The Lost Years. Anyone examining Australian society as it was in the years before 1940 must be rather bemused by the nation's lack of industrial development. The reason, of course, is that the British Empire, upon which the sun was rapidly setting, preferred its colonies to buy from the Homeland. In retrospect it is quite amazing that successive Federal Governments allowed, agreed, or otherwise did little to promote the homegrown entrepreneur for so long.
The WW2 Imperative. WW2 saw Australian ingenuity brought to the fore out of necessity. Australia built Owen guns ( after lengthy indecision, hampered by British lobbying - at first the Army could not see past the Sten-gun), Mosquitoes, Beaufighters, Mustangs, and a great variety of other equipment. Our industry was hampered however, by the general lack of prewar development.
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| CAC Boomerang |
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Three days after the attack on Pearl Harbor, Fred David, Chief Engineer at CAC, sketched a single seat fighter using the most powerful engine available in production in Australia and using as many Wirraway components as possible. On 21 December 1941, design began and on 29 May 1942, the first aircraft was test flown.
Fred David, as a German Jew, had previously worked for Heinkel in Germany and later the Japanese Aircraft Company before fleeing Japan as a refugee when it established military links with Nazi Germany. As such he was considered officially as an “unfriendly” alien and was required to report to the police every fortnight.
250 Boomerangs were built by CAC, and due to the eventual availability of fighter aircraft from the UK and USA, the Boomerang was not required to face the technically superior Japanese fighters. Instead it was employed in Army co-operation duties where its manoeuverability at low level and its 20mm Cannon made it ideal for strafing and target marking.
In the New Guinea campaign its pilots developed tactics later used by Forward Air Controllers in the Korean and Vietnam wars.
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After The War. Post WW2 saw some in Government prepared to encourage more local production and a number of aircraft crept from the doors of factories in Melbourne. The F-86 Sabre, re-engined with a Rolls-Royce Avon was the best Sabre produced. The Mirage, built here, was another winner; certainly the best choice from what was on the tarmac at that time. We could have ended up with the F-104 - a fine aeroplane when you want to go a little distance very quickly, but not so useful in some other aspects. The Winjeel was as good a trainer as anyone else made - the tandem seating is actually the best arrangement of all - the instructor can see exactly what the student is doing.
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| CAC Avon Sabre |
So it was inevitable that someone in the Department of Supply decided that we could, and should, produce a small aircraft, primarily for what was then known as the Third Level Regional market. ( First level is international, Second Level is capital-city domestic, Third Level is the bush). This was a spot hitherto filled by Beech twins, and partially by the Islander. Everyone seems to ignore or forget that the US Federal Government supported their aviation industry with generous subsidies and tax incentives which gave them a huge advantage when competing for overseas markets. Third Level Regional airlines, defining these as companies that could economically run 13 passenger aircraft. Guess who manufactured 13 passenger aircraft to meet this convenient definition? And guess who, with an established home market, could then saturate the rest of the world with subsidised production? Of course, it goes without saying that such thoughts were far beyond the Australian political minds of the era
The Design. Nomad went through a number of iterations before it emerged as the aircraft we all know and love. The writer has the impression that these iterations began with a new version of the Ceres, which was a Winjeel modified as a cropduster. Whilst a fine trainer, the Winjeel/Ceres lacked the load-carrying ability of imported aircraft, which usually had considerably greater wingspan. It was a commercial failure, however it was an attempt to enter the commercial market and lessons were learned from it.
Design Chilling. Eventually the Nomad's design was chilled (not frozen) in a high wing, twin turbine, semi-STOL aircraft, with longer range than the Beech twins and more cargo space. The writer is of the opinion that the design was chilled around the Pratt and Whitney PT-6 turbine. Back then it was the only proven, in-production engine available in the desired power range. The writer is aware of a number of competing engines, but then the PT-6 was already a mature powerplant. There is a great deal to be said for designing a new airframe with mature powerplants, and anyone who's studied the development of aircraft during WWI and WWII will see the logic in this approach.
Buying Engines. The time came for someone from GAF to visit America, to talk to Pratt and Whitney and arrange a supply of engines of suitable specification. Unfortunately, by the time that the financial, contractual and administrative experts planned the trip, there was no room left for an engineer. They were to visit not only Pratt and Whitney but also Allison. Allison had already designed the 250, a helicopter turbine intended for small recon type helos. The 250 has subsequently become a very successful helicopter engine, but when the Nomad team visited it was little more than another item number in a long series of helicopter specifications.
