The Evolution of the Messerschmitt Bf 109
By Robert Moyse
Acknowledgement: I wish to record my gratitude to Neil Stirling and Mike Williams of www.wwiiaircraftperformance.org for researching and publishing so much of the data on which this article depended.
This is the story of how the capability of the Me109 evolved during its life and how it compared with its enemies, based on the best information available at the time of writing. Although the most numerous fighter of the War, surviving documentation covering its development is not as comprehensive as might be expected, but it is sufficient to bust many Messerschmitt myths, both positive and negative. Much of the confusion lies in the fact that the designations of its various models do not necessarily correspond to the engine types used and performance was, obviously, determined largely by engine power. Even within those parameters, engine types of the same superficial designation gave different outputs at different stages in their lives. This is confused further by the Luftwaffe's use of different types of fuel.
As a coarse aggregation, the Me109 was technically competitive with the best, throughout the war, excluding a critical period during the peak of the daylight bombing offensive when it fell behind. Its fortunes in battle were determined more by strategic and operational circumstances than any failure to keep pace with the opposition and that is creditable for a design that flew before any of its enemies. The Me109 destroyed more enemy aircraft than any other fighter in history.
The basic concept behind the Me109 was to build the smallest airframe capable of accommodating the new generation of liquid-cooled V12 engines that were starting to predominate in European fighter design in the early thirties. Willy Messerschmitt had cut his aeronautical teeth designing successful gliders and had accumulated considerable experience with modern all-metal monocoque construction by 1934. This had resulted in a successful four-seat, sporting aeroplane, the Messerschmitt 108, which was widely acclaimed for its fine flying qualities. Capitalizing on the success of the 108, Messerschmitt incorporated many of its features into the 109. In many respects the 109 was a single-seat 108 with a big engine. He also understood, better than most of his contemporaries, the military importance of suitability for mass-production and designed the 109 accordingly.
The result was a technically advanced aeroplane with a number of features that raised contemporary eyebrows. All-metal monocoque construction was unusual for fighters at that time, although it had been used successfully in a number of advanced passenger aeroplanes, predominantly in the USA. The same applied to its fully enclosed cockpit and retractable undercarriage.
Although it was not noted at the time, the Me108 and 109 had certain characteristics that might, in retrospect, be considered to reflect Messerschmitt's glider heritage. They both had well harmonized controls at low speed, zoomed well, had good stalling characteristics, were resistant to spinning and, if they did spin they recovered without pilot intervention.
At higher speeds, however, things were less satisfactory. The effect of propeller torque, irrelevant to gliders, required high rudder pedal force to keep the aeroplane flying straight. The force required to move the ailerons increased linearly with speed up to an indicated airspeed of 220 mph, but became exponentially heavier thereafter.
The elevator design was also unusual, downward movement angle being almost as large as upward movement. In a powered aircraft upward movement was usually much greater, but in an un-powered glider there is little point in being able to throw the nose rapidly skywards, whereas the utility of instantaneous downward pitch to avoid stalling and gain enough speed for maneuvers to is self-evident. As might also be expected, it had a remarkably good glide angle for a powered aircraft.
The Me109 was a more highly loaded aeroplane than was considered advisable for a fighter in the mid-1930s. That is to say it contained more weight and power in a smaller volume than was usual. Contemporary thinking was that this would lead to dangerously high landing and takeoff speeds. To overcome this, Messerschmitt employed long undercarriage legs that gave the wings a high angle of attack during the take off run and Handley-Page style wing slots, which opened automatically at low speed, giving extra lift and drag. These measures, combined with well-designed flaps, achieved their aim and the 109 had short take off and landing runs.
It was also believed that high wing loading and density would lead to poor maneuverability. By some measures, especially horizontal turning, this was true. Its characteristics were more akin to fighters of the next generation than to its contemporaries, notably, high speed in level and diving flight and excellent energy retention. In 1935, most air forces did not even have a term to describe energy retention, but the concept recognizes that speed and altitude are exchangeable during maneuvering. A dense, low drag design like the Me109 made the exchange more efficiently, retaining its speed longer in a zoom climb, while acquiring speed in a dive more quickly.
Soon after the introduction of the Me109 the Sino-Japanese and Spanish civil wars broke out and the fighting in both seemed, initially, to support the traditional view that the tightest possible turning circle was what really mattered. Early Me109s had a wider horizontal turn radius than most other fighters in Spain, but soon proved that it only mattered if Messerschmitt pilots conceded to horizontal turning fights.
Instead, they learned to exploit the Messerschmitt's different characteristics against those of traditional lightly loaded biplane fighters. Provided they kept their speed high they could zoom-climb to safety, even when their opponents sustained climb rate was comparable. Against biplanes, they could also break off combat at will, using the superior diving acceleration provided by the Messerschmitt's dense, low-drag design. By and large, they refused to engage in the low-speed turning matches that characterized previously traditional fighter combat.
The Me109 was not, however, the only modern retractable undercarriage monoplane in the Spanish Civil War. The Russian Polikarpov I-16 first flew in 1933 and was present in large numbers. Prior to the Messerschmitt it was by far the most advanced aeroplane in service. It was as different visually from the lean Me109 as any fighter could possibly be, with a short, fat, flat-fronted fuselage and almost triangular wings with exceptionally long-chord roots, tapering sharply to narrow tips. By 1937 it was, arguably, at its peak. Powered by a 750hp single row nine-cylinder radial engine, it was reported to have had superior zoom and sustained climb to the 109B and a very high rate of roll.
