"The addition of the second aircraft to the testing program will speed up its completion and ensure the beginning of deliveries to our customers in 2011," Sukhoi said in a statement.
The first Su-35 successfully completed its first 6-minute demonstration flight on July 7 and has made over 40 test flights since then. All of them confirmed superior technical and combat characteristics of the aircraft.
The Su-35 fighter, powered by two 117S engines with thrust vectoring, combines high maneuverability and the capability to effectively engage several air targets simultaneously using both guided and unguided missiles and weapon systems.
The aircraft features the new Irbis-E radar with a phased antenna array, which allows the pilot to detect and track up to 30 air targets, while simultaneously engaging up to eight targets.
It is equipped with a 30-mm cannon with 150 rounds and can carry up to eight tons of combat payload on 12 external mounts.
Sukhoi earlier said it plans to start deliveries of the new aircraft, billed as "4++ generation using fifth-generation technology," to the Russian Air Force and foreign clients in 2011 and produce Su-35s over a period of 10 years up to 2020.
The company is planning to export at least 160 Su-35 fighters in the future to a number of countries, including India, Malaysia and Algeria.