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Old Jul 07, 2014, 09:46 AM
”ʇsol
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Joined Jun 2004
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Build Log
GP Spectra Build

Hi all - I've been slowly putting together a Great Planes Spectra kit I've had sitting in the closet for the past 10+ years. Haven't done anything with gliders since the mid-90s and this looked like a fun project with a few "firsts" for me.

I somehow neglected to do a real as-I-go log, so it's time to get up to date!

Popping the box and getting started -- first, I have to admit I know next to nothing about electric power. Ok, enough to be dangerous from what I read on line. My only previous experience was a Great Planes Electro Streak (got the kit for next to nothing from someone); when I built it they were still using nicad packs:



...so, modern batteries and motors were part of the learning experience with my Spectra build. I knew I could do better than the Goldfire motor and 1lb of lead batteries, and tinkering with some of the calculator spreadsheets I hope I figured it out (I'll leave those details until later).

The Spectra plans put the old nicad pack around the CG but the lighter weight brushless motor meant some changes might have to be made to make things balance. I ended up just trying to keep things light around the tail while shifting the batteries forward of the CG. The only change I made to the tail was a slightly larger rudder (based on some comments I've read).

Starting with the tail, watched by the ever-present supervisor:




Slightly larger rudder over the original drawings:


Incidentally, I used different "white" glues for most of the construction. After some experimentation I settled on Gorilla Glue - Wood Glue. I tested several balsa joints with it and it held up great, dries quickly, isn't runny, and sands very well. I used Titebond II on the rudder and didn't like it much - too yellow and too hard to sand. CA? Yup, used CA here and there but I seem to do better with traditional glues.

Stabilizer:
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Old Jul 07, 2014, 10:56 AM
”ʇsol
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Joined Jun 2004
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After the tail I jumped (well, crawled) toward building the fuselage. Fuselages: can't stand 'em. Love wings but can't stand fuselages. Have to get through this part, or as much as possible, then move on. Didn't hardly even take any pictures of the ordeal.

They made an effort to make everything self-jig and it mostly did. I didn't cut any additional lightening holes in the fuselage but I made an effort to keep the rear-fuselage fairly light. With that in mind I decided to use a pull-pull control system on the rudder. For cable guides I used the smallest nyrod material Sullivan makes (originally for very thin throttle cables). In the long-run I'm not sure I really shed any weight doing this, but it worked pretty well.

Not a lot of pictures...here's the rear fuselage, shaped, the two pull-pull guides are visible:


My first "first" during the build - using magnets on the airframe. The plans call for using a rubber band to hold the canopy down from the inside. I used that system on a Jetco glider years ago and it was really lousy. It worked, but what a pain. I played around with some small magnets and ended up giving it a shot.

Now, these magnets? Probably overkill but they worked out great. I used two sets of magnets instead of just a magnet and a metal plate. I recessed the two magnets on the canopy frame and made two small mounts for inside the fuselage. Two small hard-balsa guides keep the canopy from slipping side-to-side. The canopy is actually pretty easy to remove, even with the magnet-to-magnet setup.





Then, tinting the canopy itself. I used a small tank with two packs of black and one pack of blue RIT dye. Probably should have just used blue but it doesn' t look bad:



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Old Jul 07, 2014, 10:57 AM
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I highly recommend reading this this web page:
http://www.charlesriverrc.org/articl...spiritmods.htm

I also have a GP Spectra that I intend on building this summer and I intend to include all of those mods.
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Old Jul 07, 2014, 11:06 AM
”ʇsol
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Thanks - I read that page quite a lot. I'm aiming to start with a CG a little aft of whats on the plans, then we'll see how their suggestion for 1/4" aft really works.

I also have read lots of posts on different sites that claim the sheeted-wing mod isn't at all necessary. Other claim it helps a lot. I opted to leave it stock. We'll see
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Old Jul 07, 2014, 11:54 AM
”ʇsol
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Joined Jun 2004
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On to the wing...I elected to add spoilers as per the Spirit instructions. The Spectra parts are the same as the Spirit's (with a few exceptions). Originally I'd planned to just install the pull-cable guides and some of the other necessities, then leave it covered until later.

Yeah I know, probably overkill for a 2m electric sailplane - but the slightly added weight (two cable-guides, two pieces of trailing-edge stock and a micro-servo) didn't seem too much of a big deal. I liked having them on past projects (Olympic II, Sagitta 600, etc) so...we'll see if it was worth it.

