Click for next page ( 45


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 44
4 Sufficiency of F-22 Testing Plans Part of the committee's task was to evaluate the sufficiency of the F-22 test program to meet the requirements of the live fire test law. This chapter contains that evaluation. Discussed first are the F-22 threat environment and its replication by the SPO in the vulnerability assessment program. The vulnerability assessment program is then evaluated. Finally, after some additional observations, the committee presents its conclusions. F-22 THREAT ENVIRONMENT AND ITS REPLICATION The threat environment for the F-22 is derived from its current principal mission of conducting offensive counter-a~r operations. The environment consists of threats the aircraft would expect to face while accomplishing its mission of destroying enemy aircraft over hostile territory. These threats, as characterized by a representative of the Air Combat Command in an unclassified briefing to the committee (Hinton, 1994), are shown in Table 4-~. In addition, the vulnerability specifications (discussed in Chapter 2) reflect a high-power microwave threat and a laser threat. The committee accepts these threats for the courter-air missions. The aircraft has been designed to meet them, and its vulnerability assessment program has been structured accordingly. The following assumptions were made by the SPO in the live fire test program to replicate the threat: . The threat specimen for the F-22 is represented by: (a) two metallic fragments (45 grains and ~ 50 grains), (b) two armor-piercing incendiary (API) rounds (23mm and 30mm), and (c) two high-explosive incendiary (HEN) rounds (23mm and 30mm) (SPO, 199Sa). The effects of the fragments are to be assessed over a range of impact velocities Tom 2,000 to 9,000 feet per second (fps). The APT rounds will be assessed over a range of impact velocities Tom 44

OCR for page 44
Sufficiency of F-22 Testing Plans TABLE 4-l F-22 Threat Environment 45 Fighters Air-to-Air Missiles Surface-to-Air Missiles Current Mirage 2000 Gripen MiG-29 Fulcrum SU-27 Flanker Future New Fighters IOC by 2004 SU-35 Improved Flanker Rafale Eurofighter 2000 New (Notional) Fighters Available by 2014 Multi-role Fighter Interceptor IOC 2005-2008 Experimental Fighter Interceptor IOC 2010-2015 Reticle IR Seeker with CCM AA-NOB/D AIM-9M AA-7D Active-Radar Seeker AA-X- 12 AIM-120 Multi-element Seeker AA-11 PYTHON 4 MAGIC 2 Imaging IR Seeker AAM (IOCs in 2004) XAAM~ ASRAAM AIM-9X SA-10 SA-12 Source: Hinton, 1994. NOTE: AAM=air-to-airmissile; CCM=counter-countermeasures; IOC=initial operational capability; IR=infrared.

OCR for page 44
46 Live Fire Testing of the F-22 . . 500 to 4,000 fps, and the HEl rounds wall be assessed for a velocity of 2,500 fps. For each threat that has a range of velocities, the maximum vulnerable area (over the range of velocities) is calculated for each of the 6 cardinal views (top, bottom, front, back, left, and right). In the case of the HE} rounds, the vulnerable areas are calculated for each cardinal view for the single velocity. These maximum vulnerable areas are averaged over the 6 cardinal views to provide the maximum-allowable vulnerable area for each threat. Specifically, 36 numbers (6 for each of the 2 fragments plus 6 for each of the 4 cannon rounds) are averaged to produce 6 numbers (i.e., vulnerable areas) that are incorporated in the F-22 contract as vulnerability specifications. Vulnerabilities for specific encounters with specific weapons can be calculated using the same methodology, but they are not part of any formal requirement. The committee considered the SPO's assumptions. While the threat missiles may well change, the fragments, with the spread in velocity, seem to be a robust representation of the effects of individual fragments from missile warheads. The API and HE] rounds are reasonable representations of air-to-air cannon-fired rounds. The sole use of vulnerable areas for individual fragments to represent missile warheads does imply certain assumptions and limitations: . The fragment data are only intermediate data. The effect of a particular warhead event is a much more complicated affair involving details of the warhead and the end-game geometry (i.e., guidance and control capabilities of the missile and the action and signature of the target). The effects of multiple fragment hits are ignored (consistent with the current state-of-the-art of vulnerability analysis). The usual assumption is made that blast effects are only important for miss distances at which the fragments would certainly kill the target. However, there are intercept geometries for which this assumption is not the case, and blast must be taken into account in the analyses. When anti-air missiles detonate, a spray of fragments, often focused in a specific direction, is propelled from the warhead to He target. In addition, a significant blast wave caused by the detonation of the warhead also propagates toward the aircraft. The fragments and blast wave wait strike the aircraft at different times, sometimes resulting in enhanced kill mechanisms. The committee believes that the two discrete fragment sizes selected by the SPO for analysis and test are representative of the fragments from the spectrum

