Designed and built by Rudy J. Enstrom, the Enstrom F-28 light helicopter was flown in experimental form on 12 November 1960 as a two-seat machine with a two-bladed main rotor and an un-skinned tubular rear fuselage. It was followed into the air, on 26 May 1962, by the first of two three-seat pre-production examples, and the production version appeared in the autumn of 1963. Powered by a 134kW Avco Lycoming O-360-A1A engine, it had a three-bladed main rotor and a light alloy and glassfibre cabin section with an all-metal semi-monocoque tail boom.

VARIANTS

F-28A: introduced in 1968, the F-28A was powered by a 153kW Avco Lycoming HIO-360-C1A engine; production was discontinued in February 1970, when the R. J. Enstrom Corporation ceased operations, but restarted in 1971 when reformed as the Enstrom Helicopter Corporation

280 Shark: developed in 1973 as a luxury version of the F-28A, the Shark introduced a more streamlined cabin-section, dorsal and ventral vertical tail surfaces with small endplate fins at the ends of the small horizontal tailplanes; standard fuel capacity was increased to 151 litres; FAA certification was achieved in September 1974

F-28C/280C: improved versions, introduced in 1975, powered by the 153kW Avco Lycoming HIO-360-E1AD engine with a Rajay 301-E-10-2 turbocharger; the tail rotor was moved to the port side of the fuselage and the direction of rotation reversed; the F-28C-2 introduced a one-piece windscreen and a pedestal central instrument console for improved forward and downward vision. Production ceased in Novembr 1981.

F-28F Falcon/280F: FAA certificated in January 1981, the F-28F and 280F were powered by the turbocharged 168kW Avco Lycoming. HIO-360-F1AD engine

F-28F-P Sentinel: dedicated police version of Model 280F developed for Pasadena Police Department, and fitted with special equipment including a searchlight. First delivery in October 1986

280FX: updated version of the Model 280F fitted with faired landing gear, redesigned vertical and horizontal tail surfaces, covered tail rotor shaft and tail rotor guard. First flown in December 1983 and certificated in January 1985. Export customers include the Chilean army which bought 15

280L Hawk: work on a four-seat version of the 280C began in January 1978 and a prototype was first flown on 27 December 1978. The main rotor diameter was increased by 0.61m and the fuselage lengthened by 0.91m. Powerplant of the F-28F/280F was retained and fuel capacity increased to 170 litres. However, full development was postponed indefinitely in 1983 following a change in company ownership

Spitfire Mk 1: developed by the Spitfire Helicopter Company of Lynnfield, Massachusetts, from the basic Enstrom F-28A design, the Spitfire Mk 1 appeared in 1976, powered by a 313kW Allison 250-C20B turboshaft

D.Donald "The Complete Encyclopedia of World Aircraft", 1997

Enstrom Helicopter Corporation was established in 1959 to develop and produce light helicopters, based on Rudy Enstrom's initial design work. Extensive development and certification efforts led to start of production of the F28 helicopter in April 1965; development of turbine-powered model was initiated in 1988, culminating in certification of the TH28 in September 1992 and the 480, to FAR Pt27 standards, in December 1994.

ENSTROM F28F and 280FX

TYPE: Three-seat helicopter.

PROGRAMME: Prototype F28 flew 12 November 1960. Basic F28A and 280 replaced by turbocharged F28C and 280C, certified by FAA 8 December 1975; production of these models ceased November 1981; succeeded by F28F and 280F Shark.

