f/a-18 e/f program independent analysis

F/A-18 E/F PROGRAM INDEPENDENT ANALYSIS

T

F/A-18 E/F Program Independent Analysis

John P. Halpin, Peter P. Pandolfini, Paul J. Biermann, Thomas J. Kistenmacher,Lawrence W. Hunter, James S. O’Connor, and Daniel G. Jablonski

he F/A-18 Program Office (PMA-265) has instituted several new and innovativeprogram management tools, including a Program Independent Analysis Team, duringengineering and manufacturing development of the F/A-18 E/F aircraft. The AppliedPhysics Laboratory was invited to join this team shortly after it was established in mid-1992. As a key member of this team, the Laboratory acts as an independent technicalevaluator, applying a wide range of technical and programmatic experience to thesuccess of the F/A-18 E/F Program.(Keywords: F/A-18 E/F aircraft, Risk management.)

INTRODUCTIONThe Navy conducts its carrier-based air-to-air and

air-to-ground missions with a mix of fighter (F-14),strike (A-6E), and multirole strike/fighter (F/A-18)aircraft. The F/A-18 E/F (single-seat/dual-seat) aircraftis being developed as a major modification of the ex-isting F/A-18 C/D aircraft. The F/A-18 E/F aircraft willprovide increased mission radius, additional payloadflexibility, enhanced survivability, greater payloadrecovery capability, and space for future avionicsgrowth.

Since mid-1992, the Laboratory has been a keytechnical member of the F/A-18 E/F Program Indepen-dent Analysis (PIA) Team. This team is chartered withproviding independent, nonadversarial, proactive anal-yses of technical and programmatic issues affecting theF/A-18 E/F airframe and F414 engine engineering andmanufacturing development programs. This article de-scribes the Laboratory’s role on PMA-265’s PIA Teamand highlights selected areas of technical contribution.

JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 18, NUMBER 1 (1

PROGRAM INDEPENDENT ANALYSISIn May 1992, the F/A-18 E/F Program entered the

engineering and manufacturing development phase ofthe defense acquisition process, after the Undersecre-tary of Defense for Acquisition approved the Navy’srequest for development of the F/A-18 E/F aircraft (Fig.1) as a major modification of the existing F/A-18 C/Daircraft. At the program’s outset, the F/A-18 ProgramOffice (PMA-265) instituted several new and innova-tive program management tools. These tools were in-troduced to avoid some of the difficulties encounteredwith the A-12, P-7, and other recent naval aircraftacquisition programs and to facilitate PMA-265’s tran-sition to an integrated program team culture. Theyincluded a formal risk management program, rigorouscost/schedule control system criteria, cost-type con-tracting with unusually high award fee content, and thePIA Team.

The charter of the PMA-265 PIA Team is to inde-pendently identify, investigate, and report upon issues

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34 JOHNS HOPKINS APL TECHN

Figure 1. First flight of the F/A-18 E/F aircraft (U.S. Navy photo).

that may affect the success of the F/A-18 E/F Program.The team reports to the PMA-265 PIA Director andhas the authority to evaluate all areas and levels of theF/A-18 E/F Program. In conducting these evaluations,the team has access to all government and contractorsources of program data and information.

The PIA Team is a group of individuals from non-advocacy organizations with the multidisciplinary ex-pertise to independently assess all areas of the F/A-18E/F Program.1 It currently includes technical expertsfrom the Laboratory and operational and flight testexperts from Rail Company. This Navy PIA Teamconducts its own independent analysis efforts. It alsocoordinates these efforts with corporate-sponsored PIAteams from McDonnell Douglas Aerospace andNorthrop Grumman Corporation, the aircraft’s mainairframe developers, and General Electric, the aircraft’sengine developer.

Once an evaluation topic is identified, the Navy PIATeam members conduct their research and analysis withcooperation from knowledgeable contractor andNAVAIR personnel. Where appropriate, investigationsare also conducted jointly with one or more of thecontractor PIA teams. A typical evaluation requiresbetween 30 and 60 days to complete. It culminates inthe publication of a final report that summarizes rele-vant findings and recommendations. PIA uses a familiargreen, yellow, and red rating scale to communicate itsfindings and recommendations. Green indicates thatthe subject activity is within specification, performingto plan, and progressing satisfactorily. Yellow indicatesthat some event, action, or delay has occurred or isanticipated that requires additional effort and atten-tion. Red indicates that an event, action, or delay hasoccurred that will impair progress toward major objec-tives or requirements.

PIA findings and recommendations are reported tothe F/A-18 Program Management Team via formal

Positioning Systeming technologies, adently investigatetechnical concernment Team. Firstsystem developmeoff Weapon, the Sed Range, and thalso been applied but inside the sphe

The next sectiowhich the Laboratin support of PMA

FLIGHT TESTA major milesto

F/A-18 E/F aircrafan extensive 3-yedevelopment flighgram began in Fcompletion in Debeing conducted Center Aircraft DiMaryland, by an inNavy and contrac

In early 1994, independent evaluF/A-18 E/F flight tthe PIA Team appdistribution to deF/A-18 E/F flight vided an independquantifying flight tepotential effects of

The master tesprogram provided opment effort. A

reports and regularly scheduledbriefings. The Program Manage-ment Team retains responsibility,accountability, and authority forthe program’s success and conductsa thorough review of the PIATeam’s findings and recommenda-tions before implementing appro-priate actions.

The PMA-265 PIA Director hastaken advantage of the Laboratory’stechnical and programmatic exper-tise since July 1992. APL experts inheat transfer, thermodynamics, flu-id mechanics, aerodynamics, pro-pulsion, structures, composites, avi-onics, chemical analysis, electronicwarfare, software integration, Global

design and integration, manufactur-nd test and evaluation have indepen-d and reported on a wide range ofs to the F/A-18 Program Manage-

hand experience in related weaponnt programs such as the Joint Stand-tandoff Land Attack Missile/Extend-e Joint Direct Attack Munition hasto address issues outside the purviewre of interest of the F/A-18 Program.ns highlight selected evaluations in

ory played a significant technical role-265’s PIA Team.

PLANNINGne in the acquisition process for the

t will be the successful completion ofar engineering and manufacturingt test program. This flight test pro-ebruary 1996 and is scheduled forcember 1998. The test program is

primarily at the Naval Air Warfarevision (NAWC/AD), Patuxent River,tegrated test team that includes bothtor personnel.the Navy PIA Team conducted anation of the scheduling risk for theest program. During this evaluation,lied the mathematics of the binomialvelop a simple but useful model oftest scheduling risk. This model pro-ent and statistically based method forst scheduling margin and assessing thevarious risk mitigation strategies.t plan for the F/A-18 E/F flight testthe framework for the model devel-n integrated Navy/contractor test


team had developed this master plan based on F/A-18A/B flight test experience from the early 1980s andactual F/A-18 E/F flight test requirements. Accordingto the master test plan, approximately 2000 successfultest flights in 13 distinct categories are required to fulfillthe demonstration and test objectives for the F/A-18E/F aircraft.

A unique set of resource requirements and weatherconstraints applies to each of the 13 flight test catego-ries in the master test plan (Table 1). For example, therequirements for a flying qualities type of flight includean E/F test aircraft, a safety chase aircraft, NAWC/AD’sRemote Telemetry Processing System (RTPS), andvisual flying conditions. High angle of attack flights, onthe other hand, require an E/F test aircraft, a safetychase aircraft, RTPS, NAWC/AD’s Chesapeake TestRange, and visibility to an altitude of 35,000 ft. Thus,the success of any given flight depends on the type oftest conducted and the time of year that the test occurs.

From a scheduling perspective, a prospective testflight results in only one of two possible outcomes—success or failure. In the event of a success, the appro-priate resource requirements and weather constraintsare satisfied, and the applicable demonstration and testrequirements are accomplished during an actual flighttest. When a failure occurs, the flight test is canceledbecause one or more of the required resources failed tosupport the test and/or the weather failed to cooperate.

