ZERO-SEN Model 21 Performance: Unraveling Conflicting Data

[Graham Boak]

Referring specifically to the captured Val pilot's comment: any statement with a nice round number in it must be taken with a pinch of salt. Particularly as it does not come from a source with direct experience.

I'd certainly agree about the "highly credible" nature of the 345mph figure. This is comparable to contemporary fighters with the same power: if anything somewhat less than might be expected from 1941. It is below the Spitfire and the 109, but above the Hurricane and about level with the P-40. 331mph is only what the Hurricane could (at best) achieve on less power in 1938. A range of 331-345 is about what might be expected from "natural" variation from one aircraft (and engine!) to another, and 316 would not be unexpected from a used aircraft in a poor state.

I don't know if Sakai ever quoted any specific number. It is worth pointing out that this maximum speed was only obtained at the optimum pressure altitude, and at this altitude the pilot would be seeing Indicated Air Speed which is lower than the True Air Speed. So the quoted calculated max. speeds were not numbers that pilots actually needed to use - though I suspect they did know them, or could carry out the necessary conversion from what they did see.