An analysis of late propeller era combat aircraft

Back in the early 30's bombers were still crude: The were meant to take off, cruise, drop bombs, cruise possibly fend of fighter with machine guns and land. This was quite the same approach as in the First World War. In fact, night bombing (which happened to small extent in WW1) was included, but not exactly popular due to poor accuracy. This dominant bomber concept was so crude that Ju 52/3m passenger aircraft were adaptable as auxiliary bombers.

This primitive model of a bomber was shaken in the 30's by two new concepts; the dive bomber (for better accuracy of bomb drops; notably the Ju 87) and the fast bomber (for avoiding fighters; notably the early Blenheim, early Do 17 and SB-2).

Tupolev SB-2. Skin by Karel Chvojka, 3dz by Captain Kurt mod. by Karel C.

The machine gun defence proved to be unsatisfactory. It was difficult to add more defensive machine guns, while fighters increased their weaponry from two to up to eight machine guns. Armour plating, armoured windshields and self-sealing fuel tanks plus the increasing strength of airframes reduced the effectiveness of normal machine guns. Fighters were able to cope by adding 20 mm autocannons, while the same calibre was very unwieldy in movable installations for bomber defences.

Bombers needed better survivability than armour and machine guns could afford. Four approaches promised relief; flying higher, flying faster, flying in darkness and flying with escort fighters.

To fly higher was no good solution (for bombers) because of the inherent accident and reliability issues (due to freezing temperature), added aircraft cost, low payload and poor accuracy of bombing runs.

To fly faster was a questionable solution (for bombers) because it was a time of rapid improvements of top speeds in aviation. A bomber prototype could easily fly faster than all contemporary fighters and still find itself to be much slower than hostile fighters during a war only a few years later. The Mosquito was later on successful with this approach, but only so because it faced opposing forces that were limited in their performance (especially at high altitude) in part by an inferior raw materials base. Propeller aircraft were also bound to meet the limit of their potential at about 800 km/h, and without the introduction of turbine engines we'd have seen an air war scenario in which almost all aircraft would have had a very similar top speed again (as they had already in WW1).

To fly in darkness meant high training and avionics costs, a high accident rate and a typically poor accuracy.

To fly with escort fighters proved to be most successful, but that wasn't about bomber design itself.

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Reconnaissance aircraft of the late 30's looked still a lot like First World War reconnaissance aircraft, but they had badly fallen behind fighters in both cruise and top speed. The Hs 126 is a typical example. The poor survivability of such recce aircraft called for new approaches.

One approach was to fly higher - this proved less problematic for (photo) reconnaissance than for bombing, and the Ju 86P was one of the extreme examples.

Another approach was to fly faster, and this worked for recce better than for bombing simply because air forces needed fewer recce aircraft and the fast fighters could be adapted to photo reconnaissance. The Spitfire PR versions are a good example, also the F-4/-5/-6 U.S.A.A.F. aircraft and the Bf 109 and Fw 190 with recce kit (a specific "Rüstsatz"; mission module). There were also successful two-engined reconnaissance aircraft and even some dedicated fast photo recce aircraft.

The highly successful Japanese Mitsubishi Ki-46 III high speed photo reconnaissance aircraft

To fly in darkness proved to be a niche escape, for both illumination/flash bombs and infrared photography were apparently not fully satisfactory.

To fly with escort fighters - a typical WW1 approach - was unsuccessful because it was both uneconomical and because the ground control for interceptors enabled the defenders to face such a recce package with altitude and numerical superiority just about every time. This in combination with the fact that a single recce aircraft suffices to make photos while a single bomber doesn't suffice to bomb a target properly defined the recce aircraft as unique. They were usually alone on their missions. This influenced which survivability strategies did work and which didn't.

A unique alternative for battlefield recce aircraft was to fly too slow. Fighter had advanced in top speed at the cost of aerodynamics that led to a high stall speed. The Fi 156 was very successful as a short range battlefield reconnaissance aircraft in part because even fighter aces had difficulties to get a Fi 156 into their crosshairs if they managed to do it at all. It was just too damn slow and agile. The same effect was observed in trial mock dogfights against Fl 282 helicopters. Very slow recce aircraft were only suitable for very short range aerial recce and very vulnerable to anti-air weapons, though.

The next analysis is about fighters. There were basically two directions for fighter philosophies in the 30's; the manoeuvrability school (Italians, Japanese, Czechs) that emphasised dogfights and even aerobatics (overall a similar philosophy as in WW1 air combat) and the high speed school (Germany) that emphasised a superior speed. The Russians initially followed both schools with their I-16 (fast monoplane) and I-153 (more agile biplane).

