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Author Topic: Sweepette 36D -Build-  (Read 16629 times)
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BG
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« Reply #25 on: January 13, 2010, 11:23:35 PM »

Ok Wife is back and here is the next installment of build shots.

1. Wing prepped for sanding on new plate glass. I used small squares of double sided tape that I have detacked with a cloth (so that I can get the wing off the glass later) to hold the wing in place during sanding/shaping.
2. Sanding the back of the foil top. The space between the wing TE and glass edge determines the TE thickness. The tap at the high point prevents oversanding the high point. This method allows you to sand a nice flat rear foil.
3. Rough sanding the LE curve. Here I am using a tool to get the correct shape on the top camber.
4. Thread glued to the TE ... I make a shallow groove first and then CA the thread in place. Here you see it after sanding. I do this to keep the TE nice and clean and to strengthen it.
5. Wingtip after fine sanding
6. Wing after the top foil has been sanded in. I finish the surface with fine sandpaper held in my hand.

Tail feathers next.
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BG
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« Reply #26 on: January 13, 2010, 11:26:42 PM »

Here are a couple of shots of the Fin and stab:

1. Stab. The stab is lines with thread and has been fine sanded. THe weigh is 1.5g
2. Fin with foiled right side to generate a left turn.

Ok that is all for now.

B
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Tmat
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« Reply #27 on: January 13, 2010, 11:51:34 PM »

Looking good Bernard!

Man, that is some nice balsa in that wing! Nice to see you've done it justice with the fine shaping job.

Did you sand the undercamber before shaping the top, or will you do it now?

Tony
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« Reply #28 on: January 14, 2010, 12:35:17 AM »

Thansk Tony... yeah she is a lovely piece of wood... light stiff and very pretty. Tis an honor to work with her.... now if I could just find all of the other bits from that tree Tongue

Under camber is next. I have done the flat tip undersides with zero upsweep as per the Leepers instructions.
B
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« Reply #29 on: January 19, 2010, 12:00:40 AM »

Ok. Here goes with the next series of SWE36D build photos:

1. Shaping the upper front camber with a shaped sanding tool. I use tape to protect the high point and do the initial work with the razor plane.
2. Shaping the lower front camber (upsweep). Note the stops glued to the sides of the tool.... these do not have sand paper and prevent over sanding.
3. Shaping the under camber.... this tool also has stops etc. I found this to be time consuming.... I put in about 0.8 mm of under camber. Leeper uses 0.6 (see earlier post for details.
4. Last detail before minwax.... there is a ~ 1 mm flat spot on the bass.... I am not sure why this remained as the sanding tools should have resulted in a sharper LE....
Do I:
a. Sand in a Stan B. flat to cut the LE down to a sharp entry.
b. sand the upper and lower LE by eye to get a nice rounded knife edge.
c. Sand in a bit more upsweep.
d. Sand in more down-sweep.

Your thoughts appreciated as always.
Bernard
P.S. Wing now weighs in at ~37 grams.
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« Reply #30 on: January 19, 2010, 12:29:07 AM »

Good job Bernard. Typically, after I have finished with the curved sanding tools, I also have a leading edge that is not rounded the way I'd like it to be. I sand it by hand to the required radius. Try to make the leading edge a nice smooth, rounded, yet sharpish (if you know what I mean?) entry that blends with the top and bottom curves.

Leeper didn't use the Stanfoil flat on his Jugs, so I'd lean towards not adding one also.

Tony
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« Reply #31 on: January 19, 2010, 01:11:50 PM »

Thanks Tony... that is what I thought too... So the LE has been finished as suggested and the first coat of minwax is drying. Coat #2 tomorrow after fine sanding.

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« Reply #32 on: January 19, 2010, 05:20:29 PM »

What Paul Love and I have been doing (and now even Leeper too!) is to scan the actual airfoils after cutting the wing blank apart at the dihedral break. I place the wing vertically on the scanner and hold it steady. Paul uses Lego blocks and some such jigging to get his pics. I've attached a sample of one of my airfoil scans from my Longcat build. This allows you to record what you actually made, and it is possible trace the airfoil using Profili and analyse the performance in X-foil (if you are into that sort of detail that is Wink).
I don't finish my wings until after I join the dihedral breaks and so does Leeper. Other people finish the wing before cutting apart the d-breaks. You could (if so desired) after looking at the airfoil scans, tack the wing back together and re-sand if you thought you had goofed up the airfoil. So far (touch wood) I haven't had to do that. This is far easier to do if the wing hasn't been finished.