The contract which actually gave birth and life to the Allison 250 was the US Army's LOH contract. Initially won by Hughes from a list of about 40 proposals, the first OH-6A's were deployed to Vietnam in March 1967, and 1434 were delivered by 1970. This is dream stuff for an engine manufacturer, but in the early 60's Allison didn't expect large orders for the engine and were looking for more customers to make it a viable proposition.
Helicopter engines are sold with output shafts running at about 6,000 rpm. The helicopter designers then have to provide the rotor reduction gearbox. So for the Nomad team, Allison drew in a reduction gearbox, added a propeller, and came up with the fixed-wing B-17 model. Whether they did this over a frantic weekend's effort after the GAF team arrived is a good question. However they then sold this concept to the Department of Supply beancounters. Whilst the writer has no factual details, anecdotal evidence indicates that the 250/B-17 was much cheaper than Pratt and Whitney's PT-6. The fact that there were no other B-17 powered aircraft in the marketplace seemed to escape the beancounters; if they did take this into account then they failed to appreciate the difference between the proven PT-6 with more than several million hours of service and one which was still on the drawing board. This was a bad decision - one driven by lack of experience.
Fewer Horses. The GAF team also failed to appreciate that the 250/B-17 was not in the same power range as the PT-6. Again, while the writer does not know for which PT-6 the Nomad was originally designed, nor what power output Allison actually claimed for their B-17, there was a discrepancy of maybe 150 horses between the two company's engines. That's 300 horses per aircraft which is a very significant discrepancy for one in the Nomad category.
Total Redesign. Undoubtedly, this power discrepancy would have been received with some concern in the Design Office. People would have been running around in small circles and there are probably unmarked graves in the wastes of Avalon. The power loss meant a complete redesign of the Nomad, a redesign which would not bode at all well for the aircraft in service. Weight had to be trimmed drastically. The original undercarriage was thrown out, to be replaced by a lighter and less capable arrangement ( VH-SUR, a gate guard at the Army Aviation Centre Oakey, has the original knee-action undercarriage).
Thinner Metal. Everywhere else panel thickness was reduced to a minimum. The ailerons, later to become a problem area, were a case in point. The GAF specs were for an aileron assembled from, in addition to a lot of other parts, an upper and a lower surface, identical and fluted for stiffness. To save weight these panels were very thin. They relied on fluting for their stiffness. This is not bad design, it is design which makes the most of a thin panel, and is a technique used world-wide. (Check out the Douglas A-4 Skyhawk's "temporary" rudder. Of fluted aluminum sheet, it remained as original through the production life of the aircraft) Hawker de Havilland in Sydney were the only people to have a press which could do this thin metal fluting operation. The first batch of aileron panels which went through HdH came to a quick halt.
HdH phoned GAF : "Hey, guys, we can't do this. The panels keep cracking at the ends of the flutes!"
GAF quickly compromised by suggesting they increase the panel thickness until a reasonable production rate was achieved.
This was a good decision. It was a decision which accepts that you cannot be on the spot to massage all of the design parameters all of the time. You are trying to expand a sheet of aluminium by maybe 300% as it passes from the flat surface into the flute. From GAF's point of view, HdH own the press, and have done lots of work with it. They know how metal behaves. There is no way that the HdH engineers were going to say that they couldn't make something for which they'd tendered. They are going to bust their guts to do it - but if they really can't, you better listen. So you have to be able to delegate.
The point of this is that the aileron sheet thickness ended up well above the initial design specification, which in turn complicated efforts to dynamically balance the ailerons. And, in the early 90's, when HdH went out of business, the press disappeared, and spare parts could no longer be made in Australia. Another point is that because you specify 20 thousandths of an inch thickness on a drawing does not mean that it can be made, or, that it will work in the field. The weight saving led to much anguish - a great many panels were replaced by thicker, stiffer and heavier ones in service.
The Engines. In the long term, the Allison 250/B-17 was not a success. Few military engines ever made their TBO - one commercial operator was successful in this, but only because the pilots were instructed to use just enough torque to scrape off the ground. Army pilots tended to practice short takeoffs requiring standing on the brakes until maximum power was developed. The engines did not respond well to such treatment.
