Rorschach(DoH)
If looking at Plan view, the straight wings in Yaw lose frontal exposure at a reasonably "equal rate". The Lead wing is roughly equivalent in lift to the Trailing wing as Yaw increases.
With Sweep, the Lead wing is gaining effective frontal exposure as the Trailing wing loses it. This can be dramatic and cause inversion of the airframe with additional Yaw. One wing is 'extending' as the other "tucks". Additionally, the trailing wing is progressively "Blanked" by the fuselage further reducing its lift.
This is expressed as 'acceleration of rate', as Hazelnuts has stated. Roll rate has to do with velocity about the Longitudinal axis, and is reliant on concentration of mass about the axis of the airframe, among other factors.
Yaw produces an acceleration of wing speed in the outer wing, yes, but more important is the attendant and relative aspect ratios of the 'new' and changing frontal areas of the respective leading edges. Yaw is almost always not to be wished, hence the term "adverse". It produces a "skid", an unaerodynamic feature that greatly increases drag, some of it morphing into discrepant lift, hence Roll.
Last edited by bearfoil; 18th Jan 2011 at 14:11.