Author Topic: blades fibreglassing progress, blade mounts, nosecone  (Read 1246 times)

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jacquesm

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blades fibreglassing progress, blade mounts, nosecone
« on: November 04, 2004, 10:23:03 PM »
RonB and Mirka have spent the last few days fibreglassing the blades.



We took all the warnings about moisture in the blades and resultant rot to heart, and figured that the biggest problem is to keep the moisture OUT in the first place. We searched and found a local representative for the 'west system" epoxy,

and it works far far better than the stuff from 'ashland' that we had before. The ashland stuff would eat up foam, bond very weakly to wood (or to itself !) and would delaminate easily. It may be that it's used by large companies, but I prefer stuff that work for me :). Resin is quite pricey, you can expect to pay in excess of $100 for a gallon of resin + hardener.



The biggest problem spot we've found is where the bolts connect the blades to the mounting hardware. That's the most vulnerable area because if you don't get a good 'seal' there the water will leak in past the bolts, into the boltholes and rot the wood from the inside.



In order to combat this we have drilled the holes twice the diameter of the bolts, then filled them back in again with a heavy filler/resiin compound, which will then be re-drilled on the centers, much smaller for the bolts. This should get a perfect seal without compromising strength.



The fibreglass layer on the blades is quite thick, almost 1/8" (3mm) in all. This is one layer of 'thick' (22 Oz) cloth, woven and 'roving' stitched together, followed by a thinner coat for the trailing edge and some filler reinforced resin for the leading edge.



After every layer the epoxy has to be cleaned to get rid of the 'blush', by sanding and / or washing. Then the next layer can be applied (usually 24 hours later). The only remaining work on the blades is finishing the tips (they still need to be rounded) and the seal at the very root of the blade.



In spite of the blades being fibreglassed they remain pretty flexible and we're somewhat worried about this. Even so, the blades are far stronger than any other 8' blade that I have seen, with one exception (and that blade was made of ash and weighed an easy 10 kilos or so...).



In order to mount the blades on the machine so tha they stay on we have devised a not very elegant but effective method. (someone quipped we should dub TrueTech 'Overkill engineering' upon seeing the blade mounts). The 1" (25.4 mm) shafts that come out of the governor go into 2" x 1" flatbar (and are welded there) that spans the width of the blade. Attached to the flatbar are two plates, one 1/4" for the top connection and another 1/8" for the bottom (more pliable because there is more curvature there). Each plate is bolted with 4 grade 8 3/8 x 1" bolts to the 1"x2" flatbar.



The blade then gets sandwiched between the two plates, and is bolted with 8 bolts through the fibreglass reinforced holes mentioned above. That way the blade-to-root connection is very stiff and we reduce the chance of tower strikes.



The other end of the blade shafts has been turned down to accept a small bearing, this will slide into the blocks sitting on the other side of the governor weights.



Another piece of work that finally got started was on the nosecone. The foam 'blank' is ready to be cut (it's drying overnight) on the lathe tomorrow, then we'll build up a fibreglass layer on top of the foam, and then remove the foam by dissolving it after the fibreglass has cured.



I test raised the tower today to see if the mechanism had suffered in the time between the last time we raised it (12 months ago !) and now, but everything seemed to work just fine. I will be reinforcing the cable that pulls on the ginpole with two more ground anchors, it seems cheap insurance against the single 3/4 " thick concrete anchor holding the pulley snapping of and causing 3 months of work to come crashing to the ground. I'll set those ground anchors just behind the pulley and loop a separate steel cable with a tiny bit of slack to each of the ground anchors from there. That way if the thing should let go it won't fall very far before being caught and should hopefully survive.



Call me paranoid but I don't trust that guy murphy...



We've finally decided how we'll mount the tail on the machine, there will be

another tube running along the top of the main housing, with a slit along the top,

and tabs welded to the tube left and right of the slit will clamp down on the tube that sticks out of the back of the machine. That way it is easily broken up and yet will be very strong when put together. A similar clamp will hold the actual tail to the tube, and this will allow us to change the position of the tail a bit during our initial testing. I also went and got all the electrical bits and pieces that were still missing. The 3 phase disconnect was $300 ! ouch... that hurts when you figure it's going to be $80 or so. 300 bucks for a switch :(



We're shooting for having it all ready on Sunday, or at least early next week. I've decided on painting the metal parts blue and the blades white. Sky colours, to blend in as much as possible and not offend the neighbours. And I think it will look pretty. Over the next few days you'll see more and more parts painted.



pictures follow:



The operating theater. In the back on the table you can see the west system

containers, they have a little pump on the top that gives you a 'perfect' mixture

with a shot from each container (resin and hardener). On the right

of the picture at ground level you can see the roll of fibreglass cloth.







The patient on the table. The murder weapon is still sticking out of the

chest cavity, rigor mortis has clearly set in (position of right hand).

Notice the look of incredible terror on the face of the victim:







The pilot holes drilled at the center of the bolt holes.







