Huge, Unsuccessful Transport Aircraft

There's something about size that appeals to the rational, technically-oriented mind. In certain circumstances, that is. Circumstances where economies of scale seem applicable. The problem is, size cannot become infinitely large or even "seriously large" without the object in question becoming unaffordably expensive or key components demanding features beyond the state of their engineering art.

An instance of the first case is the "paper battleship." Naval planners during the period, say, 1910-1940 would prepare concepts of future battleships. This might begin with the idea of using really large main armament -- an 18- or even a 20-inch shell, perhaps. But the rest of the vessel would have to be scaled to support such armament. And the price of such a ship might consume much of the navy's construction budget; a class of three or four ships would be prohibitive, not to mention the tactical and strategic consequences if one of those super-battleships was sunk. The Japanese Yamato class came close to this potential overkill and the United States planned, then cancelled, its Montana class which was more a super Iowa than a Yamato.

For aircraft, there are several problems related to large scale. The Boeing 747 in its early days and the new Airbus 380 forced upgrading of various airport facilities and earlier, relatively large aircraft such as the DC-3 airliner led to the replacement of grass landing fields with airports with concrete runways.

A more serious problem has been that aircraft engines weren't capable of reliably supplying the power required by huge (for the times) airframes. This problem became acute by the early 1940s when piston engines became increasingly complex and unreliable as power requirements grew. In short, their technology was reaching its natural limits. The solution was gas turbine engines, but it took 10 or 15 years for their technology to reach the point where power, fuel economy and reliability converged to where they could be used on commercial aircraft.

Just for fun, below is a gallery featuring ultra-large transport or cargo aircraft from the period centered on the late 1940s. Some were powered by those maxed-out piston engines and one used the new, trouble-prone turbine technology. I also dealt with large aircraft a while ago in this 2Blowhards post.

Gallery

Douglas C-74 Globemaster
Several aircraft have sported the "Globemaster" name: this was the first. Only a few were built as it was succeeded by the pudgy, double-deck C-124 that saw considerable use. I once flew in one of the latter from Kimpo airport near Seoul to Tachikawa airbase in Japan many years ago. An interesting feature seen on the C-74 that must have caught the fancy of Douglas designers is the double bubble pilot / copilot canopy arrangement that gives the plane a bug-eyed look. This was also used on Douglas' XB-43 "Mixmaster" prototype bomber. All very futuristic, but impractical for cockpit operational coordination.

Convair XC-99
The XC-99 was derived from the B-36 bomber. Pan American even considered ordering some, but decided to stick with more practical planes such as the DC-6 and Boeing Stratocruiser (which itself had engines that weren't paragons of reliability). Only one XC-99 ever flew.

Lockheed R6V Constitution
This was a Navy job. As the link notes, hardly any were built.

Martin JRM Mars
Another Navy transport, this a seaplane. The original Mars had twin tails. A few were built and saw service. If World War 2 had lasted another year in the Pacific, there might have been more in service.

Bristol Brabazon
Britain's Brabazon was spawned by a government committee, as were several other prototypes and minimal-production airliners (the main exception was the Vickers Viscount) that seemed nifty at the time but didn't even match the needs of government-controlled airlines. The Brabazon's development was long and it had no real chance of seeing airline service.

Saunders-Roe Princess
Flying boat airliners had pretty well seen their day by the end of World War 2, but that didn't prevent the British giving the concept one last stab in the form of the Princess. One more instance of too much, too late.

Pusher Military Aircraft: Failed Concept

From what I read, "pusher" propeller-driven aircraft have certain theoretical aerodynamic advantages over conventional "tractor" aircraft (where the propeller is positioned in front of the engine).

Though it's not obvious from looking at a photo or a prop-driven airplane in flight, a forward-facing propeller whips a lot of air into a spiral pattern that twists around even a highly streamlined fuselage (if it's a single-engine aircraft) and disrupts airflow over the wings almost no matter where the propeller is positioned.

The solution to all this nasty propeller-induced turbulence? -- place the propeller behind the engine so that it pushes rather than pulls, leaving the churned air behind the plane rather than engulfing important parts of it.

