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Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program (1993)

Chapter: 1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results

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Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

1
Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results1

What Are the Threats to Military Aircraft?

When the military began to use aircraft in war, the opposing forces began using weapons in an attempt to destroy them. In the first half of the twentieth century, guns were the primary weapons used against aircraft. These guns were either surface-based or carried by enemy aircraft. They ranged from the small arms weapons, such as the 0.3/0.303-inch (7.62/7.7-millimeter) and 0.50-caliber (12.7-millimeter) machine guns, to anti-aircraft artillery (AAA), such as the 40-millimeter and 88-millimeter caliber guns of World War II (WW II). Contemporary guns that can be used against aircraft include the 5.56-millimeter, 7.62-millimeter, 12.7-millimeter, 14.5-millimeter, and 20-millimeter small arms, and the 23-millimeter, 30-millimeter, 37-millimeter, 57-millimeter, 76-millimeter, 85-millimeter, and 120-millimeter AAA. The small arms weapons typically fire ball ammunition, or armor-piercing projectiles, known as AP rounds, or AP projectiles with incendiaries, known as API rounds. The AAA weapons and the larger-caliber aircraft guns usually fire ballistic projectiles with a high-explosive (HE) core and a surrounding metal case. These are referred to as HE warheads or HEI warheads when incendiaries are included.2 The HE warheads may detonate on contact with the aircraft (contact-fuzed HE warheads), after an elapsed time since firing (time-fuzed HE warheads), or in proximity to the aircraft (proximity-fuzed HE warheads).

After World War II, guided missiles, both surface-based and airborne, were developed to kill aircraft. These anti-air weapons typically carry contact- or proximity-fuzed HE warheads designed to kill aircraft with fragments and blast. Guns and guided missiles are still the primary threat faced by aircraft today. However, several new threats to aircraft are in development. Directed energy weapons, in the form of low-to-medium power lasers and high-power microwaves, have the potential to damage or destroy sensors on the aircraft and the weapons they are carrying; and high-power lasers can damage major aircraft structure. Chemical and biological weapons pose a threat to aircraft, particularly on the surface, and nuclear weapons are a threat to aircraft on the surface and in the air.

What Is Aircraft Vulnerability?

Aircraft survive a mission into hostile territory by “avoiding” the damage-causing mechanisms of the enemy’s air defense and by “withstanding” the damage caused by these mechanisms when they cannot be avoided. The aircraft attribute known as susceptibility refers to the inability of

1

Much of the material presented in this chapter is based upon Ball (1985).

2

Some of the small-caliber AAA also fire API rounds.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

the aircraft to avoid (being damaged by) the man-made hostile environment and is measured by PH, the probability the aircraft is hit by a weapon while on its mission. The aircraft attribute known as vulnerability refers to the inability of the aircraft to withstand (the damage caused by the) hostile environment and is measured by PK/H, the probability the aircraft is killed3 given that it is hit. The probability the aircraft is killed by a particular weapon while on the mission is PK, which is equal to PH•PK/H. The probability the aircraft survives the encounter with the weapon is PS, which is equal to 1−PK, which is the same as 1−PH•PK/H. Thus, reducing an aircraft’s susceptibility (PH) and vulnerability (PK/H) to the weapons likely to be encountered in combat increases its survivability. An aircraft’s susceptibility can be reduced by destroying the enemy air defense elements, by reducing the aircraft’s signatures (stealth), by employing on-board and off-board threat warning systems and electronic countermeasures, and by the tactics employed. An aircraft’s vulnerability can be reduced by using redundant and separated components, by locating components to minimize the possibility and extent of damage, by designing components to contain or withstand the effects of damage, by adding special equipment to suppress the damage, by shielding components, and by removing vulnerable components from the design. A very important aspect of vulnerability reduction is that many design features are effective against a number of different threat weapons. For example, locating redundant flight control hydraulic components on opposite sides of the aircraft and inerting the fuel tank ullages will provide protection from both gun projectiles and proximity-fuzed missiles in most situations. Thus, in many situations it is not necessary to consider all of the individual threats when designing the aircraft.


Critical Components and Essential Functions. Each component in the aircraft has a level, degree, or amount of vulnerability to the damage-causing mechanisms4 generated by the threat weapon; and each component’s vulnerability contributes in some measure to the vulnerability of the total aircraft. The critical components on an aircraft are those components whose kill result in the loss of an essential function. Essential functions are those functions required to prevent an aircraft kill. The essential functions that prevent an attrition kill are lift, thrust, and control of flight, and the ability to land safely. Navigation and weapons delivery are two possible essential functions for a mission abort kill. An example of a critical component for the attrition kill is the single pilot who controls the flight of the aircraft. If the pilot is killed (i.e., he/she is unable to perform the essential function of control of the aircraft) the aircraft is also killed. An example of a critical component on an attack aircraft for the mission abort kill is the weapons delivery computer. If the computer is killed, the weapons cannot be released at the correct time; consequently, the pilot will return to base prior to mission completion.

Components that do not contribute to any of the essential functions become critical when their response to a hit (i.e., their kill mode) causes the kill of another component that is critical because it contributes to an essential function. For example, consider the bombs carried on-board an attack aircraft. The bombs do not contribute to the essential functions for flight of lift, thrust, and control. However, if one of the bombs explodes when hit by a fragment or bullet, and the explosion kills the pilot or any other critical components on the aircraft, the bombs are critical components because their kill mode (explosion) eventually leads to a kill of the aircraft.5 The propagation of damage from the hit component to other components is known as cascading damage. Pyrotechnic items, such as infrared flares, are also critical components when their reaction to a hit leads to a fire and the eventual loss of the aircraft.

The critical components can be nonredundant, such as the single pilot and single engine on a single-piloted, single-engined aircraft, or redundant, such as the two engines on a two-engined aircraft. When the critical components are redundant, a kill of more than one of the redundant components is required for a kill of the aircraft. In general, the critical components on a particular aircraft depend only upon the selected kill category (and level, if appropriate) and the assumed kill mode(s), and not upon the threat weapon.6

The procedure used to determine all of the nonredundant and redundant critical components on an aircraft is known as the critical component analysis. Two different types of analyses can be used, the Failure Mode and Effects Analysis (FMEA) and the Fault Tree Analysis (FTA). In the FMEA, all possible failure, damage, or kill modes of a component or subsystem are identified and the consequence of each

3

The word kill is used here in a general sense. The vulnerability assessment community uses several definitions of kill. Two categories of kill are the attrition kill and the mission abort kill. There are several levels of attrition kill based upon the elapsed time of kill after the hit. For example, the K-level attrition kill is defined as a kill in which the aircraft falls out of control within 30 seconds after the hit, and the A level is defined as a kill in which the aircraft falls out of control within 5 minutes after the hit.

