Stall prevention devices

[captain87]

Hello Everyone,

I'm going to open this thread by treating the stall prevention/warning devices adupted by different manufacturers (e.g. Airbus, Boeing etc.).
While Boeing usually implements a stick shacker/pusher device, Airbus philosophy is much more complex: in the last case stall prevention is given by FCC's (Flight Control Computers) who automatically limit angle of attack up to a certain value. Alpha Floor/TOGA lock automatically prevents the aircraft from stalling when operating in normal law.

The topic of this thread is not how the various systems prevents the stall but what is the better way to prevent it (i.e. Airbus or Boeing philosophy) !

Actually I deem Airbus as the best promoter of safety and technological innovation ...

:ok:
Keep writing,
captain87

[Mad (Flt) Scientist]

Shaker/pusher is not a "prevention" system. The shaker is a warning, the pusher simply provides stall identification (and deters progress to a higher, more dangerous, AoA). The only "prevention" system on such an aircraft is between the seat and the yoke.

If you wish to classify stall systems, you should include a "naturally stalling" aircraft too. In some ways an aircraft with good natural stall characteristics beats any artificial system, because it's inherently robust, whether against system failures or wing damage, for example. An aircraft with bad characteristics which are "fixed" artificially then relies completely on the effectiveness of the artificial fix.

[barit1]

My instructors were of the old school who didn't regard highly any excess runway you wasted on landing. Thus I've always regarded an aircraft with good natural stall warning (buffet), and predictable post-stall behavior, as an "honest" airplane - i.e. one in which I wouldn't hesitate to make a full-stall landing if conditions permit.

[captain87]

Hi Barit1,

... the purpose for which I created this thread is to emphasize the dispute between traditionalist pilots and progressivists.
The greater part of my instructors opt for classic solution (stick shaker/pusher) while I completely "side with" Airbus philosophy.

Cheers

__________________________________________________

Hi Mad (Flt) Scientist,

I'm perfectly aware that stick shaker is a warning system who generally activates 2 kts or 2 % below Vsr at which stick pusher activates, so Vsr is automatically reduced in order to prevent the aircraft to stall. But since this is not the topic in mind, I preferred not to specify.

;)
Best Regards,
captain87

[Pugilistic Animus]

Well, I like Boeing's philosophy, nothing to do with stalling though---more to do with artificial feel as an aid to flying through a critical situation i.e a gusty landing---Airbus stalling philosophy [what relatively little I understand of it] seems great:ok: Sidestick:ok: Lack of artificial feel/feedback system:*

what Boeing has a pusher? 717 only I thought

--- not counting MD/DC--types--- nudgers are installed on JAA certified 747 classics [so I've read] not sure about the 400 though???

Sorry for being off topic but both philosophies have withstood the test of time.

Foolishness/ complacency/ poor CRM/ airmanship/ lack of foresight/ situational awareness/ hazardous attitudes/ fatigue/ stress/ bad checklist procedures/ management...etc... etc.. have defeated all OEMs, no company can really design that out---just don't stall!

[captain87]

Hi Pugilistic Animus,

what Boeing has a pusher? 717 only I thought

I really don't know what kind of stall warning devices Boeing has implemented onboard, but I'm sure that actually Boeing is going to prefer technology to mechanics (see B787 project).

Foolishness/ complacency/ poor CRM/ airmanship/ lack of foresight/ situational awareness/ hazardous attitudes/ fatigue/ stress/ bad checklist procedures/ management...etc... etc.. have defeated all OEMs, no company can really design that out---just don't stall!

Regarding last quote above, I realized that many pilots, instructors and engineers complain that Airbus doesn't allow them to "enjoy" onboard by excluding artificial feel and feedback systems ... what do they mean with the term "enjoying" ? ... Sincerely I think that despite their lack of immagination, Fly-By-Wire (generically used to indicate innovation) means safety over feel and feedback ... unfortunately there is always a price we need to pay ... and this is the best thing eventually !

Computers are not a way to put man apart, but simply a way of helping him. Finally, if Airbus philosophy makes stall impossible to happen during the normal flight envelop (by the use of computers), this is the better way to promote safety and therefore avoiding accidents.

:ok:
Keep stalling,
captain87

[doubleu-anker]

Stall prevention devices.

One good device is the ASI. So keep an eye on it and don't load the wings too much.

[Dan Winterland]

The 747 was initially certified in the US without any stall warning or protection at all. Boeing considered it's stall performance so good, they didn't think it needed any artifial warnings and the FAA agreed. It was the UK CAA under the direction of DP Davies (author of Handling the Big Jets) who insisted on some form of warning for UK certification, so the stick shaker was fitted. This is why it is a motor with an eccentric weight, jubille clipped to the contol column and looks like it was designed by Heath Robinson.