OCR for page 44
Sufficiency of F-22 Testing Plans 47 of warheads likely to be encountered. However, vulnerability of the F-22 to these fragments is estimated on a one-fragment-at-a-time basis and therefore, in itself, does not completely represent the vulnerability of the aircraft to missile warheads. Vulnerability of the aircraft against these warheads is assessed in a subsequent analysis that considers three types of kill mecharusms: . . . Blast kill of the structure based on overpressures resulting from detonation of the warhead's high-explosive charge. Impact of multiple fragments with Me fragments spaced far enough apart so that Weir effects on the aircraft are independent; the result effectively is aggregated from independent single fragment assessments. Impact of multiple fragments that are dense enough so that their effects are not independent arid, when taken together, could result in structural kill of the aircraft. This type of kill mechanism is often accounted for by a kinetic energy threshold for structural kill; it is particularly important for annular blast fragmentation or focused blast fragmentation warheads. The first two of these mechanisms are accounted for in the vulnerability analysis currently being conducted for the SPO. The third has not yet been explicitly accounted for. It is safe to ignore this effect for many warheads and encounter geometries because, if such a kill is obtained, a kill from one of the other two mechanisms would also be obtained. However, for some classes of warheads (e.g., the annular or focused blast fragmentation warheads) this kill mechanism may be important and should be considered in future analysis and testing by the SPO. OVERVIEW OF THE AIR FORCE VULNERABILITY ASSESSMENT PROGRAM The committee received extensive briefings on the vulnerability assessment program from representatives of the F-22 SPO during its visit to Wright-Patterson Air Force Base in January 1995. Those briefings and communications with the SPO provided the basic information evaluated in this chapter.) The SPO and its contractors performed a detailed vulnerability analysis of the F-22 using revised versions of star~dardized computer models (see Chapter 51. The outputs of the analysis were estimated vulnerable areas arid overall system ~ The entire briefing is documented here as SPO, 1 995a. Several parts of this briefing are also cited individually in this chapter (e.g., Griffis, 1995a, and Ogg, 19959.

OCR for page 44
48 Live Fire Testing of the F-22 PK/H (see Chapter 3). The SPO then assessed the analytical results and identified areas of uncertainty. These areas of uncertainty were based on the following specific criteria: Areas currently treated as invulnerable based on analysis for which insufficient or contradicting data exist. Compartments where collateral damage mechanisms cannot be assessed and that represent a potential vulnerability. Components that represent a significant contribution to vulnerable area and have insufficient supporting data. Areas for which the basic material or ballistic data base is inadequate. Areas of uncertainty were next mapped against the F-22 design and the results of the vulnerability assessment to identify test issues, areas of the aircraft that needed to be tested, and specific test hardware requirements. The enumerated F-22 live fire tests and locations of the test areas on the aircraft are shown in Figure 4 I.2 As a part of establishing its test program, the SPO made several assumptions (SPO, 199Sa): . Because the threat scenario is for offensive counter-a~r missions, 60 percent of total usable fuel is assumed to remain after penetration into hostile air space. According to the design filrl-bum sequence, the fuel in certain critical tandcs would have been consumed. This assumption minimizes inlet fuel ingestion kills (see discussion later in this chapter) and reduces vulnerable areas by 30 percent. The flight is straight and level at 500 knots, and the requirements are independent of altitude. The kill category considered is the attrition kill, in which controlled flight is lost within five minutes following the hit. Vulnerable areas used in these calculations are based in part on results of individual tests against electronics modules. This approach may not take flammability of the coolant into account arid may need revision pending the results of the tests on fluid flammability that are recommended later in this chapter. Concern for survivability of the pilot is demonstrated by a double battier between the cockpit arid Me forward fuel tank. There are no 2 Tests 9 and 10 are exceptions; Test 9 is a components-related test and Test 10 is a materials test. Neither of these tests appears in the diagram because they cannot be isolated to a specific location on the aircraft. Also, Test 5 and Test 8 do not appear in the SPO's numbering system because those tests were subsumed by Tests 4 and 7, respectively.

