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Jan 08, 2020, 11:26 AM
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Build Log

Yellow Jacket GS Build Log

Someone requested a build log on the Yellow Jacket GS. I discussed it with Corky Miller, the designer, and he agreed. The current Yellow Jacket thread has become an enormously fruitful and wide-ranging forum for all kinds of RC soaring discussion, and the build aspect has become obscured. I have a brand-new Yellow Jacket GS kit (with V-tail) and have only glued together a few parts, so the timing is right.

This build log will conform to Corky's design, which is perfectly sound and developing a wider and wider number of fans. Corky's own contest performances are a strong indicator of the strengths of his design work. The Yellow Jacket is not available in Europe. But, it has been to Europe and contended with the best. The German Open in September featured the toughest soaring conditions I have personally encountered ever. The Yellow Jackets present took it in stride.

I have enjoyed my association with Corky for several years, now. I have an early Yellow Jacket myself, with both Standard and early Lite wing. There is a full ounce difference in weight between the two wings, and I can swap wings at any time, and fly again with no change to any setting on my transmitter. I have a 1.5m Yellow Jacket, and I ommitted the spoiler servo, spoiler and tow hook to save weight. I throw it, and as long as I don't over-do my throw, I don't damage my shoulder and it is a delight in light lift. I'm running nearly 50% on both elevator and rudder, and it is responsive. And finally, I have a 3M Yellow Jacket, with two different wings. One is stock, and the other is a one-off Corky made for me as an experiment. I also have two fuselages: one is the early CLM-sourced fuselage, set up for pure glider. The other is an Art Hobbies fuselage that weighs 4 ounces less, and has a recessed wing mount with (I think) reduced drag. It is not suitable for power, but both wings and both fuselages produce long flights with minimum fuss in pretty much all conditions. In short: good products. Since I got my 3M Yellow Jacket, Corky has obtained much lighter fuselages form CLM, and that is what you will get. I predict you will be happy.

I'm going to build in this sequence: fuselage, wing center section, wing outer panels, then tails. Finally, assembly and covering. I will make some choices as we go: for instance, which servos and whether servos forward or aft (Corky's latest kits allow the option).

The Yellow Jacket is not available in Europe. But, it has been to Europe and contended with the best. The September contest featured the toughest soaring conditions I have personally encountered ever. The Yellow Jackets present took it in stride.

I continue to be amazed at all the angst and hype there is regarding V-tails. When I go through this build thread, I think you be surprised your selves as to (1) how much like all other Yellow Jackets it is; (2) how basically simple it is; (3) and how easy. Really easy. I will be using Corky's excellent steel push rods, and they go in quickly and provide positive, reliable control.

Pictures and starting the fuselage probably this afternoon. Right now, I gotta go fly!

Yours, Greg
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Jan 08, 2020, 11:38 AM
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mhodgson's Avatar
Should be interesting to follow.
What does the gs mean/stand for?
Jan 08, 2020, 04:46 PM
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R2R's Avatar
I'm very interested in the GS version, so I'll be following along, as well.

Jan 08, 2020, 09:04 PM
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Fuselage, Part One

Before I start, I get out my usual tools: exacto knife, sanding blocks ( I rarely use plain sand paper any more), glue (Titebond wood glue for wood-to-wood, CA for wood-to-wood and wood-to-carbon joints), razor saw, clamps.

I start with the fuselage on the Yellow Jacket. The wood parts are all in one bag, and the boom is usually wrapped in the plan. The note-paper sized sheet will have the actual instructions. I follow the sequence of instructions, with one or two steps altered, slightly. If you follow the instructions to the letter, you will do well. I have heard from others that Corky's instructions do not always have every little detail, but he is stepping along a very fine line: enough to get the job done, versus so much instruction that the builder feels insulted.

So, today, Step #1: Find that boom, and grab it tight. Do not let it go before you do this one, crucial step: mark back five inches from the big end, and cut off five inches. Corky gets booms from a supply house, and they are too long as fabricated. Trimming is up to you. I use a cut-off wheel in a Dremel - takes about three minutes. I finish by sanding the end smooth and square to the axis.

The reason I do this FIRST, is because I have forgotten to do itat all at least twice! On the normal Yellow Jacket, that error is entirely survivable. On the V-Tail, you really, really need the small end, along with those eight 3mm holes drilled in it.

