Messerschmitt Bf 109

During 1933, the Technisches Amt (C-Amt), the technical department of the Reichsluftfahrtministerium (RLM) ("Reich Aviation Ministry"), concluded a series of research projects into the future of air combat. The result of the studies was four broad outlines for future aircraft:[7]

• Rüstungsflugzeug I for a multi-seat medium bomber
• Rüstungsflugzeug II for a tactical bomber
• Rüstungsflugzeug III for a single-seat fighter
• Rüstungsflugzeug IV for a two-seat heavy fighter

Rüstungsflugzeug III was intended to be a short range interceptor, replacing the Arado Ar 64 and Heinkel He 51 biplanes then in service. In late March 1933, the RLM published the tactical requirements for a single-seat fighter in the document L.A. 1432/33.[8]

The projected fighter needed to have a top speed of 400 km/h (250 mph) at 6,000 m (20,000 ft), to be maintained for 20 minutes, while having a total flight duration of 90 minutes. The critical altitude of 6,000 metres was to be reached in no more than 17 minutes, and the fighter was to have an operational ceiling of 10,000 m (33,000 ft).[8] Power was to be provided by the new Junkers Jumo 210 engine of about 522 kW (710 PS; 700 hp). It was to be armed with either a single 20 mm MG C/30 engine-mounted cannon firing through the propeller hub as a Motorkanone, or two synchronized, engine cowl-mounted 7.92 mm (.312 in) MG 17 machine guns, or one lightweight engine-mounted 20 mm MG FF cannon with two 7.92 mm MG 17s.[7] The MG C/30 was an airborne adaption of the 2 cm FlaK 30 anti-aircraft gun, which fired very powerful "Long Solothurn" ammunition, but was very heavy and had a low rate of fire. It was also specified that the wing loading should be kept below 100 kg/m². The performance was to be evaluated based on the fighter's level speed, rate of climb, and maneuverability, in that order.[8]

It has been suggested that Bayerische Flugzeugwerke (BFW) was originally not invited to participate in the competition due to personal animosity between Willy Messerschmitt and RLM director Erhard Milch;[nb 1] however, recent research by Willy Radinger and Walter Shick indicates that this may not have been the case, as all three competing companies—Arado, Heinkel and BFW—received the development contract for the L.A. 1432/33 requirements at the same time in February 1934.[8] A fourth company, Focke-Wulf, received a copy of the development contract only in September 1934.[8] The powerplant was to be the new Junkers Jumo 210, but the proviso was made that it would be interchangeable with the more powerful, but less developed Daimler-Benz DB 600 powerplant.[10] Each was asked to deliver three prototypes for head-to-head testing in late 1934.

Messerschmitt Bf 109 V1

A drawing of the V1 prototype

Prototype V3

Design work on Messerschmitt Project Number P.1034 began in March 1934, just three weeks after the development contract was awarded. The basic mock-up was completed by May, and a more detailed design mock-up was ready by January 1935. The RLM designated the design as type "Bf 109," the next available from a block of numbers assigned to BFW.[8]

The first prototype (Versuchsflugzeug 1 or V1), with civilian registration D-IABI, was completed by May 1935, but the new German engines were not yet ready. To get the "R III" designs into the air, the RLM acquired four Rolls-Royce Kestrel VI engines by trading Rolls-Royce a Heinkel He 70 Blitz for use as an engine test-bed.[nb 2] Messerschmitt received two of these engines and adapted the engine mounts of V1 to take the V-12 engine upright. V1 made its maiden flight at the end of May 1935 at the airfield located in the southernmost Augsburg neighborhood of Haunstetten, piloted by Hans-Dietrich "Bubi" Knoetzsch. After four months of flight testing, the aircraft was delivered in September to the Luftwaffe's central test centre at the Erprobungsstelle Rechlin to take part in the design competition.

In 1935, the first Jumo engines became available, so V2 was completed in October using the 449 kW (610 PS; 602 hp) Jumo 210A engine. V3 followed, the first to be mounted with guns, but it did not fly until May 1936 due to a delay in procuring another Jumo 210 engine.

After Luftwaffe acceptance trials were completed at their headquarters Erprobungsstelle (E-Stelle) military aviation test and development facility at Rechlin, the prototypes were moved to the subordinate E-Stelle Baltic seacoast facility at Travemünde for the head-to-head portion of the competition. The aircraft participating in the trials were the Arado Ar 80 V3, the Focke-Wulf Fw 159 V3, the Heinkel He 112 V4 and the Bf 109 V2. The He 112 arrived first, in early February 1936, followed by the rest of the prototypes by the end of the month.

