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What was considered in 1937 to be a breakthrough feat for a full-size airplane is today accomplished regularly in model airplanes. What took hundreds of pounds of generators, radio gear, sensors, and actuators to perform the first-ever fully automatic landing is now done with a few ounces of microminiaturized GPS receiver, processor, MEMS sensors, servos, and a LiPo battery. The HobbyZone Sportsman S+RTF(see video at bottom) is an example. Most modern commercial aircraft are capable of landing themselves in an emergency situation. Just today there was a news report of an American Airlines pilot that died in flight and the copilot took over to land the airplane; however, that Airbus A320 could have handled the job if necessary.
Short-Wave Radio Lands Army Plane Without Human Aid!
Radio-Craft brings you probably the first detailed story in any radio magazine, of how Uncle Sam's robot plane made perhaps the world's first entirely automatic landing, as told by Captains C. J. Crone and G. V. Holloman of the United States Army Air Corps.
Fig. A - The flight and landing paths of the U.S. Army plane C-14 Cargo as it made the world's first completely automatic airplane landing without a pilot's aid.
Much has been written in recent months concerning the personal equation during flight and the influence of this equation on accident rates. The newer developments in modern-aircraft, to insure high performance, have required an increasing number of cockpit devices, all of which demand the attention of the pilot at some time or other during any given flight.
Pilots have felt and .expressed the need for simplification of the various controls that must be manipulated and have expressed the need for this simplification in no uncertain terms. This simplification means that many of the functions now performed by the pilot in flight control and navigation must be done automatically. The landing of aircraft is no exception to this general trend. With this in mind, the personnel of the Materiel Division, U.S. Army Air Corps, over 2 years ago began active prosecution of development work to simplify the procedure of instrument landing by making it automatic.
Fig. B - Views inside the cockpit of the Army airplane showing the radio compass and relay; the automatic landing equipment (inset 1), and the frequency selector control box (inset 2).
For over a year Air Corps test airplanes have been flown automatically over distances that have indicated the thorough reliability of the devices employed. This was one step in the perfection of automatic landing. The features therefore that are built into the automatic landing system are not only useful for the landing but are used throughout the entire flight of the airplane across the radio navigational aids with which the United States is provided. Test airplanes from Wright Field have been flown automatically from Wright Field as far as Texas, and return, under automatic control. Several flights have also been made from Wright Field via Buffalo, New York, to Newark, New Jersey, and from there via Langley Field, Virginia, to Wright Field, Dayton, Ohio. Of course the automatic landing involves other factors besides control of direction. These factors are: (1) control of altitude, (2) engine control, (3) glide control, and (4) further engine control after landing.
With the provision of the Air Corps automatic landing system in an airplane and with the installation of the new "Z"-type radio range beacons, the airplane may be flown automatically from station to station, from East to West Coast. If we imagine a group of the future "Z"-type radio ranges placed in a line joining the runway of the landing field and extending to a point 5 miles therefrom, some idea will be gained of the essential features of the Air Corps automatic landing system.
By reference to Fig. A, which represents the path of flight and landing made by the Army C-14 Cargo airplane on Monday, August 23, 1937, a generally clear idea will be obtained of the path of the airplane in the horizontal plane. The insert shows the airplane flight path and landing path which the Army airplane followed in executing what is believed to be the world's first entirely automatic airplane landing! This illustration should be self-explanatory and in itself is evidence of the continuation of development on the Air Corps system of instrument landing.
Fig. C - One of 4 mobile "guiding" stations for automatic landings; (1) 1,000-meter radio compass locator antenna, (2) 4-meter marker beacon antenna. Both transmitters operate continuously; the operators in the truck do nothing after starting the L.F. compass guiding station and H.F. marker beacon.
On Monday, August 23, 1937, after over 2 years of intensive research and design with respect to automatic control features and automatic flight procedure, 2 entirely automatic landings were made in the period of an hour under adverse air and wind conditions by Capt. Carl J. Crone, Director of the Instrument and Navigation Laboratory and Capt. George V. Holloman, Assistant Director of the Laboratory and Mr. Raymond K. Stout, project engineer in automatic landing. Since that time additional landings have been made in which disinterested personnel have been carried as observers on the flights in order to check robot landings.
In the execution of an automatic landing, using the U.S. Air Corps system, it is necessary for the pilot of the airplane bring the airplane to a definite altitude, determined by the sensitive altimeter, and to place the airplane within the range of radio reception of the ground radio facilities. It is, of course, desirable to place the airplane generally in the direction in which it is expected to land, but this is not necessary as was determined in flight and can be understood by reference to Fig. A in which the airplane was actually placed in a position which headed it 180° away from the direction of final landing! When the pilot has placed the airplane at a selected altitude in the vicinity (20 miles or less) of the landing field, the master landing switch is closed and the airplane proceeds through the following routine in accomplishing the automatic landing:
(a) The selected altitude is automatically maintained and the airplane's heading is changed so that it flies in the direction of the radio guiding station most remotely located from the landing runway.
