Why aircraft mechanics are important to airline investors
Four forces an aircraft should deal with: Thrust, drag, lift, and weight
Just as familiarity with a car’s engine and gear system helps a driver adjust their driving style and improve their car’s mileage, knowing how an aircraft operates and the forces that affect the aircraft’s flight will help you understand the strategies airlines use to improve their aircraft’s fuel efficiency. The four forces that influence the aircraft’s flight and its fuel consumptions are as follows.
- Weight pushes the aircraft downward, and the magnitude depends on the mass of the airplane parts, amount of fuel, passengers, baggage, freight, et cetera.
- Lift is an aerodynamic force generated as the aircraft moves through the air to overcome the downward force generated by its weight. The magnitude of the lift depends on the shape, size, and velocity of the aircraft.
- Drag is the resistance force created by the air as it resists the movement of the aircraft, and the direction is opposite that of the flight. Less drag would lead to less fuel burn and increased cruise efficiency.
- Thrust is the force generated by an aircraft’s propulsion system to overcome the drag. The thrust from the propulsion system should exceed the drag to enable the aircraft to accelerate. The greater the difference between the thrust and the drag (excess thrust), the faster the acceleration.
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How these forces influence fuel consumption
At a given speed, the increase in the aircraft’s weight affects the drag and cruising altitude. A heavier aircraft flies at lower altitude, as it requires higher air density to provide the necessary lift. Higher air density increases the drag. Since the thrust should exceed the drag for the aircraft to accelerate, fuel consumption increases. The table above shows the fuel consumption for takeoff of an aircraft at different altitudes and gross weights. Fuel consumption increases as weight and altitude increase.
In the next article of this series, we’ll see how much United (UAL) lowers fuel consumption through weight reduction, engine modification, and winglets to reduce drag. All United’s peers, including Delta (DAL), American Airlines (AAL), Southwest (LUV), and JetBlue (JBLU), use standard winglets for fuel efficiency, but United is the first company to use the new Split Scimitar winglets.