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Author Topic: HLG Wing Shaping  (Read 8198 times)
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Dan G.
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« Reply #25 on: April 16, 2008, 02:05:04 AM »

Okay ... I figured out how to scan black & white photos.

So here's from the original article in Oct. 1974 American Aircraft Modeler's article by Ron Wittman, who had just set world records ...

Dan G.
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« Reply #26 on: April 16, 2008, 01:32:31 PM »

Great photos Dan; nice looking gliders. This type of design is what I'm looking for; your pics will help in my building process.
Looks like you have a nice big area to fly at, do you have to deal with a lot of wind like here in south Texas?
Since I've started back into this hobby I've had to carefully choose the times and days to go out to flying fields.
I'll be checking back in to let you know how things are going. I'm sure I'll have more questions as I go.

Thanks,
Curtis
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Dan G.
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« Reply #27 on: April 17, 2008, 12:05:43 AM »

Okay (he says again) ... I see that I didn't succeed with the magazine photos, so I'm trying again ...

Dan G.
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« Reply #28 on: April 18, 2008, 01:22:55 AM »

Hey Curtis ... Pedro ... I can understand why on old guy like myself can be specially attached to an older form of hlg (javelin launch), but why aren't you guys trying tip-launched gliders?

Dan G.
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« Reply #29 on: April 18, 2008, 03:15:30 PM »

Hi Dan,

Just the term "tip-launched gliders" is new to me; is this a type of glider that you fling by the wing tip like a frisbee?
I guess I still have a love for the old style HLG designs, not to mention just learning the proper technique for building and then fliying them.

Curtis
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« Reply #30 on: April 18, 2008, 04:15:18 PM »

Hi Dan

Local field is a bit small for those big tip launched jobbies, having said that might try one in a little 8 incher and have a bit of a twirl ....

Hi Curtis

Hope Dan does not mind me offering an alternative view. I have read this thread with great interest, and it is obvious that Dan actually loves and enjoys the building process as much as the flying (if not more so) at the end of the day. Dan's description of building his beloved supersweep is the result of many years experience and great craftsmanship, which he obviously relishes.

For the beginning builder, or the totally inept (myself), I would voice the view that it would be fairly difficult, if not impossible, to follow Dan's process with similar results. Having read through the tread a couple of times, I think the most important sentence is where Dan says that the trailing edge angle is constant along the whole of the span, ergo, the wing taper from root to tip will folow the shape of the high point and will be similarly elliptical. So, if you do plan to build one, Curtis I would suggest that the first point is DO NOT taper the wing first. The chance of getting the correct elliptical root/tip taper various from zero to extremely remote without the benefit of years and years experience. My alternative build process (for the super sweep) would be ...

1. Keep blank rectangular, and mark of the root high point as a constant line down the blank,
2. Mask off forward of the high point, line up against edge of board and sand down to trailing edge. This will give you the constant trailing edge angle that Dan mentions as main design point.
3. Remove initial mask, and mark off both elliptical leading edge planform and high point.
4. Cut blank to planform.
5. Mask off aft of the elliptical high point and sand forward of the high point down to the high point line. This will automatically give you the root to tip taper which will be elliptical. Duck tape is fairly immune to being sanded down. so the all important high point should be safe.
6. Sand front section to shape

I am fairly sure that the combination (2) and (5) is Graham Cs (?) light bulb moment that he alluded to earlier in the thread ...

An alternative view only ...
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« Reply #31 on: April 18, 2008, 09:15:34 PM »

Hi Curtis,

Go to the forum under outdoor, hand launched gliders, thermal Piglet Has Got Me Stalled, to Maxout's reply #11 -- that should whet your appetite a bit.

Dan G.
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Dan G.
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« Reply #32 on: April 18, 2008, 09:25:41 PM »

Hey pedr0 ... ahem ... uh, I didn't think of that ... and I don't know that I can fault it. Maybe I'll try that, if I'm not too old a dog.

