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Author Topic: Sweepette 36D -Build-  (Read 17973 times)
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BG
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« on: December 27, 2009, 08:25:59 PM »

Ok folks... I have decided to do a SWE 36D.

1st... I have a nice piece of 48 inch 3/8ths c-grain that comes in at ~7 lb/sq inch. The piece is straight and stiff with a density gradient across the sheet from ~6lb to 7lb+. My plan is to use this piece for the 36D wing with the hard side at the TE.

2nd. I am wondering what the 36D components should weigh in at? Lee if you have a mo. could you post the weights for your recent version?

3rd. Are there mods I should make to the plan to get a SWE36 the flips nicely in the transition (as per your "went flying" description).

thanks in advance for your advice and suggestions.

Bernard

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« Reply #1 on: December 28, 2009, 07:04:15 AM »

This build will be interesting! Some of the guys in my club are playing with the smaller rc TLG's of ~1 meter span and have mentioned the FF activities - which really surprised me. One was very unhappy with the way the stock wing was (NOT) performing and said that he might order a wing blank from the States. I'll steer him to HPA.

Be sure to post LOTS of pics, cause I'm also toying with going "giant scale" Grin.

Pete

PS: have you done any more testing with your "Scalded-cat"? PB
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« Reply #2 on: December 28, 2009, 11:50:56 PM »

Ok Here we go:

Last night I started the process by selecting wood for the tail feather (stiff ~5lb c grain) and the fuselage (stiff 8 lb A grain 1/4). Also cut out some 1/32nd ply cheeks for the fuzz (photo 1). I cut the ply with the shears in the photo or with regular household scissors.

Next I prepped the fuselage for a built in viscous timer:
1. I adhere one ply fuzz cheek to the balsa core (pick the side you want your DT tube to stick out of).
2. Drill a hole through the fuzz that is the same diameter as your DT tube (mine is 1/8th aluminium).
3. drill as second hole up to but not through the ply that is the same diameter as the next size up of tubing (5/32nds in my case).
4. Counter sink a 8 mm diameter hole about 3 mm into the balsa core centered on the previous hole. This will be your silly putty reservoir.
5. Cut of a piece of the outer 5/32 tubing that is about 2.5 mm long and insert it into the hole so that it is flush with the inside surface of the ply cheek. CA in place and CA all round the reservoir to stiffen and seal.
6. Cut you DT tube so that it projects ~ 1 cm out of the fuzz side while flush against the inside surface of the opposite play cheek (~17 mm).
7. Drill a 1.5 mm hole through the tube about 1 mm from one end and inset a 1.5 mm, ~ 6mm long rod (I used carbon) through the hole, center it and CA in place.
8. Drill a second hole through the tube about 4 mm from the other end...this hole will take your timer arm.
9. Cut a 2nd piece of 5/32nd that is ~1 mm long and slide this over the timer tube so that when the timer tube is inserted this collar will keep the short "paddle rod" from binding against the base of the reservoir.
10. insert timer tube and check that she rotate freely and does not stick out beyond the side of the balsa core.
11. pack your reservoir full of silly putty.
12. Adhere second 1/32nd fuselage cheek... this seals the DT mechanism in place.
See photos 2-5

I also prepped my wing blank for by gluing a ~1 inch wide strip of 8lb 1/8th to the TE because the wing has a 5 inch chord and I had a standard 4 inch wide sheet of C grain for the main portion of the wing.

The last photo shows all of the bits ready for the next step... rough shaping.

Bernard
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sweepettelee
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« Reply #3 on: December 29, 2009, 01:42:06 AM »

Hi Bernard,

Glad you have got going on your SW36D build so quickly. Let me see, where can I help you?

Firstly, the wing chord is only 4.5 or maybe 4.57" if you put a 2mm or .062" basswood strip on LE as I recommend. I think 7# stock will be a wise choice. Good strength & torsional rigidity. BTW, my two have .015 & .025" undercamber respectively, from about the max thkns curve rearward, going to zero at 16" from root. I tape off the d'dral joint lines before sanding u/c, then cut & add d'dral. See photo attached.

The outer joints have the u/c blended after joining. The center joint stays unblended til sanded flat for mounting.

Do the entire top and the LE shaping with upsweep [aka Phillips entry] before sanding u/c. Or... don't add the u/c. It IS a lot of work, but I think it really helps the glide, with little or no lost climb.

Now for my spec weights as you asked for:
Wings RTM [ready to mount] = 37.5gms for -1 & 39gms for -2.
Stab RTM = 1.7 - 1.9gm Fin = .5 - .8gm of strong balsa with .03 bass strip protection.
All 4 of the 36" TLGs I have made had ~.290" thk wings & weighed between 78 and 85gms, RTF.

We await your next posting. Cool

Ciao,
Leeper
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« Reply #4 on: December 29, 2009, 03:11:26 AM »

Good stuff.

Leeper, I think that Bernard was interested in the changes done to "Jugs2" compared to plan. I believe that you stretched the TMA n'est pas? And the dihedral is a bit more than plan is it not? New CG would certainly be of use.

