Nick + tgrendl,
The requirement for the additional power is to ensure you are able to overcome the additional settling described as 1' per second. A rate of climb capability of 2-300' per minute is more than adequate for that purpose. OGE +5% in temperate climates at heights below 3000' i.e UK would rarely limit your AUM performance. Should the temperature or density altitude preclude OGE performance then you would be in the realms of appropriate into wind techniques from the outset.
With regards payload, an SA342 in UK with 340 KGS of fuel would carry 2 pax with about 50 KGS spare. OGE +5% performance during Spring through to Autumn would be achievable to 3-4000' at AUM. The 5% thrust margin equates to being able to increase the aircraft AUM by 95 KGS and still hold a free air hover without being able to compensate for turbulence. Therefore the reduction in AUM would not affect routine UK operations. Assuming the same generic calculations are used across types the same would be so although this I cannot confirm.
As an asside, with regards tail rotor effectivness downwind, assuming the downwash from the main rotors is therefore blown away from the tail rotor, if the tail rotor is optimised to utilise downwash as in the case of the Lynx then the loss of translational lift from downwash would cause an increased power requirement downwind. Regards
[ 04 September 2001: Message edited by: ACORN ]