4

Damage, threat, or kill mechanisms are the output of the threat warhead that cause damage to the aircraft. The types of damage mechanisms associated with penetrator and high-explosive warheads are penetrators, fragments, incendiaries, and blast. Damage processes refer to the interaction of the damage mechanism with the aircraft and its components. The damage processes associated with the damage mechanisms listed here include ballistic impact, penetration, combustion (in the form of a fire or explosion), hydraulic or hydrodynamic ram, and blast loading.

5

The treatment of the on-board munitions when assessing aircraft vulnerability is a major concern to the committee, particularly for aircraft with internal ordnance storage. This concern is examined in detail in Chapters 2 and 4.

6

Refer to footnote 3 for several examples of kill definitions.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

TABLE 1-1 List of Some Subsystem Damage-Caused Failure (Kill) Modes [Ball, 1985]

Fuel Subsystem

Propulsion Subsystem

Flight Control Subsystem

Fuel supply depletion

Fuel ingestion

Disruption of control path

In-tank fire/explosion

Foreign object ingestion

Loss of control power

Void space fire/explosion

Inlet flow distortion

Loss of aircraft motion data

Sustained exterior fire

Lubrication starvation

Damage to control surfaces

Hydraulic ram

Compressor case perforation

Hydraulic fluid fire

Combustor case perforation

Power Train/Rotor

Turbine section failure

Structural Subsystem

Blade/Propellor Subsystem

Structural removal

Loss of lubrication

Exhaust duct failure

Pressure overload

Mechanical/structural damage

Engine control/accessories failure

 

Thermal weakening

Electrical Subsystem

 

Penetration

Severing or grounding

Crew Subsystem

Mechanical failure

Injury, incapacitation, or death

Avionics Subsystem

Overheating

Penetrator/fragment damage

 

Armament Subsystem

Fire/explosion/overheat

Fire/explosion

component failure/damage/kill mode upon each of the essential functions is determined.7 In the FTA, those component or subsystem kill modes required to cause the loss of the essential functions are determined.


Kill Modes. For many years, the aircraft vulnerability community has observed the results of live fire testing of components, subsystems, and aircraft and has examined the combat data on damaged and killed aircraft in order to determine all of the kill modes associated with each of the aircraft subsystems. For example, there are five kill modes associated with the fuel subsystem. When a fuel tank is holed by a penetrator or fragment, a catastrophic explosion or major fire may occur inside the tank, or fuel may leak from the hole in the tank into an adjacent void space or dry bay and catch fire, or hydraulic ram damage to the fuel tank wall may cause a major structural failure of the tank or allow fuel to dump into engine intake ducts, causing an engine kill. A list of some of the possible kill modes for each of the major subsystems on an aircraft has been compiled based upon these observations and studies. This list is presented in Table 1-1.

The kill modes listed in Table 1-1 describe different types of reaction that components or subsystems in the aircraft exhibit when the aircraft is hit. In some of the kill modes, the component hit is the only component killed, whereas in others, the component hit reacts to the hit in a mode that kills other components. An example of the former is the loss of flight control due to a hit in a hydraulic power actuator that causes a jam of the actuator and a loss of control of the control surface. An example of the latter is a fuel ingestion kill of an engine due to a hit on a fuel tank adjacent to the air inlet. Reducing the vulnerability of an aircraft to the threat weapons and their damage mechanisms involves reducing the likelihood the kill modes given in Table 1-1 will occur when the aircraft is hit.


The Failure Mode and Effects Analysis (FMEA). As an example of the FMEA process, consider a single-engine aircraft with only two fuel tanks, one in each wing. The tanks are partially full, and there are fuel vapors in the ullage8 of the tanks. The possible kill modes for the fuel subsystem are given in Table 1-1. One fuel tank kill mode is an explosion inside the tank. If the consequence of the internal explosion in either wing tank is the destruction of the wing containing the tank, which then causes a kill of the aircraft due to loss of lift, both wing fuel tanks are nonredundant critical components for the attrition kill for the internal explosion kill mode. On the other hand, suppose the kill mode of the tanks is a loss of fuel storage capability due to one or more holes in the bottom of the tank. If this kill mode occurs in only one tank, this will not lead to a loss of thrust due to fuel supply depletion when the undamaged tank can provide fuel to the engine. However, if both tanks are holed and lose their storage capability, then a fuel supply depletion

7

The relation between a component or system failure mode and combatcaused damage or kill modes is developed in the Damage Mode and Effects Analysis.

8

The ullage is the volume of the tank above the fuel level. Fuel vapors accumulate in the ullage.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

kill will occur, the aircraft will lose thrust, and an attrition kill will result. Thus, for this kill mode, the fuel tanks are redundant critical components.


The Fault Tree Analysis (FTA). In the FTA process, the selected kill category (and possibly level) is defined as the top-level undesirable event, and the component kill required to cause the undesirable event are determined. The component kill that result in the undesired event are linked together in the fault tree by using logical AND and OR gates. For example, consider an aircraft with components A, B, C, and D. An undesirable kill will occur if either component A OR B is killed, or it may occur if both components C AND D are killed. Thus, components A and B are nonredundant critical components, and components C and D are redundant critical components. In using FTA for the fuel tank example given above, one undesirable event leading to an attrition kill is loss of lift. If loss of lift occurs due to an explosion inside the left wing fuel tank, a component A kill, OR if it occurs due to an explosion inside the right wing tank, a component B kill, both wing fuel tanks are nonredundant critical components for the explosion kill mode. On the other hand, a loss of thrust will occur if wing tanks A AND B are killed (by the fuel supply depletion kill mode). Thus, the tanks are redundant critical components for this kill mode. As another example of FTA, consider a two-engined aircraft. The undesired event of loss of thrust, which leads to an attrition kill, will occur when the left engine AND the right engine are killed. Thus, these two components are redundant critical components. A list of the typical critical components on a single-piloted, two-engined helicopter is given in Table 1-2.


The Kill Tree. A visual illustration of all of the critical components and their redundancies is provided by the kill tree,9 such as the one shown in Figure 1-1 for an attrition kill of a two-engined, two-piloted helicopter. A complete horizontal or diagonal cut through the tree trunk anywhere along the trunk will cause a kill. For example, a kill of the pilot and either the copilot or the copilot’s controls will cause a kill, as will a kill of the drive train or any of the three cyclic actuators. If the kill mode of the left- and right-hand fuel tanks is fuel supply depletion, both tanks must be killed to cause a kill of the aircraft. On the other hand, if the kill mode is a fuel fire or explosion, then a kill of either tank will kill the aircraft. Once the critical components have been identified and arranged in the kill tree, a vulnerability assessment can be performed.