Nomad Design Features. The Nomad design included some very smart and very sensible features. Aircraft which carry freight need a wide Centre of Gravity (CG) range. CG range is a function of the elevator. There are other constraints, but it comes down to the "authority" of the elevator, which must balance out the discrepancy between the CG of the unloaded aircraft, which is usually at or around 25% chord aft of the wing leading edge, and the CG of the freight, which is often well aft of this - unless you're flying a slender delta. Conventional elevators are simply movable surfaces affixed to the aft end of an immovable airfoil. They comprise maybe one third of the whole aerodynamic surface. But if the traditionally immovable bit can itself be made to move, then the whole thing can make a much greater contribution to balancing the CG discrepancy. This also means that one can deal with a larger discrepancy - presto, one has a wide CG range.
This is why the Nomad had an " all flying tail", as it is termed - intended to give a wide CG for whatever weird and bulky loads prevalent in the Australian outback one might want to carry. This wasn't achieved without some pain. Somewhat surprisingly, the Nomad's elevator is not very effective at low airspeeds, such as one uses at touchdown. Other problems will be highlighted later.
The STOL Bubble. The reader should be aware that the Nomad was designed in a period during which the industry went through an unusual perturbation. The gas turbine had finally produced the reliability which the makers of big piston engines could only dream of. Air transport was coming of age; one could book a flight from Sydney to Melbourne and expect that everything would go according to plan. Travelers everywhere soon discovered that it took longer to get from their homes or hotels to Mascot, Heathrow, JFK or wherever they intended to depart from. The advent of the Hawker Harrier, which rose vertically from an obscure coal yard in Central London, and arrived in New York a few hours later, fueled this frustration.
The marketing gurus of the aviation industry proposed Short Take-Off and Landing aircraft. STOL aircraft could collect passengers from steel mesh runways laid in a field or beside a convenient river then deliver them to the international airports. This promised a boom in civil air transport. DeHavilland Canada developed the four engined STOL Dash 7 to fill this role, which later transformed into the very capable Dash 8. The twin Otter (which sold far more aircraft than DeHav Canada ever expected it to) was also a result of this thinking.
Military planners were even more optimistic. The C-5A Galaxy would depart continental USA, and deliver troops, ammunition or whatever to some grassy paddock just behind the front line in Europe. so it was hoped. Even the Soviets tinkered with the idea, the IL 76 being an example.
There were two problems with this concept. US regulatory agencies were nervous about the concept of aircraft filled with holiday makers weaving through a forest of skyscrapers to plop down on a short slippery strip of steel mesh beside New York's east river. Murphy's Law said that someone would inevitably screw up. The terrorist attack on the World Trade Center has vividly demonstrated one side of this argument. The other side is that a misshap on landing would dump thousand of litres of inflammables into the river. Casual fishermen and itinerant riverbank inhabitants would all be incinerated. Boats, even ships, would disappear in flames. The greenies wouldn't worry too much about the human casualty list, but would instead scream blue murder about the tadpoles, frogs, gnats and migratory geese which were roasted. And the media, with its usual 20-20 hindsight, would demand of the Aviation Authorities: Why did you allow it ?
The second was that the engineers had their fertile imaginations stretched by the problems associated with subsonic cruise. Aircraft wings were already full of actuators, rods and screw-jacks. Those responsible for cruise performance took little delight in the concealment and fairing of the multitude of movable surfaces which had to be extended to allow the aircraft to return to earth at the velocities which STOL demanded. Have a look at a Caribou - there are about 15 separate bits and pieces hanging off the wings. When these surfaces doubled in size to allow yet shorter takeoff and landing distances, cruise speeds suffered. If you tilt the engines a fraction so that their thrust line helps short takeoffs, it detracts from the cruise performance. There was no way to reconcile the requirements of high subsonic cruise and STOL. Almost thirty years on however, with the Boeing C-17, we seem to have got a lot closer to the answer - but we don't see lots of civil operators buying C-17's. It has all become too expensive. And if you are wondering about the Galaxy, well, it does a fine job - from one long sealed runway to another. The rough field requirements weren't practical and were never met.
But back to the Nomad. Not entirely seduced by STOL, but influenced by the unarguable fact that a great many runways in outback Australia are what the Americans would define as " unimproved strips", the Nomad was designed from the outset to take a minimum distance for takeoff and landing. Herein is one of its points of genius. The Nomad uses conventional ailerons in flight. When the flaps are lowered, to convert the cruising wing section to a high lift section for takeoff and landing, lateral control is progressively transferred to a "slot lip aileron". This is a very obscure device, which is quite unexplainable except to those who have actually investigated it. The writer has seen only a couple of very slight references to it in 30 years of studying aviation literature. Yet someone, somewhere in England had made a thorough investigation into this very efficient method of lateral control. And someone in the Nomad office knew about it.
