GB1586839A - Apparatus to overcome aircraft control problems due to wind shear - Google Patents

Description

(54) APPARATUS TO OVERCOME AIRCRAFT CONTROL PROBLEMS DUE TO WIND SHEAR (71) I, JOHN HENRY BLISS, a citizen of the United States of America of 2740 Graysby Avenue, San Pedro, California 90732, United States of America, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates generally to aircraft flight control, and more particularly concerns apparatus to aid in overcoming problems of aircraft control that arise due to the existence of wind shear.

Since there is no instrumentation in existance designed to deal with the problem to be described, and very little general knowledge of the subject of wind shear, it may be appropriate to define the problem in simple familiar terms.

Early in training, a Pilot must program his thinking in such a fashion so as to accept the fact that he does not have to hold constant rudder or aileron while enroute in a crosswind.

He has to accept the fact that once an airplane is flying, the ground has nothing to do with its flight characteristics. This fact is proven to him on every flight he makes, and it becomes an mviolate law in his mind.

As with many laws concerning physical, natural events, there are sometimes new and more accurate means of measurement introduced, which show that there may be flaws in the accepted laws. When this happens, minds must be reprogrammed to accommodate these changes.

It is easily accepted that wind is merely the movement of an air mass relative to the ground, and just as easily accepted that there is a precise quantitive relationship between airspeed, wind component, and groundspeed.

The experienced Pilot deals with these quantities routinely in flight-planning, but on a microscopic scale.

If one should mount an airspeed indicator on his car, he should clearly understand many of the relationships which follows: It is obvious that an airspeed indicator mounted on a car would show these same relationships between airspeed, wind component, and groundspeed. Until some thought is given to it, there may be some facts, not so obvious, when dealing with relationships on this scale. For example, you are the driver, and you are directed to drive the car at a constant airspeed of 70 MPH. You are driving down a long straight road with a 20 MPH headwind component, so the speedometer (groundspeed) is steady on 50 MPH.

Due to some turbulence introduced into the moving air by brush, small trees, etc. adjacent to the road, there is an area where the air speed fluctuates plus or minus 10 Kts. (knots), and you are aware of your airspeed fluctuation between 60 and 80 MPH. It is obvious to you the actual amount of the deviation of the wind component, and precisely when it occurs. You drive on and encounter two large buildings, one on each side of the road. Due to the venturi-effect on the wind between these buildings, the local wind between them increases to 30 MPH, and you must decelerate to 40 MPH on the speedometer in order to bring your airspeed from 80 back to 70 MPH. Due to the mass of the car, you find it necessary to accept the excess airspeed until the car slows the 10 MPH necessary, yielding 70 MPH airspeed and 40 MPH speedometer reading.

Immediately after the buildings you enter a tunnel where the wind is calm. At this point your indicated airspeed will drop to equal the speedometer reading of 40 MPH. You, the driver, can accelerate to 70 MPH and obtain an indicated airspeed (IAS) of 70 again by pushing on the accelerator, but during the time it takes to accelerate, you will have to accept the lower IAS. The presentation of these elementary facts is offered in an attempt to give examples within a more understandable framework than usual so as to remove the mysteries of wind shear and promote understanding.

Though the importance of airspeed in an airplane cannot be overstated, there are instances where a more comprehensive dimension of understanding is necessary. The Pilot is the one who must understand and deal with the following facts: When an airplane is flying through air in which a wind shear exists, it may encounter wind component changes, which change its airspeed and flight characteristics. When the Pilot changes the power setting to compensate, he is merely changing his groundspeed, and his IAS change is only a secondary result, in the same manner as if he were driving a car with an airspeed indicator.

He can only change IAS within the limits of the inertial acceleration or deceleration which he can bring about in groundspeed. If, along its flightpath, an airplane should encounter a diminishing headwind component which changes at 3 Kts. per second, and the airplane is capable of accelerating groundspeed with full power at 2.5 Kts. per second, then with full power there will be 1/2 knot loss in IAS each second all during the duration of wind change. There are on record changes far exceeding the possible acceleration available for jet transport airplanes.

The utilization of indicated airspeed as the sole criteria of speed control on the approach of aircraft is as hopeless as it would be on an automobile during wind shear conditions.

There is, in consequence, a need to provide apparatus by which a Pilot can control the speed of an airplane on the landing approach, such speed designed to eliminate, as much as possible, the wind shear hazard.

Thus, the present invention provides, from one aspect, in apparatus useful in determining the power setting to be applied to an aircraft engine during a landing approach, the combination comprising a) first means for monitoring deviations of actual aircraft airspeed from desired approach airspeed, and deviations of actual aircraft groundspeed from desired approach groundspeed.

b) second means coupled to said first means for providing an indication as to which of said deviations is the lower compared to the associated desired value from which engine power application may be controlled, and c) first computer means responsive to said desired aircraft airspeed and to air temperature and pressure conditions to compute a value for true airspeed, TAS.

