Flexible shafts transmit rotary motion much like a solid shaft, but can be routed over, under and around obstacles where a solid shaft cannot be used. Flexible shafts are used in a variety of applications, including many capacities in aerospace — such as in thrust reverser actuation systems, flap and slat systems, variable bleed valves, jet afterburner nozzle control systems, cargo door actuation systems, valve override and many more.
While used in many systems on various aircraft, one significant aerospace application is to manually actuate valves if the automatic system in place were to fail. Any number of valves may be manually actuated using a flexible shaft assembly, including Air Turbine Starter and anti-ice valves, as well as those applications mentioned in the paragraph above.
The ability to control the valves manually in the event of the automated system’s failure means the aircraft can still be safely “dispatched” on time, avoiding the time and costs associated with having to find a substitute aircraft.
In addition to the ability of flexible shafts to enable manual overrides of aircraft systems that are usually automated, they are also the preferred rotary motion technology in aerospace applications for a number of other reasons.
Benefits of flexible shafts include:
- eliminate alignment problems
- dampen vibration
- absorb shock
- accommodate relative movements
- possess a 3:1 weight advantage over other design solutions while transmitting greater power loads
- lower overall cost due to fewer parts needed and faster installation time
- provide greater design freedom than other shaft technologies
S.S. White manufactures custom flexible shaft solutions designed for specific applications.
The company produced its first flexible shaft in 1874 for a high-speed dental engine used for drilling teeth. Today, its flexible shafts for aerospace applications are used in thrust reverser, flap, slat actuation systems and manual overdrive systems of air and space craft, in the ammunition magazine drive of the AC-130, in many Airbus & Boeing thrust reverser systems, in the Hubble Space Telescope, on the international space station and as part of the V-22 Osprey’s rescue hoist system.