I'm with TC on this one.
However, I don't think a tailwind of, let's say, 30 kts impinging obliquely on a horizontal stabiliser will have anywhere near the same 'negative' effect as the downwash does.
Another misconception. The majority of us are taught that the rotor produces a 'mythical' column of downwash. This is of course rubbish. The downwash is more toroidal (doughnut shaped) in profile on a conventional (non BERP-type rotor). ie, there's no downwash at the hub or for a few feet outboard from it and there's minimal downwash right at the tip. The greatest downwash is just inboard from the tip which, depending upon the degree of blade washout, decreases slightly towards the hub and then drops off rapidly as it reaches the stalled area by the hub.
C'mon.......... Shoot me down in flames!
J