These and further optional features of the present invention will become clear from a consideration of the following description of specific embodiments of the method and apparatus aspects of the invention given by way of example, and not by way of limitation, with reference to the accompanying drawings in which:: Fig. 1 is an aircraft instrumentation arrangement including a fast/slow display; Fig. 2 is a simplified block diagram of a system to operate the fast/slow display as seen in Fig. 1; Fig. 3 is a more complete block diagram of a system to operate the fast/slow display as well as other devices; Fig. 4 is a set of diagrams showing index and actual indicated airspeed and groundspeed values for five different cases of wind conditions; Fig. 5 is a diagramic presentation of the essential components of the inventive system and the relationship of the various basic components; Fig. 5a is a block diagram of a portion of the central air data computer (or CADC) see in Fig. 5; Fig Sb is a block diagram of a multiplier and drivers; Fig. 6 is a plan view of an aircraft approaching to land with associated groundspeed measuring equipment;; Fig. 7 is a elevation of the approach depicted in Fig. 6; Fig. 8 illustrates a block diagram of components relative to Figs. 2 and 3; Fig. 9 is a plan view of an aircraft approaching to land, and a second groundspeed measuring device; Fig. 10 is a elevational view of the Fig. 9 approach and second type measuring system; Fig. 1 lea and 1 1b are block diagrams illustrating how GS from an area naviation device or a DME co-located with an Instrument Landing System (ILS) can be modified for use in the inventive system; and Fig. 12 is a diagram like that of Fig. 5.

With reference to the accompanying drawings, the use of the type of system to be described requires that normal approach indicated airspeed and a predetermined approach groundspeed be used as the approach criteria, whichever is the least, compared to its own predetermined index value. These two values are the commanding functions fed to the fast/slow indicator and to any auto-throttle device on the approach, along with a "caution tailwind" warning device to warn the pilot whenever the groundspeed exceeds true airs speed by 5 knots or more, for example. If this warning activates, he should consider cancelling the approach and choose an approach from a different direction, determined by surface wind and his drift at the time of cancellation. This condition is caused by a tailwind component at altitude, the value of which the pilot can determine from his airspeed and groundspeed indication.

Referring to Fig. 1 a combined airspeed and groundspeed indicator 10 includes a housing 11 and a dial face 12, the latter having speed markings in knots as shown. A calculated or index groundspeed value is "set up" or selected on the indicator, as by adjusting or rotating the knob 13, which shifts the marking 14 on rotary bezel 15 about needle axis 20. Also, a calculated or index airspeed value is "set up" or selected on the indicator, as by adjusting or rotating the knob 16, which shifts the marker 17 on rotary bezel 18 about axis 20. Markers 14 and 17 are closely adjacent the speed markings on the dial face.

In this regard, the airspeed index value is set in the conventional manner to a normal approach indicated airspeed. Also, the ground speed index value is typically set as follows: first convert the normal approach indicated airspeed into true airspeed using altitude and temperature corrections at the field elevation, then subtract 2/3 the surface headwind component, not to exceed 20 knots. These are merely representative values and do not limit the scope of the present invention; also, to set the groundspeed index for take-off, the same type of corrections are applied to V2 speed (the intended lift-off speed and initial climbout speed) and the pilot monitors these needles relative to these indexes.The preceding explanation of utilizing groundspeed and air speed during the final approach are assumed as a general explanation of this system and not to restrict the use of this type procedure. For instance, groundspeed can be relative to a runway or also relative to an aircraft carrier deck, or different speed values can be used without changing the philosophy of the procedures.

The actual or indicated groundspeed is represented by the rotary position of needle 21 in Fig. 1, and the indicated airspeed is rep resented by the rotary position of coaxial needle 22. Suitable drives for the needles are shown at 23 and 23a.

Extending the description to Fig. 2, indi cated airspeed signals at 24 may be provided by a sensor 25 such as a pilot tube and associated transducer; likewise, actual ground speed signals at 26 may be provided by sensor 27. The latter may comprise an INS, or may be part of a Doppler radar device, Doppler radar with a ground based transponder, or associated with a DME station situated in close proximity to and along the final approach track; or, if a ground transmitter, such as an ILS, is updated to transmit on a precise fre quency and the receiver in the aircraft tuned to a precise frequency, the Doppler difference can be read out as groundspeed with an associated device to detect the frequency difference.This would most likely requife a temperature controlled crystal in the transmitter, one in the receiver, and the associated equipment in the airplane to detect and read out the frequency difference as groundspeed. However, the present approach system and procedures can be utilized regardless of what type of groundspeed detection system is used, as long as it is sufficiently accurate.

In Fig. 2, the groundspeed inputs 13 and 26 are compared in comparator 28, and the air speed inputs 16 and 24 are compared in comparator 29. The outputs 30 and 31 of the two comparators are then compared at 32, and the lesser valued one of the signals at 30 and 31 compared to its own index is selected to provide a command input 33 to the fast/slow indicator or display 34. For example, the command input 33 may be fed to the display proportional drive 33a in Fig. 1. A digital display and drive may alternatively be employed. If the display reads SLOW, the pilot increases power to the aircraft engines until the display reads ZERO; and conversely if the display reads FAST, the pilot decreases power to the aircraft engines to return the display to ZERO.

Referring to the more complete system of Fig. 3, the same numerals are applied to components corresponding to those described in Fig. 2. In addition, the output of the comparator switching device 32 may be fed at 33a (or a signal from the display 34 may be fed at 59) to the automatic throttle control device 60 that controls power to the engines, the purpose being to adjust power to return the reading of fast/slow indicator 34 to zero.

Referring now to Fig. 4, all examples assume the ideal of the pilot accurately controlling power application to hold the fast/slow display at zero.

CASE 1 The left diagram indicates a condition of no tailwind or headwind between the airfield elevation (5000 feet) and 7000 feet altitude. In the right diagram, the groundspeed index marker 14 is set at 164 knots (i.e. for 5000 feet elevation at 20"C). The actual groundspeed needle readings at different elevations are shown by line 40, which is slightly inclined to show corrections for altitude. The airspeed index marker 17 is set at 150 knots, and the indicated airspeed line 41 remains at 150 knots for all altitudes. The fast/slow indicator is in this example commanded by the readout from the airspeed comparator 29, as that readout is the lowest (zero).

