In article ,
Gary Evans wrote:

I recall a picture or diagram of the tool for measuring
surface deflection. It may have been in one of Dick
Johnsons articles which are or were available at the
SSA web site. Iif not it was written up in Soaring.



t 18:36 15 September 2004, Andy Blackburn wrote:
Thanks to all for the input and theories. I'm going
to go find/build a wave guage and measure the depth
of all these emerging imperfections and report back
here. My ship arrived with perfect skin, the blemishes
didn't arrive until 'puberty' (age 18-20 months --
this year).

Anybody able to point me to a source and/or plans to
make a wing wave guage?

Thanks!

9B

After you've made or purchased the wave gauge, the next question is "How
does one actually use it?".

Be aware that the gauge alone will *not* detect errors in the shape of
the profile or thickness of the wing. For that you need accurate
templates. But I state the obvious.

Since the surface is irregularly curved in the direction of measure
(along the chord) the dial indicator will change its reading when moved
from back to front even on a "perfect" wing as indeed it must. A simple
way to use it is to look for the dial indicator reading to "back-up" in
one spot rather than gradually changing its reading as the device is
moved chordwise. If the "back-up", either bump or depression, is
greater than .003"-.004" in 2" then you should correct the wing there.

I like to use it as follows. I borrow one of my wife's cloth-tape
sewing scales. It easily lays flat on the chord. First I mark spanwise
stations on the wing every foot from root to tip. At each station,
starting from say the flap hingeline to the front of the wing, lay down
the cloth tape. I then use a small tape recorder and speak the readings
of the dial indicator corresponding to every 1 inch location on the
chord. I zero the dial indicator at the flap hingeline. Near the
leading edge the readings become essentially meaningless. I then key
the data from the tape recorder into a spreadsheet. I plot the data at
each station with the X-axis as percent of chord and the Y-axis as the
dial indicator reading. This normalizes the data for differing chord
lengths. (My wings are a constant taper and airfoil so this works well.
A multi-taper wing and/or multi airfoil wing will need to be treated a
bit differently.) The overall shape of the plotted data at each
station, for a constant taper/foil wing, should look about the same.
Inspect the plots for stations with plot shapes that deviate from the
rest. This can indicate a relatively high or low spot on the wing. Of
course also check the data for bumps or depressions that are greater
than .003"-.004" in 2". I'm sure there are other ways to do this, but
this is what I have done.

Regards,

-Doug