Hanns Klemm headed the department of Daimler Flugzeugbau based in Sindelfingen since April 1918, which in this factory he oversaw the construction of two high-wing monoplanes, Daimler fighter L-11 and two-seat reconnaissance Daimler L-14.
After the war the Daimler aeronautical workshops are changed to automobile production, because of the clauses of the Treaty of Versailles, and all aircraft production formally ceases at Daimler Motorenwerke Gesellschaft. Technical Director of the Sindelfingen plant, Hanns Klemm, however discreetly continues its aeronautical activities. It is in this context that he develops a wooden light aircraft equipped with a motorcycle engine Indian 8.1 hp: The Daimler-15. In spring 1919 the prototype suffered a landing gear failure during its first flight. Despite the withdrawal of Daimler Klemm rebuilt the L-15 glider version in collaboration with the engineer and test pilot Martin Schrenk. After flight testing satisfactory to the Wasserkuppe (Rhön) in 1922, the glider is powered with an engine of Harley-Davidson hp 12.5 in 1923 (and converted into two-seater): the L-15A.
In 1924, the plane (designated L-15W) was equipped with floats and tested 9 October 1924 on Lake Constance (Bodensee).
On September 19, 1934, the Klemm L-15 was offered by Klemm Leichtflugzeugbau GmbH, Böblingen (Württemberg ) to the Deutsche Museum

The German Daimler L-15 of 1919 is of interest because it was both a glider and a powered airplane and because it was the direct link between the last of a line of German World War I fighter planes, the Daimler Lll monoplane, and the long and famous line of German Klemm light planes.
During the wartime testing of the lighter, Dr. H. Klemm. an engineer with the Daimler firm, discovered that the L-ll could be kept in the air as a glider under certain conditions. When the armistice put a stop to most airplane construction in Germany, he designed the light L-15 as a glider for further study of the subject.
In general appearance, the L-15 was an extremely clean looking cantilever monoplane of all wood construction. While most of the contemporary German gliders appeared to be picking up where the prewar models had left off. the L-15 clearly showed its airplane ancestry. Even the landing gear was of two-wheel airplane type with the notable exception that the wheels were solid wood in the rubber-short Germany of 1919. The only unconventional feature of the design was the use of floating wingtips in place of the usual ailerons. The pilot sat ahead of the two-spar wing in order to keep the weight forward.
The L-15 was damaged during tests in 1919 and was stored for a few years. It was rebuilt in 1922, and flown again as a glider before being fitted with a second-hand Harlev-Davidson motorcycle engine and flown as a powerplane in November. 1923, with the pilot moved aft to a position between the wing spars.
Still later, a second cockpit was added and the ship became a two-seater. In this form, the L-15 served as the prototype of the Daimler L-20. which was put into production, and the later Klemm models that continued the series when Dr. Klemm formed a new company in 1927 to succeed the original firm that had closed down. Klemm trainers that could be traced directly to the L-15 of 1919 were in quantity production as primary trainers for the German Luftwaffe well into World War II.

By the end of the First World War, Hanns Klemm had moved from Dornier to the aircraft branch of Daimler Motors and had designed two prototype fighters, the Daimler L11 and L14. With military aviation ended by the terms of the Versailles Treaty, he turned to developing a low-power light aircraft. The 1919 Daimler L15 was a high cantilever wing aircraft with a 6 kW (7.5 hp) Indian motorcycle engine. Rather little detailed information on it seems to have survived; it had unusual rotating wingtips for roll control instead of ailerons and a single axle undercarriage. It suffered serious propeller damage in 1919, early in the testing programme. From then on Daimler and Klemm abandoned aviation; Klemm remained with Daimler, concentrating on streamlined racing cars and locomotives.

During 1920 some German aviation enthusiasts realised that, though Germany was forbidden by the allies to build aeroplanes, gliders were not included in that category, resulting in a series of competitions on the Wasserkuppe that became known as the Rhön contests. Perhaps stimulated by these events, Klemm proposed in 1922 that the L15 should be rebuilt as a glider and obtained approval from the Daimler management. The engine was demounted and replaced with a long, smooth nose, deliberately designed to be easily removable so that the engine could be reinstalled if desired. The pilot sat at the wing leading edge in a cockpit within the removable nose and there was a passenger cockpit between the two wing spars at about one third chord. The fuselage was formed from four longerons, positioned by formers and wire-braced into a rectangular section, but with rounded upper and lower fairings. Its smooth fuselage and cantilever wing, together with an empennage that had no external bracing, made it aerodynamically very clean for its time.

The fabric-covered, tapered wings were built around two box spars. The 1919 machine had a single piece wing but gliders need to be easily transportable and so the wings were rebuilt in three pieces. The rudder and elevators were removable and the outer parts of the tailplane could be hinged upwards, again for ease of transport.

At some point during the reconstruction the fixed axle undercarriage was replaced with a more refined arrangement where the wheels were separately mounted on hinged and faired V-struts from the fuselage underside and with vertical shock absorber struts to the wing underside, allowing much larger wheel deflections on landing than with the less than half wheel-diameter allowed by end-sprung rigid axle mountings. Unusually, the wheels, which had three-ply centres, were ash-tyred because rubber was expensive in postwar Germany.

Given the limitations of its relatively low aspect ratio (about 7.5), the L.15 performed satisfactorily as a glider. In the summer of 1922 it made flights of up to 13 minutes, with an estimated L/D of about 16.

Towards the end of 1923 the L15 received a second-hand, 9 kW (12.5 hp) Harley-Davidson motorcycle engine, mounted with its cyliders exposed for cooling and driving a two-bladed propeller though 3:1 epicyclic reduction gearing. There were again two open cockpits in tandem, but since the nose was now much shorter the pilot occupied the cockpit previously used by the passenger on the glider and the passenger sat close behind him at the wing trailing edge.

During tests, the powered L15 reached an altitude of 2,150 m  with only the pilot on board and 1,100 m  with a passenger; a solo flight lasting 185 minutes was made and one passenger-carrying flight lasted 122 minutes. Other flights covered 190 km  solo and 190 km  with a passenger. In the autumn of 1924 the L15 was fitted with floats and took off from water successfully, at first carrying only the pilot and then with a passenger. Takeoff took 12 seconds in both cases, even with 12.5 hp. Early in these tests a new engine, an uncowled Daimler-Versuchmotor F7506 was flown for the first time. This unusual small, two-stroke, six-cylinder, air-cooled radial engine, fitted with a Roots blower, had been designed specifically for light aircraft and produced 15 kW (20 hp), but could not be developed to produce higher powers and was soon abandoned in favour of the Harley-Davidson.

The last new engine to power the L15 was a much more powerful (30 kW (40 hp)) Salmson. With it in place, the L15 was considerably refined with flaps, slats and pneumatic, rubber-tyred wheels.

The flights with the low-powered Harley-Davidson engine attracted attention and launched Klemm on a path which led him, after designing at least two more Daimler light aircraft, to set up his own light aircraft company in 1926. In 1924 the L15 was finally refitted with its motorcycle engine and was eventually put on display in the Deutsches Museum with the placard "The First Light Aircraft", but was destroyed during World War II.

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