WEIGHT INDICATOR FOR AN AIRCRAFT

Abstract: Take-off performance of an aircraft is dependent upon a number of factors including total load weight and load distribution. In some instances a special supervisor is required to supervise loading and enable trouble-free take-­ off. Alternatively load transducers mounted on the undercar­ riage and monitored in the cockpit have been used in the past. However, these take no account of any slope which the aircraft may be parked upon. According to the invention a load indicator for an aircraft having an attitude meter and supported by undercarriage support members when parked includes: a plurality of load transducers, 1,2 and 3, for mounting on the support mem­ bers with outputs connected to a computing unit, 4, which also has an input for connecting to the attitude meter, 5, and a load indicator display, 12, connected to receive an output from the computing unit and display aircraft load weight. The inventive load indicator therefore automatically takes account of slope. Additional inputs to the computing unit may be intro­ duced to take account of eg air temperature, altitude. The load indicator display may indicate the maximum all-up-weight point and also give a centre of gravity display.

Description: IMPROVEMENTS IN OR RELATING TO LOAD INDICATORS The invention relates to load indicators and particularly to load indicators for aircraft, especially helicopters. The load carried by an aircraft ust be ten into account when predicting flying performance Aircraft take-off capability, for instance, is sensitive to total load weight carried and also to the distribution of the load within the aircraft. Correct positioning of the load's centre of gravity is therefore important. Apparatus for monitoring load weight and centre of gravity in a parked fixed-wing aircraft is known, but tbe knowm apparatus monitors only the component of the load weight vector acting in a fixed direction with respect to the aircraft. As the attitude changes, this component chances correspondingly so that a true reading of total weight is not given, true wei;qt being given only w:nen the aircraft is parked on level ground. Rotary-winz aircraft, particularly military helicopters, are frequently required to take off from a parked position which is not level. Compensation for a variable parking attitude is thercfore important in load monitoring. A curren-tly used, but inefficicnt system for ensuring correct loading requires a person to supervise loading according to pelsonal experience and, in scm cases, according to an inaccurate calculation. In certain circumstances, for instance, when loading men or equipment in a battle situation fast londinb of the aircraft may be necessary. In such circumstances the extra weight of a loadi,ig supervisor and also the tine used in supervision are a disadvantage. An aim of the invention is to provide an apparatus for monitoring aircraft load when the aircraft 15 parked on ground which may not be level. According to the present invention there is provided a load indicator for an aircraft having an attitude meter and supported by undercarriage support members when parked including: load transducer means for mounting on the support members with outputs connected to a computing unit which also has an input for connecting to the attitude meter such that the computing unit computes load information taking account of attitude, and a load indicator display connected to receive an output from the computing unit and display the aircraft load information. The aircraft may be a helicopter and the undercarriage support members may comprise skids connected to legs, the load transducer means comprising pressure transducers mounted on the legs. Alternatively the undercarriage support members may comprise wheels mounted on legs. The load transducer means preferably comprises a plurality of strain gauges. The computing unit may be a dedicated unit, for instance a microprocessor. Alternatively a general purpose computer which may, for exaniple, be already installed on the aircraft may be used, the computer having been programmed to process load transducer and attitude data and provide an output for the load indicator display. In addition to load weight monitoring, the load indicator may also monitor incremental changes in output from the load transducers in order to give centre of gravity of the load information and display this information on the load indicator display. The load indicator may be constructed to give an indication. on the display of the point at which the aircraft reaches its maximum all-up weight (Uli'). The j\AUW is dependent upon prevailing EMI2.1 environmental conditions. The load indicator n;ayZ additionally include means for taking account of temperature or altitude or both in the iAU4 used for the load indicator display. Load weight informstion may be displayed on the load indicator display by a series of horizontal bar lights stacked one on top of the other 9m a vertical array, the number of bar lights lit up (numbering starting from the bottom of the vertical array) giving an indication of the weight of the load carried. A distinctively coloured horizontal bar light contained in the array may therefore indicate the MAUW. Centre of gravity information may be displayed on the load indicator display by four additional series of bar lights, one series comprising a plurality of horizontal bar lights stacked in a vertical array above the bar lights for the load weight display, a second series similar to the first below the bar lights for the load weight display, a third series comprising a plurality of vertical bar lights stacked in a horizontal array to the left of the bar lights for the load weight display, and a fourth series similar to the third series to the right of the bar lights for the load weight display. Imne centre of gravity display may then operate such that if too much of the weight is loaded, for instance, aft of the aircraft, lights in the second series light up, the number lighting up depending on the amount of weight overload aft, and if too much of the load weight lies, for instance, fore of the aircraft, lights in the first series light up, the number lighting up depending on the amount of weight ovcrload fore. The invention will now oc. described by way of example only with reference to the accompanying drawings of which Fig 1 is a block diagram representing a load indicator according to the invention applied to a helicopter supported, when grounded, by three wheel assemblies, one assembly positioned fore and the re;ziilin two positioned symmetrically aft of the helicopter, Fib 2 is a diagram of a load indicator display with surrounding dials included in the load indicator of rNg 1. In Fig 1 a load indicator, 9, includes three strain gzages, 1, 2 and 3, one mounted along a line cn each of the three helicopter wheel asselolics such that their resistance gives a measure of the component of weight oI a load carried by the helicopter which is transmitted along the line througb each of the wheel assemblies. The weight monitored is that in excess of the weight of the helicopter when empty. An output from each of the strain gauges, 1, 2 and 3 is connected to convey a strain gauge signal to a microprocessor unit, 4, which is programmed to calculate the total load weight in excess of the weight of the helicopter when empty using the components of the toal weight along the lines of the wheel assemblies as registered by the strain gauges and denoted in their output signals. The microprocessor unit, 4, of the load indicator is also connected to an attitude meter, 5, already present on the helicopter so as to supply pitch and roll data to the unit, enabling it to calculate the total load weight by taking the data into account. When the helicopter is on level ground, attitude information is not necessary for the calculation, strain gauge data fro!n the three strain gauges being efficient. The microprocessor unit, 4, also has an input, 6, for outside air temperature (0iT) data and an input, 8, for altitude data. OAT data is fed to the microprocessor mlit electrically by a pilot of the helicopter manually setting a circular OAT dial, 7, which is rotatably mounted around the circumference of a circular load indicator display, 12, in the helicopter cockpit to the correct OAT setting. Altitude data is also input elecrically by the pilot setting a circular altitude dial, 10 which is rotatably mounted around the OAT dial, 7, to the correct setting. Outputs 11 and 18 of the microprocessor unit, 4, are connected to the load indicator display, 12, which gives a display representative cf the load on the helicopter. The display is made up of five series of bar lights, 13, 14, 15, 16 and 17. Scries 13 is composed of twelve horizontal bar lights staczci, one on tcp of the caber, in a vertical array. The first; nine end also the eleventh Lild twelfth ci the series cf bar lights (numbering fron -the bottom to the top) are coloured yellow and the tenth is coloured red. linen the microprocessor unit, 41 has calculated the total load weight it outputs a signal via output 11 to the display, 12, to cause a consecu'ive number of lights in the series 13 to light up. The number of lights, beginning with the bottom light of the series, which light up increases as the load weight carried by the helicopter increases. Tnus, when no lights are showing the helicopter is empty and when the first nine yellow lights and the red tenth light are lit up, the helicopter has reached MAUW. In between these two extrelnes, the number of lights which light up increases proportionately with the load weight. The i4AtYi point varies according to prevailing environnental paraneters, including OAT and altitude. The microprocessor unit, 4, is programmed to take account of these parameters, input via inputs 6 and 8, when processing the signal to be output on output 11. The load indicator also monitors the centre of gravity of a load by means of the microprocessor unit, 4, which processes incremental changes in the strain gauge signals from the three strain grdges and produces an output signal to the indicator display 12, via output i8, the output signal being supplied to series 14, 15, 16 and 17 of the bar lights Series 14 and 16 each consist of five vertical bar lights stacked in a horizontal array, series 14 to the right and serles 16 to the left of series 13. Series 15 and 17 teach consist of five horizontal bar lights stacked in a vertical array, series 15 below and series 17 above series 13. If, for instance, incremental changes in the strain age signals sent to the mieroproeessor unit vindicate too much load weight lies to port, the unit outputs a signal on output 18 which causes z number of the lights in series 16 to light up, the number increasing as the anoint of overload to port increases and the lights lighting consecutively, beginning with tie bar light nearest to series 13. The tilt of the helicopters main rotor is dependent upon the position of a collective pitch lever (not shown in the drawings) and of a cyclic stick (also not shown in the drawings). When the load indicator, 9, is in use on the paired helicopter the collective pitch lever must be fully down and the cyclic stick must be centralised so as to put the main rotor into a symmetrical position with respect to the helicopter1 fuselage. The scope of the invention is not confined to the details disclosed above, variations being apparent to those skilled in the art. Use of a dedicated microprocessor may, for instance, be substituted by use of a computer already on board the aircraft. A simpler arrangement may not, for instance, take into account OAT and altitude or a more complicated system may incorporate OAT and altitude automatically without the need for pilot intervention. The load indicator display may take on a form other than that outlined above. 12aS may, for instance, be indicated by a flashing light, or, for instance, by an audio signal. Alternatively the display may be forned on a CRT which may, for example, be included in a cockpit management system.