OCR for page 44
Sufficiency of F-22 Testing Plans Test Test Number Number Location Of Shots 1,2 3 Wing Boxes Full Wing Box 4 Aft Side of Body 4A-C Aft Side of Body 6A Forward Fuselage (Lower) 6B Amad Bay 6C Forward Fuselage (Upper) 6D Win=, Leading Edge 6E Main Wheel Well 6F Wing, Attachment Bay 7 F-1 Fuel Tank 1 1 Aileron Bay 49 3 \ few 6A& 6C 1&2 \ Age \ 6D 1 \,~ ~ 6B & 6E Wk-~;~ (~ 6F 6B 4 &4A-C FIGURE 4-] Locations of the test areas. Source: Griffis, 1995b. . detailed, formal specifications for pilot survivability, but there is a qualitative concern for maximizing the chance that the pilot can eject in case of catastrophe (Griffis, 199Sa). The pilot is included in the assessment of vulnerable area. The specifications ado not include the elects of on-board munitions. The reason given for this omission is that the design values are to be used to assess contractor performance, and the contractor is not responsible for the munitions (SPO, 1995a). However, mission analyses calculating PK,H of the aircraft account for the v uInerable area of on-board munitions. The committee accepts several of these assumptions but has the following comments about the lack of specifications covering on-board ordnance. It is difficult to consider that the system is any less than the sum of the aircraft and its ordnance. The impact of aircraft design on protection of the ordnance and on

OCR for page 44
so Live Fire Testing of the F-22 possible mitigation of the effects of damage could certainly be important to the survivability of the pilot, even if it were not so important to the survivability of the aircraft. Saying that the ordnance is not the responsibility of the contractor trivializes an important issue. The SPO identified additional areas of uncertainty for which further testing would be beneficial if funding were available (Graves, ~ 995~. These include tests on polyalphaolefin (PAO) coolant fluid flammability, hydraulic fluid flammability, and filet flammability. A second series of tests is proposed for the weapons bay, using a simulator of the weapons bay of representative size and materials. These tests would involve ballistic testing of actual AIM-9 and AIM-120 rocket motors with both protected and unprotected bays to determine the effectiveness of protecting the weapons bay against fires using ablative materials. EVALUATION OF THE VULNERABILITY ASSESSMENT PROGRAM This section evaluates the current test program. The organization is by major F-22 subsystem. Each subsection briefly describes a subsystem and attendant vulnerabilities, the analyses and tests already conducted or planned by the SPO for that subsystem, and the com- mittee's overall assessment. Finally, revisions are suggested to improve He program where the committee believes them to be desirable. Marty live fire tests are planned or have been performed on various components, subsystems, arid sub- assemblies of He F-22. Test articles range from component prototypes to engineering and manufacturing de- velopment (EMIL hardware. The threat kill mechanisms are those discussed above. .... ; I A. ^~ ~ ^~ - ^ - ^= .. . . .

OCR for page 44
Sz`~iciency of F-22 Testing Plans Structure and Integral Fuel Tanks Description and Attendant Vuinerabilities 51 Airframe outer skins are generally quite thin, highly stressed, and only slightly resistant to penetration from missile warhead fragments and projectiles. However, penetration of the skin and failure of an interior member such as a wing spar or a fuselage frame does not necessarily mean loss of the aircraft. This is particularly true for the F-22, since it is designed with multinIe (redundant) load paths and utilizes structural materials that have a high fracture toughness. The design represents a significant improvement over many past fighter aircraft, which were largely single load path structures and open utilized high-strength aluminum and steed alloys with very low fracture toughness. Figure 4-2 illustrates the structural configuration of the F-22, a largely multiple Toad path construction. For example, the F-22 has multiple wing spars; several wing carry-through fuselage frames and bulkheads; three fin attachment frames; numerous additional fuselage frames; and various stringers, stiffeners, ribs, and other miscellaneous members. The materials are shown In Figure 4-3. A design goal was that the structure be able to sustain the damage from defined threats without loss of the aircraft. The multiple load path design was intended to achieve this goal. The uncertainty in predicting hydraulic ram effects3 in the integral tanks arid Me need for developmental testing of some of these structures were recognized. While the committee agrees that the F-22 structure is predominately of multiple load path design, there are some exceptions. Such exceptions include (a) the horizontal tails, where each tail is supported by a single pivot shaft made of a titanium alloy (see Figure 4-2~; arid (b) the farthest aft fuselage frame (i.e., Frame 6 in Figure 4-2), which carries a significant portion of the horizontal tad] and vertical tail loads across the fuselage. 3 Ball (1985) gives this explanation of hydraulic ram effects: When a pene~ator enters a compartment containing a fluid, a damage process called hydraulic or hydrodynamic ram is generated. Hydraulic ram can be divided into three phases: the early shock phase, the later drag phase, and the final cavity phase .... The hydraulic ram loading on all of the wet walls of the tank can cause large-scale tearing and petalling, with openings very much larger than those made by the actual penetrator. The hydraulic ram loading can also be transmitted through attached lines, causing failure at fittings or other discontinuities in the lines.