On paper the I-16 looks more impressive than the 109B but this was not borne out in combat. The I-16 had surprisingly poor level flight acceleration. In combat this difference in acceleration led to the impression that the 109B was faster and, in practical terms, meant it usually was even though maximum level speeds were similar. It was easier to ride the edge of the stall in the Messerschmitt, as the I-16 was more prone to spin, although both aircraft had excellent spin recovery. Despite being the first serial production fighter to have pilot armour, the I-16's wooden structure proved more vulnerable to battle damage than the all-metal Messerschmitt. The I-16 also vibrated so badly that it was difficult to aim its guns.
Despite being able to out-turn the I-16, German pilots found in Spain that the safest and most effective way to employ the 109 was by dive and zoom. Dive and zoom was a tactical method developed in WWI and not the only one to be rediscovered in the Spanish Civil War. The I-16 was also quite well suited to this technique but it seems they rarely adopted it in Spain. The Luftwaffe also developed looser formations of pairs and fours, which were better suited to the high-speed combat of which the 109 was capable. These new methods allowed whole formations to execute crossover turns as quickly a single aircraft, rather than the cumbersome wheeling maneuvers still in use in other air forces.
Armament became an important issue during this period. The Me109 was designed to carry two rifle-calibre machine-guns in the engine cowl with 1000 rounds each. Anything additional demanded improvisation. The Jumo engine had provision for a gun to be fitted between the V of the cylinder banks, but it tended to overheat and was awkward to get at. The wings were not designed to carry armament, but Messerschmitt modified them in 1937 to carry one machine gun each, thus the Me109 had five potential machine-gun positions. In the 109 B, normally either two or three were fitted, while the 109C had four.
Despite the 109's popularity with its pilots, the Spanish Civil War exposed some serious shortcomings. Its small dimensions had resulted in a tiny cockpit, the sides of which touched the pilot's elbows and limited the force he could apply to the stick. The long nose obscured the pilot's view and its sideways-pivoting canopy mechanism could not be used in flight.
Even in its earliest, lightest, most benign form the 109 could be tricky to land. It needed a steep approach until just before touchdown, when it had to be flared sharply to achieve the required nose-up attitude. This needed fine judgement and there was a tendency for the left wing to drop in the event of error. Attempting to correct matters by speeding up was the instinctive reaction, but a burst of throttle exacerbated the roll to port and often led to crashes. Trying to correct with the ailerons usually led to aileron snatch and set the aeroplane rocking from left to right until one wheel touched down. Touchdown in this condition with such a narrow undercarriage exacerbated the rocking until a wing tip dug in and the aircraft ground-looped.
To add to the hazards, a hard landing was likely to collapse the delicate undercarriage legs. Once down, the long, steeply inclined nose obstructed the pilot's view and many 109s came to grief taxiing into obstacles after the wheels were safely on the ground. The cramped cockpit and hinged canopy did not allow the pilot much scope for moving his head to get a better view. Provided that it did not roll into anything, it behaved well once down with a short landing run and no tendency to nose-over under hard braking. In the lightweight B and C models the difficult traits were manageable enough and it was a safer aircraft than the tricky Polikarpov I-16, but its behavior was a foretaste of problems that would become more serious as weight and power increased.
The 109 saw active service long before its principle WWII rivals and its success in the Spanish Civil War obscured its modest engine power and armament. The contemporary Hawker Hurricane Mk I had 30% more power, 30 mph greater speed and far superior firepower. Even the older Polikarpov I-16 and FIAT CR32 biplane could give it stress in certain respects. At this stage, however, the 109 was a fledgling and the design had greater development potential than the I-16, the FIAT, or even the Hurricane, as its next development stage was to prove.
By late 1938 the 109 had evolved, via the B, C and short-lived D series, into the E series, which was a major advance over the earlier models. By 1940 it had replaced all previous variants. The DB601 and its successor, the DB605, would determine the fortunes of the Me109 for its entire wartime career. It was an unusual engine in that its supercharger was driven by a barometrically-controlled hydraulic fluid flywheel. It drove at progressively higher speed as altitude increased. Contemporary foreign superchargers ran at one fixed speed and were only fully efficient at their rated altitude.
In the skies over Poland, France and the Low Countries it out-accelerated, out-climbed, out-dived and out-sped every fighter it met. By June 1940, it ruled European skies from the Russian border to the Channel coast.
By the start of the Battle of Britain the E-4 model was in production, but most squadrons were equipped with the older E-3 model and there was still a number of E-1s in use. The E-3 was equipped with a DB601Aa engine giving 1075 hp at its military rating (equivalent to +4.4 lbs boost in British terms) or 1150hp at its combat rating (+5.9 lbs). It carried three MG FF 20mm cannons; one in the nose and one in each wing, with 60 rounds apiece. The nose gun proved as troublesome in the E3 as it had in earlier models. It was sometimes removed to save weight and even when retained was often not loaded. The nose gun reduced the ammo capacity of the two cowling machine-guns to 500 rounds each. The E3 was built originally without armour plate, but war experience made it clear that this needed rectifying. In order to protect the pilot's back, a plate was fitted in the rear fuselage, but this was some 4-feet (1.2m) behind the seat, compromising its effectiveness. Later, a second plate was attached directly to the pilot's seat.
The E-4 was introduced in late 1939 and incorporated all the lessons learned from the E-3. The nose cannon was eliminated, machine gun ammo capacity was restored to 1000 rpg and the MG FF wing cannons were improved with longer barrels and better ammo, but still carried only 60 rounds. Factory-fitted head and seat armour improved the pilot's protection. By the start of the battle of Britain, a new 1270 hp, high-compression DB601N engine had been developed, but production problems and limited availability of high-octane fuel meant that this model was not present in significant numbers until after the battle.
Only the Spitfire could challenge the Messerschmitt's maximum speed and no fighter in service with any of the belligerents could match its diving acceleration or maximum sustained climbing angle. The only area in which the Messerschmitt fell seriously short of the British fighters was in maneuverability.
