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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 45
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 46
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 47
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 48
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 49
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 50
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 51
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 52
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 53
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 54
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 72
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 2000°F 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 73
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 74
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OCR for page 75
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
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OCR for page 76
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.
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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.
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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.
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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.
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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.
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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.
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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.
Representative terms from entire chapter:
fire testing
