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Boeing / Sikorsky RAH-66 Commanche

 

rah66


A LHX request for proposals was issued 21 June 1988 as the centerpiece of the U.S. Army's aviation modernization plan with the main goal of replacing the entire OH-58s and AH-1 Cobras fleet.


Boeing and Sikorsky began collaboration on what later became the RAH-66 in June 1985 and received a 23 month demonstration/validation contract for the demonstration/validation programme on 5 April 1991. The contract was to build four YRAH-66 demonstration/validation prototypes in a 78 month programme, plus static test article (STA) and propulsion system testbed (PSTB).


LHTEC T800 engine specified October 1988. LHX designation changed to LH early 1990, then US Army designation RAH-66 Comanche in April 1991.


The prototype critical design review, completed in December 1993, authorised production of three YRAH-66 prototypes (the first item for which manufactured in September 1993). At same time, however, further R&D economies under study; December 1994 decision reduced dem/val phase to two prototypes (lacking Longbow/Hellfire capability).


Prototype construction began 29 November 1993 with the forward fuselage at Sikorsky, Stratford; Boeing built aft fuselage in Philadelphia. STA airframe delivered to Stratford 1994, at which time PSTB under construction there. PSTB trials commenced in 1995 at West Palm Beach, with 100% torque from both engines achieved during first 10 hours of running. PSTB subsequently suffered failure of left input bevel gear, which disintegrated and punched hole in main gearbox housing during 110% power test; resonance was blamed for the failure.


In early 2002, Boeing Sikorsky announced selection of Bridgeport, Connecticut, as the final assembly location for the production RAH-66. Also in 2002, the Joint Program Office moved from Huntsville, Alabama, to Bridgeport.


The front and rear sections of the prototype were joined at Stratford on 25 January 1995, and the completed helicopter (94-0327) rolled out on25 May 1995. Following transfer to Sikorsky's Development Flight Test Center in West Palm Beach, Florida, during June 1995, the first flight was accomplished on 4 January 1996. Prototype retired from flight test duty on 30 January 2002, by which time it had accumulated 387.1 flight hours in 318 sorties.


Aft fuselage section of second prototype (95-0001) was delivered by Boeing to Stratford in early December 1996 for mating with forward fuselage, and the completed helicopter was exhibited at Army Aviation Association's annual meeting in April 1998 and then to West Palm Beach. Made international debut when displayed statically at Famborough Air Show in September 1998; flew for first time on 30 March 1999. Completed initial test schedule in April 1999, recording 4.9 hours in five sorties before temporary lay-up, due to funding constraints; also used for vertical rate of climb demonstration later in year and will test integrated mission equipment package (ÌÅÐ), including digital avionics, communications, navigation and target acquisition systems. By mid-December 2000, had logged almost 53 flight hours in 50 sorties; these figures had risen to 93 and 103.5 respectively in May 2001 when it was removed from flight status to be prepared for flight testing and validation. This phase of development began on 23 May 2002, when second prototype made first flight with ÌÅÐ and new engines installed. Near-term objectives to be achieved by the second prototype include flight with the night vision pilotage system by October 2002, as well as completion of total weapon system critical design review in May 2003, including the Lockheed Martin Electro-Optical Sensor System (EOSS), which due for delivery in first half of 2003.


Engineering and Manufacturing Development (EMD) officially began 1 June 2000, following RAH-66 meeting (on 4 April 2000) seven key Defense Acquisition Board Milestone 2 criteria, including a 107m/min vertical climb rate, a specified detection range for the FLIR sensors, a radar cross-section specification, ballistic vulnerability and tolerance specifications and tower-testing of the selected FCR. Weight reduction effort under way in late 2000, to reduce from current level of about 4,310kg to target weight of 4,218kg. Under original plan, EMD expected to take six years and include production of five RAH-66 specifically for EMD testing, followed by further eight for initial operational test and evaluation (IOT&E) by the US Army. However, EMD contract and plan restructured in mid-2002, at which time IOC forecast to occur in September 2009. The new plan includes a start of low-rate initial production (LRIP) in 2007, with full-rate production set at 60 per year from 2011-12 onwards. First EMD RAH-66 expected to fly in March 2005. In meantime, second YRAH-66 will assume increasing burden of test duty. Production of components for the first EMD RAH-66 began at Boeing's Philadelphia factory in early 2003, with work on assembling the first empennage beginning on 21 April 2003; on completion, this shipped to Bridgeport and mated with Sikorsky-produced elements.


First -801 growth version of T800 turboshaft began bench runs in March 1994; -801 preliminary design review completed May 1993; critical design review March 1995; prototypes originally fitted with less powerful T800-LHT-800 engines, but first flight with definitive -801 engine made on 1 June 2001 by first prototype. Same engine subsequently installed on second prototype in time for resumption of flight test duty in May 2002.