Like its predecessors, the Me109E handled well at low and medium flight speeds. Its controls were well balanced and effective down to stalling speed. Its stalling speed in the approach glide was 75 mph ASI (95 mph TAS) flaps up and 61mph ASI (81mph TAS) flaps down. In level flight the figures were about 105 and 90 mph, which is somewhat higher than the Spitfire and Hurricane. However the Messerschmitt's benign pre-stall behavior mitigated this to some extent.
Any aircraft will naturally fly straight and level only at one speed. At slower speeds it will try to dive and faster it will to try to climb. In WWII-era aeroplanes this tendency was adjusted out using a tail-plane trimmer in the cockpit. As speed rose and fell, trim needed to be adjusted to compensate.
When trimmed to fly neutrally in level flight, the 109 resisted being held in a dive and required heavy forward stick pressure to stop it pulling up. On the other hand, if it was trimmed to fly hands-off in the dive an enormous force was needed to pull it out at speeds above 250 mph. There are several recorded instances of Messerschmitts spearing into the ground while trying to follow or avoid British fighters in fast dives.
This was unrelated to the compressibility phenomenon that afflicted fighters at high Mach numbers. It was simply that a pilot of average strength could not pull more than about two Gs at 400mph and the 109 reached 400 mph quickly in a dive.
Potentially just as bad, there was no means of trimming the rudder in flight. It took light left-foot pressure to keep it flying straight until about 220 mph, then ever-increasing right-foot pressure above this. By 350 mph it was such hard work that most pilots let the aircraft yaw, thereby increasing drag and preventing any prospect of its gunfire going where the sight was aiming.
To complete the tale of woe, its ailerons, though excellent at low speed, started to get heavy at 200 mph. They were hard work at 250 mph and rock solid by 300 mph. The narrow cockpit prevented the pilot from exerting full sideways force on the stick and some pilots used their knees to assist in forcing it over. There was not much further deterioration between 300 and 400 mph, by which the roll rate was a dismal 11 degrees per second. These problems with the three major aerodynamic controls meant that it was almost impossible for most pilots to maneuver the Me109 with any alacrity above 250 mph. At high diving speed, the Ju-88 bomber could out maneuver the Me109 quite convincingly!
It is important to appreciate that these speeds are all IAS (Indicated Air Speed), so start to take effect higher in the aircraft's speed range and are, therefore, less debilitating than the bare figures suggest. At 20,000 ft, for example, the ailerons start to weight up at about 270 mph TAS (True Air Speed) and don't become really hard work until just short of the Me 109's maximum level speed at that altitude. The "set in concrete" sensation at 300 mph IAS would start at 400mph TAS at 20000ft, only achievable in a dive.
What the 109 lost in maneuverability it regained in what is nowadays sometimes called "vertical energy management." It could acquire kinetic energy rapidly, by virtue of its superior downward pitch control and diving acceleration and potential energy by its good zoom climb. A series of short dives and zoom climbs would give a 109 more residual energy than any other 1940 fighter, even a Spitfire. This characteristic, combined with its poor high-speed maneuverability, encouraged a form of hit and run tactics using the dive and zoom.
The best type of turn from high speed for a 109 was what is nowadays called a high yo-yo; a climbing turn, exiting with a dive. The climb had to be maintained until speed dropped below 230 mph, preferably around 190-200 mph. The roll and entry into the turn shed a few more mph so the aircraft turned in its optimum speed range, exiting at 150-180 mph. It was important to maintain height in the turn, otherwise its characteristic diving acceleration would throw the aircraft wide.
If it did get caught in a dogfight, it was still possible to use its vertical superiority to avoid horizontal combat. Its zoom and sustained climb rates were very good. In British tests it achieved 2750 fpm at 5000 ft, falling to 1800 fpm at 20,000 ft. The Russians measured 2970 fpm at 10,000 ft, falling to about 1700 fpm at 20,000 ft. Although these rates were achieved at relatively shallow angles and high speeds, the Messerschmitt could also sustain very steep climbing angles at low speeds, between 120 and 140 mph. Contemporary fighters that tried to match the 109E's maximum climbing angle would stall. Even during the short time they could hold on, loss of stability made it very difficult to aim.
Although the 109's steep climbing angle suggests it should have been good at Immelmann turns, it wasn't. It needed to reach 280 mph in level flight before it could do a vertical Immelmann without stalling at the apex. British fighters could execute the maneuver from much lower speeds.
The 109's wing was not designed to carry armament and could not withstand the weight and recoil forces of a standard 20mm Oerlikon cannon. Consequently the license built MG FF in the E-3 had its barrel shortened and the propellant charge reduced, resulting in mediocre ballistics. The E-4's improved gun with its longer barrel was a little better. This made it difficult to hit moving targets, except at short range. Furthermore, the ammunition load had to be restricted to one 60-round drum per gun, in order to fit into the available space. Even with its slow cyclic rate, this gave only 9-10 seconds firing time; about three good bursts. It was simply not prudent to waste such a limited resource at long range and frequently repeated claims that its cannon gave it better long-range shooting capability ignore physics. After exhausting its drums the 109 was down to two light-machine-guns. High explosive cannon shells were a whole order of magnitude more destructive than rifle-calibre bullets, while 20mm solid shot could smash an engine block.
Messerschmitt's designs typically took some risks with structural strength in order to achieve minimum weight. It was a joke in the Luftwaffe that if a Focke-Wulf component failed they would strengthen it, whereas if a Messerschmitt component survived they would lighten it.
The 109 conformed and hard turns or heavy landings frequently resulted in corrugated skin. Even minor battle damage could leave insufficient strength for hard maneuvering, leading to catastrophic failure. Furthermore, its unprotected cooling system and connecting hoses occupied most of its underside and proved vulnerable, even though it used a non-inflammable water/ethylene glycol mix. Early Merlins used inflammable undiluted ethylene glycol.
