Yes, but will it stall?
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The Paper Aircraft Released Into Space (PARIS) team has spent the last couple of days working on a definitive Vulture 1-X wing structure, having already tried and rejected a few options. Naturally, we took on board all of your suggestions as to how we might go about making an aircraft wing entirely from paper, and reckon we've …
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I was pleasantly surprised that what popped into my head was in fact what you were talking about, good luck with that! especially keeping a long wing from warping even with all those cross-struts
Are you planning on any tensioning of the wing?.
I'd imagine the real stresses are in the wing roots. What ideas do you have to ensure the wings don't come over all origami on you? Is a piece of balsa box section throuhg the fuselage possible?
..build a straw man to put inside the craft?
would probably approve as you seem to be making a geodesic wing. Although possibly not intentionally...
This project is rather awesome.
From my Keilcraft days: I never saw diagonals inside the wings. When you skin it over it has pretty much the same effect.
There was usually a trailing edge though - maybe a double layer of card?
Rather than the diagonal bracing tubes in compression, why not diagonal bits of cotton thread in tension? That would be much lighter and be able to handle much the same by way of forces.
A leading edge profile and a trailing edge stiffener would be normal - perhaps a horizontal bit of card of the same material as the ribs, slotted into the trailing edge? and three slotted radially into the leading edge?
Imagine Lester as a Blue Peter presenter.
There'd only be one episode before the broadcasting licence was revoked, the BBC complaint line would be in melt down and a whole generation of kids in therapy - but it'd be awesome.
I don't think you'll need so much cross bracing - the paper wing surface should act as a monococque to keep the ribs from moving.
I can't help wondering if making the ribs out of several sheets of paper laminated together (or some stiff card) would be lighter/simpler than adding all that additional bracing to get round the rib stiffness problem....
Quick suggestion if I may? You've far too much going on inside that wing...
Keep the ribs, but make the holes fit the wing beams rather than flapping around them. Make the ribs thicker - three or four sheets glued together - they'll need to survive compression from the surface materials but once that's fastened on it'll remove the need for diagonal bracing. Sheet the leading edge - as you have done - but consider just squashing one side of the rear straw to make the trailing edge.
Then sheet with tissue, shrink, and dope... pinning it in place to keep the shape while the dope dries/shrinks.
What size is your planned wing and overall plane? And your overall weight?
Did you say where you got your straws? I'm tempted to play - I'm building a balsa wing today.
What is going to be the wingspan?
I'm a bit pessimistic about paper straw spars bearing the load of a cantilever high aspect wing...
Also, I think that even the tailless scheme like that of the Horten will spin on release due to low density of the air at high altitude and it will add to the stress when the plane will descend into lower atmosphere layers.
Maybe a delta wing with a keel or a tail fin (like an origami paper airplane) would be more appropriate?
From my experience of building balsa and tissue wings, I heartily endorse everything that you suggested. In particular loosing the internal bracing & relying upon the ribs.
What Tim said plus:
Double the leading edge covering and/or use cartridge paper. Same goes for the ribs. Move spars two and three so they are one above the other at the thickest part of the wing, glue the LE shell to the top and bottom spars and glue equally thick material onto the back of the spars to give a closed D-box structure. You'll be surprised at the increase in stiffness and strength.
It may pay to double up on thicker ribs too: I like the ribs to be spaced apart around 0.2 to 0.25 of the wing chord. This gives a nice, strong wing.
The trailing edge will also need attention because I'm doubtful that one will survive covering and doping the wing. Do cover the existing structure to see if I'm right about this.
Last but not least, I agree that you'll need a jig to assemble a wing with that fancy section. I'd use the good old Clark-Y section myself: its thicker, so can be made stiffer for a given weight and, because its flat bottomed, can be assembled in any flat surface.
Can we see a plan of the Vulture-1 please? Talk of high aspect ratio makes me uneasy. I wouldn't go as far as building a delta design, though I like the idea, but I think an aspect ratio of no more than 5 to 6 will be enough, and will go a long way to solving the problems of wing strength and stiffness at the initial high altitude and high flying speed. If you use a low enough aspect ratio you may even be able to get away without the struts.
Yes, I know following myself up is bad form, but...
The reason I go on about stiffness is flutter, which can destroy a wing very rapidly. Flutter depends on structural stiffness, the structure's centre of mass and true airspeed (TAS), while lift and flying ability depends on indicated airspeed (IAS). The two are the same at sea level, but as you go higher at a constant TAS the IAS drops. The consequence at extreme altitudes is that the plane's stalling speed may exceed the flutter speed and it will disintegrate before its going fast enough to fly.
To prevent this you need the wing to be as torsionally stiff as possible. A low aspect ratio and a closed D-box from leading edge to max wing thickness both help. Having the structure's balance point in front of its twisting axis prevents flutter: if the wing CG is in front of its twisting axis it won't flutter at any speed, so using a good, stiff closed D-box containing the spars and leading edge, putting the spars no further back than the maximum wing thickness and using as little structure behind that as possible are all good.
Something else that helps is to know that using a thick trailing edge has very few bad effects. You gain little but a weak structure and weight from a knife-like trailing edge. Many successful rubber powered competition models simply use a strip of 3mm square balsa for the trailing edge. Two regular drinking straws one in front of the other and tacked together with minimal glue would be a good starting point for a light, strong, blunt trailing edge.
Not only the articles, and the project itself (which I have to admit I never thought would get off the ground... er, get this far), but also the reader comments.
Thank you very much for both the project and the write-ups.
Cross-struts are nice, but much of that will be done for you by the paper glued on the outside. Think monocoque.