Tmat
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« Reply #5 on: December 29, 2009, 08:46:15 AM »

Hi Guys,

Thanks for the info Lee.

Some questions for clarity:
1. The undercamber is 0.6 mm (.025"*25.4.....sorry I prefer metric Roll Eyes) ??
2. How far back from max thks do you hit max undercamber? See my foil guestimates.
3. FOr the center joint....so you don't blend? You just sand a flat bevel that is perpendicular to the vertical joint plane so that you have a flat spot to mate to the fuzz?

Lastly, as Tony notes, I would also be interested in the TMA and dihedral values for JugsII as well as the CG of course.

thanks
B

Another general question: Why not taper the blank from the root to the tip with a constant taper? This would give you a lighter (but thinner) wing. Is it because of the loss of strength? Or is it because of the loss of lift from a thicker foil? or both? I ask because my blank is 10 mm thick and I was thinking about tapering from 10 mm at the root to 3 mm at the tip for a constant taper. Is this a bad idea in general? if so why?

Note: I will stick to the config. of jugz II but I was wondering if the alternative config. above would be ok?
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« Reply #6 on: December 29, 2009, 11:35:17 AM »

Bernard

The timer is slick! Have you used this design before? Is it pretty consistent?
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« Reply #7 on: December 29, 2009, 12:47:08 PM »

Thanks Bill,

Nope, have not tried it yet but I am confident that it will work ok.

B
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« Reply #8 on: December 29, 2009, 01:08:10 PM »

This looks neat. I just downloaded the plans and I may have to try one.

How is the incidence adjusted?

Craig
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« Reply #9 on: December 29, 2009, 01:26:46 PM »

With a screw under the tailboom in the pod.

Tmat
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« Reply #10 on: December 29, 2009, 01:36:42 PM »

Bernie,

FYI, the SW36D plan I sent you has the correct 17" TMA & d'dral for Jugs-2.
Jugs -1 has slightly shorter TMA [16.2"=411mm] & 2.25" CG.
Jugs -2 has CG back slightly @ 60mm[2.36"] due to longer TMA.
I did not chg CG on plan so the builder can start on the safe side, then fine trim CG to suit.

Q2: The u/c max of .6mm is about halfway from max thkns to TE.
So I would say back a bit from 27mm value on your foil estimate. After I removed the green tape used for u/c sanding [See my pix of u/c sanding tapeoff], I blend-sanded in front of where tape was, as there was the slightest ridge at tape edge, of course.

Re Q3: why blend u/c at CL, when you must prep that area flat[as you succinctly state [perp to joint] to mount to body? That is SOP with most HLG flyers these days. It is a useless waste of effort to try to cut & fit groove in body for wing. Flat to flat is best.

Re "Another general question": for SW shaped wings and most other shapes, I feel it is best NOT to sand taper straight from CL to tip. Especially on TLGs. As you stated, strength is needed for tip launches. By definition, an elliptical [or nearly so] LE planform will result in a near elliptically curved HP after shaping airfoil. I determine my thkns goal for center, then calculate thkns for d'dral joints as ratio. I like to think overall lift is better in doing so, but that is an unknown.

FYI: my thkns: root=.29"; at d'dral joint=.265"; & .23" @ 13" from root.

Ciao,
Leeper
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« Reply #11 on: December 29, 2009, 01:42:41 PM »

Ah, ok.

So the screw head is accessed through a hole in the boom or do you have to have it in D/T mode to adjust it? Does the boom rest against the head of the screw and loosening it raises the tail up a little?

Craig
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« Reply #12 on: December 29, 2009, 02:18:05 PM »

Craig,

Tony should have said the screw is ABOVE the boom. It is mounted in the body recess between the plywood sideplates. Adjustments made in DT position. Boom is pressing on screw head in flight mode. Can't attach pdf file to show this in planform.

Leeper
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« Reply #13 on: December 29, 2009, 03:40:42 PM »

I always think of it as being below the boom because in my muddled thinking, the plane is always upside down when I make the adjustment. But in the true sense, yes Leeper is correct, the screw is "above" the boom. To answer Craig's question, the boom must be in DT position to adjust the declage and yes the boom rests against the screw head.

You can see the screw in the photo I've attached (it's an underside view showing the plywood side cheeks creating a guide for the boom). You could probably come up with a way to adjust the screw without moving the boom out of the way, but in practice I find I am usually adjusting the declage right after a test flight that has DT'd (short DT's for test flights) and so the boom is already out of the way when I pick the model up. I keep a precision screwdriver in my pocket at all times when flying so that adjustments can be easily made "on the fly" as it were.

tony
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« Reply #14 on: December 29, 2009, 03:48:48 PM »

Again: Ah.

What are the notches on either side of the fuselage right where the screw is? Are those to keep the D/T bands in place?

Craig
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« Reply #15 on: December 29, 2009, 04:04:48 PM »

Hi Craig,

Yes the notches form a slot so that the DT band can press directly on the boom ensuring firm contact with the adjustment screw (any slop would be bad of course).

