US2127954A - Radio beam and receiving device for blind landing of aircraft - Google Patents

Description

Aug. 23, 1938. F. w. DUNMORE 2,127,954

RADIO BEAM AND RECEIVING DEVICE FOR BLIND LANDING OF AIRCRAFT Filed Aug. 5, 1932 5 Sheets-Sheet l Aug. 23, 1938. F. w. DUNMORE 2,127,954

RADIO BEAM AND RECEIVING DEVICE FOR BLIND LAND ING 0F AIRCRAFT Filed Aug.' 5, 1932 5 Sheets-Sheet 2 FIGURE 2.]

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' Aug. 23, 1938. F. w. DUNMORE 2,127,954

RADIO BEAM AND RECEIVING DEVICE FOR BLIND LANDING OF AIRCRAFT Filed Aug. 5, 1932 5 Sheets-Sheet s FSGUIZE 4 [mAeNn-uoz SCALE. m ARB'TRARY uun's] FIGURE 5 Aug. 23, 1938.

F. W. DUNMORE RADIO BEAM AND nscmvme DEVICE FOR BLIND LANDING 0F AIRCRAFT Filed Aug. 5, 1932 5 Sheets-Sheet 4 I new 00 com I com Patented Aug. 23, 1938- -RADIO BEAM AND RECEIVING DEVICE FOR. BLIND LANDING OF AIRCRAFT Francis W. Dunmore, Washington, D. 0., assignorto the Government oi the United States, as represented by the Secretary of Commerce Application August 5, 1932, Serial No. 627,625

16 Claims.

(Granted under the m of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes only without the payment of any royalty thereon.

This invention relates to the use of radio beams or landing aircraft.

The practicability of the use of directional radio as an aid to point-to-point flying has been demonstrated by over three years of service given by the radio range-beacon system on the fixed airways. By means of this system the pilot can keep accurately on his course, know approximately the points he is flying over, and proceed unerringly to his destination. Scheduled air transport operation is thus immeasurably aided; many flights are made which could not possibly be made without the use of radio direction facilities. Nevertheless, interruption of scheduled flying is still the rule whenever the landing field lies in an area completely inclosed by fog. The results secured by the development 01' instrument flying and radio navigational aids are then nullified through the lack of means for safe landing at the-desired destination, under conditions of poor visibility.

Any system of aids permitting the landing of aircraft under conditions of zero visibility must give the pilot information of the position of his airplane in three dimensions as he approaches and reaches the point of landing. Means are available for orienting the landing airplane along the proper runway and also furnishing the pilot an indication of his approximate position along that runway (see Air Commerce Bulletin", vol. 2, .No. 4, August 15, 1930, and Bureau of Standards Journal of Research, October 1930, vol. 5, paper 238). These do not form a portion of my invention except as they areused in combination with the landing beam to produce the new result of this invention. All that remains necessary for landing aircraft when the airport is completely inclosed by fog is to give the pilot vertical guidance. 1

The object of my invention, therefore, is to providea radio beam system whereby a pilot is furnished with the necessary vertical guidance to permitthe landing of an airplane under conditions of poor or no visibility. The transmitting portion of the system comprising my invention .consists of an ultra-high frequency beam directed at a small angle above the horizontal, this angle and the degree of directivity of the beam being so adjusted that a predetermined line of constant field intensity on the under side of the beam will mark out just the proper gliding path 5 clearing all obstructions and convenient for landing. The beam is oriented so that its horizontal protection or trace is along the landing runway.

-As noted in the foregoing, details of a system radiations in order to effect a safe landing also 15 form a portion or my invention. 'Briefly, this equipment comprises an ultra-high frequency antenna system, receiving set and landing path indicator. By flying the airplane along such a 2b path as to keep the deflection of the landing path indicator constant, the pilot comes down to ground on a curved line suitable for landing. If the airplane rises above this line, the deflection of the indicator reads too high while if the airplane drops below this line, the deflection of the indicator reads too low.

Other and further objects of my invention will be apparent from the following detailed description and the accompanying drawings. It is to be expressly understood, however, that these drawings are for purposes of illustration only and are not designed for a definition of the limits oi my invention. Referring to the illustrations,

Figure 1 is a drawing of typical transmitting equipment for producing the landing beam.

