Brakes SPEC 5 April 2010.doc

N00019-09-R-0296

Attachment (2)

E-6B BRAKES MODIFICATION

PERFORMANCE SPECIFICATION

Document number: AS 6226

5 April 2010 Approved_________________________

Date_____________________________

1.0 Brake Physical and Performance Characteristics…………………………………3

1.1 Physical and Design Requirements……………………………………………3

1.2 Material Requirements………………………………………………………...3

1.3 Alternative Standards and Requirements……………………………………...3

1.4 Interchangeable Parts………………………………………………………….3

1.5 Tensile Stress Concentrations…………………………………………………4

1.6 Protective Treatments…………………………………………………………4

2.0 Wheel Assembly……………………………………………………………………..4

2.1 Rated Wheel Load…………………………………………………………….5

2.2 Defect-Free Wheel…………………………………………………………….5

2.3 Wheel Roll Life………………………………………………………………..5

2.4 Wheel Corrosion Protection…………………………………………………...5

2.5 Improper Wheel Assembly and Installation…………………………………..5

2.6 Proper Wheel Clearance………………………………………………………5

2.7 Wheel Operational Requirements……………………………………………..6

2.8 Wheel Reliability Requirements………………………………………………6

2.9 Wheel Marking Information…………………………………………………..6

2.10 Wheel Thermal Protection…………………………………………………...7

2.11 Rated Wheel Rolling Distance……………………………………………….7

3.0 Brake Assembly………………………………………………………………………7

3.1 Restricted Materials

3.2 Brake Protective Treatments…………………………………………………..7

3.3 Alternative Thermal Oxidation Protection…………………………………….8

3.4 Brake Rework Allowances……………………………………………………8

3.5 Brake Moisture Entrapment Prevention……………………………………….8

3.6 Weight of Brake and Wheel Assembly………………………………………..8

3.7 Brake Degradation…………………………………………………………….8

3.8 Brake Physical Characteristics………………………………………………...8

3.9 Brake Operating Environment………………………………………………...9

3.10 Brake Auxiliary Features…………………………………………………….9

3.11 Brake Part Marking…………………………………………………………..9

3.12 Wheel Bearings……………………………………………………………..10

3.13 Over-Inflation Protection…………………………………………………...10

3.14 Eutectic Fuse Plugs…………………………………………………………10

3.15 Piston Liners………………………………………………………………..11

3.16 Piston Stops…………………………………………………………………11

3.17 Automatic Adjusters………………………………………………………..11

3.18 Brake Running Clearance…………………………………………………..11

3.19 Visible Wear Indicators…………………………………………………….11

3.20 Repair Allowance…………………………………………………………..12

3.21 Rotor Lugs………………………………………………………………….12

3.22 Heatsink Clip Wear-out Life………………………………………………..12

3.23 Brake Oxidation Protection…………………………………………………12

3.24 Carbon Brake Refurbishment………………………………………………12

3.25 Brake Torque Coefficient…………………………………………………..12

3.26 Brake Operational Characteristics………………………………………….13

1.0 Brake Physical and Performance Characteristics

This section describes the physical and performance characteristics for the design and test of the E-6 wheel and brake assembly.

1.1 Physical and Design Requirements

The components of the wheel and brake assembly shall meet the requirements specified in the SOW. Workmanship shall be in accordance with high-grade aircraft practice, maintenance, and quality to ensure safety, proper operation, and service life. The configuration shall be compatible with total aircraft performance, maintenance, and operational envelopes. General design characteristics shall include the following:

a. The brake assembly and bias/radial tires shall tolerate external loads and braking action associated with proper performance IAW SD-569-1-4 during brake application while the aircraft is steered through a turn.

b. Be designed for installation at all main landing gear axle positions.

c. Be suitably formed to provide external contours as smooth and free from projections as practical.

d. Be furnished without fairings or provisions for fairings.

e. Allow for wheel removal without removing the brake assembly.

