Aircraft Cable Tension Temperature Correction Calculator: Control Surface Rigging

Why Temperature Changes Aircraft Control Cable Tension During Inspection

Here is the scenario that plays out in shops across the country every summer. An A&P opens up a Piper Arrow on a 95-degree-F Arizona afternoon to do a conditional inspection. The aileron cable tensiometer reads 65 lbs. The maintenance manual says 40 to 55 lbs. The mechanic’s first instinct is that the cable was rigged too tight. Before touching the turnbuckle, he checks the temperature against the spec reference temperature of 70 degrees F and calculates the correction. The cable is actually within specification. The 25-degree temperature increase caused the tension to climb about 11 lbs above what it would read at 70 degrees. This is exactly what AC 43.13-1B Chapter 7 exists to address.

The physics behind this is straightforward. Aircraft control cables are made from steel wire rope. The aluminum airframe those cables are attached to expands and contracts at approximately twice the rate of steel when temperature changes. When the aluminum heats up and expands, the distance between the cable attachment points grows faster than the cable grows. The result is a net increase in tension. Conversely, on a cold morning in Minnesota when the hangar is 20 degrees F, the aluminum contracts more than the cable, reducing the effective cable span and lowering tension below the manual specification value.

Why This Matters More Than Most Mechanics Think

A 50-degree temperature swing from a cold winter morning to a hot summer afternoon produces about 11 lbs of tension change in a 1/8-inch 7×19 cable. In a system specified at 40 to 55 lbs, that 11-lb swing is enough to put a properly-rigged cable out of specification if the inspection happens at the wrong time of day. Worse, if a mechanic rigs the cable at peak summer heat and sets it to exactly 45 lbs (mid-range), the cable will read only 34 lbs at 70 degrees, which is below the 40-lb minimum. The cable will be out of spec for most of the year, introducing slack that can allow the cables to skip off pulleys or contact structure during maneuvering.

Steel Tube vs Aluminum Airframe

If both the airframe and the cable are steel (as in a Piper Cub, Bellanca Citabria, or Champion Decathlon with welded steel tube fuselage), the thermal expansion coefficients are similar and the net tension change is very small. This calculator lets you select the airframe material and applies a near-zero correction for steel tube aircraft. This is also why you sometimes see two very different rigging experiences: GA mechanics who work on Cessnas and Pipers regularly deal with temperature corrections, while mechanics on steel-tube light aircraft rarely see significant temperature-related tension changes.

How the Cable Tension Temperature Correction Formula Works in US Aviation

The AC 43.13-1B temperature/tension chart provides correction curves for each common cable size. The chart plots temperature in degrees Fahrenheit on the horizontal axis and rigging load in pounds on the vertical axis, with separate curves for each cable size. The curves slope upward to the right: higher temperature produces higher tension for aluminum airframe aircraft.

The Basic Correction Formula

For a simplified linear correction (which is a reasonable approximation within the normal operating temperature range of -20°F to 130°F for US GA aircraft):

• T_corrected = T_spec + CF x (T_current – T_reference)
• T_corrected = expected tensiometer reading at current temperature
• T_spec = tension specified in the maintenance manual at the reference temperature
• CF = correction factor in lbs per degree F (depends on cable size and airframe material)
• T_current = the temperature you are working at today
• T_reference = the temperature the spec was written for (usually 70°F)

For the rigging direction (what to set when rigging at a temperature other than 70°F):

• T_rig = T_spec – CF x (T_rig_temp – T_reference)
• T_rig = what you should read on the tensiometer when rigging at T_rig_temp

Correction Factors by Cable Size (Aluminum Airframe)

The following table shows the approximate temperature correction rates for each cable size in an aluminum airframe. These values are based on material properties per AC 43.13-1B and standard wire rope construction data. Your specific aircraft may have a different chart, and that chart takes precedence.

These values are approximate. The correction is slightly non-linear at temperature extremes. Always cross-reference with your aircraft manufacturer’s temperature/tension chart when available.

Aircraft Cable Sizes and Correction Rates for Common GA Cable Systems

Understanding which cable size is used in which part of your aircraft helps you apply the right correction factor. Most general aviation aircraft use a mix of cable sizes depending on the loads involved in each control system.

