Nazi Germany 

Ramjet powered aircraft

None built

In the later stages of the Second World War, it was becoming apparent to both the Luftwaffe  (English German Air Force) and the German Government that the Allied air forces were gaining air superiority. This realization saw them turn to new and fantastical ideas in a desperate attempt to turn the tide of the war. Some of these represented new improvements to existing designs, the introduction of the newly developed turbojet engine, and even more esoteric and experimental methods. In many cases, these were pure fantasies, unrealistic or desperate designs with no hope of success. Few of them reached any significant development, and among them were the works of Alexander Martin Lippisch. While Lippisch helped develop the Me 163, the first rocket-powered interceptor, his other work remained mostly theoretical. One such project was the unusual P 13a, ramjet-powered aircraft that was to use coal as its main fuel source. While some work was carried out late in the war and soon faced insurmountable technical problems, thus nothing came of the project.

History

Before the start of the Second World War, aviation enthusiast and engineer Alexander Martin Lippisch, was fascinated with tailless delta wing designs. Lippisch’s early work primarily involved the development of experimental gliders. Eventually, he made a breakthrough at the Deutsche Forschungsinstitut, where he worked as an engineer.  His work at DFS would lead to the creation of the rocket-powered glider known as the DFS 194. As this design was a promising experiment in a new field, it was moved to Messerschmitt’s facility at Augsburg. After some time spent refining this design,  it eventually led to the development of the Me 163 rocket-powered interceptor.  While it was a relatively cheap aircraft, it could never be mass-produced, mostly due to difficulties associated with its highly volatile fuel. In 1942, Lippisch left Messerschmitt and ceased work on  the Me 163 project. Instead, he joined the Luftfahrtforschungsanstalt Wien (English: Aeronautic Research Institute in Vienna) where he continued working on his delta-wing aircraft designs. In May 1943 he became director of this institution, and at that time the work on a supersonic aircraft was initiated.

In the later war years, among the many issues facing the Luftwaffe, was a chronic fuel shortage. Lippisch and his team wanted to overcome this problem by introducing alternative fuels for their aircraft. Luckily for his team, DFS was testing a new ramjet engine. They were designed to compress air which would be mixed with fuel to create thrust but without a mechanical compressor. While this is, at least in theory, much simpler to build than a standard jet engine, it can not function during take-off as it requires a high airflow through it to function. Thus, an auxiliary power plant was needed. It should, however, be noted that this was not new technology and had existed since 1913, when a French engineer by the name of Rene Lorin patented such an engine. Due to a lack of necessary materials, it was not possible to build a fully operational prototype at that time, and it would take decades before a proper ramjet could be completed. In Germany, work on such engines was mostly carried out by Hellmuth Walter during the 1930s. While his initial work was promising, he eventually gave up on its development and switched to a rocket engine instead. The first working prototype was built and tested by the German Research Center for Gliding in 1942. It was later tested by mounting the engine on a Dornier Do 17 and, later, a Dornier Do 217.

In October 1943, Lippisch won a contract to develop the experimental P 11 delta-wing aircraft. While developing this aircraft, Lippisch became interested in merging his new work with a ramjet engine. This would lead to the creation of a new project named the P 12. In the early stage of the project, Lippisch and his team were not completely sure what to use as fuel for their aircraft, but ramjets could be adapted to use other types of fuel beyond aviation gasoline.

Unfortunately for them, LFW’s facilities were heavily damaged in the Allied bombing raids in June 1944. In addition to the damage to the project itself, over 45 team members died during this raid. To further complicate matters, the scarcity of gasoline meant that Lippisch’s team was forced to seek other available resources, such as different forms of coal. This led to the creation of the slightly modified project named P 13. In contrast to the P 12, the cockpit was relocated from the fuselage into a large fin. This design provided better stability but also increased the aircraft’s aerodynamic properties.  The overall designs of the P 12 and P 13 would change several times and were never fully finalized.

The P 12 and 13 small-scale models, in both configurations, were successfully tested at Spitzerberg Airfield near Vienna in May 1944. The project even received a green light from the Ministry of Armaments. In the early stages of the project, there were some concerns that the radical new design would require extensive retraining of pilots. However, the wind tunnel test showed that the design was aerodynamically feasible and that the aircraft controls had no major issues. Based on these tests,  work on an experimental aircraft was ordered to begin as soon as possible.