 

RAH66-Comm-03

 

The first combat helicopter designed from outset to have "stealth" features and target acquisition radar. Embodies low-observable (LO) attributes and stated to have radar cross-section (RCS) lower than that of Hellfire missile; frontal RCS reportedly 360 times smaller than AH-64, 250 times smaller than OH-58D and 32 times smaller than OH-58D with mast-mounted sight. Also has quarter of AH-64D’s IR emissions and is six times quieter, head-on. Maximum avionics commonality required with USAF Lockheed Martin F/A-22 Raptor programme.
RAH-66 specified empty weight of 3,402kg increased to 3,522kg by early 1992, as result of Army add-ons, including allowance for Longbow radar; mission equipment package has maximum commonality with F/A-22 Raptor technology. Design has faceted appearance for radar reflection; downward-angled engine exhausts; T tail with endplates; eight-blade fan-in-fin shrouded tail rotor; and five-blade all-composites bearingless main rntor system, with latter increased in diameter by 0.3m and gaining noise-reducing anhedral tips on forthcoming EMD aircraft. New rotor incorporating anhedral tips flown for first time on first prototype on 20 July 2001. RAH-66 also features internal weapon stowage.
Split torque transmission, obviating need for planetary gearing. Upper part of T tail folds down for air transportation. Detachable stub-wings for additional weapon carriage and/or auxiliary fuel tanks (EFAMS: external fuel and armament management system). Radar, infra-red, acoustic and visual signature requirements set to defeat threats postulated by US Army. Eight deploy able inside Lockheed C-5 Galaxy or four in Boeing C-17 Globemaster III with only removal of main rotor; ready for flight 20 minutes after transport lands. Combat turnround time 13 minutes.
Flight controls wree dual triplex fly-by-wire, with sidestick cyclic pitch controllers and normal collective levers. Main rotor blades removable without disconnecting control system.
A largely composites airframe and rotor system. Fuselage built around composites internal box-beam; non-load-bearing skin panels, more than half of which can be hinged or removed for access to interior (for example, weapons bay doors can double as maintenance work platforms). Eight-blade Fantail rear rotor operable with 12.7mm calibre bullet hits; or for 30 minutes with one blade missing. Main rotor blades and tail section by Boeing, forward fuselage and final assembly by Sikorsky.
Tailwheel type, retractable landing gear, with single wheel on each unit; main units retract aft, with tailwheel retracting forward. Main units can 'kneel' for air transportability.

A stealthy multi-sensor platform able to carry out scouting and attack missions, shoot down enemy helicopters and pass data directly to the Longbow Apache attack helicopter, slow funding of the programme encouraged more roles and capabilities to be added, increasing the weight and cost. An early plan envisaged procurement of as many as 5023 Comanches, later reduced to 1400, then 1213 and finally 650. As the numbers fell, the per-unit cost rose from $12.1 million to $58.9 million.


Armament was a General Dynamics stowable XM-301 three-barrel 20mm cannon in Giat undernose turret, with up to 500 rounds (320 rounds normal for primary mission) and either 750 or 1,500 rounds per minute firing rates. Aiming coverage of gun is +15 to -45° in elevation and ±120° in azimuth. Integrated retractable aircraft munitions system (IRAMS) features side-opening weapons bay door in each side of fuselage, on each of which can be mounted up to three Hellfire or six Stinger missiles or other weapons. Four more Hellfires or eight Stingers can be deployed from multiple carriers under tip of each optional stub-wing, or auxiliary fuel tank for self-deployment. Will be compatible with Starstreak and Mistral air-to-air missiles. Maximum of 56 Hydra 70mm FFARs or Sura D or Snora 81mm equivalents. All weapons can be fired, and targets designated, from push-buttons on collective and sidestick controllers.


Crewed by a Pilot (in front) and WSO in identical stepped cockpits, pressurised for chemical/biological warfare protection. Crew seats resist 11.6m/s vertical crash landing.


Powered by two LHTEC T800-LHT-801 turboshafts, each rated at 1,165kW. Transmission rating 1,639kW. Internal fuel capacity 1,142 litres. Two external tanks totalling 3,407 litres for self-deployment; total fuel capacity 4,548 litres. Additional fuel to be contained in two 424 litre tanks in side weapon bays, which in preliminary development in mid-1999. Main rotor tip speed 221m/s; 355rpm.


The Comanche had Stealth characteristics achieved by retractable undercarriage and weapons stubs, an angular shape and engine exhaust slots under the fuselage. The propeller hub was entirely covered, and the tail rotor was a ducted fan. The tail surfaces went through many changes to avoid problems with buffeting, eventually being reduced in size and having endplate fins. The 'flowerpot' on top of the second prototypes’ main rotor hub contained a version of the Longbow radar.


The US Department of Defence decided to keep the RAH-66 at the technology demonstrator level only.


The US Army cancelled the program on 24 February 2004 and give Bell a contract to build the ARH-70 based on the Bell 407.


In the end, the expenditure of $8 billion only achieved two flying prototypes and a partially completed test programme.

 

Boe-Sik-RAH66


RAH-66
Engines: 2 x LHTEC T800-LHT-801 turboshafts, 1,165kW.
Transmission rating 1,639kW.
Main rotor diameter: 12.19m
Main rotor tip speed: 221m/s
Main rotor rpm: 355rpm.
Tail rotor diameter: 1.37m
Overall length, rotors turning: 14.28m
Fuselage length, excl gun barrel: 13.20m
Height over tailplane: 3.37m
Empty weight: 4,218kg
Max useful load: 2,296kg
Internal fuel capacity 1,142 lt / 870kg
External fuel capacity: 3,407 litres
Max fuel capacity: 4,548 litres
Take-off weight, primary mission: 5601kg
Take-off weight, max alternative: 5850kg
Take-off weight (self deployment): 7896kg
Max level speed (without radar): 324km/h
Max level speed (with radar): 307km/h
Cruising speed (without radar): 306km/h
Cruising speed (with radar): 276km/h
Rate of climb (without radar): 273m/min
Rate of climb (with radar): 152m/min
Hovering ceiling IGE: 2,745m
Hovering ceiling OGE: 1,220m
Operational radius, internal fuel: 278km
Ferry range with external tanks: 2222km

 

 


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