1.2 Material Requirements

The materials, parts, and processes used shall conform to approved specifications and be selected to accomplish the designated performance requirements. The Contractor shall be responsible for the selection of materials, parts, and processes that provide proven reliable performance with regard to all possible operating environments, particularly those environments identified in SOW paragraph 3.2.1 .

1.3 Alternative Standards and Requirements

The Contractor’s design approach may include alternative specifications and standards for materials, parts, and processes, but must show why deviation is necessary, and shall include substantiation data such as test data or in-service experience. Alternative specifications and standards shall be made available for review by the Government, and shall not be implemented without express written consent from the Government. Additionally, data rights for any unique alternative shall be delivered in accordance with contract requirements.

1.4 Interchangeable Parts

All parts of the brake assembly shall be suitably protected against corrosion internally and externally during the normal service life. The use of dissimilar metals in contact with each other shall be avoided.

1.5 Tensile Stress Concentrations

Sustained or residual surface tensile stress and stress concentrations shall be minimized to mitigate premature failures caused by stress corrosion. This requirement applies to design, manufacturing methods, assembly, and installation techniques. Practices such as the use of press or shrink fits, taper pins, clevis joints, and straightening and assembly operations that result in sustained or residual surface tensile stresses, shall be avoided.

Sustained or residual tensile stresses and stress concentrations shall be minimized to mitigate premature failures caused by repeated loads. This requirement applies to design, manufacturing method, assembly, and installation techniques. Consideration shall also be made for the damaging effect of decarburization and certain coatings that could interfere with the maintenance and safe operation of the E-6. Particular attention shall be given to optimum heat treatment procedures, corrosion protection, and material finish to minimize corrosion damage that may be the start of premature fatigue failure.

1.6 Protective Treatments

Protective treatments shall conform to approved mil standard corrosion specifications and be selected to accomplish the designated performance requirements in the SOW. The Contractor’s design approach shall include protective treatments that provide reliable performance with regard to the interface and all possible operating environments.

If in their design approach, the Contractor chooses to utilize alternative specifications and standards for protective treatment, then those alternative specifications and standards shall be made available for review by the Government, and shall include substantiating data such as test data or in-service experience. Alternative specifications may not be implemented without express consent of the Government. Additionally, data rights for any unique alternative shall be delivered in accordance with contract requirements.

2.0 Wheel Assembly

The wheel design shall be of the demountable-flange or the divided type to facilitate changing the tire. Demountable flanges or divided wheels shall be designed so that a failure of the joining bolts or retaining devices results in a benign failure where the tire pressure is rapidly released, eliminating the possibility of an explosive separation of the wheel flanges. The wheel shall be designed for a radial tire and a bias ply tire. The wheel rim contour shall conform to a 46” X 17” radial or bias tire, or a 49” X 17” radial (if feasible) tire, keeping in mind that that tire has to be compatible with the brakes, be physically able to fit inside the wheel well and meet the other requirements contained in the SOW. Other commercially available or military use tires of this size are preferred to a unique solution.

2.1 Rated Wheel Load

The wheel shall be capable of having a rated load of at least 39,600 lbs.

2.2 Defect-Free Wheel

The wheel rim between bead seats shall be free from defects or casing protrusions, and shall be smooth. No knurling or abrasion of the surface shall be allowed. Rivets shall not come in contact with the tire.

2.3 Wheel Roll Life

The main gear wheel shall be compatible with the axle currently on the E-6B, and shall be capable of a 25,000 mile roll life. The outboard diameter of the wheel shall not be greater than 23.52”, while the width of the wheel shall not be greater than 17.00”. The main gear wheel shall interface with either a 46” X 17” bias/radial tire (or a 49” X 17” radial tire if feasible).

2.4 Wheel Corrosion Protection

The wheel shall be protected from corrosion. All exterior surfaces of aluminum and aluminum alloy parts shall be anodized and shall be protected by one coat of primer, followed by two coats of polyurethane. All steel parts shall be plated (unless they are springs), unless operating temperatures prohibit steel plating. However, another form of corrosion protection shall be applied (chromium, zinc, or cadmium plating, etc.).

