TAIL ROTOR BLADE DIRECTION.
I know there are many aerodynamics experts out there with greater knowledge of this situation than mine so I am surprised none have provided answers to this old chesnut.
I have to return to the Enstrom marque although it is sometime since my sales history was linked to the Spoonair Enstrom distributorship.
Most readers will be aware that the early model Enstrom non turbo models (F28A, 280 Shark) circa 1970 to 1976 - rotated anti clockwise (when viewed from the left side of the tailboom.) I'll do my best to explain without diagrams and hope the words will cover the point.
It was always felt by the Enstrom R & D department that on the original 'right hand tail rotor' layout - the thrust lost by the downgoing blade in the main rotor induced downflow was offset by the upgoing blade's thrust increase. However further research revealed that there was a marked reduction in induced main rotor airflow speed occurring about the tail rotor hub centre line and further reducing as it extended past the tail towards the upgoing blade. So what was lost on the downgoing blade was not regained on the upgoing. Additionally as we all know, the thrust generated varies with the square of the speed, resulting in a further thrust loss.
The fix was simple, reverse the tail rotor gearbox through 180 degrees to become a 'left hand' tail rotor layout and hey presto, the upgoing blade is now receiving the benefit of the increased induced M/R airflow providing increased thrust and a more efficient rotor. (less tip induced drag !) This being the only drag that 'reduces' with increased speed !
Enstrom introduced the reversed 'left hand tail rotor' on all factory produced higher powered 'C' models and also offered a conversion kit for the earlier 28A's. Enstrom pilot's will still come across both 'left' and 'right' 28A types and a few 280's and should understand the lower tail rotor authority available to him on the unmodified right hand tail rotor. In addition the 'C' and later models were fitted with the wider 3.3 chord blade which further improved the situation.
With my selling boots on, a point I was always at pains to explain to prospective purchasers was the superb tail rotor control of the later layout, and usually demonstrated this by underspeeding the main rotor, (overpitching) to the point at which vertical lift was lost but even as the machine descended, the airframe could still be yawed to the left against the torque.
I hasten to mention this exercise was shown in a low hover !!!
Thanks for reading me and I now expect an 'expert' to enlarge on the dynamics of all this !!!
Fly safely chaps.
Dennis.
degrees and h9 so by the t