Subsonic and Transonic

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Question 1: Subsonic and Transonic

Question 2: Ice/Snow

1.0 Question 1: Subsonic and Transonic

1.1 Explain the terms Subsonic and Transonic

1.1.1 Subsonic

Subsonic refers to one of the four speed of flight. The speed of flight consists of subsonic, transonic, supersonic and hypersonic. The term subsonic refers to the speed of an aircraft that travels below the speed of sound. Subsonic aircrafts usually travels at a speed of below 250mph. In terms of Mach number (M), the subsonic aircraft travels below Mach 1. When aircraft travels at subsonic speed, all the air travelling over the aircraft are travelling below the speed of sound.

1.1.2 Transonic

The term Transonic refers to the speed of an aircraft that travels near the speed of sound. The speed of an aircraft that travels in a transonic speed is roughly around 660mph. In terms of Mach number, the transonic aircraft travels between Mach 0.8 to Mach 1.2. When aircraft travels at transonic speed, some of the air moving over the aircraft is travelling at a speed of sound.

Figure 1.0: An aircraft flying in transonic speed

Sources: http://www.flickr.com (2009)

When an aircraft is travelling at a transonic speed, there will be a considerable change on the aircraft’s longitudinal trim (nose down pitch). The situation was accompanied by lack of effectiveness of the trimming devices and a considerable increase in the force to move the controls. (EASA LBP, 2003)

Due to the lack of effectiveness of the trimming devices, the aircraft will have the tendency to:

* Snake- Yaw from side to side

* Porpoise- Pitch up and down

* Dutch roll- A combination of roll and yaw

The aircraft will be difficult to control. This is because the control surfaces are usually behind the shockwave and in the turbulent area. Therefore, the trimming devices may not be very effective. When the speed increases, the shock wave will move back over the aerofoil and over the control surfaces...