Peter Gray/KUSSNACHT, SWITZERLAND
KAMAN AEROSPACE HAS handed over the first K-MAX external-lift helicopter to be delivered to a European customer. The delivery, to Helog of Switzerland, provided an opportunity for a closer look at an unusual aircraft with a growing international presence. The K-MAX is in service in the USA and Canada, and examples will be delivered to France and Japan later this year.
The K-MAX has been designed specifically for single-pilot, under-slung-load, heavy-lift work and will easily lift 2,700kg on a long line, out of ground effect, with about 1h worth of fuel, at altitude and at high outside-air temperatures - the two factors which most affect a helicopter's lifting performance. This is a remarkable achievement for a helicopter, which weighs only 2,180kg. I can remember struggling to lift 2,000kg with another type of helicopter weighing 1,800kg in the cool of early morning, at sea level, and with the minimum of fuel.
Helog chief pilot Capt. Heinz Leibundgut, and technical manager Thomas Gugg, showed me around the aircraft. It is not until you walk around it or the helicopter flies directly overhead, that you appreciate how thin it is. This is to allow the pilot to lean out of either side to see what is happening underneath.
The peculiar undercarriage is designed to absorb a heavy landing, and to not obstruct the pilot's line of sight to the under-slung load. The belly, too, is designed to take a shock. The fuel tank is self-sealing and the pilot is protected by a stiff rollover structure. The stroking seat will absorb about 20g, and the gearbox and engine have restraints to prevent them from penetrating the cockpit in a crash landing.
The intermeshing, contra-rotating, two-blade rotors cancel out torque reaction, and there is no need for a tail rotor. When a conventional helicopter is hovering at 90° to a strong wind, its tail rotor can absorb up to 30% of the available engine power. This can cause control difficulties if the aircraft weighs a lot, and is at high altitude and high air temperature. The K-MAX has no tail rotor, so all the power from the 1,120kW (1,500shp) AlliedSignal T3517A-1 turbo-shaft, derated to 1,010kW, goes to the rotors via the 1,120kW-rated gearbox.
The rotor blades are composite. A recent blade strike during logging operations took 0.75m off one blade tip and 0.45m off another, but the pilot was able to fly a short distance and land the aircraft safely.
The K-MAX is designed so that one mechanic can keep the aircraft serviceable between major overhauls. There are steps and platforms on the aircraft sides for comfortable access. All fluid levels are easily read. Transmission- and engine-fluid lines are located on opposite sides, to avoid mistakes. All internal spaces are painted white and provided with lights for easy nighttime servicing.
There are no hydraulic controls to check. The aircraft is flown manually, a remarkable achievement given the 14.7m diameter of the two rotors. Pitch is controlled by moving small servo tabs on the blade trailing-edges, rather than by moving the whole blade. Some feedback from the rotors is apparent, but pilots find it acceptable, Helog says. There is no anti-vibration system. There is an on-board rotor-tuning system, however, which the pilot can use during flight to achieve a smooth ride.
Flying heavy under-slung loads is a demanding task. Most of the pilots concentration, is directed at approaching the load, hovering while it is hooked on, coming up vertically to take up the slack, while watching the marshaller or listening to radio instructions, checking the power used and for warning lights and transitioning to forward flight, to clear any obstructions, all this while leaning out of the cockpit and looking at the load 45m (100ft) below. The simpler the helicopter is to operate, therefore, the safer it is.
SUPERB VISIBILITY
I climbed into the cockpit, installed myself in the seat and looked around. The seat is adjustable up and down, and the pedals fore and aft, so that you can find a position where you can rest your right forearm on your right leg while carrying out delicate hover manoeuvres. Good control in the hover is essential for under-slung-load work, particularly for long-line operations. The seat is comfortable and well padded, although Helog is going to add a lumbar support.
A five-point harness, a good safety feature, gave adequate movement for me to lean out left and right with little discomfort. I found a seat position, which allowed me to do this and still look over the drooped nose, keeping the top of the instrument panel in sight. There are two huge mirrors showing the helicopter's belly. All-round and all-important downwards, visibility is superb. Everything is within easy reach.
To save the pilot having to take his hands off the controls, all essential switches are positioned on the cyclic stick and collective lever, as follows:
cyclic stick- hook release, "coolie-hat" trim, trim release, long-line hook release, and radio transmit;
collective lever- hook arming, siren, landing light, engine automatic/manual-control change-over, RPM "beep", load recording, twist-grip throttle, engine start and mechanical hook release.
