Date: 02 Sep 98 01:08:21 From: Kim Hackett <firstname.lastname@example.org> Organization: SouthWind Internet Access, Inc. References: 1
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Landing descent veocities of 500 ft per second is way too high of a number. 500 ft per minute is closer to the requirement. Federal Air Regulations Airworthiness Standards Part 25 for Transport Category Airplanes is used to certify transport aircraft ranging in size from business jets to the 747-400. FAR 25.473 specifies the limit descent velocity of 10 ft per sec at the design landing weight and a limit descent velocity of 6 ft per sec at the design takeoff weight. Under Part 25, aircraft nose gear and main gear are drop tested to 10 fps limit (once in a lifetime condition) and 12 fps (ultimate) descent velocities. For the Cessna Citation Excel, a 20,000 lb MTOW business jet aircraft, the maximum nose gear (NG) static reaction sitting on the ramp is about 2,000 lb and each main gear (MG) maximum static reaction is about 9200 lb. The gear is analyzed for a variety of landing conditions, including level landing, tail down landing, one wheel, 2 wheel, and 3 wheel landing conditions, and lateral drift landing. For the Excel NG, the max vertical dynamic landing load is about 9000 lb and the max NG drag load is about 4000 lb for a 10 fps limit landing. The MG max vertical load is about 21,000 lb, maximum side load is about 8000 lb, and the maximum drag load is 9100 lb. These are limit values and are multiplied by 1.5 to get ultimate loads for design. The Citation Excel has one tire on the NG and two tires on each MG. The main gear tire loads would be roughly half the main gear loads. I don't know about a taxi length limit to control heat and tire flexure during taxi. I believe commercial jets have a taxi length limit that is to keep the brakes from overheating. I think that Boeing aircraft have a minimum time limit between landing and takeoff which is to ensure adequate time for brake cooling. The brakes must be cooled down before the aircraft takes off in case they need the brakes in an aborted takeoff.