Ultralight Gollywock Build by Alan Cohen Thread Repost

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Alan Cohen January 18, 2010, 06:00:42 PM

Back to the build again. I have the ribs made. I think the experiment 'laminating' sliced A-grain is a go. 22 ribs weigh 2.97g.

I cut the ribs individually using a snapped razor blade and a basswood rib template, again left over from the last build. After they are all cut I install them on a mock 1/8 spar to get them aligned and then sand uniform. I square off the TE, level the tops and bottoms and then pay special attention to the V-notch front with a home made emery board made from 1/16" ply and covered with 3M Gold sandpaper. If you haven't tried it, buy some. It is simply the best for sanding balsa as it is highly resistant to loading.

This step saves a lot of time when assembling the wing and it ensures everything will fit and the 1/8" LE will fit perfectly into the V-notch avoiding unnecessary sanding later. If the groove is too small you will end up having to sand the LE smaller to meet it. Not an area where you want to save weight!

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thymekiller January 18, 2010, 09:28:52 PM

A few newbie questions, please.

When you say 5#, do you mean 5 lbs per square foot?

Totally lost on "stiffness coefficient" ?

When using 45 degree angled wood in the nose [or anywhere else] does it matter how strong that wood is? Are gussets a good place to save weight?

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BG January 18, 2010, 11:01:53 PM

Lookin good Alan,

I checked the weight of my fuze.... she is 10.5 grams with nose block and motor peg installed. So we are basically at the same weight. I plan to do mine in silk for some added strength and toughness.

My wing is 10 grams

B

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CrashCaley January 19, 2010, 10:08:12 AM

Alan, I think it is you that sells the very nice balsa strips, is it not? I am also wishing to build myself a Gollywock, but don't have the proper wood for the longerons. Seems that the wood I have is nice, but spotty along its length. In those spotty areas, they are super soft, and susceptible to easy breakage by just a gentle bump. That happened when I used it on my Majestyk, thinking it was perfect only to find I needed to do several repairs to strengthen those weak areas. Could you PM me, and let me know if you are the seller of that nice wood and what it would cost for me to get enough stick stuff for say two full Gollywocks. I prefer not to have to splice wood though, so it would have to be long enough to make full length longerons.

Caley

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A quick note on the remaining pages. For some forgotten reason, I didn't save the full size picture files on many of the photos. I'll add the thumbnail size ones if that's all I have, but the quality will be poor.

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A quick note on the remaining pages. For some forgotten reason, I didn't save the full size picture files on many of the photos. I'll add the thumbnail size ones if that's all I have, but the quality will be poor.

Hah! I found many of the larger pics. Never got them into the appropriate folder so I thought they were missing. Yay!

Original page 2 starting next.

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Alan Cohen January 19, 2010, 11:44:22 AM

Quote from: thymekiller on January 18, 2010, 09:28:52 PM
A few newbie questions, please. When you say 5#, do you mean 5 lbs. per square foot? Totally lost on "stiffness coefficient" ? When using 45 degree angled wood in the nose [or anywhere else] does it matter how strong that wood is? Are gussets a good place to save weight?

Yes, 5# per square foot.

Stiffness coefficient takes a bit of explanation. I'll take some pics and post an explanation.

Gusset wood does not need to be any stronger than the wood it is supporting. No point using 15# density gussets on a 5.3# TE for example and visa versa, no point using 5# gussets on 15# wing spars.

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F1diddler January 19, 2010, 12:33:15 PM

Quote from: Alan Cohen on January 19, 2010, 11:44:22 AM Yes, 5# per square foot.

Or maybe a square foot 12 inches deep, which would be a cubic foot. :^)

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Alan Cohen January 19, 2010, 01:10:33 PM

Quote from: F1diddler on January 19, 2010, 12:33:15 PM Or maybe a square foot 12 inches deep, which would be a cubic foot.  :^)

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Alan Cohen January 19, 2010, 07:43:46 PM

OK... the wing. Having made the ribs I need to now make the trailing edge. Wood selection for this component is more critical, IMO, than the LE or even the spar. Being 5/8" wide there is a lot of wood here so weight can be saved, but in a single spar wing like the GW, the TE also requires stiffness as it supports much of the wing. I'm using the same 5.3# very stiff wood used on the fuse. I prefer planing trailing edges rather than sanding them. Nothing weakens balsa stiffness more than crushing the vessels with sandpaper. I made a little video of me shaving and trimming the TE: (Video has been removed. Bargle)

I left 1/16" at the thinnest point. Then set my McCloud stripper to 5/8" and sliced it off. Cut to length it weighs 2.06g. I then set the stripper for 3/8" and sliced the wing spar.