2.5 Improper Wheel Assembly and Installation

The wheel shall be designed to preclude improper assembly and installation. Special provisions shall be provided for installing wheel and break assemblies without damaging chrome-plated axle journals and the area between the journals.

2.6 Proper Wheel Clearance

The wheel shall be designed so that there is adequate clearance between the wheel and brake under all conditions. The requirement shall include consideration of tolerance stack-ups, free-play, axle and brake structure deflections, and thermal expansion.

The wheel assembly shall be capable of simultaneously withstanding the maximum acceleration in the radial directions (i.e. landing) and in the rotational direction during aircraft operations without impairing the function of the wheel and brake assembly. The brake shall perform satisfactorily IAW SD 569-1-4 in any aircraft environment during service. Brake-induced vibrations shall be stable and sufficiently damped to not cause damage to the internal wheel or brake parts, nor shall the vibrations degrade braking performance or damage any other part of the aircraft structure or systems, including electronic systems.

2.7 Wheel Operational Requirements

The wheel shall be capable of meeting the operational requirements of the E-6, including operating in altitudes up to 50,000 ft., relative humidities up to 100%, and be capable of operating in a salt-water environment. The wheel shall be fungus-resistant, an environment that is commonly encountered in tropical environments. The wheel and brake assembly shall also be capable of operating after exposure to sand and dust. The wheel shall be fully capable of operating from exposure to temperatures ranging from -65 degrees F to 160 degrees F.

2.8 Wheel Reliability Requirements

The wheel shall be required to meet the following maintainability and reliability requirements:

a. Wheel assembly on-aircraft – 2,000 MCBUM / 0.8 hours MTTR

b. Wheel assembly off-aircraft – 1.5 hours MTTR

c. Wheel assembly on-aircraft – 4,000 MCBF where MCBUM = Mean Cycles Between Unscheduled Maintenance

MTTR = Mean Time To Repair

MCBF = Mean Cycles Between Failure

One cycle is defined as one take-off and one full stop landing, including taxi to and from the ramp.

2.9 Wheel Marking Information

Integral lettering shall be required; nameplates shall not be used without substantiation of overhaul durability and Government approval. The wheels shall carry the following information:

a. Size of the tire used: i.e. 46X17 (or 49X17 if feasible) radial/bias tire

b. Serial number on both wheel halves, on demountable flange and wheel bodies.

c. Date of manufacture (month and year, i.e. Date of Manufacture – Jan. 2003).

d. All tie-bolt type wheels shall carry a warning note to require deflation of the tire before loosening of the tie bolts. This note shall be highlighted in red after painting the wheel.

e. Supplier’s name and part number on both components and assemblies.

f. Tie-bolt type wheels shall carry a suitable note to clearly describe the method of torque values used in tightening the tie-bolts.

g. Raised bosses in the wheel flange region shall be provided to vibra-peen overhaul information on the wheel flange.

2.10 Wheel Thermal Protection

A wheel heat shield shall be provided to minimize the heat transfer between the brake heatsink and the wheel. The following wheel heat shield design features shall be incorporated:

a. Segmented design to facilitate wheel maintenance and spare part storage.

b. Secure and undistorted wheel installation that prevents fretting of the wheel.

c. Materials and drains to improve durability in the event that a shield is immersed in water, snow, or other type of fluid.

d. Stiffness/protection that minimizes damage from wheel/tire assemblies.

e. Stiffness/protection that minimizes cracking, especially in the indentations.

2.11 Rated Wheel Rolling Distance

The wheel and tire assembly shall be capable of rolling for a distance of at least 25 miles at the wheel rated load without dropping tire inflation pressure by more than 5% or 5psi, whichever is less.

The wheel assembly shall support the ultimate combined load for a minimum of 10 seconds, after which there shall be no cracks in any area of the wheel.