What Is a Vulnerability Assessment?

A vulnerability assessment is broadly defined here as the systematic description, delineation, test and evaluation, analysis, or quantification of the vulnerability of the individual critical components and of the total aircraft. When an aircraft is hit by one or more damage mechanisms generated by the threat weapon, the outcome of those hits is not deterministic; it is random or stochastic.10 For example, when 15 fragments from a proximity-fuzed high-explosive warhead penetrate the upper wall of an aircraft’s wing fuel tank, the flammable vapor inside the tank may explode, destroying the wing and killing the aircraft; or the vapor may not

TABLE 1-2 List of Typical Nonredundant and Redundant Critical Components on a Single-Piloted, Two-Engined Helicopter (Ball, 1985)

Nonredundant Critical Components

Redundant Critical Components

Flight Control Subsystem Components

Propulsion Subsystem Components

Rods, bellcranks, pitch links, swashplate, hydraulic actuators, collective lever, and control pedals

Engines and engine mounts

 

Hydraulic Subsystem Components

 

Hydraulic reservoirs, lines, and components

Rotor Blade and Power Train Components

 

Blades, drive shafts, rotor heads, main transmission, and gearboxes

Structural Subsystem Components

Redundant structural elements

Fuel Subsystem Components

 

Fuel cells, sump, lines, and valves

 

Structural Subsystem Components

 

Tail boom

 

9

The kill tree is also referred to as the fault tree.

10

A deterministic process has a repeatable outcome that can be predicted with certainty if all of the influencing parameters and governing laws are known. Random or stochastic processes have multiple or various outcomes, any one of which may or may not occur on any one trial.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

FIGURE 1-1 The attrition kill tree for a two-piloted, two-engined helicopter (Ball, 1985). Copyright © AIAA 1985—Used with permission.

explode, and the aircraft survives the 15 hits. The likelihood of an explosion inside the tank depends upon many random variables, such as the amount of fuel vapor, the oxygen concentration in the vicinity of the fragments, and the temperature of the fragments.

How Is Vulnerability Measured?

As a consequence of the random nature of vulnerability, the metric most often used to quantify the vulnerability of an aircraft’s critical components is Pk/h, the probability the component is killed given a random hit on the component by a threat weapon or damage mechanism.11 The value of Pk/h depends upon the intensity of the terminal effects parameters associated with the damage mechanism, such as mass and impact velocity on the component for penetrators and fragments. The set of component Pk/h values for different masses and impact velocities is known as the Pk/h function. A second metric used to quantify a component’s vulnerability is Av, the vulnerable area of the component. Component vulnerable area is defined as the presented area of the component that, if hit, would cause a kill of the component and is equal to the product of the component’s presented area AP in the threat approach direction and its Pk/h, i.e., Av=AP•Pk/h.

The metrics used to quantify the vulnerability of the aircraft to a single random hit by a penetrator or contactfuzed warhead include PK/H, the probability the aircraft is killed given a random hit on the aircraft and Av, the aircraft’s single hit vulnerable area.12 The metric used to quantify the vulnerability of an aircraft to the proximity- and time-fuzed HE warheads on AAA projectiles and guided missiles is PK/D, the probability the aircraft is killed given an external detonation by a high-explosive warhead. The PK/D is a function of the location of the detonation point with respect to the aircraft.

What Are the Two Methodologies Used to Assess Vulnerability?

In general, there are two methodologies used to assess aircraft vulnerability. One method is the a priori prediction of aircraft vulnerability by using analyses or modeling. This method is nearly always supported by prior live fire test data on component Pk/h values for the various kill modes. However, the data have often been obtained on older equipment. The other method is the a posteriori observation and

11

Other metrics sometimes used for component vulnerability are Pd/h, the probability a component is damaged given a hit, area removal, energy density, and blast.

12

Lowercase subscripts refer to a component and uppercase subscripts refer to the aircraft. Thus, Pk/h is the probability a component is killed given a random hit on the component, Pk/H is the probability a component is killed given a random hit on the aircraft, and PK/H is the probability the aircraft is killed given a random hit on the aircraft.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

possible measurement of aircraft vulnerability by using empirical data obtained from either actual combat, aircraft accidents, or controlled live fire testing.13 This method is nearly always supported by a priori predictions of vulnerability prior to testing to define the test conditions and by a posteriori analyses or evaluation of the data. A brief review of the state-of-the-art of vulnerability analysis/modeling and vulnerability testing is given below.


Analysis/Modeling. The prediction of an aircraft’s vulnerability to the ballistic projectiles and guided missiles likely to be encountered in combat can be accomplished by using standardized computer programs.14 One set of programs is applicable to a single hit by impacting penetrator or fragment. Computation of Vulnerable Area and Repair Time (COVART) is the Joint Technical Coordinating Group on Aircraft Survivability (JTCG/AS) standard program for computing the critical component vulnerable areas Av and the aircraft’s vulnerable area Av for a single random hit by a penetrator or fragment (JTCG/ME, 1984). Another set of programs computes aircraft vulnerability to contact-fuzed HE warheads that detonate on the surface or within the aircraft. High Explosive Vulnerable Area and Repair Time (HEVART) (BRL, 1978 and HEI Vulnerability Assessment Model (HEIVAM) (Datatec Inc., 1979) are examples of this type of program. A third set, known as endgame programs, computes the probability an aircraft is killed due to an external burst of an HE warhead. SCAN (Dayton University Ohio Research Institute, 1976) is the current JTCG/AS endgame model for computing an aircraft’s PK/D. Modular Endgame Computer Assessment (MECA), Joint Services Endgame Model (JSEM), SESTEM II (ASD/WPAFB, 1981), and SHAZAM (Air Force Armament Lab./Eglin AFB, 1983) are four other widely used endgame programs.

All of these vulnerability assessment programs require as input a three-dimensional data base that defines the geometric model of the aircraft. The geometric model may be contained within the vulnerability assessment program, as in SCAN, or it may be developed in a separate program, such as MAGIC, Ballistic Research Laboratory Computer-Aided Design (BRL-CAD) package, or FASTGEN III, which are used as preprocessors for COVART. This model should contain all of the aircraft’s components, equipment, and supplies, including such items as fuel, hydraulic fluid, and ordnance. However, because of the limitations on program size, available time, and manpower, many small non-critical components that are not expected to influence the results are often omitted.15 Another subsystem that has often been omitted in vulnerability assessments is the on-board ordnance in the form of bombs, missile warheads and propellants, and ammunition drums. On most aircraft, bombs and missiles are carried externally. In this position, they may shield other components from projectiles and fragments, or they may react violently to a ballistic impact (e.g., detonate) and destroy the aircraft. The new stealth aircraft carry ordnance internally in order to reduce signatures. Adverse reactions of any internally carried ordnance, such as a deflagration or a detonation, have an even greater probability of destroying the aircraft. The omission of on-board ordnance from the assessment is discussed in more detail in Chapters 2 and 4.

