Lesson Notes By Weeks and Term v4 - SHS 2
Aircraft Instrumentation
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Aircraft Instrumentation
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Aviation And Aerospace Engineering
Class: SHS 2
Term: 1st Term
Week: 7
Grade code: 2.2.2.LI.2
Strand code: 2
Sub-strand code: 2
Content standard code: 2.2.2.CS.1
Indicator code: 2.2.2.LI.2
Theme: Avionics
Subtheme: Aircraft Instrumentation
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Good morning, class. Think about the dashboard of a car or a "trotro". It has a speedometer to show speed, a fuel gauge for fuel, and temperature gauge for the engine. These instruments help the driver operate the vehicle safely. An aircraft has a much more advanced "dashboard" called an instrument panel or cockpit. Pilots rely on these instruments to know the aircraft's speed, height, direction, and whether it is flying straight and level. This is incredibly important, especially in Ghana. During the Harmattan season, when dust can make it very difficult to see, or when flying at night or through thick clouds, pilots cannot see the ground or the horizon.
Aircraft instruments are broadly categorized into three groups: Flight Instruments: Tell the pilot about the aircraft's orientation and movement through the air. Engine Instruments: Monitor the health and power of the engine(s). Navigation Instruments: Help the pilot find their way from one place to another.
Today, we will focus on the six basic flight instruments, the "six-pack," which form the foundation of flying. They are divided into two systems: the Pitot-Static System and the Gyroscopic System. A. The Pitot-Static System and its Instruments
This system works by measuring air pressure. There are two types of pressure it uses: Static Pressure: The pressure of the still air around the aircraft, like atmospheric pressure. It decreases as you go higher. It is measured by a small hole on the side of the fuselage called the Static Port. Total Pressure (or Ram Air Pressure): The pressure created by the aircraft moving through the air. It is a combination of static pressure and the pressure of the moving air (dynamic pressure). It is measured by a forward-facing L-shaped tube, usually on the wing or nose, called the Pitot Tube.
The principle is simple: Total Pressure - Static Pressure = Dynamic Pressure. This dynamic pressure is what tells us how fast we are moving through the air. Airspeed Indicator (ASI) What it Measures: Airspeed - the speed of the aircraft relative to the surrounding air (measured in knots). Principle of Operation: Inside the ASI is a small, flexible, sealed diaphragm (like a tiny balloon). The Pitot tube is connected to the *inside* of this diaphragm, filling it with Total Pressure. The Static Port is connected to the case of the instrument, *outside* the diaphragm, filling it with Static Pressure. The diaphragm expands or contracts based on the difference between the Total Pressure inside and the Static Pressure outside. This difference is the dynamic pressure. A system of levers and gears connects this diaphragm's movement to a pointer on the face of the instrument, which shows the airspeed. More dynamic pressure = more expansion = higher airspeed reading. Altimeter What it Measures: Altitude - the height of the aircraft above Mean Sea Level (MSL). Principle of Operation: The altimeter is essentially a sensitive barometer. It only uses the Static Port. Inside is a sealed, corrugated metal capsule called an aneroid wafer. A standard pressure (29.92 inches of Mercury, or 1013.2 millibars) is sealed inside this wafer. The static port feeds outside air pressure into the instrument case, surrounding the wafer. As the aircraft climbs, the outside static pressure decreases. The higher pressure inside the wafer causes it to expand. As the aircraft descends, the outside static pressure increases, squeezing the wafer and causing it to contract. This expansion and contraction is linked through gears to the pointers on the altimeter face to show the aircraft's altitude. Vertical Speed Indicator (VSI) What it Measures: The rate of climb or descent (measured in feet per minute). Principle of Operation: The VSI measures the *rate of change* of static pressure. It has a diaphragm inside, just like the ASI. The inside of the diaphragm is connected directly to the static port, so its internal pressure changes instantly with altitude changes. The instrument case *around* the diaphragm is also connected to the static port, but through a very tiny, restricted hole called a calibrated leak. When the aircraft is in level flight, the pressure inside the diaphragm and outside in the case are equal, so the needle reads zero. When the aircraft climbs, the pressure inside the diaphragm drops instantly, while the pressure in the case drops slowly (due to the leak). This pressure difference causes the diaphragm to contract, moving the needle up to show a climb. The opposite happens during a descent. B. The Gyroscopic System and its Instruments