3.0 Brake Assembly

Structural carbon-carbon composites can be used for the brake heatsink material. When used, metals in contact with the carbon material shall be considered dissimilar metals. Metals prone to galvanic attack in contact with graphite composite shall not be used. All carbon disks shall be traceable by batch or lot number to the brake serial number level. The design approach shall include material consistency tests for Government approval which shall be conducted on samples extracted directly from the production process and submitted, as required, for the acceptance tests.

The proposed brake assembly shall be of a three-rotor or four-rotor type, and shall exhibit maximum weight savings per unit weight without sacrificing stopping performance. It shall have a lightweight aluminum piston housing with a maximum of six (6) hydraulically-actuated pistons with a steel torque tube.

3.1 Restricted Materials

Beryllium, and magnesium (and alloys) may not be used for the brake heatsink material.

3.2 Brake Protective Treatments

Protective treatments (i.e. thermal oxidation coatings) shall conform to approved industry specifications and be selected to accomplish the designated performance requirements in the SOW. The Contractor’s design approach shall include protective treatments that provide reliable performance with regard to the interface and all possible operating environments.

3.3 Alternative Thermal Oxidation Protection

If in their design approach, the Contractor chooses to utilize alternative specifications and standards for protective treatments then those alternative specifications and standards shall be made available for review to the Government, and shall include substantiating data such as test data or in-service experience. Additionally, data rights for any unique alternative shall be provided in accordance with contract requirements.

3.4 Brake Rework Allowances

Sufficient rework material shall be provided to allow rework and repair of base material in historically troublesome areas, such as bearing bores, wheel drive key/beam key attachment locations, inflation valve, thermal release plug bosses, wheel tie bolt bosses, and brake attachment bushings.

3.5 Brake Moisture Entrapment Prevention

The brake assembly shall be designed to prevent the entrapment of moisture in any position, from fully extended to fully retracted. This may be accomplished by effectively sealing enclosed areas against the entrance of water or any other fluid, including hydraulic fluid or deicers. If moisture entrapment is inevitable, the design must include adequate drainage for the fluids. Cork seal, dams, and metal end plugs machined to fit shall not be used.

3.6 Weight of Brake and Wheel Assembly

The total weight of the wheel and brake assembly shall be such as to achieve the weight thresholds contained in the SOW. The weight for a combined wheel and brake assembly shall not exceed 270 pounds.

3.7 Brake Degradation

The brake assembly shall not suffer damage, deterioration or degradation of performance beyond the limits of the SOW when subjected to any environment or any natural combination of environments specified herein.

3.8 Brake Physical Characteristics

The brake heat stack shall be capable of fitting on an E-6 axle, and shall have the following physical characteristics:

a. Be capable of being fitted with a new wheel and compatible with a radial tire.

b. Have a maximum of six (6) brake pistons.

c. 25,000 mile roll wear-out life.

c. Have a 20” bead ledge.

3.9 Brake Operating Environment

The brake assembly shall be capable of meeting the operational requirements of the E-6, including operating in altitudes up to 50,000 ft., relative humidities up to 100%, and be capable of operating in a salt-water environment. The brake assembly shall be fungus-resistant, an environment that is commonly encountered in tropical environments. The wheel and brake assembly shall also be capable of operating after exposure to sand and dust. The brake assembly shall be fully capable of operating from exposure to ambient temperatures ranging from -65 degrees F to 160 degrees F.

3.10 Brake Auxiliary Features

The inclusion of any auxiliary features in the wheel or brake design, such as a tire pressure monitoring system (TPMS) or brake temperature monitoring system (BTMS) shall be optional at the request of the Government. The basic design of wheel and/or brake assembly shall include provisions for either of these two auxiliary systems, but not both. For example, provisions for a BTMS plug shall be built into the piston housing or brake assembly, but the actual BTMS plug mechanism need not be included in the design, unless specifically and explicitly approved by the Government.

3.11 Brake Assembly Reliability Requirements

The brake assembly shall be required to meet the following maintainability and reliability requirements:

a. Brake assembly on-aircraft – 1,000 MCBUM / 0.6 hours MTTR

b. Brake assembly off-aircraft – 2.0 hours MTTR

c. Brake assembly on-aircraft – 2,000 MCBF

c. Wheel and brake assembly on-aircraft – 4,400 MCBF where MCBUM = Mean Cycles Between Unscheduled Maintenance

MTTR = Mean Time To Repair

MCBF = Mean Cycles Between Failure

One cycle is defined as one take-off and one full stop landing, including taxi to and from the ramp.

