I flew a few hundred hours both ways and the holes did seem to form more drag.
Sparky Sparks
Sent from Windows Mail
From: Kenneth Wiltrout via KRnet
Sent: ?Friday?, ?December? ?26?, ?2014 ?3?:?23? ?PM
To: KRnet
I tested the board both ways. The holes seem to help slow it down.Kenny
WiltroutN6399U
On Friday, December 26, 2014 12:47 PM, Dan Branstrom via KRnet <krnet at
list.krnet.org> wrote:
I always wondered about the holes in a belly board. The T-28s I flew
had them on the belly mounted speed brake that was flush with the
fuselage when retracted. I could only imagine that the holes gave it
greater drag because of conflicting vortices generated by the holes.
At the KR gathering, I noticed that our British friend had holes in his
belly board.
I've noticed that the speed brakes on jets don't have the holes. Even
retracted, they cause some disruption of the airflow because the surface
is not smooth because of the holes. At the higher speeds of jets, since
parasitic drag goes up as the square of the speed, holes like that could
significantly add drag. A T-28 usually cruised at about 200mph. That's
just about the approach speed of jets.
Of course, as home builders, by using foam and fiberglass, bumps made on
the belly could fill the holes retracted, but at the speeds of a KR, the
drag caused by the retracted speed brake may not be significant.
Dan Branstrom
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