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BS W — Preformed Corrosion-Resisting Steel Wire Rope for Aircraft Controls (BS W 13:1973+A1:2014)
BS W 13:1973+A1:2014 — Aerospace Series Wire Rope for Controls
🔩 BS W 13:1973+A1:2014 is a British Standard for preformed corrosion-resisting steel wire rope used in aircraft control systems. It specifies the dimensions, construction, material, manufacture, testing and acceptance requirements for stainless steel wire rope used in flight-control runs such as elevators, rudders, ailerons, and in retraction and flap mechanisms. It is a key member of the British aerospace material “W” series (wire ropes). The amended edition came into effect on 31 March 2014, superseding and withdrawing the 1973 original, with updated material grades and test-method references.
💡 Wire rope in an aircraft control system transmits control force and displacement, and its fatigue life and corrosion resistance directly affect flight safety. Aerospace rope standards therefore impose far stricter material, construction and test requirements than general industrial ropes.
1. Series Overview and Positioning 📌
This article is the summary review for the “BS W” prefix of the BSB223 batch. The standard in this batch is BS W 13:1973+A1:2014. It specifies requirements for preformed corrosion-resisting steel wire rope conforming to BS ISO 2020-1 (Aerospace – Preformed flexible steel wire rope for aircraft controls – Part 1: Dimensions and loads) and BS ISO 2020-2:1997 (Part 2: Technical specification). The diameter, construction and minimum breaking strength accord with Recommendation No. 3310 of l’Association Internationale des Constructeurs de Materiel Aerospatiale (A.I.C.M.A.) and with the United States Military Specification MIL-DTL-83420M.
| Batch Prefix | Standard | Title | Status |
|---|---|---|---|
| BS W | BS W 13:1973+A1:2014 | Preformed corrosion-resisting steel wire rope for aircraft controls | Current (supersedes 1973 edition) |
Other wire-rope standards in this series include: BS W 9 (preformed galvanized carbon steel wire rope), BS W 11 (preformed corrosion-resisting steel wire rope) and BS W 12 (preformed galvanized carbon steel wire rope with ISO diameters and strengths). BS W 13 covers the corrosion-resisting (stainless) steel variant for corrosive and humid environments.
⚠️ Rope sizes larger than 6.4 mm (1/4 in) diameter, although included in MIL-DTL-83420M, are seldom used in modern aircraft and have been omitted from this standard. Always verify that the nominal size lies within the standard’s coverage.
2. Construction Types and Dimensioning System 🔧
Unlike earlier British standards that expressed nominal size by minimum breaking strength (in hundredweights), this standard expresses the nominal size by diameter. The rope construction is 7 x 7 or 7 x 19 according to size; 7 x 14 is no longer used.
| Construction | Typical Diameter Range | Characteristics | Typical Use |
|---|---|---|---|
| 7 x 7 | Smaller diameters | Better flexibility, moderate strength | Short control runs, secondary controls |
| 7 x 19 | Larger diameters | More flexible, fatigue resistant, higher load | Primary flight controls, high-load runs |
| 7 x 14 (obsolete) | – | Replaced by 7 x 7 and 7 x 19 | No longer used |
The strength/weight ratio of the new rope is higher than in previous standards, but a direct comparison is not possible because the nominal-size expression method changed. To meet the severe conditions in which rope operates in modern aircraft control systems, several aspects are specified more fully than in earlier standards.
3. Material and Manufacturing Requirements 🔥
3.1 Wire Composition and Mechanical Properties
Section 2 specifies the composition of the wire, examined for compliance with the general requirements of BS 6S 100:2010 (Aerospace series – Procedure for inspection, testing and acceptance of wrought steels, other than plate, sheet, strip and tube). Dimensional tolerances for the wire and grades of tensile strength are also given. As noted in the standard, the nearest equivalent steel is X5CrNi18-10 (1.4301) to BS EN 10264-4 (Steel wire and wire products – Steel wire for ropes – Part 4: Stainless steel wire).