Matter of fact ... between you and Graham, I'm feeling pretty stupid.

Dan G.
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« Reply #33 on: June 19, 2008, 08:05:17 PM »

As a back up to Pedro’s description of cutting a wing blank in reply#30 here is a sketch I did for a talk at the Free Flight Forum a few years ago. I shew the taper being cut over the whole chord of the wing, which is possibly the easiest, but does need a bit thicker wood. The principle does not change at all if the taper only runs from the high point at the centre of the wing as in Pedro’s instructions.

It will be realised that the same procedure can be used with tapered (and multi tapered) wings.

Dan G. Lovely work on the Supersweeps. I understand your feeling when first seeing this method of tapering wings because I felt just the same when I first saw it. I felt particularly stupid when I realized that American modellers could have been doing it since the 1930s when Frank Zaic first started selling tapered wing blanks for HLG wings, although I suppose it wouldn't be applicable until the straight trailing edges became popular

John
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Dan G.
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« Reply #34 on: June 19, 2008, 11:02:48 PM »

I have to say John (Hepcat) ... your method would more easily assure a sharp apex. I haven't done any projections, but perhaps a 5/16" plank would be thick enough to leave a 1/4" at the apex ... I could be tempted to do this except that 5/16" planks of good, light quality aren't that easy to come by.

Amazing how many different ways can be construed to achieve the same object ... amazing and wonderful.

Dan G.
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« Reply #35 on: July 06, 2008, 01:20:55 AM »

I've read this thread over several times and was facinated by the alternative methods of wing shaping employed.

I've been pondering the geometry of the methods shown all this afternoon and have some thoughts...

Dan, I wouldn't be so hasty to change your shaping method just yet.

I've just run some numbers on the geometry of a constant rear airfoil taper (hp to te) with a curved, swept back leading edge, and a straight trailing edge blank. And they don't work for me.

I get a tip thickness that is too great for my purposes. I used my 18" clg planform as a guide, and the root chord is 3.75" at 0.1875" thk (5%), the d-break chord is 3.346" (5" from center) and it works out to 0.166" thk or 4.96%, and the tip chord is 2.094" (0.625" back from tip) works out to 0.115" thk or 5.48%.

Geometrically, that's not kosher imo. I like to taper the tip thickness by about 1% from the d-break, and ideally I like about 0.5% thinner at the d-break.

My numbers would be 0.150" at d-break (4.5%), and 0.073" at tip (3.5%). That's a far greater taper than obtained by the constant rear method outlined above. I haven't worked out the actual taper geometry of the Supersweep22 (I have the plan from the original article) but my instinct says it won't work out either.

And, I know for a fact that it wouldn't work for Master Leeper's personal Sweepette wing (I have it on good authority Wink).

However, for a beginner, or as a way to get a plane built quickly it would certainly work fine. Note that Stan B's kits come with blanks pre-tapered in this manner (constant taper rear of hp).

I'm trying to think of how to create the ideal spanwise taper automatically by rearranging the blank dimensions and initial high point location. I'm thinking that I could start with a simple tapered blank and sand the rear angle to fit, and then cut the planform. I'm not sure yet as to the dimensions of the blank (nor if it is actually a worthwhile endeavor). Any ideas?

Tmat
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Dan G.
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« Reply #36 on: July 06, 2008, 02:15:04 AM »

Uhhhhh ... I'm not too sure where you're trying to go, here, Tmat. It seems to me that the major challenge is getting the required twist to accommodate your declining thickness toward the tip. Once that has been incorporated into the general thickness taper, the other parameters (chord and hp) will be fixed ...

Or ... doing it my way, you would locate the chord, do a general taper with the changing thickness, locate the max camber and sand to the TE and the twist will already be fixed.

But neither of these approaches is as easy as the original idea as long as you wish the section change along the span. In fact ... it pretty much kills that synergistic little relationship of geometry which had caught our interest.

