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Rib Thickness and Spacing

Old 02-13-2004, 01:37 PM
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SeditiousCanary
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Default Rib Thickness and Spacing

I am designing a 2M sailplane which I plan on using built up wings, which leads to my two questions.

How far apart do you guys usually space ribs for a thermaling HLG?
How thick do you usually make the ribs for such a plane?

Currently, I have them spaced every 2.5 inches with 1/8" thick ribs on the inner 19" section and every 2 inches with 3/32" thick ribs on the outer 19" section. Do you all think I can go thinner on ribs and space them further apart?
Old 02-13-2004, 02:08 PM
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Tall Paul
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Default RE: Rib Thickness and Spacing

What's your structure?
A sheeted leading edge can get by with more space between the ribs, as the airflow is better controlled, and the structure is stiffer, than sticks and spars, with the turbulence creating spars and covering sag between the ribs.
The ribs provide torsional stiffness as well. Too few on a stick and spar wing limit its useful speed, lest it flutter in a dive.
BTW Joe Wurts can handlaunch a Paragon (114") stick and spar plane, with wide rib spacing. Few of us mere mortals can do that!
Old 02-13-2004, 02:16 PM
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FHHuber
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Default RE: Rib Thickness and Spacing

Halve your rib thickness... you got it WAY too heavy. If you want you can take 1/32 ribs.. cut lightening holes and then cap strip with 1/32 X 3/16 strips. (strong and light with good area for covering adhesion)

You can space them a little further apart.. up to 3 inches for a light 2 meter airplane which will never be expected to fly fast.

Look up the Goldberg Gentle Lady. look at some pictures of that plane done in transparent... the ribs are 1/16 sheet. If you choose the balsa well and cap stripped... you could use 1/32 sheet for the ribs and come out lighter and stronger. ( a lot more work to builtd it...) I sanded the ribs of one Gentle lady kit to thin them to 3/64 on the outer panels and the ribs were still plenty strong with lightening holes drilled in them.
Old 02-13-2004, 03:41 PM
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SeditiousCanary
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Default RE: Rib Thickness and Spacing

Ahh, right. Additional useful information...

I plan on 1/32 balsa or 1/64 ply sheeting up to the top and bottom spars, using 1/2" square stock as a leading edge (though I am now thinking that may be too much) and 1/2" trailing edge.
There will be ailerons, flaps, air brakes (string pulled types) and missle racks (or not).
I plan on winglets, but I have no idea what I am doing there yet. I need to read up on them more.
I have no objection to cap straps, but no real plan for them either.
Shear webs are a must and are slated to be 1/16" balsa.
I plan on a paper and dope finish because I don't own a regular iron, let alone a covering iron. Besides, I'm old school.
Old 02-13-2004, 04:17 PM
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Default RE: Rib Thickness and Spacing

Yes the 1/2 inch LE is WAY heavy. 1/4 square on corner so you just have to sand off one corner to make it rounded. OR... slightly smaller and you overlap the sheeting on the LE instead of butting it to the LE. (the latter is stronger)

The TE... again, look at the Gentle Ladys... its about 1/4 thich at the forward end, and tapers to 1/16 over appx 1 1/4 inches. (always a good idea to compare structure to a proven design)

I would consider the 1/32 cable wire-in-sheath for your "string pull" systems... this gives a positive push for closeing the spoilers with minimal added weight. This stuff comes in a 10 ft or even a 30 ft coil package by Sullivan with some 2-56 threaded brass tube ends to solder on. Its useful for any control surface on a slow flying 2 meter aircraft. (I used this stuff for operating the flying stab on a 140+ mph 1 lb ridge racer... Good stuff. )

Its very hard to come out as light with dope and tissue as you can come out with Econokote (or Towerkote) These can easilly be applied with a common travel iron (about $15 new... $1 at garage sales) Yellow is a heat guide color... when it is ot enough to give maximu shrinkatge... it turns bright orange. (returns to yellow as it cools) NEVER go hotter than that... as it will melt. (that works for MonoKote too ) This would be cheaper (with Towerkote at about $6.50 a roll..) than you could buy the Dope for. About 10% as much labor... as painting... Its just hard to justify using tissue and dope on a 2 meter plane.
Old 02-13-2004, 04:48 PM
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SeditiousCanary
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Default RE: Rib Thickness and Spacing

ORIGINAL: FHHuber
very hard to come out as light with dope and tissue as you can come out with Econokote (or Towerkote) These can easilly be applied with a common travel iron (about $15 new... $1 at garage sales) Yellow is a heat guide color... when it is ot enough to give maximu shrinkatge... it turns bright orange. (returns to yellow as it cools) NEVER go hotter than that... as it will melt. (that works for MonoKote too ) This would be cheaper (with Towerkote at about $6.50 a roll..) than you could buy the Dope for. About 10% as much labor... as painting... Its just hard to justify using tissue and dope on a 2 meter plane.
One flaw with this idea. If I had an iron, my wife would expect me to use it. I also really like a clear dope finish over white SilkSpan. I'll sand between coats and get a glass like finish in it. I'm a freak with some 600 grit and a sponge when it comes to finishing stuff.
Old 02-13-2004, 05:19 PM
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Default RE: Rib Thickness and Spacing

ORIGINAL: SeditiousCanary
If I had an iron, my wife would expect me to use it.
LOL I stand corrected

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