speed tape, 737

[Pete the Pilot]

This is one about the high speed buffet limit hollow yellow bar below the red and black mmo bar on the speed tape.

The high speed buffet limit is said to give a 0.3g manoeuvre margin to high speed buffet. On flying into this speed zone buffet is experienced on the 737.(straight and level with no g )

Why's this? There doesn't seem to be any buffet margin at all............. :confused:

[Slick]

Pete the margins are their for all aircraft the thing is with a speed tape or indeed a MASI you are constantly reminded where they are. The upper maneuvor margin of 0.3g is/may be displayed below the Mmo/Vmo, red and black bricks if you prefer, at high altitude at reletivly high gross weights on the 73NG, just where you would expect. Straight a level flight poses no problems, if you realy want you can still fly into the upper maneuvor margin up to Mmo, what you of course must understand is that any loads whilst in this region, maneuvor or gust may induce high speed buffet, thre bottom of the bar providing 0.3g. The B73 however displays excelent high speed stability with little or no tendency to tuck.


Best rgds

[Pete the Pilot]

I hear what you're saying Slick, but buffet occurs with no loading on the aircraft as you enter the 0.3g manoeuvre margin area, I've tried it........

[CAT MAN]

From experience, to accelerate into "Hollow yellow bar" whether or not in turbulent air,will induce airframe buffet...This of course at high level...If the system detects a compromise of the .3g protection "BUFFET ALERT" will be presented on the CDU...As for high speed handling characteristics I'm no test pilot but MACH TRIM operates above .617MACH...with speed limited to .74MACH with the MACH TRIM sytem inop...

[CAT MAN]

However, to answer your question, the BUFFET one experiences is simply "high speed" buffet...

[Slick]

Pete when one talks about the onset of high speed buffet, we as you know are talking about a speed where air is starting to flow at supersonic rates over parts or a part of the wing. This occurs at Mmo in stedy undisturbed flight, not at a speed below Mmo, ie the bottom of the high speed maneuvor margin. The margins or if you prefer the envelope is small in this area of flight. I think you said earlier 0.3g is not much of a margin, If you look at wing loading in banked flight you are takling only a few degrees, however the margin is still there and I stand by my earlier comments.

TR3 if the system detects a compromise of the 0.3 protection buffet alert will indeed display in the scratch pad of the CDU, it will also display for other reasons, however this is an FMC Advisory Message. I am no test pilot either but I base my earlier statement on having flown aircraft which demonstrate quite nasty habits at high speed and some which even required stick pullers for cirtification.

Best Rgds

[Propellerhead]

My notes say that once inside the yellow bar you are above Mcrit, therefore will experience some buffet. The black and red pole can be likened to the low speed one - it isn't a structural limitation (as in Vmo), rather a performance limitation. Mmo (the black and red) will activate the high speed clacker, indicating that you are not safe, and may experience a high speed shock stall.

The buffet margin is in respect of Mmo, the clacker, and possible shock stall. eg) if you pull 1.3g at the bottom of the yellow tape, you will get the clacker. Don't forget that the 0.3g marhin is only at the BOTTOM of the yellow bar and reduces to zero at the red and black. Therefore, half way up the margin is 0.15g eg) hardly anything! Any kind of turbulence and you will get some buffet.

[CAT MAN]

I don't quite get you there PROPELLERHEAD...

[Pete the Pilot]

Say that in English Prop Head......

Lots of explanations about why high speed buffet occurs but not why in the hollow yellow bar. 0.3g protection before buffet should surely mean that in level unaccelerated flight there should be no buffet.

We get buffet, and the CDU message Buffet alert (I always look around for the cheese and wine.........).
:confused: :confused: :confused:

[CAT MAN]

"PETE THE PILOT"...Why should there be no buffet????If you fly jet aircraft then maybe a trip back through a few text books might answer your query...

[Slick]

Fellas keep this to yourselves but just to humour myself I took my a/c up to Mmo the other night. Lovely smooth night at FL370. Guess what, no buffet well into the high speed maneuvor margin. I was not surprised.

Best rgds

[Pete the Pilot]

Well I'd like to say I was wrong, but unfortunately buffet into the 0.3g manoeuvre margin occurs in the 737s I fly. Makes no sense, although we did get a buffet warning on the CDU so my senses weren't completely wrong.

Anyway thanks for replying and if you see a 737 with more swept wing than normal then you'd now I was doing some more experimental flying. :)