v1.1.1 / 2 of 4 / 01 jun 02 / greg goebel / public domain
* While the sensor suite of the Mohawk was state of the art for its time, sensor capabilities have improved dramatically since the 1960s. In the early 1990s, the US Army decided to obtain a new surveillance platform, the RC-7 "Airborne Reconnaissance Low (ARL)" aircraft, based on the De Havilland Canada Dash-7 airliner, to exploit these new technologies. The RC-7 proved so useful that the Army obtained an improved version, the RC-7B "ARL Multifunction" (ARLM). This chapter describes the RC-7 and RC-7B.
* During the 1950s and 1960s, the aircraft manufacturer De Havilland Canada (DHC) acquired extensive experience in the construction of small and medium capacity transports with short takeoff & landing (STOL) capabilities, such as the "Otter" and "Caribou". The US Army was one of their customers, and the two organizations developed a good long-term relationship.
In the early 1970s, the company decided to build a larger STOL transport for use as a mid-sized commercial regional airliner, operating on intercity routes between major metropolitan areas from small local airports. This requirement dictated a design that had good short-field capability and a low noise signature.
Construction of prototypes of what would be the "DHC-7 / Dash-7", began in late 1972, with two prototypes taking to the air in the spring of 1975. The type received Canadian certification in the spring of 1977, with the first production aircraft flying shortly afterwards. The first customer delivery was in early 1978.
The Dash-7 is powered by four Pratt & Whitney Canada (PWC) PT6A turboprops, each rated at 1,240 horsepower at takeoff and driving a four-blade Hamilton Standard propeller. The propellers are very wide, with a diameter of 3.4 meters (over 11 feet), to allow them to provide adequate thrust at relatively low RPM, reducing noise.
The aircraft features a high wing, tee tail, and an aerodynamic lift enhancement system that features double slotted flaps over 80% of the wingspan, along with an outboard spoiler on each wing to provide additional lift or control as needed. With these features, the Dash-7 can take off and land in less than 700 meters (2,300 feet). In contrast, a Boeing 737-300, which has a degree of short-field capability in the form of thrust reversers and triple slotted flaps, requires about about 1,400 meters (4,600 feet) for takeoff and landing.
The initial Dash-7 model was the "Series 100", which was a pure airliner typically fitted with 50 seats. There was a complementary "Series 101" variant, with a large freight door just aft of the cockpit, that could be configured as a cargolifter or mixed cargo-passenger transport. These were followed by the "Series 150" airliner and the complementary "Series 151" cargo lifter or cargo-passenger transport. The 150/151 are essentially identical to the 100/101, except for increased fuel capacity and a higher take-off weight rating.
Stretched variants were considered but never built. While the Dash-7 was an attractive and well-built aircraft, the urban STOL market that DHC had anticipated never materialized, and the Dash-7 didn't sell. When Boeing bought out DHC in 1986, new efforts were focused on stretched versions of the less specialized twin-turboprop "Dash-8" transport.
108 Dash-7s had been sold by 1987. It seems unlikely that many more, if any, Dash-7s were built after that time, and it is now out of production.
* Although the Dash-7 was something of a noble failure, it was nonetheless a fine aircraft that was well suited to certain applications. In the early 1990s, the US Army Southern Command (SOUTHCOM), with its domain of responsibilities in Latin America, determined a need for a "low profile" intelligence platform to participate in counter-drug operations and other missions that fell outside of the Army's traditional battlefield operations role.
The Dash-7 was an excellent choice for this purpose. As noted, the US Army had long and happy experience with DHC aircraft, and the Dash-7 coupled good endurance and load-carrying capacity with very good short-field performance. Besides, it looked like a civilian airliner and made relatively little noise, which fit the Army's need for an aircraft that didn't attract attention.
The initial contract for converting the Dash-7 into an intelligence aircraft was awarded to California Microwave Incorporated (CMI, now a part of Northrop Grumman) in the spring of 1991, with the first "RC-7 Airborne Reconnaissance Low (ARL)" aircraft delivered two years later. Three RC-7s were provided to SOUTHCOM, with two of them optimized for signals intelligence (SIGINT) and one for imaging intelligence (IMINT). These initial RC-7 variants were used in the Haiti intervention in 1994, Bosnian peacekeeping duties, operations against drug producers and smugglers, and in support of disaster relief operations.
* The RC-7 met SOUTHCOM's requirements very well, and the Army went on to initiate the acquisition of a more advanced version in the summer of 1993, designated the "RC-7B ARLM (ARL Multifunction)", that merged the SIGINT and IMINT functions of the two types of RC-7, along with new capabilities, to provide a comprehensive sensor suite.
The first two RC-7Bs were delivered in the fall of 1996, and were deployed to Korea to observe North Korean military activities. They replaced the retiring Grumman OV-1D Mohawk. More RC-7Bs were delivered in the following years.
The RC-7B carries a crew of pilot, copilot, and four systems operators. The
electronics system is highly automated to reduce workload. The RC-7B can be
regarded as sort of a combination poor-man's E-8 "Joint-STARS" battlefield
surveillance platform, described in the next chapter, and RC-135 "Rivet
Joint" signals intelligence aircraft. While it does not have nearly the
capabilities of these two larger Boeing four-jet intelligence platforms, the
ARLM is adequate for low-intensity missions, and much cheaper to operate.
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spec metric english
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wingspan 28.4 meters 93 feet
length 24.5 meters 80 feet 6 inches
height 8 meters 26 feet 2 inches
max loaded weight 21,300 kilograms 47,000 pounds
cruising speed 425 KPH 265 MPH / 230 KT
service ceiling 7,600 meters 25,000 feet
endurance 7.5 hours
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The RC-7B's payload includes:
At typical operating altitudes, the RC-7B's SAR has a maximum range of about 73 kilometers (45 miles). It has a maximum resolution of 1.8 meters, and is capable of observing traffic and road construction operations in all weather, day or night.