The purpose of this example is to merely clarify the relationship of all these values relative to altitude. The remaining cases simplify presentation relative to the airport elevation at sea level under standard conditions.

CASE 2 In the left diagram, windline 39 shows that a 40 knot headwind exists at 2000 feet elevation above a sea level airfield, and a 15 knot headwind exists at field level (as related to aircraft approach direction). The pilot sets the airspeed index marker at 150, and the groundspeed index marker at 140 (150 less 2/3 X 15). The line 40 shows that actual groundspeed is kept at 140 knots during the descent, to keep the fast/slow indicator reading "zero", this implies that the output of the groundspeed comparator 28 is commanding the fast/slow indicator. (The airspeed line 41, at 2000 feet elevation, is shown 26 knots above its index value, i.e. 180-130 30, corrected to 26 for altitude and temperature). The cases following this will not have altitude corrections, for purposes of simplicity.

Altitude correction = 2 knots per 1000 feet elevation.

CASE 3 The left diagram shows that a 40 knot headwind at 2000 feet altitude drops to a 20 knot tailwind at 1000 feet; thereafter, the wind increases to a 24 knot headwind at field level. In the right diagram, the pilot sets his airspeed index marker at 150 knots and the groundspeed index marker at 134 (150 less 2/3 X 24). His indicated airspeed is 174 knots (134 + 40) at 2000 feet. During descent to 1600 feet, the output of the groundspeed comparator commands the fast/slow indicator.

Upon reaching 1600 feet, the indicated airspeed diminishes to 150 knots due to decreased headwind, so that the airspeed comparator output becomes zero and now commands the fast/slow indicator. Upon continued descent, the tailwind increases, so that actual groundspeed increases as shown by line 41a. When the actual groundspeed reaches 5 knots above true airspeed (150), i.e. reaches 155, it crosses the tailwind warning line 43 and triggers the tailwind warning light to come ON (see in this regard Fig. 3) where the actual groundspeed output 26' of sensor 27 is compared at 44 with the output 45 of TAS 46, which sets the threshold value of line 43 in Fig. 4, case 3. The output 47 of comparator 44 triggers a switch 47a controlling the warning light 48.

This indicates to the pilot that he should consider aborting the landing. Whether he does is a matter of his judgment in relation to available altitude to handle the wind shear safely. See also Fig. 1.

In case 3, the groundspeed increases up to 170 knots at the 20 knots tailwind value (1000 feet altitude). Upon further descent, the tailwind diminishes, and as groundspeed drops below line 43, the light 48 goes off. The output from the airspeed comparator 29 continues to govern the fast/slow indicator until the actual groundspeed drops to its index setting value 134. At that time, the output of the groundspeed comparator takes over command of the fast/slow indicator, and actual groundspeed remains at 134 (i.e. due to the pilot adjusting power to keep it there, i.e. keep the fast/slow indicator at zero). The indicated airspeed rises at 41b to reach 156 at touch-down.

CASE 4 There is no wind at the sea-level surface, so the two index settings are the same, at 150 knots. At 2000 feet, a 20 knot tailwind exists, so the actual groundspeed line 40 is at 170 knots. The indicated airspeed is at 150 and is in command of the fast/slow indicator. Tailwind warning light 48 is triggered ON. If these conditions prevail down to 1000 feet, the pilot should abort the landing, and approach the runway from the opposite direction, as represented in case 5. If he should not abort the landing, he is risking a hazardous approach as described in the introduction. He knows this at the start of approach due to the present invention.

CASE 5 The fast/slow indicator is commanded by the groundspeed comparator output. The pilot reduces power as the head wind diminishes, and lands safely. The pilot has an indicated airspeed of 170 knots but he knows his speed relative to the runway is a normal 150 knots, so he knows it is safe to continue his approach, and he further knows that he will encounter wind shear between his present position and the runway. He will also get an immediate indication of its encounter when his indicated airspeed starts to decrease. The groundspeed will still be in command of the fast/slow indicator all the way to touchdown.

Advantages of the above method and apparatus include: (i) The pilot is given his wind component and the difference in wind component comu pared to that existing in the landing area at the start of his approach.

(ii) The pilot can monitor the value of any wind shear present constantly throughout his entire approach.

(iii) It is made known to the pilot if an approach in another direction is safer.

(iv) The pilot is warned of any hazardous condition of wind component all during the final approach.

(v) The pilot can tell from indications at the time of warning what direction will be safer for an approach.

(vi) Airspeed is automatically added sufficient to counteract any sudden decrease in wind component during final approach.

(vii) The prospect of arriving over the landing area with a safe speed margin is enhanced.

(viii) Landing without excessive speed is assured and thus landing distance overruns are avoided.

(ix) An additional relative, consistent quantity is added to the final approach and wind shear problem, which enables the pilot to make consistent, safer and more accurate approaches.

(x) The pilot can monitor, and have available during takeoff, an independent and accurate measure of wind component actually existing during takeoff.

(xi) Information is presented for use as a standard procedure on every approach and takeoff, so that the pilot develops high proficiency in its use.

(xii) Much of the confusion associated with wind shear is eliminated and thereby the pilot is freed to concentrate on other considerations more readily, allowing a more accurate approach, especially during adverse wind shear conditions.

(xiii) The pilot is allowed to pre-trim the airplane for expected conditions and thereby arrive at the landing area in a safer condition of flight.

