German Empire (1917)
Heavy Bomber Prototype- 4 Built

The Linke-Hofmann R.I was an experimental heavy bomber developed by the German Empire in 1917. The R.I would be unique, as one of the first prototypes to be constructed mostly out of a translucent material known as cellon, with the idea that it aircraft would be harder to spot. Unfortunately for the designers, cellon is highly reflective and ended up making the craft a much more noticeable target. After the failure with cellon, more work continued on the prototypes, now of normal fabric skinned construction. Due to poor performance caused by several design choices, the type was not mass produced and was subsequently cancelled.

History

During times of war, it is not too uncommon for companies, factories and other industrial firms to be drawn into the war effort and end up producing materials that are as far away from their specialty as possible. Sometimes, this can end in a surprise success or a total blunder. This was no exception in the first World War for the German Empire. The concept of the military airplane had seen its first successes early in the war,and the need for aircraft was on the rise, but a major problem came in the fact that there were few dedicated airplane companies in Germany at the time. Thus, the Empire would call upon many of its industrial manufacturers to begin designing and producing aircraft, even if they were not familiar with working in that field. Linke-Hofmannn would be one such company.

Linke-Hofmann, sometimes misspelled Linke-Hoffman, was founded in 1912 and was a manufacturer of railroad components, mainly locomotives and rolling stock. In early 1916, the company would enter the field of aviation by using their factories for aircraft repairs and for license built construction of aircraft. Some aircraft types they built under license were the Roland C.IIa, Albatros C.III, Albatros C.X and the Albatros B.IIa. At the same time, Linke-Hofmann was also awarded a contract to produce their own aircraft. The first of their home built aircraft would be an R-Plane type or Riesenflugzeug (giant aircraft), which was the designation given to the largest multi-engine bomber aircraft of the Empire. Linke-Hofmann’s R.I design would be a strange looking machine. Its fuselage was short and tear-drop shaped to streamline the design . Each pair of wings would be mounted extremely high and low on the fuselage in an attempt to increase lift. Four internal engines would be connected to four propellers, two in pusher configuration and two in puller configuration. Most interestingly, a majority of the tail of the aircraft would be made out of a material called Cellon. Cellon (Cellulose Acetate) is a translucent, plant-based material similar to film that was tested on several German aircraft in WWI, swapping out the normal fabric. The idea behind having the airframe covered in such material was that it was thought to make the aircraft harder to see. In addition to the Cellon, the R.I also had a very large cockpit with a number of windows to give much better visibility. Many of these design choices were made as it was thought they would make the design perform better in the long run, but they would ultimately lead to its downfall.

Work began on the first R.I in the later months of 1916 under Chief Engineer Paul Stumpf, who previously worked for the AEG aircraft works. The first R.I was completed in early January of 1917 and was named the R.I 8/15. Testing of the aircraft began, but its first flight was delayed due to the unconventional steel tires coming apart during taxiing attempts. Improved versions of the tires were built that were much more stable than the first. Shortly after, the R.I 8/15 would fly for the first time from the Hundsfeld Airfield near Breslau, but the exact date is unknown. Early test flights showed the design was flawed and as time went on, performance began to suffer, although the exact reason was not known. Noticeably, the wings seemed to be the root cause of the lag in performance. The aircraft’s controls would occasionally become heavy and unresponsive, resulting in a partial loss of control. To amend this to some degree, several additional struts were added to the main wings, but this would not save the aircraft from disaster. On May 10th 1917, during its 6th test flight, two of the wings on the R.I 8/15 would collapse mid-flight and the aircraft would slam into the ground at full speed. Remarkably, all of the crew of the aircraft would survive, but the airframe itself would be destroyed in a blaze of fire caused by the crash. Unfortunately, 1-2 ground crew would die from the flames while trying to put them out.

The destruction of the 8/15 would force Linke-Hofmann to look into designing an improved model. At this time, many of the design choices Linke-Hofmann made with the aircraft would show how ineffective and even detrimental they were. The wings themselves were the root cause of the crash, as they were not stable nor very well supported. The Cellon material, which was thought to make the aircraft invisible, actually ended up doing the exact opposite, as the material was highly reflective, especially while the aircraft was airborne. Cellon itself also was not the most stable material to make most of the tail section of the aircraft out of, as the material itself could easily bend and warp during rough weather. Even when the material worked as needed, it aged to a yellow color that would remove the translucency. Even before the aircraft took flight, Linke-Hofmann would be criticized for making an aircraft mostly out of the little tested material. In order to amend these issues, the Idflieg ,,the Imperial organization that handled aircraft development, ordered several improved models to continue the development of the type, as the 8/15 had crashed before most of the evaluation had completed. Linke-Hofmann would then begin construction on the improved models, serial numbers 40/16 through 42/16. These improved variants on the R.I attempted to fix many of the issues that plagued the 8/15. The wing structure was redesigned to be significantly more stable, with additional struts forming an overall better design. Most of the Cellon in the aircraft had been replaced with standard fabric, with only a few small patches of the tail containing it, likely to serve as observation windows. The landing gear was also heavily improved, something the Linke-Hofmann Engineers were quite proud of. Lastly, the new airframe was also built to accommodate three positions for machine gunners. These small improvements mended these few issues, but the aircraft’s design was still riddled with flaws.

Details regarding the history of the improved variants are, unfortunately, not well known. It is unknown exactly when the R.I 40/16 first flew or when it was even built, but the handling of the aircraft had been significantly improved upon over the 8/15. Maneuverability was especially stated to be superb compared to the older model, but its general performance was still considered to be unsatisfactory. Landing the aircraft was stated to be terrible due to the high location of the pilot and the slow landing speed.

