In its newly-modified single-seat fighter, the Messerschmitt Me-109F, Germany has installed a potentially formidable weapon in the shape of a 20-mm Mauser cannon which is reported to have the phenomenal rate of fire of 900 rounds per minute. This, together with the two 7.92-mm Rheinmetal-Borsig machine guns, comprising its total armament (although provision is also made for a 550-lb bomb slung between the landing gear), gives the Me-109F a weight of fire approximating that of the latest cannon-equipped Hurricanes and Spitfires.
The Messerschmitt's armament is short-winded, however; only 200 rounds being supplied the 20-mm cannon, sufficient for 13¼ seconds continuous firing (a 15-mm Mauser in the Me-109F2 probably carries more ammunition), and 500 rounds each for the two machine guns, which is considerably less than what the British fighters carry. The cannon is belt-fed from an ammunition box housed in the right wing, and is electrically cocked and fired. Apparently reliable, its amazing rate of fire equals that of the .50 Browning machine guns used by the RAF in the Boeing Flying Fortresses. Aiming is by means of a reflector sight, described by British sources as rather inferior.
A sound, well-constructed airplane, the new Messerschmitt is powered by a 12-cylinder Mercedes Benz DB-601N engine which develops 1,150 hp at 2,600 rpm at take-off, and at 16,500 ft is rated at 1,050 hp. An increase in power of about six percent over the earlier DB-601A at all heights has been achieved by changing from concave to flat-topped pistons which raised the compression ratio from 6.9 to 7.9. This has resulted in increasing maximum speed at 13,300 ft from 354 to 362 mph, and at 21,000 ft top speed is 380 mph. The ceiling has gone up from 36,000 to 40,000 ft, although it is doubtful whether the pilot could operate at that altitude without a pressurized cockpit, about which reports make no mention. Tests carried out by Boeing Aircraft have indicated that it is as difficult to breathe at 40,000 ft with an oxygen mask as it is at 18,000 without one because the rarified atmosphere cannot supply sufficient lung pressure. Moreover, without a pressurized cockpit, and so far none has been known to be incorporated in a fighter plane, the pilot flying at such extreme altitudes is subject to "aeroembolism", similar to the diver's "bends", especially in a fast combat plane which climbs and descends at great speeds.
Apart from minor alterations, few changes have been made in the fuselage construction. Such as have been made, however, have increased its length by three feet to 29'8". A new rudder, larger spinner, through which the cannon protrudes, and the re-arranged oil tank are the principal changes contributing to greater length. A fixed cantilever tail plane has replaced the antiquated adjustable braced tail plane of the Me-109E, and instead of trimming tabs, small adjusting tabs, which can be set on the ground, are provided on the elevators. The landing gear retracts outwards into leather-walled, zipper-fastened wheel wells, while the tail wheel retracts only partly, leaving half the wheel projecting.
An interesting feature is the Sperry-type blind flying panel. A master compass, connected to a repeater dial on the instrument panel, is installed in the rear fuselage. To protect the pilot, an 8 mm armor plate curves forward and over his head from the rear cockpit bulkhead. Drag has been decreased somewhat by lowering the cockpit cover and streamlining it more.
The "L"-shaped fuel tank, consisting of a rubber bag housed in a plywood casing, is situated behind and under the pilot and is protected by armor plate 10 mm thick placed in front of it. Capacity of this tank is 105 gallons. An extra fuel tank may be slung under the fuselage in a bomb rack.
Wing span has been increased nine inches to a total of 33', with an area of 186 sq ft as against 176.5 sq ft of the older model. The curved tips, 2'1" long on each wing, which modify the former rectangular wing tips, are suspected by the British to be a sly Nazi stratagem to confuse the Me-109F with the Hurricane, rather than to serve a real technical purpose. Taper ratio remains about the same.
Perhaps the most interesting feature of the wings is the rearrangement of the radiators and flaps, and a kind of boundary layer ducting over the radiators. Because they are now deeper in the wings, the radiators project only slightly below the under surface. As shown in Fig 1, the boundary layer air is picked up in the duct just forward of the radiator, over which it is led, and discharged through the hollow upper flap. This top section moves up, normally, when the under section is lowered, thus controlling the air flow and preventing a change in lift. On landing, the top flap drops and the lower moves progressively ahead of it at a greater angle, and so maintains the cooling flow through the radiator. A small auxiliary flap at the lower leading edge of the radiator duct prevents stalling of the air at the lip when the rear flap is lowered.
The new cooling system, affords a far better duct than before, a large expansion on entry and low velocity cooling with sufficient control. A third radiator is installed under the engine.
Several details of the power plant have been altered; the oil tank has been removed from behind the engine and placed atop of the reduction gear where formerly the glycol header tank was installed, and the header tank has been halved and placed on either side of the crankcase. Changing of the engine has been facilitated by the change in position of the oil tank, for there are now no oil pipes to disconnect.
The supercharger air intake is bigger, and to get a better flow it has been set farther from the fuselage. A constant speed propeller governor prevents over-revving of the engine in combat maneuvers, and a cutout is provided so that the propeller can be used either as a fixed pitch or manually controlled type for cruising speed. Although the Mauser cannon is the new Messerschmitt's outstanding feature, its real efficiency would be obtained in a larger airplane, such as the Beaufighter or the Douglas DB-7 Havoc used in RAF night fighter squadrons, which would be capable of carrying sufficient ammunition to supply several such guns.
The specifications of the Messerschmitt Me-109F, powered by a Mercedes Benz DB-601N 12-cylinder engine, as reported from England, are as follows:
|Length||29 ft 8 in|
|Height (to mid point of spinner)||7 ft 1 in|
|Wing area||186 sq ft|
|Aspect ratio||5.85 dihedral|
|Wing loading||36.6 lb/sq ft|
|Weight empty||4,740 lb (estimated)|
|Gross weight||6,000 lb (estimated)|
|Maximum speed (at 21,000 ft)||380 mph|
|Range (at 307 mph)||370 miles|
|(at 262 mph)||600 miles|
|Service ceiling||40,000 ft|
This article was originally published in the October, 1941, issue of Aviation magazine, vol 40, no 10, pp 50-51.
The original article includes 2 photos of a crash-landed Me-109F, a three-view, and the cutaway and figures above.
Photos credited to British Combine. Cutaway by Clark, ARAeS; copyright by Aeroplane