Figure 2 shows a circuit diagram of one form of an ultra-high frequency oscillator suitable for use in the transmitting system shown in Fig- 310 ure 1.

Figure 3 shows a circuit diagram of an ultrahigh frequency receiving system suitable for use on the airplane in the detection of the radio- I beam signals.

Figure 3A shows a filter suitable for ouse in the arrangement oi Figure 3.

Figure 4 is a drawing of the landing path indicator.

Figure 5 shows the directive characteristic of the landing beam in the horizontal plane.

Figure 6 shows the vertical directive characteristics of the landing beam.

Figure '1 shows a typical landing glide path obtained by the use of this system.

Figure 8 is a 3-dimensional view illustrating the use of the landing beam in conjunction with means for horizontal guidance.

Figure 9 is a conventional showing of the radio receiver carried by the aircraft for detecting and indicating, preferably by an indicator 51,-

- cult and the antenna coupled thereto is shown in Figure 2. The numeral i denotes a vacuum tube suitable for generating ultra-high fre- "quency oscillations, 2 denotes a plate inductor, 30-

3 denotes a grid inductor, ii is a small air condenser, approximately equal to the interelectrode grid to plate capacity of the tube. connected in series to reduce the capacitance of the oscillatory circuit, a condenser 3 is of relatively large capacity and connected in series as a safety measure in case of flashoverof condenser Q, and 6, I, 8 and 9 are suitable choke coils to keep the oscillatory current out of the power supply leads. The plate supply for the oscillator is secured by means of a step-up transformer. the secondary winding of which is connected between the center tap of the filament transformer and the plate choke coil 9. The primary winding is connected to any suitable source of A. C. power, such as the cycle supply mains. The use of A. C. supply permits the use of simple audio-frequency amplifying equipment and filter system in the receiving equipment on the airplane as will be shown in connection with Figure 3. The radiating antenna iii is inductively coupled to the inductor 2 of the oscillatory circuit. Since horizontal antennas are used, the resultant radio beam is horizontally polarized, requiring the use. of a horizontal receiving antenna on the airplane.

Referring to Figure 3 the detector tube ii contains a plate I? connected to one-half of a doublet antenna it, a control grid it being connected to the other half of the antenna i3 andto a grid-leak resistor 15. The tube It also contains a filament it connected to a filament heating batter-y .il. and to the negative terminal of a plate battery it. In addition'to the above-mentioned elements it contains a screen grid l9- connected to the battery it. The plate 02 is also connected throughthe primary of a transformer 20 to the positive terminal of the battery It. An amplifier tube 26 contains a plate 22 connected through the primary winding of a transformer 23 to the battery it and a grid 26 connected to a filament 2% through the secondary winding of the transformer 2@. The filament heating .battery H for the filament it also supplies current for heating the; filament 25. The terminals of the secondary winding of the transformer it are connected to the A. 0. terminals of an oxide rectifier 26. The D. 0. terminals of the rectifiers are connected to a landing indicator 2! in series with a glide angle adjustment resistor 28, the latter serving to control to some extent the angle of the glide path. If desired, a mechanically tuned reed filter t9 consisting of driving coils 50 and pick-up coils 5i may be interposed between the secondary winding of the transformer 23 and the oxide rectifier 26, as shown in Figure 3A. The reed 52 in this filter is tuned to the frequency of the power supply to the plate of tube 2 of the transmitter, shown in Figure 2, and serves to exclude all extraneous frequencies while passing the desired frequency. The four choke coils 29, 30, 3! and 32, are designed to keep the ultra-high radio frequency out of the audio-frequency circuits of the receiving set. The method of coupling of the antennas to the electron tube and associated circuits in both Figures2 and 3 may be as shown or through suitable transmission lines, which arrangements are known to the art.

The details of the landing beam indicator are shown in Figure 4. It consists of a D. C. microammeter 33 mounted on its side on the pilot's instrument board so that a pointer 33 moves vertically rather than horizontally. The deflection to be kept constant is chosen at half-scale reading, the instrument pointer being then in a horizontal position, coinciding with an arrow 35 marked On course. A rise of the-pointer 36 above this position 35 indicates that the airplane is above the proper landing path, while the reverse is true if the pointer 36 falls below the arrow 35.

