Grantville Gazette Volume 24

by Eric Flint

  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.

  Navigation is further complicated by the air you are flying through. Crosswinds, headwinds and clouds can all interfere with navigation. Many pilots have been blown far off course by a crosswind that they could not even feel while flying. Headwinds can slow an aircraft down so that while the pilot has a instrument stating one speed, in reality the aircraft is going much slower. All of these factors require that the pilot of an aircraft be very careful with his navigation, especially in the seventeenth century, because airports are few and far bet
ween.

  Creating aerial maps will require that we have the ability to identify on the map exactly where all the transmission towers and radio stations are. This allows us to build a radio direction finder that will assist us in finding our position on the map. The pilot can use a radio direction finder that gives the compass heading to each of the radio stations we can hear.

  Navigation is also possible by referencing your position to large known landmarks seen on the ground. Much like the bush-flying techniques now used in Alaska These are marked on your map. While navigating, several other things need to be taken into consideration. Among them is the fact that the air that you are in is normally moving and will push you around in the sky even though you think you're flying in a straight line. Allowance must be made for this either by continuous position checks or by calculating known wind drift as you fly and correcting for it.

  Now for the tech stuff:

  PAPI and VASI

  The lamps themselves can be constructed with large grooved glass lenses which are tinted for color and placed in a sheet metal or a wooden case. Illumination for the lamps can be provided by arc lights, or limelight, or even an intense flame. Certainly standard high wattage electrical lamps could be used, however the construction of these lamps may be difficult for some time.

  ALS

  Light rails or flashers are a little more difficult because the poles and the lights will more likely require high wattage electrical lamps. However it is possible that limelights could be mounted in the place of electrical lights. It should be noted that limelight requires a supply of gas and oxidizer, even if it is only producer gas and compressed air.

  Runway Lights

  The lights along the side of the runway and those lights indicating the beginning and end of the runway will also need to be lit, at least at night. Again these lights can be created using grooved glass lenses and a lighting system. It should be noted that the lighting system can be done with arc lights if you have electricity or even gas heated limelights without electricity. Limelight's biggest problem may be the construction of the gas delivery system for each light.

  Beacons

  In the new timeline the electronics needed to produce these devices will be necessarily crude. In technical terms, transmission frequency will be produced using mechanical resonators and the modulation will need to be mechanically induced onto the carrier frequency. In other words, while it will be difficult, it is well within the tech level we are working with. It should also be noted that any large radio broadcast station tower can be used as a beacon as long as the exact location of the tower is known. This means that radio broadcast stations in cities will be usable as beacon towers.

  Radio Direction Finder

  Direction finding radios are basically a radio with the antenna that is formed in a loop. The direction finder is operated by rotating the loop antenna until you have a maximum and minimum amount of signal. The minimum amount of signal is when your antenna is aligned so that it has the minimum amount of surface in line with the radio broadcast source. The maximum amount of signal is when the loop is at the maximum amount of surface, or at right angles to the source.

  Careful positioning of the dial can give you a direction in comparison to your flight path. This indicates the radio tower transmitter's location. Again it should be noted that with the strong beacons provided by resonators on the ground means a crystal radio circuit can be used in the radio direction finder on the aircraft.

  Localizers and Glide Slopes

  It will be necessary to use a resonator as a frequency creation device for the broadcast wave. Once the broadcast wave has been created, it will need to be sent to the antenna by shielded transmission lines. This can be done by using twin-element open-air lines that are enclosed within a metal shield. Think of two copper wires inside a large stove pipe, with the pipe thoroughly grounded. This system will get the power to the antenna without interfering with the antenna's broadcast capability, thus allowing the creation of a transmission that can be detected by the aircraft. Fortunately, we are not trying to broadcast very far, so we can use lower power in the transmission. The lower power simplifies many of the problems encountered when trying to transmit over longer distances.

