World War One Aviation: German Bombers

The Friedrichshafen G.III (factory designation FF.45) was a medium bomber was designed and manufactured by Flugzeugbau Friedrichshafen. They were used by the German Imperial Air Service (the Luftstreitkräfte) during World War I for tactical and limited strategic bombing operations. After the end of the war a number of Friedrichshafen bombers were converted into transport aircraft while a small number also saw service as dedicated airliners.

The success of the G.II paved the way for the larger and more powerful G.III, which entered service in early 1917. While it looked somewhat similar to the G.II, the G.III was longer and had a greater wingspan which caused its designers to increase the number of interplane struts to three pairs on each side of the fuselage. Operational experience with the G.II had revealed a tendency for the aircraft to "nose over" during landings with deadly consequences for the nose gunner and possibly also the pilot. Friedrichshafen engineers solved this problem by equipping the G.III with an auxiliary wheel mounted under the nose gunner's position. The G.III also used the more powerful six-cylinder 190 kW (260 hp) Mercedes D.IVa engines. The extra power increased the bomb carrying capability enabling the aircraft to carry a bomb load of up to 1,000 kg (2,200 lb), though this severely reduced operational range. In practice, the heaviest bomb load rarely exceeded 600 kg (1,320 lb). Some of the bomb load could be carried internally but most of it was carried on removable external bomb-racks and usually consisted of streamlined P.u.W bombs but specialized munitions such as air-mines could also be carried. As production continued further modifications were made to the G.III series that resulted in two sub-variants:

Friedrichshafen G.IIIa

This sub-variant reintroduced a box-shaped biplane unit which improved the aircraft's control response when it was being flown on one engine. Another modification was the installation of a third 7.92 mm (.312 in) machine gun to combat British night fighters, which often attacked German bombers from below where they were hard to spot but the bomber's silhouette was easy to see against the night sky. This gun was mounted on a tubular, sliding mounting bolted to the floor of the rear gunner's position and was fired downward through a small sloping gun-tunnel cut into the bottom of the rear fuselage. By the last year of the war, the G.IIIa had replaced the G.III in production.

Friedrichshafen G.IIIb

Towards the end of the war, the G.IIIa was further modified by re-designing the rear gunner's position, which was connected to the pilot's cockpit by an open passageway.
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The AEG G.IV bomber entered service with the German Air Force in late 1916. Because of its relatively short range, the G.IV served mainly as a tactical bomber, operating close to the front lines. The G.IV flew both day and night operations in France, Romania, Greece and Italy, but, as the war progressed, the AEG G.IV was restricted increasingly to night missions. Many night operations were considered nuisance raids with no specific targets, but with the intention of disrupting enemy activity at night and perhaps doing some collateral damage.

The AEG G.IV carried a warload of 400 kg (880 lb).] While Gotha crews struggled to keep their heavy aircraft aloft, the AEG was renowned as an easy machine to fly. Some G.IV crews of Kampfgeschwader 4 are known to have flown up to seven combat missions a night on the Italian front. A notable mission involved Hauptmann Hermann Kohl attacking the railroad sheds in Padua, Italy in his G.IV bomber.
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After factory tests proved promising, military acceptance trials commenced on 19 October 1916 and led to the aircraft being purchased for the Luftstreitkräfte. Soon thereafter trouble set in, with crankshafts repeatedly failing. This was attributed mostly to the engine design, but new engine mountings and universal joints for each end of the driveshafts were fitted to mitigate the problem. Following these modifications, the R.I was deployed on the Eastern front, where it raided Riga from Alt-Auz during the summer of 1917. On its second combat mission, the R.I crashed due to the failure of two engines, and was destroyed.
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In deciding this, he had the benefit of greater pilot experience to draw upon. The difficulties of asymmetric thrust created by losing an engine on a twin-engine design had proved to be not nearly as bad as Ursinus had originally believed, and therefore the G.I's unusual design was really an answer to a non-existent problem. Furthermore, Burkhard had the opportunity to rebuild a crashed G.I (serial number 9/15) and re-arrange its components to place the fuselage on the lower wing, and found this design workable, while also removing the grave danger to the crew that landing accidents posed.

