A 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 are conventional and manual. Trim system absorbs feedback from rotor and repositions stick datum as required by pilot.

The F-28A 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.

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

Skids carried on Enstrom oleo-pneumatic shock-absorbers. Air Cruiser inflatable floats available optionally.
One 168kW Textron Lycoming HTO-360-F1AD flat-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.
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.
Electrical power provided by 24V 70A engine-driven alternator; 12V 70A system optional. No hydraulic system.

Shoulder harnesses for three seats. Night lighting is optional for F28F. 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.

The two-seat prototype of the F-28 was flown first on 12 November 1960 with a two-bladed main rotor and an un-skinned tubular rear fuselage, followed by the first of two three-seat production prototypes on 26 May 1962. Initial FAA certification was achieved for the F-28 model in April 1965 and deliveries began in 1965. 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. Enstrom sold only nine F-28s before being purchased by the Purex Corporation in early 1968. An improved version of the F 28, powered by a 205 hp Lycoming H10 360 C1B and called the F 28A, was certificated in May 1968. Production of the three seat F-28A started in 1967 but only 35 were sold before Purex suspended all operations in February 1970.

The F 28A uses a normally aspirated 205 hp engine. The main rotor blades are of bonded construction and have no time limit, mainly be¬cause the F 28 rotor system originally was designed to be rigid in plane, so the blades are heavier and experience lower working stress levels than if the F 28 had been de¬signed initially to employ its present fully articulated three blade system.

The F 28A offers a cruise speed of 87 knots. Enstrom offers an option, called a throttle correlator, that is designed to facilitate throttle/collective coordination. It employs a cam like arrangement that partially couples the collective and throttle, but even the folks at Enstrom did not recommend it with much enthusiasm.

The rugged rotor system of the Enstrom gives the F 28A a heavier cyclic, or attitude, control feel than is found on other light helicopters, such as the Hughes 300. By fixed wing standards, however, the control pressures are low. The somewhat heavier cyclic control force characteristics combine with a fairly large, six inch offset in the flapping hinge to give the F 28A a nice harmony between stability and control over an allowable CG range of six inches. When the helicopter is disturbed either by a gust or a sudden cyclic control input, the F 28A experiences an initial divergence in roll or pitch but not the wild type of response that is frequently imagined to exist with helicopters. An electric pitch and roll trim, which is operated by a thumb switch on the cyclic stick, allows a pilot to remove residual control forces and establish a hands ¬off trim condition in cruising flight.

Because of its heavier rotor blades (at 51 pounds each, they are nearly twice the weight of those on the Hughes 300C), the F 28A does not gain lost rotor rpm as quickly as does a helicopter with a lighter rotor system. The higher inertia of the Enstrom rotors, however, does enable the F 28A to hold its rpm longer, at times when the pilot may need to use the rotational energy stored in the whirling rotor system.

In 1976 the improved F-28C was produced. The basic F28A and 280 were replaced by turbocharged F28C and 280C, certified by FAA 8 December 1975.A turbocharged conversion by Enstrom maintains full rated power up to 12,000 ft. Fixed waste gate Rajay 301-E-10-2 turbocharging on the Enstrom’s 153kW / 205 hp Lycoming HIO 360-E1AD engine enables the F 28C and the 280C to lift their 2,400 pound gross weights at density altitudes up to 13,000 feet. In addition to the turbocharging, Enstrom shifted the tail rotor from the right to the left side of the tail boom, thus placing the anti torque device where it reacts more favorably with the main rotor’s downwash and, therefore, is more effective. A tail rotor blade with a wider chord has been tested and is being retrofitted to all C models of the F 28 and the Shark 280. The FAA has approved the modification.

The F-28C-2 introduced a one-piece windscreen and a pedestal central instrument console for improved forward and downward vision. The 500th helicopter was delivered during June 1977. Production ceased in Novembr 1981, succeeded by the F28F.

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 0.5cu.m.

F-28F Falcon/280F was FAA certificated in January 1981, powered by the turbocharged 168kW Avco Lycoming HIO-360-F1AD engine. The basic F28F Falcon model was certified to FAR Pt 6 on 31 December 1980. The two major changes were incorporated into the F28F and 280F/280FX over the earlier F28C/280C series were an increase in power from 153kW to 168kW / 225shp and the addition of a throttle correlator to reduce pilot workload. 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.

