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Stall prevention correct?


PieterG

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I doubt of the stall protection of the airbus x is functioning correct.
When I'm flying in level flight and I'm holding the stick fully backwards the attitude is limited to thirty degrees as expected. Due to the steep climb, the airspeed decreases very fast.
When the airspeed drops to the alpha floor speed(top of the barber pole) the TOGA kicks in. So far so good. But to my opinion at this point also the attitude should be lowered to prevent the bus reducing the speed below alpha max speed(solid red region of the speed tape).
Actually when doing this manoeuvre with the airbus x, the speed drops below the alpha max speed before reducing the attitude of the plane. The consequence is a drop in altitude before the nose is lowered, followed by a suddenly steep dive when the nose is lowered.
A'm just a flightsim pilot, but what I've read about the airbus is, that the aircraft shall always prevent flying below the alpha max speed. So my question is: Am I making a mistake and is the stall behaviour of the airbus X correct or not?

I've also noticed that during the TOGA/LOCK and the airspeed is out of the danger zone, the EPR is reduced to about the climb level. I always thought that TOGA level shoud be maintained untill the TOGA LOCK is cleared.

By the way during normal flying you will never be in this situation and the airbus X is a joy to fly.

 

With regards

Pieter Lubout

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  • Deputy Sheriffs

Hi Pieter,

You are partly correct. With regard to the stall we do not speak in terms of speed but of angle of attack. In your example you are making it very diffecult for the high AoA protection to kick in correctly. The RW Airbus will most probably be a bit more aggresive with reducing the AoA to the max value but it is possible to exceed this limit for a short time.

FSX and P3D are not well known for their standard stall behaviour and this is also in part what you are seeing here. The devs did not put a lot of time in modeling these extreme situations and I think that within the constraints of the sim and the level of simulation AS is trying to achieve (SOP flying) this behaviour is acceptable.

With regard to the TOGA Lock. Did the autothrust "throttle" back or did the max EPR value decrease?

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Hi Frank,

I just have over thought this behaviour,
It might be correct, because at such a high attitude the speeds drops so fast that the flight control sytem is not able to correct it in time. At slow speeds the control surfaces are inefficient and due to mass-inertia of plane the flight control system will not be able to drop the nose fast enough. As far as I know a FBW system has problems if the speed of the aircraft drops to a certain  low level.  
I tried this maneouvre with less attitude and the system works better.

If the behaviour is not correct. I think that the developers cannot correct this due to the limitations of FSX. If they may change to correct this it will have a drawback in the normal flight behaviour.

With regard to the TOGA LOCK the limit changes. I've tried represent the situatation this evening and discovered that the system works well untill you recover the TOGA LOCK. After that I was not able to select TOGApower any more it stays at the climb power level.

 

Cheers Pieter

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I would think the real thing is a little more aggressive in its Alpha Max protection on the basis that one of the 'selling points' of the Airbus FBW system is that it massively simplifies the GPWS terrain escape manoeuvre: the procedure is to select TOGA, snap the stick full back and hold it there and let Monsieur Airbus do the rest. This versus a "conventional" aircraft where the pilot would have to pull to the buffet, being careful not to pull so hard as to overstress the structure, and then try and maintain an attitude just at the onset of buffet for maximum performance. Obviously the Airbus normal law load factor and high alpha protections take care of all that and the FBW is able to maintain Alpha Max far more accurately than a human pilot operating by feel could.

However, I am quite prepared to accept that programming limitations within FSX may make this difficult or impossible to replicate completely.

Sent from my GT-I9505 using Tapatalk

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