Understanding Wing Technology

PDF attached. The figures got rather ratty, unfortunately.

 

Mark, I appreciate it-thanks!

 

The manual is helpful but also more than a little hard to understand at times.

As best I could figure, a lot of the structural loads are carried by carbon tow laid up in wooden members.

For smaller items (rib strips) it is simple, for example tow laid up in a 3/32" x 3/32" groove cut into a 5/16" square section piece of wood.

For the main wing spar, the carbon it is a complicated variable cross section arrangement on sides near the top and bottom edges of 1/32" plywood 22' 3" long by 7½" wide. The end product being a 5/16 square wood center surrounded with carbon tow all inside a wood channel formed on one side with the 1/32" plywood as the base and two 3/16' wood strips to form the sides of The "box" that is filled with the tow and the center wooden "plug".

Trying to describe it in words is kind of tough, and the manual only had just enough hand sketches to aid assembly. The rest of the detail is probably in the drawings.

 

Flados - when you say 3.6oz fibreglass what do you mean? Plus can you also quote in g/m2 as this is what I'm used to. Is the glass woven, multiaxial, double bias etc etc. hand laid or vacuum bagged etc. If its woven or CSM and hand laid you may as well use more timber as the glass will be heavier and less stiff then the plywood. etc etc.

Peter S

 

Yeah, I noticed that after I posted it. From what I've gathered, a number of builders have switched to bundles of pultruded carbon rods replacing the tow in the sparcaps. Here's a more relevant description of how such a spar is built:
http://www.continuo.com/marske/ARTICLES/Carbon rods/carbon.htm
"Graphlite" is the marketing name for pultruded carbon.

 

3.6 oz./sq yd is 85 gsm. The glass is plain weave. I have seen it listed as 160 psi/in tensile in either primary axis.

Actually I did my stress calcs without the glass. At 36 lbs/ft distributed load (1.5 x righting force with one 200 lb crew on tramp) the wood for the skin was only stressed to 3,800 psi with a rating of 4,800 psi (33.1 MPa). I just rely on the glass to tie the wood strips together and distribute the load.

I think the skin is fine for loading.

I am trying to work around the shear web. I know I can probably go out and mail order some 1/32" birch ply for the shear web, but in addition to the high $30 for a 4 x 4 sheet, there is $100 shipping. I have just choked on going this route. I can use 1/16" door skin ply, but the last stuff I got was just much heavier than I want. This is why I was thinking of a truss type shear web made of either 1/8" x 1/4" wood diagonals with 12K carbon tow on both sides, or just say 1/8" x 1/2" white pine diagonals without tow.

 

Hi Flados,
I'd forget about the 85g plain weave its not worth its weight in the structure. I'm used to infusing glass laminates that are 72ksi (500Mpa in tension and compression and about 900MPs in bending and 110Mpa (16ksi) in shear. 160psi is 1.1MPa which is very poor structurally and worse then the timber, most epoxies are better then this. The problem with using carbon tow is getting all the fibres straight. If one fibre is straighter than the rest this one will take the load (as an example). A shear web and a truss element are structurally different concepts so you need to clarify your philosophy on this a bit. Mixed materials are always a problem, stay in the wood, glass or carbon world. Cheers Peter S

 

Aerofoil rudders on boats when at center setting do not try to turn the boat left or right there must be negative load on each side of the rudder and a change of angle of attack
turns the boat left or right.
www.en.wikipedia.org/wiki/zero_lift_axis.

 

Mark,

Your more recent post was a lot more help. Even though I am kind of stubborn, I must admit that the Graphlite pultruded carbon rod might have the potential for being close to a “magic bullet” for getting lightweight, cost effective, high compressive strength home builds. The pricing was also noted to be better the larger the rod. I found the 0.125” at $1.10 per foot with a 100' minimum (not including $28 shipping). The 0.158” rod I found at a different seller for $154 for a 100 foot length (not including $13 shipping) that works out to be 15% less per pound of carbon. At 200,000 psi compressive strength, a single 0.125” rod can carry 2400 lbs. The 0.158” rod calculates out at 3900 lbs of capability. I am not sure I need the bigger size, but the extra cost is only $29 more and the extra weight is absolutely negligible. Either way, I end up with left over rod that could be very handy for other uses

For both sizes, the real key to this application is integrate the rod into the other elements and to provide the lateral support needed to avoid buckling. I drew up some stuff I am mulling over to achieve this objective. Getting a quality build with the configuration shown might be tricky, but I have some ideas.

FYI Peter, I messed up the units for the fiberglass. The 3.6 oz/yd glass is 160 lbs per linear inch for a single layer, not 160 psi.

 

If shell buckling is an issue, then using poplar plywood (aka "Lite-Ply") instead of the usual birch ply should help. Poplar has about half the density, so you can double the thickness for a large local stiffness/weight increase. At least you will need fewer internal stiffeners. Lite-Ply quality is sometimes marginal, but since you're using glass on both sides, this is not much of a concern.

 

Well I have spent a while thinking through a big choice. Slotted or not.

The slotted wing is probably best for class racing with a fixed area. However, I am not a class racer.

If you can add a soft sail for downwind & for light wind, it allows more choices for the wing.'

I am leaning away from the slotted, and toward the "reversible camber" foidl I have been posting about over at

http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/what-significance-wing-thickness-45383.html

Bottom line is that at an RE of 250,000 I got a Cl of 1.85 at an alpha of 11° and a Cl/Cd of better than 50 with my N30 (NACA 30 in front of a flat flap). This should be in the ball park.

At higher REs, with less than max lift, a flapped foil should be better than any slotted foil.

 

Doug recently posted this video that contains some discussion on a modification to current wing aerodynamics. But the fellow doing the explanation is holding some 'foils' rather haphazardly and that makes the explanation a little hard to follow.

Seems as this 'modification' to the wing design is not allowed in the bigger America's Cup boats.

 

The "fellow" explains how the trim tab works on the first element of the wing. A trim tab is used to either control the downstream airflow onto element two or to allow the teo elements to be closer together ie the tab allows the elements to cross in the tack. If you have rigid elements they can only be close enough to allow then to pass in the tack. If they overlap they produce more power. Look up cascading foils.

The moth type control is not allowed in the AC class as the foils have to be manually controlled. cheers peter

 

So this tab fills the intersection of the fwd and aft foils, and is slightly overlapping in nature?

In order for it to allow crossing during a tack, does that mean the two main foils need to slightly over rotate (opening up the interesting slot) to let the 'tab' cross over??

 

No the idea is not to fill the gap. The two elements have independent airflows. The idea is to bend the air more. A single element can only bend air so far, before the element stalls or its flow unattaches. Look up cascade foils. Yes the tab can be slightly overlapped in this case as its soft. This gives the elements more overlap. The tab is used to control the airflow from element one to element two. The more you bend the air the more power you get. Look at F1 rear cascade foils they bend the air 90degs. Peter

If you look at the take off on aircraft you will see they overlap quite a bit.