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Tapered wing with same root and tip airfoil: problem?

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Tapered wing with same root and tip airfoil: problem?

Old 01-03-2006, 10:09 AM
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strawtarget
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Default Tapered wing with same root and tip airfoil: problem?

I have an airfoil that I know and love (NACA 0015). I want to build a tapered wing using this airfoil.

The wing design has a leading edge with very little sweep, and a trailing edge with a whole lot of sweep.

My plan is to simply scale the airfoil in intermediate steps from root to tip. If I do that, I get something like the following...



The red line in the graphic is drawn across the thickest sections of each rib. Is it a problem that this line is not perpendicular to the wing root?
Old 01-03-2006, 11:04 AM
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Chad Veich
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Default RE: Tapered wing with same root and tip airfoil: problem?

Nope, no problem.
Old 01-03-2006, 06:57 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

Thanks.
Old 01-04-2006, 11:25 AM
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Default RE: Tapered wing with same root and tip airfoil: problem?

Are you using a wing tube?
Old 01-04-2006, 11:32 AM
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Default RE: Tapered wing with same root and tip airfoil: problem?

Nope... it's a single-piece wing (well, two halves permanently joined).
Old 01-08-2006, 07:44 AM
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Default RE: Tapered wing with same root and tip airfoil: problem?

I'm pushing the aerofoil around all over the place, my background in the scale free flight models has driven into my mindset that they just absolutely must conform to all known protocalls. You look at that, then see one of those cheap balsa rubber powered models you get in a plastic bag at the hobby store, "just flat wings and a stick for the fuselage" and it flies well, you gotta put things into perspective as to the absolute necessity to maintain a political norm with it all, at least on the model end. My conclusions now are less upon being politically correct as much as maintaining the proper balance, the extra girth or transfer of it doesn't seem to affect it in model form nearly as much as full scale entirely because we are using much lighter weight materials and don't have to fight with gravity as much. Just my 2 cents.........
Old 01-08-2006, 11:08 AM
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Default RE: Tapered wing with same root and tip airfoil: problem?

But isn't fretting over the smallest minutae, sweating the small stuff, and generally being obsessive compulsive a large part of the fun of modeling?
Old 01-08-2006, 03:14 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

There is something other than sweating the small stuff? huh, never really came up for me

Straw- Will there be some hardwood/liteply joiner... like thru th root to the first or second rib each side? Glassing the roots together? Bailing Wire?
Old 01-08-2006, 03:20 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

1/16th basswood joiners (dihedral brace) on fore and aft of top and bottom spars (spars are 3/16 basswood). Also, root ribs of each wing will be Elmer's wood-glued together in a butt joint.
Old 01-08-2006, 04:01 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

Functionally that puts all the load onto the bit of 1/16 basswood. A butt joint has very little strength compared to sidegrain joints.

To maximise the side grain you should really do something like the options shown below. In the first the full thickness joiner provides at least as much unbroken wood cross section as the spars themselves. And this is the whole point. You want to maintain as much as possible a consistent cross section to the spar through the various glue joints and to maximise the surface area of the glue joints. The joint where the spars but butted together has very little strength.

Even better is the second option where the main spars are scarff jointed in order to get as much side grain to side grain as possible and to help maximize the surface area of the glue joint. It may not look like much but this would be more than twice as strong as the simple end to end joint. In this case the joiner is not going to be worked so hard like in the first case.

The ribs being glued together won't really do much for flight load carrying.
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Old 01-08-2006, 04:51 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

I did some joiners like this... pic is exaggurated for clarity, blue joiner lapping on spars, thru root& rib
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Old 01-08-2006, 08:50 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

KidEpoxy. You got the idea. But if you look at the first few posts you'll see that he's dealing with a swept forward spar line. The sketches I did are a top view rather than a front on view like your's.
Old 01-08-2006, 09:42 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

oops, uh... yup.
I forget which scratch model I did it on, but I had to mill the dihedral & sweep cuts on the tablesaw from some 3/8th bass joiner stock... don't recomend that route to anyone that wants to keep all 10 fingers.
Old 01-08-2006, 10:00 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

Actually my spar is straight. The red line in my first post simply indicates where the thickest part of each rib is. It was more an airfoil theory question than a construction question.

Instead of sweeping my spar forward, I just calculated the MAC and put the spar at the ideal position for the closest rib. The ribs nearest the root have the spar a little too far forward, and the ribs nearest the tip have the spar a little too far aft.

Got the ribs for one wing cut tonight. I'm scared to post my plans because someone will surely point out the many ways in which they suck, and I'll have to go back and re-do it. But I'll do it anyway.

[link=http://boxybutgood.com/jeff/ribs-2006-01-08.png]Ribs cut out with scroll saw[/link]
[link=http://boxybutgood.com/jeff/rightwing-2006-01-08.png]Preliminary wing plans.[/link]

FYI: it will be sheeted from the leading edge to the main spar, D-tube style, and sheeted 1" from the trailing edge, with cap strips between the leading and trailing edge sheeting. It will be covered with monokote, or something similar. But probably Monokote because they have exactly the colors I want.
Old 01-08-2006, 10:41 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

BTW, the ailerons will be built up, and scale. The tip rib will actually be cut short so that the aileron can extend out at the angle it does on the full scale plane.
Old 01-09-2006, 03:30 AM
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Default RE: Tapered wing with same root and tip airfoil: problem?

The preliminary plan looks good. You're right the spar isn't really in the optimum spot but it's not so far out of place that you should have any issues. Especially if the wing is sheeted so it has lots of torsional strength.
Old 01-09-2006, 05:48 AM
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Default RE: Tapered wing with same root and tip airfoil: problem?

