 The I @-@ 250 was a low @-@ wing , all @-@ metal aircraft with a monocoque fuselage . Other than the VRDK the aircraft was largely conventional in layout , although the cockpit was set very far back in the fuselage , almost to the base of the vertical tail . The two @-@ spar wings had a thickness of 10 % to preserve aileron control and avoid tip stall . They were fitted with Frise ailerons and slotted flaps . Fuel was contained in a 412 @-@ litre ( 91 imp gal ; 109 US gal ) fuselage tank and a 100 @-@ litre ( 22 imp gal ; 26 US gal ) tank in each wing . The conventional landing gear mainwheels had a levered suspension and retracted inwards . The tail wheel retracted aft into the very small ventral fin . The VK @-@ 107A engine initially drove a 3 @.@ 1 @-@ metre ( 10 ft ) VISh @-@ 105SV propeller . 