The high speed school was typically combined with low drag liquid cooled engines that were less powerful than radial engines (during the 30's) and did thus initially lack a superiority in climb rate over the more agile fighter designs. Liquid-cooled engines caught up with radials when radials grew to the limits of single radials (the solution was the double radial engine, but that brought cooling issues) at the end of the 30's. By 1939/1940, both liquid and air cooled engines were at about 1,000 to 1,300 hp. By this time liquid cooled engine-driven fighters had caught up with comparable radial-driven fighters in climb rate.

The whole competition changed during WW2. The high manoeuvrability school lost out in Europe; faster fighters were dominant because they chose when to fight and only they were able to cope with fast bombers. The Japanese stuck to the manoeuvrability school with few exceptions, Italy did too (and failed for several reasons) and the British did at least keep a better manoeuvrability than Bf 109 fighters.

The new conflict was different than the 1930's conflict between fighter philosophy schools: All fighters had to have a similar top speed to be competitive, but they proved to have different manoeuvrability strengths.

The vertical air combat manoeuvrability school emphasized climbing and diving and in some cases also a high roll rate. The horizontal air combat manoeuvrability school emphasized tight turns and a low stall speed. The vertical school won, as evidenced by the Fw 190's success over Spitfires and the 1943-1945 success of U.S. fighters against most Japanese fighters. The reason was simple; the vertical school was again dominant, for it was the key to offensive manoeuvres. The horizontal manoeuvring was only at its premium in defensive manoeuvring and at very low altitudes.

Vertical air combat manoeuvre example: A Bf 109 expert vs. defensive fighter ring

To fly tight turns was mostly about shaking off a pursuing fighter (and had little chance of success if employed offensively), while climbing and diving was mostly about attacking a fighter (often with the deadly advantage of surprise). Defence may be stronger than offence most of the time, but offence is decisive. The vertical air combat manoeuvrability school was furthermore still potent in numerical inferiority situations.

Another division between fighters was between fighters for high altitude and for low altitude. Eastern Front and Pacific air wars were mostly about low altitudes, while Western European air combat was mostly about high altitudes. There was a spiral for ever greater practical flight ceilings whenever high altitude combat became dominant in a theatre. The Allies won this race in 1942-1944 thanks to the British lead in two-stage superchargers and the American ability to supply the necessary heat-resistant alloys for turbochargers. The Germans trailed in both regards, but jumped far ahead in 1944 with turbojet engines (even though they lacked heat-resistant alloys and had a very short lifespan, poor reliability and handling characteristics).

It's also possible to divide between short range and long range fighters; long range was important for escort fighters and over the vast expanses of the Pacific theatre, while short range was sufficient for interceptors and fighters supporting ground warfare.

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The post-WW2 period saw competing philosophies for fighters as well:

# Short range ("WVR") vs long range ("BVR") air combat

# Short range fighters vs. long range fighters

# high performance vs. huge numbers

# pursuit of superior speed and altitude performance after the first Mach 2 generation (mostly MiG-25, later F-22)

# low visibility to sensors ("stealth") vs. much external hardware

# avionics with finesse vs. brute power avionics (example for the latter: MiG-25 radar)

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It's interesting stuff (to me), but I'm not so sure about the lessons.

Aircraft kept becoming more capable, more refined, more oriented at their purpose.

There's an eternal development for better survivability.

Superior offensive qualities tend to dominate over the superior defensive qualities in air combat.

Sven  Ortmann of Defense-and-Freedom Blog

Battle of Britain-Main Fighters

Messerschmitt 109.

The Messerschmitt 109 first flew in October 1935, powered by British Rolls- Royce Kestrel engines. The aircraft entered Luftwaffe service in spring 1937 and received its baptism of fire in the Spanish civil war. By the beginning of World War II, the aircraft existed in a number of variants, and 1,000 were deployed against Poland in September 1939. The 109 was superior to most other fighters at the outbreak of the war but was fairly evenly matched with the British Spitfire and Hurricane in the Battle of Britain. It did have one very significant advantage over these rivals, however. Its fuel injection system allowed for a constant fuel flow even in negative-g conditions, which meant that a pilot could dive or shear away much more quickly than his opponents. This added significantly to the plane's survivability. Counterbalancing this advantage, however, was the 109's limited range-a 300-mile operating radius for the 109G. This gave the fighter precious little combat time over relatively remote targets such as those in England. 