B
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« Reply #16 on: December 29, 2009, 04:39:52 PM »

Actually Bernard, we usually run the DT line (Nylon, or Spiderline type of material) around the bottom of the boom to provide the boom hold-down force. The only rubber band used is to pull the boom up into DT position. Here is a link to my web album showing some of Stan's DT system in detail with some photos and a short video. http://picasaweb.google.ca/tmathews180/PopUpBoomDTDetails#

You will see that the notches are to allow unfettered contact with the boom. I've attached Jim Buxton's excellent exploded view of Stan's TLG DT system as it describes the set-up better than I ever could. The only change that I make over Stan's system is that I attach the fixed end of my DT line to a pin (or a small wire loop) rather than glue it into the wing. This way I can replace the DT line if need be (not that I have had to yet mind you).

Tony
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« Reply #17 on: December 29, 2009, 05:31:24 PM »

Bernie,

I must disagree with Tony here re DT line material to use. [Note: Jim Bux does not mention line of choice in his exploded view.] I [and Stan B's customers, etc] use Dacron line of about 20# test or lower if can be found. Because it is limp. No Nylon nor Spiderwire I have ever seen is limp enuf for the job. There might be some out there, but please try to find 'flyback line' in the test poundage noted above. Micron by Courtland was the best dacron line I ever used, but it may be obsolete.

As for anchoring DT line, I drill 1/16th hole thru wing on right side of body, insert 1/16th alum tube, then pass line thru and tie off when calibrating proper tension. Put dab of CA on knot AFTER you pull it out of tube! This method allows easy tension increase adjustment, which is the normal thing that occurs. Certainly it give ease of replacing lines.

Plus it suits my style & gives me peace of mind! Grin Roll Eyes

Ciao,
Leeper

PS: And if it is not too late with your wing layout, whenever possible try to make the inside [read 'glideside'] wingtip the heavier side. But ONLY if the grain choice will still be optimised by so doing. Smiley
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« Reply #18 on: December 29, 2009, 07:02:53 PM »

I've used Dacron as well, but now prefer the low-stretch Spectra as it does not give and allow the boom to shift. So I don't need to worry about a mousetrap arrangement. It is flexible enough to wrap around the boom and slippery enough to slip between the turnaround for easy release. But to each his own of course.

Tmat
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« Reply #19 on: December 29, 2009, 07:05:44 PM »

Other than the known abrasiveness of Kevlar thread, would it work?
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« Reply #20 on: December 29, 2009, 07:30:18 PM »

Re Spectra, I have avoided it as I felt it might be TOO slippery at turnabouts to withstand aero forces.

Kevlar might work, but it is fuzzy and might snag on something. Beware Murphy's law. Why not just use some good sewing thread of proper size? Much of it is Dacron or similar [linen?] Easy & cheap to buy.

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« Reply #21 on: December 29, 2009, 07:52:53 PM »

The spectra based fishing line I've used is not as slippery as the pure Spectra so it works just fine.

The only area that I'd like to use a different line (or diameter) is the piece that runs from the coil spring to the timer. My Power-Pro braided line (30 lb test) http://powerpro.com/publish/content/global_fish/en/nl/powerpro/products/powerpro_family_of/powerpro_super_lines.html is a bit thin for finger handling at the timer end. Other than that, it works really well for me. I'm sure there are other similar Superline products that will work just as well (Spectra based).

Any decent strong thread will work and I don't think it's critical what you use.

Tony
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« Reply #22 on: December 31, 2009, 05:51:59 PM »

Hi All,

Interesting thread ( Roll Eyes) ....so here are some more pictures of progress. I spent a few hours making some tools to help me with the wing sanding process: Undercamber sanding block, top front camber block, upsweep block, squaring sander (just a piece of flat 1/4 with another piece with sandpaper mounted on it at 90 deg. so that I can square off the edges of the wing before attaching the basswood), and a marker made of 1/32nd ply that allows me to mark a groove to guide me as I attach the basswood.

Also added the basswood LE and started to plain wood off the wing.... this is some beautiful wood by the way.

B
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« Reply #23 on: December 31, 2009, 06:07:30 PM »

Yes B, it surely is beaut wood. Makes it more than pleasurable to be privileged to shape, does it not? Smiley

A good idea you had, re LE squaring up before attaching basswood. You are going to ease up on the upsweep & u/camber as you near tips, aren't you?

Looking very good... wish I was there hacking something out with you!

Leeper
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« Reply #24 on: January 10, 2010, 03:28:59 PM »

Hi All,
No photos (wife has the camera) but I did finish the tail feathers last night. 1st outlines the stab with thread and CA then sanded to foil using the methods outlined by Tmat in several posts on cat gliders (see here: http://picasaweb.google.ca/tmathews180/LongcatBuild#).

The weights for the fine sanded fin and stab are .5 and 1.5 g respectively. The fin has top camber sanded in on the right side (I am a lefty).

Bernard
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