Hello
This time I would like to present a material discussing the methods of aircraft construction before and during the Great War. How, years later, did people using the machines of the air force of the German Empire see the development of this then most modern weapon?
This time I will refer to the memories of DiplomIngenieur Madelung from Dessau, a reserve lieutenant and fighter pilot during the war. */
- Today it is hard to believe, but before the war almost all, even in 1918, our most effective aircraft in combat, were designed without taking into account the methods of loading, proven, for example, in bridge construction. However, two circumstances explain this approach - the first is the extensive use of prototypes. This concerns workshop practices. It should be realized that shortly before the outbreak of the war, aircraft were most often not fully designed in design offices and then assembled in workshops. They were simply put together from individual elements, according to sketches and data passed on orally by the designer himself, who, in addition, often introduced changes during the construction itself. Secondly, they drew on the rich, sometimes also bitter experience with attempts to load entire aircraft, which were shaped in the last years of peace by the German Aircraft Experimental Plant (DVL) in Adlershof. Until then, according to these assumptions, airfoils, stabilizers, rudders and fuselages, control systems, landing gear supports were only loaded with sandbags or weights. The entire procedure for such tests was developed only during the war by aircraft masters, who developed this experience and conclusions from the battlefields in the form of instructions. ( 1 )
- It became clear that the work methods used until then were no longer sufficient, and even dangerous for users, to be able to construct series of hundreds of aircraft or even to designate individual plants to produce a machine that we needed especially. With the growing size of aircraft factories and the speed of design changes, it was impossible for an engineer designing a new aircraft to be simultaneously responsible for the production of hundreds of aircraft that were being built in his factory. Therefore, over time, the production plant and the design office were separated.
- In order to ensure that the proper strength of the lightweight load-bearing structures was ensured, it was necessary to avoid any change in the series aircraft without prior, detailed testing of their strength. We tried to correct every deviation in the series of aircraft built on the basis of the reference aircraft. This was the most important task set by the army administration commission operating at the design offices. On the surface, this simple and logical solution was, however, difficult to implement... Even in 1918, aircraft of one type were often grounded, because it was only after the first accidents that it turned out that the aircraft had lost their planned structural strength due to arbitrary, unprofessional changes introduced in the production workshops.
- Sometimes, completely unexpected circumstances led to the disqualification of the aircraft. An example is the Roland C II Walfisch, whose unusual shapes and good military properties caused a sensation when it appeared. However, this machine was quickly withdrawn from units. It turned out that the pilot had a very limited field of vision forward during the approach to landing and during taxiing after landing. As a result, he noticed obstacles on the ground too late or did not see them at all. This error, unnoticed during the design of this machine and during experimental flights conducted at airports inland, seriously surprised front-line pilots using the Walfisch at field airports.
Such production practices were used until the very end of the war. It is enough to recall the history of the Fokker D VII, an aircraft that was designed in the f o u r t h year of the war. As even Wikipedia informs us:
... the fighter was created based on the best design solutions and achievements of aviation technology used in both German and Entente aircraft, especially French ones.
True, but it goes on to say:
Since the Fokker factory did not use detailed plans as part of the production process, Fokker simply sent the D VII airframe to be copied by the Berlin-based Albatros company.
It should come as no surprise that:
Some parts were not interchangeable between aircraft produced by different factories, and even between Albatros and its eastern subsidiary OAW. ( 3 )
Each manufacturer's aircraft differed in both the style of painting of the engine cowlings and the pattern and layout of the engine compartment cooling louvres. There are essentially four different arrangements of D.VII engine cowlings. First, we have the original V.11 and early Fokker production aircraft, with twin exhaust pipes on the right side of the 160 hp Mercedes engine. This type of cowling can also be seen on the D.VII(Alb.) 527/18, the first production Albatros aircraft. Later Fokker D.VII(F) aircraft had a different exhaust pipe for the 175 hp Mercedes or 185 hp BMW engines, and the cowling had more cooling louvers... The Albatros-built D.VIIs also had more cooling louvers, in a different arrangement... The OAW-built D.VIIs are easily identified because they have cowlings with 20 round cooling holes on each side. Some sources indicate that only OAW painted the cowlings in a diamond camouflage pattern. ( 4 )
The problem of lack of engineering experience was faced much earlier. Even in peacetime, with small, artisanal production volumes. An example of this is the case of the accident on September 4, 1913, when during the annual army maneuvers, the Rumpler "Taube" lost its wings, killing two officers.
The Rumpler and Albatros factories were to build a "Taube" type aircraft with wings that could be folded out for transport on a special truck to make them easier to transport. The "Klapptaube" or folding "Taube" was ordered from these two companies (each company ordered 12 units). After the accident, all of these aircraft were grounded.
