HELICOPTERS ARE QUEER CRAFT —But New Zealand Might Find Uses for Them

New Zealand Listener, Volume 16, Issue 407, 11 April 1947, Page 6

HELICOPTERS ARE QUEER CRAFT —But New Zealand Might Find Uses for Them

Written for "The Listener" by "E. and O.E."

HEN the ships of the Byrd Antarctic Expedition were in port recently, the people of Wellington saw hellicopters for the first Aime. Naturally there was a lot of interest eroused by them, and the mere spectator, in addition to the people who were taken for flights by the expedition pilots began to think of how these machines might be useful to New Zealand. Demonstrations were given for a number of people connected with aviation in New Zealand, on the technical and administrative sides, and _ these people saw how the helicopter can come in and land, under quite windy conditions, on a piece of deck that is smaller than the area swept by its ro ors;° how the pilot, when he wants to run up his motor before a flight, commonly lets the machine rise about nine inches from the ground (or deck) and then perhaps moves a few feet to one side, turns the machine round a bit, and settles again, to take his passenger on board. They also saw the helicopters flying at varying speeds, from hovering, up to about "110 miles an hour. I was one of the people who took a pretty keen interest in, helicopters straight away, and began to think of how we could use them in New Zealand. And I came to the conclusion that under certain conditions they could be invaluable. But the first thing we have to do is get rid of the idea that they are miracle-workers, and that we only have to buy a few and then go ahead doing all sorts of remarkable things with them-rescuing mountaineers and sailors, carrying supplies to deerstalkers, dusting crops, servicing lighthouses, and $0 on. Maintenance is a Drawback The helicopter is-a very remarkable thing already, as I'll explain in a moment when I describe how it works. But you must remémber that the last edition of the Oxford Dictionary calls it a "Flying-machine that should rise vertically by airscrews revolving horizontally." (Note the should). That definition was framed in the ’thirties. This is: 1947, but the helicopter is still very expensive to operate. It needs about two hours of maintenance work for every five hours of flying (an ordinary plane needs one hour’s maintenance for 25 hours’ flying). And its payload is low; an ordinary plane is four times as efficient in terms of payload per unit of engine horsepower. Its purchase and maintenance could not be justified for any single one of the uses I have named above. But if We could have a helicopter in each island on call for those various duties, in no time they would pay for themselves -perhaps in lives as well as in savings of time or money. The Byrd Expedition had two helicopters here. The one fited with rub"ber pontoons was the smaller. It has a 180 h.p. radial motor mounted ordinarily, driving the vertical rotor shaft through a right-angle gear. The rotor’s total diameter is 38 feet. The pontoons carry air at a pound end a-half to the square inch-you could inflate them

with your lungs. The ro-or’s tip speed remains constant at 250 miles per hour. The craft has a maximum speed of 60 m.p.h, and an average cruising speed of 40 m.p.h. The larger machine, fitted with wheels, has a 450 h.p. radial motor mounted flat, driving the rotor through planetery reduc ion gears. The rotor’s diameter is 46 feet. Its maximum speed is 110 m.p.h., and average cruising speed 80 m.p.h. Its payload (including the pilot) is 570lb., and the view from the cockpit extends through 180 degrees verticaily, and a good deal more horizon‘ally.. Both machines have lateral airscrews at the tail to counteract the tendency of the fuselage to spin round, against the rotors. Their pi‘ch (and hence the force they exert) is controlled by the pilot’s rudder pedals. An ordinary plane with the same payload (570Ib.) would need only 200 h.p. instead of 450 h.p., and it would do about 130 m.p.h. instead of 80 m.p.h. That makes it about four times as efficient. In addition, maintenance on a helicopter, as I’ve said, is needed in the ratio of two hours’ work for every five hours’ flying. But this is no worse than the: demands of the ordinary type of plane were when it was at the same stage of development. A great deal of the greasing and inspection work is needec now because the helicopter is in its early stages. We can reasonably expect developments in design that will improve the ratio. Mechanical Stresses But in the, meantime the mechanism that supports and controls the rotor is highly complicated, and subject to so many stresses that it needs this constant attention. The blades alone have to be