Save the scrap boom end! It will be handy to splice a broken boom in the event of a mishap. Been there; done that; got the coffee cup.

Next. locate the nose block pieces, usually rubber-banded together for you in the parts bag. Glue them together. I don't think Corky would mind that I cut the "tabs" off the two middle pieces, to have a little space for ballast. Clamp the nose pieces together then set aside to cure or dry.

As per instructions, I use the formers to dry-fit the longerons onto the fuselage base. The longerons are too long, but I don't trim them until they are glued down. Line them up at the front, and let them stick out the back. It may be necessary to sand the longerons to fit in the notches in each corner of each former - just do it, if necessary. The closer to flush each longeron is the edge of the fuselage base, the tighter and stronger your fuselage will be.

Now, we can start gluing things.

I start by gluing the plywood sheets to the balsa fuselage sides. Take good care to line them up. I use thinned, water-based Titebond for this, and it is never-fail. Spread glue on the plywood, and make sure every square centimeter is coated. Line up the plywood and balsa carefully, and weight it down to the building board with as much weight as you can get a hold of. Do one side, and then make pretty darn sure you make the OTHER side, so that you have a right side and a left side. Making two lefts (or two rights) is pretty not survivable.

I glue in each former, clamping it to a right-angle block to ensure verticality. Last to go on is the nose block. Before I glued on the nose block, I took it to my little belt sander and made sure the bottom was square with the sides. Formers in place, I then glued in each longeron. Note that the instruction reverse the order, and that may indeed be quicker. But, I did the formers first. I did the longeron on one side, and clamped it to my work board. After about a half hour, the Titebond had set, and I did the other side. Because everything is clamped to the flat board, it will cure nice and straight.

By this time, too, the fuselage sides are cured. Weighted to the board, they should also be pretty straight when you remove the weights.

The sun has set, and my current work space doesn't have sufficient light, so that is it today.

Note: I forgot an important part. Please skip ahead to the next installment and check out installing the plywood tow hook foundation!
Last edited by glidermang; Jan 09, 2020 at 07:26 PM.
Jan 09, 2020, 01:30 PM
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sunnybreeze's Avatar
I'm in on this build! My buddies and I are looking to build 4 YJ's so the GS version has my interest. Hurry up!

Steve in Maine
Jan 09, 2020, 02:22 PM
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R2R's Avatar
Love that you are including how much time you spent! Very useful detail, along with your always very detailed account of the construction.
Jan 09, 2020, 05:27 PM
volare est vivere
ray foley's Avatar
. . .
Last edited by ray foley; Jan 11, 2020 at 05:49 PM.
Jan 09, 2020, 07:23 PM
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Fuselage, Part 2

For all those (after all, there may well be more than one of you) who think I know what I'm doing. I have to tell you I left out a critical part last time: the foundation for the tow hook.

In my own defense, there is not one word about it in the fuselage instructions, nor a single image on the drawing that shows what Corky intended. Even so, I was aware of it, and I forgot!

However, there is this: I have built several Yellow Jacket fuselages, and made this mistake before. It is survivable, so do not despair!

Corky's intention is that the plywood foundation piece go down on the base of the fuselage, centered directly on the tow hook slot. It fits in that position exactly. The tabs match slots in each side. The basswood longerons are to extend from the nose block, to the plywood, then from the aft end of the plywood to former F3. The pieces cut out to allow the plywood to lay flat are then glued onto the plywood. They no longer contribute to the strength of the fuselage, but serve instead to keep the tow hook itself from twisting.

Here is what I'm going to do, to install the forgotten-but-necessary plywood, and still meet Corky's intent:

I marked the plywood to match the width of the fuselage between the longerons. I used a belt sander, and then sanded the plywood to fit. It took about two minutes, maybe less, once I let my baby-sized belt sander work up to speed. It dropped right in. I picked it up, applied glue, and re-inserted it.

So, you may ask, without the tabs fitting into the sides, won't it pull out? The two I've flown installed this way are going strong, no issues. The 1/8th balsa bottom is strong, the glue joints are strong, and the focused tension of the tow line is spread out across the entire plywood part. The tow line tension will never exceed the initial tension on release, anyway, which is less than ten pounds for F3RES tow lines.