The expanded holes:







Mirka and RonB closing the expanded holes on one side with a thin layer

of cloth and resin so the reinforced resin used to fill the expanded holes

will not leak out:







Also some fixes to the blade surfaces, some not so nice pieces of wood

and resin pockets that only revealed themselves after cutting:







The blades left to dry overnight, you can clearly see some of the fixes from this angle:











The oversize holes filled with the reinforced resin:












Ready to apply the first layer of cloth to the 'front' of the blades,

clearly visible in this image is the biggest change from our last 'test' blade, the reinforcement wedges at the root of the blades:







Laying the cloth into the layer of fresh resin that has been applied:







RonB uses a 'squeegee' here to firmly but gently ease the cloth into

the wet resin without messing up the structure of the 'weave' in the cloth,

this is a lot harder than it looks !:







Closeup of the squeegee at work (yes, those are scars... if you knew how sharp Ron keeps his tools you'd understand, in fact you'd wonder how come he has fingers at all...):







Finishing up the first layer:







Covering the blades with a very lightweight nylon cloth. This is to

ensure that the surface of the blades will be nearly flat when the

resin has cured. The nylon will absorb excess resin, which you can then

peel away with it, leaving only a very fine pattern that is easily sanded smooth:











Trimming off the excess cloth:







One blade covered on one side:







Filling some nasty spots near the root of the blade:







Side 'b', the back of the blades, same procedure:







Interesting view here, through 20 some ounces of cloth (which is a

pretty heavy fabric!) you can still see the wood and other details:











Backside is ready to cure overnight:







Trimming off the excess cloth again:







Three blades, both fronts and backs done. The 'fourth' blade is one

of the later test blades, used for stiffness comparision:











Now the annoying phase begins, sanding, sanding and then more sanding (Ron

really loves this phase of the work):







Yours truly just back from a trip up and down to Toronto (to pick

up Johannes, a friend that stays here to help out) inspects the work

done during his absence (conclusion: I should go away more often):







The leading edges smeared with filler goop (fairing filler + resin, fairly

easy to sand to shape):











More sanding (always more sanding...):







The leading edge is assuming its former shape again (adding the

cloth upset that quite a bit, which is why we had to reshape):







The finished leading edge:







A few pieces of the blade mounts. The flat 'bar' shapes will be

bolted to the plates with the holes in it. The blades will then

be sandwiched between those plates (one on top and one a the

bottom of the bar):







Sanding of the trailing edge:







Johannes and RonB glueing the blank for the nosecone:







The blade mounts, ready to be welded:







Closeup of one mount, notice the bearing at the hubside end of the shaft (left),

and the 'ring' welded on to the right of the shaft where the thrust bearing

will go:







« Last Edit: November 04, 2004, 10:23:03 PM by (unknown) »

monte350c

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Nice Job!
« Reply #1 on: November 05, 2004, 10:40:48 AM »
Nice work guys!


You'll find with the West Systems epoxy it will continue to harden up for about a week after the application - so the blades will probably stiffen up to some degree.


Don't forget about the anti - UV coating!


Looks like this will be a very nice installation.


Ted.

« Last Edit: November 05, 2004, 10:40:48 AM by monte350c »

gibsonfvse

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Re: blades fibreglassing progress, blade mounts, n
« Reply #2 on: November 05, 2004, 08:56:11 PM »
In spite of the blades being fibreglassed they remain pretty flexible and we're somewhat worried about this.


It's true that fiberglass really isn't meant to take structural loads.  For this, you either want an internal spar or sparcaps on top and bottom.  I can only speak from the experience of R/C aircraft construction; the composite work I've done involves using carbon fiber sparcaps on the wing top and bottom, putting extra sheets of fiberglass on the leading edge with spray contact cement, coating the entire surface with fiberglass and epoxy, and immediately vacuum-bagging the whole thing.  You really should consider vacuum-bagging since you have the blanks, and it could save you quite a bit of sanding.  Just use mold-release (car polish has worked for us) on the negatives so that they don't stick.  If your molds are smooth to start with, the vacuum-bagged blade should have a rather smooth finish that can be touched up with fine-grain sandpaper.


However, I probably am not understanding the reason why you're putting on each layer of fiberglass as a separate application.  As I mentioned above, perhaps you could consider using extra fiberglass on the leading and trailing edges held on with contact cement (this is purely just to hold the glass in place so it doesn't move when you epoxy it), and then putting the main fiberglass layer over everything.  When you "wet out" the cloth with epoxy (good, you've discovered West Systems), the epoxy should enter all layers.  I look forward to your reports on new developments.

« Last Edit: November 05, 2004, 08:56:11 PM by gibsonfvse »

gibsonfvse

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Re: blades fibreglassing progress, blade mounts, n
« Reply #3 on: November 06, 2004, 12:10:25 PM »
My apologies about that "blanks" comment... to do vacuum-bagging, you'd have to make top and bottom molds for your blades.  But you'd only have to do this once (if you treated the molds right afterward), and it should be easy to set up since you already have the top and bottom surface digital data.  Good luck
« Last Edit: November 06, 2004, 12:10:25 PM by gibsonfvse »