SW - Moskalyev SAM-7 Sigma

As early as 1933, Aleksandr Moskalyev was designing a rocket-powered, tailless aircraft with an ogival or gothic delta wing, which would be able to fly faster than sound. Because no sufficiently powerful engines were available at the time, the Moskalyev SAM-4 never left the drawing board but it did lead to two interim types, the SAM-7 Sigma and SAM-9 Strela. After the approval of NII VVS (institute for science and exploration for military and air forces) and experimental pre-prototype SAM-6, the first prototype of Sigma was built.
The Sigma was first flown in October 1935. It was judged dangerous to fly as it was hard to keep straight during take-offs and had a high landing speed of 138 km/h. Its flight characteristics were never fully explored and it never reached its estimated top speed of 500 km/h at altitude. Due to NII VVS pilots' complains to dangerous flying of a similar type Kalinin K-12 bomber, the next tests of Sigma were ordered to cancel.