Watch One Of The Most Dangerous Tests Done On A New Airliner
Before any new aircraft can carry passengers its must undergo a great deal of testing both on the ground and in the air. “Velocity Minimum Unstick Testing” (Vmu Test) is one of the most fascinating and dangerous flight tests in the certification schedule of any new airliner. Bombardier's new CSeries jet is going through that process now at their facility in Salina, Kansas. It involves dragging tail along the runway on take-off.
The test is complex and the evaluations determine the minimum aircraft speed required for takeoff in various configurations. After an accident with the De Havilland Comet in the 1950s, authorities needed re-assurance that if a pilot mistakenly pulls back on the control stick too early (putting the aircraft's tail on the ground) it won't cause an accident. The aircraft should be able to take off and climb.
Video 1 below: Bombardier have put together a great video demonstrating how and why its done.
Video 2 below: Airbus Vmu testing on their A350 XWB 2014.
Photos below the videos: Bombardier
The Comet Crashes
In a 1952 a BOAC De Havilland Comet departing Rome's Ciampino airport failed to become airborne and ran into rough ground at the end of the runway. Two passengers sustained minor injuries, and the aircraft was a total loss. A year later a new Canadian Pacific Airlines Comet 1A named Empress of Hawaii, failed to become airborne while attempting a night takeoff from Karachi, Pakistan. The delivery flight to Australia, skidded into a dry drainage canal and collided with an embankment, killing all five crew and six passengers on board. The accident was the first fatal jetliner crash. Canadian Pacific cancelled its order for a second Comet 1A and never operated the type in commercial service. These early accidents were originally attributed to pilot error as over-rotation had led to a loss of lift from the leading edge of the aircraft's wings. It was later determined that the Comet's wing profile experienced a loss of lift at a high angle of attack, and its engine inlets also suffered a lack of pressure recovery in the same conditions. As a result, de Havilland made modifications to both. Although sales never fully recovered the redesigned Comet 4 which debuted in 1958 had a productive career of over 30 years. The most extensive modification resulted in a specialized maritime patrol aircraft variant, the Hawker Siddeley Nimrod which remained in service with the Royal Air Force (RAF) until 2011, over 60 years after the Comet's first flight.