(xiv) A consistent actual speed is used all during the final approach giving a constant rate of descent on the glide path.

(xv) A tailwind warning device is included and gives the pilot information to effectively deal with it.

(xvi) The pilot has an additional final control over the amount of surface wind applied to his planned groundspeed index setting, so that late during the final approach he can change the amount of pre-planned wind applied when there may not be enough time to re-program the direction and velocity figures installed.

Prior to takeoff, the pilot sets his airspeed index on normal V2, as under present pro cedures. The grounds peed index should be set in a similar fashion to the approach setting.

The V2 speed should be converted to true airspeed by applying field elevation and tem perature corrections less 2/3 the headwind component. During takeoff, the fast/slow indi cator can only be commanded by the airspeed set index (V2); however, the groundspeed and airspeed needles, or indications, can be moni tored relative to each other and relative to their indexes to determine the actual instant aneous wind component all during the takeoff run. If the needles do not maintain proper relative proportionate values, the Pilot will be warned that his wind component is different from his pre-take-off calculated values. In particular, this will inform him if he has a tailwind component prior to reaching V speed (decision speed).

Along with this description is added a method of obtaining usable groundspeed by employing an airborne Doppler radar along with a ground based transponder-like device.

If an airplane has a Doppler radar transmitting in a fan shaped beam ahead, and there exists a transponder-like device near the intersection of an airport's runways then the groundspeed recorded will be relative to any runway used and will be accurate when inbound regardless of heading.

The following described method and instrumentation greatly simplifies the Pilot's or other flight officer's tasks required in achieving the above described objectives. The purpose of this device is to simplify the process of calculation of TAS and wind component for use in that system. It can be used to automatically program these values into the system, provide~ the means of integrating the described system into an existing approach instrumentation by adding components to achieve all the parameters previously described, and use the normally presently installed instruments as much as possible.

Presently used approach instrumentation utilizes an airspeed indicator such as is described in Fig. 1, item 10, without the coaxial GS needle 21 and index 14, but with the fast/slow needle 34 programmed entirely by IAS 223 and it's index 17 controlled by knob 16.

The text of this specification is written in such a fashion so as to conform, as much as possible, to accepted general practice. Therefore, the phrase "subtract 2/3 the surface headwind component, not to exceed 20 KTS", has been used in an attempt to conform to normallly accepted procedure in most airline operations manuals analagous to "half the headwind component plus the full amount of the gust value, not to exceed 20 KTS total added increment". The description of the setting of the groundspeed index value is meant to explain that there are other ways which may be equally acceptable. The following explanation assumes the full application of the wind component in an effort to improve clarity.

The system uses a speed parameter, "groundspeed", which is employed under some circumstances, while an airplane is on the final approach to a landing.

The system also uses either groundspeed, or the conventional indicated airspeed on the final approach, in such a manner so as to provide the command function to a third instrument, the fast/slow (F/S) instrument.

Using this system and procedure, the F/S instrument assumes a far greater importance than it has in hitherto known systems, and it is always the primary speed reference on the final approach.

In the drawings Figs. 5 to 11, I have illustrated diagrammatically and graphically the described embodiment as it is applied with present day aircraft equipment. That is, the known components are those which are currently used and improved; including an airspeed indicator Fig. 5, 10 with its indicated airspeed (IAS) needle 22, planned IAS index 17 and a fast/slow (FS) indicator F. (34).

Element (A) can be a conventional Central Air Data Computer (CADC) which ordinarily computes true airspeed (TAS) by applying pressure and temperature corrections to IAS.

The CADC is modified so as to apply the same percentage correction to the IAS index setting to obtain TAS index setting as is applied to IAS to obtain TAS. As for example, when IAS X 112% is appropriate to obtain correct TAS, then IAS index setting (17) X 112% = the setting of TAS index (101). See Fig. 5a. Element (B) can be any conventional navigation computer capable of applying wind angle and velocity corrections to TAS and inbound course signals to compute groundspeed.

The DME (distance measuring equipment) and area navigation (RNAV) systems portray known systems frequently used in present aircraft, capable of computing GS in the usual fashion by sensing mileage position change over an appropriate period of time. These are modified as described later as in Figs. 1 la and llb. In fact, each of these known pieces of equipment are often installed and available in fully instrumented aircraft. Therefore, with out showing and without describing the details of these six basic pieces of equipment, it is to be understood that they are in each instance used as commercially available equipment with the described modifications.

One purpose of this patent of addition application is to fully disclose and define means of integrating the present system into existing instrument systems, and disclose some means for obtaining groundspeed usable in the present concept. An additional purpose is to disclose the use of unit C, the wind application controller. The description is intended to dis close a fully automated system so that the only additional workload on the Pilot is the inser tion of the surface wind direction and velocity into the wind computer; however, other means for programming either the TAS index or GS index may be used.

For instance, the TAS index 101 can be set to the calculated value of the IAS index 17 at the air temperature and pressure of the airport of intended landing instead of con tinuously corrected to the conditions the air plane is flying through as described in the present disclosure.

Referring now in more detail and by reference to Fig. 5, the inventive system requires that a groundspeed parameter, new to approach systems, be used under some circumstances while an airplane is on the final approach to a landing. Either groundspeed, or the conventional indicated airspeed on the final approach, is used in such a manner so as to provide the control function to a third instrument, the fast/slow (FS) instrument. Using this system and procedure, the F/S instrument assumes a far greater importance than it has in hitherto known systems, and it is always the primary speed reference on the final approach.

