FLAP POSITION MEASURING TOOL

Abstract: A flap position measuring system (Figure 4) including three servo inclinometers (20, 22, 24) for providing a voltage proportional to the sine of the tilt angle. The flap position measuring system (Figure 4) provides the inverse sine of the voltage proportional to the sine of the tilt angle and displays the relative angle in degrees on a digital readout utilization device (100). The inverse sine of the voltage is provided through signal processing including analog circuitry (54, 56)( utilizing the first two terms of the Taylor series expansion of Sin<-1>x.

Description: -1- FLAP POSITION MEASURING TOOL The present invention relates to a method and appara¬ tus for measuring the angle between devices relative to a reference plane and, more particularly, to an electrical system for measuring the angle between inboard or outboard flaps relative to a wing reference plane of an aircraft. Heretofore bulky mechanical protractors or optical sighting techniques have been utilized for measuring angles relative to a reference plane. More particularly in the aircraft art, the patent literature includes U. S. Patent No. 3,478,569 which relates to an electronic method for rigging aircraft control surfaces. In sharp contrast to the utilization of a simple pendulum resolver configuration as- shown in U. S. Patent 3,478,569, the present flap position measuring system utilizes a plurality of servo inclinometers. These servo inclinometers employ a force balance principle, allowing a much higher degree of accuracy to be achieved. Such a high degree of accuracy is particularly important in an aircraft environment where newer fuel efficient aircraft do not permit any discrepancy in the alignment of a control surface such as the flaps which would con¬ tribute to increased drag. The flap position measuring system in accordance with a preferred embodiment of the present invention results in an accuracy of + 3 minutes of arc over a range of + 20 , an overall accuracy deemed an order of magnitude better than that shown in U. S. Patent 3,478,569, which accuracy is achievable through utilization in the present system embodiment of servo inclinometers. Accordingly, it is an object of the present invention to provide means, including a plurality of servo inclinom¬ eters, for measuring angles relative to a reference plane. . -2- It is a further object of the present invention to provide a system for measuring the angle between inboard or outboard flaps of an aircraft relative to the wing refer¬ ence plane, utilizing a plurality of remotely mounted transducers for providing a voltage proportional to the sine of the tilt angle and wherein the inverse sine of the voltage is utilized to display the relative angle in degrees, It is yet another object of the present invention to provide a tilt detection system utilizing a plurality of servo inclinometers coupled to the analog circuits for providing the first two terms of the Taylor series expansion for Sin~ x. These and other objects and advantages of the present invention will be readily apparent from the following de¬ tailed description of an embodiment thereof and accompany¬ ing drawings wherein: Figure 1 is a side elevational view taken in section of a wing section-of an aircraft showing prior art utiliza- tion of mechanical protractor for flap position measure¬ ment; Figure 2 is a bottom plan view of an aircraft showing servo inclinometer arrangement relative to the wing reference plane in the present preferred system embodiment; Figure 3 is a wing section view taken along the line 3 - 3 of the aircraft shown in Figure 2; Figure 4 is a block diagram electrical circuit system schematic of the present measuring system; Figures 5A, 5B, and 5C show a complete electrical cir- cuit schematic of the measuring system shown in Figure 4. Turning now to Figure 1, a prior art flap position measuring method is shown wherein the flap portion 12 of wing 14 includes a mechanical protractor 16 for making flap angle measurements between flap 12 position shown and the flap position shown in dotted line rendition at 18. Such a prior art flap measuring technique as shown in Figure 1, which includes the use of bulky mechanical protractors and results in inaccurate measurements, cannot be tolerated in the angle measurements required in the new fuel effici¬ ent aircraft. Proceeding now to Figure 2 it will be seen that the present measuring system shown in block diagram in Figure 4 utilizes a plurality of remotely mounted transducers 20, 22, and 24 of the servo inclinometer type and includes reference transducer 20 disposed in the wing 14 reference plane with respect to which all other pitch axis angles can be measured. Reference transducer 20 may more parti¬ cularly (not shown) be mounted on a holding fixture attached to one of the fuel -cell inspection openings of wing 14. Inboard flap transducer 22 and outboard flap transducer 24 are mounted on the corresponding trailing " edges of the respective inboard 12 and outboard 13 flaps, as shown in Figure 2. The relative angle θ the angle of inclination denoted by numeral 26 in Figure 3 is read out in utilization means comprising a display device 100, shown specifically in the full circuit diagram embodiment portion of the schematic at Figure 5C. The display device showing the angle of inclination θ is also shown in the block diagram of Figure 4 of the present preferred system embodiment at 100. The basic understanding of the operation of the pres- ent measuring system can best be obtained now with refer¬ ence to Figure 4 showing the block diagram of the system. Each of the servo inclinometers 20, 22 and 24 are coupled through respective twisted shielded cables 40, 42 and 44 to signal processing circuits downstream, including differential input amplifiers 46, 48, and 50 which reduce unwanted noise pickup. In each case, the first stage differential amplifiers 46, 48, and 50 are utilized in the signal processing of the present system to perform zero offs.et and scale factor adjustments for each of respective servo inclinometers 20, 22, and 24. Reference servo inclinometer 20, inboard servo inclinometer 22, and outboard servo inclinometer 24 provide voltages propor¬ tional to the sine of the tilt angle. Servo inclinometers 20, 22, and 24 utilized in the present system embodiment comprised model LSOC-90 type servo inclinometers manufac- tured by Schaevitz Engineering, Inc., of Pennsauken, New Jersey. These servo inclinometers produce a voltage of + 5 volts corresponding to Sin C+ 90°) . As a consequence it is necessary for the signal processing downstream to perform an arc sine CSin } operation on the signals in order to recover and display the angle of inclination. This operation is achieved by utilizing the first two terms in the Taylor series expansion for Sin " as shown mathe¬ matically at the bottom portion of the block diagram shown in Figure 4. It can thus be seen in the example that if θ is equal to 20° the error incurred in using only the first two terms is only .022 and correspondingly smaller for angles less than 20°. Continuing with reference to the block diagram of the present system shown in Figure.4, it should be noted that 3 V is obtained by means of analog multiplier circuit means 54 coupled downstream from first stage differential ampli- 3 fier circuit means 46, 48, and 50, Since the term V /6 is relatively small compared to V for θ less than or equal to 20 , the accuracy requirements of analog multiplier circuit means 54 are not very stringent. Voltages representative 3 of V and V /6 derived from multiplier circuit means 54 are summed together by summing means 56 to provide an output voltage proportional to the tilt angle β which, after suitable scaling, is displayed in degrees at a utilization device 100. Utilizing a front panel mode switch 200 (the contacts of which are shown for the specific circuit schematic at Figure 5C) , the output of the reference transducer can be displayed independently, where the difference between the inboard or outboard flap angle relative to the reference angle can also be selected. Turning now to the full circuit schematic diagram shown when Figures 5A, 5B and 5C are all connected together" with respective numerals at the ends of the circuit boards carrying the circuits, it will be noted that the inputs of the system include the aforementioned reference inclinom¬ eter 20, inboard inclinometer 22, and outboard inclinometer 24. Also the mode switching means 200 and output utiliza¬ tion display device 100 are shown at the Figure 5C portion of the entire schematic of the present system. The sche¬ matic diagram of Figures 5A, 5B and 5C taken together show one exemplary full-scale embodiment of the system shown and hereinbefore described in the block diagram of Figure 4. While corresponding signal processing portions of the system shown in block diagram in Figure 4 are denoted utilizing corresponding numerals in the full schematic diagram of Figures 5A, 5B, and 5C, by way of further explanation it should be noted that IC1 is an instrumenta¬ tion amplifier; the gain is set at 4.00. IC4 and IC5 are four quadrant multipliers that provide the second term to the inverse sine approximation. Summing and scaling is done by IC6. The final subtraction is done by digital panel meter 100 which has differential input. IC2, IC7,- IC8, and IC9 perform further similar functions respectively as IC4, IC5 and IC6 hereinbefore discussed. Also IC100 of Figure 5B performs same function as ICl and IC2 hereinbefore discussed. of further interest in the circuit embodiment of Figures 5A, 5B, and 5C is that there is further included a power supply and battery protection circuit. The system is designed such that it can be powered by 115VAC 60 hZ or by its internal battery. The battery charging circuitry consists of IC10 and IC11. IC10 limits the maximum charg¬ ing voltage to 47.0 volts + . 0.5 volt. Transistors Ql and Q2 form the battery ∑&iutdown circuitry. When the voltage on the collector of Ql goes below 32 volts + 0.5 volt, Q2 will be turned off and Ql will then be off, IC12 regulates the battery output voltage to 30.0 volts + 0.3 volts. Q5 together with Q3 and Q4 form a power splitter circuit to provide the + 15 volts DC to power transducers 22, 24 and 26 and other circuitry. IC14 supplies the +5VDC required by display meter 1Q0, While the present system embodiment has been shown for making flap angle measurements, the present system embodiment has also been used and may be utilized in calibrating pitot tubes shown at 301 in Figure 2 and angle of attack sensors 303, also shown in Figure 2. As a consequence, several applications of the present measuring method and apparatus as shown herein are illustrative of and merely exemplary of the present position measuring. Exemplary parts in the circuit schematic of Figures 5A - 5B include: IC1, IC2 LH0036C IC4, IC7, IC8, IC5 AD534 IC6, IC9 TL081 IC100 LH0036C IC10, IC11, IC12 LM317HC IC14 78L05