Another input requirement for the assessment is the kill tree (or logical kill expression) for the selected kill category (and level if appropriate). This tree defines the redundant and nonredundant components that if killed individually (the single engine on a single-engined aircraft) or in combination (both engines on a two-engined aircraft) will cause an aircraft kill. Associated with each critical component on the tree is a data base that contains the Pk/h or Av value for the component that is based upon the selected threat weapon or damage mechanism and the possible range of impact velocities on the installed component, for the kill modes considered in the critical component analysis.


Vulnerability to a Single Hit by a Penetrator or Fragment. All of the vulnerability assessment programs contain an assumption as to how the damage mechanisms associated with the weapon proceed through the aircraft. The COVART methodology assumes that the penetrator or fragment from any selected direction16 is equally likely to impact the aircraft at any location and that it propagates along a straight line, known as a shotline, through the aircraft, slowing down and possibly breaking up as it penetrates the various components. The amount of fragment or penetrator slowdown is determined by the penetration equations that are a part of the built-in data base. Ricochet of the fragment or penetrator is not considered. An additional assumption often made is that only the components that are intersected by one shotline can be killed by the hit along that shotline. This assumption rules out the possibility of cascading damage away from the shotline.17 In the analysis, the presented area of the aircraft

13

Combat and accident data are extremely valuable as adjuncts to the other methodologies, but they are limited in scope, limited in the information on the nature of the event, and not always available for direct application.

14

The Joint Technical Coordinating Group on Aircraft Survivability has established a library of computer programs for assessing the susceptibility, vulnerability, and Survivability of aircraft. The library is maintained and operated by the Survivability/Vulnerability Information and Analysis Center (SURVIAC) at the Wright Aeronautical Laboratories.

15

The COVART model for the F-22 contains 2,213 components, of which nearly half are critical.

16

The directions usually selected include the six cardinal views of front, back, top, bottom, left side, and right side, and may include the twenty 45-degree angles between these six views.

17

It is possible to modify the intersected component’s Pk/h to account for kills of adjacent components.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

FIGURE 1-2 Example of a grid and random shotlines from FASTGEN for COVART (Ball, 1985). Copyright © AIAA 1985—Used with permission.

from the selected direction is covered by a uniform grid, and one shotline is randomly located within each cell. An example of the random shotlines within the cells for a particular aircraft is shown in Figure 1-2.

The user has the option of selecting the uniform cell size. Typical cell sizes range from 12 inches to 1 inch on a side, with 2 inches being typical. A preprocessor program, known as a shotline generator program, such as MAGIC, BRL-CAD, or FASTGEN III, identifies all of the critical components intersected by each shotline. This information is input data for COVART. COVART computes the vulnerable area of each critical component and the aircraft’s single hit vulnerable area, as well as the probability the aircraft is killed by a random hit. For component vulnerable areas, each grid cell containing a shotline that intersects a component has a vulnerable area equal to the product of the presented area of the cell and the Pk/h for the shotline through the component. The total vulnerable area of the component is the sum of the vulnerable areas of those cells with shotlines that intersect the component. For the aircraft vulnerable area Av, each grid cell shown in Figure 1-2 contributes a vulnerable area equal to the product of the presented area of the cell and the probability the aircraft is killed by a hit along the shotline in that cell.18 The total aircraft vulnerable area is equal to the sum of the vulnerable areas of each of the cells. Consequently, redundant components, if separated, that both are not intersected by one shotline, do not contribute to the aircraft’s single hit vulnerable area for that shotline.19 The PK/H for the aircraft is equal to the AV of the aircraft divided by AP, the aircraft’s presented area from the selected direction.


Vulnerability to a Contact-Fuzed High-Explosive Warhead. Essentially the same analytical procedure is followed for contact-fuzed high-explosive warheads. A geometric model of the aircraft, the kill tree, and the critical component Pk/h or Av data are required. A grid is superimposed on the aircraft and a shotline is randomly located within each cell. The difference between this analysis for the contact-fuzed HE warhead and the analysis for the single penetrator or fragment is the fact that components in the vicinity of the shotline can be killed by the blast and fragments from the detonation of the HE warhead. Thus, redundant critical components that are relatively close together can be killed by a single hit, causing a kill of the aircraft. Figure 1-3 shows the grid cell and randomly located shotlines for this type of analysis. Note that in this figure the HE warhead detonation can cause a kill of both the fuel tank and the engine even though neither component was hit directly by the weapon.


Vulnerability to an Externally Detonating High-Explosive Warhead. The analysis for the externally detonating HE warhead, shown in Figure 1-4, follows the same procedure used for the single penetrator or fragment, except that the fragment shotlines emanating from the external detonation are radial rather than parallel, and the aircraft can suffer multiple fragment impacts over its surface rather than a single hit. In addition, the blast from the detonation can kill the aircraft. The assessment of the kill of the aircraft by external blast is usually made independently from the fragment assessment. Three-dimensional blast contours around the aircraft are determined as a function of HE weight. Within a particular blast kill contour for particular explosive charge weight, a detonation of a warhead with that charge weight or larger will kill the aircraft.


Results from the Analyses. The results or information obtained from an analytical assessment of aircraft vulnerability

18

When more than one nonredundant critical component is intersected by a shotline, the probability the aircraft is killed is equal to the union of the component probabilities of kill.

19

This is the result of the assumption that only those components intersected by the shotline can be killed. A modification of the Pk/h value for a component can be made to allow a hit on one component to cause a kill of another component due to cascading damage.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

FIGURE 1-3 Grid cells and shotlines for the contact-fuzed high explosive weapon (Ball, 1985). Copyright © AIAA 1985—Used with permission.

FIGURE 1-4 Aircraft vulnerability to the externally detonating HE warhead (Ball, 1985). Copyright © AIAA 1985—Used with permission.

for the single hit by a penetrator or fragment typically consists of predictions of the values of vulnerable area Av for all of the critical components, the aircraft vulnerable area AV, the probability the aircraft is killed given a hit within each grid cell, and the probability the aircraft is killed given a random hit PK/H. The assessment results for the single hit by the contact-fuzed high-explosive warhead consist of the aircraft vulnerable area Av and the probability of kill given a random hit on the aircraft PK/H. The results of an assessment for the externally detonating warhead consist of the probability of kill of the critical components intersected by the fragment shotlines from the warhead detonation, the probability

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

of aircraft kill due to blast, and the probability of aircraft kill given a detonation PK/D.


