Personnaly i dont believe that operational D9s achieved700km/h. But even more i dont believe the russian performance claims in field conditions.
I would add that the russian fighters had more pilot work load and often did not provide even basic instruments. Their ultra light construction suffered quickly in field conditions .
With proper building quality , and Mw50, the D9 was probably equal below 3000m and superior above that altitude. The wide blade propellers of the later D series aircraft, the removal of the draggy cowling hmgs , two stage superchargers,and possible use of boosted ailerons provided overall a clearly better combat aircraft
I would add that the russian fighters had more pilot work load and often did not provide even basic instruments. Their ultra light construction suffered quickly in field conditions .
With proper building quality , and Mw50, the D9 was probably equal below 3000m and superior above that altitude. The wide blade propellers of the later D series aircraft, the removal of the draggy cowling hmgs , two stage superchargers,and possible use of boosted ailerons provided overall a clearly better combat aircraft