An Analysis of Captured Nazi Warplanes

by De Witt Wendell

British aeronautical engineers have released several highly interesting reports on German warplanes shot down by the RAF. This article is based on these.

The most interesting and definite information concerning German military airplanes has come — as might be expected — from England. It has been derived from careful inspections made by British engineers who had the opportunity to survey in leisure and detail the remains of some 3,000 Luftwaffe airplanes that have been shot down on English soil.

Most of these were pretty badly damaged. Some, however, got down in excellent general condition. The result has been that virtually every type that has been used against England has come to be well known to the British. At least one of each type has been inspected, patched where patches were needed and flown again by British pilots so that full details of maneuverability, vulnerability, speeds, etc, became available to British fighter pilots.

Most of this information also has been given out for public consumption in England and herewith we present a summary of points disclosed in these inspections of four standard types of German airplanes: the Messerschmitt Me-109 and Me-110, the Junkers Ju-88K and the Heinkel He-111K.

Before narrowing the field to one ship it should be remarked that these German craft are not inferior creations. General workmanship is of the highest sort. There is no indication of the use of ersatz material — except where such ersatz materials perform their work better than natural materials. Stories about wooden wheels on German ships, shortage of instruments, shortage of rubber, shortage of gasoline, all are branded false by the evidence of the German airplanes themselves.

The British report that the German planes have radio equipment that is described as "bewildering in its profusion and complexity.” The best quality of rubber (a material in which many said Germany was exceptionally short) is found in an equal profusion. The British add that there is more rubber in German airplanes than in British machines. Tires are excellent, most of them made by German Dunlop or Continental factories.

Fuel and oil found in the aircraft indicate no shortages in these vital essentials. Most of the German planes have the signs of 87-octane fuel stamped on their tanks. But invariably analysis of the fluid in the tank shows it to be of 90 to 92 octane — better than prescribed. Oil in German engines is used slightly longer than in British ships — but airline practice in the United States indicates that oil, unless fouled by bits of carbon or metal scrapings, is improved by use.

Maintenance practices as shown by the German machines are ahead of either British or American at this time. Each particular system — electrical, exhaust, hydraulic, fuel, lubricants, etc — has its own color on all pipes, fillers, levers and controls appropriate to that service. For instance — all oil pipes are painted brown as are oil radiator connections, shutter controls in cockpits, etc.

Here is the complete list: fuel, yellow; oil, brown; hydraulics, brown with red ring; glycol and water (motor coolant), green; oxygen, blue with two white bands; compressed air gun gear, blue with one red band; undercarriage gear, blue with two red bands.

All overflow pipes or outlet pipes are painted blue with a band of the color of system they serve. All points of connection where couplings can be loosened are painted on each side of the coupling with small red crosses. The beauty of the system is that it applies to all military craft, from evidence available. The fighters and bombers had exactly the same markings for similar systems.

Now for specific types. Let us begin with the Messerschmitt Me-109. This is, as the world knows, a single-seater, single-engined fighter. The ship is really tiny with a wing span of 34 feet, length of 30 feet, but a weight of 5,500 pounds. The Me-109 has been found with but one type of engine: the 1,150-hp Daimler Benz DB601 which is a V-12 inverted liquid-cooled motor with electric ignition.

Tests have shown that this airplane has a speed of 354 mph at 16,000 feet. It has a range of 450 miles at full speed — or about an hour and 15 minutes wide open. At less than full throttle this duration can be almost tripled.

Me-109s have been found with varying armament: either four machine guns, or two machine guns and two 20-mm cannon. The latest types have two .312-caliber machine guns (this is the standard German infantry rifle-caliber weapon) in the fuselage, slowed down by interrupter gear to fire between the three blades of the propeller. In the wings, firing outside the propeller arc, are the two cannon.

The airplanes have Germany's standardized VDM electrically controllable propeller — one of the world's best and simplest types, incidentally. This prop has a hollow hub to allow the fitting of a cannon on the engine. But not a single German airplane thus far inspected has had such cannon firing through the propeller. Instead, the propeller hole is used to lead cooling air to electric generators at the back of the engine.

The latest Me-109s have a reflector sight (newest and most accurate gun sights to be developed) made by Carl Zeiss of Jena. The windshield is plate glass and not bulletproof [bulletproof windshields recently have been reported —Ed]. The curved portions of the screen and the covering over the roof and sides of the cockpit is 3/8-inch Plexiglas. The hood is hinged to raise to the right for entrance to the cockpit. Sliding windows in the screen allow ventilation and visibility. The whole screen assembly flies off so a pilot can bail out if a spring latch is pulled.