Because most fighter pilots of the Luftwaffe were used to biplanes with open cockpits, low wing loading, light g-forces and easy handling like the Heinkel He 51, they were very critical of the Bf 109 at first. However, it soon became one of the frontrunners in the contest, as the Arado and Focke-Wulf entries, which were intended as "backup" programmes to safeguard against failure of the two favourites, proved to be completely outclassed. The Arado Ar 80, with its gull wing (replaced with a straight, tapered wing on the V3) and fixed, spatted undercarriage was overweight and underpowered, and the design was abandoned after three prototypes had been built. The parasol winged Fw 159, potentially inspired by the same firm's earlier Focke-Wulf Fw 56, was always considered by the E-Stelle Travemünde facility's staff to be a compromise between a biplane and an aerodynamically more efficient, low-wing monoplane. Although it had some advanced features, it used a novel, complex retractable main undercarriage which proved to be unreliable.[11]

JG 53 Bf 109E-3, c. 1939/1940

Initially, the Bf 109 was regarded with disfavour by E-Stelle test pilots because of its steep ground angle, which resulted in poor forward visibility when taxiing; the sideways-hinged cockpit canopy, which could not be opened in flight (but could be dropped by the emergency arm). They were also concerned about the high wing loading.[12]

The Heinkel He 112, based on a scaled-down Blitz, was the favourite of the Luftwaffe leaders. Compared with the Bf 109, it was also cheaper.[13] Positive aspects of the He 112 included the wide track and robustness of the undercarriage (this opened outwards from mid wing, as opposed to the 109s which opened from the wing root), considerably better visibility from the cockpit and a lower wing loading that made for easier landings. In addition, the V4 had a single-piece, clear-view, sliding cockpit canopy and a more powerful Jumo 210Da engine with a modified exhaust system. However, the He 112 was also structurally complicated, being 18% heavier than the Bf 109, and it soon became clear that the thick wing, which spanned 12.6 m (41 ft 4 in) with an area of 23.2 m² (249.7 ft²) on the first prototype (V1), was a disadvantage for a light fighter, decreasing the aircraft's rate of roll and manoeuvrability. As a result, the He 112 V4 which was used for the trials had new wings, spanning 11.5 m (37 ft 8.75 in) with an area of 21.6 m² (232.5 ft²). However, the improvements had not been fully tested and the He 112 V4 could not be demonstrated in accordance with the rules laid down by the Acceptance Commission, placing it at a distinct disadvantage.

Because of its smaller, lighter airframe, the Bf 109 was 30 km/h (20 mph) faster than the He 112 in level flight, and superior in climbing and diving. The Commission ultimately ruled in favour of the Bf 109 because of the Messerschmitt test pilot's demonstration of the 109's capabilities during a series of spins, dives, flick rolls and tight turns, throughout which the pilot was in complete control of the aircraft.[14]

In March, the RLM received news that the British Supermarine Spitfire had been ordered into production. It was felt that a quick decision was needed to get the winning design into production as soon as possible, so on 12 March, the RLM announced the results of the competition in a document entitled Bf 109 Priority Procurement, which ordered the Bf 109 into production. At the same time, Heinkel was instructed to radically redesign the He 112.[15] The Messerschmitt 109 made its public debut during the 1936 Berlin Olympics when the V1 prototype was flown.[16]

As with the earlier Bf 108, the new design was based on Messerschmitt's "lightweight construction" principle, which aimed to minimise the number of separate parts in the aircraft. Examples of this could be found in the use of two large, complex brackets which were fitted to the firewall. These brackets incorporated the lower engine mounts and landing gear pivot point into one unit. A large forging attached to the firewall housed the main spar pick-up points and carried most of the wing loads. Contemporary design practice was usually to have these main load-bearing structures mounted on different parts of the airframe, with the loads being distributed through the structure via a series of strong-points. By concentrating the loads in the firewall, the structure of the Bf 109 could be made relatively light and uncomplicated.[17]

A Bf 109E at the Royal Air Force Museum London with its wings temporarily removed, 2016