Because a scheduled test flight results in only one oftwo possible outcomes, it can be treated statistically as

a Bernoulli trial. Additionally, because each of the 13test categories comprises a series of independent Ber-noulli trials, with identical probabilities of success, theycan be treated as Bernoulli processes. For a Bernoulliprocess with probability of success equal to p, the prob-ability of observing r successes in n independent trialscan be expressed as a binomial distribution of the form

P R r n,pn

r n rp pr n r( / )

!!( – )!

( – ) .–= = 1

The preceding binomial distribution provides themathematical foundation for the F/A-18 E/F flight testscheduling risk model. The cumulative results for thisdistribution apply to each flight test category; thus, thedistribution can be used to determine the number of ntest windows needed to ensure that at least r successesare achievable at a specified appropriate confidencelevel.

The probability of success p for the events in a par-ticular test category is unique; however, it varies sea-sonally because weather affects flying conditions.Monthly probability of success figures are computedusing resource reliability and weather data applicable tothe Patuxent River Naval Air Station. These monthlyfigures are used to compute the number of testwindows required per month. The monthly require-ments are combined for the entire 3-year test program

JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 18, NUMBER 1 (1997) 35

Table 1. Projected requirements for the F/A-18 E/F flight test program.

No. of Flight test resourceFlight test category required flights TA CA TI RTPS CTR ORD Weather

Flying qualities 265 Y Y Y Y N N a

Performance 125 Y Y Y Y N N a

Propulsion 130 Y Y Y Y N N a

High angle of attack 250 Y Y Y Y Y N a,b

Flutter 255 Y Y Y Y N N c

Empennage buffet 25 Y Y Y Y N N a

Noise/vibration 30 Y Y Y Y N N a

Flight loads 195 Y Y Y Y N N a

Dynamic store release 40 Y Y Y Y Y N a,d

Carrier suitability/ground loads 173 Y N Y Y N N a

Mission systems 74 Y Y Y Y N N a

Weapons separation 267 Y Y Y Y Y Y a

New technology 10 Y Y Y Y Y N a

Notes: TA = F/A-18 E/F test aircraft, CA = chase aircraft, TI = flight test instrumentation, RTPS = remote telemetry processing system,CTR = Chesapeake Test Range, ORD = ordnance, Y = yes, and N = no.aVisual flight rules apply.bVisibility to an altitude of 35,000 ft required.cSmooth air required.dGround visibility from 5,000 to 20,000 ft required.

J. P. HALPIN ET AL.

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36 JOH
to determine the overall number of required test win-dows for each flight test category.

The overall flight test scheduling risk is quantifiedin terms of Tm, the available scheduling margin. Tm iscalculated for a specified appropriate confidence levelas the difference between Ta, the overall number ofavailable test windows, and Tr, the overall number ofrequired test windows. Ta is defined as the total numberof daylight hours available for flight testing during a 5-day workweek divided by the duration (1.4 h) of atypical flight test. Tr is defined as the overall sum of therespective test window requirements for each of the 13flight categories.

Representative results from the flight test schedulingrisk model are presented in Fig. 2. The model providesquantitative insight into the flight test schedulingmargin available under a given resource and require-ment scenario. The results from multiple runs can becompared to quantitatively assess the potential impactof various risk-mitigation alternatives, such as aerialrefueling. Figure 2 demonstrates that enhanced aerialrefueling capabilities effectively reduce Tr, resulting inincreased Tm. Aerial refueling reduces the overall num-ber of required test windows by extending the durationof successful test flights. This enables the data collec-tion requirements of multiple flights to be accom-plished during a single operation.

The flight test scheduling model has been used toquantitatively assess other risk mitigation strategies aswell, including a 6-day workweek, compressed workschedules, the addition of other flight test resources,and enhancements in the reliability of available testresources. The model is available for use in future PIAevaluations that address flight test scheduling marginand the potential impact of risk mitigation strategies onthe F/A-18 E/F flight test program.

ALR-67 PROGRAM RISK IMPACTEarly in the F/A-18 E/F development, the Program

Manager directed the PMA-265 PIA Team to indepen-dently investigate an issue of particular importance andtimeliness to an impending programmatic decision: theselection of ALR-67 radar warning receivers for theF/A-18 E/F aircraft.

As an outcome of a joint electronic systems reviewwith PMA-272 (Advanced Tactical Aircraft ProtectionSystem Program Office), PMA-265 recognized that twoversions of the ALR-67 would be available during thedevelopment of the E/F aircraft—the ALR-67 (v)2ECP 510 and the advanced ALR-67 (v)3. Each versionwas different, but the (v)3’s capability to handle threatsincluded those of the (v)2, and each could be incorpo-rated into the F/A-18 E/F aircraft. PMA-265 encoun-tered a particularly challenging decision when theALR-67 selection had to be made because each of these

Figure 2. F/A-18 E/F flight test scheduling margin. Ta = overallnumber of available test windows, Tr = overall number of requiredtest windows, and Tm = available scheduling margin.

radar warning receivers was still under development. Itwould be acceptable if the E/F used the (v)3 and theC/D used the (v)2. However, if the E/F chose the (v)3and the receiver was not successfully developed in timefor the E/F’s operational evaluation (OPEVAL), thenthe C/D would have the (v)2 ECP 510 receiver and theE/F would have none, thereby threatening the E/F’sdevelopment schedule. An overriding program require-ment that the E/F aircraft’s capabilities must be at leastequivalent to the C/D’s capabilities also had a majoreffect on this decision.

When the PIA evaluation was conducted, the ALR-67 (v)2 ECP 510 receiver had completed both its tech-nical evaluation and OPEVAL and was preparing toenter full-rate production. PMA-272 had identifiedseveral technical issues that affected this system’s inte-gration with the F/A-18 C/D and E/F aircraft. Theseincluded the incompatibility of pre- and post-ECP 510receivers [there are earlier versions of the (v)2], theneed to aggressively finish the integration of interfaces,and the need to rewrite (v)2 ECP 510 software in ahigher order language to support advanced sensorintegration.

In the other ALR-67 development effort, the v(3)receiver had fallen behind schedule, and its supplierhad overrun its fixed-price contract. This effort wasreplanned, and the supplier continued to work underits own funds toward completion. The supplier’s devel-opment effort was focused on producing service modulesfor bench and range tests that would lead to technicalevaluation and OPEVAL over the next three years.Before completing OPEVAL, two low-rate initial pro-duction decisions were scheduled.

Because of overlapping development and productionschedules, the ALR-67 receiver implementation deci-sion had to be made for the E/F aircraft before it wasmade for the C/D aircraft. As noted previously, the

Tr (with aerial refueling)

Ta

Tr (without aerial refueling)

Tm (with aerial refueling)

Tm (without aerial refueling)

5000

0

1000

2000

3000

4000

Num

ber

of te

sts

0 0.2 0.4 0.6 0.8 1.0

Confidence level


developmental status of the receiver programs and theoverriding requirement for equivalent capabilitiesmade this a particularly challenging decision. If theC/D was able to use the (v)3 receiver after the E/F hadselected the (v)2 receiver, then the E/F would not haveequivalent capability. On the other hand, if the E/Fchose the (v)3 receiver and it was not successfullydeveloped in time for the E/F OPEVAL, then the C/Dwould get the (v)2 ECP 510 receiver and the E/F wouldbe without one, unless the aircraft was wired to accom-modate both receivers.

The history of each ALR-67 development programwas complex, but a large amount of information wasavailable. The technical issues associated with theALR-67 were sufficiently understood, and it was gen-erally accepted that the ALR-67 (v)3 receiver wouldgive the E/F aircraft increased technical capability. Itwas not clear, however, to what extent the develop-mental problems of the (v)3 receiver would impact thedevelopment of the E/F aircraft. Additionally, PMA-265 wanted to know whether pursuit of a dual-wiringapproach that would interface with either receiver wasa worthwhile risk given the difficulties that the (v)3development effort was encountering. Through theapplication of a formal risk evaluation method, the PIATeam found that it is an acceptable risk for the E/Fdevelopment program to maintain the option of usingeither version of the ALR-67. By assuming a slightlyhigher risk, the potential for a higher technical payoffwas preserved and the E/F development schedule wasprotected. An independent evaluation was needed toexamine the technical and the programmatic risksfacing the F/A-18 Program in its decision to select anALR-67 radar warning receiver.