The Messerschmitt's fuel tank was self-sealing, but it supported the pilot's seat and its armour protection was compromised by its arrangement. The fuel was very close to the pilot. All told, this was not a good combination for standing up to the 140 bullets per second fired by contemporary British fighters.
The Me109E maintained a favorable kill to loss ratio throughout the battle. Tactics, pilot experience and British concentration on the bombers were all contributory, but notwithstanding that, the fighter itself was undoubtedly at the top of the league. In the autumn of 1940, the only fighter that could match it was the Spitfire and the only other fighter even remotely competitive in capability and availability was the Hurricane.
Strategically, the 109E failed because it was used beyond its design role, as a long-range escort. Its most significant shortcoming in the Battle of Britain was not its fighting ability, but its short range. It had less than 20 minutes endurance over London and this was a factor in the Luftwaffe's defeat. A partial solution was at hand in the form of a teardrop-shaped fuel tank that could be carried under the fuselage to provide for the outward journey then jettisoned, allowing the fighter to enter combat with a full internal tank.
Fortunately for the RAF, it was not used in the Battle of Britain. The drop tank capable Me109E-7 was introduced in August 1940, but wasn't available in significant numbers until 1941. It is interesting to speculate what effect the introduction of drop tanks a month or two earlier might have had.
The New Look Me109
The British beat Messerschmitt off the blocks with new marks of Hurricane and Spitfire in late 1940. The Spitfire Mk II climbed better than the 109E at low to medium altitude and the new Hurricane Mk II was 20mph faster than the Mk I at high altitude. Messerschmitt's next generation, the 109F, did not appear in any numbers until the spring of 1941. It incorporated some controversial changes. Great attention was paid to reducing aerodynamic drag.
The main factor was a new wing. The aerofoil was changed and the span was initially reduced, but with add-on rounded tips it ended-up slightly greater than the Emil. The new wing used ducted bypass radiators, which greatly reduced cooling drag.
Other drag reducing measures included a smaller tail fin, elimination of the tailplane support struts, a retractable tail wheel and a new bullet shaped nose. The propeller was reduced in diameter and the blade shape improved. The new supercharger intake scoop stood clear of the fuselage, creating slightly more drag, but avoiding boundary layer air, thereby achieving better ram effect.
New shorter span, deeper chord, Frise type ailerons, rather than the original slotted type, were fitted and smaller flaps were used. Rolling inertia was reduced by the elimination of the wing guns. The net result was a 15-20 mph speed improvement in level flight with the same power.
Given that this new aerodynamic form was used for the rest of the war, remarkably little has been written about its effects on the 109's handling. Fortunately, records of interviews with German prisoners of war and a British AFDU test provide the answers.
Whereas the Emil's aileron response was superior to the Spitfire at low speed and inferior at high speed, the situation was now reversed. The Messerschmitt's ailerons became ineffective as the aircraft approached stalling speed, but now remained responsive up to 350 mph, rather than 220 mph. They were manageable even at 420 mph, although heavy. The contemporary Spitfire Mk VB still had fabric-covered ailerons that lost effectiveness above 300 mph.
Turn rate, though improved, was still no match for a Spitfire, but the wing slots opened more gently, making the aircraft easier to point and aim in a turning fight. Pull-out from a fast dive remained sluggish and wing and tail strength were insufficient to withstand even those forces. A number of Luftwaffe pilots were lost due to structural failure, including leading ace, Hauptman Balthasar, the Kommandant of the Richtoffen Geshwader. Landing remained tricky, but the view over the nose was considered better, which was some help. Take off was a little trickier.
According to Luftwaffe Aircraft Data Sheet No 509, the F-1 and F-2 were capable of 384 mph at 17,10 0ft and a maximum climb rate of 3660 fpm at 2600 rpm and 1.42 atmospheres of boost (combat power). However, the evidence available indicates that they were restricted in service until 1942 to 2400 rpm and 1.3 atmospheres, giving 372 mph and 3170 fpm. Nevertheless, the F represented a big improvement over the Emil and it was indisputably the best fighter in the world at the time of its introduction, slightly before the Spitfire Mk V.
The Spitfire V was a mixed blessing during its lifespan, but gained the advantage for the RAF at high altitude until late in 1941, when the F-3 and F-4 entered service with the newer 1350 hp DB601E. Initially, this engine was also restricted to 2400rpm and 1.3 atmospheres, but was cleared for full power in January or February 1942. The official data sheet gives a maximum speed of 397mph at 19,800 ft, compared to the Spitfire's 370mph. Maximum climb rate is not recorded, but a time to 19,800 ft is given as 6 minutes. RAF tests of a captured aircraft gave 390 mph and RAF pilots' memoirs from this period generally give the impression that the Messerschmitt F-4 was faster than the Spitfire Mk V in all attitudes of flight.
In order to avoid too great a disruption in manufacturing output, the E-8 and E-9 remained in parallel production with the F1 for several months. For a period, the E-8 and E-9 were getting the new 1350 hp DB601E while the F-1 and F-2 were making do with the old 1270 hp DB601N! The DB601E was the first Me109 engine to be fitted for the GM1 Nitrous Oxide (NO) injection system, which was to play a role in the life of the E, F and G-series Messerschmitts from early 1941 until early 1945.
An engine can make power only if petrol is mixed with oxygen in the correct proportions. In the thin air at high altitude, power was limited by lack of oxygen, even with the best supercharging.
Nitrous oxide acted as a high-density oxygen carrier, allowing the engine to run at the same power as it did at much lower altitude. It gave spectacular results, increasing power by more than 25% at 25,000 ft, the percentage increasing with altitude. When the Me109E7-Z engaged its GM1 at 26,400 ft, its climb rate doubled!
