The latest and most original helicopter to be designed and produced by Kaman is the K-MAX "Aerial Truck" which first flew on 23 December 1991.

By February 1995 the helicopter had gained certification in the United States and Canada and had amassed over 2000 hours on type. During 1994, the first five production K-Max had been delivered to customers and were meeting their objectives of low operating costs with high reliability and low maintenance.

The K-MAX is the first helicopter specifically designed, tested and certified for repetitive external lift operations such as logging, fire fighting, construction, reforestation and oil/mineral exploration. K-MAX is based around Kaman's unique intermeshing "Synchro-Lift" rotor technology using counter-rotating main rotors and servo-flap system with no tail-rotor, ensuring that all the power goes directly to the rotors for lift.

Powered by a single Textron-Lycoming T5317A-1 gas turbine, a commercial variant of the 1800shp T53-L-703 used by the military, the K-MAX powerplant has been derated to 1500shp to make it compatible with the transmission and to ensure longer engine life.

Designed for single-pilot operation with no room for passengers, the cockpit provides the pilot with unsurpassed visibility for external lift activities. K-MAX weighs 2120kg empty and will lift a 2255kg external load to 2400m with plenty of power to spare.

P.Allen "The Helicopter", 1996

First flight (N3182T) 23 December 1991; first public showing 22 March 1992; first flights of second prototype (N131KA) 18 September 1993 and first production aircraft (N132KA) 12 January 1994; third prototype is static and drop test aircraft to prove 20 year life at 1,000 hours per year and with 30 return logging sorties per hour. Certification to FAR Pts 27 and 133 achieved 30 August 1994 after 800 hour/32 month programme. N133KA of Scott Paper (now Kimberly-Clark) achieved 1,000 hours in eight months, 22 June 1995, as first K-MAX to reach this total. Canadian certification awarded 23 November 1994; now certified in Australia, Austria, Canada, Ecuador, Germany, Japan, New Zealand, Switzerland, Taiwan and USA. Uses include logging, firefighting, agricultural spraying, constructing and surveying.

A US$690,000 contract to demonstrate Vertrep (Vertical Replenishment) to US Navy awarded August 1995: two month demonstration period saw two K-MAXs (c/n 0010 and 0013) lift 453,592kg with follow-on assessment in Guam during May 1996 during which 142 hours were flown and 2,449,400kg was lifted. Two helicopters then began US$5.7 million six-month deployment in Arabian Gulf on 3 June 1996 aboard USS Niagara Falls. During late August 1998, the prototype K-MAX was involved in trials for Magic Lantern mine detection systems. FAA Pt 27 IFR certification received 14 May 1999 as part of bid for US Navy Vertrep contract. In November 2001, on behalf of the US Naval Undersea Warfare Center at Newport, Rhode Island, the K-MAX recovered more than two dozen torpedoes used during exercises in local waters. On 14 July 1999 USMC placed contract worth US$4.2 million for remote piloting package and another worth US$2.7 million to May 2000;

Kaman received certification for an external seat in June 1999; up to two may be fitted.

CUSTOMERS: Kaman moved from its original helicopter lease programme to a sales programme, but reinstated leasing arrangements in 2002, with Eagle Helicopters (Switzerland) and Superior Helicopters (Oregon) becoming lease customers shortly afterwards. Current operators (at July 2003) include Mountain West, Woody Contracting, Superior Helicopter (four), Petroleum Helicopters, Rainier Heli-Lift and Midwest Helicopters in USA; Cariboo Chilcotin and MacKenzie Heli Services in Canada; Helog of Switzerland; Japan Royal Helicopters (two); Rotex Helicopters AG of Lichtenstein; and Wucher Helikopter of Austria.

A K-MAX operated by Woody Contracting was the first to exceed 10,000 flying hours (increased to more than 14,000 hours by mid-2003). In December 2000, US State Department ordered five; these delivered in 2002, and in mid-2003 were performing logistics support for anti-drug operations in Colombia. Total of 38 delivered by July 2003.

COSTS: US$4.1 million (2003).