For this evaluation, the PIA Team selected a riskquantification method developed by the Defense Sys-tems Management College.2 This method models riskin a development program as the interaction of twoparameters: the probability of failure (Pf) and the con-sequences of that failure (Cf). The probability of thefailure is quantified by looking separately at the degreesof hardware maturity and complexity, the degrees ofsoftware maturity and complexity, and the dependen-cies on other items such as test facilities or associatecontractors. The consequences of failure are quantifiedin terms of effect on overall technical, schedule, andcost performance. The model is expressed mathemat-ically as the union of two sets, Pf and Cf, and an in-tegrated risk factor Rf of the following form:

Rf = Pf + Cf - (Pf)(Cf) .

Table 2 outlines the details of the evaluation matrixused. In practice, this method would be applied tomany elements of a program, and a risk factor wouldbe obtained for each element. The risk areas would


then be prioritized, and a program “watch list” wouldbe generated. For this evaluation, the risk model wasapplied to a single program element, the developmentof the ALR-67 radar warning receiver. Two questionswere formulated and addressed during this investigation:

• Question A: What is the integrated risk factor forPMA-265 in obtaining an ALR-67 (v)3 for the F/A-18 E/F development on time, within budget, and withsatisfactory performance?

• Question B: What is the integrated risk factor forPMA-265 in obtaining an ALR-67 (v)2 ECP-510 forthe F/A-18 E/F development on time, within budget,and with satisfactory performance?

The risk assessment method included weightingfactors that modify the elements of probabilities andconsequences of development failure. It was judgedthat the factors associated with the technical develop-ment should be assessed by the appropriate engineersfrom both PMA-265 and PMA-272. The programmaticconsequences should have a strong program manage-ment input. PMA-265 and PMA-272 provided theweighting factors for the Pf elements (Table 3). OnlyPMA-265 provided weighting factors for the Cf ele-ments, because the evaluation was being conductedfrom its programmatic viewpoint. Both PMAs tendedto give hardware maturity and hardware complexitymore weight than the other three probability of failurefactors. PMA-265 weighted the consequence factorsabout equally, and gave, relative to the technical con-sequences, slightly more weight to schedule conse-quences and slightly less weight to cost consequences.

For the ALR-67 v(3), the PIA Team learned thatthe basic design was complete and that some adjust-ments were being made as testing proceeded. Thehardware was judged to be extremely complex, requir-ing rebuilding of the computer, the special receiver, thequadrant receivers, and the antennas. The baselinesoftware had been written and was operational butrequired testing and additional optimization; the soft-ware performs a large amount of complex analyses. Theincreased complexities are attributed to the highercapability of the v(3) over that of the v(2). Dependencyfactors identified included the aircraft preparationneeded to incorporate v(3) kits, the movement offorward antennas into the wings, additional space re-quirements to accommodate an additional special an-tenna, and a radome redesign for the wing. Addition-ally, there was a strong programmatic dependency inthat if the (v)3 was incorporated into the productionF/A-18 C/D, then the v(3) must be on the F/A-18 E/Ffor the latter to conform to its operational require-ments. The technical consequences of failure werejudged minimal because the system was meeting itsspecification. In the cost arena, expenditures weretracking the current plan; the ultimate estimate of unit

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J. P. HALPIN ET AL.

Table 2. Mathematical model for risk assessment.

Risk factor, Rf = Pf + Cf – Pf Cf

Pf = a PMhw + b PMsw + c PChw + d PCsw + ePD,Cf = f Ct+ g Cc+ h Cs,

where

PMhw = probability of failure due to degree of hardware maturity,PMsw = probability of failure due to degree of software maturity,PChw = probability of failure due to degree of hardware complexity,PCsw = probability of failure due to degree of software complexity,PD = probability of failure due to dependency on other items

(a,b,c,d, and e are weighting factors whose sum equals one),

Maturity factor (PM) Complexity factor (PC)Magnitude Hardware (PMhw) Software (PMsw) Hardware (PChw) Software (PCsw) Dependency factor (PD)

0.1 Existing Existing Simple design Simple design Independent of existing system,facility, or associate contractor

0.3 Minor Minor Minor increase Minor increase Schedule dependent on existingredesign redesign in complexity in complexity system, facility, or associate

contractor0.5 Major change Major change Moderate Moderate Performance dependent on

feasibility feasibility increase increase existing system, facility, orassociate contractor

0.7 Technology New software, Significant Significant Performance dependent on newavailable, similar to increase increase/major system schedule, facility, orcomplex existing increase in no. associate contractordesign of modules

0.9 State of the art, State of the art, Extremely Extremely Schedule dependent on newsome research never done complex complex system schedule, facility, orcomplete associate contractor

Technical factor Cost factor Schedule factorMagnitude (Ct) (Cc) (Cs)

0.1 Minimal or no consequence, Budget estimates not exceeded, Negligible impact on program,unimportant some transfer of money slight development schedule

change compensated by availableschedule slack

0.3 Small reduction in technical Costs estimates exceed budget Minor slip in schedule (less thanperformance by 1 to 5% 1 month), some adjustment in

milestones required0.5 Some reduction in technical Cost estimates exceed budget Small slip in schedule

performance by 5 to 20% (1–3 months)0.7 Significant degradation in Cost estimates exceed budget Development schedule slip in

technical performance by 20 to 50% excess of 3 months0.9 Technical goals cannot Cost estimates increased in Large schedule slip that affects

be achieved excess of 50% segment milestones or haspossible effect on systemmilestones

Note: This table is reprinted from Ref. 2 by permission.

Ct = consequence of failure due to technical factors,Cc = consequence of failure due to changes in cost, andCs = consequence of failure due to changes in schedule(f, g, and h are weighting factors whose sum equals one).

38 JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 18, NUMBER 1 (1997)

F/A

Table 3. Weighting factors for ALR-67 evaluation.

Weighting PMA-265 PMA-272 Combinedfactor value value value

a (hardwarematurity) 0.25 0.28 0.26

b (hardwarecomplexity) 0.25 0.24 0.25

c (softwarematurity) 0.14 0.17 0.15

d (softwarecomplexity) 0.14 0.21 0.17

e (dependency) 0.22 0.10 0.17

f (technicalconsequence) 0.33 a 0.33

g (cost consequence) 0.30 a 0.30

h (scheduleconsequence) 0.37 a 0.37

a Only PMA-265 provided weighting factors for the Cf elements.

Table 4. Risk factor analysis for question A (ALR-67 (v)3 for E/F).

Factor Magnitude Rationale

PMhw 0.3 Basic design complete; some adjustmentsrequired as testing proceeds.

PMsw 0.3 Software baseline written and working;requires testing and additionaloptimization.

PChw 0.9 Extremely complex; requires rebuildingof computer, special receiver, quadrantreceiver, antennas.

PCsw 0.9 Extremely complex; performs a largedegree of analysis.

PD 0.5 Airplane must be prepared to accept(v)3 kit. Movement of forward antennasto wing. Additional space may berequired to accommodate extra polarityantenna; radome design required forwing. If (v)3 is on production C/D,then it must be on E/F.

Ct 0.1 System will meet (Nov 1992)specification.

Cc 0.3 Current expenditures tracking currentplan. Estimates of unit costs depend onvolume and rate of orders. CurrentlyNavy is only customer.

Cs 0.5(A1) (A1) Without dual wiring. 0.1(A2) (A2) With dual wiring.

Note: See Table 2 for definitions of factors.

costs depended onthe time of the ecustomer for this sdiffered, dependingequipped with or wdual-wiring optionand A(2), were cspond to an aircrrespectively.

The hardware aalready existed anv(2) had some neincluding new quadThere were some new functions, andwas to be convertseparate developmalso had to be movsequences were prsystem had passedwere firm, 230 unifollow-on producticontract award fro

Tables 4 and 5 peach question. Theof a value is listed.