An advantage of this design was that the main landing gear, which retracted through an 85-degree angle, was attached to the fuselage, making it possible to completely remove the wings for servicing without additional equipment to support the fuselage. It also allowed simplification of the wing structure, since it did not have to bear the loads imposed during takeoff or landing. The one major drawback of this landing gear arrangement was its narrow wheel track, making the aircraft unstable while on the ground. To increase stability, the legs were splayed outward somewhat, creating another problem in that the loads imposed during takeoff and landing were transferred up through the legs at an angle.[18]

The small rudder of the Bf 109 was relatively ineffective at controlling the strong swing created by the powerful slipstream of the propeller during the early portion of the takeoff roll, and this sideways drift created disproportionate loads on the wheel opposite to the swing. If the forces imposed were large enough, the pivot point broke and the landing gear leg would collapse outward into its bay.[18] Experienced pilots reported that the swing was easy to control, but some of the less-experienced pilots lost fighters on takeoff.[19]

Because of the large ground angle caused by the long legs, forward visibility while on the ground was very poor, a problem exacerbated by the sideways-opening canopy. This meant that pilots had to taxi in a sinuous fashion which also imposed stresses on the splayed undercarriage legs. Ground accidents were a problem with inexperienced pilots, especially during the later stages of the war when pilots received less training before being sent to operational units.[19] At least 10% of all Bf 109s were lost in takeoff and landing accidents, 1,500 of which occurred between 1939 and 1941.[20] The installation of a fixed "tall" tailwheel on some of the late G-10s and −14s and the K-series helped alleviate the problem to a large extent.[21]

Freely moving, automatic leading edge slats on a Bf 109E. By using high-lift devices, the handling qualities of the Bf 109 were considerably enhanced.

From the inception of the design, priority was given to easy access to the powerplant, fuselage weapons and other systems while the aircraft was operating from forward airfields. To this end, the entire engine cowling was made up of large, easily removable panels which were secured by large toggle latches. A large panel under the wing centre section could be removed to gain access to the L-shaped main fuel tank, which was sited partly under the cockpit floor and partly behind the rear cockpit bulkhead. Other, smaller panels gave easy access to the cooling system and electrical equipment.[18] The engine was held in two large, forged, Elektron magnesium alloy Y-shaped legs, one per side straddling the engine block, which were cantilevered from the firewall. Each of the legs was secured by two quick-release screw fittings on the firewall. All of the main pipe connections were colour-coded and grouped in one place, where possible, and electrical equipment plugged into junction boxes mounted on the firewall. The entire powerplant could be removed or replaced as a unit in a matter of minutes,[18] a potential step to the eventual adoption of the unitized-powerplant Kraftei engine mounting concept used by many German combat aircraft designs, later in the war years.

Another example of the Bf 109's advanced design was the use of a single, I-beam main spar in the wing, positioned more aft than usual (to give enough room for the retracted wheel), thus forming a stiff D-shaped torsion box. Most aircraft of the era used two spars, near the front and rear edges of the wings, but the D-box was much stiffer torsionally, and eliminated the need for the rear spar. The wing profile was the NACA 2R1 14.2 at the root and NACA 2R1 11.35 at the tip,[22] with a thickness to chord ratio of 14.2% at the root and 11.35% at the tip.

Another major difference from competing designs was the higher wing-loading. While the R-IV contract called for a wing-loading of less than 100 kg/m², Messerschmitt felt this was unreasonable. With a low wing-loading and the engines available, a fighter would end up being slower than the bombers it was tasked with catching.

A fighter was designed primarily for high-speed flight. A smaller wing area was optimal for achieving high speed, but low-speed flight would suffer, as the smaller wing would require more airflow to generate enough lift to maintain flight. To compensate for this, the Bf 109 included advanced high-lift devices on the wings, including automatically opening leading edge slats, and fairly large camber-changing flaps on the trailing edge. The slats increased the lift of the wing considerably when deployed, greatly improving the horizontal maneuverability of the aircraft, as several Luftwaffe veterans, such as Erwin Leykauf, attest.[23][24] Messerschmitt also included ailerons that "drooped" when the flaps were lowered (F series and later the lower radiator flap operated as part of the flap system), thereby increasing the effective flap area. When deployed, these devices effectively increased the wings' coefficient of lift.

