Nazi Germany (1944)

Experimental Engine Testing Aircraft: 1 Converted Airframe

Introduction

Few aspects of the Second World War have been so misunderstood, misrepresented, and pushed into near mythology as the Luftwaffe’s test programs. Their discussion in less academic circles is dominated by rampant speculation from those who indulge in sensationalist historical stories. With respect to that, one might be surprised to find the bizarre photographs of a Spitfire Mk. VB with a Daimler Benz engine to be one of the few remaining genuine artifacts from an obscure Luftwaffe test program. With so little information publicly available, naturally, the odd plane’s origins, purpose, and performance have been drowned in a sea of speculation. However, while it is often erroneously claimed that the so-called ‘Messerspit’ was some bizarre attempt to combine the best aspects of the two planes, in reality, the aircraft was converted to settle a technical argument which had been raging in Luftwaffe research and development circles since 1942.

Engine Trouble

The history of fighter engine development is one of ceaseless improvement in power and weight which are largely achieved through improving methods of design, production, and the use of better materials. In the case of the Luftwaffe, it was not long until the chase for power was subsumed by the need to develop engines which could more reliably run on inferior materials. Following the end of the battle of Britain in the autumn of 1940, the Luftwaffe soon found itself short of several key materials necessary in building heat and corrosion resistant alloys, most notably nickel, tin, and, later, chromium and cobalt. Nearly all of these materials were available only in limited quantities across Europe, with tin, used in heavy duty piston bearings, being almost totally unavailable. This was further exacerbated by the transition to synthetic gasoline and lubricants, whose properties differed enough from their petroleum counterparts to cause trouble.

In order to cope with the restricted access to these materials, Sparrmetall economy alloys were introduced to ensure the aviation industry would have access to enough materials, albeit ones which would cause a slate of problems. The Bf 109E had nearly finished its production run before the transition to the new materials began and was soon being phased out by the new F model in late 1940, and there the trouble began. The new production DB 601N engines in these would make use of high octane C3 synthetic fuel. However, the engine was neither designed nor properly tested around this, and had instead been developed around the petroleum based C2. Beyond this, its nickel-poor, and thus corrosion prone exhaust valves, coupled with its more fragile piston and crank bearings, would soon create a web of issues that would take weeks to sort out.

The C3 fuel reacted chemically with the 109F’s rubber bag tank, and, if stored in the tank long enough, would ruin the anti-knock qualities of this fuel. When run on this degraded fuel, these engines soon suffered absolutely horrible mechanical problems, chief of which were violent vibrations which could thoroughly wreck them. The C3 fuel could also cling to the chamber walls after failing to thoroughly disperse through the fuel injectors, and then escape into the oil system. In most other aircraft, the fuel would simply boil away, but the Daimler Benz engine ran cooler than most, and thus the fuel would eventually dilute the oil until it failed to act effectively as a lubricant, resulting in increased wear or catastrophic engine failure in the worst cases.

Expecting the issue to be one of a mechanical nature, the fuel and bag were not seen as the obvious culprit. Rather, the engine mount, the air intake position, and the cooling system were suspect. This guess would be partially correct in the case of the intake. Eventually, they tracked the fuel degradation to the tank and adjusted the fuel injectors. The unreliable engine was then phased out for the DB 601E, which ran on the more common B4 fuel and was installed in the subsequent Bf 109F-3 and 4 models. Almost all Bf 109’s built after this point were run on this more common, lower performance fuel. Prior to this, the F series were restricted from running at emergency power and were at a considerable handicap in combat for much of 1941 and 42. Regardless of this impediment, many Luftwaffe fighter squadrons often found these their most successful years.

Problems would resurface again when it came time to re-engine the 109 with the new DB 605A. Developed from the DB 601E, the new engine was to be a marked improvement, with its larger displacement, improved supercharger, and higher compression ratios promising a considerable increase in power. However, new material restrictions would sharply curtail the use of molybdenum, tungsten, and especially cobalt. Supplies of which practically dried up when Germany’s largest source in French North Africa had been lost after Operation Torch. Problems new and old emerged, the most egregious of which were exhaust valve failures, which were due to the low nickel content of the components, resulting in rapid corrosion and cracking. There were also lubrication failures, which were made worse after the switch was made from ball to sleeve bearings. The first Gustavs would enter service in early 1942, though they soon had their performance limited, off and on, to prevent engine failure rates from reaching unmanageable levels. As a result of these limitations, the Gustav was initially slower than the plane it was supposed to replace.