Somehow, I don't think I've addressed at all whatever it was you were trying to get at ...

Dan G.

I'd be interested in knowing why your choice in section change.
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« Reply #37 on: July 06, 2008, 11:29:32 AM »

Tony
Referring to wing shaping as my sketch in reply #33, which I think is the same as Graham and Pedro are talking about.

I am surprised that your calculated thickness/chord ratios vary, 5%, 4.96% and 5.48% because a big point about this method of shaping is that the t/c ratios remain constant along the wing as long as the high point position, as a percent of chord, stays constant along the wing.

That last paragraph, when you think about it, does give a simple method of reducing the t/c ratio towards the tip if that is what you want to do. Because a high point at a constant percent of chord gives a constant t/c ratio then sweeping back the high point line will reduce the t/c ratio as the tip is approached.

I would be interested to know why you want to change the t/c ratio along the wing. I am not saying you shouldn’t, I am just interested why you might want to!

John
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« Reply #38 on: July 06, 2008, 03:45:21 PM »

Hello Dan and John,

Well, it was late last night....
Seriously (well, semi-seriously Grin) I don't mean to rain on anyone's parade.

I'll answer John's points first.

I'll have to re-look at my number's John. It does make sense that for the same % hp chordwise location, the thickness % should remain constant. There will be some error if a constant te thickness is used, as the te thickness expressed as a percentage should be held constant if the goal is to produce a uniform airfoil thk %.

I don't think that this relationship is unique to a curved leading edge. A constant chord would produce the same result (although neither desireable nor what was discussed I know) as would a simple swept straight taper from root to tip. As long as the hp is kept a constant % of chord you'd get a constant airfoil thickness.

What I was getting at was that I personally don't think this is a desireable goal for best performance for several reasons.

1) - Reynold's number. As the chord gets increasingly narrower towards the tip, the ability of the airflow to follow a curved surface without loss of lift and an increase in drag diminishes. If you go back to Martyn Pressnel's Sympo article on the use of invigorators (I'll try and find ref date) you find that when using a constant thk airfoil at low Re, the optimum aspect ratio gets smaller as the model size diminishes. It becomes, in effect limited. At low Re, the airflow cannot follow the upper surface curvature without premature separation.
One "aha" moment that occurred to me while reading the article was that the rise in pressure across the chord was dependant on the actual physical curvature encountered, and that the actual curvature gets smaller (ie: steeper pressure gradiant) when you reduce the airfoil chord but maintain the thk %. Place two identical airfoils one on top of another, with the second a 50% exact scale of the first and this point becomes apparent. The smaller section has a steeper curve to the high point. As the Re gets smaller it may be desireable to maintain a max le curvature to the hp or even reduce it to prevent tip stalling. Adding washout helps, but has other speed related issues. The implication is that a reduced % thickness is desireable for low Re.

2) Drag - An Aero specialist (Brian Egglestone) recently reminded me of a fact not understood by many I believe. That is, no matter what one does with the tip shape or profile, the physics of 3d wings determine that the lift at the tip will always go to zero. However, it does not follow that the drag does the same! Secondly, the airflow towards the tip is no longer chordwise, but begins moving spanwise. His advice was to not worry about the wing tip's ability to produce lift (it will not) but rather, one should endeavor to take measures to reduce the drag at the tip as this will maximize performance. He agreed that reducing the tip thickness and camber was one way that this could be accomplished. Note too that Dr. Drela's much lauded R/c Dlg airfoils also reduce thk towards the tip.

3) Moment of inertia - keeping the extremities light is a time honoured way to help the roll recovery at launch. Reducing the chord helps, and reducing the thk would help even more.

Based on this idea I started to reduce the thk % and camber towards the tip of my F1B models starting in 1988. Andriukov began to do the same perhaps even earlier, and it is now standard practice across the board in the FAI FF events. The profiles get thinner, and flatter towards the tip. In a way, it is a means of aerodynamic "wash-out" without the speed sensitivity of actual physical wing twist and reduced drag at high speeds and low angle of attack.

