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U.S. Air-to-Air Research Expands After Years of Neglect
Aviation Week & Space Technology
05/17/2004, page 46
Douglas Barrie and Robert Wall
Eglin AFB, Fla.
Advances in foreign air-to-air missiles revitalize U.S. research efforts
Cause and Effect
After years of neglect, the U.S. air-launched weapons community is optimistic it will see a revival of research and development spending.
When the “Red threat” faded in the early 1990s, so did the impetus for developing and fielding a new generation of air-to-air weapons in the U.S. The collapse of defense expenditures in Russia effectively ended work on the R-73 follow-on, the Vympel K-30, along with a slew of medium- and long-range air-to-air missiles (AAMs), including enhancements to the R-77 (AA-12 Adder) and the R-37 (AA-X-13).
Without a compelling threat, the U.S. opted for relatively modest upgrades to its weapons. Even the latest addition to its air-to-air missile inventory, the Raytheon AIM-9X, is a comparatively conservative design, given some of its antecedents, such as the U.S. Navy-conceived Box Office missile. An incremental development approach was also adopted for the Raytheon AIM-120 Advanced Medium Range Air-to-Air Missile (Amraam), the primary beyond-visual-range air-to-air weapon for the U.S. Air Force, Navy and Marine Corps.
But there are signs of increased U.S. interest in medium- and long-term needs following the lean period, particularly in response to missile developments in the “gray” world that includes Israeli designs.
While the air-to-air research and development community is far from flush with cash, Thomas Robillard, program director within the U.S. Counterair Joint Systems Program Office, suggests there is improvement. USAF has a number of initiatives underway to develop subsystems and components applicable to future missiles, covering propulsion research, fuzing and lethal package, and new airframe/propulsion combinations.
The turnaround is spurred by the fact that Russia’s missile manufacturers have found gainful employment in the export arena, even if not domestically. One case in point is China’s Project 129 or SD-10 or PL-12 as the medium-range AAM program is variously known.
This project is effectively a Sino-Russian collaboration, with many of the missile’s subsystems drawn from the R-77 and married to what is thought to be an indigenous Chinese dual-pulse motor. One limitation of the basic R-77 was its motor-burn profile, which curtailed its range. The missile has been sold to China, but only in small numbers to the Russian air force. Moscow’s focus has been on the development of the K-77M, an improved version of the basic missile. However, the program’s status remains unclear, as does any possible crossover with China’s PL-12.
Unlike the baseline R-77, the PL-12, when it enters service, should have better kinematic performance than early models of Amraams, Chinese specifications suggest. The missile is stated to have a maximum head-on engagement range of 70-80 km. (43-50 mi.), with a peak velocity of Mach 4.
The PL-12 is now in the final stages of development, with test-firings against target drones in the offing. But test shots planned for late last year did not take place. Pakistan, which is part-funding development of the FC-1 light fighter, is seen as the first export customer for the PL-12. The missile was first revealed in dummy form on a full-scale mock-up of this aircraft.
The emergence of the PL-12 could potentially see it displace the basic R-77 as the primary radar-guided AAM against which the U.S. measures its own capabilities, thus underpinning research for technology insertion, and eventually for new missiles.
In response, the U.S. Air Force is pursuing a multi-pronged approach to enhancing its missile capability. In the near-term, it is upgrading its Amraam to the AIM-120D standard that should deliver considerably improved kinematics and lethality. In parallel, the Air Force Research Laboratory (AFRL) is examining the configuration of potential successor systems.
The AIM-120D should be fielded in Fiscal 2008 and would be the first Amraam upgrade to initially enter service with the U.S. Navy, specifically the Boeing F/A-18E/F. The D-model is intended to significantly expand the no-escape envelope and boost the ability to defeat maneuvering targets at ranges well in excess of earlier models.
Robillard suggests the AIM-120D will deliver approximately 50% more range and have increased navigational accuracy during the fly-out phase. This has benefits in the terminal phase of the engagement, particularly against maneuvering targets. This missile will also have a two-way rather than one-way data link.
The existing link is used to provide target updates from the launch aircraft to the missile. The inclusion of a two-way data link will allow the launch aircraft to receive target data from the missile’s radar seeker once it has gone active in the final phase of an engagement.
Uncertain is when the Pentagon may make the leap from the legacy program to a new-generation design. But AFRL officials are carrying out a Dual-Role, Dual-Range missile study, in conjunction with Raytheon and Aerojet, under the Variable Flow Ducted Rocket (VFDR) Flight Vehicle Concepts program. The design uses ramjet propulsion providing an increased mean velocity. Atlantic Research Corp. (ARC), which carried out the development of the VFDR ramjet design for the Air Force’s original Amraam-VFDR program, is now part of Aerojet.
This is not the first time USAF researchers have harbored hope they would be allowed to pursue a new-generation air-to-air weapon; in the mid-1990s, efforts were started for a dual-range weapon to replace AIM-9X and Amraam, but after about a year funding fell flat and the activity stalled. But this time developers have set both an air-to-air mission and anti-radar air-to-surface application for the weapon, which could bolster its chances of survival in the Pentagon’s annual budget skirmishes. The new class of weapon is tentatively seen as entering the inventory around 2017.
The complexity of packaging a ramjet missile for internal carriage in the Lockheed Martin F/A-22 is receiving special attention, AFRL officials say. ARC’s VFDR used an asymmetric design with two air intakes mounted on the lower part of the missile body. The configuration was driven by the need for semi-conformal carriage of the weapon.
The new studies do not suffer from the same constraint, allowing designers to look at a four-intake symmetric arrangement. The latter offers advantages during extreme maneuvering with regard to intake blanking–the disruption or breaking of airflow that can lead to flameout. A two-intake configuration–such as the MBDA Meteor missile now in development for six European air forces–requires considerably more careful flight management to avoid engine flameout. Meteor, like the original VFDR, is design-constrained by the need for the missile to be carried in a conformal configuration.
Alongside ramjet applications that offer the benefits of increased range and speed, AFRL is also looking at improving the maneuverability of conventional medium-range missiles under its Missile Control Technology Program.
Studies are ongoing to investigate how to provide a future missile with extreme maneuverability. Researchers are probing a six-valve arrangement around the rear section of an AIM-120-size missile capable of bleeding-off propellant motor energy from the nozzle blast tube. While all the valves can operate independently, they can also be used in combinations of up to three to generate pitch, yaw and roll forces. A flight-weight system is being designed, with final ground tests in November. Officials would like to pursue the program further, into actual flight tests.
Potential applications would allow for an over-the-shoulder type shot–now the domain of high-off-boresight dogfight missiles only–and also provide for a high-degree of maneuverability in the terminal stage of a beyond-visual-range engagement. Such control technologies would also lend themselves to a “clean-airframe missile,” allowing for the option of removing conventional control surfaces, along with the associated drag and weight penalties.
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May 18, 2004 at 3:49 am