Altra takes prototype order from helicopter manufacturer
Altra Industrial Motion, through its Formsprag Clutch business, has received the first prototype order from a leading European helicopter manufacturer for sprag retainer assemblies for a new helicopter project.
Formsprag sprag retainer assemblies offer numerous patented features that boost helicopter performance and lifespan, as well as assure safety of operation. With increasing speeds and power placing demands on freewheels that simply cannot be met by roller type clutches, Formsprag sprag retainer assemblies address this need by offering high torque density freewheels with overrunning speeds of up to 38,000 rpm.
Altra Industrial Motion is a leading supplier of power transmission solutions to the aerospace industry – a sector which has drawn on the expertise of the companies within the Altra group for over five decades. In particular, helicopter manufacturers around the world put their trust in Altra Industrial Motion to deliver the right product to meet their most demanding requirements.
Among the many products the company supplies, the Formsprag sprag retainer assembly has become the freewheel of choice in critical helicopter applications, including transmissions, engine and auxiliary power unit (APU) starters, and accessory gearboxes. For example, Formsprag sprag retainer assemblies are regularly used in the driveline gearboxes of multi-engine helicopters to allow twinning of the engines for efficient power sharing and synchronisation or disengagement of one engine.
Formsprag freewheels offer a number of unique design features that make them irreplaceable in helicopter applications, as well as in many fixed wing aerospace tasks. The Formsprag sprag retainer assembly is a free action design that permits each sprag to have free and independent action. This independence allows each sprag to adapt to variations in annular space (eccentricities) so that when the clutch is engaged, the load is proportionally shared among all sprags, eliminating the possibility of clutch damage resulting from the entire load being absorbed by just a few sprags. This ensures dependable performance without compromising size, weight or cost.
Formsprag freewheels offer many other unique features that set them apart from competing products in the aerospace industry. The Formsprag positive continuous engagement (PCE) design prevents sprag rollover during torque overload conditions – a vital safety feature in aerospace applications. The patented PCE retainer was developed specifically to meet the demands of high performance helicopter and aircraft applications. It provides reliable performance even under extremes of torsional vibration and severe transient overload, and is ideal for confined space applications where minimal weight is critical.
For extended operational life in demanding applications, Formsprag freewheels are manufactured using the company’s Formchrome process, which diffuses chromium carbide into the working surfaces of the sprag, increasing its surface hardness substantially to deliver excellent wear protection. Through a variety of specifications matched to the application requirements, Formchrome can be utilised to increase the surface hardness of the base metal – SAE 52100 steel – from 800 Knoop (approximately 63 Rc) to around 1,300 Knoop (equivalent to 75 – 80 Rc), or even 2,000 Knoop (equivalent to 90 – 95 Rc). Subsequent heat treatment ensures a hard sprag core to support the chromized surface.
In operation, springs energise the sprags into position for instantaneous engagement with no backlash. Contracting, expanding and torsional springs have been developed by Formsprag, allowing the company to provide the best possible spring technology to meet specific application requirements. For high speed overrunning applications that are typical in helicopter systems such as starters, Formsprag’s centrifugal throw-out (C/T) design locates the centre of gravity of the sprag relative to its contact point on the outer sprag diameter, such that when the outer race is overrunning the centrifugal force on the sprags overcomes the energising force of the springs. This causes the sprags to completely lift off the inner race, with the advantage that there is no rubbing contact during operation, further extending the lifespan of the assembly. Formsprag has the only true C/T system with close control over disengagement and re-engagement speeds.
Altra Industrial Motion understands the unique requirements of the aerospace market, and has in place the systems and processes to assure uninterrupted supply of product for both military and commercial applications. Because many aerospace applications are considered flight safety and mission critical, Altra Industrial Motion has established the systems and procedures necessary to support success; these include manufacture to ISO 9001:2008 and aerospace-specific AS9100 rev B quality standards. The company also holds a number of customer source inspection delegation certifications for leading global aerospace customers and is committed to continuous improvement through the Altra Business System (ABS).
“With products designed specifically to address to some of the most challenging applications in the aerospace industry, and with processes and systems in place to assure the high levels of quality that the aerospace industry requires, Formsprag Clutch is unmatched in its ability to meet customer requirements in this sector,” says Altra’s John Dunstone. “That’s why the aerospace industry has been putting its trust in Altra for over 50 years, and why Altra continues to lead the field when it comes to demanding aerospace solutions.”
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