OCR for page 44
52 Live Fire Testing of the F-22 Right Hand Horizontal Tail Right Hand Vertical Tall Left Hand Wing FIGURE 4-2 Structural configuration. Source: Griffis, 1995b. Although the committee believes that the horizontal tad! pivot shafts may be heavy enough to resist complete failure following ballistic impact, these shafts could encounter damage that would degrade their strength and ability to carry operational maneuvering loads. However, if failure should occur and a horizontal tad! were lost, it is not certain that the aircraft would be lost. Although the F-22 prime contractor has indicated that the airplane can be controlled with one tad! missing, it would appear that this capability would depend on flight conditions at the time of loss. Risk of aircraft loss given the loss of a horizontal tad] has not been adequately defined. While Frame 6 is not currently considered to be a vulnerable location, the committee believes that, if He frame fails as a result of a direct hit, loss of the aircraft might result. It appears Hat this potential vulnerability needs further investigation, as discussed below. Also, the aft fuselage booms that support the horizontal tails as well as some of the vertical tad! loads might be considered to be single load path even though Right Hand Aft Boom \~ Of I/ Elm ~ ~/ Pivot Shafts T eft Harld Torizontal Tail

OCR for page 44
Sufficiency of F-22 Testing Plans Wing Duct Skins Skins - IM7/5250-4 Composite IM7/977-3 Lower Surface Thickness 0.177 to 0.265 inches Upper Surface Thickness 0.212 to O.316 inches \ Aft Fuselage : ^ / TJpp~ Skins - Titaniurn 6-2222 & ~I7/5250-4IHC Cocure / Empennage Skins & Closeouts - IM7/5250-4 Core - Aluminum SO ~ \ / Edges Nicalor~JS2!5250-4 & Nomex Core FIGURE 4-3 Materials applications. Source: Griffis, 1995b. 53 Forward Fuselage Skins & Chine - IM7/5250-4 Composite \ Mid Fuselage Skins: IM7/5250-4 & Titanium 6-4 Composite they consist of several structural members (see Figure 4-4~. These members make up two beams, one on each side of the aircraft, that are subjected to substantial bending, shear, and torsional loads. If either of these boxes fails, it may lead to loss of the aircraft. As discussed below, some live fire testing has been done, and more is planned, for this general area. When assessing the vulnerability of the structure to ballistic threats, it is necessary to consider the effects of other potential damage mechanisms in addition to projectile impacts. These include blast effects, overtemperature due to fire, and hydraulic ram loads in fuel-containing structures. Hydraulic ram can significantly magnify the damage to wing structure, and test results could lead to redesign. It is also the primary mechanism of concern in the fuselage fired tank structures. Of particular concern is the close proximity of the forward fuselage filet tank (designated F-~) to the cockpit. The forward side and top of the tank has a double- walled barrier intended to prevent fuel leakage directly into the cockpit. The

OCR for page 44
54 Lower Skin Splice Am/ Welded Lower Skin ~ FIGURE 4-4 Aft boom. Source: Griffins, 1995b. Live Fire Testing of the F-22 i/ Access Through Keelson Forward ~ U Rum Outboard ~1 committee is concerned that, if the inner wall were ruptured as a result of hydraulic ram, the second barrier could be penetrated and fuel could leak into the cockpit. Fire could then break out because of the various ignition sources in the cockpit. Also, ram effects could damage the canopy hinge, actuator, support structure, seat rails, or other structures, which could then prevent successful ejection of the pilot. Plannec! Analyses and Tests The F-22 structure has been considered invulnerable because of the multiple load path design. However, there are some uncertainties in analytically predicting the extent of damage that watt be encountered and, to a lesser extent, the residual strength of the remaining structure after it is damaged. The uncertainty in predicting damage is probably greatest for fuel-containing structures (i.e., wings, aft sides of the body, and forward fuel tarmac) because of difficulties in predicting both the pressures and the response of the materials (particularly composite materials) associated with the hydraulic ram phenomena. It was because of this uncertainty that the developmental live fire tests of the wing