During one landing attempt while testing the 40/16, the test pilot misjudged how close he was from the landing strip due to the height of the aircraft and damaged the landing gear. Due to the teardrop shape of the aircraft, the entire thing went nose down into the ground, crushing the entire cockpit section. It is unknown if anyone was killed or injured during the crash, but no attempt was made to repair the aircraft afterwards and it was likely scrapped. Details on the 41/16 and 42/16 are even more lacking. Some sources claim they were never completed, while other sources state they were complete and ready for inspection before the program concluded. 41/16, in particular, has virtually no information or photos of the aircraft, but two photos exist of a finished 42/16 sitting outside the Linke-Hofmann factory in Breslau.

Design

The Linke-Hofmann R.I was a four engined R-Type aircraft with a large teardrop-shaped fuselage covered in fabric. The fuselage was designed in such a “whale” configuration to contain its engines and reduce drag, but this was only ever tested on smaller aircraft and likely detrimentally affected the R.I. The front of the aircraft was divided into three different floors. The first floor contained the pilot’s position and the wireless station for communication. This floor had extensive glasswork to provide a good view around the front of the aircraft. The large amount of glass used in the cockpit only helped during clear weather as, during rain or if illuminated by a searchlight, it would cause visibility to suffer from light reflection and condensation.

The second floor contained the four Mercedes D.IVa engines. The third and lowest level contained the bombardier’s station and four internal fuel tanks. The tail of the R.I differed between the two variants. On the earlier 8/15, the tail was composed mostly of Cellon, while on the later 40/16, it was covered in fabric. The tail of the aircraft had a biplane horizontal stabilizer and three vertical fins for vertical stabilizers. The two additional fins vertically and the upper wing of the horizontal stabilizers were used as control surfaces on top of the conventional placement of said control surfaces. The wings of the aircraft were placed high and low on the aircraft, with the fuselage height directly separating each wing. Only the upper wings had ailerons fitted. The wings on the 8/15 were actually the lightest of any R-Plane built, which was a likely factor in its crash. The 40/16 had improved and more stabilized wings compared to its predecessor. The aircraft originally was planned to have four propellers, two in tractor and two in puller configuration but this design aspect doesn’t appear to have ever left the drawing board. Instead, only two were used in tractor layout. The engines powered the propellers in a very unique way. Each side of the aircraft had one propeller, which was connected to a pair of engines via outrigger frames and powered through a drive shaft connected to a bevel gear. Each pair of engines powered one side. This was done so that, in the event one of the engines was disabled through either malfunction or combat, the propellers would still have power going to them. A disabled propeller would begin windmilling, or rotating without power, and cause significant drag. On larger aircraft, this would seriously alter performance and cause the aircraft to lose speed and airflow due to drag. This complex system was put into place to prevent this from happening.

No armament was carried aboard the R.I, but several proposals were made. Three machine-guns of unknown type and caliber were to be located at three positions around the aircraft. Two were located on the tallest point of the body, with one facing forward and one facing backward to cover all angles. The third gun position was located in the middle of the aircraft, with two open windows on each side to provide maximum firing range to each side. Given it was an R-Plane, the R.I would have used bombs had it entered mass production, but it’s loadout was never addressed, since the type was considered a failure.

Conclusion

With the destruction of two aircraft and the type severely underperforming to expectations, the Idflieg lost their faith in Linke-Hofmann’s R.I program and it was promptly cancelled before January 1918. The 41/16 and 42/16 were most likely scrapped before the end of the war. The type was riddled with flaws from the beginning due to the strange decisions made by Linke-Hofmann in designing their first aircraft. Despite their failure at the start of their aircraft manufacturing career, Linke-Hofmann would use the experience learned from the R.I to create an improved and much more traditional looking R-Plane aircraft, the R.II.

Variants

• Linke Hofmann R.I 8/15 – First version of the R.I. This version’s tail and rear fuselage were constructed of the transparent material Cellon.
• Linke Hofmann R.I 40/16 – Improved version of the R.I 8/15. This type had many slight modifications, such as a better wing structure, a more stable landing gear, and was no longer constructed of Cellon. 3 of this type were built.

Operators

• German Empire – The Linke-Hofmann R.I was an R-type aircraft meant to be used in the heavy bomber role for the German Empire. However, due to poor performance, the type was never mass produced or sent into service.

Linke-Hofmann R.I 40/16 Specifications
Wingspan	108 ft 11 in / 33.2 m
Upper Chord	16 ft 5 in / 5 m
Lower Chord	15 ft 5 in / 4.7 m
Length	51 ft 2 in / 15.6  m
Height	22 ft / 6.7 m
Wing Area	2851 ft² / 265 m²
Engine	4x 260 hp ( 193.9 kW ) Mercedes D.IVa engines
Weights	Empty 17,640 lb / 8,000 kg Loaded 24,969 lb / 11,200 kg
Climb Rate	Time to 9,840 ft / 3,000 m 2 Hrs
Maximum Speed	81.8 mph / 130 km/h
Crew	4-5 crewmen
Armament	3x planned machine guns of unknown type.

 

Gallery

Illustrations by Ed Jackson

Credits

• Written by: Medicman11
• Edited by: Stan L. & Henry H.
• Illustrations by Ed Jackson

Sources

• Kosin, Rüdiger. The German fighter since 1915. Baltimore, Md: Nautical & Aviation Pub. Co. of America, 1988. Print.
• Herris, Jack. German Aircraft of Minor Manufacturers In WWI Volume 2: Krieger To Union, Columbia, SC: Aeronaut Books, 2020. Print.
• Haddow, G. W., and Peter M. Grosz. The German giants : the German R-planes, 1914-1918. London: Putnam, 1988. Print.