The Stochastic Qualitative Analysis of System Hierarchies (SQuASH) Model. One of the primary criticisms of the current aircraft vulnerability models is the straight shotline assumption. Fragments and penetrators usually do not penetrate through the aircraft in a straight line. In an attempt to account for the random, irregular path of penetrators and fragments through armored vehicles, Ballistic Research Laboratory (BRL) developed the SQuASH model (Deitz et al., 1990). SQuASH is applicable to both penetrator and high-explosive weapons. It allows for deflections of the penetrators and fragments from the straight shotline, the creation of spall, and it tracks the pieces of fractured penetrators. The present version of SQuASH was developed for the vulnerability analysis of armored ground vehicles. However, its methodology could be applied to aircraft.

The model introduces the concept of Spaces. All possible warhead and target conditions at the time of the hit form the Initial Conditions Space, or Space 1. A particular set of conditions, such as the type and operational status of the target and the location of the hit on the target, is one point in the Initial Conditions Space. Due to the hit, some components will be damaged, and some will be killed. These damaged and killed components, and all other post-event observables, such as holes in plates and other terminal effects, form the damage vector. All possible damage vectors for the target form the Damage Space, or Space 2, and the specific damage vector containing the components damaged or killed by the hit is one point in the Damage Space. All possible target capabilities after the hit form the Capabilities Space, or Space 4, and the particular target capabilities remaining after the hit represent one point in the Capabilities Space.20 The vulnerability event starts with a point in the Initial Conditions Space. This point is mapped to the Damage Space either by a live fire test or by the SQuASH model. Note that because the vulnerability event is nondeterministic, one point in the Initial Conditions Space can map to many different points in the Damage Space. The mapping from the Damage Space to the Target Capabilities Space is accomplished currently by using the Damage Assessment List. In the future, the Degraded States methodology will be used for this mapping.

SQuASH is a Monte Carlo model. Each shot at the target is replicated (typically 1,000 times) with slight variations in its initial conditions. For each replication or trial, random drawings determine which events (such as kill of a component that is hit) occur. The resulting damage vector for that shot is computed, and the frequency of occurrence of the elements in these damage vectors is produced as an intermediate result. Input kill or fault trees are used to develop estimates of target and individual subsystem kill probabilities.

Some difficulties associated with SQuASH are the lack of data with respect to the broken paths and component damage, especially synergistic damage, and the problems associated with relating component damage to degradation in performance. Another difficulty is the magnitude of the number of possible outcomes from one event. This number is dependent upon the number of components that can be killed. There may be a large number of components to consider for a particular shot; perhaps between 10 and 100. The number of components in an entire aircraft might be on the order of 1,000. The damage vector consists of these M components, and each of the M components or elements in the vector is either a 0 (no damage) or a 1 (damage), and the sample space is said to have dimension M. The sample space of possible combinations of components that might be damaged by a particular shot is 2M. Thus, the sample space for a given shot can be quite large. Some sort of metric is needed to reduce the sample space to one with a more manageable size. One approach might be to create some sort of metric that quantifies the “nearness” of various damage vectors (similar to a Hamming distance).


Testing. As a result of the random nature of the vulnerability problem, the multitude of known component or subsystem kill modes, the possible existence of unknown or previously unobserved kill modes or cascading damage, and the difficulty in quantifying the vulnerability of the components and subsystems for each of these kill modes, the use of combat data21 and the results from controlled live fire22 tests have always been integral parts of vulnerability assessment. These data provide insight into the component and subsystem kill modes and any cascading damage that can occur. Furthermore, when a sufficiently large number of identical tests are performed, statistical data on vulnerability are generated. However, because of the expenses and difficulty associated with obtaining large quantities of useful results from either combat or testing, there is a general reluctance to engage in large-scale efforts that may provide little useful data or may have little applicability to present or future aircraft or analytical models. Nevertheless, many live fire tests have been conducted since WW II on targets ranging

20

Space 3 represents objective Measures of Performance and is not modeled.

21

The combat data gathered in past conflicts is stored in the Combat Data Information Center, which is part of the Survivability/Vulnerability Information and Analysis Center. SURVIAC is located at Wright-Patterson Air Force Base, Ohio.

22

The term “live fire testing” is used here in the general sense to mean firing live (both explosive and non-explosive) ammunition or fragments at the target (and hitting it).

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

TABLE 1-3 Definitions of Types of Test Articles and Type of Tests (GAO, 1987)

 

Loading

Scale

Full-Up

Inert

Full-scale (Complete System)

Complete system with combustibles

Complete system without combustibles

Sub-scale (Partial System)

Components, subsystems, or subassemblies with combustibles

Components, subsystems, or subassemblies without combustibles

from individual components to actual aircraft. Of particular interest here are the current Joint Live Fire (JLF) program and the congressionally mandated Live Fire Test and Evaluation (LFT&E) program.


General Procedure for Testing. Before reviewing the JLF and LFT programs, the general procedure for testing that has been established by the vulnerability testing community is described. Briefly, one or more targets and weapons are obtained and prepared for testing. The target can be one component, a subassembly, a subsystem, several subsystems, portions of the aircraft, or the aircraft weapon system. According to the General Accounting Office (GAO), tests conducted on the complete weapon system are known as full-scale tests, and tests on less than full-scale targets are known as sub-scale tests. Corresponding definitions also used in this report are complete system tests and partial system tests. A surrogate target or weapon is an existing target or weapon that is similar to the intended target or weapon. If the target, either the complete system or a partial system, contains all of the appropriate combustibles, such as fuel, hydraulic fluid, ordnance, and stowage items normally found on the aircraft when operating in combat, the tests are known as full-up tests. Inert targets lack all of the appropriate combustibles, and semi-inert targets contain some of the combustibles. Table 1-3 contains these definitions, which are used throughout this report.


The Test Plan and Some Important Considerations. The test plan contains the test objectives and the issues the tests are supposed to provide information on, the weapon to be used, the selection and placement of test instrumentation, the selection of the number of shots, the shotline directions, the impact locations, and any analytical methods that will be used. The test plan may contain a number of random shots as well as a number of selected shots. The tests are scheduled so those shots that are expected to cause minimum damage to the target are conducted early in the program. Those tests that are expected to cause more severe damage are conducted at the end of the program. Particular shots that have the potential to destroy the target, although of vital interest, may not be conducted at all. Preparation for testing consists of the preparation of the test site, the weapon, and the target. After each test, the target is repaired and returned to a condition as similar to the original condition as possible. If the weapon is a non-explosive penetrator or fragment, the amount of damage is usually small, the repairs are relatively simple, and the target can be hit in essentially the same location again. However, if the weapon contains a high-explosive warhead, the damage is more severe and extensive, the repair is more difficult, and it may not be possible to return the aircraft to its original condition. In this situation, the shotline for a second shot must be sufficiently separated from the first shotline so that the damage and subsequent repair of the first shot do not influence the results of the second shot.