Even though the convention was the tractor arrangement, a number of early airplanes were pusher types including the Wright Brothers' 1903 flyer and some Great War combat planes. From time to time aircraft with tractor and pusher propellers were built. But designers quickly and nearly universally preferred the tractor arrangement.

The siren song of the pusher was heard once again in the late 1930s and early 40s for military planes. This post deals with some designs that reached flying prototype status, but only two of which entered real military service.

Despite the potential advantages mentioned above, the pusher configuration had its limitations. One was that it was often difficult to provide sufficient cooling for the motors. This is obvious for air-cooled engines requiring a large blast of air passing around the cylinders, but apparently was even the case for water-cooled engines requiring radiators.

Another problem was propeller clearance on takeoff and landing. There was a risk the the props might dig in to the ground when the aircraft was assuming a nose-up attitude. Tractor aircraft had much less to worry about in this regard.

But perhaps the greatest problem was what to do when the pilot had to bail out of a single-engine plane; without special steps taken, he would be chopped up as he passed through the propeller arc. Solutions included feathering the prop or detaching it before bail-out. Another solution was the ejection seat common on jet fighters but something that didn't emerge until towards the end of World War 2.

It is possible that the ejection seat and contra-rotating props of comparatively small diameter might have let to successful fighter designs by the late 1940s. But the advent of jet propulsion along with diminishing returns to increased piston engine power ended propeller-driven fighter planes regardless of whether they were tractor or pusher. The only real pusher success was a huge bomber, as noted below.

Bell YFM-1 Airacuda
YFM-1 was a pre-war concept for a plane that could serve either as a bomber escort or an interceptor. It had a five-man crew including a 37-mm cannon operator in the front of each engine nacelle (and subject to being decimated on bail-out). The planes were too heavy for the power available and the pusher system created pitching problems. There were even more problems -- see the link for an enumeration -- so that even though a test batch had been ordered, the Airacuda never entered full-scale production.

Vultee XP-54
The XP-54, along with the XP-55 and XP-56 were results of the Army's attempt to unleash airplane designers to create wild and crazy stuff. For some reason, all three participants in the program opted for the pusher layout. Every project resulted in disappointment, one important factor being that the engines planned initially were technical failures and replacement motors lacked enough power for performance superior to existing production models such as the P-51 Mustang. The XP-54 was the most conventional design, featuring a twin-boom arrangement to support the tail.

Curtiss-Wright XP-55
The XP-55 was more radical, having a "canard" layout where instead of tail-mounted horizontal stabilizers, they are placed near the nose.

Northrop XP-56
Most radical of all was the XP-56 which had no stabilizers at all, being close to a flying wing design with a fat fuselage. Note that the XP-56 had contra-rotating props with a smaller diameter of arc than a single-prop version might have. This would lessen the risk of prop dig-in on takeoff rotation or landing.

SAAB J21
This Swedish fighter actually reached production and saw service in the late 1940s and early 50s. Interestingly, it was adapted to jet power and that version also was produced.

Northrop XB-35
Two Army pusher configuration "intercontinental" range bomber designs reached prototype and test-batch status in the late 1940s. The XB- and YB-35s are manifestations of Jack Northrop's fascination with the flying wing concept. Like the J21, the YB-35 was adapted to jet power as the YB-49, but production contracts went to the plane below.

Convair B-36
Several hundred B-36 bombers were built and served in the U.S. Air Force's Strategic Air Command during the 1950s. It featured a pusher layout soon augmented with four jet engines mounted in pods below the wings for greater target-dash speed. Although the B-36 had its problems, it stands as the most successful military pusher aircraft since the Great War. The B-36 was replaced by the eight-jet B-52 which has remained in service for more than half a century.

Spitfire Bests Hurricane, Hunter Bests Swift

Life has its ups and downs. This was even the case in the aircraft industry back in the days when that industry had a lot of firms (as opposed to the comparative handful operating today). In some cases government ministries would try to balance contract awards amongst companies so as to keep a reasonable number in business should a war erupt and large production of aircraft be required.