Problems were made even worse when the materials in the engines at Daimler Benz’s testing and development facilities did not match those on the production line, leading to considerable delays in destructive testing. It would eventually receive the improvements to allow it to use its emergency power setting, as exhaust valves were chrome plated and the oil scavenge system was improved, but it was clear that any major future increase in engine performance was only possible after a costly and extended development cycle. The DB 605A would finally be released from all restrictions in August of 1943, almost two years after the first Gustav left the factory.

The Blame Game

Continued development of the Bf 109 was in a very precarious place, as performance improvements were expected without any major increases in engine power. These goals were largely unachievable for the time being, and thus most of those involved would try placing the fault with some other party when the unrealistic plans fell through. Willy Messerschmitt would place the blame with Daimler Benz, whose engines, he claimed, had cooling requirements that were too high, and thus required the use of larger, drag inducing radiators. In part, he was correct in that Daimler Benz’ engines ran cooler, though in doing so, he seems to have neglected issues with the plane’s radiators, which were supplied by other firms. The Bf 109 was fitted with radiators that operated under considerably lower pressures and temperatures than those used on Allied fighters, and were thus very robust, but less efficient. To his frustration, Messerschmitt was unable to increase the efficacy of the system without more efficient, high pressure radiators, which his suppliers were unable to provide.

In 1942, Messerschmitt began an increasingly adversarial correspondence with Fritz Nalinger of Daimler Benz on the state of his engines, and would request that he permit the engine to run at higher temperatures. In a letter sent in December of that year, he would draw a comparison between the ailing DB 605A and the powerful Merlin 61, then in service with the RAF. He placed particular emphasis on the higher operating temperatures and its use of radiators that were 55% smaller than those in service on the Bf 109. He would leave out that British aircraft designers were working with high pressure radiators which were far more efficient than those on his own aircraft.

At a conference with Göring at Carinhall in March of 1943, Messerschmitt would openly lay blame on Daimler Benz and Nalinger, largely reiterating the points from his correspondence. Nalinger would defend the firm by stating they had put their primary focus in designing the engine in reducing the frontal area and maintaining a high power to weight ratio, but he largely side stepped Messerschmitt’s Merlin 61 comparison by extolling the promise of the still in development DB 628. At the end of the meeting, it had become clear that both men would need to work against one another to defend their own reputations. By then, the Bf 109G had been flying for well over a year under strict engine power restrictions.

The Hybrid

To try and prove Messerschmitt wrong, Daimler Benz planned a simple and clear demonstration. They would install one of the firm’s engines in a Spitfire to show that the DB 605A did not require a large radiator to run. The Spitfire in question was EN830, a Mark Vb which had crash landed in the German occupied Jersey Islands in November of 1942. Its pilot, Lieutenant Bernard Scheidhauer, crash landed his plane after being struck by ground fire during a rhubarb raid over Northern France and a fuel leak prevented him from returning to Britain. After ditching his plane, Lieutenant Scheidhauer attempted to destroy the aircraft when it became clear that he was not on a British held channel island, however, there was insufficient fuel to burn the Spitfire. Scheidhauer was subsequently sent to Stalag Luft III, in Poland. He was among those murdered by the Gestapo after the legendary mass escape.

The plane was subsequently taken in hand by the Luftwaffe, repaired, and used for trials at the Rechlin test center. It was later pulled from storage for Nallinger’s tests sometime in late 1943. The plane was re-engined with a DB 605A, though much of the rest of the aircraft was left as it was, save for the radio and armament, which were stripped out. All of the work was done at the Daimler Benz Untertürkheim factory in Stuttgart, after which it was delivered to the Luftwaffe for testing at the nearby airfield at Echterdingen. It was no simple effort to re-engine an aircraft, but it seemed to have been managed well. Testing began in the spring of 1944, with the report on the aircraft being finished May 10th.

