I was looking at the plane thinking what a tough looking machine that is and that it looks a little bit like the Fokker D.XXI from the Finish thread you posted the other day so I looked it up.
It took me by surprise that that is actually a retractable landing gear.
"The Polikarpov I-16 (Russian: Поликарпов И-16) is a Soviet single-engine single-seat fighter aircraft of revolutionary design; it was the world's first low-wing cantilever monoplane fighter with retractable landing gear to attain operational status and as such "introduced a new vogue in fighter design." The I-16 was introduced in the mid-1930s and formed the backbone of the Soviet Air Force at the beginning of World War II. The diminutive fighter, nicknamed "Ishak" or "Ishachok" ("donkey" or "burro") by Soviet pilots, figured prominently in the Second Sino-Japanese War, the Battle of Khalkhin Gol, Winter War and the Spanish Civil War – where it was called the Rata ("rat") by the Nationalists or Mosca ("fly") by the Republicans."