It was not, however, an unmitigated blessing. It was heavy at 180 kg and at low and medium altitude it was just unwanted ballast. It was restricted to a maximum of five minutes duration. Any longer would melt the pistons and spark plugs.
The F-1 carried one MG FF 20 mm cannon with 60 rounds, while the old Emil had carried two. The F-1 was almost immediately superseded by the F-2, which employed the new 15mm MG151. This installation came with 200 rounds, instead of 60. It had nearly double the rate of fire and the 15mm ammo had excellent ballistics and penetration, but minimal explosive punch.
The 109's armament change generated bitter controversy. Most aces, including Moelders and Marseilles, preferred the 15mm, considering the greater accuracy, ammo capacity and centerline mounting of the MG 151 to be an improvement. Others, including Galland, felt that less experienced pilots were better served by the heavier punch of two 20mm guns. One German ace was reportedly so unimpressed with the new armament that he refused to fly a 109F as long as his mechanics could get the spares to keep his Emil airborne.
The subsequent F-4 received the MG151/20, which was the same basic gun reworked to fire a lightweight 20mm round at somewhat lower muzzle velocity. The single MG 151/20's rate of fire was 83% of the combined rate of the Emil's two MG FFs and its trajectory was a little better.
Regardless of the controversy surrounding its introduction, the F models were probably the most successful of the whole Me 109 range. By the start of Operation Barbarossa in 1941, about 60% of Luftwaffe fighter units were using the F-1 and F-2 and the DB605E-powered F-3 had supplanted them on the production lines.
The F-3 and F-4 versions were considered, retrospectively, by many Luftwaffe pilots to have been the best balanced of all 109s. They ran up impressive scores against the enormous, but largely obsolescent, Red Air Force in 1941 and 42.
RAF opposition in the Mediterranean Theatre and the Desert comprised mainly Hurricanes and P-40s, which the F outperformed by a comfortable margin. Its only real competitor was the Spitfire MkV, present in Britain and only a handful of places in the Mediterranean.
The F1 and F2 were initially similar to the Spit in speed, slightly inferior in climb and greatly inferior in armament. Once the DB605E-powered F3 and 4 appeared and were cleared for full power, even the Spitfire Mk. V was on the back foot, its superior maneuverability and firepower negated by the Messerschmitt's performance and Luftwaffe's tactics.
Over the Channel and France, Me109s had the advantage of radar controlled interception and fighting over their own territory. Consequently, they maintained a kill to loss ratio over the RAF of better than 4:1. This period, from late 1940 to mid-1942 was the Luftwaffe's most successful, other than the opening blitzkrieg.
A NEW ERA
The pace of development during the war was unparalleled. Despite their technological leapfrog match, both the Spitfire and Me109 were surpassed in the summer of 1941 when the Focke-Wulf 190A entered service, although it was well into 1942 before significant numbers of the new fighter were available.
The FW190 was faster than a 109F at low and medium altitude, considerably superior in a dive, easier to fly, structurally stronger, rolled faster than any other fighter and had better pilot vision. Its only serious fault was its BMW engine, which was unreliable and lost power above 25,000 ft.
The aggregate superiority of the FW190 gave Messerschmitt notice that the 109 was reaching its development limit and the RLM proposed to phase it out. This was never accomplished; the need for numbers demanded that the 109 production lines continue without interruption. It was therefore necessary to push the design further. Despite the Luftwaffe's dependence on the 109, it is difficult to avoid the impression that Willy Messerschmitt had lost interest in it by this stage. The next model, the Gustav, was no more than a case of hot-rodding the old engine.
By early 1942, the DB601 engine had been developed to its limit. The only viable alternative was the new DB605. This engine was based on a strengthened DB601 block, but employed the largest cylinder bore possible on the existing centerlines and used more aggressive camshaft profiles. Consequently, it fitted the existing airframe without the need for reshaping. It still used the characteristic hydraulic supercharger drive, governed by barometric pressure, so that it pumped harder as altitude increased.
By this stage of the war, however, two-speed superchargers were common. These ran more efficiently at their two rated altitudes than the DB605, but less efficiently in the transition, where low ratio ran out of puff and high ratio was still labouring in air too thick for it to give its best.
The first production DB 605 produced 1475 horsepower for takeoff with potential for much more. Its aggressive camshaft profile meant it was less flexible than its predecessor, being happiest at full throttle and high revs.
It is one of the enduring myths of aviation history that the Me109G was greatly heavier than the F. In fact, the gross flight ready weight difference between an F-4 and G-1 was 142kg. This is not insignificant, but for comparison, the Spitfire gained about three times as much weight in its contemporary change from Mk V to Mk IX. The Me109G was considered be superior to the FW190 above 20,000ft, but one experienced Luftwaffe pilot described the later G-6 as being, "as maneuverable as a canal barge at low altitude."
Gustav Variants and Performance
There have probably been more inaccurate assertions about the performance of the generic 109G than any other important WW2 fighter. It is easiest to understand the performance variations of the different Gustav marks by ignoring the model designation and looking at which engine was fitted. In broad terms, during the first 20 months of its service life, the Gustav's engine was blocked from using combat power, while the airframe gained additional weight and drag. This was the critical period during which the battle for air superiority over Germany was fought and lost. By the time the DB605 realized its potential, in the spring of 1944, it was too late.
The DB605A-1 was the first and most numerous engine to be used in the G-series and remained in service until the end. It was designed to achieve combat power at 1.42 atmospheres of boost and 2800rpm, but like its predecessor, combat power caused so many engine failures that it was restricted to military power - 1.3 atmospheres and 2600rpm or 10% less.
Even on military power, the Gustav performed impressively. Messerschmitt factory tests of 13 randomly selected production models gave maximum speeds of between 382 and 415 mph. A spread of 23 mph suggests Messerschmitt quality control was starting to suffer as early as the last quarter of 1942.
