Helicopter With Dual-Crossing Rotors
26 August 2018
The Kaman K-MAX (company designation K-1200) is an American helicopter with intermeshing rotors (synchropter) by Kaman Aircraft. It is optimized for external cargo load operations, and is able to lift a payload of over 6,000 pounds (2,722 kg), which is more than the helicopter's empty weight. An unmanned aerial vehicle version with optional remote control has been developed and evaluated in extended practical service in the war in Afghanistan.
After being out of production for more than a decade, in June 2015 Kaman announced it was restarting production of the K-MAX due to it receiving ten commercial orders. The first flight of a K-MAX from the restarted production took place in May 2017 and the first new-build since 2003 was delivered on July 13, 2017 for firefighting in China.
Author: André Völzke (Wikimedia)
In 1947 Anton Flettner, a German aero-engineer, was brought to the United States as part of Operation Paperclip. He was the developer of the two earlier synchropter designs from Germany during World War II: the Flettner Fl 265 which pioneered the synchropter layout, and the slightly later Flettner Fl 282 Kolibri ("Hummingbird"), intended for eventual production. Both designs used the principle of counter-rotating side-by-side intermeshing rotors, as the means to solve the problem of torque compensation, normally countered in single–rotor helicopters by a tail rotor, fenestron, NOTAR, or vented blower exhaust. Flettner remained in the United States and became the chief designer of the Kaman company. He started to design new helicopters, using the Flettner double rotor.
The K-MAX series is the latest in a long line of Kaman synchropters, the most famous of which is the HH-43 Huskie. The first turbine-powered helicopter was also a Kaman synchropter.
The K-1200 K-MAX "aerial truck" is the world's first helicopter specifically designed, tested, and certified for repetitive external lift operations and vertical reference flight (Kaman received IFR Certification in 1999), an important feature for external load work. Other rotorcraft used for these tasks are adapted from general-purpose helicopters, or those intended to primarily carry passengers or internal cargo. The K-MAX can lift almost twice as much as the Bell 205 using a different version of the same engine. The aircraft's narrow, wedge-shaped profile and bulging side windows give the pilot a good view of the load looking out from either side of the aircraft.
The transmission has a reduction ratio of 24:1 in three stages, and is designed for unlimited life. The rotor blades (which turn in opposite directions) are built with a wooden spar and fiberglass trailing edge sections. Wood was chosen for its damage tolerance and fatigue resistance; and to take advantage of field experience and qualification data amassed from a similar spar on the HH-43 Huskie helicopter, built for the U.S. Air Force in the 1950s and 1960s. The pilot controls blade pitch with tubes running inside the mast and rotor blades to move servo flaps that pitch the blades, reducing required force and avoiding the added weight, cost and maintenance of hydraulic controls.
The K-MAX relies on two primary advantages of synchropters over conventional helicopters: The increased efficiency compared to conventional rotor-lift technology; and the synchropter's natural tendency to hover. This increases stability, especially for precision work in placing suspended loads. At the same time, the synchropter is more responsive to pilot control inputs, making it possible to easily swing a load, or to scatter seed, chemicals, or water over a larger area.
Thirty-eight K-1200 K-MAX helicopters had been built by 2015. As of January 2015, 11 of these were not airworthy or had been written off in accidents and five were in storage at Kaman; and in March 2015 the number of operational K-MAXs was 21. The production line was shut down in 2003.
Kaman had been developing the Unmanned K-MAX since 1998. In March 2007, Kaman and Lockheed Martin (Team K-MAX) signed a Strategic Relationship Agreement (SRA) to pursue U.S. DoD opportunities. An unmanned mostly autonomously flying, optionally remote controlled and optionally piloted vehicle (OPV) version, the K-MAX Unmanned Multi-Mission Helicopter was developed for hazardous missions. It can be used in combat to deliver supplies to the battlefield, as well as civilian situations involving chemical, biological, or radiological hazards.
Author: Cpl. Justin M. Boling (U.S. federal government)
A prototype of this was shown in 2008 for potential military heavy-lift resupply use, and again in 2010. In December 2010 the Naval Air Systems Command awarded a $46 million contract to Kaman for two aircraft, and in 2011 they completed a five-day Quick Reaction Assessment.
RESTART OF PRODUCTION LINE
In February 2014, Kaman revisited resuming K-MAX production, having recently received over 20 inquiries for firefighting, logging and industry transport requirements as well as requests for the military unmanned version. Ten firm orders convinced Kaman to put the design back into production again. As of 2014, the K-MAX line had flown 300,000 hours and cost $1,200 per flight hour to operate.
At Heli-Expo 2015 in Orlando, Kaman reported it continued toward reopening the production line building 10 aircraft. Kaman received deposits and the assembly line was restarted in January 2017. Kaman test flew the first K-MAX from restarted production on May 12, 2017.
The first new-build since 2003 was delivered on July 13, 2017 to Kaman’s Chinese sales agent Lectern Aviation, which will deliver it to Guangdong Juxiang General Aviation, Guangdong Province for firefighting as the second is to be delivered the following week. Due to production scheduling, Kaman needed to decide in 2017 whether to extend production beyond the first 10, and Kaman made the decision in June 2017 to produce a further 10 aircraft, reaching into at least 2019.
A K-MAX has been used for demolition work by having a wrecking ball as a slung load.
In December 2011, an unmanned K-MAX was reported to be at work in Afghanistan. On 17 December 2011, the U. S. Marine Corps conducted the first unmanned aerial system cargo delivery in a combat zone using the unmanned K-MAX, moving about 3,500 pounds of food and supplies to troops at Combat Outpost Payne. A third unmanned K-MAX in the U.S. was tested in 2012 to deliver cargo to a small homing beacon with three-meter precision. As of February 2013, the K-MAX had delivered two million pounds of cargo in 600 unmanned missions over more than 700 flight hours.
