What's up with these webless ribs?

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David Teahay

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Hi,I have seen a number of ultralights with wings whose ribs don't have webs e.g this Affordaplane:
I once learnt that the webs in wing ribs help to transfer shear forces as well as wing loads on the wing skin to the spars,so my question is how will these "shear forces" be transfered from the skin to the spar when the webs are absent.
Ps:1.wing ribs with webs⬇
https://www.google.com/search?q=wing+ribs&client=firefox-b-m&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi7p4_j0sjiAhUQQxUIHVDBCq8Q_AUIBigB&biw=320&bih=489#mhpiv=16&spf=1559404647211

2.wing ribs without webs⬇
https://www.google.com/search?q=webless+ribs+for+ultralights&client=firefox-b-m&source=lnms&tbm=isch&sa=X&ved=0ahUKEwil9PnmycjiAhUsVBUIHbP-Cg8Q_AUIBigB&biw=320&bih=489#mhpiv=11&spf=1559402215850
 

bmcj

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Since the leading and trailing edge tubes ARE the spars, the mechanical connection provides the load transfer. With compression struts between the spars, the fabric also becomes part of that transfer mechanism.

I’d still like to see a tie-strap mid-rib between the upper and lower surface, but it’s technically not needed.
 

flyboy2160

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Just a different explanation: Think of those laid down D shapes as bridges that have loads on their tops and bottoms from the air pushing on the fabric. This load is taken by internal bending and shear of those pieces of the D. It's the situation of a 'normal' rib with lots and lots of material removed - like it had REALLY big lightening holes.
 

Tiger Tim

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Can’t anyone comment on those aluminum rib attachments at the leading and trailing edges? I like them but can they be expected to work well?
 

bmcj

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I finally watched the video again and realized those rib ends are of his own creation. I also found examples of Afford-a-Plane builds with aluminum ribs, truss ribs, and even foam ribs.

As for the purpose of the plates, They are mostly a different way to attach the ribs to the spars without using the molded plastic joiners.

C515447C-9C5D-41A8-8460-877CBAC03445.png 1255884B-A1A6-4234-9C90-DF8FBFA68CA4.jpeg

I think the plastic provides a guard against abrasion... I hope his plates hold the ribs firmly enough to keep the tube ends from scratching the spars. One thing about his that I do like is that he drills and rivets his holes along the zero-load line of the spars.

Is all of that necessary though? Remember that many ultralights have no physical attachment of the ribs to the spars. Instead, the (sometimes) shapes ribs simply slide into a pocket in the wing’s fabric and float above the spars. The fabric does all of the lift load transfer to the spars and the compression struts hold the spar spacing.
 

bmcj

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Interesting but it looks like they put a rivet close to the top of the front spar. Not sure about that?
You can get away with that if it is near the wingtip, but it’s not a great idea if it is onboard where the bending loads are greater. As I mentioned earlier, it’s better to have your holes along the zero-load line.
 

poormansairforce

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You can get away with that if it is near the wingtip, but it’s not a great idea if it is onboard where the bending loads are greater. As I mentioned earlier, it’s better to have your holes along the zero-load line.
Thats why I pointed it out, they are on every rib and not on the zero load line.
 

Dillpickle

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Can’t anyone comment on those aluminum rib attachments at the leading and trailing edges? I like them but can they be expected to work well?
Here is
Can’t anyone comment on those aluminum rib attachments at the leading and trailing edges? I like them but can they be expected to work well?

Here is a vid By Dick Starks of the Dawn Patrol showing how Robert Baslee does it on all of those UL and replicas he builds. They have a pretty good rep and a long history.
 

bmcj

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Thats why I pointed it out, they are on every rib and not on the zero load line.
No worries... I knew that was the point you were making. ;)

But there are designs that drill into the top and bottom of tubes, even to put a vertical bolt to hold the tang for the flying wires. I always wondered about those, bu assumed they had a doubler tube inside.
 

BBerson

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In the first couple of minutes you can see the top rib cap has a rivet holding it to the spar and its not on the neutral axis. If I see it correctly....?
Right, I see it now. Probably could delete that one like he did at the trailing edge. Or wrap a small gusset and put the rivet on the neutral axis.
 
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