The *REALLY* important bit is that the wing holds its profile. That means not buggering about with thin flimsy ribs doing sod all. Glue a paper tube around the outside of each rib to make it hold its shape, and you might be in business.
You also have a major fail if you're trying to keep the same profile all the way along the wing. Look up "washout" and why you will if you don't have it. (Short answer: Your aircraft won't recover from a stall without it.)
>> You also have a major fail if you're trying to keep the same profile all the way along the wing. Look up "washout" and why you will if you don't have it. (Short answer: Your aircraft won't recover from a stall without it.)
Not correct I'm afraid. Washout isn't required either to avoid entering a stall/spin or to recover from it. What it does do is to give you 'pilot friendly' stall characteristics by making the wing stall progressively from the root outwards - thus giving you a loss of lift while still retaining control from the unstalled outer wing and aileron. In this configuration, even relatively unskilled pilots can detect the onset of stall and deal with it. Eg, typically a PA28 will mush but remain level in the stall as long as you keep it in balance.
By contrast, with no washout, the entire wing may stall at once, or it may stall from the outer end where the loss of lift has most effect in roll. Unless both wings stall simultaneously (unlikely unless very accurately aligned and flight conditions are just right), then the result is that the onset of stall is marked by a wing dropping without warning. The natural reflex is to use aileron to try and hold the wing up, but that just makes it "more stalled", and before the pilot knows it, he'll be in a spin.
'High performance' aircraft tend to have little or no washout - because the designer is looking for every last drop of performance and assumes a skilled pilot. Washout reduces the maximum lift available from a given wing because you will reach the stall at the root before reaching maximum lift at the tips.
And yes, I've just done the mandatory spin exercises in a glider that just **loves** to spin. But I made sure I did it before lunch ;) In this case, in an IS28 - it doesn't mush, it just turns over very quickly (followed very shortly by my stomach !).
How does compressed paper sound?
Make the ribsout of compressed paper, (like the cardboard boxes you get routers packaged in?
they would be stronger and if hand made with paper mush and a press you can make your own stiffer ribs, Paper is good but how are you going to make sure that the paper for the wing covering is tight, for model plane makers they use solarfilm which shrinks when heated, is there maybe some solvent which would make the paper shrink? or what if it was put on damp so it shrinks when drying?
I think the spars could be made much more rigid if you can contruct them like hollow-core doors. In the states, these are made of thin layers of lauan plywood with cardboard disk-like cylinders (similar in shape to tuna cans) inside all glued up together in a honeycomb fashion. Honeycomb lattices are commonly used in composite structures to make them extremely lightweight and rigid. If you can cut them uniformally, this could be done with the paper straws.
Sorry, got my terms backwards - use honeycomb lattice inside ribs.
I'll get my coat now, obviously had enough thinking for the day...
... on those gluelines ;-)
It's not like that hotmelt glue weighs a lot or anything :-D
Those diagonals look like they're only going to concentrate the stresses. There is no diagonal bracing between the two inmost spars, that's where the torsional stresses will end up.
You solved the wing issues! For a moment there I thought you had... well, just don't put the words 'cracked' and 'wing' in the same sentence.
Either way, keep up the good work!
Also: any plans on testing these wings in an air tunnel?
By the time you're done the weight will give you a glide path better described as the "vertical plummet".
You're over-thinking the problem.
Instead of gluing in strut after strut, consider that the paper skin itself will do much of the work of holding the spars in the proper place. Add temporary spacers and alignment blocks, add glue tabs to the aerofoil ribs and glue them to the bottom surface paper. Then carefully draw the paper over the nose of the wing and glue. Finally, remove the temporary spacers etc and glue the top surface down.
Hey Pasta! Instant (well, nearly) monocoque wing.
I dunno what they're teaching in schools today, no hope for nation, dropping standards, ASBO youth culture etc etc etc
Major Stevie (Mrs)
Can I repeat my earlier plea for some idea of the dimensions and weights of PARIS? We've got a vague idea from the previous examples, but no more than that... and it's kind of hard to advise/comment without knowing!
I roughed out a wing last night which I'll try and build when I can get the materials, which I intend to stick on a small two-channel RC model and see what happens. I'm using a flat-bottomed wing with dihedral tips, sixty inches or so across the span and about six inches on the chord.
Paris, because I know she'll be thinking about it. Or something.
I'm even learning stuff too. :-)
and most of that is glue
The material you are probably going to use on the skin will have close to zero compression strength. It will have a relatively good tension strength.
It means that the major strength should be in the spars and to a smaller extent in the ribs.
The best tubular spar would be the entire wing thickness at the maximum height of the wing.
Your multiple spar is heavier than it needs and not as strong as it could be.
A better design would have a built-up I-beam main spar with laminated paper sections increasing in number / thickness as you get closer to the wing root. This provides compressive and tension strength
A secondary trailing spar of similar design - but smaller - is required. Then a strong doped paper skin will provide tension to stop wing fore and aft flexing.
Overall resistance to skin distortion is set mostly by by rib spacing, not so much by rib thickness.
A rib thickness about the same as the skin thickness will work well. It just needs thicker and thicker spar-caps closer to to aircraft - and ribs should be closer together there as well.
OK, not fully correct - but AFAIK there isn't going to be a pilot sitting in this! Sure, if there was a control system onboard with 3-axis authority, the control system could be programmed to do this too. But we don't have that either.
So unless you've got a wing which is self-recovering (which means washout and dihedral), this beastie is going to fall over rather badly when it gets in even the slightest bit of chop. Like a previous poster, I'm thinking Monty Python sheep here for flying characteristics...
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