飞机设计导论-第5讲

2011

Introduction to Aircraft DesignLecture5: Performance Analysis and Optimization

Xu Weiqiang (徐伟强) Ph.D.

Outline1 2 3 4 5 Performance requirements and development Flight envelope and regional division Aerodynamic and stability analysis Weight analysis

Cost and other performance analysis multidisciplinary design optimizationSchool of Aeronautical Science and Engineering

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Performance requirements and development Piston fighter

Subsonic cruise( Flight speed is about M0.6 ) Liquid-cooled piston engine; Simple weapons( machine gun, canon )

P-51

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Performance requirements and development The first generation jet fighterF-86

Subsonic cruise( Flight speed is M0.95 ~ 0.98 ); altitude of about 15000 meters; Simple weapons( Infrared Air-to-Air Missile); Simple electronic devices; ejection seat; pressurized cockpit.MIG-15School of Aeronautical Science and Engineering

Performance requirements and development The second generation jet fighterMig-19

Break the “sound barrier” ( The jet engine with afterburner, about M1.3 ); Certain weapons( cannon, simple air to air missiles ); Improved electronic equipment (small airborne radar).

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Performance requirements and development The third generation jet fighterF-4

The maximum number of M reached 2 ~ 2.5; ceiling close to 20000 meters; Advanced fire control radar and navigation systems;

advanced air to air missiles .

MIG-21

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Performance requirements and development The fourth generation jet fighter Large thrust-weight ratio; Omnidirectional attack; Low-altitude transonic maneuverability; Long-range combat capability; Remote detection(up to 100 km above ); Fire control radar has a lookdown ejection function; Can track multiple targets.

F-15 Su-27

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Performance requirements and development The fifth generation jet fighter Supersonic cruise capability without open afterburner ; Low signature performance; High agility and maneuverability, especially the post-stall maneuver capability; STOL performance; Visual fighting over the horizon attack and ground attack capabilities; High reliability and maintainability

F-35

S-37

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Performance requirements and development Cruise PerformanceA typical mission is illustrated below.

The mission profile consists of two portions: the nominal mission and the reserves. Taxi and take-off:a period of about 15 minutes; There is a best altitude for cruise and this optimum altitude increases as the aircraft weight decreases (as fuel is burned).

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Performance requirements and development ATC rules specify t

hat aircraft be flown at specific flight altitudes; ―step cruise‖ profile, with 1 to 3 steps of 4000 ft in altitude due to airway requirements; stepped profiles lead to reductions in cruise range by 1%-2%; Reserve fuel is carried to allow for deviations from the original flight plan. 1. Fuel to fly 10% of planned block time at long range cruise speed; 2. Climb from sea level to cruise altitude; 3. Cruise to alternate; 4. Descend to 1500 ft and hold for 30 minutes; 5. Descend to sea level.School of Aeronautical Science and Engineering

Performance requirements and development Range

Number of Engines: Flight Condition: First Take-Off Segment Second Take-Off Segment Final Take-Off Segment Enroute Climb Approach Segment Landing Segment

4 0.5% 3.0% 1.7% 1.6% 2.7% 3.2%

3 0.3% 2.7% 1.5% 1.4% 2.4% 3.2%

2 0.0% 2.4% 1.2% 1.1% 2.1% 3.2%School of Aeronautical Science and Engineering

Required Climb Gradient (爬升梯度 )

Performance requirements and developmentSpecific Range = V / cT T = D = W / (L/D) Specific Range = V/c L/D 1/W

Breguet Range Equation

where V is the true speed, c is the thrust specific fuel consumptionSchool of Aeronautical Science and Engineering

Outline1 2 3 4 5 Performance requirements and development Flight envelope and regional division Aerodynamic and stability analysis Weight analysis

Cost and other performance analysis multidisciplinary design optimizationSchool of Aeronautical Science and Engineering

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Flight envelope and regional division

SPECIFIC EXCESS POWER:

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Flight envelope and regional division Typical Design Requirements for a Multi-Role Jet FighterMinimum performance requirements/constraints Item Combat mission radius Weapons payload Requirement 400 nautical miles 2 AIM-120 4 2000 lb MK-84 Takeoff distance Landing distance Max Mach number Instantaneous turn rate Specific excess power Sustained load factor 600 rounds 20 mm ammunition 2,000 ft 2,000 ft M = 1.8 at optimum altitude at Wmana 18o/sec at M = 0.9, 20,000 ft MSLb at Wman 800 ft/sec, M = 0.9, 5,000 ft MSL at Wman 4-g at M = 1.2, 20,000 ft MSL at Wman 9-g at M = 0.9, 5,000 ft MSL at Wman a. The maneuver weight (Wman) is the aircraft weight with 50% internal fuel, two AIM-120 AMRAAM missiles, and full cannon ammunition, but no air-to-ground weapons. b. The abbreviation MSL signifies altitude above mean sea level, the average elevation of the Earth’s oceansSchool of Aeronautical Science and Engineering

Flight envelope and regional division

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Flight envelope and regional division V-n DIAGRAMS

V-n Diagram for a Subsonic Jet Trainer

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Flight envelope and regional division Simple example

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Flight envelope and regional division Aircraft Ps Comparisons

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Outline1 2 3

4 5 Performance requirements and development Flight envelope and regional division Aerodynamic and stability analysis Weight analysis

Cost and other performance analysis multidisciplinary design optimizationSchool of Aeronautical Science and Engineering

6

Aerodynamic and stability analysis3.1 Aerodynamic Basic Concept

continuity equation:

Streamlines stream tube flowfield steady flow stagnation point stagnation streamline

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