I think Nick has been misinterpreted.
Don't forget forget that aircraft have mass - a lot of it. If you are turning downwind, the mass needs to be accelerated in relation to Mother Earth's gravity to keep the same IAS, and that takes energy - engine power or altitude. If the mass is not accelerated, you lose IAS and therefore usable energy. This applies to all aircraft, not only helicopters. Have a look at the speed vs power required curves you find in all Flight Manuals, from small helicopters to powerful fighter airplanes to big airliners.
Below Vy (best rate of climb speed, where you find the best lift over drag ratio), the power required increases with decreasing airspeed. Translational lift plays a minor role in this picture. In other words, if speed is reduced below Vy you need more power to stay airborne. Many helicopter pilots doing photo and similar missions have learned this the scary way.
Please read this report from the UK AAIB. This Super Puma, which is a fairly powerful machine, was turned downwind at a sustained low energy state with fatal results.
http://www.aaib.gov.uk/cms_resources...3%20G-TIGH.pdf
I have made it my rule when flying offshore during high wind conditions, never to turn downwind at speeds less than Vy + 10, and then keep a close eye on the airspeed indicator during the turn and never let the IAS decay.
And yes, I am a pilot, test pilot and an accident investigator too.
