The Siebel Si-201 was designed and built by Siebel in response to the German Air Ministry specification issued in February 1937 for an air observation / army co-op aircraft that had superlative Short Take-off/Landing (STOL) capabilities, excellent slow-flight performance and all-round visibility. Three aircraft were designed and built to meet this particular specification – the Fiesler Fi-156 (already being tested before the specifications were released), the Bayerische Flugzeugwerke designed and built Bf-163 and the Siebel Si-201, these latter two flying in 1938.
The Si-201 was an unorthodox design with its Argus As10 V-8 air-cooled engine mounted above the wing as a pusher, driving a four-bladed fixed-pitch airscrew which rotated above a slim, circular-section tailboom. It had a boxy, fully glazed forward fuselage with room for a pilot and observer in tandem and was a high-wing braced monoplane with a tail-wheel landing gear.
This design allowed superlative vision from the forward cockpit and so the pilot was seated towards the rear of the cockpit. The aircraft had high lift devices such as full span automatic leading edge slots and four section Fowler-type flaps with the outermost flaps also acting as ailerons and which occupied almost the entire trailing edges, the outboard sections serving as ailerons. The fuselage was of welded steel-tube construction with metal skinning and the plywood-covered wing was of wood. The pilot and observer were seated in tandem in the extensively-glazed forward fuselage, the observer being positioned ahead of the pilot with his seat offset to starboard.
The first of two prototypes of the Si-201 flew during the early summer of 1938, revealed excellent short take-off and landing characteristics, and was found to possess acceptable slow-flying characteristics closely comparable with those of the Storch, but at the upper end of the speed scale tail flutter proved troublesome. Considerable effort was expended in damping out oscillation in the tailboom which developed under certain flight conditions, and the second prototype, which featured some simplification of the high-lift devices, was flown with a somewhat sturdier tailboom. The most serious shortcoming of the Si-201 proved to be the extremely limited cg travel permitted by its configuration, and when Siebel was ordered to abandon further development of the aircraft the problem of tail flutter remained largely unsolved.
The Si-201 was evaluated against the Fieseler Fi 156 and Messerschmitt Bf 163 but did not compare well to these aircraft. The Si-201 was also flown by General Ernst Udet, then head of the Reich Air Ministry’s technical department. He was unimpressed with its ground handling and landing characteristics, essential elements in the success of the Storch. The Si 201 would also have been more costly to construct than the Fi 156 Storch. The Si-201 had a higher top speed than the Storch, but speed wasn’t an important consideration for its expected roles, and work on the Si 201 stopped after two prototypes had been built.
The Ilmavoimat evaluation team test-flew the aircraft and experienced the same issues at the upper end of the speed scale with tail flutter. While this was a concern, the aircraft remained under consideration until the decision by the Reich’s Air Ministry not to order the aircraft into production put a halt to further consideration.
Siebel Si 201
Crew: two (Pilot and Observer)
Engine: 1 x Argus As 10C, 179 kW (240 hp)
Maximum speed: 115mph
Range: 280 miles
Service ceiling: 18,000 ft