The means used to determine which speed parameter, groundspeed or indicated airspeed, controls the F/S instrument will become evident in the following: During the approach, the F/S needle 125 is commanded by either the groundspeed needle 102 relative to its index 103, or the indicated airspeed needle 22 relative to its index 17, whichever speed quantity is lower relative to its associated index. Thus, if one speed quantity is higher than its associated index and the other is equal to its associated index, the F/S needle will read zero. If one is equal to its associated index and the other is 5 knots lower than its associated index, the F/S needle will read 5 knots slow. If one is 5 knots higher than its associated index and the other is 10 knots below its associated index, the F/S needle will read 10 knots slow.

If an airplane approaches a runway with no wind present all during the approach, the GS and TAS will be equal at all times on the approach. The index 101 can be termed a "0" wind GS index since it is programmed by the CADS (item A) to indicate the TAS of the setting of index 17 through routing or paths 127 and 121. The CADS normally applies a temperature and pressure correction to IAS or equivalent to produce a TAS value. This same percentage correction can be electrically applied to the IAS index 17 value to program the TAS index 101 setting via 121. The CADS also sends this TAS index signal to the wind computer (item B) through path 122 where a correction is applied, for that component of the wind which affects the GS, for the programming of the "desired GS index" 103 through "Application Controller" (item C).

For the moment, it is assumed the FULL correction button is selected on C and that the full value of wind component is delivered to program the desired GS index 103 through routes 123 and 110. The desired GS index 103 on the GS indicator is analogous to the desired IAS index 17 on the IAS indicator.

This "desired GS index" 103 and the GS needle 102, at appropriate times, controls the F/S needle 125 through comparator 120 in the same manner as the desired IAS index 17 and the IAS needle 22 does through comparator 114 at other appropriate times through comparator/switching unit 115, via route 116.

The same signal may be used to control an existing aircraft engine automatic throttle control mechanism 126a via path 126. If no wind is inserted into the computer, index 103 will be programmed to the same setting as index 101. An illustrative computer is disclosed in U.S. Patent 3,924,111 to Farris.

This equipment and concept is designed for use in a similar fashion for all approaches, and the wind correction used to program the "desired groundspeed index" is the surface wind as given by the air traffic control tower, although the most accurate wind in the landing area, not including gusts, should be used.

The index 17 is set as described (as is normally done presently on existing instrumentation before beginning an approach). If there is no difference in wind all during the approach, the wind will be the same at all times during the approach as at the surface.

If the Pilot manipulates the airplane so as to cause the F/S needle to remain on zero, the indicated airspeed will remain equal to its associated desired speed index, and the groundspeed will remain equal to its associated desired speed index all during the approach.

If there exists a stronger headwind at altitude than on the surface, the groundspeed relative to its associated desired speed index will program the F/S needle. Whenever the present headwind is greater than the headwind at the surface, the indicated airspeed will be greater than its associated index by an amount equal to the value of excess headwind. The Pilot will have a direct measure of the amount of airspeed he can expect to lose before reaching the runway threshold. The greater the wind shear, the greater the amount of excess indicated airspeed. The great hazard of rapidly decreasing headwind, with the associated rapid loss of airspeed, is eliminated. This case describes a normal wind gradient, and therefore describes the most usual case.

In cases where there exists a lesser headwind early on the approach, the indicated airspeed and its associated index will program the F/S needle. The Pilot will control the airplane by much the same standard as is used without this system, with some important advantages.

The groundspeed will indicate higher than its index. The amount of excess groundspeed is a measure of the expected headwind increase the Pilot can expect before reaching the threshold, and it is of no concern unless the groundspeed exceeds the true airspeed index value The true airspeed value can be considered the same as a no-wind approach groundspeed value. This leads to the next case.

In cases where there exists a tailwind early on the approach, assuming the Pilot has chosen a landing direction with a headwind on the ground, as is normally accepted procedure, the following situation exists: The IAS 22 will be lower compared to the IAS index 17 than the GS 102 is compared to its associated GS index 103, and therefore the IAS 22 and its associated index 17 will program the F/S needle 125. If the Pilot controls the F/S needle on "0", the GS 102 will exceed the "0" wind GS index 101 by the amount of the tailwind value. The GS needle 102 reading is also important in that the required runway stopping distance is totally dependent on the GS 102 value over the end of the runway.If the groundspeed 102 signal through path 124 exceeds the TAS signal through path 118 by a certain amount, the output of comparator 107 activates the tailwind (TW) warning device E (48), warning the Pilot of the potential danger of his high GS 102.

The output of comparator 107 is variable as regards to the actual altitude as indicated by line 128 from a radar altimeter, and the T/W warning programming is variable, as for example: 5 KTS at 100 ft. altitude, 10 KTS at 200 ft. 15 KTS at 300 ft. depending on the characteristics of the particular type airplane's deceleration capability. In any case the Pilot can monitor the actual groundspeed value at all times during the approach.

Reference is now made to unit C, the application control This unit enables a percentage choice of the amount of wind component correction applied to the intended GS index 103.

If the wind is set into the wind calculator B, and a later wind is given by the Air Traffic Control Tower which amounts to, for example 50% of the original wind value when there is not enough time for reprogramming the calculator, the Pilot can press the 50% button on the application control unit. This action reduces the amount of wind programming affecting the setting of index 103 by 50% and gives all indications and parameters which would exist had the new wind been inserted into the wind calculator B. Fig. Sb shows a multiplier 400 in representative unit C to accomplish the appropriate percentage reduction referred to. Also, Figs. 5 and 5b show appropriate drivers 101a, 102a and 103a for the indexes.

