Peter Gray/BLOOMFIELD Exclusive: Flight International is the first magazine to flight test the Kaman K-Max

AFTER BEING introduced to the differences between flying helicopters with tail rotors and hydraulic servo systems and Kaman Aerospace's intermeshing rotors and servo-tab systems in the H-43 Husky (Flight International, 1-7 May), Kaman launched me into a full conversion course on the single-seat K-Max. Founder Charles Kaman describes it as an "aerial truck": he may well call it this, but underneath there lurks a well-designed and up-to-date machine. For example, instead of the hundreds of metres of electrical cables with, which a mechanic in the field cannot and dare not tamper, there are electronic modules, which he can change as required.


Many of the heavy external-load-lifting helicopters, which I have flown have instruments and other systems removed to reduce weight and therefore increase lifting capability. The K-MAX is not like that. It has a powerful AlliedSignal T5317A-1 engine which can produce 1,340kW (1,800shp), of which only 1,200kW is used. It does not even murmur, therefore, when 2,700kg (the maximum hook load) is picked up and taken to, say, 7,000ft (2,000m). A big advantage of intermeshers is that there is no tail-rotor-absorbing valuable power. So making provision for adequate avionics, with altitude encoding transponder, global-positioning system, and good-quality radios as standard equipment, for example, is not a problem.

As I did a pre-flight inspection of the K-MAX, I carefully checked that the droop stops on all four blades were in. The four bearingless, composite blades provide two rotor discs slightly larger than that of, say, a Bell UH-1 - the expression "two for the price of one" comes to mind. More important are the flying qualities that the resultant low disc-loading provides.

I noted the rudder, which performs just like that of a fixed-wing aircraft (although pedal movement also moves the main-rotor blades); and the horizontal stabiliser, which helps dampen the nose-up-and-down pitching

I looked underneath and checked the two fuel-pump capsules, which can be removed and replaced in about 30min without draining the fuel tank, and the cargo hook on its trolley, which allows the load to be moved laterally and fore and aft without taking the helicopter with it. I was very grateful for this when I tried long-lining. Having your 2,600kg helicopter moved by a 2,700kg load on an arm of 30-60m is no fun. When in a 30¡ banked turn (the maximum allowed for underslung-load operations), the G force will increase this to about 3,600kg, for which the hook and the aircraft is adequately stressed.

Raising the lid on the nose compartment revealed the single, but large, lead acid-battery. The battery is quite capable of starting the big engine easily, as I found out when the aircraft was detached to a satellite field with no ground support, apart from a fuel truck. The undercarriage is very different from that of most helicopters - it is designed to stay out of the way of any underslung loads (it does), to be rugged (another design criterion) and, with its "bear paw" attachments, to permit landing on soft, soggy, surfaces. It is 3.6m wide, so there is no excuse for slipping off a steep slope.

Eager to fly the K-MAX, I climbed easily up into the high cockpit, applied the five-point harness and adjusted the crash-impact-absorbing seat and pedals, to find a comfortable position. I settled in to the lumbar supports. As well as providing a lot of safety features, such as a derated, reliable, engine; simple systems; no hydraulics to cause problems and no tail rotor - should the worst happen and the aircraft crash, Kaman has provided a lot of protection for the pilot.

As I looked around, I saw that I was sitting in a well-protected cage. I also noted the superb visibility - particularly laterally and down and under the thin fuselage. This was to become important when I had a load on the long (30m) line. When checking the collective lever for full and free movement, I could also look back and see the stabiliser moving.


With the assistance of Frank Gallagher, an experimental test pilot and instructor, I familiarised myself with the cockpit.

The cockpit is a refreshing change from all the others I have used to manage or observe external-load operations, with their mishmash of underslung-load controls and instruments. The pilot leans out of the left window for extra visibility, so the instrument panel and other accessories are designed for this. The left-hand third of the panel contains temperatures, pressures, other instruments and four switches for the few systems; the middle ground is occupied by the radios and other avionics; and the right-hand side by a comprehensive set of flying instruments. So, having spent some time leaning out to manage his load, the pilot can come back in and quickly scan from left to right to see all the essentials. Instruments such as the artificial horizon are self contained, with their own gyros.

Four of the Howell Instruments gauges (loadmeter, torque, engine RPM) and exhaust-gas temperature (EGT) really are modern. Each has a window to display a white warning flag should any of the limits be exceeded. One can then touch the glass of the instrument to interrogate it and ascertain how high it has gone. All exceedances are also recorded on the loadmeter and the pilot warned. Maintenance schedules are measured in cycles, as well as time, so these, too, are automatically recorded. The pilot can have the loadmeter record every load carried. I saw that the vertical-speed indicator went to ±6,000ft/min (30m/s) - I hoped that this reflected the aircraft's climbing speed with its big engine, rather than its rate of descent.

