The integration of electronic equipment with airframe design

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    10-Apr-2017

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<ul><li><p>THE INTEGRATION OF ELECTRONIC EQUIPMENT WITH AIRFRAME DESIGN </p><p>C. W Dix and A. F. Coombs Commercial &amp; Government Equipment Department General Electric Company$ Syracuse, Y# </p><p>SUMMARY: </p><p>Progress in coordinating the design of airborne radar equipment with airframe is discussed, emphasising suoh basic design characteristics as </p><p>accessibility, form factor , heat dissipation, altitude shock - vibration. R-F noie and primary OQM&amp;T supply A review of the scope of present-day installation problems follows, giving specific examples f coordinated design* Suggestions for improving current design practices include an early exchange of information among all agencies concerned, close liaison as the design un-folds ; and throughout, an appreciative understanding of each others problems* </p><p>A, DITOODUCTION </p><p>Since the early days of airborne electronic equipment, when pilots </p><p>the aircraft, electronic equipment has come into its own as an essential aid to atrial navigation and warfare ~ In sowe instances, such as radar trapping, interception, fire control or bombing, it has become the tactical weapon around which the aircraft itself has been designed* Such programs have ac-quired a complexity which now demands the utmost in liaison and teamwork between the contracting agency, the electronics engineer, and the aircraft designer* </p><p>A-le SCOPE OF THE DISCUSSION </p><p>Let us examine the situation with which the electronic engineer is con-fronted- His basic problem involves two major variables, one the electronic equipment, the other the airframe or airframes in which it is to be installed* Th^ electronic equipsasnt may consist of a single electronic box, entirely self contained, r it may be a complicated system of fifteen or twenty major units* On the other hand, the problems involved in successfully integrating elec-tronic equipment with the airframe design may vary widely according to the primary function ox the aircraft* In a commercial aircraft the emphasis may be placed wholly en accessibility and maintenancef whereas in a military air-craft such characteristics may be compromised to seme extent in order to gain CUWISS Osrforisnce of the sXectronic ecuisssent and the aircraft in fulfiii-~ lag their joint tactical requirement* Although the basic design considra- tions are the same in general for both commercial said military aircraft, the gj 1 i ha.yy does nresent ** mnrw allinclusive x?rbXem end. therefore the suing discussion w i H presume the ^irfrasse to be military rather than commercial. </p><p>A third factor, stemming from the primary function of the electronic equipment also plays a major role in determining the design situations Perhaps the equipment is intended for universal application in all aircraft ; or, it may be destined for a single type aircraft into which it must be integrated so completely that it becomes as much a part of the aircraft as the power plant itself* If designed for a specific tactical use, the equipment may very well be installed in several aircraft of varying types -</p><p>2 </p></li><li><p>Figure No. 1 depicts an arbitrary division of the airborne electronic field, in order to place ths scope of the paper in the military field rather than the commercial, with emphasis on a large system, such a a basic search radar, rather than on a simple equipment of one or two units. Then, in order to assure complete coverage, let us assume that the equipment is to be installed in several aircraft, each of which presents a different type of installations </p><p>A - 2 . THE DESIGN SITUATION </p><p>In addition to the factors already mentioned, there is still another circumstance which has direct bearing on the engineering approach to successful integration* The integration process nay involve electronic equipment and airframes which are completed designs, strictly developmental designs, or any combination of both Furthermore in the instances where more than one aircraft is installing the equipment, some of them may be approved aircraft while others are still in the developmental stage* This makes possible a number of design situations* (See Figure 2 ) </p><p>If an existing electronic equipment is to be installed in an existing aircraft, the burden of the work falls to the installing facility in designing mounts, cabling, etc. Very little integration as such can be achieved in addition to that already accomplished in the initial design of the elee-</p><p>For a developmental equipment in an existing aircraft, there exists a good opportunity for integration with the airframe . The aircraft installation engineers will be able to provide the electronic designer with data, drawings, and an opportunity for a first hand inspection of the aircraft itself- This situation should lend itself well toward achieving a successful installation* </p><p>The case where a developmental aircraft is to receive an existing electronic equipment is quite rare, but yet possible* Such