View Full Version : Wing Contour?
Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
On Wednesday, July 31, 2019 at 12:00:34 AM UTC-4, wrote:
> Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
The best way I am aware of is to get top and bottom templates made for several stations from the root outwards to check the actual profile against the theoretical one. Not sure if any of the manufacturers offer that sort of help but if you know the airfoil designation, someone in the know can calculate the coordinates. It takes a good 'smoothing' or interpolation algorithm to get the wrinkles out of that curve. With access to a large CNC router one can then mill such template set from a thin AL-sheet.
Uli
'AS'
SoaringXCellence
July 31st 19, 11:19 PM
All,
two stories:
One of my fellow pilots wanted to re-finish his LS-4. He loved the way is glider handled and other performance so he made templates from the existing wing surface and maintained it when refinishing.
Another friend and I both have Mini Nimbus or Mosquito wings, that ostensibly were created from the same molds. He took the time to plot and make templates for the supposed airfoil. When compared to either of our ship, the templates don't fit the wing and in a different way on each glider!
YMMV, and most likely will.
Mike B.
Bob Kuykendall
July 31st 19, 11:34 PM
On Tuesday, July 30, 2019 at 9:00:34 PM UTC-7, wrote:
> Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
It depends entirely on the nature of the wing. For aggressively laminar profiles like the old FX67, it can matter a lot. For others, it matters a lot less.
In my direct experience, freedom from waviness (Johnson reading below 0.004" per linear inch) is a lot more important than absolute fidelity to contour. Time spent trying to impose some sort of theoretically ideal contour with filling and sanding is a lot better spent just getting any big waves out and then concentrating on soaring strategy and tactics.
Case in point: Do a template check on any LS6 or LS8. I can probably loan you the templates for that, though I haven't seen them for a while. Anyhow, what you find is that the camber lines for the right and left wings are substantially different. The template for one wing fits the opposite wing like maybe they're from two different gliders. This applies to all of the six or eight ships I've checked, and all of them have been different in pretty much the same ways, so I'm pretty sure that's how they come out of the molds.. But these are not dogmeat gliders-- they go like stink, fly arrow straight if they're tuned properly, and have won regional and national contests. Who's to say whether the right or the left wing has the correct profile and the other not? They both seem to work pretty damn well.
--Bob K.
On Wednesday, July 31, 2019 at 6:34:52 PM UTC-4, Bob Kuykendall wrote:
> On Tuesday, July 30, 2019 at 9:00:34 PM UTC-7, wrote:
> > Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
>
> It depends entirely on the nature of the wing. For aggressively laminar profiles like the old FX67, it can matter a lot. For others, it matters a lot less.
>
> In my direct experience, freedom from waviness (Johnson reading below 0.004" per linear inch) is a lot more important than absolute fidelity to contour. Time spent trying to impose some sort of theoretically ideal contour with filling and sanding is a lot better spent just getting any big waves out and then concentrating on soaring strategy and tactics.
>
> Case in point: Do a template check on any LS6 or LS8. I can probably loan you the templates for that, though I haven't seen them for a while. Anyhow, what you find is that the camber lines for the right and left wings are substantially different. The template for one wing fits the opposite wing like maybe they're from two different gliders. This applies to all of the six or eight ships I've checked, and all of them have been different in pretty much the same ways, so I'm pretty sure that's how they come out of the molds. But these are not dogmeat gliders-- they go like stink, fly arrow straight if they're tuned properly, and have won regional and national contests. Who's to say whether the right or the left wing has the correct profile and the other not? They both seem to work pretty damn well.
>
> --Bob K.
Bob said it well.
There is very little data available for the airfoils on the modern(last 20 years) ships.
Best bet is fill the spar shrink and don't screw up the leading edge.
If I'm doing a "serious" job I pull templates of the leading edge 4 inches back every 24 inches so it is back to "correct" before finish spraying.
Fair warning: More ships have been made worse by people who did not know what they were doing and the list of projects abandoned part way through is long.
UH
What technique do you use to make templates ("pull a set") for the leading edge as Hank states? Do you guys know if there are existing coordinates or templates for ASK21 and ASW24?