3.12 Brake Part Marking

Automated vibrapeen or stamping is the preferred way of marking parts. Brake piston housings shall carry the following information:

a. Supplier’s name and part numbers on both components and assemblies.

b. Serial number.

c. Date of manufacture (month and year, i.e. Date of manufacture – Jan 2003).

d. Approved hydraulic fluid type.

e. Caution note on carbon heatsink brakes (if applicable): “Do not apply paints, cleaners, or deicers to carbon disks.”

f. Provisions for 2-dimensional bar coding and maintenance date stamping shall be provided in an easily readable location near the part number, serial number, or manufacture date.

Assembly part numbers shall be located on the part to be readable after installation of the part on the aircraft. Subassembly and detail part numbers shall be located to be readable after assembly in the complete unit whenever possible. Markings shall be located so that they shall not be obliterated or effaced as a result of service usage or become illegible due to the application of paint. Markings shall be as large as possible for the application area.

Each part and subassembly, except the following, shall be permanently marked with the appropriate part or subassembly part numbers:

a. Those that are permanently assembled by welding, brazing, soldering, or riveting shall carry the subassembly part number.

b. Those that do not have suitable or sufficient surface for the part number.

c. Those upon which marking would impair the function or structural integrity of the part.

3.13 Wheel Bearings

Means shall be incorporated to avoid misassembly of wheel bearings. The wheel bearing bore and seat shall be designed with a 0.060-inch repair allowance to accommodate a steel sleeve repair.

Suitable retainers shall be provided to prevent lubricant from reaching the braking surface and to prevent foreign material from entering the bearings. The retainers shall be removable to allow for cleaning and lubrication of the bearings. Wheel bearings shall be sealed on a stationary surface. Wheel bearing seals shall not be designed to rub on the stationary or permanent portion of the brake housing or strut. The rubbing surface shall be on an individual part that is inexpensive to replace so that any wear shall not cause condemnation of the brake or strut.

The valve seating/sealing surface shall include a minimum 0.030-inch allowance to rework the valve boss face. Valve core assemblies shall be selected from Tire and Rim Association standards currently in use with military services.

3.14 Over-Inflation Protection

Over-inflation protection devices shall be provided. The device shall be designed to release pressure at a rate faster than the maximum allowable inflation rate considering the diameter of the inflation valve port. The over-inflation valve shall contain or deflect any objects related to its release, such as broken diaphragm or ice particles, away from a person who may be servicing the tire at the time of release.

3.15 Eutectic Fuse Plugs

Thermal sensitive pressure release devices shall be designed and qualified to be used on the brake assembly. A minimum of three eutectic fuse plugs shall be provided and located in the wheel tube-well area approximately equally spaced about the wheel. Fuse plug ports shall be designed and located to allow rapid and unobstructed release of tire pressure. The fuse plug bore shall be designed with a large bore diameter with the rated temperature permanently marked on the face of the plug body. Fuses shall be designed to protect the aircraft design integrity at any wheel clocking position and at the highest possible eutectic melt temperature, with no credit allowed for cooling breeze. Fuse plugs shall release the tire pressure before a maximum allowable operating temperature is reached at any location, including the wheel, brake, axle, and/or hydraulic fluid.

Hydraulic fluid passageway restrictions shall not be less than 0.070-inch diameter without Government activity approval. Piston cylinder design shall be compatible with the brake assembly. Seals and glands shall be drawing-controlled by the approved supplier. Special bullets and solid back-up ring resizing tools to protect the O-rings on installation and to maintain back-up rings to correct size and shape are required to prevent premature brake failures.