3.2 Construction and Manufacturing Process
Section 3, which deals with the manufacture of the rope, specifies the construction in greater detail than earlier standards and introduces limits for length of lay. Key requirements include:
- Construction: 7 x 7 or 7 x 19 construction with defined lay-length limits.
- Internal lubrication: an internal lubricant is added with the aim of achieving a longer life.
- Elongation test: a test establishes that elongation stays within specified limits at stated increments of load, safeguarding control stiffness and travel.
- Corrosion resistance: the rope relies on the inherent corrosion resistance of the stainless steel wire; no separate galvanizing is required.
🚨 Lay length, lubrication and elongation characteristics directly affect control-system response and life. During installation, never forcibly twist, crush or use mismatched end fittings; any of these will significantly reduce fatigue life.
4. Engineering Application Points 🛠️
- 📋 Material traceability: use rope of the specified corrosion-resisting steel, request material certificates and verify grade and tensile-strength class.
- 🔗 End fittings: terminate the rope with aviation-approved end fittings, such as fork or spherical terminals, and apply preload and tension adjustment as specified.
- 📏 Tension and travel: pretension the rope to the tension values in the aircraft maintenance manual to avoid slack (control lag) or over-tension (additional loading).
- 🛡️ Inspection and life: periodically inspect for broken wires, wear, corrosion and lay-length changes; replace when the specified service life or broken-wire limits are reached.
- 📊 Lubrication maintenance: apply the specified aerospace grease to the external surface as required (e.g. Def Stan 91-51 helicopter oscillating bearing grease G-366/XG-284); internal lubrication is assured by manufacture.
✅ When selecting, confirm that the end fittings, pulleys and guides are dimensionally matched to the rope, and that the bending radius over pulleys is not less than the specified minimum, to control bending fatigue stress.
5. Frequently Asked Questions ❓
❓ Q: What is the relationship between BS W 13 and the BS ISO 2020 series?
A: BS W 13 is based on BS ISO 2020-1 (dimensions and loads) and BS ISO 2020-2:1997 (technical specification); it is the UK national expression of these international requirements within the aerospace material standard system.
A: BS W 13 is based on BS ISO 2020-1 (dimensions and loads) and BS ISO 2020-2:1997 (technical specification); it is the UK national expression of these international requirements within the aerospace material standard system.
❓ Q: Why did the standard change nominal size from breaking strength to diameter?
A: To align with BS ISO 2020-1 and the international aerospace material system for unified designation and interchangeability. The new rope has a higher strength/weight ratio but cannot be compared directly with older standards.
A: To align with BS ISO 2020-1 and the international aerospace material system for unified designation and interchangeability. The new rope has a higher strength/weight ratio but cannot be compared directly with older standards.
❓ Q: Why was the 7 x 14 construction discontinued?
A: 7 x 14 was superseded by 7 x 7 and 7 x 19, which cover the different diameter and flexibility needs and simplify the standard system.
A: 7 x 14 was superseded by 7 x 7 and 7 x 19, which cover the different diameter and flexibility needs and simplify the standard system.
🔍 Q: What does the internal lubricant do?
A: During repeated bending and transmission, friction occurs between strands and wires. The internal lubricant reduces friction and wear and inhibits internal corrosion, thereby extending fatigue life.
A: During repeated bending and transmission, friction occurs between strands and wires. The internal lubricant reduces friction and wear and inhibits internal corrosion, thereby extending fatigue life.
❓ Q: How do you decide when the rope has reached its replacement life?
A: Judge by the criteria in the maintenance manual and the standard, such as the number of broken wires, diameter reduction, lay elongation and corrosion; replace if any criterion is exceeded.
A: Judge by the criteria in the maintenance manual and the standard, such as the number of broken wires, diameter reduction, lay elongation and corrosion; replace if any criterion is exceeded.