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Remediation Initiative – High Value Aerospace Gears

A new initiative is proposed to remediate high-value precision aerospace gears that have been removed from service because of surface damage (pitting, scouring etc.) before their design fatigue life has been reached. This initiative will use a unique convergence of proven technologies and test-and-evaluation methods to achieve robust and economical remediation.

Generally, surface damage in precision gears is first detected as surface staining or greying, which is in fact micro-pitting, a form of contact fatigue. Such damage can result in increased vibration, increased operational temperatures, and if continued without corrective measures, macro-spalls and a damage cascade with potentially serious consequences.

1,2,3 First-principals considerations indicate that a successful remediation of these highly critical components must meet six criteria:

  • All existing surface damage is fully removed or the effect of all surface damage is fully nullified

  • A fail-safe mechanism is incorporated in the remediation plan such that the fatigue resistance of the surface is restored to the original level (and preferably enhanced)

  • The gear meets all dimensional requirements

  • The surface finish of the gear meets or exceeds requirements

  • The wear resistance of the surface meets or exceeds requirements, and

  • The structural life and operational performance of the remediated gears is proven through a coupling of testing-to-failure and post-test failure analysis

As discussed in the next section, we propose to meet these criteria by using a unique combination of methods that comprises of:

  • The removal of surface coatings (typically black oxide) and (at least) a portion of the surface damage by superfinishing,

  • The nullification of any remaining surface damage by laser peening and the simultaneous restoration (or enhancement) of the fatigue resistance

  • The restoration of surface dimensions, surface hardness, and surface smoothness by depositing an advanced coating

  • If required, superfinishing the coated surface to further enhance the surface smoothness such that it meets or exceeds the design requirements, and

  • Implementing a test-and-analysis plan to ensure that the remediation is robust with respect to both the operational life and the mode and location of failure(s)

DTB Utilizes A Multi-Phase Approach



All gears will be dimensionally characterized to ensure that they meet all specified characteristics. Gear testing will include debris analysis and testing to failure using dual failure criteria: vibration levels, temperature rise, and debris accumulation for operational testing and crack initiation for structural testing.

Helicopter Critical Safety Item (CSI) Component Remediation

The costs, in both time and money, of replacement helicopter critical safety items (CSI’s) are a burden for all services. Very often these components, besides being expensive, have long lead times and are often made from specialized forgings that have even longer lead times.

Ramping up production rates is a multiyear process that impacts warfighter readiness and severely curtails surge capabilities to respond quickly to operational needs. Helicopter platforms such as the CH-47, UH-60 and AH-64 are all currently being operated in aggressively damaging environments that require a steady supply of new CSI components to replace those found to have dings, nicks and scratches in excess of allowable. Also when these aircraft are brought back to depots for overhaul, numerous components are replaced for wear or damage rather than due to reaching their calculated retirement life (CRL).

Data shows that 80% of CSI components that are replaced are done so due to reasons of wear or damage, not because of reaching their CRL as tracked by flight hoursi.

army helicopter life expectations graph

Figure 1. Many CSI’s Do Not Achieve Design Fatigue Lives (Ref 1)

Under the AMCOM Alternate Source Testing Contract (Contract No.W58RGZ-05-C-0318) DTB has tested over 100 different components and can easily and quickly conducted qualification fatigue testing for the following components on active helicopter platforms listed in the table below.