-18 E/F PROGRAM INDEPENDENT ANALYSIS

the volume and rate of orders. Atvaluation, the Navy was the onlyystem. The schedule consequences on whether the aircraft would beithout dual wiring. Because of the

, two versions of question A, A(1)onsidered. These questions corre-aft without and with dual wiring,

nd software for the ALR-67 v(2)d had passed OPEVAL tests. Thew weapon replaceable assemblies,rant receivers and a new computer.software changes to accommodate although operational, the software

ed to a higher-order language in aent program. The forward antennased into the wings. The failure con-

ojected to be minimal because the OPEVAL tests, the cost estimatests had already been produced, andon was about to begin pending am PMA-272.resent the risk factor calculations for rationale that led to the assignment For question A, values for the con-sequences of failure due to scheduleeffects include those with and with-out the dual-wiring option.

Figure 3 summarizes the inte-grated risk factor calculations forquestions A(1), A(2), and B. Forcomparison, the influence of theweighting factors on the results isshown. Calculations were per-formed using PMA-265 factors andPMA-272 factors separately andusing the combined numerical av-erages of the PMA-265 and PMA-272 factors. As a control, the effectof using equal weighting factors (a,b, c, d, e = 0.20) also was computed.For these cases, the general resultseems insensitive to the weightingfactor differences. The integratedrisk factor for questions A(1) andA(2) are in the 0.60 to 0.70 range.For question B, this figure is ap-proximately 0.35. An interpreta-tion of these results is necessary.

Figure 4 illustrates the integratedrisk factor as a function of Pf and Cf.In this evaluation, the PIA Teamdid not attempt to modify the meth-od; the assignment of values in thediscrete set of 0.1, 0.3, 0.5, 0.7, or

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ICAL DIGEST, VOLUME 18, NUMBER 1 (1997)
40 JOHNS HOPKINS APL TECHN
Table 5. Risk factor analysis for question B (ALR-67 (v)2 ECP 510 for E/F).

Factor Magnitude Rationale

PMhw 0.1 Existing hardware that has passed OPEVAL.PMsw 0.1 Existing hardware that has passed OPEVAL.PChw 0.5 Some new weapon replaceable

assemblies in system; new quadrantreceivers and new computer required.

PCsw 0.5 Some software changes to accommodate newfunctions. Software conversion to higherorder language needed in a separatedevelopment program.

PD 0.3 Movement of forward antennas to wing.Ct 0.1 Passed OPEVAL.Cc 0.1 Cost estimates firm; production ready

to go; contract awarded by PMA-272 (22Apr 1993).

Cs 0.1 Production schedule within manufacturingcapability; 230 units already delivered.

Note: See Table 2 for definitions of factors.

Figure 3. Calculated risk factors for F/A-18 E/F developmentprogram use of ALR-67. Figure 4. Integrated

0.9

0.7

0.5

0.3

0.1 Conse

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

Inte

grat

ed r

isk

fact

or, R

f

0.1 0Pro

B

1.0

0.2

0.4

0.6

0.8

Inte

grat

ed r

isk

fact

or, R

f

A (1) A (2)

Question

PMA-265 weighting factorsPMA-272 weighting factorsCombined weighting factorsEqual weighting factors

0.9 was permitted only for any component risk factor.Thus, the integrated result must fall into the trapezoidalarea bounded by Pf = 0.1 and 0.9 and by Cf = 0.1 and0.9, as shown in Fig. 4. The lowest integrated risk factorachievable by this method is 0.19; the highest is 0.99.Risk factors in the range from 0.80 to 0.90 can resultfrom high probabilities of development failure and/orhigh consequences of that failure. The method does notspecifically indicate which values are associated withhigh-, moderate-, or low-risk levels.

To aid in the assignment of high, moderate, or lowrisk to a value for Rf, the Pf–Cf trapezoidal regime inFig. 4 is divided into three equal areas in the Rf–Pfplane. By this partition, a low-risk area ranging fromRf = 0.190 to 0.628, a moderate-risk area ranging from0.628 to 0.810, and a high-risk area ranging from 0.810

a planned use of presented a low rpart on this indeppursue a dual-wiriF development prfor a higher techapproach, and proif the ALR-67 (vproduction C/D a

COMPOSITEComposite mat

percentage of theexternal surface arC/D aircraft (Fig.

risk factor plotted as function of Pf and Cf.

Medium

Low

High

B

A(1)

A(2)

quences of development failure (Cf)

.3 0.5 0.7 0.9bability of development failure (Pf)

to 0.990 are illustrated. Based onthese ranges, question A(1) wouldfall into the moderate-risk area,question A(2) would fall just with-in the low-risk area, and questionB would fall well within the low-risk area.

High and moderate risks do notnecessarily forecast failure; theyonly point out areas of the programin which risk mitigation is re-quired to promote overall success.In an evaluation of a system’s risk,the integrated risk factor should beinterpreted in conjunction withthe technical benefits. For theALR-67 risk assessment evalua-tion, the PIA Team concluded thefollowing: a planned use of theALR-67 (v)3 version in the F/A-18 E/F development presented amoderate risk (without dual wir-ing) to low risk (with dual wiring)with high technical benefits, and

the ALR-67 (v)2 ECP-510 versionisk with moderate benefits. Based inendent analysis, PMA-265 chose tong option for ALR-67s during the E/ogram, thus keeping open the optionnical payoff, maintaining a low-risktecting the E/F’s OPEVAL schedule)3 were incorporated first into theircraft.

MATERIALSerials constitute a significantly higher F/A-18 E/F’s structural weight andea than the currently produced F/A-185). The use of high-specific-strength

materials is an increasingly attractive option for high-performance military aircraft because of recent devel-opments in composites design, fabrication, and repairtechnology. Composites technology will play an in-creasingly critical role in the life-cycle cost and perfor-mance of the F/A-18 E/F aircraft.

Since July 1992, APL has participated in approxi-mately 25 PIA evaluations of issues related to theapplication of composites on the F/A-18 E/F aircraft(Table 6). These evaluations have focused state-of-the-art in-house composites design and fabrication capabil-ities on both near- and long-term technical concernsregarding the use of composites, as well as other non-metallic coatings, adhesives, sealants, and materials.The scope of these investigations has been particularlybroad and has encompassed a wide range of compositesdesign, fabrication, maintenance, and repair issues.These efforts have been conducted with close cooper-ation and support from organizations throughout thecountry who have an interest in the effective use ofcomposites on the F/A-18 E/F aircraft. These organi-zations included NAVAIR, McDonnell Douglas Aero-space, Northrop Grumman Corporation, General Elec-tric, naval aviation maintenance organizations(organizational, intermediate, and depot level), theNaval Aviation Engineering Service Unit, the NavalAviation Training Group and Detachment, compositefabrication equipment and materials suppliers, theGreat Lakes Composite Consortium, and other naval



aviation acquisition programs. Highlights from selectedcomposites evaluations follow.

Materials Selection

Before the F/A-18 E/F Engineering and Manufactur-ing Development Program began, engineers realizedthat the composite structures on the F/A-18 E/F aircraftwould require increased stiffness to accommodate sig-nificantly higher structural loads than those encoun-tered during flight of the F/A-18 C/D aircraft. Thisrealization led to the selection of Hercules IM-7 rein-forcing fibers for the composite structures on the E/Faircraft. The microstrain capabilities of these stifferfibers exceeded those of the Hercules 3501-6 resin sys-tem used on the C/D aircraft and demanded thatmaterials experts also identify a toughened epoxy resinsystem for the E/F aircraft.

In January 1992, Fiberite 977-3 was chosen as theepoxy resin system for the composite structures on theF/A-18 E/F aircraft. The materials selection processentailed a complex trade-off of competing design,manufacturing, and quality control requirements withequally important cost, delivery, and vendor supportissues. Shortly after the PIA Team was established inJuly 1992, the NAVAIR Materials Division requestedan independent technical evaluation of the materialselection process to ensure that the proper resin systemhad been chosen. The Navy PIA Team, led by an APL

Flyawaycompleted

aircraft

Final assemblyand installations

Operationscheckout

Radar

Radome

Noselanding

gear

Mainlanding

gear

Leading-edgeextensionvent flap Wing

assembly

Trailing-edgeflap and shroud

Arrestinghook

EnginesCenter andaft fuselageassembly

Verticaltails

Horizontalstabilators

Forwardfuselageassembly

Aluminum

Steel

Titanium

Carbon/epoxy

Other

Figure 5. Composite materials will comprise 19% of the structural weight and 60% of the external surface area of the F/A-18 E/F aircraft.

