Eric Flint: Grantville Gazette Volume 24

Indeed, aircraft will be among the first items sought after by governments in the seventeenth century once they know flight is possible. This will rapidly create a situation where many aircraft, perhaps as many as fifty, over the next five or ten years will be flying across Europe. Navigation will become a serious issue. Next time you get a chance, look out the window of an aircraft and look at the ground. Honestly, it all looks the same from the air. Getting from your start point to your destination can be fairly difficult. Especially because there are no maps that reflect the landmarks of the seventeenth century from the air.

There are a few of the up-timers who have been trained in aerial navigation. These experts will be able to pass on some of the knowledge needed to fly safely from point A to point B. Nevertheless the slightest mistake can end up with your aircraft many, many, many miles from your destination. A further concern is that there are very few designated landing sites. Of course, any open field will be suitable for most of our aircraft, but once you land there's no fuel or knowing exactly where you are, and there will be no supplies or ground crew to get you back into the air. It becomes absolutely necessary, therefore, to actually arrive at your desired destination. As a result of this, some form of aircraft navigation aids will become absolutely necessary.

Aircraft navigation aids come in two types. The first type are called landing aids, and have to do with helping the pilot to get his aircraft safely onto the ground without bending it. The second type are in-flight navigation aids. These have to do with helping the pilot find his way from origin to destination during a flight.

Landing aids are anything used by the pilot to guide himself to a safe landing. These devices can be both aircraft- and ground- mounted. Ground-mounted devices are usually lights, especially for nighttime operation. These lights are used to indicate the size of a runway, the end of a runway, and whether or not the aircraft is on the appropriate slope approaching the ground. This appropriate angle of fifty feet in a thousand, or about five percent, is called a glide slope.

Aircraft-mounted equipment involves an electronic mechanism that, by the use of needles in a dial, can indicate to the pilot whether or not the aircraft is approaching on the appropriate glide slope and whether or not the aircraft is approaching the air strip from the correct direction.

The first of the ground mounted systems is called a PAPI or Precision Approach Path Indicator. And there is the similar VASI, or Visual Approach Slope Indicator. The systems are composed of a series of lamps, white on top, and red on the bottom. These are inside a shrouded mounting that limits which lamp is visible to the pilot depending on the angle the device is viewed from.

The old saying is "if you're red you are dead." This is because when the aircraft is at the proper angle, one red light and one white light are visible to the pilot. If the pilot can see two red lights, he is coming in too low and is in danger of hitting the ground. If the pilot sees two white lights aircraft is too high and will not land at the end of the runway. This system is particularly desirable because it is fairly easy to implement..

The next ground mounted landing aid is called an approach lighting system, or ALS. It is more simply referred to as a light rail. These are a series of lamps are mounted on poles in such a manner that the pilot will only see one lamp when he is approaching at the proper angle. Light rails can also be what are called flashers, which means that the lamps themselves flash in sequence so as to appear to float towards the ground..

As long as we're talking about lamps, there are a few other lamps that need to be mentioned. The runway is normally marked by having a line of green lights that indicate the beginning of the safe landing zone of the airstrip. Additionally, many groomed airstrips have side markers to show the edges of the runway. During daylight hours they are usually short posts and painted a contrasting reflected color, at night they are usually red or blue lights.

The last light I want to mention is that of the rotating locator beacon. This is a very bright light, mounted on a tower, that indicates to the pilot where the landing area is. Later on we will be talking about other navigation aids, but these devices only get the aircraft to the general area of the landing zone. The rotating beacon is a visual indicator that will guide the pilot the last few miles to the air strip.

More complicated are the electronic landing aids. These landing aids are composed of three devices. The first device is called the localizer. This is a moderately complicated horizontal antenna mounted at the far end of the runway. Because of the physical placement of the antenna elements, a radio signal is emitted that is composed of a series of lobes radiating from the antenna. These lobes can be detected by the aircraft and can indicate the proper angle of approach to the aircraft.

The second device is called the glide slope. The glide slope is another set of antennas, designed and mounted vertically. These provide a radio signal which can be detected by the aircraft that gives a proper angle for descending to the landing strip.

The third device is called the ILS display. This is a device mounted in the airplane that can detect the radio signals from the glide slope and localizer and indicate to the pilot whether or not the aircraft is making proper approach.

For any of this to work, however, you have to be able to find the airport. Historically, airports were first indicated by a smudge pot. That is, they had a large barrel full of oily rags. This would be set on fire, creating a large smoke cloud to give a visible indication of where the airfield was. Also it is very common to have a wind sock. This device is usually a large cone of brightly colored fabric that is attached to a pole. It is open on both ends, with the more narrow end at the bottom, so as to indicate the wind direction and strength for the pilot looking for a landing site. Direction of course is indicated by the direction the sock is pointing, and the strength is indicated by how much of the stock is fully inflated and standing out.

Everything we've mentioned up until now works just fine as long as you're operating out of one airport. Navigating from one airport to different airports, especially one that is a great distance from your original point, is a very specialized skill.

As we mentioned earlier, if you view the ground from above, one part of it looks very much like another part. In fact the higher you go, the more difficult it is to determine exactly what you're looking at on the ground. Experience and training can help the aerial navigator find his way around, but what every navigator really needs is a map. Aerial navigation maps are not really like any other map used either now or during history. Much of the detail on an aerial navigation map is numbers and letters. The numbers and letters refer to different beacons that have been set up to help aircraft navigate from one point to another point.

Further, while some high points are listed, most land features lower than one thousand feet in altitude are not listed. Rivers, major roads, and large cities are marked on the maps because they are easily discerned from altitude. Nonetheless, much of the information found on a standard map is not included with an air chart. But the map is most important because of the information that is printed next to each of the marked beacons. Each beacon on the map is identified by its position, and by the radio frequency which it uses. Pilots, desiring to navigate, plot each beacon and locate themselves on the map using bearings from those beacons for themselves. This is done by finding the imaginary line to each beacon and extending it backwards towards where your aircraft is. Using two or more beacons, the lines will intersect and show where the aircraft is.