels duri= ng 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 swe= ar never to build another T-tail aircraft. I believe 'Stick Pushers' were broug= ht 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 t= he 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 "Appr= oach 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 at= tack and exceeds the critical angle of attack"

 

A Deep stall is generally defined as pushing the aircraft past the point o= f 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 descript= ion is to dynamically stall the aircraft via maneuvering [think a "tail slide" t= ype maneuver]. It is generally described as reached/developed when the elevator i= s no longer effective, either by blanking of the horizontal tail or loss o= f airflow over the tail. Typically deep stalls are pitch stable with a extreme= ly 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 pilo= ts "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 (IMMIN= ENT STALLS)=E2=80=94POWER-ON OR POWER-OFF

An imminent stall is one in which the airplan= e is approaching a stall but is not allowed to completely stall. This stall maneuv= er 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=E2=80=99s sense of feel for executing maneuvers in which maximum airpl= ane 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 mu= st ensure that the area is clear of other air traffic before executing the maneuver.

=EF=BB=BF

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 n= oted, the angle of attack must be reduced immediately by releasing the back-elevat= or pressure and applying whatever additional power is necessary. Since the

airplane will not be completely stalled, the pitch attitud= e needs to be decreased only to a point where minimum controllable airspeed is attai= ned 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, i= f 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.

=EF=BB=BF

=EF=BB=BF____________________________= ___________________________________

 

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 fir= st sign of stall [horn and buffet in my case] and then recover. However, in doi= ng 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 po= wer] the time required to react and the engines to respond, allows the aircraft t= o 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 doi= ng 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 o= f 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 simula= tor will 'simulate' the aerodynamics of a full stall or a deep stall, simply tha= t the simulator can 'simulate accurately' the effects of an approach to stall s= uch that the pilot can effectively recognise and take appropriate action to avoid/(recover from) the stall [in the bigger 'stuff' this is identifie= d at 'stick shaker']. In my comment [as you've clipped below] I didn't differenti= ate 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 al= ert is issued, the procedure is to "pitch to stick shaker", increase to max= torque, verify speed reduction to Vx and hold this pitch angle/airspeed= for climb or until the emergency is resolved".  If you don't know at what s= peed that is [due to not flight testing your airframe to those speeds], how are y= ou 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 calibr= ated 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 ta= ken an airplane (a twin turbo-prop) through the data collection process for stal= l buffets and taken a simulator through FAA approval (high level, full motion)= .=20  The aircraft was definitely not stalled, nor does the simulator simula= te a stall.  

Years ago I asked the sim experts (aero engineers) why they did= n't model the stall phase.  Their short and simple explanation when somethi= ng like this:  If you make a reasonably good paper airplane and throw it i= n 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 o= r 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@lancairo= nline.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 w= hile doing type training [in simulators which duplicate the tested results]. If y= ou think that once you get your Airline Transport License your done w/ stall/approach to stall training for the rest of your flying career, yo= ur mistaken.

 


 


= --Apple-Mail-2EE1EFE0-79EE-4994-B2BD-44115374DC15--