First project was to punch out the ribs and bore holes for the cable tubes. I made the holes with a brass-tubing tool and a drill-press, stacking/pinning the ribs to keep them aligned.



Laying out the ribs, spars, and webs. The webs were pretty accurately die-cut, the rest of it wasn't exactly perfect but not bad. Heck - it's a 20 year old kit I got for next to nothing anyway

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Old Jul 07, 2014, 12:01 PM
”ʇsol
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Building the center section with the box for the wing joiner.



Yes - stock - contrary to the suggestions on other sites. I can see where this might be an issue for zoom-launches on a winch but I kept it stock anyway. I seem to recall seeing a build/rebuild log where the builder left the second set of webs off the inboard rib bays. Maybe they changed the design at some point? In any case, the webs are doubled for a few bays after the joiner-box on this wing.



Boxing in a spoiler-bay




...and eventually moved to the outboard wing panels. The die-cut webs have the wing-taper cut into them and fit pretty nicely. Lousy picture though:
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Old Jul 07, 2014, 12:13 PM
”ʇsol
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Wing tips - this caused a lot of head-scratching. No, I didn't ask anyone what they did so maybe I misread the instructions and plans. But... it seemed to me that the tips can't be shaped the way the plans show them.



They're shown as fairly square tips, but they naturally round themselves once you add the airfoil shape. I started making them upswept (similar to the Olympic II) rather than leave them as a straight "Hoerner" style tip (I think that was their goal). The slight upswept tip actually was easy and looked good, but I decided to keep it simple.

The end result looks pretty good, but no decent pictures until later.

Putting the tips on and sheeting - pretty straightforward. If I'd had 1/32" balsa for the outboard tips I might have been convinced to go with that mod but as I already mentioned, I skipped it.

The supervisor doing his inspection again...


...and the result
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Old Jul 07, 2014, 12:52 PM
”ʇsol
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Time to start thinking about covering, and...another first for me - sort of. 20ish years ago I recovered the wings of a project with Ultracote, but otherwise I've always used Monokote (aka Super Monokote). That's what I learned to use when I was a kid and I always had great luck with it. Unfortunately I've read about and have seen first-hand a lot of problems with the later generations of the product and decided to try Ultracote again.

All things considered I've enjoyed using Ultracote. The two products are really different though, and switching is taking some getting used to. Some qualities of Ultracote are better, some are worse. The product is definitely better than what I used back in the 90s though. Back then it was a really flat looking material, but this new stuff looks very similar to Monokote (in fact the transparent looks virtually the same to me).

My first Ultracote effort was the canopy frame:


Next effort was the stabilizer in transparent red. At this point I was using the material just like it was Monokote, tacking the lengthwise edges, then width-wise, then corners, pulling the wrinkles out then finishing off with a heat-gun. I've since found that it's really not necessary to be that careful, but the results were nice:



Also, FYI, Ultracote's "True Red" is practically a dead-match for the transparent red:



The wings were a little bit more of a challenge. On previous polyhedral wings I opted to cover the outboard and inboard sections separately. On this project I decided to use one piece of Ultracote for each side of the wing. Sheeting the outboard section would have made the transition a lot easier I think, but it worked out fine.

The transition between the inboard and outboard sections is one area where the Ultracote was really amazing. I doubt I could have pulled wrinkles out of Monokote on the upper surfaces of the wing near the transition area without making permanently melted-in wrinkles. At this point I ditched the heat-gun almost completely, using it just to shrink some big areas around that transition area, everything else was done with an iron. With Monokote I almost never ironed the covering down to everything but with Ultracote I have been. The stuff is really forgiving.



I'll get better pictures of the transition areas later.
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Old Jul 07, 2014, 01:04 PM
”ʇsol
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Moving back to the fuselage, gluing the canopy. What a pain. I just don't have much talent for doing things neatly in places where it counts - and this is one of those places. The instructions called for using thin CA a little at a time to tack up the frame to the canopy. I considered other options, but that seemed like the best plan...and actually, it worked. The trick was to hold the canopy "just right" so a drop of CA can get under the canopy and bond to the wood - but not loose enough so it drips or vents up inside the canopy. After a careful trimming and finishing the edges with 1000-grit sandpaper it looks pretty good.



