Flight Envelope & Speed Tape

[flybywire380]

All,

Would someone be able to explain, physically, why the black & amber flight envelope strips on the speed tape become progressively closer together as you climb please?

I am aware of coffin/Q- corner and low & high speed buffet/stall; but would really appreciate an explanation of the physics with reference to IAS/EAS/TAS/Mach behind why, as you climb, the low-speed stall speed increases and the high-speed stall speed decreases?

Thanks in advance

[The Terminator]

As you climb the air gets colder so the speed of sound gets slower, So you will get closer to reaching crit mach at a constant TAS . Your TAS will also increase if you are flying a constant IAS as the air is getting less dense so you can reach crit mach that way.

Low speed stall does not increase for IAS, it only increases for TAS but that has nothing to do with mach speed, it is simply the air getting thin.

So to repeat; As you climb the TAS stall speed increases until it becomes the same speed as the critical mach speed. The decreasing air temperature speeds up the process but it would happen anyway as the air density decreases with increasing altitude.


Hope that is clear.

[de facto]

I am aware of coffin/Q- corner and low & high speed buffet/stall

Ahhh the coffin corner myth in transport category aircraft comes again...:}
but would really appreciate an explanation of the physics with reference to IAS/EAS/TAS/Mach behind why, as you climb, the low-speed stall speed increases and the high-speed stall speed decreases

Seems like someone threw away his ATPL books and shouldnt have.:E

[gehenna]

De Facto

Looks as if you have a problem. The question was a polite request for advice, and all you seem to have done was to be an ar**.

If you cannot have the decency to write an informative reply, don't bother, and furthermore don't make assumptions about someone's past.

I await a simliar missive from you as a reply.

[flybywire380]

Terminator,

Thanks very much for your explain - much appreciated.

The only thing I'm still a little unsure of is regarding the speed tape black & amber bands. If the low speed envelope limit doesn't change for IAS (or CAS), why does the lower black & amber limit increase with altitude (see link below), bearing in mind the speed tape is showing IAS/CAS?

Boeing 737-8K2 - Large Preview - AirTeamImages.com (http://www.airteamimages.com/boeing-737_OY-TDB_transavia_100905_large.html)


Thanks very much.

[de facto]

Stall management system(SMYD) is calculating Vmvr(the yellow band) based on FMC grossweight, ALTITUDE ,computed airspeed fed by the ADiRUs and many other factors such as AoA,use of TAI....
They provide safe margins to maneuver,1.3 G for JAA,1.2 G for the FAA.

As altitude increase,the Mach nr will be the reference as the TAS of IAS and Mnr become equal.(cross over altitude).

The black and red top and low stripes are max or min safe design operating speeds based on weight,flaps,gear....NOT altitude.

Concerning the picture,the pilot in question is asking for trouble..and having the AT un the ARM mode is another sign of ....