Understanding Wing Technology

WOW!

What great video Doug.

I had a DN (Detroit News) for three winters on Ghost Lake Alberta Canada in the late '80's.

Brings back memories, BLADERUNNER, 195 pounds plus 170 pound pilot.

FAST!!!! FUN!!!!

 

one more good news from herusails.it
the soft wing sail for A-Class
www.herusails.it

 

one more good news from herusails.it
the soft wing sail for MOTH

www.herusails.it/soft-wing-sail-for-MOTH.html

 

I thought about starting a new thread, but this really fit here pretty good.

I am trying to take the "state of the art" concepts provided by Steve Clark & Blunted and work out best practical "low budget" build technology. I have also posted over in the SA "Wing Study Plans" thread with the following:

I am trying out some build techniques that I hope will result in a functional wing.

First effort will be just a 16' constant cord section with the tapered top section put off until I am sure I have a bottom section that is worth extending. Stays will run all the way to the top and with a 16' length, I can put my Hobie 16' jib in front of it if I want.

I will go for a cord close to 85% of the study plan as best I could scale it (2' 10.25" element 1, 2' 1.75" for element 2).

For the outer surface of the structural D on element 1, I am pretty sure I can make "flat panels" of an outer 3.6 oz/sq.yd. fiberglass skin on thin strip cut wood initially laid up on plate glass and then wrapped around ribs spaced 1' apart.

I am struggling with D section shear web design at the moment. I did a wild estimate of loading and decided to plan for a max of 16 lbs per linear foot. I have a spool of carbon tow and have considered using this to re-enforce a wood truss made of 1/8" x 3/4" long strips, 1/4" x 1/2" verticals (back element of the nose section ribs) and 1/8" x 3/8" diagonals. Alternately, 1/16" ply could be used, but I worry about both weight and strength.

If anyone else has started (or finished) a wing using the stuff that Steve and Blunted have posted, it would be great to share thoughts and ideas.

 

Reinforcing wood with carbon tow looks good on paper. The big problem is that it's very prone to local delamination failure and buckling of the tow, unless the tow is held down with a class or carbon cloth wrap.

I suggest you take a look at the wing of the Carbon Dragon homebuilt ultralight sailplane. The sparcaps are bundles of pultruded carbon rods, which have very good material properties which are REALIZABLE with practical construction methods. Typically the sparcap rods are wrapped with glass cloth which also forms the shear web load-carrying material.

For torsion the Carbon Dragon has a thin plywood D-tube. I think it's wrapped with +/-45 fiberglass for durability, but I'm not sure.

 

wing build

Hi Flados - stay away from using tow. its too fiddly and unpractical. I suggest you study up on how metal airplane wings are made. Plus get into infusion. All of your structural elements can be made from glass fibre infused material. Simple mdf forms can be used for moulds and all of these can be rivetted together like the aircraft wings. If you rivet it together it becomes servicable when things break. I personally think that the current construction methods of C class and AC wings can be inproved greatly. Wings can be made like hang glider wings with no internal structure. The way C-class and AC wings are made using sandwich construction is conveinient but structurally incorrect as sandwich concept is best for out of plane loadings in flexure yet ribs are in-plane loaded. The arial weights of hang glider wings is sma eor lighter than c class wings and their loadings are similiar therefore I believe the technology is transferable. Cheers Peter S

 

You can calculate your average mast load from the righting moment. From Rm calculate heeling force then distribute that over the spar to give the same Rm. Then multiple by SF to create the design load. This is a simple starting point. Peter

 

I suggest you look at some books on homebuilt aircraft construction. After all, the homebuilders have been building economical wings for a long time! I think good ones would be "Low Power Laminar Aircraft Structures" and "Low Power Laminar Aircraft Technologies" both by Alex Strojnik. In one of them (I don't remember which), he describes a method for making a wing using fiberglass skins.

The technique involved making a male mold of the section from the spar forward, and about 1.5 m in span. Fiberglass skins were laid up on a sheet of glass and, when the resin had kicked to the rubbery stage, were draped over the mold. A plastic sheet was draped over the skin and weighted from the bottom edges to hold the skin down. The skin acquired a smooth finish from the glass, so it required very little fairing afterward.

He went into production with these skin segments, producing enough to do the constant chord section of his wing, which was most of the span. The skins were but-joined together over box-ribs. The box-ribs consisted of two half-ribs with a cut segment of wing skin between them. This acted as a doubler over the butt-joint between the outer skin panels.

The straight part of the skins that originally hung below the male leading edge mold were long enough to go to the trailing edge of Strojnik's wing. The curvature was low, so they could simply be bent together around the ribs to the trailing edge. Unless you were trying to create an Aethon-style solid skinned wingsail, I don't think you'd want to do this. But Strojnik's technique could be a good way to produce the D tube.

Strojnik was in favor of using aluminum extrusions for his wing spars, along with the glass skins. I think you could use something lighter for a wingsail spar. You may be able to find an off-the-shelf carbon beam that would be suitable, or lay up one yourself.

The part of the wing behind the spar would be built-up construction, similar to a homebuilt aircraft or model airplane. Shrink-wrap packaging material from Clysar is used as the covering for the AC45s. Clysar has a range of material weights and shrink characteristics to choose from. Just be aware that the tension from the film shrinking may be the most stressing load on your structure - more than the airloads from sailing!

