Originally Posted by Macgyver
Hey Mates,
Can someone please explain the difference between Vmo and Mmo? I'm thinking that Vmo is a limitation speed based on excessive dynamic pressure from flying at high speeds, while Mmo is a limitation based on shockwave damage from flying at high speeds. Is this correct?
Not really.
There are a slew of regulations which must be met within variously defined flight envelopes. The Vmo/Mmo limitations actually applied to an aircraft are essentially a composite of the most restrictive of the various requirements - or the most the manufacturer bothered to show, if smaller.
So, for example, one must show positive directional stability (or non-negative directional stability, if you prefer) within the Vmo/Mmo constrained flight envelope. One may find directional stability problems at high Mach, in which case one option is to simply 'cut back' the speed in ther relevant area. (That's usually cheaper by far than trying to redesign a problem away).
In addition to handling concerns, Vmo/Mmo may arise from loading or aeroelastic concerns, or the need to maintain margins to demonstrated or calculated dive/design speeds.
The difference between the two is indeed the dominance of dynamic pressure or shock characteristics in setting the limit; but it's not "shockwave damage".