Efforts were made to determine the cause of the failure. A top-level commission was quickly convened to supervise the first static load tests carried out on German military aircraft under government supervision. The load tests were carried out between September 21 and October 9, 1913.
The concept of an aircraft's "safety factor" had already been discussed among scientists at the Wissenschaftliche Gesellschaft für Flugtechnik, who initially proposed a safety factor of 10 (!), later reduced to a more realistic factor of 5.5. However, this was a purely academic approach. Up until that point, no German military aircraft had been officially tested for load, as this was not specified in the regulations for government orders. The test results were shocking. Only one monoplane (Fokker's "Taube") A.99/13 came close to an arbitrarily chosen safety factor.
In fact, all "Taube" monoplanes were structurally suspect.
During load tests, it was found that the wing rod attachments had failed, and in two cases the wing spar and landing gear strut supporting the wing rods had also failed.
The Fliegertruppe ordered all "Taube" monoplanes to be grounded until the structure could be reinforced with stronger attachments and parts to achieve a safety factor of at least 4. The "Klapptaube" (folding wing) project was abandoned. Steps were taken to improve the production guidelines, including regulations that specified rigorous load tests under military supervision before all new military aircraft were accepted. ( 2 )
As you can see, the bitter lesson, even a year before the war, did not help much. During the war, the problems only grew. Let us give the floor to the former pilot again.
- Like everything in Germany, aviation technology also suffered greatly from a shortage of materials. Light spruce wood, used for stringers, ended in 1914. Initially, it was replaced by ash wood, later it was changed to pine wood. It turned out that softwood has equal value, and even outweighs ash wood due to its greater stiffness and lightness. Unfortunately, it was also soon unavailable - there was a shortage of long sections without knots. So they tried to glue several layers together. Practice showed that this was a good solution because wood glued together in this way warped less than full beams and was safer to use. When thick wing profiles were introduced, rectangular stringers were connected from glued together elements and strips of pine wood. Thus, using little of the available material, really stiff stringers were made of good wood. ( 1 )
- By a strange coincidence, we only had a surplus of plywood, which was in short supply in England. This is why the German aviation industry introduced them so early into the construction of fuselages and stringers. Many plywood factories were established, and a supply of birch wood was guaranteed in due time. As a result, the English and French noted with surprise that in order to save on aircraft fabric, the wings of German training machines were covered with wooden plywood.
- The technique of producing fuselages from plywood gave them a form that no one had thought of before. It was more the result of a certain fashion. It was believed that by constructing a round fuselage, with carefully rounded ends and a smooth transition from wing to fuselage, it would be possible to avoid high air resistance and thus significantly increase the performance of the aircraft. However, later aerodynamic studies showed us something completely different.
Since it was not possible to construct such complex shapes from sheets of plywood, long strips of it were used to create the so-called Wickelrumpfe (covered hulls). However, this method was finally abandoned again, because it did not achieve an aerodynamic advantage, and what was created was extremely expensive and not resistant to destruction in collisions. More was offered by a new method of construction using, as in the construction of boats, alternating long, narrow strips of plywood. Such a construction did not require covering material, required less time for assembly than a similar hull wrapped in a layer of canvas, and was lighter. The good behavior of the plywood hull during accidents was one of the reasons for its advantage over the aircraft with a truss hull made of wood and wire, which in the event of an accident fell apart into a pile of small pieces of wood.
- The hull welded from steel pipes, due to its simple construction, was useful until the end of the war. With sufficient strength, they had a significant advantage over traditional machines, especially in training aviation. In case of accidents, inevitable during cadet training, this only led to bending of the pipes. The repair was therefore simple - the bent pipe could be quickly replaced by welding in another one. However, the thin-walled pipe of the front-line aircraft did not provide such advantages. In this case, the collision was not limited to bending of the part.
- The lack of rubber cords for the landing gear springs was very acute. During intensive pilot training, the schools alone used 20 kilometers of cord per week! Replacing them with steel springs was a mandatory solution. They were very heavy and their wear was enormous. Also, the wooden wheels introduced in the last year of the war, to save tires, were a very questionable replacement. Especially during landing, they wore out the aircraft components in an unacceptable way. Some types of aircraft had to be specially reinforced for this reason.
1 / George Paul Neumann, "German Air Force in the Great War"
2 / M Grosz "The "Taube" at War"
3 / Gray, Peter; Thetford, Owen (1970). German Aircraft of the First World War, 2nd edition. London: Putnam
4 / "The Aerofile - The Fokker D.VII File - Production differences". aerofile.info. 2019
5 / Wikipedia
*/ translator's note: in developing this text I did not quote the statements verbatim due to the different grammar of the German language. However, I tried to convey the idea of DiplomIngenieur Madelung.
