From Martin Gregorie
Harlow, Essex
I think I should point out to Stephen Gloor (Letters, 5 July, p 53) that Mark
Drela is well known in model glider flying circles as something of an expert at
flying indoor hand-launched gliders, which operate at the extremely low Reynolds
numbers of 15 000 or thereabouts. He has held records for this. It is extremely
unlikely that he is unaware of Michael Selig’s work).
My initial reaction to the article (“Where aircraft fear to go”, 31 May, p
34) was similar to Gloor’s. However, on reflection I realised that Drela is
right; he is looking at a flight regime which combines very high subsonic speeds
with a Reynolds number of under 300 000, something that neither the Selig
group’s wind tunnel nor the Delft group can come near.
This point should have been given greater emphasis in the article. Only a
careful second reading uncovered the mention of shock waves forming on the upper
wing surface at the high point that indicates the speed regime. A future article
comparing Drela’s results with the findings from the Pathfinder flying wing,
which operates at the other end of the speed range, would be extremely
interesting.
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