Originally Posted by
arismount
Gentlemen, I started this thread. With all due respect, discussion is beginning to drift to controllable elevators, tailplanes, etc.
That is not the question I have...to restate, does CG position have anything to do with extended range or increase airspeed in a main rotor/tail rotor configured helicopter and if so, what CG position is most favorable for decreased total drag / increased airspeed / increased fuel efficiency ("max range")?
Please address this question, with references to data if at all possible.
Thanks in advance to The Community for your consideration.
References:
Filippone A.,
Flight Performance of Fixed and Rotary Wing Aircraft, pages 346-350, 2006.
Yeo, H and Johnson, W.,
Performance Analysis of a Utility Helicopter with Standard and Advanced Rotors, 2004.
To paraphrase the above,
On average, in forward flight, a helicopter will have about 30% of the total drag attributed to skin friction, 40% from the systems interference (main rotor, fuselage, tail rotor, hub), 10% from the landing gear, and the remaining drag due to all other causes. Airframe drag is proportional to the cube of the flight speed. The drag contributed by the fuselage increases to the point of being the dominant resistance at high speeds.
There exists a relationship between fuselage drag and pitch attitude. The drag polar of the helicopter fuselage generally increases as fuselage angles of attack increase and/or decrease from zero. As Crab noted with the AW-139, in some unique cases the drag coefficient decreases as the pitch angle becomes positive.
There is an equation given in the first reference. The equation is conceptually important, because as speed increases, the aircraft must change its pitch attitude to maintain trim (complicating matters, trim effects attitude in a seemingly unending circlular manner) . But, consider as the pitch attitude changes, the fuselage drag increases, There are many confounding factors. For example, rotor hub interference drag also increases considerably at higher speeds.
Typically, aerodynamists calculate total drag using the
equivalent flat plate area method, sprinkled with well-educated guesses. The point being, there is no real hard and fast rule, and only very detailed flight testing of a particular model will yield anything definitive.