The DM-1 Life Saver 

While working on the P 12 and P 13, Lippish was approached with a request from a group of students from Darmstadt and Munich universities. They asked Lippisch to be somehow involved in the P 12 and 13 projects. Lippisch agreed to this and dispatched one of his assistants under the excuse that for his own project, a wooden glider was to be built and tested. The previously mentioned student’s and Lippisch’s assistant moved to a small warehouse in Prier and began working on the Darmstadt 33 (D 33) project. The name would be changed to DM 1 which stands for Darmstadt and Munich.

At this point of the war, all available manpower was recruited to serve the German war effort. For young people, this often meant mobilization into the Army. One way to avoid this was to be involved in some miracle project that offered the Army a potentially war-winning weapon. It is from this, that numerous aircraft designs with futuristic, and in most cases unrealistic, features were proposed. Many young engineers would go on  to avoid military service by proposing projects that on paper offered extraordinary performance in combat.

While it was under construction, preparations were made to prepare for its first test flight. As it was a glider it needed a towing aircraft that was to take it to the sky. A Sibel Si 204  twin-engine aircraft was chosen for the job. However, this was not to be done like any other glider, being towed behind the larger aircraft. Instead, the DM-1 was to be placed above the Si 201 in a frame, in a similar combination as the Mistel project. The estimated theoretical speeds that were to be reached were 560 km/h (350 mph).

Allegedly, there were four different proposals for the DM’s that were to be fully operational. The DM 2 version was estimated to be able to reach a speed of  800-1,200 km/h (500 – 745 mph). The DM 3’s theoretical maximum speed was to be 2,000 km/h (1,240 mph) while the fate of the DM 4 is unknown. Here it is important to note that these figures were purely theoretical, as there were no supersonic testing facilities to trial such a design. It is unclear in the sources if these additional DM projects even existed, even if in only written form. We must remember that the whole DM 1 glider idea was made to help the students avoid military conscription and that Lippisch himself never saw the DM 1 as any vital part of the P 13.

In any case, the glider was almost completed by the time the war ended and was later captured by the Western Allies. Under the US Army’s supervision, the glider was fully completed and sent to America for future evaluation. It would then be given to the Smithsonian Institution.

Work on the P 13

As the work on the P 13 went on, the name was slightly changed. This was necessary as different variations of the P 13 were proposed. The original  P 13 received the prefix ‘a’ while the later project’s designation continued alphabetically for example P 13b. After a brief period of examination of the best options, the P 12 project was discarded in favor of P 13. The decision was based on the fuel that the aircraft should use. What followed was a period of testing and evaluation of the most suitable forms of coal that could be used as fuel. Initial laboratory test runs were made using solid brown Bohemian coal in combination with oxygen to increase the burn rate. The fuel coal was tube-shaped, with an estimated weight of 1 kg, and encased in a mesh container through which the granulated coal could be ejected. The testing showed serious problems with this concept. While a fuel tube could provide a thrust that on average lasted 4 to 5 minutes, its output was totally unpredictable. During the testing, it was noted that due to the mineral inconsistency of the coal fuel, it was impossible to achieve even burning. Additionally, larger pieces of the coal fuel would be torn off and ejected into the jet stream. The final results of these tests are unknown but seem to have led nowhere, with the concept being abandoned. Given that Germany in the last few months of the war was in complete chaos, not much could be done regarding the Lippish projects including the P 13a.

In May 1945, Lippish and his team had to flee toward the West to avoid being captured by the advancing Soviets. They went to Strobl in Western Austria, where they encountered the Western Allies. Lippisch was later transported to Paris in late May 1945 to be questioned about his delta wing designs. He was then moved to England, and then to America in 1946. The following year,  American engineers tested the DM 1 glider at the wind tunnel facility of the Langley Field Aeronautical Laboratory. The test seems promising and it was suggested to begin preparation for a real flight. A redesign of the large rudder was requested. It was to be replaced with a much smaller one, where the cockpit would be separated from the fin and placed in the fuselage. Ironically Lippish was not mentioned in this report, as technically speaking he was not involved in the DM 1 project. Nevertheless, he was invited for further testing and evaluation of this glider. If this glider and the Lippish work had any real impact on the US designs is not quite clear.