The operation of my invention will now be described. In Figure 5 the transmitting equipment described in Figures 1 and 2 is shown located at 36 and the horizontal directive characteristic of the radio'beam produced is indicated by a graph 31. In the illustrations which follow it will be assumed at all times that the airplane is guided along the desired azimuthal direction of the landing beam by lateral guiding means.

In Figure .6 the transmitting equipment is shown located at 38 and the directive characteristic of the radio beam produced in the vertical plane is indicated by a line 39. A dot and dash line to indicatesthe line of maximum field intensity of the beam. This line is oriented at such an angle and the degree of vertical directivity of the beam 39 is so adjusted, that a glide path M will be suitable for a landing path for airplanes. Sixty-cycle -modulation of the landing beam transmitter is provided to facilitate audio-frequency amplification at the receiving end. The airplanedoes not fly along an inclined axis (40 of the beam, but on the curved path M under the inclined axis whose curvature diminishes as the ground is approached. The path M is the line of equal intensity of received signal below the axis of the beam. The diminution of intensity as the airplane drops below the beam axis is compensated bythe increase of intensity due to approachingthe beam transmitter. "Thus, by flying the-airplane along such a path as tokeep the deflection of the landing path indicator on the instrument board constant, the pilot comes down to ground on a' curved line suitable for landing. To facilitate its use by the pilot this instrument is mounted on its side so that the pointer ,moves vertically rather than horizontally. The deflection to be kept constant is chosen at half-scale reading, the instrument pointer being then in a horizontal position. A rise of the pointer above method of furnishing altitude indication.

this position indicates that the airplane is above the proper landing path, while the reverse is true if the pointer falls below its horizontal position. The indications of the position of the airplane relative to the landing path are thus made readily comprehensible.

Several important advantages obtain for this The landing path may be so directed as to clear all obstructions. The pilot following the landing path is automatically kept above obstructions and no longer needs a thorough knowledge of the terrain in order to effect a safe landing. Secondly, the landing path may be of different shape to suit diflerent landing fields. This is of particular importance in getting into a small field." A third advantage lies in the fact that in the act of following the landing path, the pilot automatically "levels oif",*th'ereby facilitating a) normal landing albeit somewhat fast. A' fourth advantage is that the landing glide may be begun at any desired altitude, within a rather wide range (say, 500 to 5,000-feet) A fifth advantage arises from the ease of using the landing beam indications. No manipulations on the part of the pilot are required. The tuning is fixed. Since a line of constant field intensity is followed no'control of volume is necessary.

A typical form of glide path is shown in Figure 7.

The field intensities are plotted as abscissas and altitude of the airplane as ordinates at each 1,000 feet of distance from the beam transmitter. The data plotted were obtained experimentally, the field intensity being measured in terms of the deflection of the landing beam indicator. It will be observed that corresponding to this glide path a pilot coming in at an altitude of 1,000 feet will observe half-scale deflection of his instrument (250m) at a distance of approximately 9,000 feet from the transmitter. If he then follows theline of constant field intensity-corresponding to halfscale deflection on his instrument, he reaches an altitude of 10 feet at a distance of 2.000 feet from the beam transmitter. This is actually the point of contact of the airplane with the ground, the receiving antenna being mounted on top of the airplane, 10 feet from the ground.

The operations involved in landing an airplane through the use of the landing beam are illustrated in Figure 8. While used in conjunction with other transmitters and devices, as noted before only the landing beam transmitting and receiving system used alone or in combination with the runway and/or marker beacon comprises my invention. An airplane 42 is approaching the landing field, being directed along the horizontal trace of the axis of a beam 43 by means of a runway localizing beacon id, which transmits the double-modulation signals 45, and is placed adjacent to a landing beam transmitter 46. As the airplane approaches the landing field, the pointer of the landing beam indicator begins to rise to midscale or horizontal position. When this position is reached, the pilot knows that he is on a point on the gliding path. To follow a gliding path 47 he must maneuver the airplane to keep this pointer in a. horizontal position. It is necessary now that the pilot keep accurately on the runway course at the same time following down on the landing path. About 100 feet from the landing-field boundary line the pilot hears a marker beacon signal from a transmitter 48, which accurately defines the landing field bound- 75 ary. He is thus warned that the landing point has nearly been reached and proceeds to follow the runway beacon course and the landing beam path to the point of landing. In following the landing path prior to receiving the marker beacon signal, the pilot maintains an air speed somewhat above the landing speed of the airplane, insuring complete controllability with some margin to spare. Upon receiving the marker indication that he is passing over the boundary of the field, the margin over the landing speed may be reduced. The landing is therefore made at a speed more nearly approaching the normal speed of the airplane.

