Redesigning for Flutter

    When the second Grob SPn prototype crashed near the company airfield in Tussenhausen-Mattsies, Germany, on November 29, 2006, both elevators and the port horizontal stabilizer were found hundreds of meters from the main wreckage. There was no data as to the test pilot's speed but the aircraft was accelerating at the time for a demonstration low pass. It crashed 1.5kms off the runway end. The highly experienced 45 year old experimental test pilot Gerard Guillaumaud did not have the time or priority for a distress call as the jet broke up. Weather and turbulence have been eliminated as factors.
    There had been redesign of key control surfaces on aircraft number two to accommodate anti-icing requirements and to provide more roll authority. The belly fairing's leading edges had also been re-profiled. Aircraft #2 [D-CGSP] was equipped with larger ailerons and a longer horizontal stabilizer (than aircraft No. 1). It also had different elevator hinges. Aircraft No. 1 had flown its full flight envelope up to 41,000 feet and Mach 0.8, but D-CGSP had yet to do so. The inference is that the flight envelope should have been restricted for the 29 Nov 06 flight because of all the un-flight-tested structural modifications.
    An initial factual statement from the German accident investigation agency BFU indicates that elevator flutter had quickly led to a separation of the control surfaces that were found scattered 400m short of the impact point.
    The $7.1 million Grob SPn is powered by two Williams International FJ44-3A engines and is designed to be flown single-pilot and have a range of 1,800 nm with six passengers. The first protoype SPn is expected to begin flying again within the next two weeks.