A dedicated police version of Model 280F, the F-28F-P Sentinel, was developed for the Pasadena Police Department, and fitted with special equipment including a searchlight. First delivery was in October 1986.
The development of a turbine-powered model was initiated in 1988, culminating in certification of the TH28 in September 1992.

The T-28 experimental version featured a 240 shp AiResearch TSE 36-1 turboshaft engine, increased fuel, larger diameter tail rotor, and a new transmission system.

Customers total 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, 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.

The basic 2004 price was US$320,000 for F28F Falcon and 280FX Shark.

Gallery

F-28

F-28A
Engine: Lycoming HIO-360-C1A, 205 hp.
Main rotor dia: 32 ft / 9.75 m
Disc loading: 2.67 lb/sq.ft.
Pwr loading: 10.48 lb/hp.
Length: 29 ft 6 in / 8.99 m
Cabin max width: 5 ft 1 in / 1.55 m
Empty wt: 1450 lb / 657 kg
Max wt: 2150 lb / 975 kg
Equipped useful load: 642 lb.
Payload max fuel: 402 lb.
Max sling load: 500 lb.
Range max fuel/ cruise: 204 nm/2.1 hr.
Range max fuel / range: 240 nm/ 237 mi / 381 km / 3.3 hr.
Luggage cap: 7 cu.ft or 60 lbs.
Vne: 98 kts.
Cruise: 87 kt / 100 mph / 161 kph
Max cruise: 93 kt.
Max range cruise: 74 kt.
Service ceiling: 12,000 ft / 3660 m
Hover IGE: 5600 ft.
ROC: 950 fpm / 290 m/min
Best climb/glide speed: 58 kts.
Fuel cap: 240 lb / 30 USG.
Endurance: 2.5 hr.
Baggage hold: 8 cu ft / 0.33 cu m
Seats: 3.

F-28B
Engine: Lycoming TIO-360, 275 hp

Enstrom F-28C
Engine: 1 x Avco Lycoming HIO-360-E1BD, 153kW
Main rotor diameter: 9.75m
Length: 8.94m
Height: 2.79m
Max take-off weight: 1066kg
Empty weight: 680kg
Max speed: 180km/h
Cruising speed: 172km/h
Ceiling: 3660m
Range: 435km
Crew: 1
Passengers: 1

F-28C-2 Falcon
Engine: Lycoming HIO-360-E1AD, 205 hp.
TBO: 1000 hrs.
Main rotor: 32 ft.
Seats: 3.
Length: 28.2 ft.
Height: 9.2 ft.
Max ramp weight: 2350 lbs.
Max takeoff weight: 2350 lbs.
Max wt (100mph restriction): 2500 lbs.
Max wt (90mph restriction): 2600 lbs.
Standard empty weight: 1562 lbs.
Max useful load: 788 lbs.
Max landing weight: 2350 lbs.
Max sling load: 800 lbs.
Disc loading: 2.9 lbs/sq.ft.
Power loading: 11.5 lbs/hp.
Max usable fuel: 240 lbs.
Max rate of climb: 1200 fpm.
Service ceiling: 12,000 ft.
Hover in ground effect: 9700 ft.
Hover out of ground effect: 6000 ft.
Max speed: 97 kts.
Normal cruise @ 3000 ft: 90 kts.
Fuel flow @ normal cruise: 78 pph.
Endurance @ normal cruise: 2.9 hr.
Max range cruise: 74 kt
Range max fuel / range: 196 nm/ 2.7 hr
Range max fuel/ cruise: 178 nm/1.9 hr

F-28F
Engine: Lycoming HIO-360-F1AD, 225 hp.
TBO: 1000 hrs.
Main rotor: 32 ft.
Seats: 3.
Length: 28.2 ft.
Height: 9.2 ft.
Max ramp weight: 2600 lbs.
Max takeoff weight: 2600 lbs.
Standard empty weight: 1562 lbs.
Max useful load: 1038 lbs.
Max landing weight: 2600 lbs.
Max sling load: 1000 lbs.
Disc loading: 3.2 lbs/sq.ft.
Power loading: 11.6 lbs/hp.
Max usable fuel: 240 lbs.
Max rate of climb: 1450 fpm.
Service ceiling: 18,000 ft.
Hover in ground effect: 12,400 ft.
Hover out of ground effect: 7500 ft.
Max speed: 97 kts.
Normal cruise @ 3000 ft: 94 kts.
Fuel flow @ normal cruise: 96 pph.
Endurance @ normal cruise: 2.4 hr.

T-28
Engine: AiResearch TSE 36-1 turboshaft, 240 shp