ENGINEERING FOR AIRFRAME CONTROL AND BALL BEARING ROD ENDS

Product catalog summary

General Information: RBC Airframe Control Bearings and Ball Bearing Rod Ends are designed to meet U.S. Government and Aerospace Industry Standards. They are lightweight, corrosion-protected, grease-lubricated, and typically sealed, suitable for oscillatory and limited rotation applications.

Precision: Bearings are available in "Standard" and "Precision" series, with the "M" prefix indicating precision. Ball Bearing Rod Ends are only available in the "Precision" series.

Material: Bearings are made from hardened AISI 52100 alloy, with cadmium or zinc nickel plating for corrosion protection. Stainless steel AISI 440C is also used for enhanced corrosion resistance. Ball Bearing Rod Ends use AISI 8620 or RBC AeroCres© Fracture-Tough material.

Performance: Performance data are guidelines, with load ratings assuming intermittent slow rotation. Consultation with RBC is recommended for continuous rotational applications.

Design Features: Bearings offer inch and metric sizes, corrosion resistance, high load capacities, PTFE seals, extended inner rings, and self-aligning designs allowing up to 10° misalignment. They conform to SAE-AS7949 and SAE-AS6039 standards.

Types of Bearings: Bearings are categorized into full-complement (no ball separators) and those with ball-separators. Full-complement bearings are for oscillatory motion, while ball-separator bearings can handle continuous rotation under light loads.

Standards of Quality: RBC bearings are manufactured to high standards, utilizing advanced manufacturing technologies to meet customer expectations.

Bearing Selection Considerations: Key factors include loads, motion, speed, bearing life, temperature, and operating medium. RBC Engineering can assist in selecting the optimal bearing.

Load Ratings: Limit Load Ratings are based on a study from 1949, with a formula involving load rating constant, number of balls, and ball diameter. Oscillating load ratings are available for 10,000 complete 90° oscillatory cycles.

Example Calculations: Examples illustrate bearing selection based on equivalent load calculations and oscillatory life requirements.

Specifications and Standards: The document outlines the specifications for ball bearings, particularly focusing on airframe control and ball bearing rod ends. It mentions the life basis for bearings at different RPMs and advises consulting RBC for other conditions. The SAE-AS7949 specification is highlighted as a key standard for airframe control bearings, with details on radial play and grease variations.

Procedures for Bearing Selection: Guidelines are provided for selecting bearings under combined loading conditions, including radial, thrust, and moment loads. The document provides formulas for calculating equivalent thrust load and safety factors, with examples for single and double row bearings.

Torque Considerations: Torque in ball bearings is categorized into inherent and induced torque. Inherent torque is influenced by factors like geometry, internal fit, bearing type, and lubricant, while induced torque is affected by external factors such as loads, speeds, fits, temperature, and contamination. The document emphasizes the customer's role in managing induced torque.

Design Criteria: Designers are advised to provide comprehensive application details to manufacturers to minimize torque. This includes information on speeds, loads, temperature, lubrication, materials, and environment.

Shaft and Housing Fits: The importance of maintaining specified limits for shaft and housing fits is discussed, as interference fits can significantly affect internal clearance and bearing performance.

Temperature Effects: Low temperatures can increase torque due to changes in housing fits and lubricant viscosity, particularly in applications with dissimilar metals like aluminum housings and steel bearings.

Misalignment and Loading: Misalignment can cause high torque and potential bearing failure. The document advises allowing for the largest possible bearing size to manage high torque due to loading.

Seals and Starting Torque Levels: Information on seal materials and their resistance to chemical attack is provided. The document also includes a starting torque chart, noting that laboratory conditions may not reflect real-world applications.

Inspection Limits: A comparison of inspection limits for standard versus precision series bearings is provided, detailing tolerances for bore, O.D., width, parallelism, squareness, radial eccentricity, face runout, and internal fit.

Overview: The document provides detailed specifications and guidelines for the engineering of airframe control and ball bearing rod ends, focusing on precision and standard series bearings. It includes recommendations for mounting, fit tolerances, and radial clearance considerations.

Specifications: The document outlines different series of bearings, including Precision MB544(DD) and Standard B544(DD), among others. It specifies the importance of mounting small, heavily loaded bearings with a light but positive interference fit to ensure proper operation.

Procedures: Recommendations are provided for staking or spinning the housing over the outer ring chamfer to secure the bearing axially. In applications with significant thrust load, a housing shoulder is advised.

Fit Tolerances: The document details minimum and maximum press fits for steel and aluminum or magnesium housings. It emphasizes maintaining housing bores within specified tolerances to avoid excessive interference, which can lead to preloading and reduced bearing capacity.