a situation might occur if a particular equipment, such as a fire-control system for fighter aircraft, for instance, had proved to b outstanding in accuracy and reliability since released to the field and therefore any new fighters still in the development stage might very well be expected to install it as their basic fire-control equipment* If the aircraft is a large one, the installation problems are fewer In either case, complete data on the system is available fpcm the contracting agsncy, and ths electronic supplier ssay b^ called on only if it becomes necessary to give technical advice or to supplement the information already available* </p><p>The fourth possibility occurs whan both the electronic quipant and the airframe are being developed simultaneously. This is indeed the most ideal situation for integration with the airframe. Close liaison and a </p><p>a superior installation </p><p>It should be pointed out here that in the case of a developmental electronic equipment the situation may be complicated even further, if more than one aircraft is involved because the electronic engineer may have to design for both existing and developmental aircraft at the same time. Both Case 2 and Case 4 in Figure 2 apply in this situation </p><p>3 </p></li><li><p>* FACTORS AFFECTING INTEGRATION </p><p>The factors affecting the intgration of electronic equipment with airframe design fall into three general categoriess </p><p>1. basic design considerations 2. exchange of information 3* schedules and timing </p><p>In other words, the designer must know how to achieve the desired results, he must exchange information continuously to determine what the current requirements are, and he must knew when to schedule each phase of his work* These three factors are interrelated and interdependent 9 They apply to the contracting agency, the electronic designer and the airframe designer alike, and jointly determine the success of the installation0 </p><p>B-la. FORM FACTOR </p><p>Foremost among the basic design considerations is the form factor of the unit. Form factor may be defined as the basic configuration of an electronic unit The basic form factor of any electronic package is determined primarily by the sise and shape of the electrical and mechanical component" aw* the marmot* in which they must be assembled for optimum performance as a xmlt* The design specification for airborne electronic cases and mounting bases is JAN-C-172A. If the form factor does not require special tailoring to fit the space available in the airframe, then this specification will serve as a guide for determining case size and mounting base design for those major assemblies with regular outlines. Some units such as receivers, synchronisers and power supplies, (which are primarily electronic) lend themselves to designing for a form factor which is regular in sise and shape- Others, such as r-f units, antennas, air pumps and the like, must, of necessity, assume an irregular shape. Their basic form factor must be determined, for the most part, by the layout required. </p><p>In addition to the basic size and shape of a package are other considerations involving mounting, cabling, waveguide connections, hose connections for pressurization or cooling, adjustments, controls and switches, intake and exhaust openings for cooling and provisions for maintenance accessibility. A large measure of the success achieved by the electronic designer in establishing a satisfactory form factor for each unit is depen-dnt~oa hi ability to interpret these' features ir terms of the installation situation in the aircraft. </p><p>After an initial consideration for the internal layout of a unit* the designer must then examine the unit externally. First, some method of fastening the unit to the aircraft must be provided. In most cases, its mounting is called upon to protect it from shock and isolate it from vibration. It may be mounted from the top, bottom, sides, rear, front, in the horizontal or vertical planes, or at some angle* Only an early exchange of information with the airframe designer can enable him to prescribe the most efficient mounting for a particular aircraft. </p><p>Nearly all units have soss control knobs, switches, or adjustments available externally. They may be used either for operation or maintenance, but in any case must be placed for easy accessibility after installation. </p></li><li><p>Another item for consideration is external cabling* On sosse units the cables may be most efficiently connected to the front of the unit, where they may be easily disconnected for removal of the unit to the maintenance bench* On other units, (where, for instance, the front panel is filled with operational controls) it becomes necessary to connect the cables at the rear where they cannot possibly interfere with the operational use of the box. -The cables may, of course, connect to any face of the box* However, it is good design to use ^ of the- faces US possible to facilitate installation. </p><p>Air Intake and exhaust openings must be located where there is sufficient space to allow for the necessary exchange of air. The location of pressuriza-tion or cooling connections is not too critical, and for waveguide connections the unit layout dictates the location, and the aircraft cr^w sust pick up frois there* </p><p>Accessibility for maintenance is of major importance to an aircraft installation* Tubs s, crystals, (and any items normally changed in performing first echelon maintenance) muet be located where they csn be changed with ease. </p><p>Quick-diSeonnect fastened of ail types are recommended for securing covers, panels, or evsn components in order that maximum access for maintenance . 