OCR for page 44
72 Live Fire Testing of the F-22 units are installed adjacent to the high-pressure bleed ducts in each engine compartment to detect leaks that may impinge on critical structure or component or constitute an ignition source. Coverage is divided into three zones. Both left and right bleed zones provide detection within the respective engine compartments for the sections of duct between the engine arid the bleed air manifold and along the engine ar~ti-icing duct. The center bleed zone provides detection from the bleed air manifold to the primary heat exchanger (SPO, 1995a). Dry Bay Fire Protection. Fire detection and suppression is provided for the left and right main landing gear wells and the left and right wing attachment bays aft of the main landing gear wheel wells. Detection and suppression is provided by a dry bay fire protection unit that combines an infrared optical fire sensor and a pressurized Halon-filled cylinder in an integrated unit (an agent to replace Halon is being sought). The extinguishing agent is automatically discharged when a fire is detected. For fire containment and control, firewalIs separate the engine compartments, engine nozzles, and APU compartment from adjacent compartments. The firewalIs are designed to prevent flame penetration for IS minutes when subjected to a 2000F flame. Critical components are fire hardened to prevent damage from exposure to flame or fire-generated thermal energy. A fire extinguisher provides suppression capability to either engine or APU compartments. The extinguisher contains approximately five pounds of Halon (a one-shot system) (SPO, 1995b). Dry bay fire remains the largest vulnerability contributor of the file] system. As a general rule, dry bay fire occurs anywhere a fuel tank, component, or line is adjacent to an internal dry bay that is not protected by fire extinguishing. Fire protection is included in 15 separate bays. Foam is located in strategic areas around the F-l fuel tank (behind the pilot) where the maioritY of hit-in~tiated fires could occur (my' llama). These areas were unique in the design because they were also unoccupied by components and could easily be filled with the foam. Fuel System Explosion Suppression. The fite! system is designed who functional redundancy arid component separation so that a single hit will not interrupt fuel to both engines. The current fuel usage schedule buns fuel from selected tanks, which are assumed to be emptied early. The fuel ingestion kill mechanism associated with this assumption was discussed earlier in this chapter. OBIGGS (discussed earlier) protects against ullage explosions. Planned Analyses and Tests Dry Bay Fire Extinguishing. The fire detection sensors are to be tested under laboratory conditions. The fire detection sensor's field-of-view analyses are

OCR for page 44
Sufficiency of F-22 Testing Plans 73 completed. The plan for Test 6 details the ballistic dry bay fire tests that wall evaluate the dry bay fire protection system (SPO, ~ 995b). The areas of interest for Test 6 are illustrated in Figure 4-9. It is expected that the Halon replacement agent (see below) wall be less efficient. Therefore, containment bottles may need to be resized accordingly web some size and weight increases. Evaluation Plan for Halo n Replacement. The Halon Replacement Program for Aviation covers more than just the F-22 program. An alternate fire suppression agent for Halon has been identified for use in aircraft dry bays and engine cells. The replacement program involves a three-phase effort for both applications (SPO, ~ 995b): . . Phase ~ studied the operational parameters that affect the amount of agent needed for each fire environment. The four most significant parameters were fourth to be surface temperature, air temperature, fire location, and fuel type. Phase IT was art operational comparison of three selected agents. Testing was conducted to screen and compare performance data on alternative agents, arid one agent (known as HFC-125) was selected. Phase Ill is under way now to establish design criteria methodologies. A product of Phase Ill watt be design equations for use in sizing suppression systems that use the new agent. The F-22 program will not need to evaluate the Halon replacement agent. It will test and evaluate the installed F-22 dry bay extinguishing system. Dry Bay Foam. The SPO feels confident that the characteristics of dry bay foam are well understood foam is expected to provide protection only against missile fragments and small caliber API threats. For this reason, no tests are planned to evaluate the material specifically (SPO, 1995a). Synergistic Elects. Synergistic events, such as fires caused by arcing electrical power wires being sprayed by environmental control system coolant or hydraulic fluids, are poorly understood. These events must be recognized as a potential kill mechanism with a high degree of uncertainty. Test 6 will examine the synergistic effects of PAO liquid coolant fluid, reduced flammability hydraulic fluid, aircraft fuel, and electrical power in protected and unprotected, cluttered aircraft dry bays. Test 6 will also examine fire detection and extinguishing capability in protected aircraft dry bays of the F-22.

OCR for page 44
- ~ en - c, ~ o I c.i A ;^ ~m en ;^ ~ - : 05 is ~ e id cat v ;- ~> a ;^ l-, ~ ~es 2 ED ~5 ._ Art o To Cot o ~5 a_ U) Cal _ - cat ~ C) C: ~ ~0 ~ ~ ~ C ~ TV 'of ;~ - \ en - U. 3 o Cal c _ _ ~ Cow .~ ~< TIC ;~m en ;^ 74 an - C: C) .e C) O EM ~ ;~ - es . . v AS o V, it_ A: i_ Can o V, At: 1 ~3 ~