Despite no aircraft being ever completed, one full-size replica of this unusual aircraft was built after the war. It was built by Holger Bull who is known for building other such aircraft.  The replica can now be seen at the American Military Aviation Museum located in Virginia Beach.

Technical characteristics

DM 1

The DM 1 glider was built using wooden materials. Given that it was constructed by a group of young students, its overall design was quite simple. It did not have a traditional fuselage, instead, its base consisted of a delta wing. On top, a large fin was placed. The cockpit was positioned in front of the aircraft within the large vertical stabilizer. To provide a better view of the lower parts of the nose, it was glazed. The landing gear consisted of three small landing wheels which retracted up into the wing fuselage. Given that it was to be used as a  test glider, no operational engine was ever to be used on it.

A good example of DM 1 (to the right) and P 13a models that showed the difference between these two. The P 13a could be easily distinguished by its engine intake and the different position of the pilot cockpit. Source: Wiki https://imgur.com/a/QW7XuO5

P 13a

The P 13 is visually similar but with some differences. The most obvious was the use of a ramjet. This means that the front, with its glazed nose, was replaced with an engine intake. Here, it is important to note, that much of the P 13a’s design is generally unknown, and much of the available information is sometimes wrongly portrayed in the sources. The P 13a never reached the prototype stage where an aircraft was fully completed. Even as the war ended, much of the aircraft’s design was still theoretical. Thus all the mentioned information and photographs may not fully represent how the P 13 may have looked or its precise characteristics, should it have been finished and built.

The exact ram engine type was never specified. It was positioned in the central fuselage with the air intake to the front and the exhaust to the back. As the main fuel, it was chosen to use small pieces of brown coal which were carried inside a cylindrical wire mesh container. The total fuel load was to be around 800 kg (1,760 lbs). Combustion was to be initiated by using small quintiles of liquid fuel or gas flames.  The overall engine design was changed several times during the work on the P 13 without any real solution to the issues of output consistency. Given that the ramjets could not work without an air thrust, an auxiliary engine had to be used during take-off, though a more practical use would be to tow the P 13 until it could start its engine. A rocket takeoff ran the risk of the engine failing to ignite, leaving the pilot little time to search for a landing spot for his unpowered aircraft.

The wing construction was to be quite robust and provided with deflectors that would prevent any potential damage to the rudders. The wing design also incorporated a sharp metal plate similar to those used for cutting enemy balloons cables. These proposed properties of the wings are another indicator that the P 13 was to be used as an aircraft rammer. Another plausible reason for this design was the fact that given it had no landing gear the aircraft design had to be robust enough as not to be torn apart during landing. The wings were swept back at an angle of 60 degrees. The precise construction method of the wings (and the whole P 13 a on that matter) are not much specified in the sources. Given the scarcity of resources in late 1944 it is likely that it would use a combination of metal and wood.

The fin had to be enlarged to provide good flight command characteristics. In addition, given that the position of the cockpit was in the fin, it had to be large. The fin was more or less a direct copy of one of the wings. So it is assumed that it too would share the overall design.  The fin was connected to the aircraft by using four fittings.

The cockpit design was to be simple and cheap to build. The pilot was to have plenty of room inside the large fin. The cockpit was provided with a large glazed canopy that provided a good view of the front and sides. The seat and the instrument panel were bolted to the cockpit floor and walls. These could be easily detached for repairs. The instrument panel was to include an artificial horizon indicator, altimeter, compass, and radio equipment, Given that it was to operate at a high altitude oxygen tanks were to be provided too. Despite being intended to fly at high altitudes the cockpit was not to be pressurized. Another unusual fact was that initially the P 13 was to have a crew of two, but this was quickly discarded.

Here it is important to note that the version of the P 13 with the large fin is often portrayed as the final version of this aircraft. However, Lippisch never fully decided whether he should go for this version or the second that used a smaller fin with the pilot cockpit placed above the engine intake. Depending on the proposed version they are drastically different from each other. Lippisch, for unknown reasons, presented the British intelligence officer with the version that used the smaller fin and the American with the second version.

