High Altitude Stalls – how well do you understand them?

Very interesting. Thanks for sharing. I am not yet at the point in my flying that takes me to the flight levels, it was a very interesting read and explanation.
 
I love it. It is alarming that we have been teaching stalls the way we have in jet aircraft. Only in the last couple of years has the mentality of no loss of altitude changed. It is downright scary to see how an aircraft behaves at 410 during a stall.
 
There was an amazing write up the UK did on a citation that stalled and spun from FL430. This was brought up in the "Don't spin a Citation" thread here:

http://forums.jetcareers.com/threads/dont-spin-a-citation.212334/#post-2386023

Link to the NTSB report:

http://www.aaib.gov.uk/publications/bulletins/january_2015/cessna_525a_citation_cj2___n380cr_.cfm


And the AIB's official write up, with some good content on high altitude stalls.

http://www.aaib.gov.uk/cms_resources.cfm?file=/Cessna 525A Citation CJ2 N380CR 01-15.pdf
 
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I thought I understood them. But apparently, I don't. Or didn't until now. I'll have to read this a few times and let it sink in. Thanks.
 
Well written article overall.

To be clear, they were in "alternate law," where the ailerons are now being directly controlled. Load factor change remains commanding the pitch.
It is incorrect that there are no stall protection features that remain when degraded to alternate law- you now have high and low speed "stabilities" where it will insert a slight pitch up for high speed protection and pitch down for low speed.

I've had it in alternate and direct law in the 20's. It is quite twitchy!

Also, don't forget that pitching to 17 degrees nose up at FL350 is never a good idea on any transport jet.

Very correct in regards to the sim modelling the stall- only the approach to stall is required to be modeled. We're actually negotiating with the FAA on the new requirements on modelling full stall in the sims.
 
I am not sure you have those "stabilities". Where did you get that information? I appreciate the feedback, and will correct that if accurate. For reference, my friend, Clive, who "chopped" this article was chief aerodynamicist for Concorde as well as chief UK engineer on the A330. I would think he would have caught an error like that, but I will make some inquiries just the same. The French chief engineer on the A330 is also an acquaintance of mine.

As for the 17 degrees, true, but I don't think it is as salient as you might expect, particularly when the FD is pitching upwards. I think the HF issues in my article on Salient Symbols and the HUD are applicable to this issue.
 
I dunno but it seems to me like this kind of stuff should be day 1 stuff when going to ground school on a swept wing jet.
 
seagull said:
I am not sure you have those "stabilities". Where did you get that information? I appreciate the feedback, and will correct that if accurate. For reference, my friend, Clive, who "chopped" this article was chief aerodynamicist for Concorde as well as chief UK engineer on the A330. I would think he would have caught an error like that, but I will make some inquiries just the same. The French chief engineer on the A330 is also an acquaintance of mine.
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Most of the time you will have these high and low speed stability protections in alternate law. There are certain flight control failures (Can't remeber which specifically) where you can lose these stabilities.
 
seagull said:
My latest article on high altitude stalls.
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Seagull

I have no idea who you are, and would like to continue this offline if you like

First, a question. How many high altitude stalls have you done and in what type of airplanes? As an experimental test pilot and FTE, I have done literally 100s (probably closer to thousands) of them in 737, 757, 777, 747-4, G-V, citations, and even king airs. And I will throw in a MS in Aero to back up the theoretical side. I say this as a basis of what I am going to say next, so you know it isnt some high school troll

First of all, your article is fine, but incomplete. I didnt read past the AF447 part, because it is not really relevant to high altitude stalls, as there were so many other factors in that crash. The second most important part to talk about in high altitude stalls, after the stall ID, is that the lack of Ps is going to highly influence the recovery. Most modern jets are going to require 4000-5000 feet to recover, and that is with no startle factor and near perfect recovery. I could continue, but I am not really at a place to write a novel here. And as a small, but regularly misstated point, lift does not increase with AOA, Lift Coefficient does. No true areo weeenie would ever use the word lift max, it is Cl max.