Below the left window sill is another small instrument-panel, in the pilot's line of sight, but not in his field of view of the load below, giving him the weight of the load on the hook, power being used, rotor speed, engine-fire warning light and master caution light - all the basics that he needs to operate safely.

The design operating philosophy is similar to that applied to combat helicopters - the ability to manage all the important functions without removing one's hand from the controls. The cyclic stick and collective lever contain everything necessary, therefore - throttle; releases for the belly hook and that on the end of the long line (repeated on both stick and lever); a manual hook release; a hook arming switch; a switch for changing from automatic engine control to manual; a trim and trim release; RPM beeper; engine-start switch; and a clever single switch to illuminate, switch off and direct the landing light through 360¡ and up and down. Finally, I noted the siren, which can be used to attract the attention of those on the ground. Because of the lack of a tail rotor, the aircraft is quiet and can creep up on one. If this fails there is a loud hailer.


With the cockpit familiarisation over, I was keen to start up and get flying. I reached for the one-page checklist, which contains everything one needs to do to start, fly and shut down the K-MAX. I was ready in about 1min to pull the starter switch. The engine can be started with the rotor brake on or off, depending on the wind. A lock on the throttle prevents you opening it beyond ground idle with the brake on - a nice safety touch. The throttle has four positions, with detents, which cannot easily be accidentally overridden - off, ground idle, flight idle and fly.

The mighty engine growled coolly and slowly into life and, after completing the rest of the checks on the page, I was directed to the pre-flight checks posted on the instrument panel. They are very simple: brakes off, nose-wheel lock as required, plus two more quick items.

Such is Kaman's confidence in its product and good instruction, that the company had positioned my K-MAX downwind on the small apron next to (but not too close to) another aircraft. There seemed to be hundreds of eyes peering through the windows as I pulled up tentatively to my first hover, remembering to keep the pedals level and not to move them. Gallagher had warned me that the feel is different from that of the Husky and to expect some overcontrolling. I obliged accordingly, and moved off to the nearby runway without getting too near the aircraft beside me. I had practised all the hover manoeuvres practised in the Husky and was ready for my first circuit. This was uneventful, even in the crosswind, although I took the precaution of reminding myself that I had 1,200kW power available and that I was strapped in to a $3.5 million aircraft.


Over the next few hours, I practised all the usual manoeuvres to convert on to the aircraft, plus some others such as tracking the blades in flight. I remembered most of the time to keep the pedals level and to use my feet only during turns. Turns required pedal, followed by the cyclic, then a glance at the ball once the required angle of bank was reached. I found balance control much more "slippery" than in the Husky. Although the flight manual limits the maximum angle of bank with no load on the hook to 45¡, Gallagher cleared me to go to 50¡.

The nose up-and-down pitching with lever movement was much reduced in comparison with the Husky, thanks to the stabiliser. I went into a confined area. Despite the excellent visibility over the drooped nose, I still had to hold the nose slightly sideways to keep my target in sight throughout the very steep approach. I found that accurate taxiing can be challenging, because of the greatly diminished pedal control at low pitch settings, but the good brakes solved the difficulty. Both the Husky and the K-MAX have very flat power-required curves at the hover end, so I was able to move away from the hover into forward flight with no additional power and lose only a couple of feet. As I experimented, I found that the difference in power required to hover in and out of ground effect is very little, an indication of the efficiency of the two rotors. A transition into forward flight from a 200ft hover required no additional power and entailed only a few feet loss of height. This augured well for long-lining.

Making use of the hands-on cyclic and stick capability, I wound off the throttle to flight-idle, checked the engine instruments, lifted the flap of the change-over switch on the lever with my thumb and flicked it into manual throttle.

Engine-off landings from straight-in, 90¡ and 180¡ are a delight, as they are from the hover and hover taxi. Kaman tells me that one test pilot was convinced that one could flare and land without the use of any additional collective lever. Another, in the Husky, not noticing that the wind had changed, did a downwind autorotation and engine-off landing and still managed to land with almost zero groundspeed. These qualities are reassuring to the pilot when using the K-MAX to go about its business of hauling heavy loads, often over hostile terrain. The power-off rotor RPM limits are from 200 to 270 - an enormous range. The rotors, even under power, turn comparatively slowly. This, and the lack of a tail rotor, makes the aircraft remarkably quiet.

