 A contract for another 50 Su @-@ 35s was signed in August 2015 , but parent company United Aircraft Corporation ( UAC ) stated in January 2016 that delays in finalizing the order was due to a lack of clarity in Russia ’ s 2016 federal budget , which was only signed by Russian President Vladimir Putin in mid @-@ December 2015 . The fighters will be delivered at a rate of 10 aircraft per year starting in 2016 . 