OCR for page 44
Sufficiency of F-22 Testing Plans Assessment The infrared sensors used in the fire detection system are a strength of the system. They are dual-char~nel sen- sors, each with a 90-degree field of view. Their response time is between 5 milliseconds to detect a fast growing fire and 5 seconds to detect a slow growing fire. Their wiring logic incor- porates power interrupt detection. Accessibility for maintenance was a major consideration in design instal- lation. The integrated vehicle subsys- tem controller is designed to provide essential redundancy for cockpit in- dication of any existing fire (SPO, 1995b). Test 6 is a comprehensive and systematic way to evaluate and optimize the effectiveness of dry bay protection. Test article frames are designed to withstand multiple ballistic impacts, can be easily reconfigured after each test, and contain representative bay sizes. Environmental control system airflow wart be used when necessary. Electrical wiring with operating voltage and currents wait be incorporated, significantly adding to the validity of the tests. Test 6 is a valuable subsystem type test Mat cost-effectively uses other-than-flight hardware and allows optimization should problems be uncovered. Test ~ ~ was discussed earlier. In Test 6 and Test ~ ~ together, a large number of shots (approximately 70) have been made or are planned. Even though the test articles do not contain all of the fluid lines and electrical wires, but only the major ones, it seems likely that this number of tests wall allow the development of a robust methodology that can be extrapolated to estimate differences under entirely realistic conditions. Test 6A will examine the synergistic effects of pressurized PAO coolant lines and PAO-cooled avionics modules and the adjacent powered electrical wiring in the F-22 forward fuselage lower avionics bays. The SPO indicated that it may use the prototype air vehicle fuselage in Test 6A and will include all sources of PAO fluid and electrical wiring in this test (Griffis, ~ 995a). Greater realism in this type of test has merit. The test program is quite thorough, but the committee believes that the prototype air vehicle fuselage should be used in Test 6A in order to achieve greater realism. 75 S ., ~erg,lst ~e~=,,.~ !~e ~ ~ . ~t}al ~ag.e to one sub.syste.m.m s It: ::: :-::~:::: :: :::: :::: :::::::::::::::::::::r:: ~ ::::::: '::::;::: ;:; ::::::;:::;:::::::::::::::::::::::::::: .:. In . e3Ie.GIS...t lat. Came ..=tner.. ~ A. .IQ tone . . o.r . more .~er e s ........... , , , ...... , ~; ; ~ , ~ ~ ...... . ~. ~t ~- ., . - ......... ..... . - - - - - . . - . For exempt' ; ....... w. Ir~g ~d . - s. on. A ~ -my fl id . ... condoner. (e.g.~2..~.~u'6 r: .:, , .: , , . ; ... . lme~ Without m~lat~g a f ~frOm Be . ~.~ e~ cot . . . . . . . . . : ~]e ~o. ~ g ~ ~ ~ ..................... ~ . I ..... . .. . ........ .. ............... .....severe~ele~rlca. -.ca ~ es, ~ ~ ~ con ~ .msu~ ........... ~,8 ,~. . . . . ... . : . : .. :. . .: . s~.~tlc eats. cowd Q~.~. ............. : : ' ' """''""'''""""""'""'"'""""'"''"''''' ~..............

OCR for page 44
76 Suggested Revisions Live Fire Testing of the F-22 The committee urges use of the prototype air vehicle fuselage in Test 6A but has no other suggestions for the planned test program. ADDITIONAL OBSERVATIONS The F-22 SPO has devised and implemented a program consisting of m~lnerahilitv reduction design assessment. and testing that is founded on (a) comprehensive analysts ot the venerates of the aircraft, (b) identification of areas of uncertainty (as discussed in the introduction to this chapter), and (c) tests and assessments required to address these uncertainties. The committee believes that this program is well conceived and sufficiently realistic to support the request , _ ~ ~ ~ O . t ~ ~ ~ . , ~ ~ ~_, ~ ~ ~ , ,_ , . 1 for the waiver of the live fire test law. If modified as suggested earlier in this chapter, the program watt be strengthened as the F-22 proceeds with EMD and initial production. However, vulnerability assessment is a complicated and difficult problem. Therefore, the committee carefully considered the need for continued testing of the vulnerability of the F-22, beyond the current scope. In the process, the committee held detailed discussions with the vulnerability and lethality assessment communities. At China Lake (Navy and Air Force personnel and a consultant to OSD were present), members of the committee were briefed on recent and planned live fire test programs for Navy aircraft (Tyson and Wise, 1995~. The committee has considered the Navy's assessment methodology in comparison to that of the Air Force and the F-22. While there are some philosophical differences between the Air Force and the Navy, there is a great deal in common where aircraft are concerned. The opinions below are held by the China Lake team and were not disputed in the meetings by the Air Force representative present. . Given a complete aircraft, more information can be extracted by testing its major parts than by testing the entire vehicle at one time. It is possible that additional data could be obtained from such testing of the F-22 that could result in revisions to the aircraft design to further reduce its vulnerability. Similar large assembly testing has been conducted and is planned for variants of the Navy's F-] ~ even though the China Lake team does not expect to discover unanticipated outcomes.