Fighters with liquid-cooled engines were vulnerable to hits in the cooling system. For this reason, on later Bf 109 F, G and K models, the two coolant radiators were equipped with a cut-off system. If one radiator leaked, it was possible to fly on the second or to fly for at least five minutes with both closed.[25][26][27][28] In 1943, Oberfeldwebel Edmund Roßmann got lost and landed behind Soviet lines. He agreed to show the Soviets how to service the plane. Soviet machine gun technician Viktor M. Sinaisky recalled:

The Messer was a very well designed plane. First, it had an engine of an inverted type, so it could not be knocked out from below. It also had two water radiators with a cut-off system: if one radiator leaked you could fly on the second or close both down and fly at least five minutes more. The pilot was protected by armour-plate from the back, and the fuel tank was also behind armour. Our planes had fuel tanks in the centre of their wings: that's why our pilot got burnt. What else did I like about the Messer? It was highly automatic and thus easy to fly. It also employed an electrical pitch regulator, which our planes didn't have. Our propeller system, with variable pitch was hydraulic, making it impossible to change pitch without engine running. If, God forbid, you turned off the engine at high pitch, it was impossible to turn the propeller and was very hard to start the engine again. Finally, the German ammo counter was also a great thing.[28]

A Bf 109E-3 of JG 51 ‘Mölders’ showing the 20 mm MG FF installations in the wing.

Reflecting Messerschmitt's belief in low-weight, low-drag, simple monoplanes, the armament was placed in the fuselage. This kept the wings very thin and light. Two synchronized machine guns were mounted in the cowling, firing over the top of the engine and through the propeller arc. An alternative arrangement was also designed, consisting of a single autocannon firing through a blast tube between the cylinder banks of the engine, known as a Motorkanone mount in German.[7][nb 3] This was also the choice of armament layout on some contemporary monoplane fighters, such as the French Dewoitine D.520, or the American Bell P-39 Airacobra, and dated back to World War I's small run of SPAD S.XII moteur-canon, 37 mm cannon-armed fighters in France.

When it was discovered in 1937 that the RAF was planning eight-gun batteries for its new Hawker Hurricane and Supermarine Spitfire fighters, it was decided that the Bf 109 should be more heavily armed. The problem was that the only place available to mount additional guns was in the wings. Only one spot was available in each wing, between the wheel well and slats, with room for only one gun, either a 7.92 mm MG 17 machine gun, or a 20 mm MG FF or MG FF/M cannon.[30]

The first version of the Bf 109 to have wing guns was the C-1, which had one MG 17 in each wing. To avoid redesigning the wing to accommodate large ammunition boxes and access hatches, an unusual ammunition feed was devised whereby a continuous belt holding 500 rounds was fed along chutes out to the wing tip, around a roller, and then back along the wing, forward and beneath the gun breech, to the wing root, where it coursed around another roller and back to the weapon.[30]

The gun barrel was placed in a long, large-diameter tube located between the spar and the leading edge. The tube channeled cooling air around the barrel and breech, exhausting from a slot at the rear of the wing. The installation was so cramped that parts of the MG 17's breech mechanism extended into an opening created in the flap structure.[30]

The much longer and heavier MG FF had to be mounted farther along the wing in an outer bay. A large hole was cut through the spar allowing the cannon to be fitted with the ammunition feed forward of the spar, while the breech block projected rearward through the spar. A 60-round ammunition drum was placed in a space closer to the wing root causing a bulge in the underside. A small hatch was incorporated in the bulge to allow access for changing the drum. The entire weapon could be removed for servicing by removing a leading edge panel.[30]

Luftwaffe ground-crew positioning a Bf 109G-6 equipped with the Rüstsatz VI underwing gondola cannon kit. Note the slat on the leading edge of the port wing. JG 2, France, late 1943.

From the 109F-series onwards, guns were no longer carried inside the wings. Instead, the Bf 109F had a 20 mm gun firing through the propeller shaft. The change was disliked by leading fighter pilots such as Adolf Galland and Walter Oesau, but others such as Werner Mölders considered the single nose-mounted gun to compensate well for the loss of the two wing guns.[31] Galland had his Bf 109F-2 field-modified with a 20 mm MG FF/M autocannon, the "/M" suffix indicating the capability of firing thin-walled 20mm mine shells, installed internally in each wing.[nb 4]

In place of internal wing armament, additional firepower was provided through a pair of 20 mm MG 151/20 cannons installed in conformal gun pods under the wings. The conformal gun pods, exclusive of ammunition, weighed 135 kg (298 lb);[32] and 135 to 145 rounds were provided per gun. The total weight, including ammunition, was 215 kg.[32] Installation of the under-wing gun pods was a simple task that could be quickly performed by the unit's armourers, and the gun pods imposed a reduction of speed of only 8 km/h (5.0 mph).[32] By comparison, the installed weight of a similar armament of two 20 mm MG 151/20 cannon inside the wings of the Fw 190A-4/U8 was 130 kg (287 lb), without ammunition.[33]

