Taming the Sky: The Art and Science of Radio Navigation Inaugural Flight of US Airmail Max Miller, Pilot (1918)
Out with the Old... • Pilotage served the pre-WWI aviator • Dead Reckoning improved the ability of the navigator to fly vast distances… • Both are limited… ?? By what ?? • WINDS!!! • Today both serve a role in the modern aviator’s toolkit, but have been improved upon with new methods of navigation.
In with the New! • Radio Navigation Systems • V.O.R. • Very high frequency Omnidirectional Range • N.D.B. • Non – Directional Beacon • L.O.R.A.N. • LOng RAnge Navagation • G.P.S. • Global Positioning System
V.O.R.s An analogy works well for understanding the principle behind a VOR stations operation. Imagine a rotating beacon of light broadcast in only a single direction at any given moment. The beacon is rotating at a constant rate. An omnidirectional (all directions) strobe goes off every time the beacon points in a specific direction, such as towards the North. If you determine the delay between the flash of the strobe and the time that the sweeping beacon is observed, you can tell how many degrees your direction is from that of the specified direction… or from North, in this case.
V.O.R. Basics True North Magnetic North Magnetic North is used as this is the only reference direction that can be determined with a vacuum system and electrical failure. It is the basis for ALL navigation. West East South
V.O.R. Radials • A radial is a specific “beam” transmitted by a V.O.R. station. • There are 360 radials, or one per degree. • Radials are named based on their clockwise bearing from Magnetic North. • The 90° radial points to the magnetic east from the V.O.R. station.
V.O.R. Compass Rose On the Wisconsin Aero and on Sectional Charts, every V.O.R. has a compass rose printed around it in BLUE ink. The compass rose shows MAGNETIC direction of each radial transmitted. Note the alignment of the Victor Airway V 228…
V.O.R. Benefits • Create 360 courses TO and FROM station • Multiple stations, so multiple cross checks • VERY little interference from lightning • Accurate navigation to 1° of precision • Straight line courses • Automatic wind drift correction!! • Course and radials are Magnetic • Effective at 1000’ AGL • Works regardless of aircraft orientation
V.O.R. Limitations • Ground Based Transmitters • Line of Sight (VHF) frequencies • Limited range at low altitude • Limited range at higher altitudes… not a global solution.
Creating the Zero Radial Reference Signal: Omni-directional Radial Signal: Electronically Rotated Beacon Signals are “In-Phase”
Creating any other Radial Reference Signal: Omni-directional Radial Signal: Electronically Rotated Beacon Delay due to location other than the Magnetic North = Phase Shift!!
V.O.R. Phase Shift Phase Shift between the reference signal and the rotating beacon equals the radial on which you are located. Magnetic North True North West East South
Airborne V.O.R. Equipment V.O.R. instruments only operate when they are tuned to the correct station frequency. Most GA aircraft have two V.O.R. receivers called Nav1 and Nav2. They are typically tuned to two different V.O.R. stations for “cross checking”. Some aircraft use a combination of radio based navigational instruments.
Nav1 Nav2 Airborne V.O.R. Equipment • External Antennae that are “V” shaped, typically on the rudder • Cockpit Instruments, one for each navigational tuner in the radio stack