By Bjorn Fehrm
May 12, 2023, ©. Leeham News: This is a summary of the article New aircraft technologies. Part 12P. Airframe efficiency improvement. The article discusses the different drag types that affect an airframe, their magnitudes, and the physics behind them. Airframe efficiency improvements are about reducing these drags.
Figure 1. The drag types that affect our single-aisle airliners. Source: Leeham Co.
Reducing the drag of an airliner
To increase the airframe efficiency of an airliner, we need to reduce the drag of the airframe. Figure 1 shows the drag types that affect a typical single-aisle airliner and their portion of the total drag.
We can divide the drag types into three buckets:
- Drag due to size. In aero speak, we talk about the largest portion of parasitic drag, the friction drag, which is over half the aircraft’s drag. Ìts magnitude depends on the type of friction drag (laminar or turbulent) and the total friction area of the aircraft, called the wetted area.
- Drag due to weight. In aero speak induced drag. It’s due to the global air circulation from under the aircraft and wing to its overside, Figure 2. The drag level is dependent on the aircraft’s weight, its wingspan, and the pressure distribution along the span.
Figure 2. The global flow of air from the aircraft’s underside to the top of the aircraft. Source: Google Images.
- Apart from these two dominant drags, we have smaller contributions as part of Parasitic drag from pressure drag (drag due to form) and interference drag (drag due to air being squeezed). Finally, we have transonic drag (parts of the airframe have supersonic flow pockets).
Airframe designers have worked to reduce these drag types for the last 100 years. We will go through them and discuss what has been done over the years and what modern technology and new ideas can do to reduce their size.
We start next week with Drag due to size, air friction drag.