Although the additional armament increased the fighter's potency as a bomber destroyer, it had an adverse effect on the handling qualities, reducing its performance in fighter-versus-fighter combat and accentuating the tendency of the fighter to swing pendulum-fashion in flight.[31][34]

Some of the projected 109K-series models, such as the K-6, were designed to carry 30 mm (1.18 in) MK 108 cannons in the wings.[35]

Originally the aircraft was designated as Bf 109 by the RLM, since the design was submitted by the Bayerische Flugzeugwerke (literally "Bavarian Aircraft Works", meaning "Bavarian Aircraft Factory"; sometimes abbreviated B.F.W.,[36] akin to BMW) during 1935. The company was renamed Messerschmitt AG after 11 July 1938 when Erhard Milch finally allowed Willy Messerschmitt to acquire the company. All Messerschmitt aircraft that originated after that date, such as the Me 210, were to carry the "Me" designation. Despite regulations by the RLM, wartime documents from Messerschmitt AG, RLM and Luftwaffe loss and strength reports continued to use both designations, sometimes even on the same page.[37]

All extant airframes bear the official[5] "Bf 109" designation on their identification plates, including the final K-4 models.[38] The aircraft was often referred to by the folk-designation, 'Me 109', particularly by the Allies.

The aircraft was often nicknamed Messer by its operators and opponents alike; the name was not only an abbreviation of the manufacturer but also the German word for "knife". In Finland, the Bf 109 was known as Mersu, although this was originally (and still is) the Finnish nickname for Mercedes-Benz cars.

Soviet aviators nicknamed the Bf 109 "the skinny one" (худо́й, khudoy), for its sleek appearance compared, for example, to the more robust Fw 190.

The names "Anton", "Berta", "Caesar", "Dora", "Emil", "Friedrich", "Gustav", and "Kurfürst" were derived from the variant's official letter designation (e.g. Bf 109G – "Gustav"), based on the German spelling alphabet of World War II, a practice that was also used for other German aircraft designs.[39] The G-6 variant was nicknamed by Luftwaffe personnel as Die Beule ("the bump/bulge") because of the cowling's characteristic, bulging covers for the breeches of the 13 mm (.51 in) MG 131 machine guns, with the separate Beule covers eliminated by the time of the G-10 model's introduction of a subtly reshaped upper cowling.

In July 1937, not long after the public debut of the new fighter, three Bf 109Bs took part in the Flugmeeting airshow in Zürich under the command of Major Seidemann. They won in several categories: First prize in a speed race over a 202 km course, first prize in the class A category in the international Alpenrundflug for military aircraft, and victory in the international Patrouillenflug category.[16]

On 11 November 1937, the Bf 109 V13, D-IPKY flown by Messerschmitt's chief pilot Dr. Hermann Wurster, powered by a 1,230 kW (1,672 PS; 1,649 hp) DB 601R racing engine, set a new world air speed record for landplanes with piston engines of 610.95 km/h (379.63 mph), winning the title for Germany for the first time. Converted from a Bf 109D, the V13 had been fitted with a special racing DB 601R engine that could deliver 1,230 kW (1,672 PS; 1,649 hp) for short periods.[40][41][nb 5]

Heinkel, having had the He 112 rejected in the design competition of 1936, designed and built the He 100. On 6 June 1938, the He 100 V3, flown by Ernst Udet, captured the record with a speed of 634.7 km/h (394.4 mph). On 30 March 1939, test pilot Hans Dieterle surpassed that record, reaching 746.61 km/h (463.92 mph) with the He 100 V8. Messerschmitt, however, soon regained the lead when, on 26 April 1939, Flugkapitän Fritz Wendel, flying the Me 209 V1, set a new record of 755.14 km/h (469.22 mph). For propaganda purposes, the Me 209 V1 aircraft (possibly from its post-July 1938 first flight date) was given the designation Me 109R, with the later prefix, never used for wartime Bf 109 fighters.[5] The Me 209 V1 was powered by the DB 601ARJ, producing 1,156 kW (1,550 hp), but capable of reaching 1,715 kW (2,300 hp). This world record for a piston-engined aircraft was to stand until 1969,[42] when Darryl Greenamyer's modified Grumman F8F Bearcat, Conquest I, broke it with a 777 km/h (483 mph) record speed.[43]

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