There is only one fuel tank — immediately behind the pilot in probably the most vulnerable position in a fighter aircraft. None of the Me-109s inspected in England have had the self-sealing type of tank and there have been many of these fighters shot down in flames because of the tank arrangement. Its position, well behind the center of gravity, necessitates constant changes in trimming of the airplane in flight as fuel is consumed.

Flush riveting is used throughout the plane, as it was in all German craft inspected here. The wings are held on the fuselage by only three bolts, but apparently are amply strong. Trim is attained by a moveable horizontal stabilizer (an anomaly in today's more usual tabbed aircraft). Slotted flaps extend from the ailerons to the fuselage, their setting being indicated by lines painted on the upper surface marked with 0°, 10°, 20°, 30° and 40°. Handley-Page wing tip slots extend some eight feet from the wing tip to the mounting for the wing cannon, giving slow speed aileron control.

The cockpit is comparatively barren. The pilot's seat is adjusted by a lever on the left hand side. The control column is short, with a rubber grip and gun controls at the tip. Rudder pedals fit the whole foot with a flanged edge to prevent slipping. Brakes are operated by toe pressure. Also on the left is the trimming wheel and throttle controls. At right are oxygen bottles and lines, a hand gear for the main wheel retraction — this is manual with a simple, fool-proof worm or screw linkage.

Instruments are adequate but not plentiful. They include two sensitive altimeters, a turn and bank indicator, a magnetic bowl-type compass, an airspeed indicator that reads up to 750 kilometers per hour (446 mph), a boost or manifold pressure gauge, fuel pressure and oil pressure indicators, motor coolant temperature gauge, a fuel tank capacity gauge and oil temperature gauge. The electric system included radio receiver and transmitter switches, formation lights, signal lights, instrument dash lights, etc.

The wheels of the little plane are magnesium. The engine mount — with but four points of suspension for the engine — is a standard magnesium alloy forging with rubber shock absorbers for the motor. German mechanics are able to make a complete motor change on bombers or fighters with these mounts and the carefully designed control, fuel, lubricant, electrical connections, in less than two hours. Most British or US engine changes mean that an airplane is out of action for at least 48 hours.

The big point of interest is that the ships inspected thus far show how extremely widespread is the German system of subcontracting. On one of the Me-109s it was discovered that 11 different subcontractors had contributed parts. One of the Heinkel He-111Ks inspected in England indicated that 27 subcontractors had supplied parts. This is one of the methods adopted by the Germans to get large-scale production of their aircraft — one that is being adopted in the United States as well.

So much for the Me-109. Here is a tabulation on the Me-110:
Span53' 8"
Length40' 5"
Height11'
Wing area414 sq ft
Weightempty9,900 lb
payload4,900 lb
gross14,800
     Loadings
Wingat takeoff35.8 lb/sq ft
Power(takeoff)6.44 lb/hp
Span4.9 lb
     Performance
Maximum speed365 mph
Range
at 15,000 ft
at 301 mph565 mi
201 mph1,500 mi
175 mph1,750 mi

Obviously this airplane is in another class altogether than the Me-109. It is the best-looking, best-armed, best-built and best-equipped of German fighters investigated thus far — although even better machines are said to be in the immediate offing in Germany. The superlatives are those of the British engineers who examined it.

Construction of the Me-110 is all-metal, following the general practices of the Me-109, but here resemblance ceases. The pilot has a very complete set of instruments including a huge Paten gyrocompass mounted in the tail with repeater dials in both the pilot's and gunner — bomber and gunner radioman cockpits. The crew can be either two or three — depending on mission. This ship has been used as a short-range fighter, as a long-range fighter-bomber and as a reconnaissance ship with cameras.

Automatic wing-tip slots and slotted flaps are standard. Flaps are connected with the adjustable tailplane so that when flaps are lowered the tailplane is trimmed to counteract the change that otherwise would occur in the center of pressure on the wings. At the same time the ailerons are drooped to increase the drag and lift.

All forward-firing armament of the Me-110 is in the nose. A cover that slides forward and lifts off hides four of the rifle-caliber machine guns mounted there. Two 20-mm cannon are in a trough underneath the belly at the nose. The cannon are loaded by the radio operator-rear gunner from a sliding hatch in the floor at his feet. This gunner has a double machine gun firing backward over the tail. This gun has a field of fire 60° vertical and 120° horizontal and is the only rearward protection.

There are ample engine instruments, a Sperry gyro horizon and turn and bank. The radio includes a short-wave transmitter for Morse or voice, a long-wave transmitter and receiver for Morse only and a loop receiver for homing and direction finding. Finally there is a blind approach receiver and indicator for the Lorenz system. All this weighs 358 pounds and is standard for all multi-motored equipment whether fighter, reconnaissance or bomber.