97) 41

J. P. HALPIN ET AL.

Table 6. List of selected PIA evaluations on composite materials.

Subject ObjectiveQuality assurance Evaluate the adequacy of quality assurance procedures to address the

increased quantity and complexity of composite structures on theF/A-18 E/F aircraft.

Materials selection Confirm that an appropriate toughened epoxy resin system wasselected for the F/A-18 E/F aircraft.

Carbon/carbon brakes Determine the cause of lost brake efficiency on the F/A-18 C/Daircraft.

Fiber placement technology Assess the risk associated with application of fiber placement technologyto fabricate composite parts for the F/A-18 E/F aircraft.

Resin transfer molding technology Assess the risk associated with application of resin transfer moldingtechnology to fabricate composite parts for the F/A-18 E/Faircraft.

Composite repair technology Examine the technology and infrastructure available to support anincreased level and complexity of composite repair activities forthe F/A-18 E/F aircraft.

Advanced composite materials supportability Evaluate the status of plans and processes for ensuring the supportabilityof advanced composite materials in the fleet.

Shelf-life critical repair materials Evaluate the ability of the supply infrastructure to properly handle shelf-life critical composite repair materials for the F/A-18 E/F aircraft.

Future environmental regulations Investigate the impact of changing environmental regulations on themanufacture and repair of composite parts.

composites expert, completed this investigation inOctober 1992. On the basis of an in-depth analysis ofmechanical, physical, and manufacturing test data fromthe materials selection process, the PIA Team concludedthat Fiberite 977-3 would satisfy the operating require-ments of the composite structures for the F/A-18 E/Faircraft. The extended temperature capabilities of thestiffened fiber resin system ultimately led to the in-creased use of composites on the E/F aircraft and, as aresult, reduced weight and improved performance.

Fiber Placement TechnologyThe Navy has encouraged its airframe and engine

suppliers to pursue a prudent number of new technol-ogy demonstrations during engineering and manufac-turing development of the F/A-18 E/F aircraft. Thebenefits of and lessons learned from these demonstra-tions are to be applied during the follow-on phases ofthe F/A-18 E/F Program. With this philosophy in mind,the airframe suppliers decided to explore the use of fiberplacement technology to fabricate a selected set ofF/A-18 E/F composite parts.

Fiber placement technology uses a specially designedroller head to contact and press multiple fiber-resinbundles, or tows, into the desired location on a toolsurface to form composite parts. Parts curing occurs atthe appropriate temperature on the surface of the fiberplacement tool itself or after the parts are transferred

42 JOH

to a separate cure tool. The technology provides anattractive alternative to hand lay-up methods for fab-ricating relatively complex composite parts. For theF/A-18 E/F aircraft, the selected set of parts includedengine intake ducts, horizontal stabilizer skins, and rear-body panel skins.

Before investment in fiber placement equipmentoccurred, a joint Navy, McDonnell Douglas, andNorthrop Grumman PIA evaluation was conducted toassess the technical risk associated with the use of fiberplacement technology to fabricate composite parts forthe F/A-18 E/F aircraft. This evaluation focused onthree key technical questions:

• Could fiber placement technology produce compos-ite parts for the F/A-18 E/F aircraft that are equivalentto manually produced parts?

• Should a slit tape or pre-impregnated tow raw mate-rial feedstock be used if fiber placement technology ispursued?

• Which manufacturer’s fiber placement equipmentbest suited the needs of the program?

To address these questions, the PIA Team visited theindustry leaders, Cincinnati Milacron and Hercules,Inc., to witness fiber placement equipment demonstra-tions and to inspect composite parts fabricated withfiber placement technology. On the basis of these sitevisits and a comprehensive review of manufacturing


and test data, the PIA Team concluded that equivalentparts could be produced using fiber placement technol-ogy, either feedstock form was acceptable (economicsshould drive the choice), and either manufacturer’sequipment could satisfy the requirements of the F/A-18 E/F aircraft.

Shelf-Life Critical Repair MaterialsComposite repair materials frequently require refrig-

erated storage because of their limited shelf lives underambient storage conditions. Thus, the ability to ef-fectively repair the composite structures on the F/A-18E/F aircraft will depend heavily on the packaging, han-dling, storage, and transportation (PHS&T) of shelf-life critical materials.

Considering the enhanced use of composites on theF/A-18 E/F aircraft, the PIA Team conducted an inde-pendent evaluation of the supply system’s capability tosupport the projected composite repair requirementsduring deployment. This evaluation entailed a com-prehensive review of the projected requirements forF/A-18 E/F composite repair materials and examinationof the practices and procedures that the supply systemuses to package, handle, store, and transport shelf-lifecritical materials.

The PIA Team discovered during its investigationthat the PHS&T of composite repair materials involvesa complex network of individuals and organizations.The team formulated its findings based on meetings anddiscussions with PHS&T experts from NAVAIR, theNaval Aviation Engineering Service Unit, the DefenseLogistics Agency, the Aviation Supply Office, the ShipsParts Control Center, the General Supply Agency, andorganizational, intermediate, and depot-level mainte-nance organizations. More importantly, the PIA Teamdiscovered that some organizations treat shelf-life crit-ical composite materials differently. These PHS&Tdifferences were attributed to a variety of operational,equipment, and training issues. For example, the needto expeditiously clear the flight deck after an at-seareplenishment, the lack of adequate hazardous materialrefrigeration and freezer space on combat stores andsupport ships, and the failure of some personnel tounderstand the temperature sensitivity of compositerepair materials has frequently led to the inadvertentexposure of composite materials to temperatures thatreduce their usable lifetime.

As an outcome of this evaluation, the PIA Teamrecommended that PMA-265 choose a single organiza-tion to develop an integrated support plan that addressesthe PHS&T requirements for composite repair materialsfor all F/A-18 aircraft. In response to the team’srecommendation, PMA-265 requested that the NavalInventory Control Point form a team to investigate thePIA Team’s findings further and to develop an



appropriate integrated support plan. A representative ofthe Navy PIA Team was assigned to support this team’sefforts.

WINDSCREEN COATINGSTransparent conductors are being routinely incorpo-

rated today into a variety of state-of-the-art electronicand optoelectronic devices—from electrodes andheating elements to anti-reflective, anti-static, and anti-electromagnetic solar coatings. Because these conduc-tors provide a means to reversibly modulate the opticalcharacteristics of different transparent materials, boththe commercial and military aviation communities areinterested in the utility of thin-film ionic coatings inaircraft windscreen applications.

In late 1995, an F/A-18 E/F supplier was encounter-ing difficulty in applying stable and consistently uni-form solar films on F/A-18 E/F windscreens. Thesetransparent-conductive films must satisfy stringentelectrical resistance and optical transmission require-ments to comply with the overall performance speci-fication for the F/A-18 E/F aircraft. The windscreensupplier was unable to routinely meet these require-ments when the PMA-265 PIA Director asked theNavy PIA Team to provide an independent technicalreview of the process that was being used to apply solarcoatings on F/A-18 E/F windscreens.

A PIA Team representative conducted an on-sitereview of the manufacturer’s solar-coating applicationoperation in October 1995. The key elements of theprocess used to apply solar coatings on F/A-18 E/Fwindscreens are similar to those used in APL’s MiltonS. Eisenhower Research and Technology DevelopmentCenter and Microelectronics Facility. Windscreen coat-ing occurs in an 8-ft-dia. by 20-ft-long cylindricalchamber using an appropriately designed target. Thechamber is pumped down before coating deposition.The windscreen is held in close proximity to the targetwhile the solar coating is applied.