OCR for page 44
Sufficiency of F-22 Testing Plans 77 The committee grappled with the question of whether to recommend similar testing for the F-22. The paradox seems to be the question of recommending tests that are not expected to yield unanticipated results, especially for such an expensive aircraft. The Navy's rationale seemed to be that ongoing testing makes sense in that something is always learned, vulnerability assessment methodologies are improved, models and other tools are evaluated, and, like the industrial base, the live fire test base cannot be allowed to wither. After much deliberation, the committee agreed that the Navy's approach made sense for the Air Force's F-22. This fighter wall be in the inventory for decades and can be expected to undergo an evolution that includes other missions arid new configurations. That life cycle dictates a continuation of live fire testing. Accordingly, Me committee believes that the Air Force should pearl for expeditious vulnerability assessment testing of the F-22 similar to that being conducted or planned for variants of the Few. In particular, . . As soon as a source of large assemblies can be identified (e.g., from a damaged aircraft or other test hardware that is representative of production aircraft, including assemblies from early production or one of the nine dedicated test aircraft), these assemblies should be provided to the vulnerability assessment community. The committee recognizes that such assets may not become available until after production begins. It is assumed that the most useful information could be derived from the resulting test specimen if it is tested for vulnerability in major subassemblies rather than as a complete system configured for combat. The testing should be directed at (a) verifying predictions derived from the current live fire test program and the models used, and (b) testing the effects on the overall vulnerability assessment brought about by configuration and mission changes through the years. It is recognized that the results of such testing will likely not impact the design of the initial production aircraft of the F-22. The committee believes that this level of risk is acceptable in view of the comprehensive nature of We ongoing program modified to accommodate the revisions suggested by the committee. However, the results of such tests would certainly influence future production blocks or modifications of the F-22 to perform future missions. Techniques for repairing battle damage to the F-22's new composite materials arid new systems could be verified. Vulnerability assessment tools might also be improved.

OCR for page 44
78 Live Fire Testing of the F-22 CONCLUSIONS Adequacy of F-22 Threat Definition and Replication The committee accepts the threat environment defined for the current mission of the F-22. The assumed AP} and ~} rounds are reasonable replications of air-to-air, cannon-fired threats. The two discrete fragment sizes are representative of the fragments from the spectrum of warheads likely to be encountered. However, for some classes of warheads (e.g., annular or focused blast fragmentation), the kill mechanism that involves dense multiple fragment impacts may be important for the F-22 and should be considered in future analyses and tests. Overall Sufficiency The Air Force and its contractors responsible for the design of the F-22 have incorporated a large number of features in the design of the aircraft that watt reduce its vulnerability. These features include a structural design with largely multiple (redundant) load paths, inerted fuel tanks using OBIGGS, dry bay foam, double-walled barriers between the cockpit and fuel, redundant fuel pumps and cross-feed between tanks, multiply redundant electric power, redundant hydraulics and flight control actuators, separated triple redundant air-cooled mission computers, fault tolerant avionics, dual engines, and engine blade containment. In addition, the Air Force and its contractors have performed a detailed vulnerability analysis to determine the vulnerable area of the F-22 using revised versions of standardized computer models. They assessed the uncertainties in the analysis and then constructed a comprehensive live fire test program to address these uncertainties and validate several of the design features. The committee reviewed this overall assessment program and suggested specific actions by the Air Force and others to alleviate some concerns that the committee has. Given the F-22's current counter-air mission, the program is sufficiently realistic to support the requested waiver. With the committee's suggested actions and Me implementation of possible corrective measures as a result of the program findings, the committee concludes that the Air Force program will be strengthened as the F-22 proceeds with EMD and initial production.

OCR for page 44
Su~c~ency of F-22 Testing Plans 79 Specific Actions The specific actions suggested by the committee are listed below. For easy cross-referencing, the actions are ordered as in the evaluation section of this chapter. Structure and Integral Fuel Tanks . . . Conduct additional live fire testing to determine the `damage that can be expected from a hit in the Frame 6 aft boom attachment area. The Air Force should determine the most critical shot lines. Expand analyses to predict damage sizes and residual strengths of the aft boom, Frame 6, and horizontal tad] pivot shafts after being hit by 30mm HE] rounds. Also, determine the risk of aircraft loss should it be fourth that loss of a horizontal tad! is possible. Conduct further analysis of the aft filer tank (A-~) prior to the conduct of Test 4D. This analysis should be focused on determining the adequacy of the test specimen, with particular emphasis on its ability to simulate accurately the reaction of the entire tank. Fuel System and Associated Dry Bays Make the operational community fully aware that a fuel ingestion risk to the aircraft exists at a filet state higher than 60 percent. Flight Control ant! Auxiliary Systems . Conduct the tests and analyses proposed by the F-22 SPO on the flammability of coolant and other fluids and We attendant vulnerability of the aircraft. Weapons Bay and Ordnance . Undertake the analysis and test, proposed by the SPO, of ablative materials in the weapons bay. Also, conduct furler analysis of the tradeoffs associated with additional ordnance protection or defensive measures.

