Technical data
Type DI-1, 2I-N1
Function Fighter
Year 1926
Crew 2
Engines 1*450hp Napier Lion
Length 9.75m
Wingspan 12.00m
Wing area 27.15m2
Empty weight 1153kg
Loaded weight 1700kg
Wing Load (kg/m2) 62.5
Power load (kg/hp) 3.8
Speed at 0m 268km/h
Landing Speed 92km/h
Landing Roll 200m
16sec
Takeoff Roll 100m
7sec
Turn time 12sec
Range 800km
Flight Endurance 3h
Ceiling 7100m
Climb
1000m 1.8min
2000m 3.8min
3000m 6.1min
5000m 13.0min
Armament
Guns 2*mg 7.62mm

DI-1, 2I-N1 by N.N.Polikarpov

20k b/w photo "History of aircraft construction in the USSR", Vol.1 p.382

Two-seat biplane fighter of very clean design. Fuselage was a monocoque made of cross-grain glued strips of thin wood. Wing struts (droplet-shaped cross-section) were made of aluminum alloy. Wing had wooden frame and plywood skin. Similar to contemporary two-seat reconnaissaters, it was smaller and lighter. It carried less equipment than reconnaissaters, as well as less fuel.

DI-1 structure design was based on detailed calculations (including structure vibrations). The result of those efforts was an exceptional performance of the (armed and fully loaded) prototype.

DI-1 was ready in early 1926. Due to winter time it was flown on skis (extra drag). Despite of this, its performance was similar to contemporary single-seaters flown on wheels.

Factory trials did run smoothly, Polikarpov himself participated in test flights as a rear gunner, including flight to the maximum altitude (flight number eight). But the next flight on March 31, 1926 turned into catastrophe.

Test-pilot V.N.Philipov and chronometrist V.V.Mikhailov already performed several passes along the one kilometer base at the Central Airfield (also known as Khodynskoe Pole). To push aircraft to extreme they performed a shallow dive to 100m and entered the control kilometer in horizontal flight at speed close to 300km/h. Suddenly upper wing exploded - plywood skin was stripped away by the lift force... In matter of seconds the upper wing collapsed, followed by the lower one. The crew was killed on impact.

Careful study revealed the cause of a crash. It was found that wing construction was hermetic. In this case wings had to be 'punched' to balance air pressure inside and outside the wing. During high altitude flight internal pressure 'unglued' the wing skin from the ribs. Excessive negative load on the upper wing surface during high speed trial simply pulled the skin out of the ribs, 'exploding' the wing.

The project was terminated, despite the crash reason could be easily eliminated. Few tiny holes punched in the wing could secure aircraft from the failure! Other negative 'echo' of this accident was excessive structural strength (and overweight) in follow-up designs (I-3, DI-2, U-2).



ReferencesLinks
  • "History of aircraft construction in the USSR", Vol.1 p.341-342;
  • 2I-N1, D-1
  • 2I-N1, Polikarpov
  • DI-1, Polikarpov

  • Modified July 17, 1998 Back to
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