> The low drag bucket in sailplanes occurs at lower speeds (referenced to
> the stall speed) than are being considered for the Europa. It is not
> necessary to use a wind tunnel. All that is necessary is a performance
> curve carried out on the whole aeroplane. It is also possible to
> temporarily install a drag measuring probe at the trailing edge of the
> wing. The world expert is probably R.H. Johnson at the Texas Soaring
> Center at Caddo Mills airfield near Dallas.
> Ken Whiteley
Now that you've mentioned that method, Ken, some may want to know if
it's practical on the Europa at cruise, or even a self-cobbled
device? What is it measuring back there and how? I wonder if a some
crude method would imply something going on. Laminar bucket and
laminar flow back to about 60% of chord I thought went hand-in-hand
(Arnold's AR-5 is said to be close to 70%), whereas Dykin's book hints
he's happy with 50%. I've read where glider enthusiasts simply affix
thin tubing to the wing, and squirt food coloring with a syringe and
observe.
Another thing, though, if anyone has viewed the "Arnold Tapes," it may
be all moot without a perfect surface, particularly with the especial
Mk1 mess at the region around the spar. He used a dial indicator to
keep irregularities to within a few thousandth's over span of 2-3
inches. Believe me that ain't easy; cannot feel or see (with gloss
coat) that level of error!
Happy Holidays,
Fred F.
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