The next step is to orient the TE on the plan and mark where the rib notches will go. I make two lines for each rib and notch in between. It makes it easier for me to maintain uniform spacing that way. I've made a few tools for sanding notches of various widths and depths. I started using my 1/16 x 1/16 notching tool, but soon realized the plan calls for 1/8" deep notches so I switched. I can sand each notch with a pass of only a few inches of the tool. After all the notches are made the TE is replaced on the plan. This is where well made matched ribs and a notching tool bear fruit. Since every notch is exactly the same depth and my ribs are all identical, the wing spar will be dead straight by default. I glue a few ribs in spaced wide apart to hold the spar in position and then start installing the rest of the ribs. Magnets hold them vertical while drying. It's hard to tell from the pictures, but I placed a couple of 1/8" x 1/16" strips left over from the rib laminations under the very front of the trailing edge which allows tipping the rear of the TE down so there is a smooth airfoil transition from rib top to TE. This way the undercamber is maintained through the TE.

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Dave Andreski January 19, 2010, 10:45:46 PM

Hi Alan,

Great work so far!
Regarding reply # 15-RIBS. You stripped A grain, turned each stick a quarter of a turn then glued 'em up? What glue did you use on the ribs?

Dave Andreski

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Dave Andreski January 19, 2010, 11:01:59 PM

Alan,

Are you using the 'reconstituded dried glue on plate glass' method?

Dave Andreski

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Dave Andreski January 19, 2010, 11:17:31 PM

Here's what I'm talking about.
"I have found that different batches of glue, Duco, SIG, whatever, can use different solvents in different ratios. This can result in very variable drying times and holding power. I have taken to drying out my cement (I'm using 527 these days) on a pane of glass and then redissolving it in a mixture of 3 parts MEK and 1 part butyl acetate. The BA slows the drying a bit which I prefer. It is also the component in dope thinner that smells soooo good. It almost smells like cotton candy. Again... be careful. Just because it smells better, doesn't mean it is better for your brain cells".
Alan
-------------------
 Dave Andreski

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BG January 19, 2010, 11:34:34 PM

Nice video Alan,

That is how I have been doing it for years. Good to finally see someone make a video of this procedure.

B

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Alan Cohen January 20, 2010, 12:22:26 AM

Yes, Dave, I'm still reconstituting my cellulose glue. Where did you dig up that gem?  I don't use it for much these days so a little goes a long way. I will be using it to attach the tissue to the undercamber of the wing. Glue stick doesn't seem to work for me there, nor does straight dope for some reason. I like the security of a little extra holding power for the big undercamber shrink.

For my 'built up' ribs I used Titebond. Just trickled it out of my glue bottle down the edge, stuck another strip on and repeated and repeated and repeated. Then I squeezed them between two straight edges and pressed them down with some magnets like you see in the picture. Worked like a charm. Not the quickest way to make ribs, but the result is great and I glued them together while waiting for each fuselage bay to dry.

Glad you liked the vid Bernard. Sadly, the Academy has still not phoned.

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Dave Andreski January 20, 2010, 12:25:26 AM

Nice crisp sound on that video too! I use my David Combi Plane the same way.

Before I start the planing I generally use my Master Airscrew or Pete Money stripper to make a partial slice as a guide for the TE width.

Dave Andreski

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Alan Cohen January 20, 2010, 12:29:24 AM

Dave Andreski on January 20, 2010, 12:25:26 AM Before I start the planing I generally use my Master Airscrew or Pete Money stripper to make a partial slice as a guide for the TE width.

I did a similar thing with that red marker and ruler you see in the video. I just shaved to the red line. With a good plane and a little practice, no sanding needed until the final pre-cover once over.