1 1 ~ J U C G L U O a j L i l C U * </p><p>Blb* PRIMARY POWER SUPPLY </p><p>Variable frequency engine-driven alternators are specified as the prime poorer supply in most electronic equipment specifications* The associated frequency range for equipment operation is usually 30 to 1000 cycles per second This range is dictated by the engine speed and drive ratio selected and is unavoidable. For servicing without external power , the frequency may drop below the minimum requirement due to low engine RFM* To prevent permanent damage to the equipment under sue conditions th specifications state that the equipment shall not suffer damage from input voltage at frequencies between the lower specified limit ox 360 cps to 200 ops at the specified voltage level and from 200 to cps with the voltage decreasing linearly to zero at zero frequency* Such a requirement leaves the equipment designer two alternatives* One, to design his transformers, reactors, etc., for this extended range, thus throwing away the space and weight saving advantages of a high frequency supplyj or two, to provide frequency sensitive relays to disconnect his equipment from the line if the voltage falls below a given frequency- Neither of these choices is satisfactory the first from the obvious space end weight penalty; the second from the fact that frequency sensitive relays have not been dependable components in the past and must be duplicated in every separate electronic unit or system installed in the aircraft* A much more logical and satisfactory solution is to place the control at the source - the alternator itself* A completely dependable and compact low frequency interlock, utilizing a device similar to conventional speed governors, would disconnect the alternator from the line at dangerously low frequencies* The responsibility for low frequency protection has been assumed by the airframe manufacturers in every case to the best of cur Imowledge, and it is expected that eventually the low frequency requirement will be deleted from future equipment specifications* </p><p>VOLTAGE VARIATION </p><p>Specifications state that a 5% variation in input voltage must not W - ^ A ^ r t ^ - . - R . / fynf 4 1 . - a . 4 M A M s i n 1 * ^ ^ * V * ! 4&gt; </p></li><li><p>the capabilities of the voltage regulation equipment in present-day aircraft -Even the specifications add the requirement that the equipment continue to operate over the 10% range, if possible, with no decrease in performance and no increase in size or weight. This performance can be maintained, but not without a sacrifice in sise and weight* If the input voltages could be held to l% or better the following penalties would not exist* </p><p>1* Extra series tubes and high gain amplifiers in regulated power-supplies* </p><p>2. Precision ranging circuits and accurate off-centering circuits for indicators* </p><p>3* Some type of regulation for oscillators, hydrogen thyratron capsule heaters, power supply amplifiers, etc-</p><p>4 Existing line voltage, regulators would be unnecessary* </p><p>Specifically, the designers of one large indicator system have felt justified in adding a 70 pound unit to provide accurately regulated line voltages for ths whole systemc </p><p>The increased demand for more accurate and more complex systems will require similar units for each separate system* The expense of solving this problem at the alternator end would be returned many-fold when the need for expensive regulators disappeared from the requirements of each system-</p><p>To date, no solution other than the above appears to be in sight-Admittedly^ the problem is severe, particularly where three-phase machines are involved, but it is felt that the immediate possible reduction in size, weight, and complexity of the airframes electronic complement is of suffi-cient magnitude to warrant a considerable amount of effort towards develop-ing a satisfactory voltage regulating device* </p><p>OVERLOAD PROTECTION </p><p>Although specifications call for overload protection, the service personnel at the contracting agency insist fuses or circuit breakers be eliminated or held to a bare minimum in new design* Their philosophy is to accept transient overloads which would normally shut down the equipment, until conditions develop to the "smoke" stage, thus affording a maximum amount of operation* </p><p>In new designs, automatic recycling overload circuits are used where a bum=out would be criOoling in terms of expensive oosponents and repair time, . modulators^ transmitters and Bplus supplie3* Filament trans...</p></li></ul>

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