Following the on-site review, scientists from theMilton S. Eisenhower Research and Technology Devel-opment Center also performed in-house chemical andphysical analyses of solar-coated samples furnished bythe F/A-18 E/F windscreen manufacturer. These analysesfocused on four key performance-related parameters:

• Chemical composition using energy dispersive analysisfor X rays

• Electrical properties using the van der Paaw technique• Structural characteristics using X-ray scattering

methods• Optical properties from dual-beam absorbance mea-

surements

On the basis of its findings, the PIA Team prepareda comprehensive final report for PMA-265 and the

97) 43

J. P. HALPIN ET AL.

windscreen manufacturer. In addition to summarizingthe quantitative results of the team’s investigations,this report recommended the implementation of threeimportant process modifications:

• Altering the shape of the target• Adjusting the oxygen concentration in the coating

atmosphere• Allowing sufficient time for annealing of the

windscreen after the solar coating is applied

These investigative results and recommendationshelped the manufacturer overcome its processing dif-ficulties and produce solar-coated windscreens thatcomply with the overall performance specification ofthe F/A-18 E/F aircraft.

TEST ENGINE COMPRESSORBLADE FOULING

General Electric’s F414-GE-400 engine entered a4-year engineering and manufacturing developmenttest program in early 1993 to verify its capability tosatisfy the enhanced thrust and performance require-ments of the F/A-18 E/F aircraft. This test programprogressively validates the F414 engine’s qualificationsfor F/A-18 E/F flight testing, low-rate initial produc-tion, and full-rate production. A significant portion ofthis test program is being conducted at the Air Force’s

44 JOH

Arnold Engineering and Development Center (AEDC)in Tullahoma, Tennessee.

In early 1995, AEDC test engineers encountered ananomaly during preflight qualification testing of theF414 engine. They reported unexpected reductions inmeasured compressor efficiency as engine testing pro-ceeded. Additionally, they noted that measured com-pressor efficiency recovered mysteriously after over-night shutdown of the AEDC engine test facility.When testing resumed the following day, the compres-sor efficiency returned to its nominal value. Represen-tatives from NAVAIR, AEDC, General Electric, andAPL formed a tiger team to investigate and address theroot cause of this anomaly.

Early in the team’s investigations, test engineersdetected an unusually high amount of unknown depos-its on the F414’s compressor blades (Fig. 6). Preliminarycalculations by General Electric indicated that theseresidues were the probable cause of the apparent lossin compressor efficiency. Two theories emerged toexplain the origin and magnitude of these deposits.First was the hypothesis that the enhanced perfor-mance characteristics of the F414 engine, particularlyits high bypass ratio, made the compressor increasinglysusceptible to the rust and dust buildup that frequentlyoccurs in full-scale test facilities. Second was the theorythat the observed coatings originated from an inadver-tent increase in rust and dust in the AEDC test facility.

Dire

ctio

n of

airf

low

Figure 6. Potassium phosphate deposits on sixth and seventh stage blades of the F414 compressor .



After chemical analyses of the deposits were com-pleted, the team focused its attention on the facility’srust and dust conditions. The analyses indicated thatthe deposits contained a high concentration of potas-sium phosphate. The test facility’s refrigeration plantwas subsequently identified as the likely source of thecompressor blade deposits. The plant uses refrigerationcoils to cool test air to high-altitude conditions. An-tifreeze is sprayed on the refrigeration coils perpendic-ular to the test air stream to prevent ice buildup duringhigh-altitude engine testing. Potassium phosphate actsas a rust inhibitor in the antifreeze. Some antifreezedroplets were entrained in the test air and proceededthrough the demister screens installed to remove them.In the event that a droplet evaporates completely beforeentering the engine intake, the compressor inlet airincludes vaporized antifreeze and a potassium phosphatedust that can collect on the compressor blade surfaces.Those droplets that reach the engine intake beforeevaporating completely will boil upon contact with thehigh-temperature compressor blades to produce anti-freeze vapor and a potassium phosphate coating as well.

To understand the distribution of deposits in thecompressor, APL proposed an initial theory based onhow a droplet behaves when it contacts a hot metalsurface. This theory also considered the impact ofpressure variations in the compressor on the boilingpoint of antifreeze. Bench tests at APL’s AdvancedTechnology Development Laboratory confirmed thatthe heat transfer rate to droplets decreases and dropletlifetime increases when the temperature is high enoughto produce an insulating film of vapor between thedroplet and a hot metal plate. These theoretical andempirical results agreed qualitatively with the observeddistribution of deposits through the compressor at dif-ferent engine test conditions. They also supported thetheory that antifreeze droplets were impinging directlyon the compressor blades.

As the effort progressed, the team made anotherimportant discovery. The antifreeze in the refrigerationplant is circulated through a closed-loop system, andfresh antifreeze must be added periodically to make upfor evaporation losses. When antifreeze evaporates, thepotassium phosphate rust inhibitor remains behind. Asa result, the phosphate concentration had increasedconsiderably over time, resulting in an inadvertentincrease in the level of rust and dust circulatingthrough the engine test facility. As soon as AEDC testengineers recognized the problem, they refilled thesystem with reduced-phosphate antifreeze. Evaporativelosses are now made up with phosphate-free antifreeze.

How did compressor efficiency recover overnight?Conditions in the test cell became humid overnight,and NAVAIR pointed out that potassium phosphatehas an unusually high affinity for water. Bench tests atthe Advanced Technology Development Laboratory


confirmed that the compressor blade deposits couldextract enough moisture from the test cell air overnightto dissolve themselves. Follow-on tests at AEDC repro-duced these results in greater detail.

VERTICAL TAIL ASSEMBLYThe original design philosophy for the F/A-18 A/B

aircraft in the late 1970s called for vortex sheddingfrom the aircraft’s leading-edge extension and across itsvertical tail assembly (VTA) to improve controlauthority at high angles of attack. At the time, designengineers recognized that the resulting buffet loadswould induce fatigue into the VTA. However, theoriginal service use profile indicated that the F/A-18A/B aircraft would rarely be flown at high angles ofattack. Nobody informed the pilots. High angle ofattack maneuvering in a controllable fighter gives thepilot a tactical advantage in combat. In fleet service,the pilots routinely flew the plane at high angles ofattack, and buffet fatigue resulted. Thus, a considerablemaintenance effort was required to keep the F/A-18A/B aircraft in the air.

When the F/A-18 C/D aircraft was designed, theaircraft’s service use profile was adjusted to reflectadditional operating time at high angles of attack. Thefatigue life of the VTA became a key design parameterfor the F/A-18 C/D aircraft. Analyzing and designingstructures that will experience fatigue loads in a highbuffet environment are relatively complex tasks. Con-sequently, a high visibility inspection and maintenanceeffort has been conducted for the F/A-18 C/D VTA aswell. The results of this inspection and maintenanceeffort have validated the success of previous analysisand design efforts, as some F/A-18 C/D aircraft areapproaching one service lifetime of use with normalfatigue-related maintenance.

Given the historical significance of the VTA as ahigh-maintenance item for the F/A-18 aircraft, theNavy, McDonnell Douglas, and Northrop GrummanPIA Teams have coordinated two joint evaluations ofissues critical to the development of the F/A-18 E/FVTA. The earlier of these efforts was the first-ever jointPIA evaluation. These evaluations were conductedjointly to ensure that the findings and recommenda-tions were representative of the combined interests ofMcDonnell Douglas, Northrop Grumman, and theNavy. McDonnell Douglas is responsible for estimatingthe buffet load spectra; Northrop Grumman is respon-sible for the VTA’s design, fabrication, and testing.Both companies share responsibility for developing thefatigue material allowable stresses for the VTA. Theseallowable stresses are a function of both VTA materialand load profile.

The first evaluation focused on the design effort forthe VTA. PIA representatives met for two days at the

97) 45

J. P. HALPIN ET AL.

McDonnell Douglas facility in St. Louis, Missouri, tointerview the personnel who developed the loads andfatigue allowable stresses for the F/A-18 E/F VTA. Theteam subsequently interviewed the VTA Integrated Prod-uct Development Team at Northrop Grumman’s facilityin El Segundo, California. The PIA Team was impressedwith the Integrated Product Development Team’s appli-cation of lessons learned from previous F/A-18 experi-ence. The primary load-carrying structures in the VTAare either titanium or carbon fiber composite, bothfatigue resistant materials. The design team had used thedirectional material properties of the carbon fibercomposite material to give the E/F VTA the same vibra-tion characteristics as the smaller C/D VTA.