In other cases fortunes of aircraft manufacturers rose and fell according to the quality of the airplanes they designed. That was to some degree the case for fighter plane builders Hawker and Supermarine in England.

By the mid-1930s, fighter production was dominated by Hawker with its Fury which competed mostly with Gloster with its Gladiator, Bristol with its Bulldog, and to a lesser degree Fairey and Blackburn. Supermarine formerly specialized in flying boats and high-speed racing floatplanes, but now was entering fighter design competitions.

In 1936 production was ordered for the Royal Air Force's first "modern" fighters -- the Hawker Hurricane and the Supermarine Spitfire -- the latter based on the racing-craft knowledge gained by designer Reginald Mitchell who died the following year of cancer, age 42.

Mitchell was succeeded by Joe Smith who presided over as series of modifications that kept the Spitfire competitive and in production throughout World War 2. He also led Supermarine's jet age design teams that created several production fighters, including the Supermarine Swift of the 1950s.

The Hurricane's designer was Sydney Camm whose teams produced outstanding aircraft over a period of decades, including the Hawker Hunter jet fighter that was developed about the same time as the Swift.

I'm not an aeronautical engineer, so I can't offer a professional assessment of the three men. From what I read, the consensus is that Mitchell and Camm rank among the "great" designers and Smith does not.

Given this background, how did the Hurricane, Spitfire, Swift and Hunter stack up? In brief, Supermarine won the first round, Hawker the second. Let's take a look:

Hawker Hurricane Is, 111 Squadron - late 1930s
The Hurricane was "modern" in that it had the following features that characterized fighters designs that emerged in advanced industrial countries starting in the mid-1930s: It was a monoplane (as opposed to biplane or triplane styles of the Great War), its landing gear retracted, the cockpit was fully enclosed, and its construction was largely of metal. In the case of the latter feature, the Hurricane lagged its equivalents in that the part of the fuselage aft of the cockpit was fabric-covered and not aluminum-skinned. This might have been because in some respects the Hurricane was a monoplane evolutionary step beyond the Hawker Fury biplane which also had its fuselage clad in metal to the front and fabric to the rear.

The Hurricane had a thick wing (compared to the Spitfire), was chunkier and had other features that resulted in lower top speed and inferior maneuverability. It was also inferior to opposing German fighters such as the Messerschmitt Bf 109E and the later Focke-Wulf FW 190. Hurricanes represented the majority of the RAF's fighter strength during the Battle of Britain in the late summer of 1940, but the somewhat sad experience of British and Belgian Hurricanes against the Germans in the Battle of France in the late spring of that year resulted in the RAF opting to send Hurricanes against attacking bombers rather than the escort fighters -- where possible, Spitfires were to attend to the Messerschmitts. Hurricane production ended in 1944 (Spitfire variants were built as late as 1948), being succeeded by Typhoon and Tempest fighter-bombers.

Speaking of being slightly behind the times, note the formation shown in the photo above. The six Hurricanes are in V ("vic" in RAF-speak) formations of three aircraft each. This formation was intended for interceptors, the three fighters attacking a similar formation of bombers. It proved inferior in fighter-to-fighter combat, so the British and American eventually adopted the German schwarm or "finger-four" formation comprised of two two-plane elements, each with a lead plane and a protective "wing-man."

Early Supermarine Spitfire I
The Spitfire was Britain's outstanding World War 2 fighter. Thanks to its wing design, it was both fast and maneuverable. Rolls-Royce kept it competitive by providing ever more powerful motors. Joe Smith eventually replaced the original wing with one that reduced the plane's potential maximum speed (the new wing had a greater thicknes-chord ratio) but allowed additional armament.

The main defect of the Spitfire was that it was designed as an interceptor tasked with defending geographically-small England from bomber attack and therefore it traded range for limited fuel-weight. The result was that the Spitfire could not accompany bombers on missions to targets as distant as Germany; that role fell to the American P-51 Mustang.