Doug
On Thursday, August 1, 2019 at 12:03:56 PM UTC-4, wrote:
> What technique do you use to make templates ("pull a set") for the leading edge as Hank states? Do you guys know if there are existing coordinates or templates for ASK21 and ASW24?
>
> Doug
I make templates out of 1/4 inch plywood cut to a very close profile to the leading edge.
I wax the wing well, then put a thick coating of aerodynamic fairing compound(body filler) on the inner surface of the wood template and squish into place.
When cured remove a clean up. Label immediately.
'21 has published airfoils. No idea why anyone would want to profile one.
Have '24 templates for B mod.
UH
Papa3[_2_]
August 1st 19, 05:42 PM
On Wednesday, July 31, 2019 at 6:34:52 PM UTC-4, Bob Kuykendall wrote:
> On Tuesday, July 30, 2019 at 9:00:34 PM UTC-7, wrote:
> > Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
>
> It depends entirely on the nature of the wing. For aggressively laminar profiles like the old FX67, it can matter a lot. For others, it matters a lot less.
>
> In my direct experience, freedom from waviness (Johnson reading below 0.004" per linear inch) is a lot more important than absolute fidelity to contour. Time spent trying to impose some sort of theoretically ideal contour with filling and sanding is a lot better spent just getting any big waves out and then concentrating on soaring strategy and tactics.
>
> Case in point: Do a template check on any LS6 or LS8. I can probably loan you the templates for that, though I haven't seen them for a while. Anyhow, what you find is that the camber lines for the right and left wings are substantially different. The template for one wing fits the opposite wing like maybe they're from two different gliders. This applies to all of the six or eight ships I've checked, and all of them have been different in pretty much the same ways, so I'm pretty sure that's how they come out of the molds. But these are not dogmeat gliders-- they go like stink, fly arrow straight if they're tuned properly, and have won regional and national contests. Who's to say whether the right or the left wing has the correct profile and the other not? They both seem to work pretty damn well.
>
> --Bob K.
Just to amplify what both Bob and Hank are saying, I'm currently in the midst of an LS3 refinish project with our club. While there ARE published coordinates (though even there some uncertainty exists about the intended thickness of the outer section), we are finding that there is a lot of work involved just in getting the templates correctly situated. This is a glider that won the sports class nationals last year, and so far we are finding a lot of very big deviations from the supposedly accurate profile in the outer third. It is much too blunt. The work involved to "fix" that would be significant. Could we actually make the glider worse - yup. Would anyone notice the difference if we got it "right". Probably not.
Meanwhile, we are paying a lot more attention to building up the spar lines to get rid of the shrinkage there and smoothing everything out.
We pulled the coordinates from Soaring articles published by Dick Johnson and updated later with "corrections". We cut the templates for the LE out of 1/4 inch ply on a CNC router. To do the full chord we will need a bigger router, but we've got plenty of guys in the club who have access to what we need. But, at this point (first pass of priming and filling), we're leaning toward smoothing and leaving the profile alone.
One group's experience...
Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?
Doug
On Thursday, August 1, 2019 at 12:50:22 PM UTC-4, wrote:
> Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?
>
> Doug
You understood correctly.
First 10% or so. About 3 inches inboard and 2-1/2 outboard.
Purpose of the templates is to have finished wing with same profile it started with. "Normal" sanding will usually make the leading edge too blunt.
UH
GliderCZ
August 1st 19, 08:07 PM
On Tuesday, July 30, 2019 at 9:00:34 PM UTC-7, wrote:
> Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
Please see the linked facebook page from AlphaZulu Composites in Kingman, AZ: https://www.facebook.com/AlphaZuluComposites/
Scroll down a bit to see pictures and description of how Paul Gaines fabricated templates and refinished the leading edges on my Ventus 2c a few years back.
CZ
GliderCZ
August 1st 19, 08:17 PM
On Thursday, August 1, 2019 at 12:07:09 PM UTC-7, GliderCZ wrote:
> On Tuesday, July 30, 2019 at 9:00:34 PM UTC-7, wrote:
> > Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
>
> Please see the linked facebook page from AlphaZulu Composites in Kingman, AZ: https://www.facebook.com/AlphaZuluComposites/
>
> Scroll down a bit to see pictures and description of how Paul Gaines fabricated templates and refinished the leading edges on my Ventus 2c a few years back.