Upon completing its investigation, the PIA Teamreported that the technical risks of the VTA develop-ment effort were understood and that adequate stepshad been taken to mitigate those risks. The team alsoreported that the development effort faced a significantscheduling risk because of the impact of recent leading-edge extension design changes on the design loads forthe VTA. The PIA Team recommended that the pro-gram assign an additional stress analyst and computerworkstation to alleviate this scheduling risk.

The second evaluation addressed the FT-55 groundtest for the VTA. This test was designed to measure theexpected fatigue life of the F/A-18 E/F VTA. The FT-55 test requires almost 2 years to complete; it is the mostexpensive ground test in the F/A-18 E/F Program.Originally, this test called for subjecting the VTA to itsexpected fatigue-load profile during two service life-times, followed by nondestructive inspection to identifyany failures in the VTA’s composite skins and substructure.After this testing was complete, the plan was to keepthe test fixture intact for approximately 2 years untilthe actual buffet-load profile was measured during F/A-18E/F flight testing. This approach would enable addi-tional test cycles to be conducted in the event that theactual fatigue-load profile exceeded the expected profile.

As an outcome of its investigation, the PIA Teamrecommended disassembly and inspection of the FT-55test article shortly after it is subjected to the expectedfatigue-load profile. This recommendation was moti-vated by the team’s concern about the inability ofexisting nondestructive inspection techniques to detectfailures in the composite substructure of the FT-55 testarticle. Although early disassembly of the test articlewould preclude follow-on testing if deemed necessary,it would allow for earlier diagnosis of potential fatigueproblems while the FT-55 test team is still intact.

GLOBAL POSITIONING SYSTEMWEAPONS/AIRCRAFT INTEGRATION

With the advent of smart weapons and precisionguided munitions, such as the Standoff Land Attack

46 JOH

Missile (SLAM), the Joint Standoff Weapon (JSOW),and the Joint Direct Attack Munition (JDAM), theinterface for communicating Global Positioning Sys-tem (GPS) information between a military aircraft suchas the F/A-18 E/F and its wing- and fuselage-mountedweapons has become increasingly sophisticated. Be-cause of the complexity of this communications inter-face and the fact that many integration issues fallbeyond the formal scope of responsibility of individualaircraft and weapons program managers, the Navy PIATeam selected GPS weapons integration as the topic fortwo independent evaluations. These evaluations ad-dressed F/A-18 E/F GPS integration with JSOW andSLAM/ER (the expanded response upgrade to SLAM).

Early in these evaluations, the PIA Team discoveredthat implementation of the MIL-STD-1760B Aircraft/Store Electrical Interconnection System, commonlyreferred to as 1760B, would play a critical role in thesolution of most GPS integration issues. This standardestablishes a common hardware interface that supportsall aircraft and weapons data communications. It alsoprovides a foundation for integrating advanced weap-ons with aircraft of other services and other countries(e.g., our NATO allies).

Among the communications issues that 1760B wasdeveloped to address is the means by which a militaryaircraft might transmit raw GPS signals and/or pro-cessed GPS data to its wing-mounted weapons. Al-though SLAM, JSOW, and JDAM do not have anexplicit requirement to track GPS “on the wing” today,it is still necessary for their host aircraft to communi-cate GPS-derived position, heading, and velocityinformation before weapons launch. Under certainsituations, it can be advantageous for the aircraft toprovide additional GPS information as well, such as theraw GPS signals received by the aircraft’s GPS anten-nas, or precision timing information derived from thesesignals by the aircraft’s GPS receiver.

From a hardware perspective, the transmission ofraw GPS data via the 1760B interface appears to be arather straightforward procedure. The 1760B standardprovides the ability for an aircraft to transmit unproc-essed L-band GPS signals to its weapons over a 50Vcoaxial cable known as the high bandwidth-1, or HB-1, line. From a signal processing perspective, however,the transmission of unprocessed GPS signals via theHB-1 line is a considerable challenge. Cable losses, fan-out as the signal is delivered to multiple weapons, andstanding-wave ratio changes as weapons are releasedfrom the aircraft introduce complex signal handlingdifficulties.

The transmission of derived information between anaircraft’s GPS receiver and its weapon’s GPS receiversalso represents a considerable challenge. This informa-tion is usually broadcast over the digital data linkportion of 1760B, the MIL-STD-1553B serial asyn-


Figure 7. The F/A-1board wing from left On the port wing, alsinteresting to note thevolved from the HMaverick missile forweapons. The GPS rslightly different vercourtesy of McDonn

chronous interface, which operatesat 20 MHz. Whereas using this typeof interface can introduce queuingdelays in the transmission of GPS-derived information, these delaysare considered an acceptable limi-tation of the 1553B digital datalink because an asynchronous databus greatly simplifies the wiring in-terfaces between the aircraft’s GPSreceiver, mission computer, andweapons stations. The 1553B datalink can be implemented with asingle twisted-pair cable thatbranches off to multiple equipmentand weapons stations. This inter-face is preferred from a manufactur-ing and aircraft weight perspectiveto that needed for a synchronous,parallel data bus such as that usedin a personal computer.

In addition to queuing delays,the twisted-pair 1553B interfacenecessitates complex handshakingand identification protocols. Thecombined impact of protocol andqueuing delays can increase thetime required to send a messagebetween the aircraft mission com-puter and a wing-mounted weapon.

As a result of these findings, the Navy PIA Teamconcluded that the F/A-18 E/F aircraft has two realisticoptions for providing accurate GPS assistance to JSOWand SLAM/ER (Fig. 7). Both of these options involveuse of the HB-1 line. The F/A-18 E/F aircraft canforward raw GPS signals from its antenna over the HB-1 line, or the aircraft’s GPS receiver can be designedso that high- resolution time-mark information can betransmitted over the HB-1 line to the timing and nav-igation hardware on the weapon’s GPS receiver. Theteam quantified the performance improvements foreach option, as well as the benefits of improved GPSintegration in the case of jamming.

For SLAM/ER, the PIA Team recommended that theF/A-18 E/F Program pursue the HB-1 time-mark commu-nications option because these signals are much easier tohandle than the low-power, noise-laden, raw GPS signals.For JSOW, the team recommended that the program pur-sue the HB-1 time-mark communications as well, alongwith further exploration of the raw GPS alternative.

Additionally, the PIA Team confirmed that theseadvantages can be gained in the future as plannedproduct improvements through additional or modifiedelectronics equipment and software upgrades withoutthe need for significant change to the existing designof the aircraft. This is an important finding, as it

JOHNS HOPKINS APL TECHNICAL DIGEST, VO


8 E/F with its complement of wing-mounted weapons. On the star-to right in the picture are the AIM-9, HARM, Harpoon, and SLAM/ER.o from left to right, are JDAM, JSOW, Maverick, and Sidewinder. It ise design overlap of some of the weapons. For example, SLAM/ER

arpoon antiship missile but also incorporates the sensor from the infrared imaging. SLAM/ER, JSOW, and JDAM are all GPS-guidedeceivers to be used on the aircraft and on both SLAM/ER and JDAM aresions of the same receiver and use similar software. (Photographell Douglas Corporation.)

permits PMA-265 to avoid additional cost today whilekeeping its options open for improved aircraft/weaponintegration in the future.

SUMMARYThis article described efforts in which the Laboratory

has played a key technical role in support of the PMA-265 PIA Team. The PIA Team continues to conductindependent, nonadversarial, proactive evaluations of awide range of technical and programmatic issues affect-ing the success of the F/A-18 E/F Program. The PIATeam’s efforts continue to evolve with the F/A-18 E/FProgram.

REFERENCES1PMA-265 Program Independent Analysis: An Overview and Guide, pp.1-10 (Dec1994).

2System Engineering Management Guide, 2nd Ed., Defense Systems ManagementCollege, pp. 8-13 (Dec 1986).