Whenever reference is given as a Pilot action to control speed it is assumed to also mean similar means of speed control by an automatic device, such as an automatic throttle.

Figs. 6, 7 and 8 refer to methods for providing groundspeed information for use in systems dedicated to overcoming wind shear problems. The illustrated system uses an airborne Doppler radar system similar to those used to detect traffic speed on highways.

Doppler radar unit A1 on approaching aircraft 90 transmits a wide, cone or fan shaped beam 91, at frequency fl, of electromagnetic radiation (for example radio waves) forwardly of the aircraft. The beam is received by unit B1 based at or near the landing strip. The receiver "sees" the frequency (fl + A), the term A representing the increase in frequency due to Doppler effect. The unit not only includes a receiver, but also a transmitter including an oscillator, antenna and appropriate circuitry to re-transmit back toward the aircraft a "like" beam 92 of radiation; that is, the re-transmitted beam has the same frequency (fl + A) as that it received. The re-transmitted beam may or may not be in phase with the received beam.

The unit A1 on the aircraft receives the retransmission, which it "sees" as increased frequency (fl + 2A), due to Doppler effect. The magnitude of the return frequency, or the increase 2A, is used to determine actual closure (or ground) speed of the aircraft 90 relative to unit B1. For example, the return frequency may be detected at 93 in Fig. 8, or processed to derive 2a, and the output 94 may be fed to a calibrator 95 which produces a closure speed signal to readout 96.

Advantage of the Figs. 6-8 system include the following: unit A1 may be lightweight, relatively low-power device, and can be employed to obtain accurate groundspeed values even though the aircraft heading is somewhat different from its direction of travel, due to drift. Normally, the axis of the cone of beam 91 is generally lengthwise of the aircraft 90.

Also, unit B, can be used to serve multiple aircraft approaching from different directions, if it is placed near the intersection of the runways. Through use of pulsed signals in beam 92, several aircraft can be accommodated on the final approach at the same time, and accurate groundspeed provided to each.

In Figs. 9 and 10, the in-flight aircraft 96 is shown approaching a runway 97 on which an Instrument Landing Glidescope is installed; however, the transmitter at A2 can be either part of an existing unit, or a special separate unit, installed for the express purpose of providing a groundspeed signal. Transmitter A2 produces an accurately on-frequency signal, of frequency f2, transmitted as beam 98. The airborne receiver unit at B2 receives the signal as frequency (f2 + A), A being due to Doppler effect, and compares it with a standard frequency f which is the same as that transmitted by A2. The magnitude of The difference A represents the groundspeed, and may be processed and readout as such, on board the aircraft.

Figs. ila and 116 illustrate a device for improving aircraft groundspeed information as derived from existing navigational devices and its use in improved systems. Basically, the system utilizes inertially derived information to improve the accuracy of groundspeed (GS) information as derived from existing devices, and also concerns new applications of such GS information. The device produces a GS signal of high accuracy and fidelity which may be used in aircraft systems designed for wind shear protection and/or improvement in Area Navigational (RNAV) devices to improve a computerized phantom glideslope for use in an approach to a runway which may not be equipped with a full Instrument Landing System (ILS).Thus, GS is derived sufficiently accurately so as to be useful in instrumentation designed for low level wind shear protection on the approach and for improving phantom glideslope accuracy in RNAV systems.

Present DME devices have a lag of 5 to 40 seconds in GS accuracy due to a combination of necessary elements including smoothing of the signal of distance measurement, the necessary memory circuits, noise received along with the distance sensing signal, and the delay involved in pulsing the interrogation and return signals. The GS as derived from such rudimentary distance data over a factor of time is necessarily only an approximation when actual changes in GS occur. Presently used DME and RNAV systems derive GS information of sufficient accuracy for navigational purposes, but not accurately enough for use in systems designed to maintain or utilize a specific GS.

Existing RNAV devices detect GS from the computerized position changes as detected from changes in Omnidirectional Radio (OMNI) bearings and/or DME distance changes. These computer calculated position changes are generally subject to an even more broad approximation in position than that obtained from DME alone. Since both systems are capable of resolving a steady state GS measurement, a similar updating system may be used in either case to increase the fidelity of GS measurement when changes in actual GS occur.

In Figs. 11a and 116 I have illustrated by block diagrams the device as it is applied with present day aircraft equipment. That is, the known components are those which are currently used and improved, including the Distance Measuring Equipment (DME) or Area Navigation Device (RNAV)-J, a timing device K, and groundspeed (GS) computer L.

The accelerometer P in unit 0 and associated existing gyro positioning or compensating devices are also known and assumed to be commercially available pieces of equipment.

Therefore, these five basic pieces of equipment will not be described in detail. It is understood that they are often installed and used in a fully instrumented aircraft, although in the present case, the previously mentioned smoothing and conventional memory characteristics of the output of the computer L is removed from signal 203, as these functions are performed in the condenser circuit M.

