Dick's Waves

[David Crimmins]

In his flight test reports Richard H. Johnson usually included an
assessment of the glider's wing condition.
He often sites 0.004" as being a acceptable degree of waviness. I'm
assuming this is wave height, but over what length?

The reason for asking, is I'm current having my wings refinished and I want
to determine how much of the spar shrinkage needs to be corrected.
I'm thinking that a flat spot in the wing profile can be tolerated as long
as the transition is gradual. The current distortion isn't too bad and
could most likely be fixed with a extra coat or 2 of gel confined to the
spar area. However, not sure thick gel is a good idea on an asw20 with
such flexible wings.

Thanks
David

[[email protected]]

On Thursday, January 14, 2016 at 8:30:07 AM UTC-5, David Crimmins wrote:
> In his flight test reports Richard H. Johnson usually included an
> assessment of the glider's wing condition.
> He often sites 0.004" as being a acceptable degree of waviness. I'm
> assuming this is wave height, but over what length?
>
> The reason for asking, is I'm current having my wings refinished and I want
> to determine how much of the spar shrinkage needs to be corrected.
> I'm thinking that a flat spot in the wing profile can be tolerated as long
> as the transition is gradual. The current distortion isn't too bad and
> could most likely be fixed with a extra coat or 2 of gel confined to the
> spar area. However, not sure thick gel is a good idea on an asw20 with
> such flexible wings.
>
> Thanks
> David

The measurement Dick did used a dial indicator mounted in the middle of a block with 2 legs 1 inch away and 1 leg 1 inch away in the opposite direction. This was described as measuring over 2 inches.
If the glider is in refinishing now is the time to contour. This is a small amount of fill if the waves are as you describe. If there is some surfacing filler being used before final finish, a couple extra coats on that area, then contour sanded out will do the job.
Good luck
UH

[Charlie M. (UH & 002 owner/pilot)]

On Thursday, January 14, 2016 at 8:56:17 AM UTC-5, wrote:
> On Thursday, January 14, 2016 at 8:30:07 AM UTC-5, David Crimmins wrote:
> > In his flight test reports Richard H. Johnson usually included an
> > assessment of the glider's wing condition.
> > He often sites 0.004" as being a acceptable degree of waviness. I'm
> > assuming this is wave height, but over what length?
> >
> > The reason for asking, is I'm current having my wings refinished and I want
> > to determine how much of the spar shrinkage needs to be corrected.
> > I'm thinking that a flat spot in the wing profile can be tolerated as long
> > as the transition is gradual. The current distortion isn't too bad and
> > could most likely be fixed with a extra coat or 2 of gel confined to the
> > spar area. However, not sure thick gel is a good idea on an asw20 with
> > such flexible wings.
> >
> > Thanks
> > David
>
> The measurement Dick did used a dial indicator mounted in the middle of a block with 2 legs 1 inch away and 1 leg 1 inch away in the opposite direction. This was described as measuring over 2 inches.
> If the glider is in refinishing now is the time to contour. This is a small amount of fill if the waves are as you describe. If there is some surfacing filler being used before final finish, a couple extra coats on that area, then contour sanded out will do the job.
> Good luck
> UH

To clarify a bit (to help David), imagine a capital "T" on a block, the 3 "contact points" are at each end of the top bar of the "T" & the 3rd "contact point" is at the bottom of the vertical part of the "T".
The dial indicator is mounted in the middle of the vertical part of the "T"..
I believe we used nylon screws for the contact points so as to not leave marks on the wing when checking for waves.
[When the block is made and laid on a flat surface, it will contact the surface in 4 spots, the 3 screws and the dial indicator tip with the long axis of the indicator & screws perpendicular to the surface, you can easily make it in aluminum and drill it in a drill press]

As you go over the curve, the indicator will move up & down due to the curve, you're looking for rapid changes as you measure highs & lows.

Hope that helps a bit.

[[email protected]]

I have a wave gage, but frankly it's only good to put numbers on Dicks flight test reports. One needs to watch closely for a rapid change, then go back and find it by feeling by hand............if you can feel a bump, it needs to be dealt with. I have filled a spar depression with gelcoat, leveled the wing, masked off the depression, sprayed on something like 6 coats, let it cure for 12 hours, then block-sanded it level using 400 wet, then 600, then buffed it out after curing for a week. Worked well, the big problem is in matching the color exactly, so your efforts don't show.
JJ

[Per Carlin]

When I refinished my wings did I try to correlate Johnssons waviness too surface roughness values (https://en.wikipedia.org/wiki/Surface_roughness) as I have access to that kind of measuring devices. But I never got it, surface waviness (https://en.wikipedia.org/wiki/Waviness) is something else.

[[email protected]]

Another way to find divots and bumps and such is to shine a bright flashlight across the surface. Hold the flash light next to the surface, at almost 90 degrees. Those formerly invisible holes, scratches, bumps and divots will jump out at you.

John

[ND]

The current distortion isn't too bad and
> could most likely be fixed with a extra coat or 2 of gel confined to the
> spar area. However, not sure thick gel is a good idea on an asw20 with
> such flexible wings.
>
> Thanks
> David

if your refinish is being done properly, they wont fill any low spots or spar bumps with gelcoat. by the time the wings get painted they should already be smooth. an even topcoat of gelcoat is sprayed, so i wouldn't worry about that.

In any case an extra pass or two of gelcoat won't make much of a difference, as far as wingflex is concerned.

-Andy