The Enstrom 480 Turbine is a classic example of how a good original design can be adapted and modified for the demanding modern operating environment. It is also remarkably flexible for its size.
At its maximum capacity, one passenger occupies the front right-hand seat next to the pilot on the left, and three passengers take the rear seat, all in the same cabin and with no pedestals or other obstructions.
The front passenger has lots of leg room and two of the rear passengers can stretch out comfortably, but the one in the middle has restricted leg room. The width of the rear seat is tight, but there is plenty of head clearance, as Flight International's photographer, who is 1.86m (6ft 1in)-tall, proved.
The large baggage area in the tail cone will accommodate up to 70kg (155lb) of luggage and a further 22kg is available at the rear of the cabin. The front seat can be removed to provide a larger baggage stowage area, using the seat rails for tie-down restraint.
Originally designed for the US military as the TH28 training aircraft , the 480 has a three-seat configuration with the instructor and student in the front seats and a third student overlooking from the rear seat. This configuration can be converted to five in just a few minutes. Headsets for all occupants enhance communications: almost as much can be learned from observation as from actually flying the aircraft.
Michigan-based Enstrom was founded in 1959 and has been designing and building helicopters for 30 years, and has built about 1,000 piston-engined versions. It has been producing the TH28 since 1992, and the 480 gas-turbine model since 1993, of which 40 have been sold, nearly half in the UK. The 480 has been certified in the UK, Germany, Belgium, Brazil, Canada, China, France, Switzerland, Sweden, Thailand, South Africa and Japan, and is also operating in Russia and Spain. Enstrom is a small company, producing about 18 helicopters a year which are tailor-made from a vast list of options to the purchaser's requirements.
The design criteria of the 480 were to provide a safe, easy-to-fly, forgiving aircraft with a large, spacious cabin, versatility with quick-change capability, provision for a second student when used for training, low purchase price and low direct operating cost (DOC).
The aircraft is aimed at the private and commercial market (it has a UK public transport category licence) and is used for flight training, patrol operations, police work, news gathering, aerial photography, powerline/pipeline inspection and light cargo, both internal and external.
Enstrom has incorporated all of its proven design features into the 480. Indeed, the machine retains familiar components, such as the main and tail rotor systems and the modular construction around a strong central pylon frame, to which are attached the engine, cabin, undercarriage, tail cone, main rotor gearbox and fuel tanks. The modules are manufactured separately and added on or changed as required, in the event of damage, for example.
The piston-engined models have an excellent safety record:the main rotor has accumulated two million hours of flight time without a major failure, for example. US National Transport Safety Board statistics show that, in the USA, Enstroms have one of the lowest accident rates among single-engine helicopters. In the UK there have also been few accidents - and not one was fatal.
Southern Air has been selling Enstroms for 25 years. It is the Enstrom distributor in the UK and sponsored Flight International's visit. At its facility at Shoreham airport, I was shown two accident-damaged aircraft. One had rolled over, but the cabin was intact and all the occupants walked away from the accident, proving its crashworthiness design features. The other had suffered a very heavy landing but the well-designed undercarriage, with its energy-absorbing oleos, had done its stuff and again the occupants walked away. The landing gear has drag struts which prevent it folding back under the aircraft during hard run-on landings. It has an impressive 2.44m (8ft) spread, for better resistance to rolling over.
The 480 is well below the FAA's latest noise criteria and, in terms of the noise it makes, falls between the Kaman K-Max - the quietest aircraft of its size - and the Boeing Explorer. Neither of these has a tail rotor - the main source of helicopter noise.
Only seven of the 480's components are 'lifed' - nearly all the rest are on condition only. This is a major achievement and helps to keep the cost down. So, for example, a private owner who flies only a few hundred hours a year does not have to change major components because of time expiry; the maintenance component of DOCs is thus kept to a minimum. In the UK, these are about £100-£110 ($165-$180) an hour, including fuel. DOCs are subjective, so Enstrom gives a complete breakdown of how these costs are calculated.
The flight manual contains much more information than normal, such as considerations for operating in cold weather, snow, desert, icing and high altitude. There are good descriptions of autorotations, engine-off landings, tail rotor failures and loading.
My pilot was Wayne Chandler, Southern Air's managing director. The day was cool, at 8íC, but with a surface wind of 20kt (37km/h). Conditions such as these always make for a realistic test flight and enable you to learn about important performance details, such as how the tail rotor copes out of wind. Our pressure altitude was 100ft (30m) and we were at the maximum gross weight of 1,295kg with the centre of gravity in the middle of the range. Our aircraft's empty weight was 870kg, 58kg heavier than normal because of the flotation system (this aircraft usually operates over water). With a normal empty weight of 812kg, a 77kg pilot and full fuel of 263kg, this leaves 143kg for payload (passengers/freight). Carrying a pilot plus four passengers leaves 1h 15min fuel endurance (with no reserves).