Common Applications by Cable Size

• 1/16″ 7×7: Trim tab pull-springs, secondary control links in light experimental aircraft. Rarely used in certificated GA aircraft primary flight controls. Very low correction rates due to small cross-section.
• 3/32″ 7×7: Throttle and mixture cables in older aircraft, pull cables for carb heat and cowl flaps. Sometimes used for aileron trim and flap control in very light aircraft.
• 1/8″ 7×7: Secondary control cables, trim systems in heavier single-engine aircraft. Less common than 7×19 of the same diameter.
• 1/8″ 7×19: The most common primary flight control cable size in US general aviation. Used for ailerons, elevator, and rudder on Cessna 172, Piper Cherokee, Beechcraft Sundowner, and many others. Medium correction rate.
• 5/32″ 7×19: Primary flight controls on heavier single-engine aircraft and light twins. Common on Cessna 182, Piper Arrow, Mooney M20 series. Higher correction rate than 1/8″ cable.
• 3/16″ 7×19: Used in primary flight controls for heavier aircraft, landing gear systems on light twins, and high-load secondary controls. Notable correction at temperature extremes.
• 1/4″ 7×19: Heavy structural uses, main landing gear actuating cables on retractable singles, cargo door systems. Largest correction rate in the common GA size range.

How to Find Your Cable Size

The cable size is specified in the aircraft’s Illustrated Parts Catalog (IPC) and the maintenance manual rigging section. On older aircraft, you can also measure the cable diameter directly with calipers (measure across the cable, not a single wire). The markings on the cable itself may also indicate the size. When in doubt, check the IPC by following the cable run from the control surface to the attachment point and identifying the part number, which will include the diameter and construction.

Three Real Rigging Temperature Scenarios from US General Aviation Shops

Expert Tips for Cable Tension Checks and Temperature Compensation in the Field

Check Early Morning or After Temperature Soak

The most reliable cable tension readings happen when the aircraft has been sitting in a stable temperature environment for at least 30 minutes. An aircraft that has been in direct sunlight can have skin surface temperatures 30 to 50 degrees hotter than the ambient air, especially on dark-painted surfaces. The internal structure and cable attachment fittings may be close to ambient, but the tension reflects a mixed temperature state that makes correction unreliable. Whenever possible, pull the aircraft into shade or into a temperature-stable hangar before checking tension.

Use a Calibrated, In-Date Tensiometer with the Right Riser

All the temperature correction math in the world is useless if your tensiometer is reading incorrectly. Most shop tensiometers should be calibrated annually. Make sure the riser number matches the cable size you are measuring, and that the calibration chart serial number matches your instrument. Pacific Scientific, Tensitron, and Sprague Instruments are common US manufacturers. Keep calibration records with the tool so you can verify validity at any inspection.

Record the Inspection Temperature Alongside the Tension Reading

When you enter cable tension in your maintenance records, always note the ambient temperature at the time of measurement. Without the temperature, a tension reading of 65 lbs on a 1/8-inch cable is meaningless: it could be in spec at 105°F or way out of spec at 70°F. Most FAA-compliant maintenance record entries for rigging include the inspection temperature as a matter of course.

Respect Automatic Cable Tension Regulators

If your aircraft is fitted with automatic cable tension regulators (common on heavier singles and light twins like the Piper Seneca or Cessna 310), do not attempt to use this calculator. The regulators are spring-loaded devices that maintain tension automatically within a set range across temperature changes. Adjusting turnbuckles to match a tensiometer reading on these aircraft will throw the regulator out of its operating range. The manufacturer’s maintenance manual will specify the correct procedure for checking and adjusting these systems.

Double-Check Both Sides of Symmetric Control Systems

Flight control cables typically come in pairs: one for each direction. Check both cables in any symmetric system (left and right aileron, forward and aft elevator loops). A temperature-driven tension change affects both sides simultaneously, but if one side was previously rigged differently or has more cable stretch, the two readings may diverge. Both readings should track with the temperature correction.

16 FAQs About Cable Tension, Temperature, and Aircraft Control System Rigging

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