The maximum tankage for which provision is made is 400.4 gallons or 1,820 litres. Most of the Me-110s, however, have 282-gallon tanks, four in number with one in front and one behind the single spar inboard of each motor. The two front tanks hold 82.5 gallons each and the two aft tanks 58.3 gallons each.

A curious fact is that the landing gear legs are not held up or down by locks as is standard with most other aircraft throughout the world. Hydraulic pressure alone does the job. This probably explains why so many German craft drop an undercarriage leg after combats with British fighters. In the battle a bullet has pierced a pressure line and the resultant loss of pressure releases the retracted leg.

The Heinkel He-111K is Germany's first modern bomber to go into service and is its heavy bombardment plane even today. The series numbers on the latest He-111Ks are H or No 8 in the modified types. It is a large machine as the following tabulation will show:
Span74' 3"
Length54' 6"
Height13' 9"
Weightempty14,400 lb
disposable load10,600 lb
gross25,000 lb
Maximum overloaded27,400 lb

Nearly 20 feet less span in the He-111K is carrying slightly over a ton more load than the Douglas DC-3 of approximately the same class, as to power. The normal gross of the He-111K is the absolute maximum for the DC-3. Where the DC-3 cruises at 190 mph at 7,000 feet with its 1,100-hp Cyclone motors, the Heinkel buzzes along at 215 mph. Where the Douglas has a range with full load of 1,100 miles, the Heinkel has 2,100 miles. The Douglas lands at sea level at 65 mph; the Heinkel at 74.

The British report that the Heinkel is a nice airplane to fly, comfortable and maneuverable. It is well-built and well-planned. It is entirely of metal with the standard German flush riveting. The pilot sits on the port side of the unsymmetrical nose. He has no extruded cabin, merely sitting in a fully streamlined and pointed nose section which is highly efficient aerodynamically. This nose is almost entirely Plexiglas so that, despite being sunk well inside the fuselage, the pilot has wonderful vision and must feel very exposed.

Instruments (of which there are a full complement) are arranged on a dashboard on the cabin roof. Throttles are at his left side as in a single-engined ship. There is no co-pilot's place, although the wheel control may be lifted over as in American Waco biplanes and other small craft, so an auxiliary or relief pilot may fly the Heinkel from a makeshift seat. Because the pilot is open to glare of sun or searchlight, circular glare shields that resemble fans that once were standard equipment for milady in the Victorian era, are fitted on the control column, on the roof and at each side of the cabin. When not unfolded into their round shield shape, these fans collapse into a compact line.

At the pilot's right is the tip-up seat for the navigator-bomb aimer. A padded trap in the floor covers the bombsights, which are used by lifting off this cover. The bomb aimer also becomes the front cupola gunner in combat, fitting a single .312-caliber gun on a pin fitting that is not particularly maneuverable nor does it have an effectively wide field of fire.

Behind the pilot is the bomb compartment between the wing spars. Bombs are carried in vertical racks and provision is for eight 550-pound bombs in most ships examined thus far. With this bomb load of 4,400 pounds the ship is given a maximum fuel load of 760 gallons weighing 5,700 pounds, since these are Imperial gallons (one quart more than standard US gallons).

The rear top gunner has a swinging cradle seat from the roof. The aft lower gunner lies in a trough firing a gun backward and downward. Two other guns have been provided the crew for firing directly out to port and starboard, since British fighters have commenced making what they call beam attacks to take advantage of the lack of protection at angles of 90° to the line of flight.

The loop antenna in the Heinkel is just inside the Plexiglas shield over the rear top gunner's firing position, where it adds no drag in flight. It is somewhat in the way of the gunner and, in one ship the British brought down, it was found the rear gunner had fired right through the mast holding this antenna.

A label found in the cockpits of the Heinkels gave the following flying directions: Take off with propellers at 11.50 on the clock dials that show the propeller pitch position. At this reading they are in fine pitch and allow high revs. Take off and climb for one minute at 2,400 rpm and 1.35 atmospheres of boost (a manifold pressure of about 38 inches of mercury). For continuous cruising below 19,685 feet, 2,100 rpm and 1.10 atmospheres (30.8 inches of mercury). Cruising above 20,000 feet, 2,300 rpm and 30 inches. In a dive, rpm must not exceed 2,500. Flaps must not be lowered at more than 200 kilometers (124 mph) or 1,700 rpm.

The Junkers Ju-88A1 is a 25,000-pound dive bomber. Most surprising of all facts elicited from an examination of this plane is its size as evidenced by the following dimensions: span, 59 ft.; length, 46.6 ft.; height, 15 ft.