The differently modulated beacon signals 45 are picked up by a radio receiver 59 of the conventional type, the output of the receiver being connected to the filtering means 54, which may beeither of the mechanically tuned type or of the electrically tuned type. At any rate the filter 54 is to be of such means as will separate the two modulated frequencies of the beacon 44 and rectify the two separated frequencies so that the resultant direct voltages connected in opposition to the course indicating microammeter 51 will furnish lateral guidance to the pilot by means of the needle 58.

A receiving apparatus for receiving the marker beacon signal is shown in Figure 10, which may be a standard radio receiver having ear-phones it connected to the output thereof, or suitable indicating device.

The foregoing description comprehends only a general and preferred embodiment of my invention and changes in my method and details of my apparatus may be made within the scope of those claims which may be allowed, and therefore these claims are not intended as restricted to the specific details of my invention as disclosed herein.

What I claim is:

1. A method of guiding aircraft approaching a landing surface which consists of transmitting a directive radio beam at a suitable angle with respect to said landing surface, and guiding said craft to follow a. predetermined line of constant received signal below the angle of maximum radiation of the beam.

2. A method of guiding aircraft approaching a landing surface which consists of transmitting a directive radio beam at a suitable angle with respect to the landing surface, and so guiding said craft that a line of constant received signal below the angle of maximum radiation of the beam will be followed thereby traversing a path suitable for the proper landing of the craft.

3. A system for guiding in a vertical plane aircraft gliding to a landing surface which comprises means for transmitting from a ground station a. signal radio beam directed upwardly at a fixed inclined angle, means carried on aircraft responsive to said beam and means actuated by said second mentioned means for indicating to the pilot deviations in the vertical plane from a path along which the received energy from the said radio beacon s in a predetermined amount at every point of glide.

4. In a system of guiding in a vertical plane aircraft gliding to or taking off from a landing surfacewhich includes means for transmitting from a ground station a radio signal, the intensity of which signal increases with altitude up to an altitude which makes an angle of approximately degrees between a straight line from said aircraft at said altitude to said ground station, and the horizontal radio receiving and signal intensity indicating means on said aircraft responsive to said signal, said intensity indicating means being such as to indicate to the pilot of the-craft deviations of the aircraft in a vertical plane relative to a desired landing path.

5. In a system for blind landing or taking ofl of aircraft, a combination of a single radio beam directed at a vertical angle relative to the land-' said instrument being such as to hold said position in register with said index mark when said craft is gliding to or taking off from the field in the proper path of flight in the sector of the beam underlying the line of maximum transmission thereof and to indicate vertical deviation from said path.

6. A system of guiding in a vertical plane at a continually decreasing altitude an aircraft approaching a landing surface comprising a transmitter emitting a single directive radio beam signal at a fixed inclined vertical angle with respect to said landing surface, a receiver on said aircraft responsive to said beam signal, an ,end zero pointer-type indicating instrument connected to the output of said receiver and responsive to the intensity of said beam signal, said indicating instrument being mounted so that its pointer moves on a vertical plane in front of a scale carrying an index mark in the center of said scale, said pointer and said index mark coinciding during the gliding approach of said aircraft in said radio beam to said landing surface.

.7. A method of guiding aircraft approaching a landing surface which includes transmitting a directive landing path course signal and following said signal for lateral guidance, transmitting a directive radio beam at a suitable vertical angle with respect to the landing surface, and controlling the power radiated by said beam, following a line of predetermined received signal below the angle of maximum radiation of the beam, whereby the craft will follow a path suitable for the proper landing of the aircraft.