 

Mark,

I very much understand the buckling concerns. I feel that when using carbon tow, it needs to either be a major item with lots of carbon, or as re-enforcement where the application is limited to mostly tensile loading. For example on a truss beam with a X pattern of diagonals, there will always be one in tension that can carry the load.

Peter,

I did use righting moment. However, it does not consider dynamic loading. A gust will generate much more force (and roll acceleration) than the stead state loads. I am leaning towards a 1.5 X safety factor to address the dynamic component. Also, there is more than a little uncertainty on the righting moment given the most likely initial platform (Hobie 14) would just be an interim step to a boat built for the wing.

Tom,

The Homebuilt airplane stuff is indeed great and much of what they do has influenced my choices. However, for the typical homebuilt airplane wing, the safety implications have resulted in designs that are very very strong and rigid with much more weight than I would ever consider for a boat. As far as Alex Strojnik, a previous discussion of his methods is what made me to think of a flat initial layout. I did a test section of just glass and it was not nearly stiff enough. If I add thin strip cut white pine (1/32” thick close to the front, 1/16” thick where the bend radius is less tight) behind it, I should get a more reasonable stiffness without too much weight. I would really like to do most of the rest of the wing structure in the “stick built” methods I used in my model airplane days as a kid. I have built the 17 “nose ribs” this way and without being picky with my wood I still kept the total to less than 1 lb.


General:

This build is really more about getting the best result possible without carbon cloth, carbon tubes, engineered foam and vacuum infusion. Properly used, these materials and methods make great wings. However, unless you are already good at mold making, vacuum infusion etc, (along with having the shop space and tooling) you are sure to spend a ton on the materials with no real assurance of super performing wing at the end of all of you effort. This combination is a big barrier to most garage builders. If a decent wing can be made with stuff more in the “Average Joe” garage builder comfort zone, many would be more interested. If a less expensive first build wing proves to be worth using, then the builder can consider an upgrade to the better stuff.

 

Hello Flados - If you need to stay in the realm of average Joe's garage then you need to investigate aircraft plywood and perhaps double luffed soft sails vs wings. Its unlikely Joe will get to a satisfactory weight and performance without using "advanced" materials in a "proper" wing. Thin Sheet metal aluminium will outperform hand laid fibreglass and poorly built carbon. Ply and timber are satisfactory materials if they are used within their limits. You are going to have to buy high modulus materials vs trying to make them. eg fibreglass battens, aircraft ply, pultrusions, thin aluminium. If you can post a quick dwg I can help with the structure if you like. I think you would find the dynamic loading to be quite small on a Hobie 14 rig, I think the gust load would be the biggy. If you used a x1.5 on static and did a good engineering job on all components I think you would be fine. The problem is determining the mechanical data on many of the materials you, me and others have mentioned. Over the years I have had all of these tested for different projects so have a good idea of what can be acheived. Every design has to be considered on a boat by boat basis to acheive reasonable weights so you either need to forget about the "next" boat and build for the Hobie or decide on the next boat and then compromise the design between the two. Cheers Peter S

 

You are exactly describing the rationale behind the Carbon Dragon sailplane. It was intended for garage builders with no special molds or tooling. Still, it has an amazing strength/weight ratio rivalling or exceeding fully-molded sailplanes. It has a 13.5m span and an empty weight of only 145lb. Compare this to a typical 15m molded sailplane which weighs roughly 350-500lb empty.

And I think you are too quick to discard pultruded carbon as a spar material. For a required tensile or compressive strength, pultruded carbon is actually CHEAPER than aircraft-grade spruce, because you need so little of it. From the Aircraft Spruce catalog, I get the following:

0.158" CF rod: $1.50/ft, 0.014 lb/ft, 5880lb max comp. load (300000psi)
1"x1" spruce: $2.35/ft, 0.174 lb/ft, 5600 lb max comp. load (5600 psi)

So for a given strength, the CF is 60% of the cost, and 13x lighter than spruce. And it won't mildew or rot. Seems like a no-brainer.

 

Hi Mark - I'd knock down the 300ksi (2000MPa) a bit on that carbon once its in a bundle. Std Cf has a modulus of 235GPa so a pultrusion at Vf=0.6 has a modulus of 0.6x235=141GPa and in direct compression may get to 1% strain so its best stress at failure is 0.01x141=1410MPa which is a bit short of 2000MPa. Even at Vf=0.65 its a bit short of 2000MPa. But its still miles ahead of spruce. Is it intermediate CF? Just looked at some test data and probably could get strain at failure to 1.3% which just scraps in. Cheers Peter S

 

The CF solid rod does look good if you can figure out how to use it.

One problem with CF solid rod is integrating into the remaining structure. For small parts, the rod will usually be passing loads to a distributed surface. Unless these are also strong CF, the load capacity of the rod can not be fully utilized.

For longer items, you get back into buckling. This is why CF tube is so much more popular for engineered structures.

My concept for the nose section is to try to leverage as much as I can off of the strength of the “skin” surface. At the back where it ties into the shear web, will be 1/8” x 1.5” wood under 3.6 oz fiberglass.

 

I think this answers most of these concerns:
www.carbondragon.us/builders_manual.doc

 

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Mark, any chance of you converting that to a pdf-I can't so if it's not too much trouble I'd sure appreciate it.