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Technology update
Carbon-fiber GROBs
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GROB-Werke is to supply the UK Royal Air Force with its
G 115E aircraft for basic training. The G 115E is the latest in the 115 series and is manufactured almost entirely of carbon-fiber-reinforced composite. According to the company, repairs are to be both quick and less expensive to achieve. The airframe is designed to be damage-tolerant. "Therefore no life-limitation is applicable," said GROB. This was shown for all certified aircraft during an extensive series of static and fatigue testing, taking into account the damage tolerance requirements of the FAA. GROB adds that the aircraft has been designed to avoid "as far as practicable" points of stress concentration where variable stresses above the fatigue limit are likely to occur in normal service. An initial fatigue life of 12,000 h (with a time between major airframe inspection of 4000 h) has been established for the G 115E by the certification authorities.
The fatigue life of the aircraft is based on an evaluation of its wing, which was tested for up to 36,000 h with a safety factor of 3. In general, the evidence from the company's testing and operation of the composite aircraft revealed that metal parts of the structure were more likely to suffer fatigue. To reduce the likelihood of fatigue failure, low stress levels and high safety factors are used for metal parts. All critical metal structural parts can be replaced without the need for special jigs or tools. In some cases, a composite repair shop is required.
The G 115E uses a four-cylinder Lycoming engine and is fully aerobatic. The RAF will take delivery of 99 units, which will join other GROB aircraft including gliders and motorgliders.
The lead version of the G 115 range is the TA, which was designed to meet U.S. MS33574 and Mil. Std. 850. It is manufactured from carbon/glass-fiber-reinforced composite. GROB said that the aircraft structure has demonstrated an initial life of 15,000 h, which can be extended on the evidence of a structural audit. It includes a new composite seat recessed to accommodate a parachute and designed by specialist manufacturer Fischer Developments. It has a mass of
7 kg and is stressed to withstand accelerations up to +25 g. The airframe of the G 115TA is certified to +6 g and -4 g. Equipment of the TA includes an aural prompt facility giving spoken warnings of mishandling in flight, or potential systems problems. An air conditioning unit may be specified; the airframe is certificated to operate in temperatures up to 72°C. The TA's powerplant is a six-cylinder Lycoming driving a Hartzell three-blade constant speed propeller. The undercarriage is retractable.
Stuart Birch
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