The mechanical transfer of control from conventional ailerons to the slot lip aileron is accomplished by a very sophisticated system of levers and bell cranks. The draftsman who drew it included simple methods of alignment, so it was a piece of pie to assemble and adjust. And it never seemed to fail, or to have any vices. I just wish the whole aircraft could have been drawn by that particular draftsman. It is not often appreciated that much design of machines and aircraft is done by draftsmen. Design Engineers design by indicating what they want to the draftsmen, they don't always actually sit down and work things out in detail. These days of course, CAD/CAM design helps greatly, but "back then" it was still mainly slide rules and intuition.
In the context of the DC-9 passenger door which failed in France, dropping the whole aircraft, Roger Bacon of Flight Magazine is reported to have said something like this:
"My first thought was that if I had drawn this (door) when I was a draftsman, my boss would have said, let's go back and have another go at this."
While the writer has taken this from memory and somewhat out of context, the essence remains the same. There are things which are just right. The slot lip aileron and the linkages which transfer lateral control to it on the Nomad, are very right. If the same draftsman had done the rest of the controls, maybe Nomad would have been a great airplane.
Loading and Unloading Cargo. Getting cargo in and out of airplanes can be a pain in the butt. The Curtiss C-46 Commando is generally regarded as the largest tailwheel cargo aircraft ever built. Few realise that it is actually larger than either the B-17 or the B-24. During WW2 most of the cargo flown over the Hump in Burma went on C-46's. Originally intended to be presurised it was designed on the double-circle principle - the fuselage was two intersecting circular sections, like the Boeing Stratocruiser ( C-97 to military afficionados). This puts the one and only cargo door on the upper circle, about 15 feet off the ground. Wasn't it a pain in the butt to load and unload ! The same can be said to a lesser extent of the venerable C-47. Another tail dragger, not only was it difficult to get bulky loads in through the side door (even with the C-47s double cargo doors) but it had to then be fidgeted and squirmed up a 20 degree incline inside the cabin. Not easy when it all had to be done using muscle power.
The Swinging Tail. Nomad was originally intended to have the whole tail section swing out to one side so you could drive up without worrying about running into it. Somewhere along the line this idea was dropped. They left the hinges out but everything else was still there. There was a double bulkhead and the control wires ran down the starboard side, so they could swing with the tail. Because of this control cables run ran thru the hinge points. It was not ideal, it was workable, but it had to be watched. This particular control run was the source of much anguish to maintainers and operators - it got stiff, then got loose, all as if by magic. The problem was never satisfactorily overcome.
Engine Controls. The Book on Light Twin-Engine Controls has been written. The Author is de Havilland Aircraft of Canada. Go look at a Twin Otter, or a Caribou. They are both high wing, twin engine aircraft. The engines and propellers are controlled by cables. Just like the flight controls they have pulleys to enable them to go around corners. These cables originate from control levers which are roof mounted. Sounds strange I know, particularly when the traditional cockpit layout shows central levers in a floor console. But sit in the bird, lift your hand to these roof mounted levers. They work and are a fine example of lateral thinking. We humans can lift our arms, can we not ? And because of this we get simple cable layouts. The average pilot is indifferent to such things.
But ask him to replace a Nomad throttle cable. The cable is a teleflex - it has an inner and an outer. The point is that every time there is a curve or corner, one slides against the other, creating friction. The cable starts at the center console. Down to the floor, Right Angle 1 across the floor, Right Angle 2 , go back a bit, Right Angle 3 up to the wing root, Right Angle 4 out to the engine. Four critical friction points around radii which are, if not less than the bare minimum radii recommended by the manufacturer, pretty damn close to it. I have seen Nomads where failure of one cable meant replacing both - you just could not get the same feel with one new and one old cable. And how long does that that take to replace? Which one does the owner want to pay for ? Which one do you want to sit around and wait till it is changed ?
Flight Controls. De Havilland also wrote the book on Flight Controls. They use a yoke, pivoted on a stick, connected to the floor. The conventional layout, with a spectacle pushing a pole into the panel, leaves you with the need to turn this motion through 180 degrees and get it under the floor. Maybe DHC have patented this. The de Havilland Canada method is the lightest, cheapest and smartest way of doing this. GAF would have been well advised to pay the licence fee if it was so, but I guess the Not Invented Here syndrome appears everywhere. Pride has its price. |