Landing operations were a bit unusual. To save weight no standard landing gear was to be used. Instead, Lippisch reused the Me 163 landing procedure.  As the  P 13 was immobile on its own, a small dolly would be used to move the aircraft. Once sufficient height was reached the dolly was to be jettisoned. In theory, this was an easy process, but in practice, this operation offered a good chance of failure and was much less safe than conventional landing gear. Sometimes the dolly either failed to eject or it bounced off the ground hitting the Me 163 in the process, with often fatal consequences.

The aircraft was to land with the nose raised up from the ground. This limited the pilot’s view of the ground. In addition due to its small size and in order to save weight, nontraditional landing gear was provided, instead, it carried a landing blade skid. To help absorb the landing impact, additional torsion springs were to be used. This bar had to be activated prior to the landing, it would emerge from beneath the aircraft fuselage, with the rotation point located at the front. Once released it was to guide the aircraft toward the ground. After that, the torsion springs were to soften the landing. This whole contraption seems like a disaster just waiting to happen and it’s questionable how practical it would be.

One interesting feature of the P 13 was that it could be easily disassembled into smaller parts which would enable effortless transport. Another reason was that due to the engine’s position in order to make some repairs or replacement of the engine, the remaining parts of the wing and the large fin had to be removed.

Was it an aircraft rammer? 

The precise purpose of the P 13a is not quite clear, even to this day. Despite being briefly considered for mass production, no official offensive armament is mentioned in the sources. So how would the P 13a engage the enemy? A possible solution was that it would be used as a ram aircraft that was supposed to hit enemy aircraft damaging them in the process. In an after-the-war interrogation by British officers, Lippisch was asked if the P 13 was to be used as an aerial ram aircraft. Lippisch responded the following “

“.. The possibilities of using the P.13 as a ramming aircraft had been considered but Dr Lippisch did not think that athodyd propulsion was very suitable for this purpose owing to the risk of pieces of the rammed aircraft entering the intake. This would be avoided with a rocket-propelled rammer…”

This statement contradicts the building description issued by the LFW issued in late 1944. In it was stated the following about this potential use. “…Due to tactical considerations, among other things, the speed difference of fighters and bombers, preferably when attacking from behind, though the thought was given to the installation of brakes ..  and although ample room for weaponry is present, the task of ram fighter has been taken into account – so that the ramming attack will not lead to the loss of the aircraft, thanks to its shape and static structure.”

This meant that this concept may have been considered by Lippisch at some point of the project’s development. The P 13 overall shape resembles closely to aircraft that was intentionally designed for this role. That said, it does not necessarily mean that the P 13 was to ram enemy aircraft. The use of such tactics was considered but their use was discarded, as it was seen as a futile and flawed concept. The project itself never got far enough to have an armament decided for it.

Conclusion

The Lippisch P 13 is  an unusual aircraft project in nearly all aspects. Starting from its shape, which proved, at least during wind tunnel tests, that the concept was feasible. On the other hand, its engine seems to have simply been abandoned after discouraging test results. It is unlikely that such a combination would have worked to the extent that the P 13 designer hoped it would. During the testing, they could not find a proper solution to providing a constant thrust with sufficient force to reach a speed that was expected of it. So the whole concept was likely to be doomed from the start.

The DM 1 however, while it was never seriously worked on by Lippisch himself, managed to save a group of young students who used the project to avoid being sent into combat.

Illustrations

Credits

• Article written by Marko P.
• Edited by  Henry H.
• Ported by Marko P.
• Illustrated By Medicman11

Source:

• A. Lippisch (1981) The Delta Wing History and Development, Iowa State University Press
• D. Nesić  (2008)  Naoružanje Drugog Svetsko Rata-Nemačka. Beograd.
• D. Monday (2006) The Hamlyn Concise Guide To Axis Aircraft OF World War II, Bounty Books.
• J. R. Smith and A. L. Kay (1972) German Aircraft of the WW2, Putham
• B. Rose (2010) Secret Projects Flying Wings and Tailless Aircraft, Midland
• D. Sharp (2015) Luftwaffe Secret Jets of the Third Reich, Mortons