The plane flew quite well and proved Nallinger right in that the DB 605A could work using a significantly smaller radiator area. It also made for an interesting comparison with the Bf 109’s radiators, as it was found that the high pressure model fitted to the Spitfire Mk V was 50% smaller but provided only 4% less cooling capacity. The tests also showed that the ‘Messerspit’ was about 25 km/h faster at lower altitudes than the original Spitfire Mk Vb thanks to its fluid coupling supercharger, which proved more efficient at low altitude. Between 4 and 6 km in altitude, the standard Mk V proved faster, before its single stage supercharger again proved less capable than the fluid coupling type on the DB 605A. The hybrid aircraft proved to be between 10 to 20 km/h slower than a Bf 109G-6 at all altitudes save for above 10.5 km, where the ‘Messerspit’ held a slightly higher speed and service ceiling. The experimental aircraft also out climbed the Bf 109 at all altitudes, however, this data is not particularly useful as the plane was unarmed and no ballast to account for its absence was installed.

Overall, the experiment produced mixed results, but proved Messerschmitt right. On one hand, the DB 605 ran effectively throughout the tests using radiators significantly smaller than were found on the Bf 109G. On the other, the type of high pressure radiator used on the Spitfire was not something that could be replicated, owing to numerous material and industrial limitations. In the end, it was Daimler Benz’s requirements that the DB 605 run cooler, and the inability of German radiator manufacturers to produce high temperature, high pressure models, that kept the Bf 109 from achieving greater performance. Following the end of the tests, the aircraft was placed in storage and was likely written off after an 8th Airforce bombing raid on the airfield at Etcherdingen on August 14, 1944.

The Ultimate Fighter?

Unfortunately, due to this unique aircraft’s strange appearance and obscurity, it has been at the center of a number of bizarre theories. Perhaps the most popular of these theories is that the Germans were trying to build a plane that blended the strengths of both the Spitfire and the Bf 109. Some go as far as to claim that the Germans had managed to build something superior to both. This first theory can immediately be written off. By early 1944, neither the Bf 109 nor the Spitfire were considered state of the art, or at the forefront of design in either country. They simply would not be considered an acceptable starting point for any new aircraft design.

However, beyond that, the ‘Messerspit’s’ performance was not particularly impressive for its day. In the official tests, it was compared to both an early Spitfire Mk Vb, which was thoroughly obsolete by the end of 1943, and a Bf 109G-6, which was mediocre by the standards of early 1944. Even then, it compared rather poorly with the G-6, possessing only a higher service ceiling while being considerably slower at almost all but the most extreme altitudes, where it held a slim advantage. To add to this, this low altitude performance gap with the Mk Vb only exists when its Merlin 45 engine is limited to +9 lbs of manifold pressure. When that engine was cleared to run at +16 lbs in November 1942, the Mk V exceeded the DB 605A powered ‘Messerspit’ at altitudes below 5.5 km in linear speed by a margin similar to the Bf 109G-6.

*Values for the Spitfire Mk IX and Mustang indicate use with 100 Octane fuel and not high performance 150 octane, which became fairly common after mid-summer 1944 amongst the strategic fighter forces based in England. Likewise, Bf 109G-6 and Fw 190 performance does not reflect the use of MW50 or higher power clearances, respectively, as they were not in widespread use at the time of the tests. Unrelated, the P-51B-15 made for 627 km/h at 6.5 km with wing racks.

Compared to other contemporary frontline fighters of its day, its performance was far less impressive. The contemporary Spitfire Mk IX, with its Merlin 66 running at 18 lbs manifold pressure, outstripped the hybrid aircraft at all altitudes by a much wider margin than the Bf 109G-6. A further comparison with the Fw 190A-8 and P-51B-15 also demonstrates the continued extreme disparity in linear speed against more modern fighters. While the aircraft did demonstrate a very high climb rate, approximately 21 m/s at sea level (a Spitfire Mk IX made for 23 m/s), this can be explained by the lack of any weapons aboard. The Mk Vb was initially equipped with 2 Hispano 20 mm cannons and four .303 caliber Browning machine guns. The absence of these, and other pieces of equipment, reduced its weight by over 300 kg compared to the Mk Vb used in RAF and Luftwaffe performance trials. This resulting lightening of the aircraft, and the subsequent loss of drag with the removal of the protruding wing cannons, more than explains its high climb rate. The plane’s performance overall was very modest, and frankly did not compare well to any of its contemporaries. In the end, despite being a fusion of the Bf 109 and Spitfire, it compared rather poorly to either one.

