By David Humble
This lesson gives a brief introduction to the minimum equipment that needs to carried on a plane for VFR flight and what is fitted to a typical modern light aircraft as the additional instruments reduce the workload on the pilot and increases the pleasure of the flying.
In general the formal requirements for the equipment to be carried on a plane flying VFR are lower than for a plane flying IFR. However there is nothing stopping a pilot who has had suitable training in using the IFR instruments to assist in navigation. This section gives a brief overview of VFR flight instruments. The other navigation Instruments are covered under the IFR sections.
The list of instruments required, in Australia)to meet the minimum requirements is quite short
- Airspeed Indicator
- Accurate Timepiece (A Watch is acceptable)
Note that there is no reference to navigation equipment to be fitted to the plane. This is because it is assumed that the pilot will be able to see the ground and be able to use what is visible to do a lot of what the instruments are required for when flying under instrument conditions, however there still is a need to be able to navigate correctly as getting lost, and not reaching the destination airport is frowned upon.
The aircraft compass is a very simple piece of equipment, a magnetized bar mounted so that it points toward the magnetic poles. Ther are a number of things that affect the compass which need to be taken into account when using it for navigation
- The compass points to Magnetic North. For any place the difference between the direction to True North and the magnetic North ( the magnetic deviation) pole is measured and indicated on the appropriate chart. This is either by lines drawn indicating positions of equal magnetic deviation, or for charts covering a small area a note in the legend. The pattern of the magnetic deviations is not simple over the planet, and is slowly changing with time.
- The plane has a number metallic components built into it as part of its construction. These will affect the direction that the compass points. On regular basis the plane, when on the ground swung ie pointed in known directions and the direction on the compass recorded. A table of the actual compass readings for the measured directions is provided to allow the pilot to correct for the error
- Forces on it associated with making it balance in the plane ( in the Northern Hemisphere the compass is sluggish turning through North and Skitish turning through South)
VFR Flight Instruments
On most modern aircraft there are 6 main flight instruments that the aircraft is fitted with , layed out in a standard arrangement as illustrated below.
<IMAGE of 6 flight Insts to go here>
From Left to Right, top to bottom the instruments are
The airspeed indicator acts by suddenly stopping some of the air flowing towards the plane and using increase in pressure above ambient to determine the airspeed. Most small planes have a pitot tube (normally about 10cm long mounted away from the body of the aircraft to get a clean measure of the dynamic pressure.
The air inlet hole at the front of the pitot tube is normally quite small ( 3-5mm) and can get blocked up, and therefore not see the airflow, under icing conditions, Therefore most light aircraft have a heater built into the pitot tube to ensure that any ice that forms is melted and continuous correct operation occurs.
The coloured sections of the airspeed indicator indicate safe ranges for airspeed for various configurations of the aircraft.
White Section - Safe operation with flap extended
Green Section - Normal operation range.
Yellow Section - caution range where operation is allowed in smooth air - extending up to the red line which is the Maximum speed for the aircraft.
The attitude indicator gives information about the pitch and roll angles of the plane. As the plane pitches up the indication of the horizon drops (the same as happens with the horizon seen through the windshield). The amound of pitch up or down can be read off the scale. In this case the plane was about 5 degrees nose up). As the plane rolls while turning the horizon in the attitude indicator remains horizontal, and as with the pitch angle the roll angle can be read from the scales on the side. The AI indicated above has scale marks at 10,20,30 and 60 degrees.
The altimeter is used to show the elevation of the aircraft above a known reference level, normally sea-level. As the air pressure decreases with altitude it is simple to measure the pressure, a pressure measuring device (similar to that in an aneroid barometer), which is calibrated to show the altitude.
This method has the disadvantage that the local air pressure changes both with time and location and calibration the altimeter at one point will not be valid at another. To make the altimeter correct for the prevailing local conditions a offset needs to be applied to the altimeter to account for the pressure difference. The method used is for the equivalent air pressure at sea level to be set on the altimeter (Kohlsmann setting). This is the QNH figure either given by the controller or in the ATIS, and the altimeter is then correct for local operation. If the flight covers a long distance, or takes a long time the QNH local to the plane may change as the flight progresses and a new QNH set.
The typical VFR altimeter shown has two hands, with the longer one indicating hundreds of feet and the smaller one thousands in this case the aircraft is at 440 feet, The Kohlsmann scale can be seen to the right of the dial and is set to 29.9 inches
Turn and Bank Indicator
This Instrument shows the rate-of-turn of the aircraft. When the diagrammatic plane is leaning with its wing pointed at the mark on the side of the instrument the plane will complete one 360 degree turn in two minutes. Note that the angle of the plane does not follow the actual angle of bank of the plane. Accurately flying turns at a given rate is not normally important in VFR flight but becomes vital when flying such maneuvers as holds in IFR conditions
The bottom half of the Turn and bank indicator shows whether the turn is coordinated. If the ball is in the centre the apparent weight of the aircraft is perpendicular to the wings and the plane is turning as efficiently as possible.
Directional Gyro (DG) Indicator
The compass is the prime method for determining direction; in addition planes are fitted with a gyroscopically controlled indication of direction. This does not suffer from the same errors during turning as the magnetic compass. The DIGprovides a top down view of the aircraft with the card rotating to be correctly aligned. In the example above the plane was pointing at about 340 degrees.
As the DG is driven by a gyroscope over time it will drift away from indicating the correct direction. It is recommended that the DG be checked against the compass every 15 minutes or so in flight and it readjusted to the correct heading. (The effects of Gyro Drift are controllable in FS9 under Realism Settings )
The Australian rules for VFR flight state that the pilot must be able to navigate the aircraft by visual reference to ground or water, and must be able to positively fix the aircrafts position with respect to features shown on charts at intervals not exceeding 30 minutes. For Long routes, techniques such as Pilotage and Dead Reckoning <See page DedReckonPilotage> can be used to keep the plane on track between defined fixes
Obviously when near airports, or flying close to or in controlled airspace it is necessary to be able to fix ones position more frequently due to the proximity of other aircraft and the need to keep away from airspace in which on is not allowed ( e.g. other airports in the vicinity , Restricted and prohibited areas
Visual Reporting Points
As the controller and pilot have no formal way of passing information about distance and bearing from specific locations a system of visual reporting points are used close to some major airports. These are usually easily identified features on the ground, which are also named and marked on the appropriate navigation chart. At specific airfields the pilot may have to make the approach or departure to the airfield over on of these named points.
The Requirements for carriage of radios depend on the type of airspace through which the plane will be flown, If the route enters controlled airspace, or uses a uncontrolled airport where the use of radio is mandatory then a radio needs to be carried.
The current pilot clients, (squawkbox and FSINN) provide the capabilities needed for radio communication, either to a controller for operation in controlled airspace, or pilot to pilot comms (UNICOM - 122.80) when operating away from controllers. Even if the plane is not fitted with a radio the clients allow a radio frequency to be selected with a text command.
Most FS9 altimeters allow the QNH be entered directly by turning a knob at the side of the Altimeter. Hovever depending on the location of the flight the figure quoted by the controller may not be in the same units as the display (The US uses Inches of mercury and most of the rest of the world quotes the figure in hectopascals ( for conversion 1013Hpa = 29.92"). FS9 by default assigns the "B" key to correctly set the Altimeter depending on the local weather
The default scenery provided with FS9 provides a reasonable implementation of the major features found in the real world, built up areas, hills, roads, rivers etc are modeled such that a pilot can navigate using them, To make life easier there are many addons, both pay and freeware which make the scenery closer to the real world.