Intermeshers have an inherent lateral vibration. When I took the aircraft to its never-exceed speed of 100kt (185km/h), the vibration was more pronounced. Intermeshers are built for lifting capacity, not speed, however, but it is still there at normal cruise of 70-80kt. K-MAX pilots say that they find it slightly fatiguing after a long day, but they can weigh this against the advantages - no tail rotor absorbing power or, worse still, malfunctioning.


The K-MAX has no hydraulic system to aid stick, lever and pedal forces, nor does it need one - the servo-tabs do a good job. All of us on the course found, however, that, after a long day, our cyclic arms were more weary than usual. The built-in trim forces are quite high and the trim release takes a second or two to catch up with the actual stick movement. The lateral stick displacement when transitioning from forward flight to the hover is quite noticeable and I had a little trouble initially coordinating the trim. No doubt more practice would result in a suitable technique. One pilot said that it takes about 100 flying hours to feel really comfortable.

We both found the K-MAX unpleasant to fly in significant turbulence. As mentioned earlier, the balance is slippery. Test pilots talk of neutral stability: the aircraft will neither recover to its original position after displacement nor go even wider. I found this so on sustained long legs with the aircraft trimmed out accurately, but, when doing circuits and, later, with heavy loads on the hook, there is not time to allow the aircraft to find its own position, so one is working hard.

The built-in safety features more than compensate for these minor disadvantages. The big advantage is that, at last, long-line pilots have an overpowered aircraft. It is designed to lift 2,300kg all day up to 8,000ft. I had recently come from a seismic operation in South America, where a conventionally tail-rotored helicopter with the same engine had struggled with 1,200kg in half ground effect at 3,800ft density altitude. In reality, the K-MAX will lift more, lift it higher and stay well within all the limits.

The K-MAX lever, with its counter weights, friction and limiter, was a delight to use. There is a mechanical link between the lever and the throttle to try to keep the RPM constant. It is simple and effective, and there is no complicated system to malfunction.

I practised the two checks for power assurance and trend analysis. AlliedSignal and Howell have eliminated the need for the pilot to select, or rather try to select, certain fixed parameters during flight and record others. Instead, AlliedSignal relies on the accuracy, recording and other qualities of the instruments. Furthermore, the results can be downloaded onto a lap-top computer, as can other parameters such as exceedences and loads carried. With the simple tests done, they showed that the engine in my aircraft, despite having spent some time at sea, was well above minimum specification power (on which all the flight-manual performance graphs are based) and showed only a minor trend-analysis diversion.


Having mastered (most of) the intricacies and peculiarities of intermeshers, I was ready to set about the real purpose of the K-MAX - heavy, repetitive, external-load lifting.

The search for oil and gas goes on worldwide. Petroleum companies need to move heavy seismographic-exploration equipment from one seismic line to the next. Once oil and/or gas has been found, heavy drilling equipment is next required. Logging companies, meanwhile, move whole trees out of the forest to the collection points. Navies need to replenish their ships at sea. The petroleum and logging companies use roads and rivers when available, or even make their own paths. Navies use ship-to-ship transfers. These, can be hazardous, or even impossible, when the waves or winds are high.

When the going gets too tough, the modern solution to all these problems is to move everything by helicopter.

The petroleum and logging companies can do a lot of damage to the environment, even when using helicopters, for example by cutting out landing pads. The least damaging technique - and also the safest by not requiring the helicopter to land - is to carry everything on the external-load hook. To be even safer and stay above obstructions - primary jungle trees, ships' aerials, masts and so on, a long line is used between the helicopter's belly hook and the load. There is another hook on the bottom end. The line may be 25m, 50m or even 70m long. Various techniques have been tried to establish the best method - a talk-down by someone on the ground, or just hand signals; a loadmaster sitting in the back of the helicopter and doing likewise; and the pilot using mirrors, or even a video-screen. All these methods are in use. Indeed, my own experience consisted of a mixture of the above techniques, and all on a much shorter line than that put on by Kaman.

While these techniques may be adequate for short lines, they are inadequate for long ones. The only satisfactory way to extract a log from a forest, place the load exactly into a jungle clearing, or a loaded pallet on to a moving deck without bashing it into the surrounding obstructions is for the pilot to lean out and view what is happening below. The technique is known as "vertical-reference flying".

