Bjorn’s Corner: Aircraft stability, Part 2

By Bjorn Fehrm.

April 20, 2018, ©. Leeham News: In the last Corner, we discussed how to stabilize an aircraft in pitch so it could fly stably straight ahead. For this, we needed a horizontal tail which had a negative lift.

This will buy us a short-term pitch stability, but not a long-term one. Why we will explain in this Corner.

Figure 1. The long-term pitch instability, Phugoid. Source: Leeham Co.

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Bjorn’s Corner: Aircraft stability

April 13, 2018, ©. Leeham News: In the last Corner we discussed the pressure distribution on a conventional airfoil and compared it with a modern Supercritical airfoil. The Supercritical airfoil (which is used on all modern airliners) achieves a higher cruise Mach and a lower transonic drag by accelerating the air over the wing to a lower supersonic speed than conventional airfoils.

What conventional and supercritical airfoils share is a pressure distribution making them unstable. We need to stabilize them on an aircraft.

Figure 1. The primary forces on an airliner. Source: Leeham Co.

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Bjorn’s Corner: Aircraft lift, Part 3

By Bjorn Fehrm

April 06, 2018, ©. Leeham News: In the last Corner, we discussed the pressure distribution of an aircraft’s wing when producing lift. This was with a conventional airfoil (though of the more laminar flow type).

Now we continue by looking at how a modern airliner wing achieves lift by using a “supercritical” airfoil.

Figure 1. The airliner using the wing profile we study, the Emb145. Source: Embraer.

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Bjorn’s Corner: Aircraft lift, Part 2

March 30, 2018, ©. Leeham News: In the last Corner, we described how lift is produced on the aircraft’s wings. Now we continue with studying the lift a bit further.

We explore the effect of angle of attack on lift for a wing and the resulting pressure distribution.

Figure 1. Lift of wing when the angle of attack varies. Source: Leeham Co.

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Bjorn’s Corner: Aircraft lift

By Bjorn Fehrm

March 23, 2018, ©. Leeham News: In the last Corner, we finished our series about aircraft drag, by studying an airliner flying a mission and noting how the drag changed.

Before we leave the subject of airliner aerodynamics, we shall recap how lift is produced.

Figure 1. Computer Fluid Dynamic output of a Boeing 787 during cruise. Source: Boeing and Leeham Co.

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Bjorn’s Corner: Aircraft drag reduction, Part 21

By Bjorn Fehrm

March 16, 2018, ©. Leeham News: In the last Corner, we looked at the drag of an airliner during cruise. We could see the thrust required to counter the drag in the thin air of 37,000 feet was low, about 4,000lbf per engine.

Now we continue with the drag created by the aircraft during descent and landing.

Figure 1. Drag of an aircraft at different airspeeds. Source: Leeham Co.

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Bjorn’s Corner: Aircraft drag reduction, Part 20

By Bjorn Fehrm

March 9, 2018, ©. Leeham Co: In the last Corner, we started to go through a typical mission for an airliner and study which drag types are important when and why.

We went through the take-off and climb phases, now we continue with the cruise phase.

Figure 1. An aircraft’s drag profile as airspeed varies. Source: Leeham Co.

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Bjorn’s Corner: Aircraft drag reduction, Part 19

February 23, 2018, ©. Leeham Co: In the last Corner we wrapped up the discussion on different drag types by discussing some less dominant drags.

To finish the series we will go through a typical mission for an airliner and study which drag is important when and why.

Figure 1. An aircraft’s drag profile as airspeed varies. The main part of Parasitic drag is air friction drag Source: Leeham Co.

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Bjorn’s Corner: Aircraft drag reduction, Part 18

By Bjorn Fehrm

February 23, 2018, ©. Leeham Co: In the last Corner we discussed transonic flow and drag. Now it’s time to finish the drag type discussion by adding some less dominant but still important drag types.

Knowing their origin will help us understand why aircraft are made like they are.

Figure 1. Low-pressure (green) shows areas with high flow speeds for the 787 during cruise. Source: Boeing and Leeham Co.

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Bjorn’s Corner: Aircraft drag reduction, Part 17

By Bjorn Fehrm

February 16, 2018, ©. Leeham Co: In the last Corner, we discussed supersonic flow and drag. Now it’s time to talk about the drag created by transonic flow on an aircraft.

Figure 1. Pressure distribution of 787 during cruise. Source: Boeing and Leeham Co.

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