Another theory presupposes that the plane was part of an effort to actually produce Spitfires for the Luftwaffe. The foundations for nearly all of these claims rest with an often misunderstood quote from the battle of Britain. When Reichsmarschall Herman Göring asked fighter group commander Adolf Galland if there was anything he needed, Galland responded “I should like an outfit of Spitfires for my squadron”. Galland would later clarify in his memoirs that he meant this rhetorically. In truth, he wanted a plane which could serve better as a bomber escort, something he felt the RAF’s Spitfires were better suited to, with their better visibility and low speed handling, than his own Bf 109’s, which he felt were more capable on offensive patrols. Beyond that, reverse engineering and then manufacturing an aircraft which was designed around the industrial standards and practices of another country was totally unfeasible. It also seems rather implausible that anyone would go to the trouble of building an airplane on the basis of an off hand remark made three years earlier.

Construction

The ‘Messerspit’ was built using the airframe of a later production Spitfire Mk Vb. The Mk V differed from earlier models in that it used a heavier engine mount to keep up with increases in output from new engines. It was otherwise much the same as the Mk I’s and II’s which preceded it. These planes were fairly innovative during the interwar period, being all-metal and using a semi-monocoque structure, though these features were soon made commonplace in the earliest days of the Second World War.

The fuselage contained the engine, behind which sat the fuel tank, the firewall, and then the cockpit. The tail boom was of a semi monocoque construction and contained the oxygen bottles, and radio. Aboard the ‘Messerspit’, the engine mount had to be reworked to accommodate a DB 605A, the fuel tank was likely changed to fit the new volume, and the instruments and most of the electronics were swapped for German versions. The radio appears to have been removed entirely. In all likelihood, Lt. Scheidhauer most likely smashed the instrument panel when he knew his plane was in enemy territory. Beyond that, they would have needed to convert the voltage to the German standard, and simply replacing all the equipment would have proven easier than modifying all of the existing components. There were also some instruments, like the DB 605’s RPM governor readout, that would not have had a British analogue.

The wings were elliptical with a large surface area, which granted the aircraft an excellent rate of climb and low wing loading. On the ‘Messerspit’, the inboard pair of 20 mm cannons and the outboard four .303 caliber Browning machine guns were removed and the ports were faired over. Most importantly, the radiator under the starboard wing was connected to the DB 605A engine’s oil and coolant lines. The wings were otherwise unchanged. Generally speaking, the better wheel brakes, greater visibility out the bubble canopy, and its wider wheel base would have likely made this a far more pleasant plane to fly than a Bf 109G.

The engine was a Daimler Benz DB 605A, an inverted, 35.7 liter, V-12. The reason for it being inverted was to ensure the propeller shaft was as low as possible. This would enable a low mounted, centerline cannon to fire through its center without its recoil seriously jeopardizing the aircraft’s stability. They were able to achieve this using direct fuel injection, which was fairly common practice in German aviation by the start of the war, though rare elsewhere. The engine also possessed a high level of automation, which let the pilot manage the engine and most of its associated systems just through the throttle lever. These were essentially a series of linkages between components that adjusted one another as the pilot increased or decreased engine power. As such, it did not possess a true engine control unit, as was used in the BMW 801. Perhaps most impressively, the engine used a single stage, centrifugal supercharger which used a hydraulic coupling for variable transmission. The fluid coupling supercharger automatically adjusted itself barometrically, and was easily the most impressive feature of the engine, allowing it to smoothly adjust for boost as the plane climbed or descended. This allowed the aircraft to avoid the engine performance gaps between certain altitudes that were otherwise encountered with engine superchargers with multiple stages and fixed speed settings. These gaps were the result of running the supercharger at fixed, unnecessarily high speeds for a given altitude.

The engine used B4 87 octane aviation gasoline, as most of the C3 high performance stock was dedicated to squadrons flying Fw 190s. In comparison to the Merlin 45, which was originally in the Spitfire Mk.Vb, it produced 150 bhp more at sea level thanks to the fluid coupling supercharger, which saw lower pumping losses compared to the Merlin 45. The Merlin 45’s supercharger was geared to medium altitude use, and allowed the engine to outperform the DB 605A between approximately 4 and 6 km.

