Control Cables
Swaging end fittings; inspection for broken strands and wear; tensioning with a tensiometer and temperature correction; turnbuckle rigging and locking; Bowden and push-pull controls.
Control cables — summary notes
Free- Flexible control cables transmit pilot inputs to the control surfaces in a cable-operated system. They are made of stranded steel wire (carbon or corrosion-resistant) and terminated with swaged end fittings.
- A swaged fitting is formed by compressing the fitting onto the cable; the swage is checked with a go/no-go gauge for the correct compressed diameter, and a completed terminal is proof-loaded.
- Cable TENSION is set and checked with a TENSIOMETER, correcting for temperature because the airframe and cable expand differently — a rigging chart gives the tension for the ambient temperature.
- Inspection for BROKEN STRANDS is done by wiping a cloth along the cable (it snags on broken wires) or by passing it through the fingers; the acceptance limit is a stated number of broken strands per given length. Cable is also checked for corrosion, wear, kinks and 'birdcaging' (distortion of the strands).
- Cables run over pulleys and through fairleads; pulleys are checked for wear, flat spots, seized bearings and correct guarding, and the cable must not rub structure or a fairlead.
- Turnbuckles adjust cable length and tension and MUST be safetied — locked with locking clips or safety wire — with no more than three threads showing outside the barrel on either end.
- Bowden and push-pull (Teleflex) controls are alternatives for smaller ranges; they are inspected for free movement, backlash and security.
- ⚠ Exam trap: tension is temperature-corrected from the rigging chart, and a turnbuckle must show no more than three threads exposed and be positively locked.
- Tension
- set with a tensiometer, corrected to ambient temperature from the rigging chart
- Turnbuckle limit
- ≤ 3 threads exposed either end, and positively safetied
- Broken strands
- reject beyond the stated number per unit length
Why is control-cable tension adjusted according to the ambient temperature?
The airframe structure and the steel cable expand by different amounts with temperature, changing the cable tension. The rigging chart gives the tension to set for the current temperature so that the correct working tension exists across the operating range.
A turnbuckle in a control run is found with five threads showing at one end. Is it acceptable?
No. No more than three threads may be exposed outside the barrel; five means insufficient thread engagement, so the turnbuckle is not developing its full strength. It must be re-rigged to bring the exposed thread within limits and then safetied.
Control cables concept map
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Control cables quiz
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