ASW27B spar shrinkage

[Gabriel Duford]

Hi,
How long does it take for the spar shrinkage to appear on an ASW27B?
I've been told that if after 5-6 years it has not yet developed, then it is safe to think that it will never really become a problem.
Thanks,

gabriel

[Bob Kuykendall]

On Aug 21, 2:36*pm, Gabriel Duford > wrote:

> How long does it take for the spar shrinkage to appear on an ASW27B?
> I've been told that if after 5-6 years it has not yet developed, then it is safe
> to think that it will never really become a problem.

Somewhat counterintuitively, spar shrinkage on the top rarely accounts
for much performance degradation. Here's how I understand it from the
engineer who does my aerodynamics:

The spar is near the chordwise station of maximum depth, aft of which
the upper surface flow is going to transition to turbulent anyhow. So
if you get a .002+ whifferdill at the spar that flips it, you've lost
what, maybe an inch of laminar run? Meh. Learning more effective
thermalling can totally submerge that kind of performance difference.

But on the bottom surface of a well-designed profile, the pressure
gradient is such that you might be able to maintain laminar flow all
the way back to the hinge line, and with good mylar maybe onto the
control surface as well. If you have a contour disruption at the spar
that trips the lower surface flow to turbulent, you're losing
something like 10" or 20" of laminar run. That could be huge.

Thanks, Bob K.

[[email protected]]

On Tuesday, August 21, 2012 2:36:56 PM UTC-7, Gabriel Duford wrote:
> Hi,
>
> How long does it take for the spar shrinkage to appear on an ASW27B?
>
> I've been told that if after 5-6 years it has not yet developed, then it is safe to think that it will never really become a problem.
>

I had the wings on my 2003 -27B sanded after 3 years and nothing has come back. It was kept in the desert in case that makes a difference due to heat or lack of humidity.

9B