tail rotor drift
im havin a bit of bother figurin out what tr drift is. dose any one no how to explain it in layman terms? and hw dose it effect a h369 (hughes c with a c18 alison)
PPRuNe Enigma
Joined: Feb 2001
Posts: 427
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From: Scotland
OK - your tail rotor is there to generate a torque to counteract the turning effect of the engine pushing the main rotor around.
To do this, the tail rotor shoves a load of air sideways, thereby generating a horizontal force. Because the tail rotor is a long way from the main rotor mast - stuck out at the end of the tailboom - this makes a torque (force * distance from the axis of rotation) that stops the body of the helicopter spinning around.
BUT - there is now a net sideways force on the helicopter, so it will start to drift to the right (for anticlockwise turning rotors). Often this is counteracted by rigging the main rotor mast a degree or two off vertical.
Of course it doesn't stop there... Because the tail rotor is lower than the main rotor you now have a couple that will roll the body to the left, so the machine tends to hover left skid low, which is one reason why the pilot has to sit on the right.... and so on it goes.
To do this, the tail rotor shoves a load of air sideways, thereby generating a horizontal force. Because the tail rotor is a long way from the main rotor mast - stuck out at the end of the tailboom - this makes a torque (force * distance from the axis of rotation) that stops the body of the helicopter spinning around.
BUT - there is now a net sideways force on the helicopter, so it will start to drift to the right (for anticlockwise turning rotors). Often this is counteracted by rigging the main rotor mast a degree or two off vertical.
Of course it doesn't stop there... Because the tail rotor is lower than the main rotor you now have a couple that will roll the body to the left, so the machine tends to hover left skid low, which is one reason why the pilot has to sit on the right.... and so on it goes.
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
Sometimes called "Translating Tendency" it is the sideward drift to the left when you do an engine cut in a hover.
The bank angle in a hover (3 degrees or so) is needed to fight the force the tail rotor is shoving against the aircraft. This bank angle is proper when there is torque on the main rotor (and therefore thrust on the tail rotor). When you chop throttle in a hover, you put a boot full of right pedal to keep the nose straight. This reduces the tail thrust to near nil, so you must take out the left bank angle. If you don't, you get the left sideward drift.
The bank angle in a hover (3 degrees or so) is needed to fight the force the tail rotor is shoving against the aircraft. This bank angle is proper when there is torque on the main rotor (and therefore thrust on the tail rotor). When you chop throttle in a hover, you put a boot full of right pedal to keep the nose straight. This reduces the tail thrust to near nil, so you must take out the left bank angle. If you don't, you get the left sideward drift.
Joined: Oct 2003
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From: Over here
The tail rotor is just a variable-pitch propeller. It's trying to propel the helicopter to the side, and the main rotor is banked to prevent that. When the pitch of the propeller is changed, the thrust is changed. Not much more to it than that.
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
Posts: 10,959
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From: EGDC
The tail rotor blows air sideways pushing the helicopter the opposite way - to stop the drift you tilt the main rotor in the opposite direction to the drift with lateral cyclic. When the rolling couple formed by the TR thrust and the horizontal component of MR thrust are balanced by the opposite rolling couple provided by the mass acting through the C of G and the vertical component of MR thrust - then you should be in a hover over the ground with one skid lower than the other. Try putting the 'wings level' in the hover and the helicopter will translate laterally (move sideways).
Once you have that sorted then start thinking that TR thrust never goes away and that 'inherent sideslip' is a fact of life in a single rotor helicopter, you can fly in balance or wings level but not both at the same time.
Once you have that sorted then start thinking that TR thrust never goes away and that 'inherent sideslip' is a fact of life in a single rotor helicopter, you can fly in balance or wings level but not both at the same time.
