Monday, June 22, 2015

General topics on how do airplanes fly?

Primary Flight Instruments in a Cessna 172

In this post, we will go inside the airplane and see the primary flying instruments in the cockpit of a Cessna 172.

Since there are many instruments at the cockpit and to easily orient the pilot with them, engineers had layout the primary instruments in a T-shaped order. Please refer to the image below.

These primary flight instruments and their functions are as follow:

On the top left hand side: 

The Air Speed Indicator (ASI). This instrument is operated through the pitot (that we saw being uncovered pre-flight in the video right under the outboard wing)

The ASI is very helpful instrument at times of the flight, as it provides the pilot with the various speed to fly the aircraft.
  • Let us start with the white band. There is the lower limit speed and the upper limit speed. The speed below the lower limit of the white band is the stall speed or Vs. The speeds at the white band is the operating speed when flap are extended or Vf
  • The green band speed limits is the normal operating speeds of the airplane or Vo
  • The yellow band speed limits is the maximum structural cruising speed or Vno
  • The red dash is the never exceed speed or Vne
On the top center:

The Attitude Indicator (AI). It is a gyro instrument and it requires a suction devise to create vacuum within the AI instrument to operate properly.

The AI provide the pilot with the pitch up and pitch down attitude of the airplane, in addition to the bank of the airplane, either to the left or to the right.

While pitching up or down, there are lines that indicate the angle of the pitch in degrees, i.e. 10 degrees up or up to 30 degrees down.

While banking the airplane to turn left or right, the AI provides the pilot with the angle of banking. Any turn or bank exceeding 30 degrees is considered to be a steep turn, and it requires special skills to handle.

On the top right hand side:

The Altimeter. The altimeter works by measuring the differential of the pressure of the atmosphere. It need a static pressure devise that is attached on the fuselage of the airplane to operate properly.

The altimeter is require to indicate the altitude of the aircraft above the ground level. In order to give the right and proper indications or readings, it has to be adjusted to the pressure altitude of the airfield the airplane is operated and it is called the QFE. When above the flight levels the pressure altitude is adjusted to the standard pressure altitude which is called QNH or above mean sea level and usually is set at 29.92".

On the bottom center:

The Heading Indicator. This instrument is also a gyro instrument. 

The HI is used to indicate the heading of the aircraft in relevance to the magnetic north. This is used in flight to help the pilot find his way or to follow the air traffic control (ATC) instructions of the headings.


The Glass cockpit of modern jetliners


2 comments:

  1. Do large passenger planes also use that T formation? I'm curious about the latest planes, like the Boeing Dreamliner, does it use modern and different instrumentation and cockpit placement?

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  2. Hi Rosemary,

    The modern jetliners like the Dreamliner, the B777, the B747 and Airbus 321 etc., have a different concept for the cockpit, and it is called the Glass Cockpit. The glass cockpit was introduced in the early 80s with the Jumbo Jet - Boeing 747. The glass cockpit concept is based on having all the gauges in a screen. Please refer to the image above, I have added in the post.

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