>
> CZ
Scroll down a bit further, and you'll see Paul also posted a short video
On Thursday, August 1, 2019 at 1:12:02 PM UTC-4, wrote:
> On Thursday, August 1, 2019 at 12:50:22 PM UTC-4, wrote:
> > Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?
> >
> > Doug
>
> You understood correctly.
> First 10% or so. About 3 inches inboard and 2-1/2 outboard.
> Purpose of the templates is to have finished wing with same profile it started with. "Normal" sanding will usually make the leading edge too blunt.
> UH
I am interested in doing a resurfacing on a Libelle 201b. I have been loaned templates which appear to be well made, possibly water jet cut, about the size you describe. My wings, in the very leading edge portion are off(differently at different stations and on opposite wings) by as much as 1/4 to 5/16. I too have the spare bump. My plane thermals better to the left but shows no fall off in stall. I was expecting to sand and contour maybe 1/10 of an inch but what product is useful for 1/4 of and inch? I know, and have used Bondo to that depth on other things, but aircraft?
Thank you for the insight and expertise you have shown in the answers you have give.
Charlie Quebec
August 2nd 19, 12:35 AM
I had MDF templates made on a CNC laser cutter, they cost $30 Australian each.
In my case, the templates were for measuring control deflections, so were one piece.
Particularly with the FX67 series airfoils, accuracy is critical.
Do not believe getting rid of waves will be all you need to do, despite some other posters.
Two local reprofiled a Mosquito and A mini Nimbus.
Mike Borgelt reprofiled the mini, and beat all the ASW20 to win an Oz nationals.
SoaringXCellence
August 2nd 19, 12:36 AM
Several years ago (1970 time frame) Wil Schumann did a re-contour of the H301 Libelle leading edge. It required a bit of build-up with balsa to the extent you're talking about. My father glued the balsa directly to the existing surface and roughed it to shape, slightly undersized on the templates.
The Bondo was then added to create the actual contour and was followed by a thin fiberglass layer, filler and paint.
It lasted until I bought the glider in 2015(!) and it's still there with no damage, other than a few chips that needed to be refilled.
I think if you check back in the archives you can find an article describing Wil's process.
Mike B.
Charlie Quebec
August 2nd 19, 12:49 AM
One last point, most of the gliders that use the FX 67 series start with 67k170 17% thick, then at some point,
either from the root or the taper change at the aileron, transition to 67k150 15% thick at the tip.
This means that special care in needed to calculate the templates for intermediate stations.
My DG200 is 67k170 all the way. The 40 year old wing is very accurate still, something that cannot be said of
the PIK20 (one locally is 19% thick) the Mosquioto, and the Mini Nimbus, all of which seen to have suffered moulding errors.
As I recall, the reprofiled mentioned previously required special calculations for each individual aircraft.
Delta8
August 2nd 19, 01:06 AM
On Thursday, August 1, 2019 at 12:50:22 PM UTC-4, wrote:
Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?
Doug
You understood correctly.
First 10% or so. About 3 inches inboard and 2-1/2 outboard.
Purpose of the templates is to have finished wing with same profile it started with. "Normal" sanding will usually make the leading edge too blunt.
UH
Next step ? So you then wax the female end of the template and fill the wing stations and place the template into the filler . Remove and that becomes a screed point between stations?
I've seen a recently refinished wing that had lots of small cracks every few inches on the leading edge . Bad filler product? Does the filler shrink ?
Bob Kuykendall
August 2nd 19, 01:34 AM
On Thursday, August 1, 2019 at 4:26:22 PM UTC-7, wrote:
> ...I know, and have used Bondo to that depth on other things, but aircraft?
> Thank you for the insight and expertise you have shown in the answers you have give.
There are a variety of fillers you can use. I'd suggest a mix of glass microballoons and laminating epoxy resin. Before you start the actual work, make a few test batches of filler to see how dry you can mix it before it does not spread properly. You want it as dry and light as you can practically work.