OCR for page 44
80 . Engines . Flight Crew . Live Fire Testing of the F-22 Fund the ITCG/AS and the Joint Live Fire Test Program to assure the completeness of data on the vuInerabilities of on-board ordnance. Fund the proposed Joint Live Fire testing of F! 19 engine components to alleviate the paucity of testing against those components. Emphasize continuing efforts by the F-22 SPO and ITCG/AS to develop improved methodologies for reducing flight crew vulnerability. Fire Protection Systems . Use the prototype air vehicle fuselage in Test 6A in lieu of a mock-up. (The Air Force has considered using this fuselage for Test 6A.) Additional Action As discussed above, the committee believes that continued testing of the vulnerability of the F-22 is desirable. This testing should be conducted expeditiously against representative production hardware in the form of large assemblies when they become available. These tests should be similar to those being conducted or planned for variants of the Navy's F-! 8. The committee recognizes that large assemblies from a damaged aircraft or other production-representative hardware, from any source, may not become available until after production begins, and the subsequent recommended testing will likely not impact the initial F-22 design. The committee considers this arrangement to be acceptable. However, test planning should begin soon. The use of this hardware and the results of these tests would influence fixture production blocks or modifications ofthe F-22 to perform future missions. Additional positive consequences may well include (a) verification of techniques for repairing battle damage to the F-22's new composite materials and systems, and (b) improved vulnerability assessment tools.

OCR for page 44
Sufficiency of F-22 Testing Plans 81 REFERENCES Ball, R.E. ~ 985. The Fundamentals of Aircraft Combat Survivability Analysis and Design. New York: American Institute of Aeronautics and Astronautics, Inc. GiorIando, ]. ~ 995. High Power Microwave. Presentation to the Committee on the Study of Live Fire Survivability Testing for the F-22 Aircraft, F-22 System Program Office, Wright-Patterson Air Force Base, Ohio, January 19. Graves, I.T. 1995. National Research Council Questions on Live Fire Test. Memorandum from Deputy Director, F-22 System Program Office, to Mike Clarke, Commission on Engineering and Technical Systems, National Research Council, February 14. Griffis, H. 199Sa. Live Fire Test Program. Presentation by to the Committee on the Study of Live Fire Survivability Testing for the F-22 Aircraft, F-22 System Program Office, Wright-Patterson Air Force Base, Ohio, January 19. Griffis, H. 1995b. National Research Council Questions on Live Fire Test. Memorandum to National Research Council, April 28. Hinton, W.S. 1994. Threat, Mission, and Operational Requirements for the F-22. Presentation to the Committee on the Study of Live Fire Survivability Testing for the F-22 Aircraft, National Academy of Sciences, Washington, D.C., December 21. Holthaus, T.M. 1994. Live Fire Test No. ~ I, F-22 Live Fire Test Plan, Live Fire Test of Aileron Dry Bay Fire Test Program. Wright-Patterson Air Force Base, Ohio: Wright Laboratory. Ogg, I. ~ 995. Vuinerability Program Overview. Presentation to the Committee on the Study of Live Fire Survivability Testing for the F-22 Aircraft, F-22 System Program Office, Wright-Patterson Air Force Base, Ohio, January 19. SPO (F-22 System Program Office). ~ 993. Live Fire Test 4A Renort. ~ ~ ~ , ~ ~ ~ ~ r _ . r.. _ 1vl~moranuum ro Roland ~ ancey, ~oemg Alrcrart ~omparly. Memo L8932- AL93-059. Wright-Patterson Air Force Base, Ohio: F-22 System Program Office. December 15.

OCR for page 44
82 Live Fire Testing of the F-22 SPO. ~ 995a. Combat Survivability F-22 Live Fire Test Program. Presentation to the Committee on the Study of Live Fire Survivability Testing of the F-22 Aircraft, F-22 System Program Office, Wright-Patterson Air Force Base, Ohio, January 19. SPO. ~ 995b. National Research Council Questions on Live Fire Test. Memorandum to National Research Council, March 23. Tyson, H., and T. Wise. 1995. Live Fire Test Program for the F/A-18E/F and V-22. Presentation to the Committee on the Study of Live Fire Survivability Testing for the F-22 Aircraft, Naval Air Warfare Center, Weapons Survivability Laboratory, China Lake, California, February 21.