Some of the important test considerations are the external and internal environmental conditions at the time of the test, such as the requirements for external air flow over the target, and the proper fuel vapor states and temperatures inside the target; the requirement for jig arrangements to introduce loads on the aircraft structure; and the requirement for all of the equipment to be operating at the time of the hit. For example, must a helicopter rotor blade or tail rotor drive shaft be turning when it is hit by the weapon? Must the hydraulic fluid be at the normal operating temperature when the line is hit? What internal structural loads are appropriate for the test, those associated with normal flight, or those associated with a violently maneuvering aircraft?


The Test Results. The results or information obtained from controlled live fire tests typically consists of a list of the components that were damaged or killed, the nature and severity of the damage, the kill modes observed and any cascading damage, and an estimate or measurement of the ability of the aircraft to continue the operation of essential functions. Specific events, such as the initiation of a fire and the intensity and duration of the fire, are also noted.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

Due to the randomness of the reactions to the hit, some of the observed results in one test may not be observed in any of the other tests. For example, firing a 12.7-millimeter API into a partially empty fuel tank may not result in an internal explosion on the first test shot, but the second shot may cause an explosion that destroys the tank. On the first firing of a 12.7-millimeter API projectile into a helicopter engine nacelle, the projectile may ricochet into the cockpit; on the second shot, it may ricochet into the transmission.

What Are the Joint Live Fire and Live Fire Test Programs?

Joint Live Fire. In 1983, the Office, Secretary of Defense (OSD) Director, Defense Testing and Evaluation nominated to the Services a joint test and evaluation initiative for the live fire of munitions, foreign and U.S., made against currently operational full-scale targets, both U.S. and foreign. This program is known as the Joint Live Fire program. The U.S. targets originally included land, sea, and air; however, the sea targets were eventually excluded from the program. Candidate aircraft included the F-15, F-16, F/A-18, AV-8B, fixed wing aircraft, and the UH-60 and AH-64 helicopters. The threats initially considered consisted of armor-piercing projectiles with incendiaries (12.7-millimeter, 14.5-millimeter, 23-millimeter, and 30-millimeter API), warhead fragments (45, 70, 110, and 220 grains), and contact-fuzed high-explosive rounds with incendiaries (23-millimeter and 30-millimeter HEI). A number of specific tests on various components and subsystems of these aircraft have been conducted, such as tests on the UH-60 main rotor blade, the F-15 and F-16 hydraulic fluid, the F-15 and F-16 steady state and quick dump fuel ingestion, and the F-16 emergency power subsystem. In 1989, the results of the JLF tests were presented to more than 100 industry, government, and military specialists in vulnerability and vulnerability testing. The JLF program is still active. The test data gathered during the tests are currently being examined to determine the Pk/h values for the tested components, and the empirical values are being compared to the previous values in order to decide whether the previous values should be revised.


The Live Fire Test Law. As a result of the controversy over the vulnerability testing of the U.S. Army’s Bradley Fighting Vehicle, Congress in fiscal year 1987 amended title 10 of the U.S. Code, adding Section 2366. “Major Systems and Munitions Programs: Survivability and Lethality Testing; Operational Testing.” This legislation, known as the Live Fire Test (LFT) law, applies to covered systems. According to the law, “A covered system means a vehicle, weapon platform, or conventional weapon system that (A) includes features designed to provide some degree of protection to users in combat; and (B) that is a major system within the meaning of that term is section 2303(5) of title 10” (U.S. Congress, 1986–1989). A major system is one that costs $75 million in Research Development, Testing, and Evaluation and/or $300 million in procurement, in 1980 dollars, and is determined by the Secretary of Defense not to be a highly classified (i.e., black) program. Several modifications have been made to the law since FY1987.23

According to the LFT Test Guidelines established by the law, “Survivability and lethality tests required under subsection (a) shall be carried out sufficiently early in the development phase of the system or program to allow any design deficiency demonstrated by the testing to be corrected in the design of the system, munition, or missile before proceeding beyond low-rate initial production.” Note that survivability is used when vulnerability is intended. The primary requirement of the law is that “a covered system may not proceed beyond low-rate initial production until realistic survivability testing of the system is completed” Realistic survivability testing is defined as “testing for vulnerability of the system in combat by firing munitions likely to be encountered in combat (or munitions with a capability similar to such munitions) at the system configured for combat, with the primary emphasis on testing vulnerability with respect to potential user casualties and taking into equal consideration the susceptibility to attack and combat performance of the system.” “The term configured for combat, with respect to a weapon system, platform, or vehicle, means loaded or equipped with all dangerous materials (including all flammables and explosives) that would normally be carried in combat”

A waiver from the law is provided. “The Secretary of Defense may waive the application of the survivability and lethality tests of this section to a covered system, if the Secretary, before the system or program enters full-scale engineering development, certifies to Congress that live-fire testing of such system or program would be unreasonably expensive and impractical.” Also, “the Secretary shall include with any such certification a report explaining how the Secretary plans to evaluate the survivability or the lethality of the system or program and assessing possible alternatives to realistic survivability testing of the system or program” (U.S. Congress, 1986–1989).

The intent of the LFT law is to determine the inherent strengths and weaknesses of adversary, U.S., and allied weapon systems sufficiently early in the program to allow any design deficiency to be corrected. According to the FY1988–1989 DoD Authorization Act Conference Report, Congress intended that the Secretary of Defense implement

23

The law and the amendments to the law are included in this report in Appendix A.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

the LFT law “in a manner which encourages the conduct of full-up vulnerability and lethality tests under realistic combat conditions, first at the sub-scale level as they are developed, and later at the full-scale level mandated in the legislation” (U.S. Congress, 1988). All live fire tests conducted as part of the program to satisfy the Live Fire Test law will be referred to here as Live Fire Tests. Developmental tests using live fire that are not intended to be part of the mandated LFT&E program will be referred to as live fire tests, with no capital letters. The distinction between the two categories of tests is important.

In response to the law, the Department of Defense (DoD) chartered an administering office, the Director of Live Fire Testing, under the Office of the Director of Defense Research and Engineering. The responsibilities of this office include the establishment of policies under which Live Fire Testing is conducted by the Service components, the approval of the Services’ Live Fire Test strategy and test plans for each covered program, the review of the test results, and the performance of an independent assessment that is forwarded, via the Secretary of Defense, to the Congress (O’Bryon, 1991).