Four machines' results were rejected, presumably as aberrant. The remaining nine gave a mean of 408 mph at 21500ft. Even with the rejected results included, the average is 401 mph.
Corresponding climb tests show a time to 5.7 minutes to 19,800 ft. A comparison of factory tests between the Me109G-1 and RAE tests of the Merlin 61 powered Spitfire Mk IX are slightly in the Messerschmitt's favour, especially in the altitude band from 15,000 to 26,000 ft, although the Spitfire retained superior maneuverability.
G-1 aircraft had pressurized cockpits and all the plumbing and controls for GM1, but the heavy gas cylinders were usually fitted only for high altitude missions. The weight of the cylinders cost little speed, but had a more noticeable effect on climb. Although GM1 did not give the DB605 as much extra power as Daimler Benz had anticipated, the effect of activating it was still worthwhile, giving 19-25mph from 27,000 ft up to the service ceiling.
In early 1943, the Gustav started getting slower. The Messerschmitt had long tended to dig its wheels in on grass strips, which was now addressed by wider, larger diameter main wheels and a bigger, non-retractable tail wheel. The big wheels demanded bulges in the wings which, along with the exposed tail wheel, added drag.
The firepower of the basic model was always marginal, so Messerschmitt replaced the rifle-calibre machine guns with 13.2mm MG 131s. Compared to the US-issue Browning 0.5-inch, the MG 131 fired a less powerful round, but at a higher rate. Cowl bulges necessary for their breaches caused yet more drag.
In an attempt to improve rudder authority, a larger, heavier wooden tail fin was fitted, demanding a lead counterweight in the nose to maintain balance, generating more drag and weight. The greater heat generated by the DB605 had an adverse effect on various components within the engine bay, including the ignition system, and numerous minor cooling scoops and vents appeared to prevent them overheating.
The Me109G-5 and G-6, in which all these changes were standardized, averaged a maximum of only 387mph. Climb was also affected, but less than speed.
It was at this stage that the Gustav's weight gain started to become serious. The increase in the calibre of the cowling mounted machine guns was not enough to deal with the sturdy, well armoured and increasingly numerous American bombers or the seemingly indestructible Russian Sturmoviks.
For home defence aircraft, which initially operated beyond the range of Allied fighters, the solution was to fit the wing cannon pods, first used on the F. The bomber-killing versions of the 109G would ultimately carry over 700 lbs of additional armour plate and armament. Three 30mm MK108s and two MG131s, designated R-4, gave staggering weight of fire for such a tiny fighter, three times that of a P-47 Thunderbolt. In explosive power the difference was an order of magnitude greater.
If the Me109 G-6/R-4 pilot could shoot well, nothing could withstand its firepower. Even with three 20mm MG151s (the R-6 version) it out-gunned the P-47.
The assertion by some pilots that fighters could fly through the gaps in a cannon stream, but not through US fifty calibre gunfire, does not stand scrutiny. A three-cannon Me109 fired about 75 rounds per second, while a six-gun P-51 fired 84.
The under-wing pods dragged the Gustav down to just 380 mph in level flight, but pilots were more averse to the effect on maneuverability and climb. Later, under wing 21cm rocket tubes were added, which had a far more unpleasant effect on handling.
These disadvantages proved intolerable when the American long-range escort fighters appeared in quantity in 1943 and the bomber destroyers had to be escorted by clean, lightweight 109s. Even when bare, the Gustav's landing was tricky and the extra load frequently made it lethal to pilots of the low standard that the truncated Luftwaffe training machine could produce at this stage of the war.
Just as the Messerschmitt was getting heavier and slower, the Spitfire received Merlin 63, 66 and 70 engines, cleared for +18 lbs boost. This gave the Spitfire the advantage in almost every respect, except initial diving acceleration.
More importantly, the P-47D-25RE appeared with increased range and a new paddle-bladed propeller, which increased its rate of climb and acceleration. This model could now escort the bombers further into German airspace. At the altitudes where most of the fighting was taking place, the latest Thunderbolt was decidedly faster. Above 28,000 ft, the Thunderbolt could even beat the Messerschmitt in climb, unless the 109 employed GM1.
Luftwaffe losses mounted and pilots longed for better speed and climb. Then, on 5 December 1943, the first Mustangs appeared over Germany.
After a long decline the Messerschmitt\'92s competitiveness began to revive quite suddenly, starting in October 1943 when the DB605A-1 was finally cleared for combat power, giving a 6-15mph improvement, depending on altitude, and averaging 12 mph. The necessary field modifications took four months to fully implement.
In January 1944, the DB605AS with a larger supercharger was introduced. It was a little slower at low altitude, but above 23,400 ft, the AS-equipped models became increasingly superior, reaching 417 mph at 27,000 ft. This engine was not fitted for GM1.
At the same time, low altitude performance was improved with MW50 water methanol injection, which acted as an anti-detonant and allowed both A and AS-series engines to run up to 1.7 atmospheres (+25 lbs) of boost, even on the poor quality petrol the Luftwaffe was by then using. The MW50-equipped DB605A and AS were suffixed with an \'93M\'94 (AM and ASM, respectively).
Water methanol injection gave big improvements below the engine\'92s full throttle altitude. Compared to the restricted 1943 DB605 A, the AM equipped Gustav was fully 44 mph faster at sea level and at 15,800 feet.
MW50 was a more flexible system than GM1, employable over a wider altitude band and for longer duration. Initially, GM1-equipped airframes were converted to MW50, using the existing plumbing. Later, the heavy high-pressure GM-1 system was replaced with a lighter, larger, purpose-built MW50 tank with which the Messerschmitt could sustain emergency boost for twice as long as Allied fighters.