A rabbit will cover more area then any butt-joint, if you want to get really hard core, bolt in some micro lag screws with micro lock washers, be sure to recess them 1/132 hehe "response to those that are obsessing upon endless details" . I use gorilla glue in the hard stress points, particularly in a design prone to breaks in certain areas, just use it sparingly, it expands, it just doesn't go anywhere once it's dry, expect sanding, the set up time is nice as well, there are many other compounds that will do the job equally as well in your case.

I build in the real world for a living, much, much larger, heavier structures, this type of thinking you guys are giving wordplay to is just gold, in the future when/if you fill out a job ap, not only list your hobbies, elaborate upon what you guys have done in constructing your works, this shows you really are cut from a different cloth, seeing intelligence like this is refreshing.
Old 01-09-2006, 09:14 AM
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Default RE: Tapered wing with same root and tip airfoil: problem?

The wing will only be sheeted from the leading edge to the main spar(s), and also 1" from the trailing edge. Do you think this should be adequate for torsional strength? I suppose I can sheet the whole thing without gaining too much weight.

Also, for future reference, would the ideal location for a spar be farther forward so that it would match the tip rib's "sweet spot" more closely? When I measured MAC and placed the spar accordingly, I was thinking that would be a happy medium. But now that I think about it more, I wish I'd have used a location that put the spar the same distance from the tip and root rib ideal locations, but as a *percentage* relative to the chord of the rib. After all, an absolute measurement like 1" too far aft on the tip rib has a lot more impact than 1" too far forward on the root rib because the root rib is so much larger. I suppose with the way I have it set up, with the spar too far aft near the tips, a really high speed pull up might want to twist the leading edge of the wingtips into a higher angle of attack, making for a really dramatic accelerated stall. [8D]

I can stay sane by telling myself that this is a prototype, and that a 2nd plane will be built using all of the lessons learned.
Old 01-09-2006, 12:47 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

AAAAAAAAAARGH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!

I just got my Paul Matt CD with 3-views. I ordered it primarily because I wanted the fuselage cross sections when it came time to cut formers. I figured the generic "from the internet" 3-view I'd been using would be adequate for making the wing.

"Oops."



The red is the 3-view I *was* using, and the black is the Paul Matt 3-view.

Well, at least I can friggin' fix my friggin' spar situation. And I won't have to deal with that obnoxious angled aileron nonsense. And the quality of the 3-view is absolutely amazing, with lots of extra info.

P.S. - would anybody ever notice this difference but me? Probably not. Heck... the silver fuse and blue wings would probably be enough for people to know what it was. But it's back to the drawing board anyway. Maybe I'll scratch the landing gear (as has been suggested in my other thread) and just sheet the bottom of the wing with some seriously thick balsa to withstand the grass-o-granite landing surface.

In closing, *insert four letter word of choice here*.
Old 01-09-2006, 02:36 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

Any aerodynamical ingineer would have questioned the angled ailerons in the red drawing, looking at the root and tip rib angles.
We is simple folk, and prefer to finger things out in straight lines..
Perpendicular to some reference for ribs and things, fer instance, that being the easiest way to loft the lines of the airfoil.
Bein' as the War40PeaHawk had a tapered wing, ALL the ribs would have been different, and doodling out the shapes with a slide rule difficult enough without adding any angles...
So the aileron ribs would also parallel the ribs which would be perpendicular to the wing reference, which was probably the spar on the P-40.
The whiz-kids of today would think nothing of it, and let the computer do all that stuff.
Having the ribs attach to a swept spar and still be straight fore and aft is lots simpler to design than do all that angle-side-angling for a cattywampus set of ribs.
Old 01-09-2006, 03:02 PM
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Chad Veich
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Default RE: Tapered wing with same root and tip airfoil: problem?

This may be of some use to you, if you have not come across it already.
http://www.aafo.com/racing/history/hughes_racer/
Old 01-09-2006, 03:48 PM
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Tall Paul
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Default RE: Tapered wing with same root and tip airfoil: problem?

Looking at a couple 3-views of the P-40, the ribs in the flaps and ailerons appear to be perpendicular to the spars they hinge from.
Looking at the ammo bays for the wing guns, these run straight out behind the main spar, which is not swept forward.
Can't find a good photo of a P-40 in plan view, top or bottom to see what the actual metal looks like.
Old 01-16-2006, 08:36 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

The plot thickens!

After spending the weekend making an absolutely fantastic set of ribs, I have yet again discovered a fatal problem.

The Paul Matt drawings are superb, as I've noted before. However, the airfoil sections do not seem to be labeled correctly. That is, he has drawn a scale root rib that is correct, but he has labeled it NACA 23012. If I trace the rib in my 2D vector graphics program, I discover that this rib is really 23015. That is, the max thickness is 15% of the chord. The tip airfoil is also not labeled correctly.

Well, my root rib is a 23012 since I followed the label rather than the drawing. The problem is, a head-on view of the H1 reveals a nice fat thick wing section near the fuse... so fat that the top of the wing reaches the fuse "tube" midpoint. My wing will not reach that far.

Hopefully the third time will be the charm!
Old 01-16-2006, 09:31 PM
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Default RE: Tapered wing with same root and tip airfoil: problem?

I've been looking for a good 3-view of the P-40, and can't find a "real" one.. that resembles the real metal.
A 15% wing would be normal for a plane of that era.
I found this cross-section of the H-1.. but I don't trust it!
The wing isn't that thick. The fillets are misleading in the photos..
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