What Does the Law Require? During the course of the committee’s examination of the current direction of Live Fire Testing and Evaluation, it became apparent that because of the ambiguity of the law’s requirements regarding the system testing, there were different interpretations of the LFT law. One interpretation was that the law did not explicitly stipulate that a complete system had to be tested, even though no waiver from the law was requested. The opinion was held that the law was satisfied by an LFT&E program in which Live Fire Testing was conducted only on components and subsystems, provided that these tests showed that no complete system testing was necessary; all vulnerabilities had been found in the partial system tests. In an attempt to determine the intent of Congress as to the meaning of realistic survivability testing, members of the committee interviewed Mr. Joseph Cirincione, the congressional staff member who drafted the Live Fire Test legislation in 1987. Mr. Cirincione believes that the intent of the law, as seen by the Congress, is “full-scale, full-up” testing. This, to him, means that the complete aircraft must be tested and must be configured for combat (i.e., engine running, fuel in the tanks, loaded with ammunition, etc.). He believes that anything other than full-scale, full-up testing requires a waiver in accord with the terms of the above paragraph. In support of his position is the statement in the FY1988–1989 DoD Authorization Act Conference report that says “the conferees intend that the Secretary of Defense implement this section in a manner which encourages the conduct of full-up vulnerability and lethality tests under realistic combat conditions, first at the sub-scale level as sub-scale systems are developed, and later at the full-scale level mandated in the legislation” (U.S. Congress, 1988). Furthermore, the events that led to the law and the fact that Congress included a waiver process in the law are further evidence that Congress intended that live fire tests be conducted on full-scale, full-up systems. If tests on the full-scale, full-up system were not intended, no waiver would be necessary, and any live fire tests would suffice, as long as they were realistic. Based upon the evidence gathered by the committee and its study of the law, the committee is unanimous in the opinion that the LFT law requires a full-scale, full-up aircraft to be tested, regardless of the outcome of the sub-scale tests, unless a waiver is granted.

What Are the Applications of the Results of the Assessments?

Vulnerability assessments are a part of the weapon system acquisition process. This process is described in DoD Instruction (DODI) 5000.2, February 23, 1991. According to DoDI 5000.2, survivability is identified as a critical system characteristic and consequently must be addressed in cost-schedule-performance trade-offs throughout the acquisition process. This instruction requires that survivability be considered from all threats found in the various levels of conflict, including the conventional gun and missile threats, the nuclear, biological, and chemical threats, and the advanced directed energy weapons. At Milestone 0, the expected threat environment is identified and discussed in the Mission Need Statement. At Milestone I, the system threat assessment identifies the expected likelihood for each threat. In addition, initial survivability objectives are defined and validation criteria established in the Operational Requirements Document (ORD). Key objectives are included in the Concept Baseline. Critical survivability characteristics and issues that require test and evaluation are identified and included in the Test and Evaluation Master Plan; this includes the Live Fire Test program. Critical survivability technology shortfalls are identified and research requirements established. At Milestone II, survivability issues are addressed in the Integrated Program Summary; at Milestone III, an assessment of how well the survivability objectives have been met has been completed, and all survivability issues should have been resolved.

Vulnerability objectives are part of the survivability objectives required by DoDI 5000.2.24 If any vulnerability objectives or requirements have been defined in the ORD, they are satisfied and validated by using vulnerability assessments

24

Note that only survivability objectives are required. Thus, a system could meet the requirements in DoD 5000.2 by requirements on susceptibility alone.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

in the form of analysis/modeling and testing. Thus, the primary application of a vulnerability assessment in the weapon system acquisition process is to aid in the design of the aircraft and in the validation of the design. Additional applications are to satisfy program requirements, to develop data bases in support of subsequent analytical assessments, to predict test outcomes, to satisfy the requirements of the Live Fire Test law, and to support acquisition decisions.


Aid in Design and Design Validation. The results of a vulnerability assessment must be available early in the development cycle of an aircraft and used to influence the design. Analytical modeling can provide guidance on the placement of the critical components and the protection that should be given to the various contributors to vulnerability, such as the fuel subsystem, flight control subsystem, and propulsion subsystem. Controlled live fire developmental tests can be conducted on early designs of components, and possibly subsystems, to determine any adverse reactions, either expected or unexpected. Any design vulnerabilities revealed by the full-scale, full-up LFTs should also impact the design. For design validation, the analytical models provide information on vulnerable area, PK/H, and PK/D; and live fire tests are conducted to verify that certain vulnerability requirements for the design of the aircraft have been satisfied. For example, if an aircraft has a design requirement to be able to take a single hit by a 12.7-millimeter API anywhere on the aircraft and fly for 30 minutes after the hit, live fire testing of the design is the best procedure for verifying the compliance of the design.25


Satisfy Program Requirements. The DoD MIL-STD 2069, “Requirements for Aircraft Nonnuclear Survivability Program,” requires that analytical vulnerability assessments be made as part of the normal development process. Aircraft development programs that stipulate MIL-STD-2069 will have assessments conducted throughout the development cycle.


Development of Data Bases in Support of Subsequent Analytical Assessments. As data from live fire tests on a variety of components and subsystems are gathered, qualitative information on kill modes and cascading damage effects and quantitative information on individual component Pk/h functions can be put into a data base and used to improve subsequent analytical assessments. The JLF program is an example of this application in action. Another application of this type is the use of the results from the analytical vulnerability assessments in trade-off and campaign or similar large-scale war game models that require an aircraft attrition data base.


Predict Test Outcomes. The results of an analytical vulnerability assessment can be used to predict the possible outcomes of a controlled test prior to the conduct of the test. The particular components that will be damaged or killed by the weapon or by any cascading effects can be identified, and the consequences of the damage or kill of these components to the essential functions can be predicted. However, due to the random nature of vulnerability, no deterministic prediction of the test outcome can be made. Consequently, predictions take the form of statements such as “the flammable vapors in the wing tank have a 0.3 probability of exploding and destroying the wing when the tank is hit by a 12.7-millimeter API.”


Satisfy the Requirements of the Live Fire Test Law. The Live Fire Test law requires that a full-scale (the complete weapon system), full-up (configured for combat) aircraft be tested for vulnerability using munitions likely to be encountered in combat, unless a waiver is given from the law. A primary intent of the law is to obtain information on any design weaknesses in time to allow them to be corrected. Thus, the testing required by the law is in some sense an aid in the design (a discovered weakness can be corrected) as well as a validation of the design (if no weaknesses are discovered, the design is presumably validated). Analytical vulnerability assessments can assist in determining the issues that require examination in the Live Fire Test program. The Live Fire Test plan is developed using the information provided in the Live Fire Test and Evaluation Planning Guide. A typical Live Fire Test plan will include early testing of components, sub-systems, and sub-assemblies, both inert and full-up, and later testing of full-scale, full-up targets.