Referring now in more detail to Fig. 1 la, J represents a normally used radio activated navigational device such as a DME or RNAV system from which is produced a raw signal, not smoothed nor influenced by a memory circuit. Unit K is a timer which produces an electrical impulse fed via path 201 to the computer L. Computer L samples the amount of position change from unit J over a factor of the time impulses from unit K, and produces a GS signal 203 to condenser circuit M, an example being an electrical signal of varying voltage, such that the higher the GS sensed, the higher the voltage charge to the condenser M. This pulsed voltage charges condenser M in such a manner so that the voltage charge in condenser M is at all times effectively equal to the peak voltage of the pulses.The voltage charge of condenser M is monitored through path 206 by unit N, which contains a voltage following circuit calibrated to read out the appropriate voltage as GS. The condenser unit M feeds this same voltage as a base voltage via path 205 to the acceleration detection unit 0 which is utilized in such a manner so as to provide an additional voltage control for the condenser charge. A more detailed description of unit 0 is presented in Fig. 116, where section P consists of either a gyro stabilized accelerometer, or as is more generally utilized, a body mounted gyro compensated accelerometer. In either case, the accelerometer must measure the horizontal acceleration along the longitudinal path of the aircraft to program the voltage control 0 such that a deceleration sensed at, as for example, 1 Knot per second lowers the condenser voltage charge so as to cause the voltage following circuit N to indicate 1 Knot per second less GS. Conversely, when the accelerometer detects an acceleration the charge of condenser M is increased a commensurate amount to cause an increase in GS readout equal to the amount of acceleration.

Whenever a change in GS takes place, the accelerometer detects the change, and the signal from the computer L then corrects or confirms the new speed as necessary, via path 203 from the GS computer.

There is a source of GS signal at 207 which, for example, may be fed back to the RNAV device so that a more accurate position may be used to program a phantom glideslope.

In- Fig. 12, the principle part of the system is, of course, the groundspeed (GS) indicator D, with its GS indicating needle 102 and index markers 103, set by thumbscrew adjuster R, and 101, set by thumbscrew S. This system is used in a manner similar to that in Fig. 5 except in this instance it is utilized in an air craft which is not equipped with a Central Air Data Computer nor a Radio Altimeter.

The Pilot sets the indicated airspeed (IAS) index 17, as is normal, to his planned approach IAS. He then calculates what the true airspeed (TAS) will be over the runway threshold at this IAS using the airport pressure altitude and temperature and sets index 101 to this value. The index 101 setting can then be termed the planned TAS or planned zero wind GS index. He then calculates the surface headwind component, subtracts this value from the index 101 setting, which forms the value for setting index 103, the planned GS index.

Since there is no Central Air Data Computer to compute TAS, the tailwind warning (T/W) is programmed in the following manner; Basically, the comparator 107 is set to acti vate the T/W device E 48 whenever the actual GS 102 exceeds the zero wind GS or TAS index 101 by a pre-programmed amount, such as SKts. Under this circumstance the IAS 22 and its associated index 17 will program the F/S needle 125. If the Pilot has allowed the airspeed to become 10Kts. faster than planned, the IAS 22 will be 10Kts. higher than its associated index 17, and the F/S indicator 125 will indicate 10Kts. fast. Comparator 107 is then variably programmed via route 106 so as not to activate the T/W warning E 48 un less GS 102 exceeds the TAS index 101 by 1SKts. or more.Effectively, the input 106 programs comparator 107 such that when the F/S needle 125 is at -15 the T/W warning is activated when the GS needle 102 is above the value of index 101 minus 10Kts, and when the F/S needle 125 is on zero the T/W warning E 48 is activated whenever the GS 102 exceeds 101 index by more than SKts.

The systems provide an instantaneously cor rect measurement of GS and a signal accu rately depicting GS with good fidelity for use in other systems. The systems use presently available and commonly used devices to pro vide this GS, with little expense, for aircraft which would not normally require an expensive INS. The systems provide an improved GS signal, not available without INS, for use in a wind shear protection system in particular, and in other systems where an accurate GS signal may be desirable to improve the accuracy of a system, for instance: when an RNAV is used as a localizer for an approach using phantom waypoints in line with a runway, an accurate GS can be used through a computer to estab lish an accurate phantom glideslope between these phantom waypoints.

WHAT I CLAIM IS: 1. In apparatus useful in determining the.

power setting to be applied to an aircraft engine during a landing approach, the com bination comprising a) first means for monitoring deviations of actual aircraft airspeed from desired approach airspeed, and deviations of actual aircraft groundspeed from desired approach ground speed, b) second means coupled to said first means for providing an indication as to which of said deviations is the lower compared to the associated desired value from which engine power application may be controlled, and c) first computer means responsive to said desired aircraft airspeed and to air tempera ture and pressure conditions to compute a value for true airspeed, TAS.

2. The combination of claim 1, including a means to display said TAS value.

3. The combination of claim 2 wherein said last named display means includes a speed scale, a TAS marker associated with said scale to display said TAS value and there being a GS marker associated with said scale to dis play said actual aircraft groundspeed.

4. The combination of claim 3 including a GS index marker associated with said scale to display said desired approach groundspeed.

5. The combination of claim 4 including a second computer means coupled with said first computer means to be responsive to output thereof corresponding to said TAS values, and also responsive to wind direction and velocity values at the landing surface locating thereby to provide correction values for adjusting the position of said GS index marker relative to said scales.

6. The combination of claim 5 including wind velocity percentage correction selector means, and means responsive to selection of a percentage correction to effect adjustment of the position of the GS marker in correspond ence to said percentage correction.

7. The combination of claim 1 including an aircraft FAST/SLOW indicator, and means to drive said indicator as a function of whichever of the actual airspeed and the actual groundspeed is Tower compared to its associated desired airspeed and groundspeed, respectively.

8. The combination of claim 1 including a tailwind warning device, and a comparator responsive to said TAS value and to actual groundspeed to actuate said device when groundspeed exceeds said TAS value by a selected amount.