ACKNOWLEDGMENTS: Numerous individuals made significant contributionsto the efforts that are summarized here. We wish to acknowledge the support of theF/A-18 Program Office, NAVAIR’s Competency Aligned Organization, MDA,NGC, GE, and their respective PIA Teams. In particular, we wish to acknowledgeCookie Herdt and Denise Scott, NAVAIR PMA265’s Program Sponsors for the F/A-18 Hornet Task; Ivan Behel and Stuart Fitrell (Rail Company) for theircontributions to the flight test planning model development effort; Lee Kennedyand Arthur Williamson (APL) for their contributions to the ALR-67 Program Risk

LUME 18, NUMBER 1 (1997) 47

J. P. HALPIN ET AL.

Impact Study; Bob Kogler (Prometheus), John Shupek (NGC), Gail Hahn, AlexRubin, and Kermit Wilkerson (MDA), and Doug Perl (NADEP, North Island) fortheir contributions to the composites evaluations; Brent Bargeron (ChemicalComposition), Wayne Bryden (Electrical Properties), and Dennis Wickenden(Optical Properties) of APL’s Eisenhower Research Center for their contributionsto the windscreen characterization measurements; the following individuals fortheir contributions to the Test Engine Compressor Blade Fouling investigation:John O’Connor (GE) for compressor blade fouling calculations, Chris Eddins andBill Metzler (APL) for bench test measurements, Penny Miller, Al Turrentine, andCharles Vining (AEDC) for theoretical and empirical analyses, and Dan Squire(NAVAIR) for insight into the hygroscopic properties of potassium phosphate;

48 JOH

Ray Skubic (MDA) for his contributions to both Vertical Tail Assembly evalua-tions, Charlie Hyde (NGC) for his contributions to the VTA design evaluation,and Charlie Burdsall (NGC) for his contributions to the VTA FT-55 evaluation;Stan Cox (APL, retired) for his contributions to the SLAM/ER evaluation, andThomas Corrigan (APL) for his contributions to the JSOW evaluation. Finally, wewish to acknowledge the contributions of the following APL staff members whohave supported F/A-18 E/F Program Independent Analysis efforts since July 1992:Bruce Coury, Thomas Duerr, Kelly Frazer, Richard Hammer, Richard Hildebrand,Thomas W. Johnson, James Kouroupis, Robert Malalieu, Robb Newman, JamesPerschy, and Ron Stevens. The F/A-18 Hornet Task is sponsored by the Naval AirSystems Command. This work was supported under contract N00039-95-C-0002.

THE AUTHORS

JOHN P. HALPIN is a Senior Professional Staff engineer in APL’s PowerProjection System Department. He is the Program Manager of APL’s F/A-18Hornet Task. Mr. Halpin received B.S. degrees in physics and mechanicalengineering from Drexel University, an M.S. in mechanical engineering fromStanford University, and an M.B.A from the University of Maryland. Mr. Halpinjoined APL’s Strategic Systems Department in 1984 and specialized in vibrationwhile supporting test and evaluation of the Poseidon and Trident submarine-launched ballistic missile systems. Between June 1991 and 1994, Mr. Halpinserved as APL’s Strategic Weapons Systems Advisor on the staff atCOMSUBPAC in Pearl Harbor, Hawaii. Before joining the Laboratory, Mr.Halpin was employed at General Electric Company, Koppers Company, andBooz, Allen and Hamilton, where he participated in the design, test, and analysisof advanced energy conversion equipment including evacuated tube solarcollectors, vertical axis wind turbines, Stirling/Rankine heat pumps, and heatrecovery steam generators. Mr. Halpin is a Registered Professional Engineer inMaryland. His e-mail address is [email protected].

PETER P. PANDOLFINI is a member of APL’s Principal Professional Staff. Hegraduated summa cum laude from the City College of New York’s Engineering& Architecture School in 1968. He received a Ph.D. in mechanical engineeringfrom Rutgers University in 1971 and an M.S in technical management from theJHU G.W.C. Whiting School of Engineering in 1984. Since joining APL in1972, Dr. Pandolfini has worked on air-breathing engines and on alternateenergy conversion power systems. Under his direction, APL’s Ramjet Perfor-mance Analysis code was brought to nationwide use and has evolved into arecognized standard for evaluating advanced airbreathing engine concepts. In1992, Dr. Pandolfini established APL’s participation on the Navy’s ProgramIndependent Analysis Team, serving as the APL Program Manager from July1992 until August 1995. He is currently the APL Program Manager to the JointStrike Fighter (JSF, formerly JAST) Program Office and works with the JSF’sPropulsion Integrated Product Team. Dr. Pandolfini is a Registered ProfessionalEngineer in Maryland. His e-mail address is [email protected].

PAUL J. BIERMANN is a member of APL’s Senior Professional Staff. He hasserved as a member of the F/A-18 E/F PIA Team since 1992. He received a B.S.in materials engineering from Rensselaer Polytechnic Institute in 1980. He spent6 years in the aerospace composites industry, conducting R&D related tocomposite material fabrication and testing. In 1986, he joined APL’s TechnicalServices Department to establish and operate a composite materials prototypefabrication facility. His accomplishments include design and fabrication ofcomposite components for spacecraft, biomedical applications, underwater deploy-ment, and materials test design. Mr. Biermann has published 10 papers on compositematerial fabrication and testing. His e-mail address is [email protected].



LAWRENCE W. HUNTER is a member of APL’s Principal Professional Staff.He holds a B.Sc. (hons.), first class, in chemistry (Carleton University, Ottawa,Canada, 1967) and a Ph.D. in theoretical chemistry (University of Wisconsin,Madison, 1972). He has been employed at APL since 1973 and has worked onmany different interesting projects, including projects related to combustion,propulsion, and materials. Dr. Hunter has coordinated several APL independentresearch and development (IR&D) activities. He has contributed to over 80refereed publications including one listed in “The Twenty-Two Most FrequentlyCited APL Publications,” John Hopkins APL Tech. Dig. 7(2), 221-232 (1986).His e-mail address is [email protected].

THOMAS J. KISTENMACHER is a Principal Professional Staff chemist inAPL’s Milton S. Eisenhower Research and Development Technology Center. Heobtained a B.S. degree in chemistry from Iowa State University and M.S. andPh.D. degrees, also in chemistry, from the University of Illinois. During 1969-71,he was a junior fellow in the A. A. Noyes Laboratory for Chemical Physics atthe California Institute of Technology. From 1971 to 1982, he served on thefaculties of The Johns Hopkins University, Homewood, and the CaliforniaInstitute of Technology. Dr. Kistenmacher joined APL in 1982 as a member ofthe Microwave Physics Group. He subsequently served in the Materials ScienceGroup and currently is a member of the Sensors Science Group. His principalresearch interests include the fabrication and analysis of thin films for a varietyof structural, electronic, and optical applications, X-ray diffraction, and crystal-line structure and structure-property relationships in a variety of electronic andmagnetic materials. His e-mail address is [email protected].

DANIEL G. JABLONSKI received B.S. and M.S. degrees in electricalengineering from MIT in 1976 and 1977, respectively, and a Ph.D. in physicsfrom Cambridge University in 1982. Before joining APL’s Power ProjectionSystems Department in 1991, he was a Scientist and Engineer for the NavalSurface Weapons Center (1974-86) and the Supercomputing Research Center ofthe Institute for Defense Analysis (1986-91). His current activities includeresearch in microwave digital electronics, infrared sensors and imaging, andapplications of the Global Positioning System. His e-mail address [email protected].

JAMES S. O’CONNOR is a member of APL’s Principal Professional Staff. Hereceived a B.S. in mechanical engineering from the University of Detroit and anM.S. in aeronautical and astronautical engineering from Ohio State University.Since joining APL in 1968, Mr. O’Connor has participated in the mechanicaldesign of guided missile systems, spacecraft, automated transportation systems,and the ocean thermal energy conversion power plant. After 25 years at APL, heis delighted to have finally worked on an airplane. His e-mail address isJames.O’[email protected].

JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 18, NUMBER 1 (1997) 49

f/a-18 e/f program independent analysis

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