Some 109 variants had a cannon placed in the hollowed-out nose cap. In early models, this created an unacceptable level of vibration, which, however, was eliminated in later versions. Additionally, most of the fighters were fitted with two wing-mounted cannons and two machine guns mounted on the top of the nose cone that were synchronized to fire through the propeller arc. The 109G, introduced in 1942, was powered by a Daimler- Benz DB605 1,475-horsepower engine to a top speed of 387 miles per hour at 23,000 feet. Wingspan was 32 feet 6 ½ inches. The backbone of the Luftwaffe, some 30,000 109s were built before the end of the war.

Hawker Hurricane 1.

Although less celebrated than the Supermarine Spitfighter, the Hawker Hurricane, not the Spitfire, was responsible for 80 percent of the German aircraft shot down in the Battle of Britain. Designed in 1935, the Hurricane was introduced into RAF service in 1937. At the beginning of the Battle of Britain, the RAF had 32 squadrons of Hurricanes versus only 19 squadrons equipped with Spitfires. Less agile than the Spitfire and slower than Germany's premier fighter, the Messerschmidt Bf109, the Hurricane was deployed against German bomber formations, whereas the Spitfires were used against German fighters. 

At the start of the war, the RAF had 497 Hurricanes. Before the end of the war, the Hawker company delivered 10,030, the Gloster company 2,750, and the Canadian Car and Foundry Company 1,451. Powered by a single 1,030-horsepower Rolls-Royce Merlin III 12-cylinder engine, the Hurricane had a wingspan of 40 feet and a top speed of 328 miles per hour at 20,000 feet. It was armed with eight wing-mounted .303-inch Browning machine guns.

Supermarine Spitfire.

Introduced in 1938 and produced in some 40 variants, the Supermarine Spitfire became the single most celebrated fighter aircraft of World War II. Driven by a Merlin Mk III engine making 1,030 horsepower, the version that first entered service had a top speed of about 360 miles per hour and was armed with eight .303-inch machine guns. The Spitfire XIV, introduced in 1944, had a ceiling of 40,000 feet and a top speed of 440 miles per hour and was responsible for shooting down more than 300 German V-1 buzz bombs. The XIV version and several earlier versions as well also had increased armament: two 20-millimeter cannon were added either to the four .303-inch machine guns or to two .50-inch machine guns. Some versions also carried one 250- or 500-pound bomb under the fuselage and one 250-pound bomb under each wing. The Spitfire survived the end of the war and was used by the RAF for photoreconnaissance until 1954. Wingspan for all versions was 36 feet. 

An aesthetically beautiful aircraft, the Spitfire incorporated a light-alloy monocoque fuselage and a single-spar wing with stressed-skin covering and fabric-covered control surfaces. The aircraft proved highly maneuverable and was more than a match for the best German fighters during the Battle of Britain, where it earned its first and most enduring glory. Some 20,334 Spitfires (all versions) were produced during the war, and a naval variant, the Sea fire, was produced in a quantity of 2,556.

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Following the fall of France in the Battle of France, Adolf Hitler contemplated launching Operation Sealion, the cross-channel invasion of England. Encouraged by the claims of Luftwaffe chief Hermann Göring, Hitler believed that bombing raids on principal English cities and industries would, at the very least, prepare the way for the invasion and, even more important, might well render the invasion unnecessary by bringing Britain to its knees. 

At Hitler's disposal were the forces of the Luftwaffe now based on French and Belgian airfields. The available forces amounted to approximately 2,679 aircraft, including 1,015 medium bombers, 350 Stuka dive bombers, 930 fighters, and 375 heavy fighters. These included some of the most advanced aircraft of the war at this time. To oppose these forces, the British Royal Air Force (RAF) could muster no more than about 600 Hurricane and Spitfire fighters. Outnumbered as they were, these were excellent planes, and they were manned by superbly trained, highly skilled, and extraordinarily motivated pilots under the command of the venerable Air Chief Marshall Hugh Dowding. 

The battle, the first in history fought entirely in the air, unfolded in three successive, albeit overlapping, phases, beginning on July 10, 1940, with a heavy German air raid. This signaled the start of the battle's first phase, which was directed at destroying the southern ports from Dover west to Plymouth. This area was the most likely site for invasion landings, and Hitler sought to neutralize its defenses. Almost every day, German medium bombers, escorted by fighters, crossed the English Channel and bombed ships as well as port installations. On August 15, the first phase of the battle reached its point of greatest intensity when approximately 940 German aircraft attacked in the south as well as in the north. The RAF managed to shoot down 76 of the German planes, losing 34 fighters in the exchange. The Germans also destroyed 21 British bombers on the ground. 

