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Wing Reinforcement Question (Read 196 times)
Reply #8 - Nov 10th, 2019 at 4:22pm

alfakilo   Offline
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Here's an attempt to summarize much of what I learned from others.

Green is the sheet diagonals that replace the ribs aft of the spar, alternating in a W pattern. Very effective in reducing twisting.

Red is the shear web that Tom described. Sheet infill between the top and bottom spars, grain is vertical. May only need webs in the first couple of bays. Very effective in reducing wing flex up and down.

Yellow shows gussets on the trailing edge/rib joints.

Blue shows bracing that runs from the top of one rib to the bottom of the adjacent rib. May help in reducing twist. Arrange in W pattern.

Pink shows bracing that runs in an X pattern in the bottom of each rib bay. May be combined with the blue bracing.

Not shown is something called a D Box which is a method of building up the leading edge to resist twisting. I thought the discussion of this was more appropriate for larger, RC type planes.
« Last Edit: Nov 10th, 2019 at 8:09pm by alfakilo »  

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Reply #7 - Nov 10th, 2019 at 7:33am

New Builder   Offline
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Amherstburg, Ontario, Canada

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AK - Absolutely great work and showing a great touch. You got some great advice from everywhere but the diagonals for ribs is great. I'm thinking this would work at any scale if the diagonals were spaced a bit closer together. I'll add this to my techniques file.
Mike
 

Have no fear of perfection - you'll never reach it. (Salvador Dali 1904 - 1989)
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Reply #6 - Nov 9th, 2019 at 3:28pm

Sky9pilot   Offline
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Looks great AK... Smiley
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #5 - Nov 9th, 2019 at 12:08pm

alfakilo   Offline
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Both here and at HPA, I got a lot of really helpful advice. Here's the start of a 10" P-51A (NA-73X) where I'm trying out some of those ideas.

Notice the 1/32" sheet diagonals that replace the aft ribs. This has significantly reduced the tendency to twist. Left wing is the basic construction, right wing shows diagonals sanded to shape.

The fuselage keel bracing will be removed once the formers have been added.
 

na73_build_2.jpg (26 KB | 6 )
na73_build_2.jpg
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Reply #4 - Nov 5th, 2019 at 4:29pm

Sky9pilot   Offline
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I think you'll find the gussets a great addition.  Sorry for not clarifying the "Shear Web" suggestion. 

For those who haven't Googled it yet=
Shear webs essentially turn a pair of spars into an I-beam. There is a reason why this shape is used for construction of buildings. It is light and strong. The webs add tremendous strength to the wing construction and help prevent a spar from compressing to the point of failure. (please note that the shear web has vertical grain between the spars for additional compressability strength.)
Pic below shows the shear web between the two spars, upper and lower spars.  Usually added to the wing beyond the fuselage out past the location of landing gear for support and strength and sometime clear out to the tip bay of the wing panels.
 

shearweb_pic.jpg (8 KB | 4 )
shearweb_pic.jpg

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #3 - Nov 5th, 2019 at 8:02am

alfakilo   Offline
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Thanks to all for some good info! Thanks to Google, now I know what a 'shear web' is!!

I also posted this question at HPA and again received some excellent info.

Since my objective is minimum weight, I've decided to add a second 1/16" spar under the top one (thanks, Tom!) and will add gussets to the TE rib joint (thanks to HPA). The TE is pretty soft and needs some stiffening.

 
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Reply #2 - Nov 4th, 2019 at 7:05pm

pb_guy   Offline
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Not an engineer, but for the 3-D structure, in order to be effective, the angle from top of rib to bottom of the next rib would likely have to be at least 15 degrees to have any appreciable affect on stiffening. I just use an I-beam spar for that purpose. But the X-structure for the ribs adds a lot of stiffness.
ian
 
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Reply #1 - Nov 4th, 2019 at 3:55pm

Sky9pilot   Offline
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Not an engineer by any means, but couldn't resist throwing in my "2-cents" worth.  The blue and green lines show a partial "truss" style with the blue giving you some 3D effect.  The black lines give you the full "truss" build techniques with the complete 3D effect.  If you're going to add balsa to the wing to avoid twist I'd go with the black lines.  You do realize that the drawing shows a full spar and your Cessna doesn't have a full spar but just an upper spar of 1/16" sq balsa if I'm correct. I think an additional ventral spar will add some twist resistance.  You might even include some shear webs from the middle out to the 3rd or 4th rib on each side for strength...but that's really over kill.  Our senior modelers before me (that makes them really seniors) were able to make em fly with just the upper spar and strong leading and trailing edges... Roll Eyes Shocked Wink
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Nov 4th, 2019 at 12:07pm

alfakilo   Offline
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Here's a question for the structural engineers in the group!!

I'm considering adding some 1/16" stringers to a very basic wing structure, the idea is to 'stiffen' the wing a bit to resist twisting.

In the attached pic, the blue stinger runs from the top of one rib to the bottom of the adjacent rib (three dimensional). The green stringer shows a stringer running from the bottom of one rib to the bottom of another (two dimensional).

Does the 'three dimensional' arrangement provide more resistance to twisting than the 'two dimensional' arrangement?

Should the stringers be placed in a 'W' (sawtooth) arrangement, or should they be placed parallel to each other?

Or should I use some other design?
 
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