Messerschmitt had intended to supersede the DB605A family of engines with the new DB605D. This engine was designed for MW50. The first DB605DM gave 1700hp initially, rising to 1850hp in the DB605 DB and 2000 hp in the DC. When fitted with a D-series engine the Gustav was designated a G-10 and achieved 425 mph at 25,000 ft. The plan to supersede the DB605A family of engines failed. Production of the new engine was inadequate to meet demand, so DB605A derivatives remained in production until the end of the war. Late versions of the Me109 G-6 were fitted with the improved Galland Hood cockpit canopy, which gave better visibility and re-designated the G-14. The same aircraft with the later DB605 ASBM and ASCM engines was designated G-16.
By mid-1944, Me 109s had better power-to-weight ratios than all their principal opponents, but this was offset by surprisingly high aerodynamic drag. The net result was tolerably competitive performance at all altitudes, which was an impressive feat given the age of the design and the poor quality German fuel.
Amazingly, a Me109 G-14 with a DB605AM was equal in speed to the P-51D on War Emergency Power at around 3000 ft and 16,000 ft, although the Mustang was considerably faster from 18,000 ft upward. Conversely, with a DB605ASM, it was only about 10mph astern of the P-51 at high altitude.
Unfortunately for the Luftwaffe, Messerschmitt build quality deteriorated steadily from mid-1943 onward and production aircraft often failed to match their performance specifications. By 1944 German documents complain of misshapen and poorly fitted panels, warped surfaces, binding and loose pivots and hinges, loose and missing fastenings, rough paint and loose controls. Ground crews spent hundreds of hours checking newly delivered aircraft and rectifying what faults they could.
Flying The Gustav
The 109G was a demanding aeroplane to fly. Like most engines with aggressive valve-timing, the DB605 was cantankerous at low revs and small throttle openings, which made precise control of the power somewhat challenging.
The extra power and weight exacerbated all of the Messerschmitts most unpleasant flying characteristics. It was now nearly as difficult to take-off as it was to land. Its poor visibility was compounded by an increased tendency to roll and swing, as the swirling air from the propeller tried to rotate the aeroplane about its longitudinal axis and push the tail right, while the narrow undercarriage did not provide a sufficiently stable base to resist.
The 109's rudder was small and it required deft footwork to keep the aeroplane pointing along the runway. If allowed to rise as soon as it had enough lift, it would go straight into a fatal roll. The nose needed to be held down until at least 115 mph was achieved; only then it could be allowed to take off of its own accord. Once airborne at takeoff speed, it needed heavy right rudder pressure while climbing at full power, while the ailerons were sloppy up to 180 mph.
Things improved as speed built up and it was fairly happy between about 180 and 350mph. Once it got up to its fighting speed it was subject to acceptable high-speed control forces, similar to the F.
The Messerschmitt's small wing area meant it needed a high angle of attack to generate the lift necessary for hard turns and that caused high drag and loss of energy. The Gustav's extra power meant the point of equilibrium, where thrust balanced turning drag, was higher, which was an advantage in combat. It was, however, still inferior to its principle opponents in general maneuverability.
Landing was subject to the same problems as earlier 109s, but more severe. In the landing circuit it was reputed that it would not hold height in a turn with wheels and flaps down at less than full throttle. Landing speed was also higher.
Once its speed fell to 100mph, it tended to drop its port wing. Its ailerons were ineffective at this speed and any attempt to accelerate by opening the throttle caused an even worse anti-clockwise torque reaction than on earlier models.
The only solution was to dip the nose to increase speed, but that was not always practicable during the approach glide. Even once it was on the deck, the narrow undercarriage led to crashes. The Gustav's landing characteristics accounted for a high proportion of its losses.
The root of the Gustav's problem was that the109 airframe was designed for 700 hp and 4300 lbs, albeit with growth potential. It reached its growth limit in the F, at 1300 hp and 6300 lbs. A late model Gustav, at 1800 hp and over 7000 lbs, was well beyond its intended limit. This was awkward for the Luftwaffe, as it had no obvious alternative, given the FW190's high-altitude lethargy.
The Luftwaffe never recovered completely from its losses in the Battle of Britain. Even during its dramatic successes in 1941 and 42 it was still trying to catch up on pilot training.
During 1943, American industrial strength began to make itself felt. The Luftwaffe inflicted terrible losses on unescorted USAAF bombers, but even when unescorted the heavily armed bombers were knocking down one fighter for every two losses. As USAAF long-range fighters escorted the bombers further and further into Germany the attrition worsened markedly.
The Luftwaffe was stretched between watching the English Channel, defending the Reich, looking after the Mediterranean and Italy and attempting to hold back the Russian steamroller. It simply could not afford the losses and its pilot training system never caught up.
Soon, the number of experienced pilots was too small to maintain standards. In desperate attempts to maintain pilot numbers basic training was repeatedly shortened, exacerbated by fuel shortages. By late 1943 the Luftwaffe was frequently outnumbered in its own airspace and was losing pilots faster than it could train them.
The nature of the air war in the East was quite different. The Russians were one of the first nations to appreciate the practical realities of both strategic and tactical airpower and, in the mid-1930s, were world leaders doctrinally and technically, only to lose both during Stalin's purges.
Not surprisingly, the air war in the East was about supporting the ground forces. During the early part of the war the effects of the purges were still reverberating through the Soviet Air Force and it was an unwieldy, inefficient organization.
Its tactics were inflexible and its once cutting-edge aircraft were obsolete. It provided little effective opposition to the Luftwaffe and Me109 pilots ran up huge scores against brave, but poorly trained, opponents.
During late 1942 and 1943, however, Russia's scientific and engineering talents began to make themselves felt. Slowly, but inexorably, Russian quality and quantity improved and the pilots got better training and better leaders. After Stalingrad the Luftwaffe was on the back foot in the East.