@Derg will give you my private email if you like
 
Good discussion. Would be nice to keep here in the thread, rather than back-channel, if at all possible. @Jimflyfast

Been a nearly a decade since I've flown swept wing at high altitudes, and that was fighter-type, but high altitude aerodynamics was extensively covered for us since there were flight regimes we may find ourselves in just from operational needs, whether induced or accidently encountered, where stall/departure was possible. Knowing the clues and signs, as well as what to do following, could very well be the difference between recovery or a nylon letdown for us.

The number of people I've encountered over the years who are flying swept wing jets, yet without a good grasp on the aerodynamics of the same, has been surprising.
 
PeanuckleCRJ said:
Very correct in regards to the sim modelling the stall- only the approach to stall is required to be modeled. We're actually negotiating with the FAA on the new requirements on modelling full stall in the sims.
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The issue is that there may not be enough actual data to verify the the aero model in those regimes.

We had a case in the Air Force where some of us believed we were teaching the wrong spin recovery procedures in the sim because the sim had an unchecked aero model in it.
 
Roger Roger said:
I dunno but it seems to me like this kind of stuff should be day 1 stuff when going to ground school on a swept wing jet.
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You would think... This book has only been around for 50 years or so....

image.jpg
 
Aerodymamics for Naval Aviators is interesting but not exactly an easy read, especially for the Math challenged.

I've flown with guys who couldn't average two numbers on a performance chart, no way in hell they're understanding anything here.
 
Jimflyfast said:
Seagull

I have no idea who you are, and would like to continue this offline if you like

First, a question. How many high altitude stalls have you done and in what type of airplanes? As an experimental test pilot and FTE, I have done literally 100s (probably closer to thousands) of them in 737, 757, 777, 747-4, G-V, citations, and even king airs. And I will throw in a MS in Aero to back up the theoretical side. I say this as a basis of what I am going to say next, so you know it isnt some high school troll

First of all, your article is fine, but incomplete. I didnt read past the AF447 part, because it is not really relevant to high altitude stalls, as there were so many other factors in that crash. The second most important part to talk about in high altitude stalls, after the stall ID, is that the lack of Ps is going to highly influence the recovery. Most modern jets are going to require 4000-5000 feet to recover, and that is with no startle factor and near perfect recovery. I could continue, but I am not really at a place to write a novel here. And as a small, but regularly misstated point, lift does not increase with AOA, Lift Coefficient does. No true areo weeenie would ever use the word lift max, it is Cl max.

@Derg will give you my private email if you like
Click to expand...

The article was written for pilots, first, so intentionally tried to stay out of the weeds. I am wondering what verbiage regarding lift and AoA you refer to? Did I write "lift max" somewhere? I agree on the requirement on altitude loss to recover, and chose not to include that as it varies so much with q etc. the AF447 part is directly related to the topic.

Were you FTE or test pilot on the Boeings?
 
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PeanuckleCRJ said:
Well written article overall.

To be clear, they were in "alternate law," where the ailerons are now being directly controlled. Load factor change remains commanding the pitch.
It is incorrect that there are no stall protection features that remain when degraded to alternate law- you now have high and low speed "stabilities" where it will insert a slight pitch up for high speed protection and pitch down for low speed.

I've had it in alternate and direct law in the 20's. It is quite twitchy!

Also, don't forget that pitching to 17 degrees nose up at FL350 is never a good idea on any transport jet.

Very correct in regards to the sim modelling the stall- only the approach to stall is required to be modeled. We're actually negotiating with the FAA on the new requirements on modelling full stall in the sims.
Click to expand...

You might wait until those requirements are sorted out. Hopefully a paper on the topic will be forthcoming soon on it, but it is still in draft right now last I heard.
 
Baronman said:
Aerodymamics for Naval Aviators is interesting but not exactly an easy read, especially for the Math challenged.

I've flown with guys who couldn't average two numbers on a performance chart, no way in hell they're understanding anything here.
Click to expand...

Agreed, there are better out there.
 
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