Southern Air tells me that, because of the excess power available, it is asking Enstrom to consider increasing the maximum weight by between 25kg and 70kg.
The aircraft looks good and closer examination reveals the attention to detail to reduce drag. The doors fit well, with flush door handles and fairings. The fully articulated main rotor system is deliberately heavy to give high inertia and good autorotation characteristics. I reached up but could not touch the tip of the lowest main rotor blade, though it will probably flex lower in strong, gusty winds when the rotor is being stopped or started. The three-bladed main rotor is driven by a simple splash-lubricated gearbox. This solution eliminates the need to install an oil pump and associated risk of pump failures, nearly all of which have extremely serious consequences.
The gearbox is driven by an Allison 250-C20W engine which lies beneath it, below the level of the two fuel tanks. The engine is capable of producing 313kW (420shp), but Enstrom uses only 216kW, which gives the pilot the luxury of having plenty of power in hand and of retaining that power as he flies hot, high and heavy - the real killers of aircraft performance.
The engine has a Pall, Land and Marine particle separator. This keeps it clean and prevents foreign object damage, also keeping it running in the event of inadvertent entry into icing and heavy snow. The aircraft is certified for light snow conditions without requiring an auto relight system. The exhaust directs the gases under the tail cone, the efflux being cool enough to prevent ground fires if landing on dry grass. There are no fuel boost pumps to manage, the engine using its own pump to draw in fuel from the two tanks, which are positioned above and either side of the fuselage in crash-proof and fire-proof containers.
A single, big, Goodyear drive belt with 30 grooves carries power between the engine and the gearbox. The belt is Kevlar-backed, using long-lasting rubber compounds with anti-oxidising agents to preclude ageing. It is not fatigue-critical and is replaced on condition. This design, which has been used by Enstrom for over 20 years, does away with a complicated reduction gearbox. The engine is protected by a firewall and, in the event of fire, the cabin can withstand 2,000íC long enough for the occupants to get out.
There is no hydraulic system to inspect - more evidence of the simplicity of design. The lack of hydraulics requires a trim system to absorb feedback from the rotor and reposition the stick datum as required by the pilot. If the trim system fails, the forces required by the pilot to overcome them are about 7kg. This is not excessive, but the pilot would want to land somewhere convenient fairly soon.
The two vertical fins are designed to help keep the aircraft in balanced flight and thus give directional stability - a feature which was proven when we flew the aircraft hands and feet off the controls.
The tail rotor, that most critical and potentially performance-restricting component, has longer blades than the piston-engined model to ensure it provides adequate power in all conditions, especially when in hot, high and heavy flight. To check this, we went to the maximum outside ground effect hover at near maximum weight, and later flew the aircraft to its flight manual limitations of at least 35kt sideways and backwards. There are no critical hovering areas with winds up to 35kt from all directions.
Chandler offered me the captain's seat on the left side. This position makes the 480 an excellent vehicle for vertical reference flying, where the pilot has to lean out to view his load on the end of a long line and remain leaning out until he has got the load off the ground, clearing any obstructions. Doing this from the right-hand seat often restricts the pilot from leaning out far enough because his left hand needs to stay on the collective lever and throttle. The Enstrom can be flown with the doors off, which helps such an operation.
Strusts hold the two big doors open - useful when managing passengers. I strapped myself in, adjusted the seat along the rails (there is no height adjustment) and the pedals for reach - there is a 200mm (8in) fore/aft travel adjustment. The passengers also have shoulder harnesses, an important safety addition because most of the injuries to occupants of any aircraft in a crash occurs when the top half of the body hits something solid.
The 480 has a well-designed, ergonomically pleasing cockpit and cabin. The initial impression is the excellent amount of visibility. About 60% of the cabin is devoted to doors and window space. I later explored this when doing a very steep approach to a target, a vertical climb and descent and steep turns. There is no overhead panel to obscure vision or cause neck strain. All the necessary instruments, controls, warning lights, even circuit-breakers, are neatly positioned on the instrument panel, centre console and just below the console (anti-ice, heater, particle separator and vent.)
Our aircraft had a full set of (single) blind flying instruments, including air-speed indicator, attitude indicator, barometric altimeter, radalt, directional gyro, vertical speed indicator, clock and the usual engine, rotor and temperature, pressure and fuel contents indicators. Three prominent red lights dominate the top of the instrument panel: Fire, Engine Out and Rotor RPM. The engine out and low rotor rpm also have an audio warning, and although it does not come through the headset, it can still be heard. Because both events are potentially lethal, I would prefer the audio to be routed through the headsets as well. Overhead, in the centre, are small, compact charts giving Vne for all conditions of height, weight and temperature.