John's point about changing the hp line to achieve a thinner % thkness would work geometrically, however, a more rearward hp is not desireable for performance esp at lower Re.

I'd like to think of a simple geometric "trick" that could achieve a reduced % thk, and keep a constant hp % automatically, but haven't as yet.

Tony Mathews



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« Reply #39 on: July 06, 2008, 06:25:51 PM »

A quick note to Dan, the complete Supersweep article is available online as a .pdf file here: http://www.indoorduration.com/ftp/supersweepHLG.pdf
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« Reply #40 on: July 06, 2008, 07:20:12 PM »

Thanks, Tony ... for the most comprehensive assembly of the relevant pages on the "Supersweep" I have.

And, I quite agree with all of the reasoning behind your desired wing peculiarities ... and while building Nordics, I followed the same reasoning. But, when I see what I have to do to my wing tips to get my hlgs to fly ... the amount of washes I "warp" in on the field ... beyond what I've built-in which is already substantial ... I pretty much gave-up any idea of the level of accuracy you describe while building my hlgs.

I would point out ... as a point of amusement really because I don't think it's of consequence ... amongst the myriad of complexities to look at and consider ... as the flow, approaching the tip, traverses more spanwise, this has the effect of elongating the airfoil as seen by the air. I am not offering this as argument against thinning the tip's airfoil ... only as a point of interest ... I believe in thin tips and have practised such since 1968.

I've a hunch that you're going to be thinking for a long time on that simple trick to help shape that wing.

Dan G.
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« Reply #41 on: July 06, 2008, 07:39:18 PM »

Hi Dan,

It has occurred to me that the Supersweep benefits or requires such a large amount of washout in the tips likely due to the extreme aspect ratio resulting in a very narrow tip chord. Not much to do about this as I know you really like the design.

Personally, for outdoor gliders I prefer a "blunter" tip for increased chord and higher Re. But to each his own of course.

As to my "desired wing peculiarities" Wink, I think you will find that they are about standard on many good hlg and clg designs now. The measurements that Mr. Hines has recently given me taken from his Batcat (clg) and Sweecat show the same characteristics. Basically, I'm just copying the Masters.

And, I would suspect that they are what you would find on Supersweep anyway!

As to the perceived level of accuracy required to do what I suggested... well I don't find it requires any more work than what you described in your shaping notes.

When compared to Hepcat's method, well yes, it does require more work to reduce the wing thk spanwise. I think it's worth it, but that's my personal decision.

And yes, I'll likely not find a "simple" trick to aid my shaping...however, I'm a simple, lazy man and if there is an easier way, I'm sure I'll find it eventually! Grin

Tmat
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« Reply #42 on: July 06, 2008, 10:52:59 PM »

Hi Tony ... the wash I'm adding on the field is the differential, mostly as wash-in on the inside tip. I use it to maintain a consistent circle throughout the speed envelope.

If those slender wingtips are so ineffective ... why would I, and Ron Wittman, be so impressed with the performance? Admittedly, I've not seen many other gliders (I fly alone unless I travel hundreds of miles) and don't have much against which to compare, but ... Ron Wittman ... ? He has such a high recorded time. You don't exactly denigrate these slender wingtips ... you do speak softly ... but hardly in favour ...

Dan G.
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« Reply #43 on: July 06, 2008, 11:01:45 PM »

Easy there Danny boy! Grin

I rather like those slender wingtips of the Supersweep, and I have a soft spot for Whittman's 90 sec record. Truly iconic. Sadly, it may be finally broken this summer with a tip launch glider! That's a whole other topic...

We must keep in mind that the Supersweep is an indoor glider. As such there are aspects to the design that are not common on outdoor gliders (which is what I mentioned). Performance in still air? Superlative naturally.
Am I in favour of such slender tips? For indoor, why yes I am. For outdoor in thermals and turbulence? Why, no I am not.

