ROTORCRAFT EFFECTS OF COUNTERING RPGs
By: Marty Krammer and Nathan Conde
Rocket-propelled grenades (RPGs), such as those shown in Figure 1, are a highly prolific threat that pose a significant danger to U.S. forces abroad. Accordingly, these weapons have been the basis for multiple vulnerability studies, including the one presented herein. To counter this threat, the U.S. Department of Defense (DoD) is researching numerous potential active protection system (APS) solutions for vehicle and aircraft applications. In addition, the Navy has undertaken a project, sponsored by the Joint Aircraft Survivability Program Office (JASPO), to determine the potential effects of countering the RPG threat, as well as the residual debris created by the encounter, on military rotorcraft and the persons on board.
Over the last half century, from Vietnam through recent operations in Iraq and Afghanistan, U.S. aircraft combat losses have indicated a growing need to provide aircraft protection against RPG-rotorcraft encounters. RPGs, once launched at a target, are a difficult challenge to defeat, and thus they pose a unique problem for Aircraft Survivability Equipment (ASE) countermeasure solutions. They fly toward the target unguided and cannot be countered by traditional countermeasures that seek to jam, degrade, spoof, or decoy guided antiaircraft weapons. And once they arrive, the relatively large power of their warheads, combined with the relatively lightweight structures of aircraft, can give them devastatingly destructive results.
Solutions to RPG protection fall into three major areas:
- Prevent or distract the launch.
- Intercept and degrade or destroy the RPG in flight.
- Harden the aircraft to survive the engagement.
Recent technological advancements in APS for defeating or degrading the RPG have centered on the development of a guided countermeasure munition (CMM), or RPG kill vehicle (KV), launched from an AN/ALE-47 Countermeasure Dispense System, providing 360° protection to the rotorcraft against approaching RPGs (see Figure 2).
Both warhead-kill vehicle (WKV) and kinetic-kill vehicle (KKV) CMM concepts have emerged from Army and Navy APS research efforts for countering the RPG threat. Each concept, however, poses a unique engagement and defeat mechanism challenge against unguided aircraft weapons, such as the RPG. The KKV, sometimes referred to as Hit-to-Kill (HTK) vehicle concept, accomplishes RPG defeat through precision CMM guidance and targeting, with physical body-to-body impact on the RPG warhead. The WKV concept accomplishes RPG defeat or degradation through CMM guidance and lethal fragmentation targeting of the RPG warhead.
ROTORCRAFT VULNERABILITY TO RPG DEBRIS PROJECT
In 2017, JASPO initiated a 3-year effort to understand rotorcraft effects of countering the RPG threat with APS CMMs. The first year included developing and demonstrating unique test capabilities to replicate KKV and WKV CMM engagements against the RPG. The second year included live fire RPG debris characterization testing and RPG debris threat model development. The third year (2019) has included vulnerability analyses and reporting on results and findings.
Project objectives have included the following:
- Characterizing RPG reactions and debris caused by KKV and WKV engagements.
- Performing analyses to understand effects on rotorcraft, crew, and passenger survivability for RPG engagements.
- Understanding the benefits of APS in reducing vulnerability and improving the survivability of the Warfighter.
Both APS WKV and KKV RPG defeat concepts were evaluated for the purpose of:
- Determining their effectiveness in defeating the RPG threat at standoff distances away from the rotorcraft.
- Understanding the RPG’s reaction to different engagements.
- Understanding the residual debris (threat) effects created by the engagement and impact on rotorcraft vulnerability.
Several locations on the RPG (high-lighted in Figure 3) were targeted during RPG debris characterization testing. These included the warhead’s fuze, warhead, motor, and tail sections. The APS RPG threat engagement scenario (illustrated in Figure 4) that was selected for testing represented a realistic engagement, producing maximum downrange RPG debris scatter and potential energy effects.
Two standoff distances from the rotorcraft were evaluated for RPG debris characterization and vulnerability analyses.
The KKV used in testing reflected a Navy research APS CMM concept that was representative in size, mass, and materials composition. Several WKV warhead concepts were evaluated in testing and reflected anti-RPG warhead designs developed under a related JASPO project, which focused on the development of an effective low-collateral effects warhead for APS application. The anti-RPG warhead designs tested used a consumable fragmentation approach for RPG defeat.
For testing, a unique RPG launcher, KKV launcher, and targeting-firing control system was used to replicate body-on-body KKV-to-RPG intercepts and WKV warhead side-offset RPG engagement conditions (as illustrated in Figure 5). These RPG launcher, KKV launcher, and intercept capabilities were developed and demonstrated in 2017 under this project.
In 2018, live fire RPG debris characterization testing was performed at the Weapons Survivability Laboratory of the Naval Air Warfare Center Weapons Division (NAWCWD) in China Lake, CA. Unique test capabilities, data collection methods, and test setup were developed to replicate APS CMM-to-RPG threat engagements. Data acquired in testing included RPG debris shapes, sizes, masses, speeds, and trajectories, as well as RPG shaped charge jet (SCJ) scatter, trajectories, and downrange penetrations (when formed).