3.16 Piston Liners

Piston liners shall be included in the piston assembly and be designed to be replaceable. If aluminum pistons and piston liners are used, the surfaces wiped by dynamic seals shall be anodized. The piston liner-to-piston housing thread shall be on the wet side of the static seal to facilitate corrosion prevention.

3.17 Piston Stops

Piston stops shall be provided and installed to stop the piston from falling out and prevent leakage of the hydraulic fluid when overextended. The piston stops shall allow piston travel after a maximum design gross weight rejected takeoff at the 100% worn brake condition with the maximum hydraulic operating pressure applied. The stops shall be designed for 150% of the maximum operating pressure without the brake disks installed.

3.18 Automatic Adjusters

Automatic adjusters shall be provided to compensate for brake lining wear. Friction adjusters shall not be used. Brake assemblies shall be designed for the most practical protection of the brake adjusters and shall be designed so they are integral with piston assemblies and the adjusting mechanism (swage ball and tube) shall operate dry. The adjuster swage tube shall be replaceable with requiring removal of the piston assembly. Hydraulic seals and fluid shall be kept at a maximum distance from the brake heatsink.

3.19 Brake Running Clearance

The designed running clearance shall be maintained at all wear stages and operating conditions of the brake. Running clearance shall be designed so that a dragging brake shall not be possible with consideration for tolerance stack-ups, free-play, axle and brake structure deflections, thermal expansion, etc. Running clearance shall be designed to minimize brake hydraulic response time.

3.20 Visible Wear Indicators

The brake assembly shall have wear indicators visible when performing a walk-around inspection with readily identifiable “go no-go” limits without requiring measurement. Wear pins shall require no adjustment or trimming (i.e. spring-loaded mechanism)

3.21 Repair Allowance

The brakes shall be designed with 0.060-inch repair allowance so that the bolt holes can be reworked with replaceable bushings to correct for wear or corrosion of the base metal. The brake backup structure shall be designed to promote even brake disk pressure and wear radially across the friction surface.

3.22 Rotor Lugs

If the brake employs a structural carbon heatsink (if applicable), the rotor lugs shall use clips or metallic structure to protect against damage. Chamfered entry shall be used on wheel keys and/or clips to facilitate alignment during wheel installation. Stator lugs shall be protected against wear and oxidation damage by either clips or some treatment on the steel brake structure.

3.23 Heatsink Clip Wear-out Life

Brake heatsink clips shall last the wear-out life of the heatsink. Clips shall be retained either directly or indirectly with stainless steel. Monel rivets shall not be used in a carbon-carbon heatsink. Flat head (tapered) solid rivets that might experience security problems in service shall not be allowed for clip fastening.

3.24 Brake Oxidation Protection

Exposed surfaces of a carbon-carbon heatsink, if applicable, shall be coated to protect against oxidation. The coating shall be formulated to provide adequate protection and not have an effect on the friction properties of the wear surfaces. The oxidation coating shall provide continuous protection throughout the life of the heatsink at least as long as the wheel thermal fuses have not released. The oxidation protection shall also be resistant, to the maximum extent possible, to fluid absorption, i.e. deicers, water, and hydraulic fluid.

3.25 Carbon Brake Refurbishment

If the brake disks employ a structural carbon heatsink, the heatsink shall be designed to take advantage of refurbishment methods such as 2-for-1 and thick-thin disk bonding. Refurbished heatsink qualification shall be approved by the Government before implementation. The refurbished brake disks shall be capable of providing the same service life as that of an original disk.

3.26 Brake Torque Coefficient

The average brake torque coefficient shall be repeatable with +/- 15% for a specific stopping condition at brake energies equivalent to service energy and up to brake energies equivalent to the overload energy condition. Above overload energies the requirement shall be repeatable within +/- 10%.

3.27 Brake Operational Characteristics

The brake assembly shall be capable of operating at a maximum of 3,000 psi of brake hydraulic pressure with removal of the deboost valves. The new brake assembly shall be capable of being integrated with the current Mark II anti-skid system and the current hydraulic system. The brake assembly shall also be capable of operating with the E-6 pneumatic (emergency) braking system.

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