Head above the parapet, shields up!
MG:
The maths, physics and aerodynamics are way above my pay scale, but I have benefited from the answers given. I asked the question originally because since becoming a student again, my long held belief that an aircraft hung low on one side because I was sitting on that side no longer holds true, as I sit behind or in front of my other crewmember. On asking an old sweat IP he tells me that the AH64, hangs left wheel low, not because of tail rotor drift and roll, but the balanced centrifugal forces acting through the fully articulated head.
So firstly I posted the question, secondly I watched the aircraft in the hover and though even though it sits 5 deg nose-up the TR is about level with the mast, which is higher (more level in the hover) than I’ve seen on my previous types because they were designed to be level in forward flight; my reasoning being that with the moveable stabilator on the AH64 the attitude can be controlled more throughout the speed ranges, so the hover attitude has been optimised for missile launch constraints/sensor sweeps etc.
So with a TR almost level with the MR, yet still hanging left wheel low, it must be to do with the TR drift, requiring a tilted disc – all normal. Because of the fully articulated mast, with offset hinges and a static mast, I reasoned the MR Head is canted off, so the body of the aircraft will tilt.
I enjoyed the discussion about c of g and disc relationships, as I had not thought of it anything other than the height of the discs before, but all are important. But when someone asks me why it hangs low, I shall tell them – “tail rotor drift (or the US equivalent), fully articulated head, static mast and balanced forces of c of g, wind, rotor heights and the way it was designed for maximum effectiveness to get hardware down range.
Now if only I could get a board plan, diagrams and some simple maths.
Nick:
Do hurry with that blue book, it may well be a best seller.
MG - PS after 4 weeks of flying and academics, it is calming down a bit. I start the bag on Friday, so I’m in the calm before the next storm. I shall let you know.