737NG questions

[Busbar]

Hi All,

I was asked two questions today and I didn't know the answer. I did a search on here but to no avail. So can you help?

1. On the 737NG why does the Airspeed Indicator on the speed tape show 45kts when stopped on the ground?

2. Why are the wings on the 737NG set at a sweep angle of 25 degrees rather than 27 degrees?

I even google searched this and no joy!

I look forward to your responses.

Many thanks.
:ok:

[JeroenC]

RYR interview? The answer to your last question should have been: "because the engineers deemed 25 degrees to be the optimal".
Puzzled by the first one though.

[Lord Spandex Masher]

Super critical wings.

[BOAC]

Puzzled by the first one though. - because it does? It is generally thought that, Air France excluded, pilots will not try to fly conventional swept wing aircraft at less that 45kts.

[tdracer]

Airspeed isn't valid below a certain value (the difference between total and static pressure is too small to be dependably resolved). Some Air Data Computers use 30 knots (that's what's used on 747/767 that I work), presumably on the 737 they use 45 knots.


When they went to the NG, Boeing didn't do a complete redesign the 737 wing, they did a 'reloft' where they changed the aerodynamic profile but not the basic structure. Since the 737 wing dates back to the 'short haul' airplane concept of the 1960s, there really wasn't much they could do to the wing sweep within the design constraints of keeping the same basic wing structure.

[Busbar]

Many thanks folks! :ok:

[aveng]

Don't know why 45kts but maintenance manual for classic used to refer to 45 kts indication of serviceable air data computer.

[STBYRUD]

I was told (always a bad way to start a sentence) that the NG wing was redesigned to allow for a higher cruise mach number - while the NG is obviously cruising somewhat faster than the classics supposedly Boeing wanted to raise MMO as well over its current 0.82. The problem this posed was that this would have required a complete airframe recertification... If this is true this would explain the relative speed instability of the NG in cruise - it definitely wants to fly at lower AOA!