You'll want to sand the wing somewhere around 120 to 220 grit before applying filler to get a good bonding surface. Degrease the surface before applying filler with acetone to rid it of contaminants.
One common technique is to use your templates to cast in place a series of raised ribs of microballoons. Then apply and sand your filler between the raised ribs.
--Bob K.
Delta8
August 2nd 19, 02:07 AM
On Thursday, August 1, 2019 at 4:26:22 PM UTC-7, wrote:
...I know, and have used Bondo to that depth on other things, but aircraft?
Thank you for the insight and expertise you have shown in the answers you have give.
There are a variety of fillers you can use. I'd suggest a mix of glass microballoons and laminating epoxy resin. Before you start the actual work, make a few test batches of filler to see how dry you can mix it before it does not spread properly. You want it as dry and light as you can practically work.
You'll want to sand the wing somewhere around 120 to 220 grit before applying filler to get a good bonding surface. Degrease the surface before applying filler with acetone to rid it of contaminants.
One common technique is to use your templates to cast in place a series of raised ribs of microballoons. Then apply and sand your filler between the raised ribs.
--Bob K.
http://www.archive.jimphoenix.com/archive09/jimphoenix2/pages/Nimbus/LH%20UP%20wing/subLH%20UP%20wing.html
Is this the technique you were referring to ? Would be curious as to how his finish held up as it appears he used filler over old Gelcoat .
Also seems he went full chord with the templates . Overkill?
Bob
Somewhere buried on www.jimphoenix.com are pictures of how he reprofiled the wings on a Nimbus 3. It’s worth taking a look.
On Tuesday, July 30, 2019 at 11:00:34 PM UTC-5, wrote:
> Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
My primary reason for starting this thread was to help me know how to evaluate whether an FX-67 winged glider has suffered from "spar shrinkage" and if so, how much and how badly it will impact the performance. I've heard so much about and that it can profoundly decrease the performance so I'm trying to figure out whether to worry too much about it. As a relative newcomer to working with composites I'm not sure I could actually fix it...or might make it worse.
Thoughts?
Stephen Struthers
August 4th 19, 07:14 PM
At 17:26 04 August 2019, wrote:
>On Tuesday, July 30, 2019 at 11:00:34 PM UTC-5,
wrote:
My primary reason for starting this thread was to help me know how to
evaluate whether an FX-67 winged glider has suffered from "spar
shrinkage" and if so, how much and how badly it will impact the
performance. I've heard so much about and that it can profoundly
decrease the performance so I'm trying to figure out whether to worry
too much about it. As a relative newcomer to working with composites
I'm not sure I could actually fix it...or might make it worse.
Thoughts?
Personally I think there is a load of BS spoken about performance,
biggest improvement in performance in my humble opinion is pilot
improvement. I suspect you would spend hundreds of man hours trying
to make the wing shape perfect and it won't alter your cross country
ability one bit, spend the hours flying and / or save hard and buy the
best new glider on the market today - whatever that is!
On Sunday, August 4, 2019 at 6:26:30 PM UTC+1, wrote:
> On Tuesday, July 30, 2019 at 11:00:34 PM UTC-5, wrote:
> > Can anyone tell me specifically how to tell how closely a wing is following its intended shape or to know if it has "issues"? Also, if I'm sanding, polishing or refinishing it, how do I accurately correct for any deficiencies? Asking for a friend... : )
>
> My primary reason for starting this thread was to help me know how to evaluate whether an FX-67 winged glider has suffered from "spar shrinkage" and if so, how much and how badly it will impact the performance. I've heard so much about and that it can profoundly decrease the performance so I'm trying to figure out whether to worry too much about it. As a relative newcomer to working with composites I'm not sure I could actually fix it...or might make it worse.
>
> Thoughts?