Leeper could attach his SW36 MKII airfoil scans for you to compare with yours. Leeper?

Tony
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« Reply #33 on: January 19, 2010, 05:50:08 PM »

Hmm that is a good idea....I will make the cuts do the scan for a check, then tack the bits back together for finishing while flat (or reshaping etc). When the second to last coat of minwax is on I will rebreak the joints and sand them for joining etc. then I will add the ply d'hedral braces and glass the wing joints. Last thing will be a coat of tinted minwax. I am gonna use thinners with pieces of sharpie wick dropped in to tint my minwax deep blue for the undersurfaces). For the top I will use the same procedure but with florescent sharpie wicks. The undersides of the tips will have a florescent orange or pink slash.

Glassing wing joints: This is a problem area for me I have to admit.....how do you guys do it so that you get a nice smooth finish with a seamless transition from the glassed area to the unglassed wood? What do you use to adhere the glass? Duco? Dope? MinWax? Epoxy? Is it thinned or straight? Do you tack the glass to the wood with spray mount first? I would hate to ruin this wing with a poor glassing job.

thanks in advance.
Bernard
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sweepettelee
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« Reply #34 on: January 19, 2010, 06:53:00 PM »

Hi All,

Back from Eloy and had a great time. My newest Sweepette 36D [aka Jugs 2] is really flying well and took the win at SWR 2010.

Bernie: very good to see your fine progress! Yet I wonder why you apply finish before gluing the bits to the body? I fear less than ideal adhesion under stress.

Tony: I did not scan Jugs 2 airfoil. The critical dims are near identical to Jugs I: .295 thk @ 1.25hp, .06 upsweep blending ~ 1" from LE & .025 u/c going to zero near tips. But you both already know that, eh?

Re glassing the critical areas: It is easy. Put Duco Cement drops where you will lay the fiberglass & spread out some
with finger. Quickly position piece on glue spots & flood with MEK [dope thinner might do] then use dowel or equiv to squeegee the glue evenly thru the cloth. Blot the wetness with blue paper towel pieces. Allow some drying time. Glassing is best done after dihedral joinings and wing attached to body. Sand glass lightly. Then apply finish of choice, IMO.

Attached are current pix of Jugs 2. One shows bottom colors. The Maroonish Red is a Design Masters color called Cranberry. It seems to show up well per my timekeeper.

Ciao,
Leeper
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« Reply #35 on: January 19, 2010, 09:21:29 PM »

That's a gorgeous model!
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sweepettelee
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« Reply #36 on: January 19, 2010, 09:27:23 PM »

Gee, thanks Bill... Embarrassed Embarrassed Cheesy

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« Reply #37 on: January 19, 2010, 11:05:38 PM »

I'll second that... this is a nice looking model you have produce Lee.

On my version.... point taken it does not make much sense to apply the finish under the areas where the glass patches will go or where the wing mates to the body. These areas will get a roughing prior to glass application to ensure proper adhesion.

B
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« Reply #38 on: January 19, 2010, 11:12:24 PM »

I'm with Leeper on this one. Why finish the wing before glassing at all??

I do prefer to finish the wing before gluing it to the fuselage though. I mask the area off at the joint so that no finish is applied to the glue joint area. I find it easier to handle just the wing when finishing and sanding. But I'd rather have the glass bond to the bare balsa.

But Buxton and others finish their wings before doing the dihedral joints so you are not alone Bernard.

Leeper, remember the photo below?
You said it was a scan of SW36RDT from Dec 01st aprox. If not from JugsII, then what? Memory going again?? Grin Wink

Tony
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sweepettelee
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« Reply #39 on: January 19, 2010, 11:39:06 PM »

OOPS! Yep, real gone. Embarrassed

But Tony, that was way back 50 days ago. How am I supposed to recall that? Roll Eyes But you see, remembering this stuff is what I trust you will do to assist me! Grin Will you be my caregiver in my [future] dotage? Wink

Back on subject: Bernie, it seems you have everything under control and the build will turn out fine. Oh yes, your wing weight is nearly same at my two: 37-38gr RTM, as I expected when viewing your fine wood. Cool

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« Reply #40 on: January 19, 2010, 11:41:50 PM »

Will you be my caregiver in my [future] dotage? Wink

Whada ya mean future??? Cheesy Shocked Wink Roll Eyes

Tmat
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« Reply #41 on: January 20, 2010, 09:20:07 AM »

Several of you refer to Minwax for finishing bare balsa wings, which Minwax product do you use, is it the water based oil modified polyurethane or water based wipe on poly? Or something else?