Differential twist is another animal altogether.

Cheers!

Tmat
-btw, what's your best time in still evening air with your Supersweeps?
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« Reply #44 on: July 07, 2008, 04:00:25 PM »

Tony
Thanks for the usual, very full, reply #38 which was much as I expected - we must read a lot of the same books! I agree with most of your arguments but I think there are some points that are worth further discussion. First off though I must say thanks for the ‘aha’ moment. I have often said to people that if they want to use a high median line camber then the section should be thin otherwise the curvature of the top surface might be high enough to disrupt the flow.. I had not thought to extend this to the fact that maintaining a root section to a narrow chord at the tip would give a similar increase in top surface curvature.

Martyn Pressnell’s paper was in the 1982 Sympo and re-written somewhat for the 1986 Sympo. It would be good if you could reread and comeback on Martyn’s figures because my reading of his graphs is that there is an improvement in sinking speed with reduction of Reynolds Number as long as the aspect ratio is increased. I’m sitting on the fence at the moment because wind tunnel tests always make me nervous, particularly when done by a degree student who has to get his paper out by the end of term Smiley.

Of course I agree with Brian Egglestone about lift dropping to zero at the tips but that still leaves judgements to be made. What is the tip? The last ten percent of the wing, a chord length from the tip? What should we do? Increase the chord length to increase the RN? Is it worth doing that if the tip is not lifting anyway? (Probably of more interest is that Brian’s ‘Creep’ design is still flown by a few flyers here in the NW and even against modern stuff the climb is still breathtaking.)

I think some of the early changes of tip section in FAI were due to modellers building on curved boards which automatically reduced the camber if the tip panel was tapered. Having found that performance was not impaired, in fact probably improved, it became adopted as a feature.

John
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Dan G.
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« Reply #45 on: July 07, 2008, 11:16:54 PM »

Tony ... it's been many years since a watch has been put on my flights. As a younger thrower, I would regularly break a minute, but I know the altitudes and the times have diminished considerably by now. On occasion, I have recently flown with another guy who flies a variety of gliders and I am not disgraced during these sessions. I do wish that there were other hlg flyers around here ... I would fly more, for one thing.

Dan G.
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« Reply #46 on: July 08, 2008, 12:10:24 AM »

Hi John,

You read books? Grin

Seriously, I'm sure we've read much of the same stuff too.

I will reread Martyn's article, but I don't recall the effect you mentioned. Perhaps' it's an interpretation thing?
As I recall, the aspect ratio had a defined optimum peak depending on Re. The lower the Re (for the B6356b tested) the lower the optimum aspect ratio. However, with the addition of invigorators, the airflow could stay attached longer at the lower Re's. Therefore, one could increase the aspect ratio and gain an advantage. In other words, with invigorators, the optimum aspect ratio increased regardless of the Re, (except for very low Re). Re corresponding to F1G, for example didn't really change even with invig, but the performance did.

I don't think increasing tip chord is the answer (although there is likely a point when tip chord can be too small). Some sort of low drag tip shape, with airfoil going almost symetrical (or semi) is likely the best solution. As to where the tip actually is? That's a good quetsion. Likely depends on rate of spanwise flow and Re. I'll ask Brian for his thoughts on this next time I see him. I'll also tell him that Creep is still being flown in U.K.! I'm sure he'll get a kick out of that!

Regarding the use of constant camber boards and tapered wings for FAI...

When I designed my No 23 Wake in 88/89, I spent a lot of time thinking about what to do with the airfoils, and the tip. Finally came up with a solution I thought good for the 3D shape of the wing (planform, twist distribution, profile change to tip, tip shape etc.). I realized that this would require 4 separate building jigs for the wing. Each panel had to have it's own jig. Much work and effort went into to building a set of quite elaborate (and accurate) jigs.

Only later did I learn that the (former) Soviet modellers were using a simple 1 jig, constant camber method, skewing the panels to achieve desired twist. Really wish I had heard of this before we built those jigs!