The MTI display shows targets on a map background, with those moving towards the aircraft displayed as red dots and those moving away as green dots. A target that stops moving will remain on the display for three minutes and then disappear.
The MTI operates in three modes: a 90 degree / wide-area search mode; a 5 degree / narrow sector search mode; and a 2 degree single-beam "spotlight" mode for examining individual targets.
The signals intercept system can be configured in flight to sort out signals with different characteristics. While it can't analyze burst communications or decipher signals with advanced voice encryption, it can store them on tape and transmit them to US National Security Agency stations for analysis.
The current direction finding gear on board the RC-7B cannot link particular communications to specific vehicles, except if the aircraft is operating in conjunction with direction finding equipment on other aircraft or ground stations.
The Army has considered adding a new "measurement & signature intelligence (MASINT)" system to the RC-7B that could perform remote chemical analysis of factory smoke, rocket exhaust plumes, and waste water runoff. The MASINT system would use "hyperspectral" sensing techniques that perform observations over a large number of infrared and optical bands.
The RC-7B's sensing and comlink capabilities permit realtime targeting of adversary assets, allowing ground forces to react quickly to distant threats. Intelligence collected by space satellites may take up to three days to reach its ultimate users, but battlefield commanders down to the battalion level can obtain near-realtime SAR-MTI displays from the RC-7B to give them a view of their tactical environment.
The RC-7B, while hardly invisible to radar or other sensors, has adopted a clever kind of "stealth" of its own. The aircraft's "Low" designation implies "low profile", and it is rigged in such a way as to attract little attention, There is not much in its external appearance to distinguish it from an ordinary Dash-7, as most of the antennas and other gear are retractable. It is painted to look like a commercial airliner, with military markings kept to a discreet minimum. During Haiti operations, Caribbean charter pilots took the RC-7 for a new competitor.
* On 23 July 1999, one of the original RC-7s was operating under low-visibility conditions in support of "anti-narcotic" operations in Columbia when it flew into a mountainside. All on board, including both US Army and Columbian military personnel, were killed. The incident revealed both the use of the aircraft in low-profile military operations and the increasing US involvement in the guerrilla war in Columbia.
At the time of the crash, the Army had a total of eight RC-7/7Bs, plus a Dash-7 used for flight training and another used as a technology demonstrator. The RC-7 that crashed was the single pure IMINT variant, while of the other seven, two were updated RC-7 SIGINT variants and five were RC-7Bs. Three of the RC-7Bs are currently deployed to Korea, where they keep an eye on North Korean military activities north of the demilitarized zone.
The US Congress has provided funds to replace the RC-7 that was lost. CMI is now working on the replacement, and the Army hopes to have it in service by 2003. The replacement will of course be built to RC-7B standards.
The Department of Defense has projected a fleet of 18 RC-7/7B aircraft, but the Army only plans nine, with seven currently available, one on order, and one currently unfunded. The fleet is expected to remain in service up to 2017.
There has been some talk of updating the two SIGINT-only variants to RC-7B specification, though so far nothing much seems to be happening, and a few years ago there was a proposal to replace the fleet's PT6A engines with the LHTEC T800 engine used on the RAH-66 Commanche attack helicopter. This idea didn't go anywhere either, but the idea of reengining the fleet with a new turboprop engine to increase time on station and reduce maintenance costs is still attractive.
* Exactly how much the RC-7B will be updated is uncertain, as the Army is also considering a next-generation aircraft, the "Aerial Common Sensor (ACS)", which will replace both the RC-7B and the RC-12 "Guardrail".
The Guardrail is a SIGINT platform currently based on the Beech Super King Air twin-turboprop transport, modified to carry an impressive array of antennas. Earlier Guardrails were based on the smaller Beech Queen Air twin. The Guardrail was developed in later part of the 1960s to deal with North Korean military activities, following a series of commando intrusions performed in 1967 through 1969. There have been a confusing range of different Guardrail variants, but all appear to have focused on the SIGINT mission. They do little or no on-board processing of data, relaying it to a ground station for analysis.
The ACS, which will combine the functions of the RC-7B and the Guardrail, will probably be based on a business jet or small commercial transport. Concept studies for the ACS were initiated in 2000, and selection of an aircraft is expected in 2003. Production is scheduled to begin in 2007, with operational introduction in 2009.
The ACS will feature a precision SIGINT suite to allow it to perform communications intercept, as well as emitter location, classification, and targeting; an electro-optic sensor system; and SAR-MTI. It will have high-speed datalinks. The ACS will probably be initially fielded with the SIGINT suite, with the other payload systems added incrementally.
The Army wants low cost and a degree of autonomy, with the ACS providing useful intelligence immediately on arriving in a battle theatre. This means that the ACS will not heavily rely on ground systems for analysis.
The ACS is expected to have a modular configuration, with equipment swapped out to suit the aircraft for a particular mission. The ACS is also expected to operate closely with UAVs operating in the intelligence role. UAVs are not being considered for the ACS role itself, as UAVs lack the payload capacity and flexibility for the role.
Since three aircraft are required to obtain a precision location for an emitter, the ACS will operate in sets of seven aircraft, allowing round-the-clock operation in relays and spare. The Army hopes to obtain at least five sets of ACS aircraft.
The ACS program is under pressure because of funding limitations, and because of the cancellation of an Air Force SIGINT effort, the BAE Systems "Low Band Subsystem", which the Army had hoped to use as a key element of the ACS. The Army is now scrambling to find an alternative system.