The Kaman K-MAX (Company designation K-1200) is an American helicopter with intermeshing rotors (synchropter) built by Kaman Aircraft. It is optimized for external load operations, and is able to lift a payload of over 6,000 pounds, which is more than the helicopter's empty weight. A remote controlled unmanned aerial vehicleversion is being developed and in extended practical service in the war in Afghanistan.

Development
In 1947 Anton Flettner, a former German teacher and inventor, was brought to the United States as part ofOperation Paperclip.[1] He was the developer of the former German helicopter Flettner Fl 282 "Kolibri" (Hummingbird), which had the principle of counter-rotating side-by-side intermeshing (combing) rotors, as the means to solve the problem of torque compensation, normally countered in single rotor helicopters by a tail rotor or vented blower exhaust. Anton Flettner stayed 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 are 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 aircraft's narrow, wedge-shaped profile and bulging side windows gives the pilot a good view of the load looking out either side of the aircraft.

The transmission has a reduction ratio of 24 in three stages, and is designed for infinite life.The rotor blades are built with a wooden spar and fiberglass trailing edge sections. Wood was chosen for its damage tolerance, fatigue resistance and to take advantage of field experience and qualification data amassed from a similar spar on the HH-43 helicopter, built for the U.S. Air Force in the 1950s and 1960s.

The K-MAX relies on the two primary advantages of synchropters over conventional helicopters. The first of these is the increased efficiency compared to conventional rotor-lift technology; the other is 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, to scatter seed, chemicals, or water over a larger area.

A K-MAX has been used for demolition work by having a wrecking ball as sling load.

Thirty-eight K-1200 K-MAX helicopters have been built. As of February 2012, 13 of these were not airworthy or have been written off in accidents.[7] The production line was shut down in 2003, but may restart if the U.S. Marine Corps orders more autonomous K-MAXs.

Unmanned remote control version
An unmanned remote-control 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. 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.

In December 2011 an unmanned K-Max was reported to be at work in Afghanistan. On December 17, 2011, the United States Marine Corps conducted the first unmanned aerial system cargo delivery in a combat zone using an unmanned version of the Kaman K-MAX. The unmanned KMAX moved about 3,500 pounds of food and supplies to troops at Combat Outpost Payne.

As of February 2013, the K-MAX has delivered 2 million pounds of cargo in 600 unmanned missions, with over 700 flight hours.

A third unmanned K-MAX, based in the US, was tested in 2012 to deliver cargo to a small homing beacon with 3 meter precision.

On July 31, 2012, Lockheed announced a second service extension for the K-MAX in Afghanistan for the Marines. This extended operation time to the end of March 2013, with the option to extend through to the end of September 2013. On March 18, 2013, the Marine Corps extended their use of the unmanned K-MAX helicopters indefinitely. The Marines do not currently have plans to buy more, but the two aircraft in use will remain "until otherwise directed." At the time of this announcement, they had flown over 1,000 missions and hauled over 3 million pounds of supplies. Assessments for their use after deployment are being studied. While proving useful, their "niche" in future Marine Corps aviation is not yet clear.

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 is under investigation. Pilot error has been 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. On August 14, 2013, the Navy said the K-MAX could resume flying by the next week, with the final decision resting with operational commanders. The week before, the K-MAX flew 16 hours. No decision has been made on repairing the crashed model, while swing load is seen as the prime reason behind what caused the crash. The Marine Corps is considering turning the K-Max into a program of record, with possible uses including ship-to-shore deliveries.

At the 2013 Paris Air Show, Kaman promoted the unmanned K-MAX to foreign buyers. Several countries have reportedly expressed interest in the system.

The K-MAX supporting Marines in Afghanistan will remain in use there until at least August 2013. The Marine Corps is looking into acquiring the unmanned K-MAX as a program of record, and the U.S. Army is also looking into it to determine cost-effectiveness. If it would be accepted into service, the adapted commercial rotorcraft would re-enter production and reopen the facility to build it. Lockheed and Kaman estimate re-establishing the line would take nine months, with the first aircraft delivered three months later. In theater, the unmanned K-MAX performed most missions at night and successfully lifted loads of up to 4,500 lb (2,000 kg). Hook-ups of equipment are currently performed in concert with individuals on the ground, but Lockheed is looking into performing this action automatically. They are building a device that sits on top of the package that the helicopter can hook up to by itself. Other features are being examined, including the ability to be automatically rerouted in flight, and to fly in formation with other aircraft.