The G.II carried a crew of three and a defensive armament of two 7.92 mm (.312 in) machine guns. The forward section of the fuselage was skinned in plywood, with the remainder covered in fabric. The fuselage and two very large nacelles were mounted on the lower wing. Each nacelle contained fuel and oil tanks beneath a geared eight-cylinder 160 KW (220 hp) Mercedes D.IV engines driving pusher propellers. The undercarriage was unusual, being quadricycle in arrangement with a pair of wheels mounted at the front and rear of each engine nacelle. This feature was intended to remove the possibility of a nose-over on landing. In fact, the nacelles and undercarriage constituted fully self-contained, wheeled units intended to facilitate construction and maintenance. The entire aircraft was intended to be easily dismantled so that fuselage, engines, and wings would easily fit onto three railway flatcars.

The G.II prototype first flew in March 1916, and testing revealed several shortcomings. The most significant problem was that the aircraft was not capable of carrying the bombload that was specified by the Idflieg. This was solved by a redesign of the wing cellule to extend its span. At the same time, it was changed from a two-bay to a three-bay structure. The second issue was that the undercarriage arrangement made for very long and uncontrollable landing rolls. This was solved by changing it to a conventional tailskid configuration. Other revisions included horn-balanced ailerons and a triangular vertical fin. In this configuration, production commenced in April 1916.

The G.II entered operational service in August 1916, with eight of the initial production batch of 10 deployed to the Balkan front. Of the two others, one remained with Gothaer and the other was severely damaged in an accident during evaluation. Nothing today is known about the type's performance in combat, but of the eight on active service, no more than four appear to have been operational at any one time (October 1916). By February 1917, this number had dwindled to one aircraft only, and from April none remained in service. Part of the problem no doubt lay with their engines. The Mercedes D.IV was plagued by severe crankshaft vibration that resulted in frequent crankshaft failures.
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In November 1916, Gothaer received a production order for 35 aircraft; this was subsequently increased to 50 in February 1917. A further 80 aircraft were ordered from the Siemens-Schuckert Werke (SSW) and 100 from Luft-Verkehrs-Gesellschaft (LVG). Compared to the Gothaer aircraft, these license-built aircraft were slightly heavier and slower because Idflieg specified the use of a strengthened airframe. In order to counteract this, SSW built a number of highly-modified examples, including one driven by tractor instead of pusher engines, one with an extra bay added to its wing cellule, two with a new airfoil section for the wings, and one with a supercharger. None of these modifications had been fully evaluated by the end of the war. Late-production SSW G.IVs also usually incorporated the Stossfahrgestell auxiliary nosewheels and Flettner servo tabs developed for the G.V. Responding to a different performance issue, LVG overcame the tail heaviness of its machines by increasing the sweepback of the wings. Late production SSW and LVG built G.IVs were already obsolete as bombers, and many were finished as training aircraft with lower performance engines (Argus As.III or NAG C.III). Additionally, the SSW-built trainers relocated the fuel tanks from the engine nacelles to within the fuselage, as on the G.V.

In March 1917, the G.IV entered service with Kagohl 1, which was redesignated Kagohl 3 upon receipt of the new machines, and the G.IVs were soon to be put to use in Operation Türkenkreuz - the strategic bombing of London. This operational use was delayed when practice missions revealed faulty engine bearings that had to be replaced, and that the prevailing winds were stronger than expected, requiring the addition of extra fuel tanks. Additionally, it was discovered that the design of the fuel system prevented the main tanks from being completely utilised, and this problem had to be addressed as well.

Around 30 LVG-built G.IVs were fitted with Heiro engines and .315 in (8 mm) Schwarzlose machine guns for Austro-Hungarian service. Another one was experimentally fitted with a 20 mm Becker cannon for ground attack.

Polish forces found one abandoned G.IV at Poznan' during the Greater Poland Uprising of 1918 and 1919. Once repaired, the aircraft joined the 21. Eskadra Niszczycielska (21st Destroyer Squadron) on April 30, 1920. After operational use in the Polish-Soviet War, the aircraft was withdrawn from service in the summer of 1920 due to lack of spare parts.

All other surviving Gotha aircraft were destroyed in accordance with the terms of the Treaty of Versailles.
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The Gotha's pilot seat was offset to starboard with the bomb bay immediately behind. This allowed for a connecting walkway on the port side allowing crew members to move between the three gun stations. The Gotha included an important innovation in the form of a "gun tunnel" whereby the underside of the rear fuselage was arched, allowing placement of a rearward facing machine gun protecting from attack from below, removing the blind spot.

The G.V entered service in August 1917. It offered no performance improvement over the G.IV. The G.V was up to 450 kg (990 lb) heavier than the G.IV due to additional equipment and the use of insufficiently seasoned timber. Inferior quality fuel prevented the Mercedes D.IVa engines from producing the rated 190 kW (260 hp). For these reasons, the G.V generally operated at much lower altitudes than the G.IV.

