Matching of Propulsion Systems for an Aircraft P M V Subbarao Professor Mechanical Engineering Department Matching of Flying Machine and Power Plant…..

Flight Missions and Constraints Analyses There exist an optimum match point between an engine and a configuration of an aircraft. This match point depends on ; the available engine propulsive performance, flight mission profile and the constraints. Demands an optimization process, which includes aerodynamics and flight performance module coupled with another module for engine performance prediction.

Typical flight mission profile for a passenger airplane Engine capacity Thrust Flight Velocity Turn Turn Cruise Climb in Altitude Descent Takeoff Landing

Cruise Flight Strategy Cruising Speed The objective of flight designer is, during the cruise flight the flight must use as few fuel as possible. There are two strategies selected for this purpose. Endurance & Range

Endurance Vs Range If the flight is to stay as long in the air as possible, it should have maximum Endurance. The endurance E is the time which flight can stay in the air with a given amount of fuel. To maximize E the fuel consumption rate must be minimized. If the flight is to go as far as possible, it should have maximum the Range. The range R is the distance a flight can cover with a given amount of fuel. So the distance ds per unit mass of fuel used dmf should be maximized.

Design for Maximum Range Maximize For cruising: For jet engines the fuel flow varies linearly with the thrust,

Cruise Flight Strategy Cruising Speed Lift and drag coefficients CL and CD are defined as:

Cruising for Maximum Range Define lift to Drag Ratio , L/D For cruising:

Lift to Drag Ratio Vs Mach Number : Cruising

The Parameters of Concern to Reach Cruising Altitude The parameters for reaching the cruising altitude: field lengths at takeoff and landing, climb rate/time, optimum cruising speed, and Cruising altitude. The segments of takeoff, climb, cruise, and landing are considered as the critical phases . These phases are assessed separately in terms of thrust-to-weight ratio T/WTO and wing loading W/STO referring to takeoff conditions.

Optimization for Match Point

Force Balance on a Climbing Aircraft

Speed Vs Rate of Climb

Feasible Domains for Constraints

Feasible Domains for Constraints

Typical Airplane Characteristics

Engine Capability Flight Velocity

Convergent-Divergent Nozzle Under Take off Conditions

Steady Cruising Design Conditions