NOTAR Maintenance - No Sweat

NOTAR® Maintenance — No Sweat By Greg Napert September 1999 NOTAR (No Tail Rotor) helicopters were introduced in 1991 as a revolutionary way to provide anti-torque to helicopters while reducing noise and vibration associated with...


Strocks explains the pilot's pedals actually control three systems simultaneously. They control the vertical stabilizers, the pitch of the fan blades, and the thruster output. The vertical stabilizers are controlled differently depending on which model helicopter you're talking about. The 500N, for example, has one of the vertical stabilizers connected to the pilots rudder pedal — the other is controlled with the Stability Augmentation System (SAS). Both stabilizers are connected to the rudder on the 600 series, there is no SAS. And on the 900 series, each stabilizer is connected to the rudder pedal, and has a built in stability augmentation system.

The amount of air which is allowed to exit the tail boom at hover vs. at takeoff is controlled through rigging and is connected to the rudder pedals. When the pedals are in neutral, you have 25 to 27 degrees of pitch on the blade. So in a hover condition, you have enough air pumping through the boom for stability of the helicopter. If everything is rigged properly, the pilot should be able to hover without even having to touch the rudder pedals. When the pilot pushes a rudder pedal to turn the helicopter, the fan blade pitch is increased — which increases the amount of air exiting the tail boom and thruster.

Directional control of the tail boom is achieved through the rotating thruster. The rotating thruster is a two-piece assembly, which consists of a stationary thruster with cascades (airfoil shaped vanes) with two opposing openings and a rotating portion installed over it which rotates to either side.

Rigging
Rigging the anti-torque system involves rigging the vertical stabilizers, the fan, and the rotating thruster. A splitter assembly (bellcrank) at the top of the helicopter accepts the input from the rudder pedals and splits it into three outputs: for the fan, the thruster, and the vertical stabilizer(s).

Rigging starts at this bellcrank. The rudder pedals are placed in the neutral position, and the bellcrank is pinned for each item to be rigged. The bellcrank requires pinning at different locations depending on what you're rigging. Essentially, each system is rigged to the rudder pedals and is adjusted for neutral, full right rudder, and full left rudder. It's important to follow instructions in the appropriate maintenance manual for rigging each item.

Items to remember for rigging the NOTAR system include the following:
Fan controls
After adjustments are made to the fan controls, ensure blade is at 26 degrees ± 1 degrees. Note that the re-rigging of the thruster and empennage surfaces is not required when the tail boom is removed or reinstalled. Note that every 60-degree turn on the bearing retainer is equivalent to a 0.6 degree change in the fan blade pitch angle.
Thruster Control
In order to properly accomplish thruster control rigging, the fan assembly, tailboom, rod assembly, and stationary thruster cone must be installed. Also, if the stationary and rotating thruster cones are not properly aligned, hover performance is significantly affected.

With respect to rigging the thruster control, there are two important items to remember:

First, the NOTAR control system must be re-rigged after replacement of control rods, linkages and components, or if helicopter operation reveals a rigging deficiency.

Second, do not adjust the control rod end beyond the witness hole, or tighten jam nuts until after final adjustment.
Vertical Stabilizer Assembly
Rigging In order to rig the vertical stabilizers; the fan assembly, tailboom, rod assembly, and vertical stabilizers must be installed.

During the rigging procedure, it is important not to adjust the control rod end beyond the witness hole, and not to tighten the jam nuts until after the final adjustment.
Pilot's Pedal Rigging
The marked pin holes on the splitter assembly are as follows:
L = Full left pedal rigging hole
R = Full right pedal rigging hole
M = Mid pedal rigging hole

When rigging the pilot's pedal, the fan assembly must be connected. It is also important to remove the Pilot and Copilot pedal assemblies to prevent damage to the window glass during rigging.

If the optional dual controls are installed, adjust the copilot's pedals to the same limitation as the pilot's pedals. Both sets of pedals may be adjusted at the same time.

Maintenance
In addition to 100-hour and annual inspection requirements spelled out in the maintenance manual, there is relatively little to be done to the NOTAR system.

Although rare, one of the more common maintenance items that needs to be addressed is vibration of the fan assembly.

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