Supermarine Swift F.1, (or possibly an F.2), 56 Squadron - 1954
Whereas the Spitfire glows in glory, the Swift was an expensive failure. Like the Hunter, it was ordered into "superpriority" production once the Korean War started. But it only briefly served in fighter service. Years later, a version was moderately successful in the reconnaissance role.

The Swift's nearly endless teething problems centered around handling characteristics and difficulties introduced by one of its engine manufacturers. Its portly shape stemmed from the original intent to power it with a chubby centrifugal-flow Nene engine. But the Nene was bypassed in favor of the slimmer axial-flow Avon; the fuselage bulk then became a useful place for extra fuel tanks.

Hawker Hunter in Swiss service: 25th anniversary commemoration paint-job
The Hunter had its initial problems too, the worst being engine-surge and flame-outs when the 30-mm Aden cannon were fired. Once teething was taken care of, the Hunter proved to be an excellent fighter; nearly 2,000 were built and it served in many air forces besides the RAF

Thus were the tables turned, Hawker emerging from second-fiddle to First Violin and Supermarine becoming an aviation footnote.

Huge, Unsuccessful Transport Planes

There's something about size that appeals to the rational, technically-oriented mind. In certain circumstances, that is. Circumstances where economies of scale seem applicable. The problem is, size cannot become infinitely large or even "seriously large" without the object in question becoming unaffordably expensive or key components demanding features beyond the state of their engineering art.

An instance of the first case is the "paper battleship." Naval planners during the period, say, 1910-1940 would prepare concepts of future battleships. This might begin with the idea of using really large main armament -- an 18- or even a 20-inch shell, perhaps. But the rest of the vessel would have to be scaled to support such armament. And the price of such a ship might consume much of the navy's construction budget; a class of three or four ships would be prohibitive, not to mention the tactical and strategic consequences if one of those super-battleships was sunk. The Japanese Yamato class came close to this potential overkill and the United States planned, then cancelled, its Montana class which was more a super Iowa than a Yamato.

For aircraft, there are several problems related to large scale. The Boeing 747 in its early days and the new Airbus 380 forced upgrading of various airport facilities and earlier, relatively large aircraft such as the DC-3 airliner led to the replacement of grass landing fields with airports with concrete runways.

A more serious problem has been that aircraft engines weren't capable of reliably supplying the power required by huge (for the times) airframes. This problem became acute by the early 1940s when piston engines became increasingly complex and unreliable as power requirements grew. In short, their technology was reaching its natural limits. The solution was gas turbine engines, but it took 10 or 15 years for their technology to reach the point where power, fuel economy and reliability converged to where they could be used on commercial aircraft.

Just for fun, below is a gallery featuring ultra-large transport or cargo aircraft from the period centered on the late 1940s. Some were powered by those maxed-out piston engines and one used the new, trouble-prone turbine technology. I also dealt with large aircraft a while ago in this 2Blowhards post.

Gallery

Douglas C-74 Globemaster
Several aircraft have sported the "Globemaster" name: this was the first. Only a few were built as it was succeeded by the pudgy, double-deck C-124 that saw considerable use. I once flew in one of the latter from Kimpo airport near Seoul to Tachikawa airbase in Japan many years ago. An interesting feature seen on the C-74 that must have caught the fancy of Douglas designers is the double bubble pilot / copilot canopy arrangement that gives the plane a bug-eyed look. This was also used on Douglas' XB-43 "Mixmaster" prototype bomber. All very futuristic, but impractical for cockpit operational coordination.

Convair XC-99
The XC-99 was derived from the B-36 bomber. Pan American even considered ordering some, but decided to stick with more practical planes such as the DC-6 and Boeing Stratocruiser (which itself had engines that weren't paragons of reliability). Only one XC-99 ever flew.

Lockheed R6V Constitution
This was a Navy job. As the link notes, hardly any were built.

Martin JRM Mars
Another Navy transport, this a seaplane. The original Mars had twin tails. A few were built and saw service. If World War 2 had lasted another year in the Pacific, there might have been more in service.

