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AH64 tail rotor
Hi Tim,
When Hughes Tool Co., Aircraft Division experimented with the OH-6A to make it very quiet, the engineers knew that a big source of noise was the tail rotor. To make the tail rotor quieter, they decided to increase the blade area and decrease the rpm. The most convenient (i.e., least costly) method was to simply add another set of teetering blades to the tail rotor. In addition to the addition of more blades, Hughes engineers experimented with blade phasing to decrease the noise level as much as possible. As I remember, the phasing they decided upon was about 45 deg. When the AH-64 Apache came along, the Hughes engineers incorporated what they had learned from the OH-6A development work. The same basic design for the tail rotor of the quiet OH-6A was incorporated into the Apache design; two pairs of teetering rotor blades. The same concept was used on the 4-bladed tail rotor option on the MD 500D, E, and FF series of helicopters. The one additional requirement for the Apache was to fit into a C-130 transport without disassembling the rotors. In order to meet this requirement, the tail rotor blade spacing was changed to the 30 deg spacing you found. The noise signature suffered a litttle bit, but the transportaion requirement was met. |
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