On July 31, 2012, Lockheed announced a second service extension for the K-MAX in Afghanistan for the Marines, then on 18 March 2013 the Marine Corps extended its use of the unmanned K-MAX helicopters indefinitely, keeping the two aircraft in use "until otherwise directed". At the time of the announcement, they had flown over 1,000 missions and hauled over three million pounds of supplies. Assessments for their use after deployment were being studied. The unmanned K-MAX has won awards from Popular Science and Aviation Week & Space Technology, and was nominated for the 2012 Collier Trophy.
On June 5, 2013, one of the unmanned K-MAX helicopters crashed in Afghanistan while resupplying Marines. No injuries occurred and the crash was investigated. Pilot error was ruled out, as the aircraft was flying autonomously to a predetermined point. The crash happened during the final stages of cargo delivery. Operational flights of the remaining unmanned K-MAX were suspended following the crash, with the Navy saying it could resume flying by late August. Swing load was seen as the prime cause. The investigation determined that the crash was not caused by mechanical problems, but by unexpected tailwinds. As the helicopter was making the delivery, it experienced tailwinds instead of headwinds, causing it to begin oscillating. Operators employed a weathervane effect to try and regain control, but its 2,000 lb load began to swing, which exacerbated the effect and caused it to contact the ground. The crash report determined that it could have been prevented if pilots intervened earlier and mission planners received updated weather reports; diverging conditions and insufficient programming meant it could not recover on its own and required human intervention.
At the 2013 Paris Air Show, Kaman promoted the unmanned K-MAX to foreign buyers. Several countries reportedly expressed interest in the system. The K-MAX supporting Marines in Afghanistan was planned to remain in use there until at least August 2014. The Marine Corps was looking into acquiring the unmanned K-MAX as a program of record, and the United States Army was also looking into it to determine cost-effectiveness. In theater, the aircraft performed most missions at night and successfully lifted loads of up to 4,500 lb (2,000 kg). Hook-ups of equipment were performed in concert with individuals on the ground, but Lockheed was looking into performing this action automatically through a device mounted atop the package that the helicopter can hook up to by itself; this feature was demonstrated in 2013. Other features were being examined, including the ability to be automatically re-routed in flight, and to fly in formation with other aircraft. The unmanned K-MAX was successfully able to deliver 30,000 lb (13,600 kg) of cargo in one day over the course of six missions (average 5,000 lb (2,270 kg) transported cargo per mission). Lockheed and Kaman discussed the purchasing of 16 helicopters with the Navy and Marine Corps for a baseline start to a program.
The unmanned K-MAX competed with the Boeing H-6U Little Bird for the Marine Corps unmanned lift/ISR capability. In April 2014, Marines at Quantico announced they successfully landed an unmanned K-MAX, as well as a Little Bird, autonomously using an iPad-like mini-tablet. The helicopters were equipped with Autonomous Aerial Cargo/Utility System (AACUS) technology, which combines advanced algorithms with LIDAR and electro-optical/infrared sensors to enable a user to select a point to land the helicopter at an unprepared landing site. The Office of Naval Research selected Aurora Flight Sciences and the Unmanned Little Bird to complete development of the prototype AACUS system, but Lockheed continued to promote the K-MAX and develop autonomous cargo delivery systems.
Both unmanned K-MAX helicopters in use by the Marine Corps returned to the U.S. in May 2014, when the Corps determined that they were no longer needed to support missions in Afghanistan. After deploying in December 2011, originally planned for six months, they stayed for almost three years and lifted 2,250 tons of cargo. The aircraft were sent to Lockheed's Owego facility in New York, while the service contemplated the possibility of turning the unmanned K-MAX from a proof-of-concept project into a program of record. Formal requirements for unmanned aerial cargo delivery are being written to address expected future threats, including electronic attack, cyber warfare, and effective hostile fire; these were avoided in Afghanistan quickly and cheaply by flying at night at high altitudes against an enemy with no signal degradation capabilities. Officials assessed the K-MAX helicopter that crashed and planned to repair it in 2015. The helicopters, ground control stations, and additional equipment are stored at Lockheed's facility in Owego. The two unmanned K-MAXs, designated CQ-24A, were to be moved to a Marine Corps base in Arizona by the end of September 2015 to develop tactics and operations concepts to inform an official program of record for a cargo UAV.
Lockheed Martin demonstrated a fire fighting version in November 2014, and again in October 2015, when it delivered over 24,000 pounds (11,000 kg) water in one hour. A casualty evacuation exercise was performed in March 2015 in coordination with an unmanned ground vehicle and mission planning system. A medic launched the UGV to evaluate the casualty, used a tablet to call in and automatically land the K-MAX, then strapped a mannequin to a seat aboard the helicopter.
Capacity: 6,000 lb (2,700 kg) external load
Length: 51 ft 10 in (15.8 m)
Rotor diameter: 48 ft 3 in (14.71 m)
Height: 13 ft 7 in (4.14 m)
Empty weight: 5,145 lb (2,334 kg)
Useful load: 6,855 lb (3,109 kg)
Max. takeoff weight: 12,000 lb (5,400 kg)
Powerplant: 1 × Honeywell T53-17 turboshaft, 1,341 kW (1,800 shp), flat rated to 1,118 kW (1,500 shp) for take-off / 1,350 shp in flight)
Maximum speed: 100 knots (185 km/h, 115 mph)
Cruise speed: 80 knots (148 km/h, 92 mph)
Range: 267 nmi (495 km, 307 miles)
Service ceiling: 15,000 feet (4,600 m)
Fuel consumption: 85 gallons/hour
|Written by: Laura Cozzo|