What is the percentage lost to powering the tail rotor? I read different figures: 10 to 30%...
The main rotor absorbs most of the helicopters power, but there are other losses as well. The engine and transmission absorb 3% to 5% of the total power with turbine engines, or 5% to 9% with reciprocating engines. The turbine engine has larger transmission losses since its high rotational speed requires more reduction, whereas the piston engine has significant losses for cooling.
The tail rotor absorbs about 7% to 9% of the total helicopter power in a hover and as much as 10% to 15% during max sideward flight to hold heading. You’ll have to see what flight regime they were testing to get that 30% number on the tail rotor.
Additional loss of about 2% due to aerodynamic interference rotor-fuselage and rotor-rotor. The tail rotor and aerodynamic interference power losses are much smaller for the helicopter in forward flight. Because of the fuselage download produced by the rotor wake, the rotor thrust is 4% to 7% larger than the gross weight, producing a corresponding increase in required power.
What you need to gain from this is the relationships between the dynamics, such as, how the Disk Load affects the performance and power required, not always an exact number, but an approximation. I can’t count the number of flight test that I have done, were after all the data had been compiled, the Chief Engineer (name prefixed with "Dr.") comes back and says, we don’t really understand why the data doesn’t match our calculations, we’ll need to do additional testing to understand what the dynamics are and what’s missing.
In your search for exactness, don’t feel bad if it sometimes alludes you. Sometimes it’s not achievable under the circumstances.
It is the mark of an educated mind to rest satisfied with the degree of precision which the nature of the subject admits and not to seek exactness where only an approximation is possible.
Edited by iChris, 23 May 2017 - 04:09.