Claims: -7- We claim: 1. A method for measuring the angle between a flap sur¬ face and the wing reference plane of an aircraft comprising the steps of: disposing a servo inclinometer transducer in the wing reference plane of the aircraft; disposing a further servo inclinometer trans¬ ducer on the trailing edge of a flap surface of the aircraft; processing signals from said servo inclinometer and said further servo inclinometer by performing an arcsine operation with respect to said signals to provide the measured angle. 2. A system for measuring the relative angle between a reference plane and an object in a further plane comprising: a first servo inclinometer disposed in said reference plane; a further servo inclinometer disposed in said further plane; said servo inclinometers providing a voltage proportional to the sine of the tilt angle; Signal processing circuit means responsive to said voltage proportional to the sine of the tilt angle for providing a further voltage representative of the inverse sine of said voltage proportional to the sine of said tilt angle; and, readout means responsive to said inverse sine of said voltage for displaying said relative angle in degrees. 3. A system for measuring the angle between an inboard or outboard flap of the wing of an aircraft relative to the wing reference plane of the aircraft comprising in combination: a first servo inclinometer mounted on the trailing edge said inboard flap; a second servo inclinometer mounted on the trailing edge of said outboard flap; a third servo inclinometer mounted in said wing reference plane of the aircraft; differential amplifier circuit means responsive to the outputs of said first, second, and third servo inclinometers; display means; and multiplier circuit means and summing circuit means connected in series circuit between said differential amplifier circuit means and said display means for displaying said angle.

Inventors: CHAU ALBERT WING-PING, GEITHMAN GLENN ALLEN, LUMLEY LAURENCE ARTHUR, CHAU, ALBERT, WING-PING, GEITHMAN, GLENN, ALLEN, LUMLEY, LAURENCE, ARTHUR
Applicants: BOEING CO, THE BOEING COMPANY
Application year: 1982
Main classification: G01C25
IPC codes: B64C9, G01B7