Although I haven’t read the book by PJ Swatton, the wording of those definitions are very similar to those that I remember. So; maybe Mr Swatton is quoting from the book that I read, or the book that I read used Mr Swatton’s work as a reference, or both Mr Swatton’s book and the one that I read are quoting from the same third source. Is this subject mentioned in ‘Handling the Big Jets’? Maybe I read it there.
Anyway, Ghengis, could you please elaborate on what is wrong with Mr Swatton’s exposition? I have no axe to grind, just looking for accuracy. Also, his definition of the Newton seems ok to me? What’s wrong there?
A quick thought experiment:
Three aircraft of the same type are flying in formation, sufficiently spaced so as not to interfere with each other’s pressure sensing.
They are at the same altitude, in the same air mass and are keeping perfect station.
Therefore, they must be flying at the same TAS.
Aircraft A has been blessed with an ASI that has been constructed ‘perfectly’ and has no instrument errors.
Aircraft B and C have been fitted with ASIs that were made on a Friday afternoon and unfortunately suffer from some instrument error.
The ASI readings are as follows:
Aircraft A: 200kts
Aircraft B: 199kts
Aircraft C: 201kts
If one assumes that the ASI reading is actually IAS, then entering the three values into a computer to calculate the TAS would yield three different results. This cannot be correct, as the three aircraft are flying at the same TAS.
Therefore, the three IAS values must actually be identical, even though the ASI readings differ.
Should we care? No, of course not. In practice, we can assume that ASIR is equal to IAS, which is what is assumed by the handbooks and publications quoted above. But a test pilot might care, if the error was significant enough.