mach buffet
 

Hello All,

I've been reading 'Fly the Wing' by Jim Webb, where he talks about the generally *bad things* that happen if you fly past the MMO limit.

He says that some planes will 'tuck up', others 'tuck under', and that you may even get 'control reversal'.

I'm wondering what the effects are on specific aircraft, or at least what you have experienced in the sim.

Mike

In the Westwind you got a solid rumble just on the Mmo limit, and 0.1M over it would abruptly drop the nose about 2 or 3° - which at that speed is alarming.

The BAe 146 never got anywhere near its limits, and you could (in the sim) hammer past Mmo with almost no noticeable effects.

Haven't tried it in the 737 sim yet.

Mach buffet in the 737-200 will occur below MMO. As the aircraft speed increases in the Mach regime airflow seperates from the wing and this causes turbulence that the horizontal stabilizer encounters causing the buffet. This buffet is benign.

The BAC 111 would, in an extreme overspeed condition, exhibits rudder reversal. I would think that it would be nearly impossible to force this particular aircraft into this situation.

The USAir BAC 111 simulator had this programmed into its flight characteristics. As I recall it required a signifigant amount of will power to force the airspeed and pitch down required to get rudder reversal.

Checkers,

do you know if the 146 sim has been programmed for mach buffet or Vmo exceedence?

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bottums up !

Capt Claret points out a very important consideration - we all like to play pilots with the sim and do interesting things in spare playtime - and these activities have a very useful potential in their training value.

However, many forget that the sim is a computer, not an aircraft, and that what we observe is the computer-generated response, not that of the real aircraft. In those regions of the envelope where the fidelity is tested and proved to be adequate, then the result is pretty much that the aircraft response is produced - otherwise the response may be quite unrepresentative, and only of a generic training value.

To highlight this consideration -

(a) some months ago I was co-opted (a disadvantage of being around at 2 in the a.m.) to fly a comparative test sequence pre- and post-software mod on my current sim. The results were quite impressive - the pre-mod responses in regard to the particular control problems were quite unlike those alleged of the aircraft, while the post-mod were very believable.

(b) in similar vein, we routinely do fairly extreme UA departures for confidence building during endorsement programs. While there are no rational acceleration cues, nor are the instrument dynamics necessarily anything like those on the aircraft - there is still a useful value to the student in building confidence to recognise the various situations and to apply the conventionally recommended recovery protocols.

It would have to be, I would think, in order to gain certification. The comment above was from a memory of my endorsement six years ago - It isn't really a problem, as the "coffin corner" for the 146 is well above the max altitude, and you would have to be pretty distracted to exceed the Mmo at any time :)

I do remember that the 146 that crashed after the pilots were killed by a passenger apparently exceeded M1.0 on the way down, with nothing comming off - although this says a lot for the airframe strength it doesn't really cover controlability issues, which is what Mmo is all about.