British engineers who examined several of these airplanes decided that it originally was conceived as a heavy bombardment plane but changed to a dive bomber when in production. The wing spars show how they were strengthened after originally conceived, the diving brakes were added afterward and, as a result, they do not retract into the wing but merely lie against its lower surface. Finally, there are the external bomb racks for releasing of bombs in the dive when their release from internal racks became impossible.

The original Ju-88 was a two-crew bomber of highly streamlined shape and with two 1,200-hp Junkers Jumo 211 engines, did 324 mph for 1,200 miles over a two-way course in which wind could have had no effect. But the service form of the ship has a top speed of only 290 mph due to all these excrescences which cut down its performance radically.

As it is in service, it is capable of being used both as a dive bomber and as a horizontal bomber. There is a bomb-aimer's position in the nose, with a nose machine gun for horizontal bombing. The pilot also has a Zeiss dive-bombsight in front of his windscreen. This is altogether different than the horizontal sight. Just what the maximum angle to which Ju-88s are dived is not known. One ship shot down in England had a diving line on the fuselage at 45°. This is the line which the pilot brings the horizon when diving at 45°. Others, however, have lines at 40°, 50°, 60° and 70° Apparently these were put on by the pilots at their own discretion. Dive bombing is not very effective unless it is done from angles of 60° to 80° when great accuracy and penetration is obtained.

The Ju-88s have one amazing feature — the so-called automatic pullout for diving. Actually, this device merely indicates to the pilot that it is time to pull out and helps him do this. It works like this:

When the diving brakes are lowered (by hydraulic ram) hydraulic pressure is applied to one side of a piston and moves the elevator servo tab to the nose-heavy dive position. When the bomb is released electrically, a quick-release of pressure on the piston comes into play and this reverses the servo control at the tail and endeavors to return the tab to level flight position. The pilot feels the movement backward of the control column and is helped in raising the nose.

For dive-bombing this plane carries four 500-pound bombs externally. In addition, internally for horizontal bombing it can carry 16 bombs each of 110 pounds. This gives a gross bomb load of 3,960 pounds. Total fuel capacity for the airplane can be 770 gallons. But maximum bomb and maximum fuel loads cannot be combined. The plane can take either 510 gallons and its full bomb load, or its full fuel load and four 500 pound bombs.

The Ju-88 first came out with no defense under the tail — apparently its speed was expected to be its defense. But combat changed that. A backward firing gun was installed in a cupola under the nose. The one gun firing upward over the tail was augmented by three others.

A device unusual on American planes that the Ju-88 has as standard, is a "control surface brake." This is a hydraulic brake put on movement of all control surfaces at the pilot's will. Apparently it is put there to prevent flutter in its early stages. No brake could do anything against really well developed flutter, of course. But this is apparently used because speeds developed in dives have caused the Ju-88s controls to develop incipient flutter. This is a unique approach to the flutter problem.

Last of all, the Ju-88 has exhaust-heat wing deicing. Air taken behind the engine radiator is heated by contact with the exhaust stubs and then flows along piping to the leading edge of the wing. Here it enters a D-shaped duct formed by the curve of the leading edge and a vertical sheet of metal. In its passage the air heats the wing tip and is then discharged at the wing tip into the interior of the wing so that control hinges and pulleys do not freeze at high altitude. A standard Goodrich-type of pulsating boot deices the leading edges of the tail.

All the multi-engined German planes have the now famous German self-sealing fuel tanks. These are of five layers: the outer one of vulcanized rubber. Under this is a series of layers of partly hardened rubber. Then comes a layer of raw rubber that swells and plugs holes when gasoline reaches it. Under the raw rubber is a layer of tanned leather and finally the fuel is held in a fiber tank. The whole affair is light, immensely strong and works to perfection. It weighs about half a pound to the gallon — a figure comparable to that of dural tanks.

Because of space limitations we can merely touch on the German engines — Daimler-Benz and Junkers. Both types have direct injection of solid fuel into the cylinder and both have the fine hydraulic-coupled supercharger drive. This drive is similar to the fluid drive now developed for certain US automobiles, with this exception: oil for the coupling is supplied according to an inverse ratio of outside air density. Little oil in thick air at the ground, much oil in the thin air at altitude. The result is that there is considerable slippage in the blower drive near the ground but great efficiency at altitude.

The effect is to prevent the engines from being abused by opening throttles on the ground. Many of these engines also have a mechanism that prevents them from being abused at takeoff. This gives the pilot a predetermined period of full throttle operation after which the engine will revert to its maximum power rating for continuous operation.

This article was originally published in the March, 1941, issue of Flying and Popular Aviation magazine, vol 28, no 3, pp 14-17, 64, 66, 68.
The original article includes 8 photos of the planes described.
Photos are credited to Acme, International, British Combine.