It was subsequently fitted to all 747s.

[captain87]

Hi doubleu-anker,

One good device is the ASI. So keep an eye on it and don't load the wings too much.

:rolleyes: Until your post I thought that the first stall reference was the AOI (Angle of Attack Indicator) and load-factor for wing structural limit ... not ASI. An aircraft can always stall regardless we're flying too low or too fast ... Probably I should review my theory ...

;)
Best Regards,
captain87

[doubleu-anker]

Agreed. If your a/c has AOA indication.

Don't worry about the books. You have passed!:}

[captain87]

:O :O :O :O :O ;)

Thank you very much Doubleu-anker !
I was going to think there was something wrong ...

:ok:
Best of all,
captain87

[Pugilistic Animus]

I should be sleeping---but to answer your question it's not about enjoying [very subjective] some even find the C-152 Aerobat to be aerobatic:}

but re lack of AF, well when all has gone down the toilet--- sometimes you need to rely on all natural senses---including touch especially in a situation where seconds may count!

disregarding an AOA indicator or "eyebrows" etc---- you do have an excellent stall warning device ---your stick/ yoke anytime it's aft of neutral][upright stall] or fore of neutral [I] while trimmed from steady level coordinated flight] then you're on the road to stalling---a wing always stalls at the same angle of attack, but may be stalled at any airspeed because a descending flight path may appear to give a normal pitch attitude however the AOA is excessive due to the relative wind hitting down from below

keep up the diligent study:ok:

[captain87]

PugilisticAnimus
Thank you for your precious answer ! :ok:

Best of all,
captain87

[barit1]

My father instructed in AT-6 (T-6, Texan/Harvard...) aircraft during WWII - and at one point their curriculum including partially blanking off the ASI window so that the student could not read anything below 100 mph (90 kt). The objective obviously was to give the student confidence in tactile and attitude airmanship (airwomanship actually; his students were WASPS). Although this practice didn't last too long, Dad regarded it as a good exercise.

[Pugilistic Animus]

Put some edits above---

---think about it why no stall during the top of a loop or the summit of a hammerhead [near zero on the ASI sometimes]?

[Pugilistic Animus]

Barit1[ I like it]--- another good training technique is to cover the AI and and altimeter and do level steep turn---really emphasizes feel, coordination and and use of the horizon as the best flight instrument ever [this is done VFR of course]

[Pugilistic Animus]

"---think about it why no stall during the top of a loop or the summit of a hammerhead [near zero on the ASI sometimes]" ?

No Takers? OK then,


---because, the flightpath of the aeroplane has been adjusted to 'keep up' with the relative wind'---so at no time is the stall AoA achieved:8

[dartagnan]

can the 320 be recovered from a stall?
spin?

[Dan Winterland]

Quote "---because, the flightpath of the aeroplane has been adjusted to 'keep up' with the relative wind'---so at no time is the stall AoA achieved"

It would be more correct to state that as there is very little loading, there is a vastly reduced stall speed. The stall speed is a function of the square root of the load factor. If your 1g stall speed is 60kts, at 2g it will be 60 x 1.41 = 85kts, at 4g it will be 120kts. At 0g, you won't be able to stall.


the A320 will stall and recover like any other aircraft. What is true to say is that the protections will prevent you in normal control laws. In Direct law (where stick movement will move the control surfaces in proportion to the movement - as in a conventional aircraft) it would be perfectly possible to enter and recover a stall. And I suspect it's the same for a spin, although swept wing aircraft can have markedly different spinning characteristics to straight wing aircraft.

[Fangio]

Hi Pugilistic Animus

you asked-
what Boeing has a pusher? 717 only I thought

Some years ago, the Boeing 727's on the UK register had stick pushers, I believe that the CAA airworthiness division insisted upon then being fitted following the deep stall characteristics of 'T'tail aircraft.

Regards,
Fangio

[barit1]

"---think about it why no stall during the top of a loop or the summit of a hammerhead [near zero on the ASI sometimes]" ?

No Takers? OK then,


---because, the flightpath of the aeroplane has been adjusted to 'keep up' with the relative wind'---so at no time is the stall AoA achieved

...which also results in the airplane being in a near-zero-G (ballistic) state, thus wing loading is very low.

In a hammerhead, the wingtip on the inside of the turn may actually be flying backwards, if only for a second.

[Pugilistic Animus]

Dan Winterland and Barit1 that's the other correct way to see it---now the COMPLETE perspective has been elucidate---I love discussing the stall !

Fangio: Thank you very much for the info- interesting

the discussion much appreciated Gentlemen!

PA