Allgemeine Elektrizitäts Gesellschaft (AEG) G.IV Grossflugzeug
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Historical Background
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The AEG series of twin engine bombers are largely the forgotten member of the German bomber triad consisting of the AEG, Gotha and the Friedrichshafen.
The Gotha was the long range workhorse, however they were very tail heavy and tiring to fly, especially after the bomb load was dropped and the center of gravity shifted. Friedrichshafens were considered mid range bombers and the AEG was the short range cousin.
The AEG G.IV is considered by some to be the best airplane of the three. It was the fastest and had a payload 623 lbs greater than the Friedrichshafen. While Gotha crews struggled to keep their heavy aircraft aloft, the AEG was renowned as an easy machine to fly.
As testimony to its good flying qualities the crews of Kampfgeschwader 4 are known to have flown up to seven combat missions a night on the Italian front. When the war ended in November 1918 the allies were surprised that only 320 AEG G. IV aircraft existed. By flying five or more missions a night the allies were led the believe that the German bomber force was much larger than it actually was.
The AEG G.IV also had a quality that endeared it to the men who flew it - it was an extremely rugged aircraft. Unlike the other German bombers the AEG featured an all metal welded tube frame. Photos of AEG crashes usually show the wings crumpled while the crew compartments stayed intact, allowing the men to walk away from the crash.
Preceding models:
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In the early months of WW1, the necessity for strategic bombers quickly became apparent, and Germany started developing this type of aircraft.
In 1915, Allgemeine Elektricitäts-Gesellschaft (AEG) presented its first model, the G.I, fitted with 100 Hp Mercedes D.I engines, but it was hopelessly underpowered, and only 10 units were built.
The G.II quickly followed, of which 24 were built, with class 3 (min 150 hp) Benz Bz.III engines that delivered 165 Hp at sea-level. These could already carry a payload of 440 lbs, but still had insufficient power.
The next version, the 1916 G.III, had a larger payload, 660 lb. It was fitted with 220 Hp, Mercedes D.IV "straight-eight" engines, which were better but suffered from frequent crankshaft breakages. Only a few were built.
Series production did not come about until further development led to the improved G.IV in 1917, of which 500 were built:
- It now had a rugged, plywood-covered, welded steel-tube frame.
- Payload was increased to 880 lb.
- Mercedes D.IVa high-compression, throttle gated aero-engines were fitted, altitute rated for 267 Hp at 1300 Metres. For more details, see "Early German High Compression Aero Engines" further below.
However, the endurance of the AEG G.IV was not as expected, so they were only used tactical bombers on East and West fronts. The G.V, an improved variant with a biplane tail, came too late to see any action. When the war ended, 6 of these were sold to Sweden, who was mainly interested in the engines, and some G.IV´s continued in service for civil purposes,
SPECEFICATIONS
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Country of Origin: Germany (German Empire)
Primary Function: Bomber/Reconnaissance Biplane
Manufacturer: Allgemeine Elektrizitäts Gesellschaft (AEG)
Crew: Three to Four
Year: 1917
Powerplants
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Two specification 4 (min 260 HP) Mercedes D.IVa, 6 cylinder inline, water cooled, throttle gated, high compression piston engines, altitude rated for 267 Hp at 1300 metres (4265 ft), and fitted with automatic mixture control.
Performance below rated altitude was 83% - i.e. 221 Hp.
Performance
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Maximum Level Speed: 103 mph (90 Kt) at 4265 ft
Maximum speed below rated altitude, at 83% Power: 84 Kt
Cruising speed: 78.3 Kt
Service Ceiling: 14,765 feet
Climb to 1000 metres: 5 min
Endurance: 4.5 to 5 hours
Armament
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Fixed Armament: One 7.92mm Parabellum machine gun on ring mounting in forward cockpit; One 7.92mm Parabellum machine gun on rail mounting in aft cockpit; Underwing pylons for maximum bomb load of 882-lbs
One version, the G.IVK, was fitted with a 20-mm Cannon in the nose.
Early German High Compression Aero Engines
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Summarized from a text by FSAviator, November 2002.
Due to the inconsistent quality of the petrol supplied to combat units during the Great War, well designed engines tended to suffer from premature detonation of the fuel/air mixture from time to time. Pilots soon learned to throttle back to cure the problem. After a short interval, the hottest parts of the engine, (usually the exhaust valves), cooled enough to prevent detonation. Pilots also found that engines rarely pinked at high altitude.
As an aircraft climbs through the atmosphere, outside air pressure and temperature reduce. To keep petrol to air ratio constant in the cylinders, pilots reduce fuelflow to the engine, adjusting mixture control. For a compression ratio of four to one at sea level, the engine compresses the fuel/air mixture from one atmosphere to four at the moment of ignition. This engine, at an altitude of 22,000 ft, will compress the air pressure of half an atmosphere to only two atmospheres on ignition, and lower gas pressures reduce the possibility of premature detonation.
It soon occurred to the German high command to increase the compression ratio for their Zeppelin engines. Such an engine would be impossible to operate at full throttle at low altitude, as it would literally explode, but would outperform all other engines at high altitude, where it could compress the thin air to four atmospheres instead of two or less. A Zeppelin did not need maximum power for take off, landing or combat maneuvering at low level. Various means were employed to prevent the pilot from advancing the throttle too far, too soon.
The altitude from which full throttle was safe, was referred to as the rated altitude, where the engine would produce its maximum power.
These High Compression engines needed no new or improved construction techniques but the price of improved performance at high altitude was poor performance at low altitude. For example: a high compression engine rated for 215hp at 5000 feet would have to be throttled to give no more than 180hp at sea level. Climbing towards 5000 feet, power in this or any other engine which gave 180hp at sea level would fall with air density, coming down to about 150hp at 4,999 feet. Passing 5000 feet the pilot would give full throttle and power would suddenly increase to 215hp. From 5000 feet upwards power would fall off at the same rate as in any other engine, but starting from 215hp rather than 150hp.
It soon occurred to the Germans that such engines could be used in high altitude photo reconnaissance aircraft, and also for high altitude bombing. This simple idea does not seem to have occurred to the allies, who were astonished when they began to meet German aeroplanes with High Compression engines at high altitude.
There were two high compression, six-cylinder engines. One was the Mercedes D.IVa, rated for 267 Hp at 1,300 metres, and the other was the Maybach MbIVa, rated for 245 Hp at 2,500 metres. At higher altitudes, the Maybach was the more powerful of the two.
From the invention of the High Compression engine onwards, it was necessary to state rated altitude together with maximum power for an aero-engine, as well as power at sea level to give an accurate impression of the power diagram of the engine.
At first, German aircraft with high compression engines which saw service during the Great War, usually had two or three throttles mounted on the same quadrant. Each could be advanced once some limiting altitude had been reached. This idea was replaced later by a single throttle with one or more gates or détentes cut into the quadrant, beyond which the throttle was not to be advanced until specified altitudes had been reached.