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Dave Andreski January 20, 2010, 12:39:32 AM

Alan, I dug up/saved that 'little gem' from an old Yahoo Indoor group posting of yours. I love gems. Sometimes I even use 'em. Wink

Dave Andreski

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Alan Cohen January 20, 2010, 10:43:54 PM

I managed to get a little done on the wing. I'm not going with sheet wing tips, but bending some bamboo instead. It worked great on my first one and I've used them a few times hence so I'm getting comfortable with working with bamboo. I believe it was the original Gollywock plan that had bamboo tips so this should be legal. The first pic is a shot of what I have so far. I elongated the terminal rib so it will meet the thin bamboo strip. I also elevated the rear of the rib so I can get a smooth transition from the LE to the TE.

On the next pic I'm installing the LE. I went with a little more beef up front, using a 36" stick of 1/8" (.13") that weighed 1.26g. It's a shade under 8# density and very stiff. In order to get it to take the bend to the terminal rib I brushed on a little H2O and let it soak in for a minute. I needed 3 magnets to come close to holding from bending back and, even at that, could only get it half way there. I feared it snapping so when I left for work this morning I left both ends sitting half bent all day with a bead of water to soak in.

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Alan Cohen January 20, 2010, 10:49:04 PM

When I got home all was dry and molded into position. I little more water, a few more minutes to soak and it bent all the way. Whew!

The time taken trimming up the front of the ribs neatly was worth the effort. The LE fits perfectly and will not need much sanding at all.

It's 7.8g now, including all the ribs, but no wing tips or ply dihedral reinforcements and the TE still needs to be trimmed.

The next step will be to separate the outer panels from the inner panels, install the wingtips, sand in the dihedral angle and glue it back together. Maybe tomorrow...

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Art356A January 20, 2010, 11:54:51 PM

Alan, re: undercamber glue. Next time you're in Target or someplace like that, grab a tube of 3M Scrapbooker's Glue. Try it out on a test panel and see how you like it. I've used it so far on two indoor jobs with Ultrafilm covering, and for Esaki repair work on a few normal models. Way better than glue stick, and slower than cellulose glue. The applicator lets you put on only as much as you want, and right where you want it (once you get a little practice, anyway). Although it doesn't smell like it, it seems to have some water in it because there is some wrinkling of the tissue directly where it's applied, which goes away when it dries. As soon as I zero in on my next attempted build, I'll definitely use it. I haven't been able to contact 3M to find out what the correct solvent is for it, though.

Art.

EDIT... I found an MSDS; it's 80% water, 20% polyvinyl alcohol, whatever that is. I ran ribbons out on a piece of aluminum and a piece of depron, also glued two pieces of depron together. Tom'w when it's dry, I'll fool with solvents. If you use it to apply tissue, the alcohol soak doesn't seem to soften it like it does to gluestick, though.

Edit #2... Further examination of the MSDS indicates water as the solvent. This is why the 91% alcohol doesn't affect it, and nothing in dope will either. Future? I dunno, maybe.

a.

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Alan Cohen Yesterday at 08:04:18 AM

Thanks for the tip, Artie. I'll try it out. I've come full circle with glue stick. I started out with Uhu purple because that's what everyone said to use. Then I started experimenting with other more tacky glue sticks and thought I preferred them. But the tacky ones are really hard to apply without globbing and when you're doing every crosspiece and every rib it gets to be a mess. So I'm back with the more waxy Uhu and am liking it very much. The trick is you really need to wait until it dries completely before you water shrink. But I'm always willing to try something new.

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CrashCaley Yesterday at 08:09:08 AM

Very interesting on the glue talk. I've had the same problems with my glue stick, globbing. End up using a Q-tip to remove the globs as quickly as I can.

Alan, how long do you let things dry after applying tissue with glue stick? Apparently I am too quick, and on one model that had undercambered wings, the tissue popped up in a few places. Guess I must be in too much of a hurry to shrink the tissue.

Caley

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Alan Cohen Yesterday at 08:25:27 AM

I don't trust glue stick on undercamber, Caley. I use my trusty Duco bottle and coat the bottom of the ribs, let it dry, and apply thinner as if it were dope. It might be overkill, but nothing ruins my day more than waking up expecting a nice shrink job and finding the tissue pulled away from one or all of the ribs. I apply the tissue dry and then shrink with water. Everywhere else I apply tissue wet.

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CrashCaley Yesterday at 08:32:01 AM

Hmmm, DUCO, eh! I'll give it a try on the next undercambered wing. I need to get adventurous and try laying tissue on wet. Always done it dry with glue stick, and just stretched the best I could.

Thanks Caley