waarschijnelijk omdat het een veroudert profiel is
net zoals bv het clark y profiel
het 3520 profiel komt uit de jaren 40

hier een verhaaltje er over uit 1966

Summary.
Flight measurements made by Mair in 1942, with the wake-traverse method, are used to extend to
high Reynolds numbers (2 x 107) and a thick section (18 per cent t/c) the verification that the sub-critical
creep (slow increase with increasing Mach number) in profile-drag coefficient can now be predicted
accurately. Good agreement is also obtained between the absolute magnitude (as distinct from creep)
of the measured drag and of that predicted on the basis of boundary-layer transition having occurred
near the leading edge. Similar agreement is obtained with a drag coefficient measured on a twodimensional
aerofoil (R = 1.6 x 106) of an almost identical section with transition positions now known
to have been at 39 per cent chord.
The analysis shows that predicted profile drag, particularly at high sub-critical Mach numbers, is
sensitive to the actual compressible-flow pressure distribution used in its derivation, and that the errors
due to inaccuracies of the older compressibility laws can be especially important for sections of this
thickness, with the particular type of velocity distribution involved. This last point is shown to be the
probable reason for the failure of the analysis of Young and Winterbottom 6 to predict any significant
sub-critical drag creep.


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