CURRENT VERSIONS:

• F28F Falcon: Basic model certified to FAR Pt 6 on 31 December 1980. The two major changes incorporated into the F28F and 280F/280FX over the earlier F28C/280C series were an increase in power from 153kW to 168kW and the addition of a throttle correlator to reduce pilot workload. Most recent changes to the F28F and 280FX are the redesigned main gearbox with a heavy wall main rotor shaft (standard equipment on all new aircraft and retrofittable to all existing F models); optional lightweight exhaust silencer, which reduces noise in the hover by 40% and gives a 30% reduction when flying at 152m (can also be retrofitted to F28F, 280F and 280FX); and a lightweight starter motor.
• F28F-P Sentinel: Dedicated police patrol version; first delivery October 1986; can be fitted with a PA and siren system, Spectrolab SX-5 or Carter searchlight, specialised police equipment, FLIR and datalink. F28F-P has same specification and performance as F28F. No recent production.
• 280FX Shark: Certified to FAR Pt 6 on 14 January 1985. Prototype N280FX. Improvements over previous 280 series include new seats with lumbar support and energy-absorbing NASA foam, new tailplane with endplate fins, tail rotor guard, covered tail rotor drive shaft, redesigned air inlet system, and completely faired landing gear. Optional internal auxiliary fuel tank extends range to 627km.

CUSTOMERS: Total of 735 of earlier versions (14 F28, 315 F28A, 121 F28C, 56 F28C-2, 21 280, 206 280C and two 280L). Last of 135 F28F delivered 1999 to Fresno Police Department, California, but further nine produced in 2002 and 2003. Total of 98 280FX built up to mid-2003, increasing Enstrom piston-engined helicopter production to 966; further two 280 registered in early 2003, Chilean Army operates 15 280FX for primary and instrument training; Peruvian Army has 10 F28F for flight training; Colombian Air Force operates 12 F28F for primary and instrument training, Numerous US police departments operate F28F-P for patrol and surveillance missions. Most recent military customer is the Venezuelan National Guard, which took delivery of four 280FX for training in January 2002.

COSTS: Basic 2004 price US$320,000 for F28F Falcon and 280FX Shark.

DESIGN FEATURES: Conventional light helicopter with skid landing gear and tubular metal tail rotor protector; horizontal stabiliser with fins at tips. High inertia, three-blade fully articulated rotor head with blades attached by retention pin and drag link; control rods pass inside tubular rotor shaft to swashplate inside fuselage; no rotor brake: blade section MAC A 0013.5; blades do not fold; two-blade teetering tail rotor. Thirty-groove belt drive from horizontally mounted engine to transmission.

FLYING CONTROLS: Conventional and manual. Trim system absorbs feedback from rotor and repositions stick datum as required by pilot.

STRUCTURE: Bonded light alloy blades. Fuselage has glass fibre and light alloy cabin section, steel tube centre-section frame, and stressed skin aluminium tailboom.

LANDING GEAR: Skids carried on Enstrom oleo-pneumatic shock-absorbers. Air Cruiser inflatable floats available optionally.

POWER PLANT: One 168kW Textron Lycoming HTO-360-F1AD fiat-four engine with Rotomaster 3BT5EE10J2 turbocharger. Two fuel tanks, each of 79.5 litres. Total standard fuel capacity 159 litres, of which 151 litres are usable. Auxiliary tank, capacity 49 litres, can be installed in the baggage compartment. Oil capacity 9.5 litres.

ACCOMMODATION: Pilot and two passengers, side by side on bench seat; centre place removable. Removable door on each side of cabin. Baggage space aft of engine compartment, with external door. Cabin heated and ventilated.

SYSTEMS; Electrical power provided by 24V 70A engine-driven alternator; 12V 70A system optional. No hydraulic system.

AVIONICS: Variety of fits from Honeywell and other avionics suppliers.
Instrumentation: Standard equipment includes airspeed indicator, sensitive altimeter, compass, outside air temperature gauge, turn and bank indicator, rotor/engine tachometer, manifold pressure/fuel flow gauge, EGT gauge, oil pressure gauge, gearbox and oil temperature gauge, ammeter, cylinder head temperature gauge, and fuel quantity gauge. Eight-light annunciator panel consisting of low rotor rpm, chip detectors (main and tail rotor transmissions), overboost, clutch not fully engaged, low fuel pressure, starter and low-voltage warning lights.

EQUIPMENT: Shoulder harnesses for three seats. Night lighting is optional for F28F and standard on 280FX. Night lighting includes instrument lighting with dimmer control, position light on each horizontal stabiliser tip, anti-collision light and nose-mounted landing light. Optional equipment for both F28F and 280FX includes fixed float kit, wet or dry agricultural spray kit and cargo hook for utility missions. Wide instrument panel available for IFR training.