The setup developed for testing was extensive and spread over a relatively large area (as pictured in Figure 6). Testing used a custom RPG launcher gun, KKV launcher gun, and targeting-firing control system to replicate both body-on-body KKV and WKV engagement test conditions. A total of eight high-speed cameras, combined with grid board and virtual measurement references, helped to determine residual RPG debris positions, velocities, and trajectories downrange. Time synchronization and positioning of cameras, combined with post-processing parallax correction tools, also aided data collection efforts.
In addition, to assist with RPG debris observations, a witness wall was erected to help identify RPG debris trajectories and penetration capabilities. The RPG debris data acquired from testing led to the development of RPG debris threat files to support vulnerability analysis. WKV testing used the same setup as the KKV testing, with the exception of the KKV launcher gun, which was replaced with the WKV warhead fixture, and break-screen trigger arrangement (shown in Figure 7).
Testing (shown in Figure 8) was able to successfully characterize RPG debris resulting from KKV and WKV CMM engagements. The testing also acquired data of RPG SCJ dispersions at long standoff distances (as shown in Figure 9). The data supported the development of several RPG debris threat models supporting follow-on rotorcraft vulnerability and passenger survivability analyses efforts.
VULNERABILITY AND CREW AND PASSENGER SURVIVABILITY (CAPS) ANALYSES
Data captured from the Weapon Survivability Laboratory testing performed at China Lake were used to develop an RPG threat, which would feed into the Advanced Joint Effectiveness Model (AJEM). This RPG threat, in conjunction with AJEM, was used to estimate rotorcraft vulnerability, as well as CAPS. The objective of this analysis was to develop and demonstrate a modeling and simulation (M&S) methodology for assessing rotorcraft vulnerability to RPG debris as a result of a Navy CMM intercepting an incoming RPG at a specified distance from the rotorcraft.
The objective was twofold:
- Determine the change in the rotorcraft’s vulnerability as a result of an RPG engagement with and without the Navy CMM.
- Determine the change in the rotorcraft’s CAPS metrics as a result of an RPG engagement with and without the Navy CMM.
The project analysis leveraged work performed under a previous JASP project, a CH-53E integrated CAPS analysis. As part of the project, the Navy developed a methodology to assess the survivability of aircraft personnel against hostile threats in the context of aircraft survivability. The AJEM data files created for the previous project were modified and subsequently used for this project.
A total of 33 aspect angles were assessed for the AJEM runs. Figure 10 illustrates these angles on a notional aircraft.
Table 1 lists the five crash levels that factored into the primary CAPS metrics (the Probability of Exactly “i” Casualties [Ei] and the Expected Number of Casualties [EC]). These metrics both depend on the crash level of the incident.
In addition to the five crash levels specified above, the CAPS analysis also considered casualty mechanisms (shown in Table 2) responsible for crew and passenger casualties. A crash mechanism defines how the casualty occurred.
For the project, the five crash levels (in Table 1) and the four casualty mechanisms (in Table 2) were used to assess the rotorcraft’s CAPS metrics. The CAPS metrics were assessed for each of the five scenarios (shown in Table 3) to satisfy the overall objective of the analysis.
Results gathered from the AJEM runs involving the five aforementioned scenarios were successful in determining an optimal standoff distance from the rotorcraft, allowing for minimal casualties while also minimizing the rotorcraft’s probability of kill (P) in the event of an RPG engagement. Additionally, this project’s analysis created a methodology framework that can now be used in future analyses involving APS CMM engagements with incoming RPG threats.
ABOUT THE AUTHORS
Mr. Marty Krammer is an aircraft vulnerability engineer at the Naval Air Warfare Center Weapons Division in China Lake, CA, currently leading live fire test and evaluations activities for several Navy aircraft programs. With more than 28 years of experience, he has supported numerous aircraft vulnerability reduction and live fire test programs, including the AV-8B, F-15, F-14, F/A-18, JSF, AH-1, UH-1, H-60, V-22, and CH-53, and he has provided subsequent recommendations to reduce the vulnerability of these aircraft. Specializing in aircraft fire, fuel tank self-sealing, and explosion protection, Mr. Krammer also serves as the Navy co-chairman of JASPO’s Vulnerability Reduction and Analysis Subgroup, as well as the Navy Deputy Test Director for the Joint Live Fire Aircraft program, investigating vulnerability issues associated with fielded Navy aircraft.
Mr. Nathan Conde is an aircraft vulnerability engineer with 10 years of experience in M&S at the Naval Air Warfare Center Weapons Division in China Lake, CA. He is also the lead data developer for J-ACE (a Joint air-to-air and surface-to-air simulation program), and he has supported the analysis of numerous Navy aircraft platforms. Mr. Conde also serves as the Navy representative for the System Characteristics Working Group.