In February 1918, Gothaer tested a compound tail unit with biplane horizontal stabilizers and twin rudders. The new tail unit, known as the Kastensteuerung, improved the aircraft's marginal directional control on one engine. The resulting G.Va subvariant incorporated the new tail as well as a slightly shorter forward fuselage with an auxiliary nose landing gear. All 25 G.Va aircraft were delivered to Bogohl 3, the new designation for the former Kagohl 3.

The G.Va was followed by the G.Vb, which carried an increased payload and operated at a maximum takeoff weight of 4,550 kg (10,030 lb). To reduce the danger of flipping over during landing, Gothaer introduced the Stossfahrgestell ("shock landing gear"), a tandem two-bogie main landing gear. The Stossfahrgestell proved so good that it was fitted to all G.V's in Bogohl 3. Some G.Vb aircraft also had Flettner servo tabs on the ailerons to reduce control forces.

Idflieg ordered 80 G.Vb aircraft, the first being delivered to Bogohl 3 in June 1918. By the Armistice, all 80 aircraft were built but the last batch did not reach the front and was delivered direct to the Allied special commission.
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The Zeppelin-Staaken R.VI was a four-engined German biplane strategic bomber of World War I, and the only so-called Riesenflugzeug ("giant aircraft") design built in any quantity. The R.VI was the most numerous of the R-bombers built by Germany, and also one of the first closed-cockpit military aircraft (but the first was Russian aircraft Sikorsky Ilya Muromets). The bomber was reputedly the largest wooden aircraft ever built until the advent of the Hughes H-4 Hercules built by Howard Hughes, its wingspan of 138 feet 5.5 inches (42.20 m) nearly equaling that of the World War II B-29 Superfortress.

In September 1914, at the start of World War I, Ferdinand von Zeppelin visualised the concept of a Riesenflugzeug (R) bomber, to be larger than the Gotha G. Using engineers from the Robert Bosch GmbH, he created the Versuchsbau Gotha-Ost (VGO) consortium in a rented hangar at the Gotha factory. Alexander Baumann became his chief engineer, although later the team included other noted engineers including Zeppelin's associate Claudius Dornier, Hugo Junkers and Baumann's protogé Adolph Rohrbach. All of these Zeppelin-Staaken Riesenflugzeug designs used some variation of push-pull configuration in the setup, orientation and placement of their powerplants.

The first Riesenflugzeug built was the VGO.I flying in April 1915, using three Maybach Zeppelin engines; two pusher and one tractor. This was built for the German Navy and served on the Eastern Front Later modified with two extra engines, it crashed during tests at Staaken. A similar machine, the VGO.II was also used on the Eastern Front.

Baumann was an early expert in light-weight construction techniques and placed the four engines in nacelles mounted between the upper and lower wing decks to distribute the loads to save weight in the wing spars.

The next aircraft, the VGO.III was a six-engined design The 160 hp Maybach engines were paired to drive the three propellers. It served with Rfa 500.

In 1916 VGO moved to the Berlin suburb of Staaken, to take advantage of the vast Zeppelin sheds there. The successor to the VGO III became the Staaken R.IV, the only "one-off" Zeppelin-Staaken R-type to survive World War I, powered by six Mercedes D.III and Benz Bz.IV engines that powered three propellers, a tractor configuration system in the nose, and two pusher-mount on the wings. By the autumn of 1916, Staaken was completing its R.V, R.VI, and R.VII versions of the same design, and Idflieg selected the R.VI for series production over the 6-engined R.IV and other R-plane designs, primarily those of Siemens-Schuckertwerke AG.

With four engines in a tandem push-pull arrangement, it required none of the complex gearboxes of other R-types. Each bomber cost 557,000 marks and required the support of a 50-man ground crew. The R.VI required a complex 18-wheel undercarriage to support its weight, and carried two mechanics in flight, seated between the engines in open niches cut in the center of each nacelle. The bombs were carried in an internal bomb bay located under the central fuel tanks, with three racks each capable of holding seven bombs. The R.VI was capable of carrying the 1000 kg PuW bomb.

Although designed by Versuchsbau, because of the scope of the project, the production R.VI's were manufactured by other firms: seven by Schütte-Lanz using sheds at Flugzeugwerft GmbH Staaken, Berlin; six by Automobil und Aviatik A.G. (Aviatik) (the original order was for three); and three by Albatros Flugzeugwerke. 13 of the production models were commissioned into service before the armistice and saw action.

