Rotation direction of Tail Rotors: merged threads
Mightygem - nothing about wastelands would surprise me! One thing is for sure though, changing the direction of rotation on the Lynx TR to a clockwise one stopped the regular pirouettes of the Mk 1s - I think it is almost impossible, even in display manoeuvres, to run out of TR authority in a Mk7. Even when one of the Blue Eagles display pilots got clearance to experiment with yaw rates of 120 deg/sec in hover manoeuvres, the aircraft coped admirably. I have to say I have never seen Hampshire spin past the window quite as quickly since! Mac where are you?
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Igor Sikorsky always wanted the bottom blade to move toward the aircraft, if possible. The increase in efficiency is a good thing, but not critical, if one has a big enough tail rotor with enough collective pitch. The direction of rotation has a net influence of perhaps 5% on the available tail rotor thrust, easy to overcome if the tail rotor is powerful enough, but that 5% could be a whole bunch if the tail rotor is marginal.
On the old Cobras I flew (AH-1G's) the yaw was so poor that we ran out of tail authority in IGE hovers all the time, especially when the wind was from the left rear quadrant. Later models flipped the box over to the other side of the pylon, and the opposite rotation made things a bit better, but still not wonderful. The later model Cobras have a plot in the flight manual to show where you will run out of tail authority if you try to HOGE with a slight downwind at altitude.
On the old Cobras I flew (AH-1G's) the yaw was so poor that we ran out of tail authority in IGE hovers all the time, especially when the wind was from the left rear quadrant. Later models flipped the box over to the other side of the pylon, and the opposite rotation made things a bit better, but still not wonderful. The later model Cobras have a plot in the flight manual to show where you will run out of tail authority if you try to HOGE with a slight downwind at altitude.
Gatvol
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Nick
Not only true on the Cobra but the various models of the Huey. The difference between the UH-1 M (204) and the UH-1H (205) was so critical that folks had to be checked out to drive the UH-1M for things other than gun missions at High DAs. Major difference was a shorter tailboom on the M Model. I remember it well and as a Unit Trainer made sure those hot dogs flying M's were well aware that the reason for the Left Pedal smashing through the chin bubble meant you were too high, too hot and fast coming into a mountainous LZ. Next was the aircraft spinning when ETL was completely lost.
Not that it matters, but lots of folks dont know that the Military Huey (UH-1D, H, V etc) has the tail rotor on the left side, wheras the Civilian 205 has a larger corded one on the right side. Much better.
Not only true on the Cobra but the various models of the Huey. The difference between the UH-1 M (204) and the UH-1H (205) was so critical that folks had to be checked out to drive the UH-1M for things other than gun missions at High DAs. Major difference was a shorter tailboom on the M Model. I remember it well and as a Unit Trainer made sure those hot dogs flying M's were well aware that the reason for the Left Pedal smashing through the chin bubble meant you were too high, too hot and fast coming into a mountainous LZ. Next was the aircraft spinning when ETL was completely lost.
Not that it matters, but lots of folks dont know that the Military Huey (UH-1D, H, V etc) has the tail rotor on the left side, wheras the Civilian 205 has a larger corded one on the right side. Much better.
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History repeats itself
To: Mighty Gem
I can't believe that Westland would make a mistake like that considering that Sikorsky did the same thing on the H-37.
When they built the first H-37 they found that there was structural interference on the tail rotor drive shaft. In order to get around it they installed another gear set which made the shaft turn in the opposite direction. They reversed the tail rotor and changed the gears in the intermediate and tail boxes but they forgot to change the Archamedes (sp) pump in the tail rotor gear box and instead of moving oil to the outer bearings the pump took oil away from the bearings.
This may be apocryphal, but there was a story that when Westlands changed the direction of rotation of the Lynx tail rotor, they forgot about the worm drive in the gearbox that lifted the oil for lubrication. Hence it was going the wrong way and seized on the first test flight.
When they built the first H-37 they found that there was structural interference on the tail rotor drive shaft. In order to get around it they installed another gear set which made the shaft turn in the opposite direction. They reversed the tail rotor and changed the gears in the intermediate and tail boxes but they forgot to change the Archamedes (sp) pump in the tail rotor gear box and instead of moving oil to the outer bearings the pump took oil away from the bearings.
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Anyone know why there is a difference in the direction of rotation of the tail rotor between the R22 and the R44 ?
Early R22's used a cantilevered output shaft in the tail rotor gearbox (p/n A021) for a small form-factor (volume) and thus minimal weight. Cantilevering the output shaft placed the output gear on the left side of the input gear (when viewed from above), which results anti-clockwise tail rotor rotation.
To enhance serviceability, later R22 tail rotor gearboxes (p/n B021) do not use a cantilevered output shaft but still maintain anti-clockwise rotation direction to allow direct retrofitting. Advances in casting and machining methods result in no increased weight compared to the earlier A021 gearbox.
The R44 could afford a heavier tail rotor gearbox and therefore did not require a cantilevered output shaft. Since having the tail rotor's advancing blade closer to the main rotor downwash is more efficient, the R44's output gear was placed on the right side of the input gear, resulting in clockwise tail rotor rotation.
Both helicopters have significant tail rotor authority due to the use of asymmetrical tail-rotor-blade airfoils.
Google "square-cube law" for more on the importance of volume versus mass (i.e. size versus weight).
Fly safely.
