My buddy Tom & I are planning to build a new wingmast in the near future, so I thought I’d photograph the project & post them here as the work proceeds. The process is adapted from the methods developed by the model airplane guys: http://www.pilotsguide.com/rc/vacbag.shtml .
The mast will be 68" long with chord lengths of 4" at the base & 2.25" at the tip. The airfoil section is NACA 0021 which means the thickness is 21% of the chord width & is a standard teardrop shape. http://tinyurl.com/5ou9v
The foam core (Dow Hi-Load 60) was cut out of the blank with a CNC hot wire cutter by a fellow in California, which is MUCH more precise than I have the patience to carve by hand. Since the wire can’t be too long before it starts to distort, the core arrives in 2-34" sections which need to be glued in a butt joint. At this stage, the long skinny core is like a piece of spaghetti, as virtually all of the strength will come from the stressed skin of the 6oz fiberglass that will be applied with epoxy in a vacuum bag.
These pix show the core & it’s blank that it was cut from, the butt joint, the vacuum bag, table & the vacuum pump.
Well, summer sailing weather & other projects put the wingmast project on hold until yesterday. Cold & rainy weather made for a good time to be working in the shop. The following sequence of photos show the actual laying up of the mast (using epoxy & 6oz glass).
Foam core on layout table
2)Mylar (4 mil) on table
3)core & glass
4)core wrapped with glass & mylar
Since we’re limited to 4 attachments per post, here is “the rest of the story”
1)Wingmast in vacuum bag- note the bed frame caster that I use to “roll down” the edges of the bag over the sealant.
2)vacuum pump guage- I later turned it up to about 18"Hg
3)closeup of bag with suction
Well, the mast should be cured by now, so it’s time to open the bag & find out how it turned out. Always an exciting moment…
And the results are … @^#()%$*&@$#%$#@ ARRRGH !! :censored: :censored: :censored:
Just kidding !
Question: with only one point for vaccuum evacuation, have you had any problems with that area being evacuated first - preventing the other end from having a vaccuum ? In other words - does the bag “collapse” equally, or does it start from the tube end - or the end opposite the tube?
Have you tried using breather and bleeder cloth? You would have to go back and apply a skim coat or two, but I think in the end the light up would still be lighter.
Dick,
Fortunately, the results were good, although it came out a bit heavier than previous at 195 g, probably due to excess epoxy used in order to avoid pinholes. My lightest came in at 140g, but that was with 3oz cloth. To answer your question, the vacuum appears to draw down uniformly, despite the lack of breather cloth. There is a tube drawing from each end, so the relatively small size allows a complete vacuum.
These pix show the new mast:
out of bag with mylar still on
2)mylar coming off
3)mylar off, cutting off excess cloth at edge.
Dan,
Good question. The limited size allows good vacuum without the use of a breather layer, per this method: http://www.pilotsguide.com/rc/vacbag.shtml
Also, placing a breather over the mylar skin would obstruct vision of proper placement & air pockets needing to be worked out. The layer of mylar acts as sort of an exterior mold to produce a mirror like smooth finish. Early prototype efforts include the use of a bleeder layer of peel ply under the mylar, but it resulted in too much epoxy being sucked out & a VERY rough surface. This is fine when used on the inside of a female mold, but doesn’t really work with this method. I think the key to lightness is using just enough epoxy to wet out the glass, and then filling in any pinholes with a lightweight fairing compound such as West System 410. In this case, the mast is will be finished by my friend Tom Bridge who is a real perfectionist, so we wanted to produce a good surface. I agree that weight is critical, especially aloft. This one comes in at about half as one made with balsa with a Sitka spruce leading edge.
Speaking of surface roughness, there is an arguement to be made that a bit of roughness can be a good thing. For the same reason that golfball dimples allow a straighter & longer flight, it could very well be that some sort of turbulater strips or texture will have the desired effect of thickening the “boundary layer”, hence increasing aerodynamic efficiency.
Below is a shot of Tom’s first mast. The mylar sail has since been adjusted to eliminate the wrinkles, BTW.
The “down” side in the vacuum bag couldn’t be seen & had developed an air pocket that needed filling with a lightweight fairing mix. We plan to create a swivel joint in the vacuum lines to avoid this problem in the future.
The mast base has been cut to the rake angle of 70 deg & the jig is set up to drill the pivot hole. This needs to be in close alignment with the axis of rotation, so I used the end spindle from a cheap benchtop lathe I had found at a garage sale. The far end of the mast is propped up to be parallel.
3)The 30w soldering iron has it’s tip filed to a knife edge for cutting (burning)the luff groove in the trailing edge of the mast foam. The iron’s temperature is limited by a dimmer switch in order to minimize the width of the cut.
4)Cutting the groove (photo taken afterwards)
Yar,
Thanks, but it will look alot better after Tom is done painting it. These have been used on both landyachts & iceboats without a jib. However, I hope to use a pair of them on an F-48 catamaran when I finally get around to building
one. The mast is stayed at about the 70% height.
Bill
Thought you might be interested in seeing the new rig my friend Tom Bridge & I just finished making. Tom gets full credit for the paint job & square top rig design. Our ice season has been mediocre so far with good early ice, but then an extended thaw that melted everything. It recently refroze but is now snowing, so I guess we’ll be restricted to the City skating rinks for testing.
1)overall shot at the pond across the street from my house. This is with my
“K1-SS” model which is 6’-6" (2 m) long X 4’-6" wide.
2)closeup of lower portion with boom//Note the cantilevered front section with the tensioned “vang” line, which tensions the leach for better sail shape while still allowing the mast to rotate freely.
3)square top, sorry about the fuzzy focus. Not sure how well this will work, but if not, I’ll get out the scissors.
4) from my back porch showing sail camber. I was rotating the mast with my thumb & it was a bit over-rotated, but you get the idea.
I’m curious … is there a way engineering the rig so it could be plugged into a variety of test platforms … a monohull for instance?
The subect seems to raise its head frequently enough that I’d love to see a practical application of your wingmast on a boat … you’ve done a wonderful engineering and building it, btw.
could this be applied to a footy?
it seems like a simple’er rig for someone like me, that doesn’t know a lot about
main/jib set ups.
or is this more complicated/advanced, than the main/jib set up?
Upsides in a Footy (as in cat/iceboat …) more efficent, especially at higher windspeeds (so less adavantage overall than in say a iceboat sonce they ‘make’ their own wind).
Downsides, centre of gravity higher, so tippier. More sensitive to poor helmsmanship than a soft sail in a boat that is already typically not easy to steer.
Might wor, but not they way I personally would go.
Yeah - if you want a headsail at all, you got to keep the luff tight. You can do it with all the paraphenalia of a normal full-size rig but it seems a pity. Give it a whirl anyway.
Reynolds Numbers, if I understand the correctly, indicate that the advantages of a wingmast, or wing sail, become less evident as the size of a foil scales down.
You’ll notice on small rc airplanes that often a single thickness foil formed to an appropriate profile is used. This (again if I understand correctly) is because the smaller the foil, the exonentially thinner it needs to be to achieve the most efficient lift.
A better thought might be to use camber inducers (not that complex really) inside the mast-tube sleeve.
Similar to a windsurfer with a flexible carbon allowing sail to spill wind in gusts … easy to rig, efficient … I believe they’ve published a paper analyzing effects … worth a look. Trevor
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