8. A method of guiding in a vertical plane an aircraftgliding to or takingofi from a landing area, which method includes projecting a beam of radiant energy with maximum radiant energy at a suitable vertical angle with respect to the landing area, receiving the radiant energy from the beam on the aircraft, holding the aircraft at such altitudes during the period of reception of said "radiant energy on the craft that said received radiant energy shall remain at a predetermined intensity.

9. A system for guiding aircraft approaching a landing surface which includes, in combination, means for transmitting from a ground station a signal beacon course, for lateral guidance of the aircraft to a landing path, and another radio signal, the intensity of which increases with altitude up to an altitude which makes an angle of approximately 20 degrees between a straight line from the aircraft at said altitude to said ground station and the horizontal; radio receiving and signal indicating means on said aircraft responsive to said signals, one of said indicating means being responsive to the field intensity of said second signal for indicating to the pilot of the craft deviations of the craft in a vertical plane relative to said landing path.

10. A system for guiding aircraft approaching a landing surface 'whichincludes, in combination, means for transmitting from a ground station a signal beacon course for lateral guidance of the aircraft to a landing path, and another radio signal, the intensity of which increases with altitude up to an altitude which makes an angle of approximately 20 degrees between a straight line from the aircraft at said altitude to said ground station and the horizontal, radio receiving and signal indicating means on said aircraft responsive to said signals, one of said indicating means being responsive to the field intensity of said second signal for indicating to the pilot of the craft deviations of the craft in a vertical plane relative to said landing surface, and means for transmitting a marker signal across said course for indicating distance to said landing surface.

11. A system for guiding l'aircraft approaching a landing surface which includes, in combination, means for transmitting from a ground station a radio beam directed at an inclined angle relatively to said surface, means for transmitting from said station an approach course signal for the lateral guidance of the aircraft, means on the aircraft responsive to the course signal and the field intensity of said beam, said responsive means including an indicator for indicating to the pilot deviations in a vertical plane from the desired landing path.

12. A method of guiding in a vertical plane" an aircraft leaving a landing area which includes transmitting from a directive radio beam transmitter a radio beam at an angle to the horizontal, receiving said beam on said aircraft, guiding said aircraft so that the signal received on said aircraft shall remain at a predetermined intensity during the period of climb.

13. A method of guiding an aircraft gliding to a landing area which includes flying into a signal defining a landing path and following said signal for lateral guidance; transmitting from a directive radio beam transmitter a radio beam at an angle to the horizontal, receiving radiant energy from said beam on said aircraft, holding said aircraft at such altitudes that the radiant energy received on said aircraft from said radio beam transmitter shall remain at a predetermined intensity'until said aircraft makes contact with said landing area.

14. In a method for vertical guidance of an aircraft gliding to or taking off from a landing surface whereby said aircraft may be guided along the proper vertical landing path which includes transmitting a radio beam from the ground at a vertically inclined angle, receiving said beam from said radio beam transmitter and following along the under half of said beam where the radiant energy received on the aircraft from said beam is a predetermined value during the night to or from the said landing surface.

15. A method of guiding in a vertical plane an aircraft approaching or taking ofi from a landing area which includes transmitting a radio signal from a ground transmitting station of such a. character that the intensity increases with altitude, and receiving said signal on said aircraft and holding said aircraft when landingat such decreasing altitudes that the signal received on said aircraft from said ground transmitting station shall remain at a predetermined intensity during the period of glide to said landing area and conversely when taking oil.

16. A method for guiding in vertical and horiaontal planes aircraft approaching to and taking oif from a landing surface, which includes transmitting radiant energy, such as to produce on the aircraft a signal, the intensity of which is a function of the altitude of said aircraft, and signals which give indications of the azimuthal 10 position of said aircraft with respect to predetermined course in azimuth, receiving said radiant energy on said aircraft. guiding said aircraft to and holding it at such altitudes that energy received from said radiant source remains substantially at a predetermined intensity, and further guiding the aircraft to and holding it in an azimuthal plane to a position where the azimuthal signals received on said aircraft are of a predetermined relative intensity.

FRANCIS W. DUNMORE. 10

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