Top level speeds at low altitude: Mustang, Tempest V, and Spit XIV

[niklas]

Those performance curves rather look like calculations instead of real flight test data.

Those 2 pages cover a report (from Mr. Stirling) where a Mustang III did use +25, and iŽd say 379mph at sealevel for +25lb looks a bit more realistic
Interesting numbers for +18lb too





niklas

[mw]

Niklas, you must have overlooked the bit "performance measurments were made..."

Here you can see the actual data points:



Of course all measurments need to be calculated to account for position and compressibility errors, convert from IAS to TAS, correct for standard atmospheric conditions, etc. Clearly all points on a curve are not measured.  Knowing that clipping wings on Spits gave x mph from a previous test and "making allowance" for that in this curve doesn't discredit the result.  It tells you with a fair degree of certainty how the plane would perform with those conditions.  

That A & AEE Mustang IV report is proof positive that the tested planes were not in pristine condition when tested