9. The combination of claim 8 including

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   signal from the computer L then corrects or confirms the new speed as necessary, via path 203 from the GS computer.

   There is a source of GS signal at 207 which, for example, may be fed back to the RNAV device so that a more accurate position may be used to program a phantom glideslope.

   In- Fig. 12, the principle part of the system is, of course, the groundspeed (GS) indicator D, with its GS indicating needle 102 and index markers 103, set by thumbscrew adjuster R, and 101, set by thumbscrew S. This system is used in a manner similar to that in Fig. 5 except in this instance it is utilized in an air craft which is not equipped with a Central Air Data Computer nor a Radio Altimeter.

   The Pilot sets the indicated airspeed (IAS) index 17, as is normal, to his planned approach IAS. He then calculates what the true airspeed (TAS) will be over the runway threshold at this IAS using the airport pressure altitude and temperature and sets index 101 to this value. The index 101 setting can then be termed the planned TAS or planned zero wind GS index. He then calculates the surface headwind component, subtracts this value from the index 101 setting, which forms the value for setting index 103, the planned GS index.

   Since there is no Central Air Data Computer to compute TAS, the tailwind warning (T/W) is programmed in the following manner; Basically, the comparator 107 is set to acti vate the T/W device E 48 whenever the actual GS 102 exceeds the zero wind GS or TAS index 101 by a pre-programmed amount, such as SKts. Under this circumstance the IAS 22 and its associated index 17 will program the F/S needle 125. If the Pilot has allowed the airspeed to become 10Kts. faster than planned, the IAS 22 will be 10Kts. higher than its associated index 17, and the F/S indicator

   125 will indicate 10Kts. fast. Comparator 107 is then variably programmed via route 106 so as not to activate the T/W warning E 48 un less GS 102 exceeds the TAS index 101 by 1SKts. or more.Effectively, the input 106 programs comparator 107 such that when the F/S needle 125 is at -15 the T/W warning is activated when the GS needle 102 is above the value of index 101 minus 10Kts, and when the F/S needle 125 is on zero the T/W warning E 48 is activated whenever the GS

   102 exceeds 101 index by more than SKts.

   The systems provide an instantaneously cor rect measurement of GS and a signal accu rately depicting GS with good fidelity for use in other systems. The systems use presently available and commonly used devices to pro vide this GS, with little expense, for aircraft which would not normally require an expensive INS. The systems provide an improved GS signal, not available without INS, for use in a wind shear protection system in particular, and in other systems where an accurate GS signal may be desirable to improve the accuracy of a system, for instance: when an RNAV is used as a localizer for an approach using phantom waypoints in line with a runway, an accurate GS can be used through a computer to estab lish an accurate phantom glideslope between these phantom waypoints.

   WHAT I CLAIM IS: 1. In apparatus useful in determining the.

   power setting to be applied to an aircraft engine during a landing approach, the com bination comprising a) first means for monitoring deviations of actual aircraft airspeed from desired approach airspeed, and deviations of actual aircraft groundspeed from desired approach ground speed, b) second means coupled to said first means for providing an indication as to which of said deviations is the lower compared to the associated desired value from which engine power application may be controlled, and c) first computer means responsive to said desired aircraft airspeed and to air tempera ture and pressure conditions to compute a value for true airspeed, TAS.
2. 2. The combination of claim 1, including a means to display said TAS value.
3. 3. The combination of claim 2 wherein said last named display means includes a speed scale, a TAS marker associated with said scale to display said TAS value and there being a GS marker associated with said scale to dis play said actual aircraft groundspeed.
4. 4. The combination of claim 3 including a GS index marker associated with said scale to display said desired approach groundspeed.
5. 5. The combination of claim 4 including a second computer means coupled with said first computer means to be responsive to output thereof corresponding to said TAS values, and also responsive to wind direction and velocity values at the landing surface locating thereby to provide correction values for adjusting the position of said GS index marker relative to said scales.
6. 6. The combination of claim 5 including wind velocity percentage correction selector means, and means responsive to selection of a percentage correction to effect adjustment of the position of the GS marker in correspond ence to said percentage correction.
7. 7. The combination of claim 1 including an aircraft FAST/SLOW indicator, and means to drive said indicator as a function of whichever of the actual airspeed and the actual groundspeed is Tower compared to its associated desired airspeed and groundspeed, respectively.
8. 8. The combination of claim 1 including a tailwind warning device, and a comparator responsive to said TAS value and to actual groundspeed to actuate said device when groundspeed exceeds said TAS value by a selected amount.
9. 9. The combination of claim 8 including

   means to display said TAS value, in association with a display associated with said device.
10. 10. The combination of claim 1 including means to provide desired approach groundspeed as described including INS, Doppler radar providing a Doppler fan shaped beam projected ahead of the aircraft, and utilizing a ground based transponder-like device to eliminate errors of groundspeed detection due to drift of the aircraft or heading different from direction of travel.
11. 11. The combination of claim 1 including DME or area navigation groundspeed whether updated inertially or not or the Doppler detection of groundspeed from any existing or refined ground based transmitted and airborne receiver, for instance the ILS; said apparatus used for the purpose of groundspeed detection in the described system.
12. 12. The combination of claim 1 including cooperating instrumentation on the aircraft and on the ground near the landing area to produce on the aircraft a Doppler frequency shifted signal indicative of actual groundspeed of the aircraft.
13. 13. Apparatus for determining the power to be applied to an aircraft engine during a landing approach substantially as hereinbefore described with reference to the accompanying drawings.