There is no manual friction on the cyclic pitch stick (the stick), nor does it need one. The collective pitch lever (the lever) is fitted with one, and carries the landing light controls, engine starter and idle release buttons and engine rpm beeper switch. The stick has the fore/aft, left/right trim switch, turbine rpm beep switch, guarded flotation inflation switch and press - to - transmit trigger. The centre console has room for at least seven selections of radios, navigation aids and whatever else you may want, including the control box. We had dual VHF, dual navigation, a transponder and Skyforce colour moving map with a global positioning. There was room for one more item.
EXTERNAL POWER POINT
There is a small pocket in each door and ample space behind the pilot's seat for stowing other items. The baggage compartment in the tail cone is quite large, but the door is small, allowing only light luggage to be stowed.
The engine can be started from the battery, although there is an external power point on the right-hand side. This is out of the pilot's sight, so, in the absence of a warning light, care would have to be taken that the power unit was disconnected before take-off.
There is no provision for a rotor brake. Engine and rotor start was straight forward, as one would expect with the Allison 250 C20 engine, with the starter button and idle stop both conveniently positioned on the lever head. It is best to use both hands in case of a shutdown. In an emergency relight in flight, however, one hand can be used. As usual, the start was rapid and cool.
Post-start/pre-takeoff checks were few but relevant. Take-off was uneventful and the aircraft sat in an accurate hover, requiring little input from me. At the maximum permissible weight of 1,295kg, we used only 3.45 bar (50lb/in2) of torque with 4.69 bar (5min take-off power) available. Even though we had 20kt of wind and the air temperature was cool, this indicated there was plenty of excess power in hand. Because it is so derated, the engine will almost always be limited by torque and not by temperature or rpm. Interpretation of the engine power instruments was easy.
The minimum recommended rotor rpm is 370, but Chandler wound off the throttle while we were in the hover to 320 and then did a spot turn. This shows how much tolerance there is in all three systems.
The usual sideways, backwards hover manoeuvres, spot turns and landings and take-offs into and out of wind were quite straightforward and easy to accomplish accurately. The disc is responsive, the controls nicely balanced and the trim system easy to use and quick to act. The crisp handling is no doubt due to the fully articulated main rotor head, the offset flapping hinges and the well designed control systems.
There was a slight vibration from the main rotor which persisted throughout the flight, apart from during autorotation. Chandler said this was unusual, the 480 normally being much smoother. (On landing at the end of the flight, the engineers found a defective seal on the main rotor head.) We moved into forward flight and while still heavy, selected maximum continuous torque in straight and level, though slightly turbulent flight. We achieved 105kt at a density altitude of 1,000ft which equates to 104kt true air speed, 9kt slower than the speed given in the brochure (because the aircraft was carrying pop-out floats).
We went into a slight dive to the never-exceed speed (Vne). This is 125kt, but at our height, temperature and centre of gravity, the speed reduced to 117kt. There was no increase in vibration levels and the aircraft continued to handle well, with turns in both directions. The flight manual gives no limit to the amount of bank, so steep turns were performed in both directions at a constant 65kt with no complaints from the aircraft. I had to dodge my head around the cockpit windscreen pillars to keep the look-out going in the turn. Visibility throughout was excellent.
We climbed to 4,000ft to try vortex ring/settling with power on. This is a condition of helicopter flight at low speed (less than about 20kt), power on, and with a rate of descent in excess of 400ft/min (2m/s) where the vortices around the main rotor blades can destroy all of the lift, causing blade stall, increased rate of descent and partial, sometimes total loss of control. The condition has caught out many a pilot when close to the ground and can often lead to an uncontrolled heavy landing. Some helicopters will enter the condition easily, while others are more difficult and a few are impossible. Some helicopters will self-recover; other machines, provided the pilot still has adequate control, need pilot response.
The wind was strong and gusty, so we made the first attempt flying into it. Sure enough, with 2 bar torque, less than 20kt IAS and a 400ft/min rate of descent, we felt the aircraft waffle slightly but continuously and watched the rate of descent increase slowly to 1,000ft/min. These were the good, evident incipient conditions which the pilot should immediately recognise and recover from. There was still plenty of control, so the aircraft was accelerated forward, more power applied and the 480 immediately came out of the vortex ring. Chandler tried another one crosswind. The symptoms were more severe, but again the aircraft flew easily out of the condition, a pleasing and safe characteristic and a good demonstration to someone learning to fly helicopters.