The engine can be switched from automatic governing to manual twist-grip throttle control without the pilot taking his hand away from the lever. The throttle need not be backed off for the switch over. In "automatic", the throttle is fully open, the required RPM adjusted with the beeper switch on the lever, and the engine governor does the rest. As the pilot raises and lowers the lever, the governor feeds more or less fuel to the engine to keep rotor RPM constant.
For a day-only, visual-flight-rules helicopter, the K-MAX is well equipped. Helog's aircraft has a full set of flying instruments, radios and navigation aids, including a global-positioning-system receiver for ferry flights. This probably accounts for this aircraft's fairly high empty weight of 2,180kg, compared with the published 2,045kg. The extra weight does not inhibit performance, however. Because of the derated engine, the aircraft will still lift 2,720kg all day.
There is a large, well-calibrated, fuel-contents gauge, plus low-fuel warning lights, and a similarly large load-meter, which gives the load weight. Load weight can be recorded for print out. Load-meter, torque-meter, engine gas-temperature and rotor RPM gauges all automatically record in memory the highest values reached. Lifting cycles, vital for determining component lives and maintenance times, are also recorded. Certain engine-limit exceedences are allowed within laid-down parameters and these are recorded. Lights warn of an exceedence.
When long-lining, K-MAX pilots can lean to the left or the right over the collective lever, because of the thin fuselage. To the left, just below the window sill, directly in the pilot's line of sight to the load, is a small instrument panel containing duplicate load, torque and RPM gauges, and master caution and fire-warning lights. The master caution light directs the pilot's attention to the warning capsules at the top of the instrument panel.
Kaman is not yet prepared to let anyone other than prospective customers fly the single-seat K-MAX, and even they must undergo intermeshing-rotor familiarisation training in a refurbished Kaman H-43 Huskie. Helog's Leibundgut, therefore, staged a demonstration.
FLIGHT DEMONSTRATION
The K-MAX starts easily, simply and quickly. Despite the lack of any hydraulics or stability augmentation, it is stable in the hover, but with some feedback from the rotors to the cyclic, says Leidbundgut. Lateral cyclic stick is more sensitive than fore and aft, and most newcomers to the aircraft tend to over-control laterally at first. When hovering in a crosswind, an inexperienced K-MAX pilot can more easily get into a crossed-control condition - ie, too much left or right cyclic, with too much, opposite pedal.
Leibundgut says that the aircraft handles well out of wind and sideways and backwards flight up to 70kt (130km/h) is achievable. Starting in 70kt winds is also possible, a rare quality for any helicopter. Turns on the spot are limited to 45¡/s. Translational lift - the sudden boost as the aircraft accelerates into forward flight - comes in at about 12kt, enhancing its lifting performance early in the take-off.
The canted, intermeshing, rotors produce a more stable aircraft, which is important for long lining, with greater lifting efficiency, because of the absence of the tail rotor and the greater volume of air passing through the rotors. The penalty is a lower top speed. The K-MAX is certificated to a never-exceed speed of 100kt, although it has been flown faster.
The rotors turn relatively slowly (200-270RPM); disc loading is low and inertia is high. A sudden engine failure allows the pilot plenty of time to enter auto-rotation. The rate of descent is a modest 1,200-1,400ft/min (6-7m/s) at 50kt, with plenty of lift available to stop all forward speed if necessary, and land the aircraft engine-off. The undercarriage design will allow safe landings on rough terrain and steep slopes.
For the demonstration flight, at a density altitude of 2,500ft, Leibundgut used the aircraft to pick up timber weighing 2,720kg, the maximum permissible weight on the hook. With the load on a long line, he climbed vertically, then transitioned to forward flight, with a steep climb out to clear the many wires, trees and other obstructions. Leibundgut then returned and repositioned the load at exactly the same spot.
The noise level is below US Federal Aviation Administration limits. US operators have been able to use the K-MAX where other, noisier, aircraft, such as the Bell UH-1 and Eurocopter Super Puma, are forbidden, Kaman says.
The aircraft handles well in forward flight, with a lot less pedal required in turns to stay in balanced flight, Leibundgut says. Again, pilots have to be aware of getting into a crossed-controls condition.
After the flight, we examined the instruments, to check the maximum torque, engine speed, gas temperature, load weight and number of cycles. Even with a load of 2,720kg, all parameters were well within limits.
In the K-MAX, operators at last have a commercial helicopter designed for long-line lifting. The price is $3.5 million, and more than 3,000h accumulated by US launch customers have shown the aircraft to be reliable, easy to maintain and comparatively economic to operate. Pilots say that they are satisfied with its ease of operation, good handling characteristics, superb visibility and power margin. Engineers like the accessibility, simplicity and ease of maintenance.
Source: Flight International