The German Naval Air Service had an interest in float-equipped seaplanes so it is no surprize they turned an eye to the prospect of a giant float plane. One Zeppelin-Staaken R.VI was ordered to be converted on September 5, 1917. The new was designatied the Type L and issued the serial number 1432. The Zeppelin-Staaken Type L was powered by four Maybach engines using a 2 tractor, 2 pusher propelller configuration. Unfortunatly the prototype crashed during testing on June 3, 1918.

The project did not die with the 1432. The German Naval Air Service thought results were promising enough to continue development. They showed their confidence in the design with an order of four improved giant float-planes. The Type 8301 was developed from the Zeppelin-Staaken R.VI and the data from the Type L tests. Several important design changes made it an elegant. First change was elevating the fuselage above the lower wing which improved water clearance. To enhance mission flexibility, range became a major factor in mission sucess. The logical choice was to replace munitions with fuel. By eliminating the bomb bays, the range could be extended. enclosing the open gun position on the nose. Production ended after the war, of the four aircraft ordered only three were delivered.

R.VI serial number R.30/16 was the first supercharged aircraft, with a fifth engine - a Mercedes D.II - installed in the central fuselage, driving a Brown-Boveri supercharger. This enabled it to climb to an altitude of 19,100 feet (5,800 m). This same aircraft was later fitted with four examples of one of the first forms of variable-pitch propellers, believed to have been ground-adjustable only.

The R.VI equipped two Luftstreitkräfte (Imperial German Army Air Service) units, Riesenflugzeug-Abteilung (Rfa) 500 and Rfa 501, with the first delivered June 28, 1917.

The units first served on the Eastern Front, based at Alt-Auz and Vilua in Kurland until August 1917. Almost all missions were flown at night with 1,700 pound (770 kg) bomb loads, operating between 6,500 and 7,800 feet (2,000 and 2,400 m) altitude. Missions were of three to five hours' duration.

Rfa 501 was transferred to Ghent, Belgium, for operations against both France and Great Britain, arriving September 22, 1917, at St. Denis-Westrem (Sint-Denijs-Westrem) airdrome. Rfa 501 later moved its base to Scheldewindeke airdrome south of group headquarters at Gontrode, while Rfa 500 was based at Castinne, France, with its primary targets French airfields and ports.

Rfa 501, with an average of five R.VI's available for missions, conducted 11 raids on Great Britain between September 28, 1917, and May 20, 1918, dropping 27,190 kg (29.97 short tons) of bombs in 30 sorties. Aircraft flew individually to their targets on moonlit nights, requesting directional bearings by radio after takeoff, then using the River Thames as a navigational landmark. Missions on the 340-mile (550 km) round trip lasted seven hours. None were lost in combat over Great Britain (compared to 28 Gotha G bombers shot down over England), but two crashed returning to base in the dark.

Four R.VI's were shot down in combat (one-third of the operational inventory), with six others destroyed in crashes, of the 13 commissioned during the war. Six of the 18 eventually built survived the war or were completed after the armistice.
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The R.II was approximately three times the size of a conventional single engined bi-plane. The Linke-Hoffman R.II was probably the largest single propellor aircraft ever built and flown, with a wing span of 138 ft, length of 66 ft and height of 23 ft. The design was powered by a single 22 ft. 7.5 in diameter propeller. Power was supplied by four 260 h.p. Mercedes D.IVa engines, arranged in two tandem pairs inside the fuselage, driving the propellor through clutches, shafts and gearboxes. Each of the four engines could be disconnected from the shaft by means of special couplings, and R. II was able to perform normal flight with two engines.

The airframe was constructed largely of wood with plwood covering the forward fuselage and a steel-tube v-chassis main undercarriage with two wheels and a tail-skid at the aft end of the fuselage. Two examples of the R.II were completed by the time the Armistice were designated, R 55/17 and R 58/17.

Flight testing of R 55/17 was carried out after the Armistice in 1919, demonstrating acceptable performance and handling, being able to fly happily with only two engines running / connected. Normal endurance was estimated to be 7 hours, but with adjustment of load and a cruising speed of 74mph it was estimated that the R.II could stay aloft for 30 hours. After several test flights the aircraft was destroyed.

There were plans to make it a 12 passenger airliner after the war, but the restrictions of the Versailles Treaty ended further development. Despite its short life, the R. II remained in history (and in the Guinness book of records) as the largest single-propeller aircraft.
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