Malc.
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« Reply #42 on: January 20, 2010, 11:00:11 AM »

Malc, I believe most of us us the MinWax Spar Urethane which can be found at Home Depot, Ace Hardware and Michaels. I don't think it is waterbased. The Spar Urethane is intended for outdoor use and has a UV inhibitor which is helpful to avoid warps in the sun. I know some use thinned Nitrate (non-tautening) over powdered bat's wing applied with chicken bones but you should avoid those people.
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« Reply #43 on: January 20, 2010, 11:55:22 AM »

Hah! RR, I don't recall telling you of the batwing powder finish, but luckily you left out the most critical ingredients: Eye of newt & ... something else... oh yes, tongue of frog! Lips sealed Cheesy

Serious now: the Minwax most try to find is petrol-based. I & some other folk use good mineral spirits if you want to thin it. I usually go about 20% thinner. Dries in about 6-10 hrs. Try to cure it in warm place, like sunny patio, etc. You can brush or swab it on, then evenly spread-wipe with blue paper towel squares.

I haven't had to resort to the powdered batwing stuff since we found Minwax. Cheesy

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« Reply #44 on: January 20, 2010, 12:24:23 PM »

Malc,

When I was living in Germany I searched Obi, Bauhause, the other big hardware store for Minwax... they don't have it. I did find a urethane varnish that boaters use to varnish wood on yachts etc. This stuff has a UV inhibitor and is water proof etc. I think it will do the same job. Just ask for a yacht varnish with UV protection.

B
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« Reply #45 on: January 20, 2010, 06:12:03 PM »

Lee and all,
Any chance that I could use acetone instead of Mek (I don't know what this is or where to buy it). I thin Duco with acetone for building etc. I hope to cut my wing tonight... just to confirm... I do cut wedges out of the outer poly jnts to get washout per plan correct?

thanks
B
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« Reply #46 on: January 20, 2010, 07:01:02 PM »

Bernie,

Just cut the joint on the line which the plan describes, sand and glue d'dral joints. No wedge cuts required. They would add sweepback, which is not needed really. The towout line should measure .13" from perpendicular, but even .19" is fine. You will notice as you raise the tip how the TE comes up slightly higher than the LE. Hence, automatic washout. [Tho I do always sand in just a bit in the last part of each tip.]

Acetone is OK to flood the Duco with. Not much different from MEK as I understand things, chemistry-wise. MEK is Methyl-Ethyl-Ketone. I seem to recall acetone is one level down the ketonic scale. Chemical engrs, please jump in here, if I am off-base. I can get both MEK & Acetone at nearby boat-maker suppliers, btw.

Leeper
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« Reply #47 on: January 20, 2010, 08:16:43 PM »

One thing to do after cutting the wing and sanding the dihedral angles is to to "proof" the cuts by placing the panels back to back and using straight angles with a small trisquare to make sure everything is accurate. Sanding in these angles is a lot tricky than you might think and I can testify that this is the step that can turn a excellent flyer into a nightmare.
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« Reply #48 on: January 21, 2010, 02:39:01 PM »

Ok folks the wing has been cut... here is a scan of the root and dihedral break foils... NOTE: this image does not accurately represent the foil as the undercamber still needs to be added at the root cut line and will only be completed after she is glued up etc. Also... I used a rubber band to hold the panels to the red block and this caused the panels to flex flat against the block removing the undercamber and cause the reflex along the rear portion of the foil.

Anyway it is what it is.

B
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« Reply #49 on: January 21, 2010, 02:59:08 PM »

Bernie,

A key suggestion at this time:

Undercamber sanded at center [root] chord is unnecessary & waste of effort.
Just prior to gluing wing to body, sand the center joint flat for ease of mounting. Use rough sandpaper block, or jig it above a sandpaper covered flat surface, then sand bottom such that the upsweep is about half gone.
It takes but a minute to do.

That is our standard operating procedure re wing mounting prep.

Leeper
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