Radial Clearance: A small radial clearance is provided in most aircraft bearings. The document warns against excessive press fits that can eliminate this clearance, leading to preloaded bearings and reduced load capacity.

Tables and Data: The document includes tables with specific measurements for housing and shaft fits in both standard and precision series. These tables provide detailed dimensions and tolerances for various bearing sizes and materials.

Recommendations: For oscillating service, it is recommended to use shaft diameters slightly smaller than the nominal bearing bore size. The document advises against allowing housing bores to consistently run to the low side of tolerance to prevent extreme fits.

Catalog excerpts

ENGINEERING FOR AIRFRAME CONTROL AND BALL BEARING ROD ENDS-3

tightness and/or roughness when the bearing isspun in a misaligned position.A study of the internal design will show that in pure misalignment (not accompanied by rotation) the balls do not roll but skid across the ball raceway due to their wedging action.Any inspectors insistence that bearings be loosely fitted to insure ease of misalignment would be unjustified and might cause flutter because of sloppy controls.A reasonable amount of tightness in self-aligning bearings (not excess binding) will insure the desired rigidity in the control linkage system. Please adhere to instructions on shaft...

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ENGINEERING FOR AIRFRAME CONTROL AND BALL BEARING ROD ENDS-4

∑ K it is possible to calculate one equivalent load whichwould give the same number of cycles average life as the various loads.No one load may be greater than the limit load rating of the bearing.The equivalent load may be calculated from the formula:P = [ > AIRCRAFT CONTROLBEARINGS Taking the 1208 lb.Equivalent load (above) in anapplication where the heaviest of three radial loads is 2000 lbs.,we can proceed through the KP and KP-A Series locating the smallest acceptable bearing as follows.If there is no oscillatory life requirement stated andwe are setting up an overhaul period acording to...

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ENGINEERING FOR AIRFRAME CONTROL AND BALL BEARING ROD ENDS-5

AIRCRAFT CONTROLBEARINGS LIFE FACTOR CHART 1.0 -.9 -.8 -.7 -.6 -.5 -.4 -.3 - .2 - > Life Factor 10,000100,000 1,000,000 > Average Life Complete 90װ Oscillatory Cycles 5 size="-1">

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ENGINEERING FOR AIRFRAME CONTROL AND BALL BEARING ROD ENDS-6

We want to figure the Equivalent Thrust Load andthe safety factor on a KP10 (Single Row) bearing in an application where the radial load imposed is 4000 lbs., the thrust load is 200 lbs.,and the overturning moment load is 425 in.lbs. Substituting in the formula:Equivalent Thrust Load= (.44 X 4000 lbs.) + 200 lbs.+ (4.09 X 425 in.lbs.) = 3698 lbs. Safety Factor =(6200 lbs./3698 lbs.) X 1.68 > AIRCRAFT CONTROLBEARINGS When Radial Load,Thrust Load and Moment Loadare encountered in combination (all three or any two) on a single bearing mounting,we obtain an equivalent thrust limit load and select...

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ENGINEERING FOR AIRFRAME CONTROL AND BALL BEARING ROD ENDS-8

Once the bearings are ordered,the designer mustinsure that the mating components are consistent with his requirements.Particularly,he must hold housing and shaft fits within specified limits and maintain close control on roundness of these two dimensions.Interference fits directly affect the internal clearance in ball bearings,as much as 50% to 80% of the interference translates into reduced radial internal clearance,depending on the size of the bearing involved.Paralleling this situation,unequal heating of the inner and outer rings can have the same effect.Frequently,both conditions exist simultaneously;...

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ENGINEERING FOR AIRFRAME CONTROL AND BALL BEARING ROD ENDS-10

Standard Radial Reduced Radial Standard Radial Reduced Radial Play Play Play Play MS Fafnir MIL-G-81322 MIL-G-81322 MIL-G-23827 MIL-G-23827 Series Series Grease Grease Grease Grease MSFAFNIR MSFAFNIR MSFAFNIRMSFAFNIR Suffix Suffix Suffix Prefix/Suffix Suffix Suffix Suffix Prefix/Suffix 27640KP27641KP-A NONE FS464 R M/FS464 GFS428 RGM/FS428 27643DSP 27645KSP 27644DPP27646B500DD27648KP-BS NONE FS464 N⁄AN⁄A G FS428 N⁄A N⁄A 27649AW-AK 21428MB500DD 27647DW NONE FS464 R M/FS464 L M/FS464 RL M/FS428 27642KP-B(1) S > (1) FS464 G SG > (1) FS428 (1) MKP-B Series are used for MS27642 bearings with an S...

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