In spite of these innovative features, the engine’s output was fairly modest for its day. It produced up to 1475 PS, though this was only possible after several major modifications, such as replacing the exhaust valves for chrome plated sets and modifying the oil scavenge system by adding additional pumps and a centrifuge to improve flow and reduce foaming, respectively. Between 1942 and late 1943, the high power settings on almost all of these engines were disabled in order to keep failure rates manageable. The supercharger too would eventually lag behind its contemporaries, as despite its smoothness, its volume became a bottleneck. This was most apparent in comparison to the two-stage, intercooled models of the Rolls Royce Merlin engine. Some later models would mount an enlarged supercharger, taken from the larger DB 603, though the upgrade was not universal. Nearly all would be equipped with an anti-knock boost system in the form of MW50 in the weeks after the ‘Messerspit’s’ tests, which would boost output up to 1800 PS, though the corrosive mixture of methanol and water decreased the engine’s lifespan. Engines with the larger supercharger were designated DB 605AS, those with the boost system being DB 605M, and those with both were 605ASMs. These upgrades gave late war Bf 109’s a good degree of performance after nearly three years of mediocrity. Neither of these upgrades were present on the ‘Messerspit’.

The engine measured 101.1 × 71.9 × 174 cm, had a bore and stroke of 154 mm (6.1 in.) x 160 mm (6.3 in.), and weighed 745 kg (1,642 lb). The aircraft was equipped with the prop spinner from a Bf 109G, used the same supercharger scoop, and was likewise fitted with a two meter VDM propeller. The engine cowling of this aircraft seems to have been built for requirement.

Conclusion

In the end, the ‘Messerspit’ was built to serve a single, fairly mundane purpose. It was never meant to set records, achieve any kind of technical breakthrough, or somehow be an unbeatable synthesis of two planes that had already seen their day in the sun. Above all, it was never meant to see combat nor produce a plane that would. Its only battlefield would be a corporate one.

Illustration

Sources:

Primary:

Bf 109G-2 Flugzeug Handbuch (Stand Juni 1942).Der Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe, Berlin. November 1942.

Bf 109G-4 Flugzeug Handbuch (Stand August 1943). Der Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe, Berlin. September 1943.

Bf 109G-2 Flugzeug Handbuch (Stand August 1943). Der Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe, Berlin. October 1943.

Daimler-Benz DB 605 Inverted V-12 Engine. National Air and Space Museum Collection. Inventory number: A19670086000.

Flugzeug Flugleistungen Me 109G-Baureihen. Messerschmitt AG Augsburg. August 1943.

Flugleistungen Normaljager Fw 190A-8. Focke-Wulf Flugzeugbau G.m.b.H. Abt. Flugmechanik.L. October 1944.

Horizontalgeschwindigkeit über der Flughöhe: Normaljäger Fw 190A-8. Focke-Wulf Flugzeugbau G.m.b.H. November 1943.

Leistungen Me 109G mit DB 605 AS. Messerschmitt AG. Augsburg. 22, January 1944.

P-51B-15-NA 43-24777 (Packard Merlin V-1650-7) Performance Tests on P-38J, P-47D and P-51B Airplanes Tested with 44-1 Fuel. (GRADE 104/150). 15 May, 1944.

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Spitfire Mk. VB W.3134 (Merlin 45) Brief Performance Trials. Aeroplane and Armament Experimental Establishment Boscombe Down. June 1941.

Spitfire Mk. VC AA.878 (Merlin 45) Climb, speed, and cooling tests at combat rating. Aeroplane and Armament Experimental Establishment Boscombe Down. 25 November, 1942.

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Secondary:

Scheidhauer, Bernard W.M. Traces of War.

Douglas, Calum E. Secret Horsepower Race: Second World War Fighter Aircraft Engine Development on the Western Front. TEMPEST, 2020.

C. Douglass, personal communication, November 25, 2022.

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Credits

• Article written by Henry H.
• Edited by Stan L. and Henry H.
• Ported by Henry H.
• Illustrations by Godzilla