Vmo versus Vc

[MilPilot]

Something puzzles me. According to FAR 25:
VMO/MMO must be established so that it is not greater than the design cruising speed VC

But that doesn't make sense to me. Can somebody explain the rational behind this?

[Obs cop]

As I understand it,


Vc is the "Design Maximum Cruising Speed" which is a speed used during testing and certification to assess the structural strength of the aeroplane. The airoplane must be able to withstand vertical gusts of +/- 50 fps (at 20,000'). If flying faster than Vc for example in a shallow dive, then the aircraft only needs to witstand +/-25 fps gusts.

A safety factor is applied to this in the same way as an aerobatic aircraft may be permitted to say 6g with a wing which is known to fail at 10g. You wouldn't want to manouever at 10g if you knew the wings would fold at 10.1g! Same thing with the speeds.

Vc is the design speed which then has a safety factor applied to give Vmo/Mmo.

At least that's how I understand it,

Obs

[MilPilot]

You are correct. I made the mistake of using Wikipedias definition:
V speeds - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/V_speeds)
VCDesign cruising speed, also known as the optimum cruise speed, is the most efficient speed in terms of distance, speed and fuel usage.[ (http://en.wikipedia.org/wiki/V_speeds#cite_note-faacfr-5)