Support Acquisition Decisions. One of the principal applications of both analysis/modeling and Live Fire Testing is to provide information in support of acquisition decisions. This is accomplished by providing timely information on the vulnerability of the complete system to decision-making bodies, such as the Defense Acquisition Board.

Table 1-4 presents a summary of the applications of the analysis/modeling methodology and the Live Fire Testing methodology, including both sub-scale and full-scale testing.

Previous Studies of Vulnerability Assessment with Emphasis on Live Fire Testing

Two previous studies of the vulnerability assessment and live fire testing of military vehicles have been conducted;

25

The design requirement that an aircraft be able to withstand a single hit by a particular weapon and continue to fly for a specified period of time does not automatically mean that the aircraft will be unable to withstand a second hit. Building into the aircraft an ability to take a single hit anywhere also gives the aircraft a significant capability to withstand multiple hits.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

TABLE 1-4 Applications of the Methodologies

 

Aid in Design

Design Validation

Satisfy Program Requirements

Develop Data Bases in Support of Analytical Assessments

Predict Test Outcomes

Satisfy Requirements of LFT law

Support Acquisition Decisions

Analysis/modeling

X

X

X (MIL-STD-2069)

X (War games)

X

 

X

Live Fire Testing

Sub-scale

X

X

 

X (Pk/h values)

 

X (with waiver)

X

 

Full-scale

X

X

 

 

 

X

X

the 1987 U.S. General Accounting Office study Live Fire Testing, Evaluating DoD’s Programs (GAO, 1987) and the 1989 Board on Army Science and Technology (BAST), National Research Council (NRC, 1989), study Armored Combat Vehicle Vulnerability to Anti-Armor Weapons: A Review of the Army’s Assessment Methodology. Both studies addressed vulnerability issues similar to those reviewed here. However, the GAO study, which was conducted at the same time the LFT legislation was enacted, concentrated primarily on the JLF program. The purpose of this study was to answer four questions: (1) What is the status of each system originally scheduled for live-fire testing under the JLF program? (2) What has been the methodological quality of the test and evaluation process? (3) What are the advantages and limitations of full-up live fire testing, and how do other methods complement full-up testing? (4) How can live-fire testing be improved? Of interest here are questions 2, 3, and 4.

The BAST study examined the Army’s assessment methodology, including both analysis and live fire testing, for armored vehicles. The committee conducted an independent review to (1) address issues that will help the Army define the objectives of its vulnerability assessment program, (2) define and analyze alternative ways to balance computation and live fire testing in reaching conclusions about vehicle vulnerability, (3) identify technical deficiencies where they exist, and (4) suggest alternatives for improvement as appropriate. All four tasks are of interest here.

Although neither study specifically addressed the Live Fire Test legislation and the DoD LFT&E program, and the BAST study did not consider aircraft, both studies examined issues and arrived at conclusions that are pertinent here. Furthermore, the personnel and organizations involved in the JLF aircraft program also are the ones involved in the LFT aircraft program. Consequently, the major issues and conclusions of these two studies as they apply to aircraft are presented in Appendixes B and C.

References

• Aeronautical Systems Division (ASD), 1981. Impacts of Engine Vulnerability Uncertainties on Aircraft Survivabilities, Wright-Patterson Air Force Base, Ohio, AD Number:C037839.

• Air Force Armament Laboratory, 1983. User Manual for the Air-to-Air Missile Program SHAZAM, Eglin Air Force Base, Fla., AD Number:B104959.

• Ball, R.E., 1985. The Fundamentals of Aircraft Survivability Analysis and Design, American Institute of Aeronautics and Astronautics, Inc., New York.

• Ballistic Research Laboratory (BRL), 1978. “HEVART-An Interim Simulation Program for the Computation of HEI Vulnerable Areas and Repair Times, Aberdeen Proving Ground, Md., AD Number:C030817L.

• Datatec Inc., 1979. High-Explosive Incendiary Vulnerability Model (HEIVAM), Volume 1, User Manual, Fort Walton Beach, Fla., AD Number:B107811L.

• Dayton University Ohio Research Institute, 1976. SCAN-A Computer Program for Survivability Analysis, Volume 1, User Manual, AD Number:B068149L.

• Deitz, P.H., et al., 1990. Current Simulation Methods in Military Systems Vulnerability Assessment, Ballistic Research Laboratory, Aberdeen Proving Ground, Md., BRL-MR-3880.

• Joint Technical Coordinating Group for Munitions Effectiveness

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×

(JTCG/ME), COVART II—A Simulation Program for Computation of Vulnerable Areas and Repair Times—Users Manual, 1984. Government Report Number:61 JTCG/ME 84-3.

• National Research Council (NRC), 1989. Armored Combat Vehicle Vulnerability to Anti-armor Weapons, A Review of the Army’s Assessment Methodology, Committee on a Review of Army Vulnerability Assessment Methods, Board on Army Science and Technology, Commission on Engineering and Technical Systems, Washington, D.C.: National Academy Press.

• O’Bryon, James F., 1991. Presentation made to the Committee on Weapons Effects on Airborne Systems, July 24.

• U.S. Congress, 1986–1989. Survivability and Lethality Testing of Major Systems, DoD Authorization Acts, FY86—Sec. 123, FY87—Sec. 910—Sec. 910, FY88–89—Sec. 802.

• U.S. Congress, 1988. FY88–89 DoD Authorization Act Conference Report, Live-Fire Testing (Sec. 802).

• U.S. General Accounting Office (GAO), 1987. Live Fire Testing, Evaluating DOD’s Programs, GAO/PEMD-87-17, Washington, D.C.: U.S. Government Printing Office.

Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
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Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
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Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
Page 13
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
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Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
Page 15
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
Page 16
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
Page 17
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
Page 18
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
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Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
Page 20
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
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Page 21
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
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Page 22
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
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Page 23
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
×
Page 24
Suggested Citation:"1 Review of Current Methodologies Used to Assess Aircraft Vulnerability and Identification of Applications of the Results." National Research Council. 1993. Vulnerability Assessment of Aircraft: A Review of the Department of Defense Live Fire Test and Evaluation Program. Washington, DC: The National Academies Press. doi: 10.17226/12470.
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Page 25
Next: 2 Evaluation of the Cost, Effectiveness, and Deficiencies of These Methodologies »
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