Overlapping the first offensive phase was the second, which targeted airfields, aircraft factories, and radar installations. The objective was to achieve air supremacy by attacking Britain's airfields (and the aircraft there) and aircraft production as well as its highly advanced radar capability. In the space of two weeks, from August 24 to September 6, the Luftwaffe destroyed or severely damaged 466 Hurricane and Spitfire aircraft; 103 British pilots were killed and 128 wounded, representing a quarter of the RAF's entire fighter pilot strength. Yet the cost to the attackers was so heavy as to be a pyrrhic victory. The Germans lost more than twice the number of planes the British lost and more than twice the number of pilots. Worse, Hitler directed his bombers to cease their attacks on RAF facilities and aircraft factories and, beginning on September 7, to bomb civilian targets. The first objective was the air defenses of London, which was raided by some 300 German airplanes in a daylight mission. On September 15, more than 400 bombers attacked the British capital in what would be the largest daylight raid on London, with 56 of the bombers downed by RAF fighters or ground-based antiaircraft fire. 

Göring was badly shaken by his losses on September 15 and concluded that daylight raids were too costly. This led to the opening of the third and final phase of the Battle of Britain, the exclusive concentration on night bombing. Historians generally identify September 7 as the beginning of the Blitz. For its first week, the Blitz included daylight and nighttime raids, but from September 16 on, only night raids were carried out. The Blitz portion of the Battle of Britain proceeded continuously, without intermission, for 57 nights. On average each night, 200 bombers dropped both incendiary and high-explosive ordnance on London. The worst night was that of October 15, when 480 bombers dropped 386 tons of high explosive and 70,000 incendiary bombs on the city. They were met by six squadrons of British night fighters and the massed fire of some 2,000 antiaircraft guns. 

There is no question that the 57-night Blitz was devastating. More than 43,000 British civilians were killed, and some 200,000 were wounded. Property damage was staggering; ultimately, about 20 percent of London was destroyed. Food production was diminished, but no major food crisis was created. Nevertheless, the Blitz was futile. Hitler had made a disastrous and unrecoverable mistake in diverting the raids from the RAF facilities and factories, which turned out Spitfires and Hurricanes at an incredible rate. When Göring was forced to abandon daylight raids, he effectively conceded victory to the RAF. Although the Battle of Britain would not end until November 3, the Germans had lost it back in September. 

Between July and November, the RAF lost 915 fighters, 481 pilots killed, missing, or taken prisoner, and 422 pilots wounded. The RAF claimed 2,698 kills against the Germans, but documented German aircraft losses amounted to 1,733-still a crippling number. 

After the November 3 raid on London, the Battle of Britain proper ended, but the Blitz continued as the Luftwaffe turned to raids on industrial centers, especially the Coventry air raid (500 bombers dropped 600 tons of ordnance on the night of November 14) and Birmingham (hit mercilessly from November 19 to November 22). London was struck again on December 29, mainly in a massive incendiary attack that triggered more than 1,500 uncontrollable blazes. All through the winter of 1940-41, raids hit port cities, and on May 10, 1941, London was hit by an incendiary attack that was the worst and last of the Blitz. In the more than 2,000 fires started, some 3,000 were killed or injured. Defenders shot down 16 German bombers, the most shot down during any nighttime raid. 

Rather than see his air force destroyed, Hitler broke off the Blitz after the May 10 raid and redirected the bulk of the Luftwaffe to the eastern front war against the Soviet Union. Operation Sealion, the invasion of Britain, would never be carried out.

Further reading: Bishop, Patrick. Fighter Boys: The Battle of Britain, 1940. New York: Viking, 2003; Bungay, Stephen. The Most Dangerous Enemy: A History of the Battle of Britain. London: Aurum Press, 2002; Clayton, Tim, and Phil Craig. Finest Hour: The Battle of Britain. New York: Simon & Schuster, 2002; Wellum, Geoffrey. First Light. New York: Wiley, 2003. Gunston, Bill, and Chris Westhorp. The Illustrated Directory of Fighting Aircraft of World War II. St. Paul, Minn.: MBI Publishing, 2000; Jane's Information Group. Jane's All the World's Aircraft of World War II: Collector's Edition. New York: HarperCollins, 1994; Mondey, David. The Concise Guide to British Aircraft of World War II. London: Book Sales, 2002; Wilson, Stewart. Aircraft of World War II. Fishwyck, Australia: Australian Aviation, 1999.