replaced completely after 500 hours’ flying. And when you realise how many different movements go on at the hub, you realise why so much care is needed. The blades are hinged so that they can actuaily fold right up above the hub. Only centrifugal force keeps them spread when the helicopter is in flight. So they are going round, and they are also free to fold upwards. In addition, their pitch has to be variable. When the

machine is flying forwards, say at 100 m.p.h., the tip speed of the blades on one side will be 250 plus that forward speed of 100 m.p.h, But on the other side, where the blades are flying backwards, the tip speed through the air will be 250 minus 100 m.p.h. Therefore the lift would be much greater on the "fast" side than on the other, unless there was an automatic device to alter the pitch of every blade twice in every rotation. When you flick a card through the air so that it spins as it goes, you find that it turns over, because it strikes the air much faster on one side than it does on the other. So in order to prevent this happening to the helicopter, it’s necessary to have a device that constantly feathers the blade, making the pitch less on the fast side and greater on the slow side. But that’s not the end of the story: the same device has to be made subject to the pilot’s control, so that he can increase the pitch of the blades on any chosen sector of the arc-that is how he tips the plane to change its direction. And finally, he has to be able to increase or diminish the pitch of all the

blades together, to give more lift or less. All this is done by a. mechanism (fixed above the hub) whose name is its best description-it’s called a "spider." It doesn’t require much imagination to reelise that there’s going to be a high degree of fatigue in a mechanism that has all those stresses-plus one I haven't mentioned-the torsional vibration set up by the intermittent thrusts from each cylinder of the motor. The spar of each blade is a steel tube tapering by steps-like a steel golf club. And its diameter at the boss is 2in, It has short projecting arms near the boss, to which the spider’s "legs" are fixed. Pilots Must be Fit Neither is metal fatigue the only kind of fatigue involved in flying a helicopter. Pilot fatigue is so great that an exceptionally fit man, used to the job, is done in after five hours’ flying in a day. A normal aeroplane is inherently stable. It rights itself, as long as there is room. But a helicopter’ is inherently unstable. The pilot must be in full control all the time-and by that I mean from second to second. If he wants to wave to a girl friend on the ground he can only spare one hand for a very short flap at the window. He has to have both feet on his rudder controls, one hand on the stick, and the other hand on the combined elevating lever and throttle. The throttle is made so that ordinary vibration shakes it shut-so he can’t relax his control at all. The helicopter’s equivalent of a stall -and what the pilot has to avoidoccurs if its speed falls below a certain critical point, and at the same time there is not enough power in the engine : (continued on next page)