If its spar shrinkage you are worried about you don't need a template; if it is significant then it will be easily visible and palpable along the spar cap line. If you can see that and feel that it is worth the effort for cosmetic reasons you could fill and smooth that area. It is not likely to be worthwhile worrying about it aerodynamically on an old Wortmann FX-67K-150/170 wing as that aerofoil has an inherent property of rather early airflow separation on the top surface. It was, IMHO, not a very good section as shown by the fact that ASW 17s and 20s with older 1962 Wortmann sections performed better than all the comparable gliders with 67 sections and also were not so susceptible to bugs and rain
I bought a near new LS-7 for 39k because the word was, “I had a climb problem!” Got it home and in the shop and found a big spar depression on the bottom of both wings! Couldn’t bring myself to jump on this new wing with 40 grit, so I carefully marked out the low areas which were behind the spar up to an inch wide and 7 to 10 feet long! Masked the low areas off and then sanded them with 220 grit to give the gelcoat “tooth”. I carefully leveled the wing both fore/aft and span-wise.. Mixed up a batch of gelcoat and brushed in everything with repeated coats until it was thicker than the depressions. Gave it a minimum cure time, about 4 hours as I remember, then wet sanded the edges with 400 grit while the stuff was green and very soft, switching to 600, then 800 as the depression disappeared. Buffed everything out after completely cured. She climbed with everyone else as far as I could see. Loved that bird, should have never sold it!
JJ
I contoured my LS-3 wings after 3 years because there was a flat spot over the spars. Made a big difference in glide, especially at high speed (impressed ASW 20 drivers asked me what I'd done). I thought I could feel it and the sanding soon confirmed it.
A few years later, I actually profiled the area over the spar on the upper surface. I should have used templates but wrote a program that allowed me to do it with a dial gauge. Yes, it can be done. If you know the dimensions of the dial gauge and the profile, then moving it X mm should cause the radius of curvature to change Y amount and the dial gauge to reflect that. If it changes Z amount, there's something wrong, and you can eventually figure out what. Anyway, we sprayed over the spar and built it back up and profiled it in that one area. Again, made a big difference. This time it was the ASW 20 C drivers asking me what I'd done. :)
Years later, I contoured it one more time but the profile hadn't changed much; the shrinkage over the spar caps apparently occurred fairly quickly. I could still climb and run with anything of that generation (Ventus, LS-6, ASW 20 C/B). The airfoil was more sensitive to rain but it didn't fall out of the sky like some brands were reputed to. But I tended to follow the advice of the PIK drivers: i.e., slow it up and add a little more flap than usual. And until I sold it, I kept the gel coat unwaxed and in 400 grit so the water didn't bead up.
I spoke to one guy (Jim Cox) who actually profiled the whole wing on his LS-3. He said the leading edge was too blunt, especially on the outer portion and he had to build that up. I believe that's what P3/ACA discovered on their LS-3, which they're refinishing. Jim had the same remarkable experience I did in terms of better performance. Would my glider have been even better if I'd done the whole wing? I don't know.
Most don't recall that Dick Johnson's flight tests of the LS-3 and ASW 20 showed essentially identical performance when new, which I confirmed. But the LS-3 deteriorated over several years. Not completely coincidentally, most competitive pilots moved over to the '20 after a year or two and the LS-3 became a forgotten airplane, with a few exceptions.
There's no doubt that a competent reprofiling job will help gliders like the LS-3. But that's a fair amount of work. IMO, it's only worth it if a) you want a great Sports Class machine and b) you're refinishing it anyway. The original LS-3 still climbs great and flies beautifully regardless of the spar cap shrinkage.
My comments apply only to the LS-3, not the later LS-3a with the split aileron/flap. Apparently the wing molds warped a bit and some later 3a models ended up with thicker wing sections. The factory disputed this.
UH's comments about pulling templates from the existing airfoil before you start a refinish job are spot on. When he managed/assisted with my ASW 24 refinish in his shop last year, we pulled templates for the whole wing AND made new ones for the "B mod" leading edge for the outer section. I don't know how much difference it made but my glider goes at least as well now as it did before so I'm happy. The templates didn't take that long to make with UH's expertise and alacrity.
Yes, you can usually get more bang for the buck by becoming a better pilot. But if you have trouble keeping up with your buddies and/or you're interested in Sports Class, it can be worth tuning an older ship like the LS-3. If you have time and some expertise (or able friends), it can also be good for the soul. :)
Chip Bearden
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