To emphasise the accuracy, an experienced vertical-reference pilot at the Kaman factory, after discussing the pros and cons of the method with some doubters, placed a 2,300kg solid-concrete block on to the top of a small bollard and left the doubters to recover it. The other advantage is that, if the load develops a swing (and they often do, especially the ones I carry), there is only one person who can stop it - the pilot. He does this by jinking the helicopter directly over the load as it passes beneath. A large swing will take several corrections. The way he can get the timing right is by leaning out and seeing for himself.

Apart from the Sikorsky CH-54 Skycrane and the large Russian Mil Mi-10, no other helicopter has been specifically designed for repetitive underslung-load work. All the disadvantages of the tail rotor come to the fore in this work. The pilot's seat may be some way from the edge of the floor, making it difficult to lean out, the shoulder harness may do what it is designed for - restrict upper-body movement. Manufacturers of most helicopters used regularly for underslung-load operations are nervous about their products being used for such work. During normal use of their aircraft, take-off and landing cycles (when high or full power is used) usually occur about twice an hour. Pulling full power every few minutes to get an underslung load off the ground and into forward flight and back down again at the delivery point causes premature wear and tear on all the dynamic components, especially the tail rotor, cracks in the constantly twisting airframe and premature engine deterioration.

Experience so far indicates that these problems have been eliminated, says Kaman.


When making an approach to the hover and leaving the hover for forward flight, a pilot receives and processes many visual cues to orientate himself in space, and to detect and control the six axes of motion of which the helicopter is capable - pitch, roll, yaw, heave, sway and surge (acceleration/deceleration). He can also glance at flight instruments to confirm what he sees and what he wants the helicopter to do - the altimeter to tell him his height and/or rate of change of height, the airspeed indicator to show speed and its rate of change, the vertical-speed indicator to tell how fast he is climbing or descending and the artificial horizon to confirm the attitude.

When flying a load on a long line beneath the helicopter, the first problem the pilot encounters is how to interpret and control the six axes while leaning out of the helicopter and looking down at the load 100ft or so beneath him. The second problem is physically handling the helicopter while head-down over the side. The third problem, the object of the procedure, is to pick up the load, get it the right distance off the ground, clear all the obstructions, monitor his power instruments, transition into forward flight, and clear all other obstructions in his path, before bringing in his head and upper torso. At the other end, once on short finals, the head goes out and down again and he now has to keep the aircraft descending at the appropriate rate, judging the deceleration to arrive over the target in the hover at the right height - the target may be just a hole in the trees - and, most important, clearing all the obstructions with the load. Some experienced pilots can slow down the helicopter, let the load fly forward and plant it exactly where they want it, releasing it at the same time. The additional challenge on the Kaman course is not only flying an unfamiliar helicopter, but flying one which is different - an intermesher.

The K-MAX has an adjustable torso-support pad which I found useful. It not only supports the top half of the body, but forces you to lean out sufficiently far to do the job properly. There is also an elbow-support pad. I was able to find a position to lean out, rest my forearm on the ledge and crook my left collective lever/throttle arm around and under the rest. I decline to describe the position as "comfortable" - bearable is more appropriate.

When learning vertical-reference flying, there is a great temptation to mix it with horizontal-reference flying, with the result that you immediately start to lose control of the helicopter and the load. You have to grit your teeth, keep your head down and have faith.

Weather conditions were not ideal - a strong gusty wind caused the real experts to cease operations, but I soldiered on, not wanting to spend a second weekend with no flying possible. I eventually achieved our aim and finished up putting the load exactly where I wanted.

Experts say that, as there is no danger of vortex-ring settling with power and lots of power available, downwind approaches are possible, depositing the load while feeding in pedal. This will bank and turn the helicopter and get it going on its return flight as the load is touching down - a manoeuvre unique to the intermesher.

I shut down the aircraft with a sigh of relief and interrogated the loadmeter to ascertain the maximum load I had picked up, the highest engine RPM, torque and temperature.


Although the aircraft is described as an "aerial truck", it is modern and well designed. Attention to detail is apparent everywhere. I like its capability to warn about and then record all exceedances. Despite the minor inconveniences, such as cyclic forces, poor stability in turbulence and vibration levels, the advantages are overwhelming, particularly the power available, the lack of a tail rotor, and the aircraft's many safety features, including autorotation and engine-off landing characteristics.

Its design criteria of ruggedness, ease of maintenance and simplicity of operation were proven to me. All-round visibility, essential for the job to be done, is excellent. It is ideal for repetitive underslung load flying using the vertical-reference technique. The USNavy performs vertical-reference long lining at night - I was happy to leave it to day only.

Source: Flight International