IanfromRussia
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Airbus elevator deflection rate

Sat Feb 08, 2020 9:49 am

Does anybody know what is the elevator deflection rate in Airbus aircraft (A320/330/340, those with sidestick)? How much time it takes to swing the elevator from the full up position to the full down position (or vice versa)?
 
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Starlionblue
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Re: Airbus elevator deflection rate

Sat Feb 08, 2020 2:43 pm

I haven't timed it but it takes at most a couple of seconds while doing the flight control check.
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IanfromRussia
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Re: Airbus elevator deflection rate

Mon Feb 10, 2020 5:14 am

So it would lag behind the stick, if You pulls it aggressively? Can't it cause rate saturation PIO?
 
IanfromRussia
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Re: Airbus elevator deflection rate

Mon Feb 10, 2020 6:13 am

I apologize for my nasty grammar. I ment: "if You pull it..." I have a bad habit of adding "s" to verbs in second person since my school years.
 
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Starlionblue
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Re: Airbus elevator deflection rate

Mon Feb 10, 2020 8:44 am

It does indeed lag behind the stick if you yank it. The ailerons lag more for the matter. If you pull full left/right they go almost all the way rather fast, but the last little bit of aileron travel takes a bit longer.

PIO is definitely a possibility. It happens sometimes, typically on final approach, and especially for low experience pilots new to the 'bus. The guidance if it happens is just to let go of the stick and let the aircraft settle. Either way, given the mass of the aircraft and all that inertia you need to wait for any corrections to have an effect. Set, wait, evaluate, repeat.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
IanfromRussia
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Re: Airbus elevator deflection rate

Mon Feb 10, 2020 5:52 pm

And nobody screwed it up? In military fast jets PIO led experienced test pilots to crashes or near crashes (Su-27, YF-22, Gripen).
 
thepinkmachine
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Re: Airbus elevator deflection rate

Mon Feb 10, 2020 6:07 pm

I would say if there’s any PIO it is more likely to be in roll rather than in pitch (fairly common on A320 series in gusty crosswinds, plenty of examples on YouTube)

I’m my time on the Bus haven’t seen anyone doing elevator PIO.

Also, bear in mind that in flight you don’t control the elevator directly with the side stick. You give the FBW computer a maneuver demand (required g and/or pitch rate) and the computers adjust the elevator and THS accordingly.
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Starlionblue
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Re: Airbus elevator deflection rate

Tue Feb 11, 2020 2:37 am

Compared to fast jets the control authority is less, plus the aircraft is much larger. We just don't get that instant response to inputs. You'd have to be really hamfisted (or doing it on purpose) to get into a Gripen/F-22 sort of fast PIO situation. It would probably happen so slowly that you'd instinctively let off on the stick. By then the other pilot would have first yelled at you, then verbally announced he was taking control, or as a last resort held the instinctive disconnect button on the stick to take over control.

Agreed that PIO in roll is more common. It happens in pitch but not in a kind of fast up and down. More like making a correction, not waiting for the aircraft to catch up, then countercorrecting too much and/or too early.

The elevator does go into direct law at 100ft on approach, deflection proportional to stick movement.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
IanfromRussia
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Re: Airbus elevator deflection rate

Tue Feb 11, 2020 11:28 am

https://mak-iac.org/upload/iblock/c01/report_ra-89098_pr_en.pdf

Here is an example of fatal PIO of an airliner with Airbus-style FBW flight controls ( see page 25 ). The aircraft was in "direct mode" (i. e. in what is called "direct law" in Airbus' terminology) due to dual data hub malfunction (as a consequence of a lightning strike).

NOTE On the diagram positive stick displacement figures are nose down and negative are nose up. Perhaps that's trivial, but I don't know, whether the same notation is used abroad.
 
IanfromRussia
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Re: Airbus elevator deflection rate

Sat Feb 15, 2020 6:50 pm

Does it look like the aircraft have sharper response to the elevator than bigger Airbuses and goes astray too fast or like the response of the aircrew was unusual?
 
Nicoeddf
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Re: Airbus elevator deflection rate

Sun Feb 16, 2020 12:45 am

IanfromRussia wrote:
Does it look like the aircraft have sharper response to the elevator than bigger Airbuses and goes astray too fast or like the response of the aircrew was unusual?


I would suggest, from the interim report, that the plane did as designed. The CPT of the flight deliberately yanked the stick full aft and full forward and the plane reacted accordingly and, fitting to the aggressive input given, aggressively. I am confident that any plane, FBW or not, given the aggressive nature of the inputs, would have reacted quite similar.

I know we are not discussing the specific accident, but my take on it is, that the pitch control inputs were largely inadequate for the flight situation.
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IanfromRussia
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Re: Airbus elevator deflection rate

Sun Feb 16, 2020 4:33 pm

I'm sure that the aircraft reacted "as designed" as well as that the CPT's inputs were objectively inadequate. The question is whether the designed behavior of the aircraft (especially, the phase shift introduced by lagging elevator actuation) is conducive to pilot's overreaction?
 
CRJockey
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Re: Airbus elevator deflection rate

Sun Feb 16, 2020 9:15 pm

IanfromRussia wrote:
I'm sure that the aircraft reacted "as designed" as well as that the CPT's inputs were objectively inadequate. The question is whether the designed behavior of the aircraft (especially, the phase shift introduced by lagging elevator actuation) is conducive to pilot's overreaction?


No idea and I wouldnt want to deduct anything from this single event. The large scale of inadequate inputs with max deflection overshadows anything with regards to your specific question.

But maybe somebody else is able to deduct a little more.

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