Russian fighters, post-Stalingrad, were still crude in many ways, with airframes constructed largely of steel tube and wood, but they were effective at low altitude where most of the fighting took place. Below 15,000 ft the Yak 9 could more or less match contemporary Me 109Gs in speed and climb and the Yak handled better. By late 1943, the unimpressive LaGG-3 had evolved into the powerful La5FN, which could out run, out climb and out turn the contemporary Me109G.
Russian ground forces had a standard drill of firing everything they had at attacking aircraft, regardless of ammunition expenditure or hit probability, as compensation for their shortages of anti-aircraft artillery. This also caused steady attrition and, as the war progressed, they got more and better anti-aircraft guns. With improved Russian flak, aircraft, pilot training and tactics and incidental damage, German losses in the East became serious.
The Final Push
Despite the Messerschmitt\'92s obsolescence, the Luftwaffe was stuck with it. Output in 1944 exceeded all previous years. By this stage, poor quality control was becoming very serious. Factory-delivered aircraft usually needed a lot of work from squadron technicians to make them fit for service, while the technicians were being drafted to fill gaps in the infantry.
The K-series was a much-needed attempt to rationalize the design and ensure as much commonality across the range as possible. It standardized on specifications based on the late G-series, with attention to some aerodynamic details, most visibly the smoothing out of the machine gun bulges.
As an attempt to reduce manufacturing chaos the K was a failure, as the late-series G models remained in parallel production to the end of the war. As an attempt to produce a more competitive fighter, the K was more successful. The only mass production version, the K-4, was estimated by Messerschmitt to be good for 437 mph at 25,000ft, on emergency power. Unfortunately, no flight test data exists.
Considering the age and flaws of the basic design, it is remarkable how competitive with their opponents the late model G and K series Me109s were. Colonel Jesse Thompson of the famous 55th Fighter Group observed:
"The Me109G and P-51D were fairly evenly matched in level maneuvering flight, but the P-51 could climb and dive faster, although the 109 had an advantage in initial acceleration in a dive, which often was sufficient to allow them to get away."
In fact, the Me109 did not have the spectacular initial diving acceleration with which it is so often credited. Its secret was its large maximum downward elevator angle, which allowed it to pitch into a dive quicker than any opponent; thus, it gained the advantage of gravity sooner. By the time a pursuer started diving the 109 had been accelerating for a second or so and therefore pulled away, creating the impression of great acceleration.
At any given diving angle, the P-51's acceleration was actually superior, but it was a fraction slower to achieve the angle. The effect was similar to giving a slightly slower accelerating car a short start in a drag race.
Despite its speed and climb, the K was still an over-powered 1935 airframe with poor high-speed maneuverability, heavy controls, a cramped cockpit and marginal structural strength. It was only really competitive against the latest Allied types if it was flown by one of the few remaining experten, who knew how to cope with its character flaws and exploit its strengths. An average pilot would do much better in a P-51 or a Spitfire. For the average Luftwaffe novice it was a dreadful aircraft.
The K4 was the best of the Me109 series to see combat in any quantity. In an effort to restore maneuverability it was not fitted with wing guns. It is often credited with a MK103 30mm cannon and two 15mm MG151s on the cowl. This would have been a formidable armament, but it is almost certainly perpetuation of a misprint in some early history of the aircraft. In fact, its cowling guns were the standard 13.2mm MG131s.
Photographs of K4s show clearly that the gun ports are in the same place as the G series, leaving inadequate length in the cowl for the long barreled MG151/15. In some pictures the characteristic perforated cooling jacket of the MG131 can be seen. One Me109 was tried out with a modified version of the 30mm MK103, but it failed trials and was not proceeded with. The K4 had the same low-velocity MK108 as earlier models.
Remarkably, in the hands of the experten, the late G and K models were still deadly tools and the greatest German aces preferred them to the Focke-Wulf 190. These pilots could not only cope with the 109's vicious handling, but could exploit it. Such men were few by 1944, but in their hands the old-warrior was still a danger to any allied fighter.
Erich Hartman shot down more aircraft than any other pilot in history and must be regarded as the arch-exponent of the Me109. He had an excellent understanding of his aircraft's strengths and weaknesses and knew how to exploit them to defeat theoretically superior aircraft, such as P51Ds Yak 3s and La 7s.
Extravagant claims have been made for the final K-14 model. There is no evidence that it ever saw service. It was intended to use the 2000 hp, two-stage DB605L, running 1.98 atmospheres of boost, which surviving documents indicate continually self-destructed and never passed any acceptance tests. Furthermore, Messerschmitt estimates of performance were based on a new four-bladed propeller that was never fitted.
It is fascinating to track the 109's progress through its service life. Well ahead of its time at its conception, it was introduced into service as an immature fledging and grew to dominate the skies over Europe, North Africa, Russia, the Balkans and the Mediterranean. The statistics, unreliable as they are, indicate that the109 destroyed more aircraft than any other fighter in history and in the right hands it remained a deadly foe until the last day of the war. In these terms it must be regarded, warts and all, as one of the truly great aircraft of all time.
The evolution of the 109 was limited by its original concept, which demanded small dimensions. It was also handicapped by the division of Messerschmitt\'92s efforts between far too many projects. From 1943 onwards, technical evolution overtook the 109, but even in its declining years it had a revival in performance in 1944 and was still the Allies' main aerial opponent until the end of the European war. The struggle to keep the Messerschmitt competitive is one of the most fascinating engineering stories in the history of fighter aviation.
The Me109 had periods during which it was undisputed World leader. While it was surpassed by 1943, its new lease of life in early 1944 brought its performance back to competitiveness with its best opponents until the end of the war. Pilot training, manufacturing quality and fuel supply problems (all a result of the Allied strategic bombing offensive on the Western Front), rather than performance, meant its actual competitiveness failed matched its potential post-1943.
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