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

The R J Enstrom Corporation was established in 1959 to produce and then market in developed form an experimental light helicopter designed by Rudolph Enstrom. The experimental machine first flew on November 12, 1960, and resulted in a development programme to evolve the F-28 production model, the prototype of which first flew in 1962.

Production of the F-28 began in 1963, and a limited number of this type were built before the improved F-28 A appeared in 1968. In October of that year Enstrom was bought by the Purex Corporation as part of its Pacific Airmotive Aerospace subsidiary. The new owners continued development of the F-28 type, producing the F-28B with a turbocharged piston engine, and the T-28 with a turbine engine.

In January 1971 the Purex Corporation sold the Enstrom helicopter company to F Lee Bailey, and under this new ownership, the Enstrom Helicopter Corporation restarted manufacture of the definitive F-28A light helicopter with the 500th helicopter delivered during June 1977.

The F-28A is an interesting but in no way remarkable light helicopter, its useful performance depending on light structure weight and careful streamlining rather than brute power. The forward fuselage, consisting of the extensively glazed compartment for the pilot and two passengers seated side-by-side on a bench seat, is made of light alloy and glassfibre. The centre section of the fuselage, accommodating the engine, transmission and fuel tanks, as well as providing anchorage points for the steel-tube undercarriage skids, is more substantially built of steel tube. The rear fuselage, carrying small vertical tail surfaces and the two-blade teetering tail rotor of bonded light alloy construction, is a semi-monocoque structure basically conical in shape and built of aluminium.

The 205shp Lycoming HIO-360-CIB piston engine is located in the centre fuselage, and fed from two fuel tanks with a total usable capacity of 151.4 litres. The engine's output is led through a right-angle reduction gearbox to drive the main rotor through a Poly V-belt drive. The main rotor is situated at the top of a tall rotor mast, and is a three-blade fully articulated unit with blades of bonded light alloy construction.

Since its inception, the basic F-28 has been the subject of numerous improvement programmes, with the result that in 1980 there were seven models currently in production or under development. The first of these is the basic F-28A. The Model 280 Shark is an improved F-28A, with revised nose contours of better aerodynamic shape, a larger dorsal fin, horizontal tail surfaces, and increased standard fuel capacity.

The F-28C is based on the F-28A, but is powered by the 205shp Ly coming HIO-360-E1AD piston engine fitted with a Rajay 301 E-10-2 turbocharger; unlike the F-28A and 280 Shark, the F- 28C introduces a tail rotor on the left side of the tail rotating in the opposite direction to the rotors of its two preceding models. The Model 280C Shark is basically the F-28C equivalent of the 280 Shark.

The F-28F Falcon is based on the F-28C but incorporates a one-piece windscreen and pedestal-type instrument panel to improve the pilot's downward view; maintenance has been simplified, and power is provided by a 225shp Lycoming engine. The Model 280L Hawk is a four-seat development of the 280C Shark. Finally, the Model 480 Eagle is a development of the 280L Hawk, with seating for five and power provided by the Allison 250-C20B turboshaft.

Although the Enstrom helicopters are intended mainly for light passenger operations, the F-28C and Model 280C can be used in the agricultural role with two side-mounted chemical hoppers and their associated spraybooms. Liquid chemical capacity is 340 litres, and powder chemical capacity 0.5m³.

Bill Gunston "The Illustrated Encyclopedia of Commercial Aircraft", 1980

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- First flight of the Enstrom Shark was on 26 May, 1962. it was the first of two three-seat pre-production models.

- The helicopter features a light alloy and glass-fibre cabin section.

- The US Army has shown an interest in the design, as a training helicopter.

- Military versions of the Shark serve with the Chilean and Peruvian armies as observation helicopters.

- A four-seat version was developed and flew in 1978; it was called the Hawk.

- The most recent development of the Shark is the five-seat Eagle.