(b) The new robot landing controls the "take over" as described below.
Sequence of Operations
The altitude control device, shown at A in insert 1, Fig. B, maintains the proper altitude during the initial approach as just noted. The directional relay, which interlocks the radio compass and the gyro pilot and which therefore causes the change in heading of the airplane, is shown at B in Fig. B. Adjacent to this relay is shown the radio compass marked C, the frequency of which is automatically set by the interaction of the marker beacon receptor D working in conjunction with the frequency selector E (insert 1, Fig. B). The pilot of the airplane is informed as to the correctness of automatic settings by observing the frequency selector indicator F (insert 2, Fig. B). (That is, when the airplane passes over the marker beacon, the frequency changer in the airplane is set automatically in order to select on the radio compass receiver the frequency of the next succeeding station. In other words, the impulse received in the airplane from passing over the marker beacon is used to start in operation the frequency selector and changer.)
Fig. D - The automatic throttle control used for automatic landings. The inset (1) is a close-up of the control apparatus.
Through the automatic and cooperative action of these devices, the airplane heads to the compass guiding station (Fig. C) farthest from the landing field as shown in Fig. A. Upon reaching that station the frequency is automatically changed to Station No.3 where it is again automatically changed to the frequency of Station No.2 where the frequency is again automatically changed to that of Station No. 1 while at the same time the engine throttle is automatically operated by the throttle engine shown at G (insert 1, Fig. D); and again shown in H, Fig. D. (That is, the ground radio equipment operates the same as lights burning on the ground. They are placed in operation by ground operators and nothing is done to them until their use is no longer required and they are turned off. The effective range of the markers, at low altitude, is throughout a circle 1/8-mile in diameter.)
The throttle engine is interconnected with the altitude control in such a manner that should the airplane reach its minimum altitude prior to reaching radio station No. 1 the throttle engine will be so actuated to control the airplane in such a manner that it will maintain accurately the minimum altitude required for the operation of the automatic landing system.
Fig. E - Left, 1 - side view of the Army test plane C-14B showing the various antennas used in connection with the automatic landing system; right, 2 - a switch on this landing strut of the plane automatically controls the engine-throttling apparatus just as the plane makes contact with the ground.
After passing Station No.1 the throttle engine is so actuated that the airplane maintains a selected glide angle and rate of descent until "ground contact" is made. When ground contact is made, the throttle engine is further actuated by the landing-gear switches, one of which is shown at I in Fig. E2, which in turn causes the engine to be idled and proper braking applied.
There are 4 mobile (truck) ground transmitting stations as shown in Fig. A. Each truck, shown in Fig. C. carries 2 transmitters; one (which has a transmitting range of about 35 miles) is for guiding the airplane by means of the radio compass to the truck position. These transmitters operate in the radio beacon band of 200 to 400 kilocycles. The other, or marker beacon transmitter, operates on the ultra-short wavelength of approximately 4 meters.
At the present writing, the automatic landing system has been flown so that all of the landings made to date have been made under cross-wind conditions varying in intensity as high as 11 miles per hour.
Fig. F - The gyro pilot or "automatic pilot" shown at J permits automatic flight control for an almost indefinite period. The master landing switch (1) and the axillary reset switches (2, 3, 4 and 5) are additional items for use in automatic landing.
The Sperry gyro pilot has been used throughout as the automatic flight control feature of the airplane. Certain additions to the Sperry pilot have been required in order to provide for the automatic control of direction. At J, Fig. F, is shown the Sperry gyro pilot installation; left of this unit is shown the master landing switch (1) and the auxiliary reset switches (2, 3, 4 and 5).
The series of tests conducted through the last 2 years have brought many humorous incidents not the least of which have been such terms as "nervous shoe laces" and jittery hands" which have always been evident to the observer watching the pilot keep "hands off" during the automatic landings.
Figures G and E1 are views of the airplane used in the conduct of all of the experiments on the Air Corps automatic landing system. In these photographs, the various antennas are identified as: 11, the antenna for the communications transmitter and receiver; 12, the balanced antenna for the radio compass; 13, the radio compass loop antenna; and 14, the marker beacon receptor and its antenna.
Fig. G - At 11, the communications transmitter and receiver antenna; Fig. E, shows others.
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