DESIGN FEATURES: Kaman intermeshing, contrarotating rotors ensure all engine power produces lift; rotor disc loading is very low and airspeed is limited to reduce rotor stresses; all internal spaces painted white and provided with lights to ease night-time servicing; freight compartment beneath transmission casing allows carriage of special tools or parts; no hydraulics; transmission and engine fluid lines located on opposite sides of helicopter to avoid servicing errors; fuselage is narrow to give good downward view; panels in domed side windows can be opened to give direct vision or doors can be removed altogether. Electronic engine instruments and hook load measuring sensor record engine cycles and exceedances, but also give the pilot an immediate record of operations for billing purposes, avoiding paperwork for pilot. Lead-lag stops can be removed so that blades are folded fore and aft for parking in narrow spaces.

Normal rotor rpm is 270, giving maximum blade tip speed of 200m/min; translational lift is attained at 22km/h; rpm reduced to 200 for autorotation and airspeed of 92km/h then gives a power-off descent rate of 366 to 427m/min.

FLYING CONTROLS: Blade angle of attack controlled by trailing-edge flaps and light control linkage, avoiding need for hydraulic power; an electric actuator on each rotor is operated by pilot to track the blades on ground or in flight.

In normal powered flight, turns at or near the hover are effected by applying differential torque to the rotors by means of differential collective pitch commanded from the foot pedals; a small fore-and-aft cyclic pitch change also occurs; at low powers near autorotation, this would produce directional control reversal, because differential collective pitch change would cause drag on the unwanted side; so a non-linear cam between collective lever and rotor blade controls phases out differential collective from a 'dwell zone' at about 25% collective demand and replaces it progressively with differential cyclic.

Intermeshing rotors cause pronounced pitch attitude change in response to collective pitch change; the K-MAX tailplane is connected to collective to alleviate this, to reduce blade stresses and produce touchdown and lift-off in level attitude; fixed fins on tailplane are in rotor downwash and rear fin is outside rotor discs; rudder is connected to foot pedals to help balance turns.

STRUCTURE: Semi-monocoque fuselage constructed from 2024T-3 and T-4 aluminium; GFRP and CFRP rotor blades and flaps. Tail assembly weighs 36.3kg and can be removed quickly by two people. Rotor blades fold to fore and aft.

LANDING GEAR: Fixed, tricycle; nosewheel is out of pilot's field of view; impact sustaining suspension with transverse mounting tube for mainwheels; rubber-in-compression suspension for mainwheels; oleo for nosewheel; bear paw plate round each wheel for operation from soft ground and snow; nosewheel swivels and locks; mainwheels have individual foot-powered brakes and parking brake.

POWER PLANT: One 1,119kW Honeywell T53- 17A-1 turboshaft (civil equivalent of military T53-L-703), with particle separator; flat rated at 1,007kW for take-off up to approximately 8,875m. Transmission designed for 1,119kW, but operated at 1,007kW with a 10,000 hour life with 3330 hour overhaul intervals.

Fuel capacity 865 litres located at aircraft CG of which 831 litres usable. Hot refuelling capable; dual electric fuel pumps. Oil capacity 12.1 litres in both engine and transmission tanks. Cargo compartment can accommodate a 238.5 litre auxiliary fuel tank for approximately 1 hour additional endurance.

ACCOMMODATION: Pilot only, in Simula crash impact-absorbing seat with five-point harness; external seats for one passenger per side can be attached rapidly immediately ahead of the mainwheel legs. Pilot's seat and rudder pedals adjustable; heater and windscreen demister; doors removable for operation in hot weather; curved windscreen. Tool/cargo compartment 0.74m³ fitted with 2,268kg stress tiedown rings.

SYSTEMS: DC electrical system with starter/generator; no hydraulics.

EQUIPMENT: Pilot-controlled swivelling landing light; standard configuration is for lifting slung loads, but fittings provided for 2,650 litre capacity, twin-barrel IFEX 3000 water cannon, which can fire 18 or 25 litres per shot and can traverse 90 to 180°. Kits planned for patrol, firelighting tank and snorkel system, agricultural applications and similar missions.

Jane's All the World's Aircraft, 2004-2005

- The K-MAX was originally known as MMIRA (pronounced 'Myra') for Multi- Mission Intermeshing Rotor Aircraft.

- The US Navy evaluated the type for use in resupplying warships at sea.

- In 1996 the price for one of these helicopters was $3.5 million.

- The K-MAX was the first helicopter structurally designed for repetitive external lift operations.

- Production rate at Kaman's Connecticut factory in 1996 was six per year.

- Kaman claims a 20-year life for K-MAX's airframe, at 1,000 hours per year.