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toughwings
17th Oct 2009, 05:30
We all know that Va stand for maneuvering speed.
Dose anyone know why FAA defined maneuvering speed as Va but not Vm
What dose 'a' stand for??

Checkboard
17th Oct 2009, 09:51
'a' stands for the first letter of the alphabet. :} 'm' is usually reserved for "minimum", so a was chosen at the same time as 'b' - and the two are thus designated and separated from each other.

Vb the design speed for maximum gust intensity or the maximum gust penetration speed. Vb is developed by the designer as a recommended turbulence penetration speed for commercial passenger aircraft rather than using Va, so that higher cruise speeds can be maintained and there is no danger of inadvertent stall. Stalling larger aircraft is not a good idea, not least because of height loss and possible excessive loads in the recovery.

Genghis the Engineer
17th Oct 2009, 14:24
If you draw the flight envelope, or V-N diagram, the points labelled around in in clockwise order are a (Va / manoeuvre speed), Vb (rough air speed), Vc (cruise speed), Vd (design limit speed)...

http://upload.wikimedia.org/wikipedia/en/1/13/PerformanceEnvelope.gif (Courtesy of Wikipedia.)

That's one of the reasons we have Vfe not Vf, and don't use Vg for the gear limits - structural engioneers already use f and g for negative g structural points.

In aircraft structural engineering, the curve between the origin and the manoeuvre speed/g-limit point is called the O-A curve.



So, really it's just a labelled point around a diagram.

G

toughwings
18th Oct 2009, 16:50
now i got it ,thanks guys!!

Pugilistic Animus
20th Oct 2009, 00:10
hey, the gust lines are missing:suspect:

there's so much information in a flight envelope and at the same time so many assumptions and lack of information:\

PA

Pugilistic Animus
20th Oct 2009, 00:49
oh and don't start at zero g start at one g:)

krujje
21st Oct 2009, 15:21
Genghis;

That's one of the reasons we have Vfe not Vf, and don't use Vg for the gear limits - structural engioneers already use f and g for negative g structural points.

Actually Vf is defined in 25.335(e) as the design flap speed. Vfe, the flap extended speed, is always less than or equal to Vf, as noted in 25.1511.