Now for the other big fuselage challenge - covering the sucker. Really not knowing what I could get away with using Ultracote, I'd planned on doing a bottom piece, two side pieces, and a top piece. Originally the front of the fuselage was going to be an inverted u-shaped piece with seams over the two side pieces.

That plan would have worked, but as I used the material on the bottom and one side I ended up covering the opposite side and the front with a single piece with one seam on the opposite side. There are a couple of areas where the material started to "bunch up" but it's mostly pretty good. Far better than I'd have expected



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Last edited by vulturetec; Jul 07, 2014 at 01:36 PM.
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Old Jul 07, 2014, 01:36 PM
”ʇsol
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Finally things are going downhill. At least a little bit. Time to start hinging and another almost first: CA hinges. I know there discussions about the good and bad of them. I used them once on another project a long time ago and they worked out pretty well so I figured I'd try them again. These are Great Planes hinges with holes punched in the middle (recommended in a thread or two online, somewhere). Even with my tendency to make thin CA run everywhere (even with glue-tips) they came out pretty well. I made a test piece up when I was building the tail and I couldn't make them fail - hopefully they'll last.



Gluing things up - I'm lousy at lining things up and getting them straight. Honestly... so to help I installed two pins in the vertical, and drilled slightly undersized holes to match on the fuselage. The pins and holes were all on center-line making alignment fairly easy. Amazingly it was virtually perfectly square without any adjustment too. Glued on with 30-minute epoxy using thick CA on the pins to clamp it together while the epoxy set up.

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Old Jul 07, 2014, 03:32 PM
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That's a really stunning-looking airplane.

I love that red transparent Ultracoat. That'll be my first choice for covering my Marston Pterodactyl when I finally get around to building it.
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Old Jul 07, 2014, 06:56 PM
”ʇsol
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Thanks - the red is very nice. I haven't added much trim yet though, it's a little overwhelming
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Old Jul 07, 2014, 07:37 PM
”ʇsol
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Joined Jun 2004
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Back to wingtips I mentioned earlier. Here's how they finally came out.





And the transition between inboard/outboard wing panels. On previous projects (like my Olympic II) I covered the outboard and inboard separately, here I used one piece. Whatever...it worked.



Saturday's project was getting the servos installed and the pull-pull system in.
The rudder control exits came out a lot better than I'd expected. The nyrod guides didn't blend in with the balsa very well. It looked and felt nasty but I think the Ultracote really went over the bumps pretty well. Aside from that, just two little pin holes for the exits were needed.



The control horns are reshaped 1/2a-size Dubro horns. They ship in pairs that are mirror-images of each other so the holes line up properly in this type of installation.



Sunday's project was adding a little trim. Again another first - hadn't trimmed Ultracote with Ultracote before. Fairly straight forward but the material is relatively thick. I was going to just add a stripe but really wanted to see how the material handled - it worked out ok. There's more I want to do here, maybe...we'll see.

The number is the last two digits of my AMA number.



Tonight's project was tinkering with the spoilers. Worked out pretty well but the Ultracote "hinges" may not last. The material sticks just fine but it also peels away from itself easily. I may switch to Monokote or use some clear tape I have with a silicon adhesive. I'd originally planned to use small springs to hold the spoilers tightly shut but ended up using magnets with a small piece of razor-blade. So far it works ok.

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Old Jul 08, 2014, 10:40 PM
”ʇsol
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Joined Jun 2004
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Tonight's project was building the battery. Before getting involved with this build I was intrigued with the A123 cells and built a 3-cell pack for my Electro-Streak (which worked GREAT by the way).

So, like the Electro-Streak I opted to do my calculations for the Spectra around A123 cells. Everything I've come up with indicates a 2-cell pack will be ok for what I want to do. We'll see... I can always put a 3-cell pack in without much problem.



I've found the exterior tubing on the packs can nick pretty easily around the edges so I added a little tape to help with my peace of mind.

Awhile later and violą, a 2S-2300mah pack.



The pack fits as I'd planned, at an angle. I'm planning on adding a small velcro mount for it later. A 3-cell pack will fit stacked lengthwise if I need to (or go with a Lipo alternative if I want to at some point).



So far so good - just looking for enough to get it flying, hopefully it'll have enough ooompf.
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Old Jul 08, 2014, 11:28 PM
fa2
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beautiful - you sure can cover well - what a nice job - if i could build that well, i'd be afraid to fly it - lol
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