  ILS Detector in the Aircraft

  The detector in the aircraft can be constructed using crystal radio techniques. The glide slope and the localizer both use different frequencies allowing each to be separately detected. The output of the crystal detectors can be connected to the coils that operates the needle in a dial. Normally the dial contains both needles with the localizer needle (left to right approach control) being vertical and the Glide Slope (up to down approach control) being horizontal. The dial arrangement allows the pilot to guide his aircraft down the proper angle by keeping its two needles crossed at right angles. Modern equivalents in our timeline work the same way but are made using modern semi-conductors. Substitutes for the new timeline will be bulkier and moderately heavier, but will work just fine.

  In our time line these developments came over a period of fifty years. First with a smudge pot at the airstrip and a man with hand flags guiding the aircraft to the ground. Then the development of early PAPI and VASI, and then with the development of more complicated glide slope and localizer installations. Point-to-point navigation went through many incarnations, including celestial navigation much like was used by ships on the ocean. Then radio locator would guide aircraft to cities that had radio stations. Eventually beacons were developed that contain their own direction finders and with broadcast to the aircraft where they were and how far away they were.

  So what does all this mean in Grantville? First, as air traffic increases there'll be a large increase in the amount of navigation equipment maintained so as to guide the flyers. As we already have airplanes in the air, we can assume that they have at least a smudge pot and windsock at the airport, allowing the pilot of the aircraft to find the airport.

  The next improvement will probably be some form of air chart or map that will have major landmarks and directions for getting to desired destinations. These charts or maps will probably be in a continuous state of change, as good information is obtained. The more flying in an area, the more information will be collected for new charts.

  Another early improvement will probably be radio direction finders mounted on the aircraft. As earlier stated, these radio direction finders will allow us to locate ourselves on our chart by finding the directions to known radio stations and using those directions to define a location for our aircraft on the chart. Pilots can be trained in this system in just a couple of days, so this will not change much of the current pilot training. Electronic glide slopes, localizers, and light rails will come as open grass fields give way to defined runways.

  As destinations become identified in the USE, it will be essential that radio tower beacons are established at each destination. Especially in the beginning, these will likely take the form of large radio broadcast towers for the local radio broadcast station. But as navigation becomes more and more complicated, dedicated beacons may be established simply to provide waypoints for the pilots of the aircraft finding their way from one location to another. Eventually the beacons will be used to transmit valuable information to the pilot. Items such as weather conditions, wind speed and visibility alerts can all be transmitted over the beacon signal, and can provide valuable enhancement and additional safety for those who are flying in 1632 universe.

  So how will this work? The typical flight would begin with the pilot getting as much information on the weather as he could, then performing his ground checks on his aircraft, starting the aircraft and taking off. Once in the air, the pilot would set course for his destination, and en route make allowances for the drift caused by crosswinds or headwinds slowing them. During the flight, navigation would be checked by using his radio direction finder to get directions or bearings on various beacons and radio stations within the USE.

  When a pilot is close to his destinatio
n, he would begin to scan the area for the various indicators of where the airstrip is. On a good clear day, the airstrip should put up enough smoke in a column to let them know where it is, or use the flashing lights of the beacon tower or even the run of lights of the VASI. Setting his instrument landing system for the proper frequencies and using the directions given by the ILS, the pilot would bring his airplane in for a successful landing. This all presumes a good weather day. Navigation instrument landing systems will provide really big benefits when the weather gets bad or if the pilot is caught in the air after dark. These instruments and landing navigation aids could make the difference between life and death

  Finally, as traffic increases it may become necessary to have some form of air traffic control. In the beginning air traffic control may be limited to tower operators at the individual airports. These tower operators will determine which aircraft has priority in landing. An increase in traffic will eventually bring the need for enroute air traffic control, definition of traffic routes, and all of the modern systems that we have in place in our timeline. However, all this will not come until air-traffic levels are much higher.

  While the above information is moderately simplified, it should serve to give you a feeling for the difficulties involved in aerial navigation. The navigational aids described here are those most familiar to small aircraft pilots. As the existing up-time pilots are primarily of small aircraft, that is where we would start.

  Of course, one large concern is going to be: who is going to pay for all this? This is a question that will have to be addressed by the local governments and the organizations of pilots themselves. In the early days, a subscription service supported by the pilots themselves is most likely. But as the control becomes more and more complicated, the expense will need to be borne by a larger part of the flying public. But then we are in the area of taxes and that is up to the politicians.