descent_performance_1

descent_performance_1 - Virginia Tech - Air Transportation...

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Unformatted text preview: Virginia Tech - Air Transportation Systems Laboratory Aircraft Performance Calculations: Descent Analysis CEE 5614 Analysis of Air Transportation Systems Dr. Antonio A. Trani Professor Virginia Tech - Air Transportation Systems Laboratory Aircraft Descent Performance • The top of descent point typically starts 80-120 miles away from the destination airport (depending upon the cruise altitude assigned) • A descent on commercial transport aircraft is initiated by setting the engine thrust to a very low power condition (i.e.,idle thrust) • The analysis done for climb is now reversed • Once in the airport terminal area, thrust adjustments are necessary to compensate for altitude holds or flap configuration changes as needed 2 Virginia Tech - Air Transportation Systems Laboratory Sample Descent Profle (LAX Data) • Shown are sample descent profiles for Boeing 767-300 flying into LAX International airport • Clearly, not all aircraft fly the same descent profiles 3 Altitude holds used by Air TraFfc Control to separate traFfc Virginia Tech - Air Transportation Systems Laboratory Arrival Flight Profles into the LAX Airport Terminal Area 4 ! Red dots = entry points into the terminal area Shortest Path Actual Path LAX Airport Virginia Tech - Air Transportation Systems Laboratory Aircraft Descent Performance Analysis • The pilot reduces thrust to near idle conditions • If we let the reduced thrust be T d , then the analysis done for the climb procedure applies to the descent • The most economical descent would be a continuous descent flown at idle conditions until a point where flaps and landing gear are deployed. At such point adjustments in thrust are required to maintain a safe rate of descent in the final approach 5 Virginia Tech - Air Transportation Systems Laboratory Example - Aircraft Descent Performance Controlling the Speed ProFle • Very large capacity transport aircraft (http://128.173.204.63/ courses/cee5614/cee5614_pub/AirbusA380_class.m ) • The aircraft descent speed is controlled by the last two lines of data in the aircraft data file • Vdescent is the vector of descent speed for altitudes (altc) • altc is a vector of altitudes to complete the table function of speed vs altitude • For example: The aircraft below descends at 300 knots indicated at the top of descent. However below 3000 meters, the aircraft slows down to 250 knots or below. 6 Virginia Tech - Air Transportation Systems Laboratory Example - Very Large Capacity Aircraft Data File • An aircraft similar in size and performance as the Airbus A380 • Four turbofan engines each developing 34,400 kg (338,000 N) at sea level. Assume idle thrust produces 1/10 of the full continuous thrust • Top of descent mass is 400,000 kg....
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This note was uploaded on 12/31/2011 for the course CEE 5614 taught by Professor Staff during the Fall '10 term at Virginia Tech.

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descent_performance_1 - Virginia Tech - Air Transportation...

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