A Soviet copy of the Junkers Jumo 004B turbojet, known as the RD-10, was hung under each wing in a streamlined nacelle. The aircraft had a tricycle undercarriage that retracted into the fuselage. The Su-9 was designed with a very high wing loading which increased the aircraft's speed and reduced its dimensions. This consequently increased the take-off and landing speeds so it was equipped with a provision for two JATO bottles 11.27 kN thrust for 8 seconds mounted on the sides of the fuselage. These reduced the take-off distance by nearly 50 percent and a braking parachute was fitted to reduce the landing distance.
The nose housed the armament of one 37-millimeter Nudelman N-37 autocannon and two 23-millimeter Nudelman-Suranov NS-23 autocannon. The N-37 could be replaced by a 45-millimeter Nudelman N-45. The aircraft carried 100 rounds for each NS-23 and 40 rounds for the N-37. Two 250-kilogram FAB-250 high explosive bombs could be carried underneath the forward fuselage, but the N-37 had to be dismounted to do so.
As the TR-1 engines originally intended for the Su-9 were not yet ready for flight testing in late 1945, Pavel Sukhoi suggested substituting a pair of Jumo 004 engines and this was approved on 15 December. The full-scale mockup was found to be acceptable on 16 February 1946 and the Council of People's Commissars issued an order on 26 February that the manufacturer's flight testing was to begin on 1 November. This goal was not met because the OKB was heavily committed to other projects like the trainer version of the Tupolev Tu-2 bomber, inexperience with JATO units, and late delivery of RD-10 engines. The first prototype was completed in mid-October and made its first flight on 13 November. The test pilots found the aircraft easy to fly, but the control forces were very high at speed and it lacked enough directional stability. Enlarging the vertical stabilizer cured this last problem and hydraulic boosters were fitted for the control system.
The aircraft was revealed to the general public on 3 August 1947 at a flypast at Moscow's Tushino Airfield and the aircraft began its state acceptance trials three days later. Flight testing was completed by 25 May 1948 after 136 flights had been completed. It demonstrated a top speed of 885 kilometers per hour at an altitude of 8,000 meters and an endurance of one hour and 44 minutes. It had very docile handling qualities with one engine inoperative. The aircraft was recommended for production, but it was significantly slower than the Mikoyan-Gurevich MiG-9 and Yakovlev Yak-15. The government declined to do so and the program was terminated.
A two-seat trainer version, the Su-9UT, was planned during 1946, but it too was cancelled. The cockpit for the student would have been positioned ahead of the instructor's cockpit and each would have had a separate canopy. The armament would have been reduced to a pair of 20 millimeters Berezin B-20 autocannon, each with a hundred rounds of ammunition. The armor would have been removed to save weight.
Length: 10.546 m
Wingspan: 11.2 m
Height: 3.4 m
Wing area: 20.2 m2
Empty weight: 4,060 kg
Gross weight: 5,890 kg
Fuel capacity: 1350 kg
Powerplant: 2 × RD-10 turbojets, 9 kn thrust each
Maximum speed: 885 km/h
Range: 1,200 km
Service ceiling: 12,800 m
Armament: 1 × 37 mm Nudelman N-37 cannon with 40 rounds
(a 45 mm Nudelman N-45 could be fitted instead)
2 × 23 mm Nudelman-Suranov NS-23 cannon with 200 rpg
Up to 500 kg of bombs