Claims: CLAIMS 1 A load indicator for an aircraft having an attitude meter and supported by undercarriage support members when parked including: load transducer means for mounting on the support members with outputs connected to a computing unit which also has an input for connecting to the attitude meter such that the computing unit computes load information taking account of attitude, and a load indicator display connected to receive an output from the computing unit and display the aircraft load information. 2 A load indicator as claimed in claim 1 wherein the load indicator display indicates load weight with respect to maximum all up weight. 3 A load indicator as claimed in either of the preceding claims wherein the load indicator display gives an alerting output when aircraft load weight reaches the maximum all up weight. 4 A load indicator as claimed in any preceding claim wherein the load indicator display gives a measure of load centre of gravity. 5 A load indicator as claimed in any preceding claim which includes additional inputs to the computing unit for receiving status information relating to additional aircraft pax'anete rs of which take-off performance is a function. 6 A load indicator as claimed in claim 5 for an aircraft having aircraft parameter monitoring apparatus for monitoring aircraft parameters of which take-off performance is a function whereby the additional inputs are connected to automatically derive the status information from signals on the apparatus. 7 A load indicator substantially as herein described with reference to the accompanying drawings.

Inventors: TIPPEN, JOHN FRANK
Applicants: NATIONAL RESEARCH DEVELOPMENT CORPORATION
Application year: 1980
Main classification: G01G19
IPC codes: G01G19