I wrote an article at that time that suggested that some of the airfoil changes made towards the tip were, in fact, an "artifact" of the building method (1 jig) and had the good fortune to also follow good aero practice and provide some benefit as well!

Although, a long discussion with E. Verbitsky in early 80's showed him already varying profiles towards tip of his F1C's and I can assure you, it was done on purpose with improved performance as the goal! He also was a firm believer in washout. Washed all the panels progressively from root to tip. Much of the Soviet F1B and F1A models did not follow this practice, in fact AA still doesn't use much (if any) washout in his tips!

Tony

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« Reply #47 on: July 08, 2008, 12:41:15 AM »

I've been thinking about a simple wing shaping trick (or jig) that could get my desired profile camber changed towards the tip automatically.

I have come up with one possible solution. I don't have a useable sketch yet, but I'll try and descibe the method:

First caveat - this method requires each half of the wing to be shaped separately. Not typical hlg practice I know, but with that in mind...

The wing blank (half) can be of any shape to begin with. Rectangular, tapered or cut to desired outline. (As long as the desired outline can be cut from the blank after shaping).

A simple shaping jig is made described as follows:

A flat, hard surface (such as glass or metal plate etc.) is required for the base. The blank is placed flat on the base and the trailing edge is set back from the edge in such a way that the desired te thk will be obtained when the sanding block hits the base edge. For my wings the wing actually has to be skewed with tip forward a bit due to the reduced rear angle of the airfoil. (that's the reason for half wings shaped at a time).

A shim of constant height is place in front of the blank. I suggest a steel, alum, plastic or hardwood shim (suitably protected with tape). This shim will create the desired angle for the rear of the airfoil, when the sanding block hits the shim and the base edge. For my 0.1875" thk, 3.75" root chd, 5% profile (for my new Clg), I chose a shim of 0.250" high (just to get a round number and something easy to find) set in front of the le.

Here's the trick:
The shim, needs to be skewed forward (away from the tip) such that the thk of the airfoil at the tip is reduced to the desired amount. That is, the shim is not set parallel to the te.

For my wing blank, I'd need to set the shim at 4.478" forward from the root te, and 8.182" from the tip te.

This produces a wing thk taper of 5% (root) to 3.5% tip.

However, one thing I found with the calcs was that to get the desired d-break thk, I will need a curved shim (almost a straight taper to d-break, and then curved out toward tip) :'(. I would probably go with a 1/4" x 1/4" alum bar, and just bend it to form the desired shape.

To get a 4.1% d-break (chosen only to match the te thk target with simple te skew) and a 3.5% tip, the shim must be 5.85" forward of te at d-break, and then bend forward 0.839" away from tip to the 8.182" distance mentioned earlier.

To use the jig, you'd rough shape the wing with a razor plane, and then place the half blank on the jig at the correct te skew setting (I use removable stencil spray). Then a wide sanding block (with coarse followed by finer paper) is used to sand the wing rear taper by sanding from shim edge to base edge.

The result should be a perfectly twisted rear profile taper and perfect thickness taper produced in minutes.

Of course the upsweep and forward portion of the airfoil still needs to be shaped by conventional means.

What do you think?

Tmat
-like all jigs, not worth it for a "one off" model, but possible useful for multiple copies...
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Dan G.
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« Reply #48 on: July 08, 2008, 01:46:04 AM »

Tony ... yes ... your jig would work ... or at least, I don't see why it wouldn't.

The twist -- no matter how you do it -- will always result in a very delicate surface which can be touched only with a narrow sanding block held only parallel to the chord ... but you already know that.

Dan G.
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« Reply #49 on: July 08, 2008, 12:03:43 PM »

Thanks for the feedback Dan.

I might actually try this method on my next glider just for the hell of it.

I'll be curious to see if it saves time over my usual methids (much like yours I see).

Tony
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