LOW BACKGROUND NOISE
I invited Chandler to raise and lower the lever as fast as he dare to check the engine governor and for any change of aircraft attitude. He did so and we got no more than 1% change in turbine rpm and no change in attitude - a satisfactory result which should give comfort to even the most heavy-handed pilot.
The background noise with headsets on is benign. With the headset off in cruise the level of noise was still comfortable. Passengers should be able to talk among themselves with no difficulty, although there are headsets available to all.
The aircraft was trimmed for straight and level flight and the controls released. Even in the slight turbulence, the 480 carried on by itself, unusual in a helicopter lacking electronic stabilisation.
A malfunction will bring on the master caution light at the top of the instrument panel in line with the pilot's eyes and a light on one of the 15 segments of the caution panel which is also situated high up. Both will flash until the pilot cancels the master caution. This resets itself, ready for any subsequent malfunction. I like this flashing sequence - a pilot would have to be really unobservant not to notice it.
While still close to maximum weight - the engine uses a modest 80kg/h (175lb/h) of fuel - we went to the maximum out-of-ground effect (OGE) hover height of 6,250ft and came to the hover. It was even more turbulent up here, so it was impossible to establish our exact power requirement, but the torque gauge moved between maximum continuous and full power. We still had plenty of left pedal remaining to do a left turn, proving Enstrom's claim that the pilot is given ample tail rotor power.
We paused on our way down to explore the main rotor inertia characteristics. Chandler levelled out into a cruise and chopped the throttle. I started the stopwatch and recorded four seconds as the rotor rpm reduced to the minimum permissible and the lever was lowered. The aircraft's attitude remained stable, with no tendency for the nose to rise or fall. This rotor system is very forgiving. Although minimum power - off-rotor rpm is red-lined at 334rpm, the flight manual gives a transient minimum of 300rpm. It goes on to warn that recovery below 240rpm is not possible; 334rpm is at the eight o'clock position on the large dual-tachometer gauge, 240 is at the six o'clock position. The low rpm audio and light also activate, so a pilot would have to be particularly unobservant not to notice that something was wrong. Chandler repeated the demonstration, this time flaring the aircraft. The stopwatch ticked away six seconds before we needed to lower the lever - ample proof of the high inertia characteristics.
Steady autorotations showed benign control of rotor rpm with no rapid rises or decelerations. Rate of descent was between 1,600 and 1,900ft/min, depending on throttle position.
We joined Shoreham's busy circuit by flying almost overhead the hover circle at 600ft downwind, Chandler entering autorotation, doing a 180í turn and engine-off landing right in the middle of the small circle. There was plenty of time to judge the flare. I felt it bite, saw a momentary increase in rotor rpm, and again there was adequate time to level and pull in enough lever to land vertically with no forward speed. I carried out a steep approach to a target and, as expected, the excellent visibility, especially down, allowed me to keep it in view all the way to the ground. A vertical climb to 100ft was also uneventful and easy to perform accurately.
We now explored fast sideways and backwards flight. Despite the strong, gusty wind, we achieved 35kt sideways to the left, with some right pedal remaining, 50kt to the right, with some left pedal remaining, and 31kt backwards with no tendency for the nose to tuck down.
The aircraft has been landed on slopes of 15°, a remarkable achievement. The steepest we could find was 7° The main rotor head is designed so that the main rotor drive shaft will not touch the sides of the rotor head, which has caused damage in some other types. The aircraft accepted the 7° left and right skid on and facing up with no control problems and there was plenty of room between thigh and stick. In some helicopters, this can be a limiting factor.
An autorotation from 600ft overhead the circle, a 360° turn and engine-off landing was carried out, followed by one straight in from a 400ft, 90í, out-of-wind hover and one from a 5ft hover. The skids were usually touching the ground by the time the rotor had slowed to 325rpm, leaving plenty of lever in hand. All were benign and confirmed Enstrom's claim.
With its low DOC and initial purchase price of $532,000, the Enstrom 480 can compete on cost with all other single-engine, five-seat turbine-powered helicopters. The same money would probably buy a three- or four-year-old out-of-warranty Bell 206B3 with, say, 2,000h of flight time, or a new one at $715,000.
The Enstrom 480 is well designed with good attention to detail. It was easy and pleasant to fly, with crisp, balanced controls, more than adequate engine power and plenty of available tail rotor power. The good visibility for all occupants and the safety features should make it attractive in both the commercial and private markets. There is provision for many extras and a customer can choose his own paint scheme, interior, instrumentation and avionics.
Source: Flight International