Engineering Smart Technologies

SmartTab - Active Trim Tab for Rotor Blades

SmartTab Background

Helicopter blade systems are constructed to tight tolerances, but slight manufacturing variations and installation variances cause lift to vary from blade to blade at specific flight conditions.  The resulting unbalanced lift forces cause undesirable 1/rev vibration in the airframe.  Significant maintenance activity is required to ensure acceptable 1/rev vibration levels from main and tail rotors.  These flight and ground based maintenance activities translate into significant cost and downtime for the helicopter operator.  The rotor tuning adjustments typically used are blade pitch rod length adjustment, trim tab angle adjustment, and rotor weight balance adjustment.  These adjustments are manually implemented in a relatively inefficient way that is time consuming and sometimes prone to error.  Ultimately an overall system is desired that would enable relation of the results of the computerized diagnostic algorithm to the automated rotor adjustment implementation system in an automated way such that the changes are made in a quick, efficient, accurate, repeatable, and error free manner. 

The 1/rev vibration is minimized during rotor track and balance procedures that are required when vibration is determined to be out of balance and any time specific rotor maintenance has been done (e.g. blade replacement, rotor re-rig).  The current practice calls for aluminum trim tabs to be manually attached to the main rotor trailing edge (Figure 1) and adjusted in order to make slight adjustments to the lift.

Approach

Midé has developed an active trim tab system to help reduce the amount of maintenance required to perform track and balance procedures in the field.  Although the trim tab is only a portion of the complete track and balance procedure, the ability to adjust the setting automatically in conjunction with the other required adjustments, during operation, will save large operators like the US Army millions of dollars over the life of a fleet.  An active trim tab system also enhances the survivability of the rotorcraft, enabling changes to the rotor to make possible either the completion of the mission or a safe return to base.

Midé partnered with Sikorsky Aircraft during Phase II of a SBIR program funded by the (Aviation Applied Technology Directorate) AATD of the Army to develop an active trim tab.  Midé’s solution was based on implementing shape memory alloy (Nitinol) sheets as the trim tabs.  These tabs can deflect without manual input from maintenance personnel. 

Midé’s approach to automating trim tabs is highly advantageous over many prior attempts for a number of reasons.  The actuator is a solid-state device, meaning there are no mechanisms or motors that are more susceptible to failure during operation.  The tab itself is the actuator, thereby minimizing additional mass and complexity that other embedded systems inherently had.  No mechanisms need to be placed in a pocket in the blade, which simplifies blade manufacturing and trim tab installation.  Only power wires need to be run to the tabs, which can be accomplished relatively easily.

For more information:

Please email Attila Lengyel (Products), or call: 781-306-0609 x225

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