‘continued from previous page) tu spin the rotor at the speed necessary to keep the blades spread. If that happens, the blades may fold upwardsand that’s that. It’s known as "coning" of the blades. A free-wheel clutch, which permits the blades to go on spinning without power, prevents this happening as long as. the air speed is over 20 m.p.h. In that case the machine can glide forward like an autogyro (in which the blades spin freely). As long as it has wheels, it can then be landed safely. What Could be Done? Now when you look at all those conditions and limitations, you can see that no operator in New Zealand could justify the expense of running a helicopter (and providing spare pilots) for ordinary transport work. I doubt whether it would be worthwhile for the jobs that are done by the P.W.D. and Internal Affairs Department-which are co-operating for the control of wild life and soil erosion. Even for sending supplies to the most inaccessible spots, the cost of running a helicopter would not be justified. Nor would the State Forest Service be likely to have enough work for one at present-or the Marine Department (for rescues, and servicing lighthouses). But-these various uses, plus the rescue of mountaineers, could all be worked in together if there was a helicopter in each island, maintained and flown by the R.N.Z.A.F. (thus giving some pilots a kind of training that is likely to become essential in due course). An analysis of mountain rescues over the last 25 years proves (what is fairly obvious anyway) that the danger spots in the North Island are Egmont, Ruapehu, and the Tararuas. Ohakea is centrally placed for those. In the South Island, the accidents all happen between points a bit south of Mt. Cook, and a bit north of Arthur Pass-or Arthur’s Pass as most people call it. Wigram aerodrome is strategically situated for that region. And the point about the helicopter is this*-that although most of the time. you think twice about the cost of the thing, against the use you're likely to get out of it, there comes the time when you would give anything to have one at hand. Actually helicopters are no good for urgent missions involving long distances. For the rescues of air crash victims near Gander in Newfoundland last year, helicopters were dismantled and carried from New York to Newfoundland in big transport planes. Then they were reassembled in four hours to do their mercy flights. But in New Zealand, two helicopters placed as I’ve suggested could handle all the likely work, as well as being ready for emergency missions. And if it happened that there was an emergency that called for a helicopter doing several hours’ flying without its usual maintenance, no one is, likely to worry about the machine’s life being shortened for the sake of saving human lives. You can fly a helicopter beyond its usual limits if you have to. It just wears out sooner if you do. Air-Sea Rescues One place where a third helicopter might be justified would be Auckland, where most of the yachting accidents happen. A helicopter fitted with a power winch can hover over a capsized crew, and haul the victims aboard without landing on the water. > And there is a way by which a helicopter can carry a load far exceeding its payload. When it is very near the

ground, a helicopter sits on a cushion of air of its own making-the downwash swirls up again from the ground, and gives the craft much more lift than it has at a greater height. That explains why the Sikorsky company is able to advertise its helicopters with a photograph showing a helicopter with men hanging on to it. In an extreme emergency, a helicopter fitted with pontoons could pick up and carry a number of men to land by skimming low across the sea on this cushion of air. Crop-dusting is another use for the helicopter that might become practicable in New Zealand. In the United States a great deal of crop-dusting is done from ordinary planes, but that is possible there because in a continental climate there are plenty of flat calm days. . Here the air is seldom calm enough to make the job economical. But the Americans have found that there are two very good reasons in favour of the helicopter for this purpose. One is that its operating expense is offset by the fact that you don’t have to fly away to a landing ground to take on a new load. You can simply drop down in a corner of the field you are working on and reload. That cuts out a lot of dead flying. The other reason is that the downwash swirls the dust or spray into the foliage, and does a far more effective job than an ordinary plane, which has to let the stuff drift on to the crop by its own weight-with a good deal of waste if there is any breeze at all. In the United States it has been found that crop-dusting can go on under what the Americans would call windy conditions. In most parts of New Zealand "normal" conditions are similar to what the Americans call windy. So if crop-dusting is ever going to be considered here, the helicopter is the machine to do the job. . Two major difficulties remain. One is common to all helicopters anywhere in the world, and the other is a special one arising out of New Zealand’s climate. The first is that no one has yet devised satisfactory flight instruments for the helicopter, particularly for blindflying. At present the helicopter can only fly under "contact" conditions. At night, or in cloud, where there are no reference points for the pilot to check his height and direction, the helicopter will quickly get out of control. The second difficulty is that pressure-altitudes in most parts of New, Zealand are high. For the purpose of fi ying, the "altitude" at sea-level (in terms of air pressure) varies from place to place. At Wellington it is usually 900 feet. That’s to say, a helicopter taking off from Rongotai is already at a pressure-altitude of 900 feet. And if it had to land on or take off from a Wellington hilltop 1000. feet high, it would be as if the altitude were really 1,900 feet-all of which affects the behaviour of a helicopter fairly considerably when taking off or descending vertically. So there are some problems still to be thought out. Budding New Zealand inventors can get to work if they like end try to devise flight instruments that will work in a helicopter. And perhaps some day the helicopter will be able to cope with those two problems that still vex the handyman about the house-replacing a broken halyard on a 40-foot wireless pole, and getting out of the corner of the living room when all the rest of the floor is varnished, |