Bristol Brabazon
Britain's Brabazon was spawned by a government committee, as were several other prototypes and minimal-production airliners (the main exception was the Vickers Viscount) that seemed nifty at the time but didn't even match the needs of government-controlled airlines. The Brabazon's development was long and it had no real chance of seeing airline service.

Saunders-Roe Princess
Flying boat airliners had pretty well seen their day by the end of World War 2, but that didn't prevent the British giving the concept one last stab in the form of the Princess. One more instance of too much, too late.

Tri-Motor Aircraft, 1930-1950

Most aircraft either have a single motor or a number of motors evenly divisible by 2 (2, 4, 6 etc.). Odd-number engine counts such as five and seven are possible, but only tri-motor aircraft saw significant production in the odd-count, multi-engine category.

There are two main reasons for going the three-motor design route. One has to do with safety. In the days when reciprocating engines were the norm, reliability of such motors was often questionable. In the early days of aviation, motors were comparatively crude and their design imperfectly understood. By the 1940s, engine design was pretty well understood, but reliability was compromised by the quest for ever more power. In the case of radial, air-cooled motors, the route to more power was through adding cylinders and accessories such as turbocharging. The result was complexity that led to unreliability that plagued aircraft such as the B-29 bomber and Super Constellation airliner.

So, if four engines couldn't be justified, then why not have three if the loss of one motor on a two-motor plane was too risky.

Actually, this implies that only one working motor might not have the power to maintain flight. And this is the second reason for tri-motor craft: in many cases (especially in the years around 1930) two motors weren't really sufficient to power large (at the time) transports and bombers.

Tri-motor aircraft have some disadvantages. The odd engine count precludes having engines driving propellers turning in opposite directions in order to cancel out torque effects imparted by propeller rotation. A motor mounted at the nose of an aircraft usually impaired visibility for the pilot. Post-World War 2, the center engine would also occupy space that would ordinarily be used by a radar set.

The initial heyday of tri-motors was the early 1930s. Three-engined jet airliners were common for a number of decades starting in the early 1960s. But that's a subject for another time.

Below is a gallery of tri-motor aircraft in the years before 1950.

Ford Trimotor and three-engined Boeing 727
This photo was taken in 1964 or 1965 showing both planes in American Airlines livery. I saw this restored Ford at the 1965 New York World's Fair.

Fokker F.VIIb
This was a rival to the Ford. Pictured here is the one flown by Sir Charles Kingsford-Smith on some of his long-distance flights. It also was the type of plane that crashed, killing famed Notre Dame football coach Knute Rockne. A factor in the crash was Fokker's use of wooden construction for the wings, spelling commercial doom for the F.VII: Fords were all-metal.

Stinson SM6000
Yet another high-wing monoplane tri-motor.

Stinson Model A
This was a low-wing tri-motor representing a trend away from high-mounted wings for monoplane transports. Several airlines used it during the mid-1930s, as indicated here.

Pander S-4

Pander S-4 at Mildenhall, England
Pander was small Dutch aircraft company (Wikipedia entry here) that built the S-4 as a prototype fast mail plane. It was perhaps the sleekest piston-engined tri-motor ever built, but unreliable. It was destroyed in a crash in the 1933 London-Melbourne competition.

Junkers Ju 52
The Ju 52 (alias Tante Ju) was by far the most successful piston-engined tri-motor, nearly 5,000 being between 1931 and 1952.

Savoia-Marchetti SM79 Sparviero
Both bomber and transport versions were built of this general design. Three motors were used for the bomber because Italy lagged behind Germany, Britain and, to a lesser degree, France in engine horsepower.

Northrop YC-125C
Three-engined planes were considered passé after World War 2, yet for some reason Northrop produced the archaic-seeming YC-125 in test-batch numbers.

Martin Martin XB-51
This flashy prototype jet attack bomber classifies as pre-1950 because its first flight took place 28 October, 1949. The "T-tail" and positioning of the forward engines are tell-tales of the influence of World War 2 German design as well as active participation by Hans Multhopp who helped design the Focke-Wulf Ta 183 fighter that was never built, but influenced the later Saab J-29 (Sweden) and MiG-15 (USSR).