Leeham News and Analysis
There's more to real news than a news release.
Bjorn’s Corner: Aircraft stability, Part 4
By Bjorn Fehrm
May 4, 2018, ©. Leeham News: In the last Corner, we discussed basic autopilots used in general aviation aircraft. The key components for such a system are shown in Figure 1.
Now we will go to more advanced autopilots. We will start with describing the sensors such autopilots need.
Figure 1. The S-TEC 30 roll and pitch two-axis autopilot. Source: Genesys.
Bjorn’s Corner: Aircraft stability, Part 3
By Bjorn Fehrm
April 27, 2018, ©. Leeham News: In the last Corner we discussed the problems with the long term stability of an aircraft. The aircraft deviates gradually in pitch, roll and in a combined yaw and roll mode if left without pilot input.
To hand fly such an aircraft on long routes is tiresome (been there, done that). For these occasions, one needs an assistant, an autopilot.
Figure 1. Simple one-axis autopilot for small aircraft. Source: Genesys S-TEC.
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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.
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.
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.
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.
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.
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.
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.
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.