Cantilever Internal Braced Fabric Covered Wing

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wsimpso1

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was thinking of saving a little weight on the drag-anti drag wires (double drag wire system). Talking to Piet builder today ..... the compression ribs on it are top and bottom 1x1 wood......because of the geometry of my design which is the same as the one that failed .....any D-nose style torque prevention is lots of skin and weight .... Were the wing location and geometry different from the start it might make sense but this is the last piece of the puzzle and I am locked into certain geometry........ though is to have total internally design/braced for all loads and fabric cover. I currently have a preliminary designed cantilever spar of 15 lb.....5.33+ G limit.... one issue is there is only so many thickness of material .....another argument for composites as one can tailor the thickness.
Look close at what your attachments and fittings weigh. Dyneema will stretch when left tensioned. On sailboats it is slacked when not sailing, and tensioned when it is time to sail. Whether you leave it tensioned or slack it when parked, you will need hardware that allows you to make these adjustments.

Are you trying to get torsional stiffness with Dyneema cables inside the wing? I want to see how that is done.

Billski
 

WonderousMountain

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21st century Stubby Guppy is retaining the Anti-Drag/Rack system of the original, I do not see a reason to use internal rigging, synthetic wire. It's getting a Box Beam also, which Subs in for the Spruce Plank spar. However, a torsion Box, is probably worth the few pounds of ply required. It sounds bad to say 15% heavier, but three pounds doesn't incense. If you are using a Double spar that could work. The guppy web is 84mm metric, not deep or heavy enough to freak out about. Note, my spar weight is under original.
Screenshot_20211121-162055_kindlephoto-1606669.png
Screenshot_20211122-123217_kindlephoto-7722940.png
Added the Interplane strut sketch.
Note how top & bottom are bound
together.
 
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proppastie

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Are you trying to get torsional stiffness with Dyneema cables inside the wing? I want to see how that is done.
we/I are still in the concept stage here but this is a picture of the Piet compression rib with wires (perhaps or not Dyneema) ...It looks like the compression members could be attending to the torsional stiffness issue. .....probably less weight ( working today on the whole wing setup) than a box spar. Controversy with Dyneema....one has said once it is stretched to to tension (a percentage I need to find) that it does not creep more....not sure if that is right......might run some tests

compressionstrut.JPG
 

proppastie

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On sailboats it is slacked when not sailing, and tensioned when it is time to sail.
they are using it on mast main support wires for big boats......I can not imagine adjusting every time they go out,....but really do not know.....if that is the case then it certainly would not be suitable for my needs...link?
 

challenger_II

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The compression members do not add substantially to the torsional stiffness: the angle is too shallow to be of much effect.

For what you wish to attempt, a D-Cell front spar, tubular spar, or a Box spar, is your best bet.
If you build your wing with too low of a torsional stiffness, you may find that the ailerons will act more like trim tabs, causing the wings to twist under flight loads, causing a control reversal. Food for thought.
 

proppastie

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The compression members do not add substantially to the torsional stiffness: the angle is too shallow to be of much effect.
would that be a strength issue of the compression members?....in other words if there was enough strength in them it would work?
 

proppastie

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one thought as the Dyneema is very light.....having 2 lengths top to bottom at each compression rib for added strength....(if it did not creep when sufficiently tensioned)
 

challenger_II

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Angle is the critical issue. You are looking for a vertical stiffness from a narrow horizontal column. The center of the twisting action is the forward spar, and the vertical force is well aft of the forward spar.


would that be a strength issue of the compression members?....in other words if there was enough strength in them it would work?
 

TFF

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The compression ribs just keep the spars spaced so the wires can do their job. They don’t do anything else. The Starduster series use a zigzag of tubes. Compression tubes have a drag/ anti drag tube from drag spar to main spar. 3or 4 sets across the panel.
 

Vigilant1

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they are using it on mast main support wires for big boats......I can not imagine adjusting every time they go out,....but really do not know.....if that is the case then it certainly would not be suitable for my needs...link?
Some posts on Dyneema/similar creep:
simple retractable landing gear
(See several posts in that thread, search term "creep")
Post 23, 24, 26, 31, 45, 84.
 

proppastie

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all aircraft will deflect/twist under load.....any good thoughts on how much is too much....same with torsion?
 

challenger_II

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Well, you know when you are one the edge when you give right aileron, and the plane rolls left...
The Air Tractor wing, which is a metal frame, metal clad, cantilever unit, will flex to the point of the skins wrinkling very noticeably when banking for the turn. Is rather uncomfortable to watch. And, that wing cell is a BSH structure.

One method of wing structure that hasn't been been mentioned is the Geodetic structure. Think "Fisher Flying Products" and Ritz Model A. Before folks jump in and point out that those were strut-braced machines, bear in mind that there are several cantilever-winged aircraft that utilized the geodetic structure. Vickers Wellington, and Wellesley come to mind.


all aircraft will deflect/twist under load.....any good thoughts on how much is too much....same with torsion?
 

proppastie

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some more still digesting.......apparently there is experience out there for main stay rigging
 

proppastie

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I am wondering if the creep is a problem with tensions as shown below for a Stinson when wires/Dyneema are properly sized.

192-Stinson-drag-wire-tension.jpg
 

wsimpso1

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If you build your wing with too low of a torsional stiffness, you may find that the ailerons will act more like trim tabs, causing the wings to twist under flight loads
That would make the trim tabs into servo tabs. Might as well hook the aileron controls to the the trim tabs instead. Sorry, being facetious. Soft in torsion is bad as you can get into whole wing flutter pretty easily...

Colligo Dux sounds like great stuff. The caution to oversize in order to get enough stiffness really needs to be listened to here. Using it inside a wing, you need to size it to be as stiff as traditional steel. Match or exceed EA of the steel rod that would be there instead.

Sailboaters have historically eased tensions on standing rigging when not sailing. With aluminum masts and steel standing rigging, fiberglass/polyester hulls slowly get pulled out of shape if rig tension is left on. Many keelboats used to get rig tension from a hydraulic backstay. Yep, a tension cylinder with a hand pump and both a length gage and a pressure gage to allow repeatable settings. Similar things are being done at the gooseneck and boom vang. Most centerboard boats tension the rig with things like a block and tackle on the forestay (in the jib) or running the forestay through a pulley below deck and aft to an overcenter latch. Tension that can be eased is not impossible, but it might need pulleys at each direction change so you tension them all together instead of tightening one then the next through the whole system. That all adds up, maybe to the point of steel looking light. With Dux though, maybe the stretch has gotten small enough that you could use it inside the wing with only an annual check and adjustment on the tension.

Billski
 
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