AH-64 Drive Shaft and Plate UH-60 Swashplate Assy, Stationary M/R Head
AH-64 Strut Assemblies UH-60 Forward Longitudinal Swashplate Link
AH-64 Controllable Swashplate UH-60 T/R Gearbox Housing Assembly
AH-64 M/R Head Lead Lag Link Assy. UH-60 Main Rotor Bifilar Support
AH-64 AH-64 UH-60
AH-64 Rotor Support Assembly Self Locking Bolts UH-60 Lateral Servo Rails
AH-64 Pitch Link Rod End UH-60 Main Rotor Shaft Extension
AH-64 Pitch Link Assembly UH-60 M/R Spindle Horn Assembly
AH-64 Main Rotor Drive Shaft UH-60 Stabilator Actuator Clevis Assembly
AH-64 Rotor Brake Actuator and Disk UH-60 Forward Push Rod
AH-64 Pitch Housing Assembly UH-60 Main Rotor Spindle Horn Assembly
AH-64 Fwd. Long. Mixer Bellcrank UH-60 M/R Pitch Control Barrel
AH-64 M/R Upper Controls, Scissors Assy. UH-60 Stabilator Actuator Assembly
AH-64 Lateral Mixer Bellcrank Assy CH-47 Yoke Shaft Support
AH-64 Bellcrank, Aft Longitudinal Mixer CH-47 Horizontal Hinge Pin, Aft Pitch Shaft
AH-64 Upper Collective Bellcrank Assy. CH-47 Aft Pitch Housing Assembly
AH-64 Fwd Longitudinal Bellcrank CH-47 Swashplate Rotating Ring
AH-64 Stabilator Actuator Fitting CH-47 Outboard & Inboard Pin Assemblies
AH-64 Main Rotor Damper Trunnion Assy CH-47 Vertical Hinge Pins
AH-64 Tail Rotor Driveshaft Studs CH-47 Housing Assy Blade Lag Shock Absorber
AH-64 Bellcrank CH-47 Hydraulic Cylinder
UH-60 Aft. Long. Swashplate Link CH-47 Drive Coupling
UH-60 Clevis Assembly, Stab. Act. Attachment CH-47 Fwd. Slider Shaft Assembly
UH-60 Push Rod CH-47 Aft Yoke Assembly
UH-60 Bifilar Assembly CH-47 Fwd. & Aft Rod Assemblies
UH-60 Manifold, T/R Servo Coupling CH-47 Fwd. Yoke Shaft
UH-60 Main Rotor Spindle, Spindle Nut - Axial Load CH-47 Swashplate Rotating Ring
UH-60 Main Rotor Spindle - Damper Attach CH-47 Outboard Tie Bar Pin Assy.
UH-60 Main Rotor Spindle - Horn Attach CH-47 Vertical Hinge Pin
UH-60 Main Rotor Spindle - Droop Stop CH-47 Upper Drive Arm & Bolt Assys
UH-60 Transmission Dowel Pins CH-47 Slider Shaft Assembly
UH-60 Pitch Control Rod Lower & Upper Ends CH-47 Aft Yoke Assy/Aft Yoke Support Shaft
UH-60 Main Rotor Spindle CH-47 Fwd & Aft Fixed Link Rod
UH-60 Push Rod CH-47 Fwd. Yoke Support Shaft
CH-47 Rotor Hub CH-47 Aft Slider Shaft Assy.

Remediation techniques that will be utilized include, but are not limited to:

a. Finite element analysis of the components

b. Laser peening

c. Interference fit bushings

Cold Spray Aluminum:


1P. J. Dempsey, R. F. Handschuh and A. A. Afjeh, Spiral Bevel Gear Damage Detection Using Decision Fusion Analysis, Fifth International Conference on Information Fusion sponsored by the International Society of Information Fusion, Annapolis, Maryland, July 8–11, 2002.

2S.B. Rao, Gear Technology, May 2009 44-45.

3 S. Rao, D. McPherson, and G. Sroka, Repair of Helicopter Gear, American Gear Manufacturers Association, 05FTM15, October 2005.

4T. Uros, Ž. Sebastjan, G. Janez, and O. Jose Luis, Pre-Print, Emerald Group Publishing Ltd.

5P. Niskanen, A. Manesh, and R. Morgan, The AMPTIAC Quarterly, Volume 7, Number 1, 2003.

6Bodycote, Conover, NC.

7Diamonex Division of Morgan Advanced Ceramics Inc., Allentown, PA.

8Balzers Tool Coating Inc, North Tonawanda, NY

9R. F. Handschuh, NASA TM−106518 (1995).

10 R. F. Handschuh, NASA/TM—2001-210743 (2001).

iWhite and Vaughan, Fleet Usage Monitoring is Essential In Improving Aging U.S. Army Helicopter Safety, Availability and Affordability, 9th Joint FAA/DoD/NASA Aging Aircraft Conference

iiCold Spray Process Development for the Reclamation of the Apache Helicopter Mast Support by P. F. Leyman and V. K. Champagne, August 2009


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