Correct answer is... 178 km/h. It is equal to 96 kn or 110 mph. It is lower value then max speed of other aircrafts of a similar size. Average is about 310 km/h (167 kn or 192 mph).
The maximum speed most frequently is a term for so-called never exceed speed. Above this speed, the Armstrong Whitworth Argosy can suffer considerable damage. There are also three other types of speed that can be called "maximum speed": Vno (normal operation speed) is the maximum allowable speed of normal operation, Vb (design speed for maximum gust intensity) is the maximum speed in rough air, and Va (design maneuvering speed) is the maximum speed at which the rudders can be maximally deflected.
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