Ground School Class 2

Fuel Systems

Fuel Systems
There are two types of fuel systems: gravity fed and pressurized. Gravity fed systems are utilized in high wing aircraft (like the C-150) and are just like they sound, gravity allows fuel to flow from the wing tanks down to the engine. In low wing aircraft, the engine is higher than the wings and a pressurized system that utilizes an engine driven pump pushes fuel up from the wing tanks. Pressurized systems also have electric fuel pumps so that fuel can be pumped with out the engine turning and can serve as booster pumps.

The fuel tanks are (usually) located in the wings. Fuel tanks are either a bladder inside the wing or what is called a wet wing, where the tank is an integral part of the wing itself. All planes must have at least one fuel quantity gauge. However, they are notoriously inaccurate and flight plans are based on fuel consumption rates which will be covered later on. A fuel selector valve allows the pilot to switch between tanks and keep the weight of fuel in the wings balanced while in flight. Each wing tank has a fuel strainer on the bottom that allows fuel to be drawn out and be inspected for water contamination. There is now only one grade of av-gas (100LL) that is tinted blue so you can distinguish it from jet fuel.

Oil System
Oil does four things in the engine. Provides lubrication and cooling as well as carries particulates away and removes them via the oil filter and finally provides a seal in the cylinder. Aircraft are required to have two gauges: oil temp and oil pressure.

Cooling System
Aircraft engines are air cooled. The cowling is designed to maximize the air flow over the cylinders. Some aircraft are equipped with cowl flaps, that are pilot controlled and can increase cooling during climbs, but can be closed to reduce drag during cruise speeds.

Props
There are two types of props - fixed and constant speed. A fixed prop is a single blade that comes in two types of configurations: climb and cruise. Climb props are efficient climbers, but not good for cruising. Cruise prop is just the opposite. Prop is chosen based on the most common use of the particular aircraft. A constant speed prop is also referred to as a variable pitch prop, as is pilot adjustable in flight. Fixed prop engines speeds are monitored via an tachometer. Constant speed prop engine speeds are regulated using a combination of a tachometer, a manifold pressure gauge and the chosen prop pitch.

Electrical System Diagram

Electrical System
Aircraft systems use either a generator (in older planes) or an alternator. An alternator system creates an A/C that is then converted to D/C to power the avionics and other systems. Aircraft use either 14V or 28V systems and are monitored via a load meter or an ammeter. The electrical system is controlled by a master switch that is a two part rocker switch, with one side for the battery and one side for the alternator. The system is protected by either fuses or circuit breakers. All the electrical components are usually tied together via two bus bars, a primary bus and an avionics bus.

Flight Instruments
The discussion on flight instruments starts with a primer on atmospheric pressure. A standard day refers to sea level elevation and 15 C (59 F) which is 29.92 inches of barometric pressure. There is a loss of 1 inch of pressure for every 1,000 ft change in elevation. Atmospheric pressure is measured via two instrument ports: the pitot tube and the static port. The pitot tube is just what is sounds like , a small tube that points forward and the amount of air pressure that passes thru the tube changes with the speed of the aircraft. The static port is a small port that is located perpendicular to the forward direction and and measures the static atmospheric pressure. The airspeed indicator (ASI) measures the difference between the pitot tube pressure and the static port pressure. Two other gauges are attached to the static port: the altimeter and the vertical speed indicator. The airspeed indicator has gauge markings for several V speeds.

ASI

V_s = stall speed indicated by the bottom of the green arc.
V_so = stall speed in the landing configuration (flaps extended and gear down) indicated by the bottom of the white arc.
V_fe = flap extension speed, or the maximum speed that you safely extend flaps
V_no = normal operating range indicated by the top of the green arc.
V_ne = never to exceed speed indicated by the red line.

The difference between the Vno and the Vne is the caution range indicated by the yellow arc.

There are several other V speeds that are not indicated on the ASI because they vary with the weight of the aircraft or other parameters that are listed in the POH.

V_a = maneuvering airspeed.
V_x = best climb angle
V_y = best rate of climb
V_glide = best glide speed
V_lo = landing gear operating speed
V_le = landing gear extended speed

There are four different types of airspeed:

IAS = indicated airspeed
CAS = calibrated airspeed
TAS = true airspeed
GS = ground speed.

We'll be covering this more when we get to flight planning.