About Va
'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.
'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.
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)...
(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
(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
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Genghis;
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.
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.