Now, on to the rest of the fuselage.

Here, we must face our first Builder's Decision Point: Corky thoughtfully provides for mounting the servo tray either aft or forward. Since I hugely resent any nose ballast, I am glad for this choice. But, I do not make it quickly. I moved the servos forward in my previous YJ, but without moving the servo tray: I just wrapped each servo in green Frog Tape and glued them to the side of the fuselage, butting up against former F1. That left space between them to pass the power leads from the battery. In this case, given the provisions, I elected to mount the servo tray in the froward position.

Before I glued the servo tray to anything, I applied some scrap spruce to the underside, to provide secure grip for servo screws.

Now, I've played this song before. I first made sure everything fit, then lined up all the equipment: clamps, blocks, glue, and all the parts. Once the glue is applied, you have to go all the way to the end without stopping for anything: text messages, lunch, the apocalypse, anything at all. During the dry fit, it became obvious that there was some minor misalignment between the sides and base - I therefore took the base (with its square formers) as the foundation, and let everything else follow that. The base was nearly perfectly flat on the table, anyway.

I gathered all my big clamps, plus various blocks and wood to act as a means of applying spread out pressure. The granite blocks are bases from discarded trophies (who needs trophies, anyway?). The wood cubes are true cubes, available from Hobby Lobby; about $10 for a dozen in a bag. The wood tablet-looking things, like dominoes, are also from Hobby Lobby, much cheaper than the cubes, actually. The orange bench clamp is old school, but works. The trigger clamps are all from Harbor Freight, less than $2 each.

Corky recommends CA for this job, and if you are not allergic to CA as I am, I say go for it. Start at the front, and work aft. Originally, epoxy was called for, and I've done it that way, but use at least 30-minute epoxy, or slower - otherwise, you won't get done before the epoxy starts to cure. This time, I used good old Titebond, my favorite wood glue, and it went fine.

You can look at the pictures. First of all, insert the formers F4 and F3 onto the boom, but keep in mind that the boom must not be glued during this process. I glued the servo tray to one side, then buttered up the contact areas of both sides. The sides went onto formers F1 and F2, then I clamped the granite blocks between those two formers. That brought each side into full cantact with the (1) base; (2) formers F1 and F1; and (3) the servo tray. Using more clamps and various pieces of straight wood and blocks, I then worked alternating forward and aft, until the entire fuselage was clamped up for curing the glue. I concluded by making sure the boom could still rotate in formers F3 and F4 (it does!). We are done for the day. Total time for me, including taking pictures, was roughly two hours. Most of that fretting over forgetting the tow hook foundation.

The bext morning, I removed all the clamps/blocks/pads and examined everything. I am very happy with this fuselage. There is excellent bonding between the sides, formers and base (with the minor exception of a short gap between the sides and right longeron, aft of former F3). I am very happy. It is easy now to glue up the wing saddles and clamp them in place.

Note for those who might think wood glue could be difficult to use: I use Titebond, original formula. It is water soluble. I use it "raw" or mxed with a little water (about three drops to a half teaspoon of glue) It typically sets well enough to handle in twenty minutes or less. Full strength is achieved in an hour or so. It sands well, and can be mixed with sawdust for cheap, light, sandable filler.
Last edited by glidermang; Jan 10, 2020 at 11:12 AM.
Jan 09, 2020, 07:36 PM
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I am absolutely sure that everyone would be truly interested in your build. Please start a thread of your own, and that could easily grow into a forum for other people interested in powered sailplanes.

I am all for powered sailplanes, just not there, yet. I do act as CD for our annual Buzz Averill Memorial, and appreciate the cagey risk taking that carries the winners to the trophies in F5J. I can see RES F5J being a coming thing.

Yours, Greg
Jan 10, 2020, 12:50 PM
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sunnybreeze's Avatar
Not to get off the track of this great build, but someone correct me if I am wrong but it was my understanding that the 2meter RES class was minimum use of composites. I was under the impression a composite pod was not allowed for competition. Can someone please clarify this for me.

Steve in Maine

PS: Good save on the Tow-Hook!
Jan 10, 2020, 01:50 PM
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banjo328's Avatar
I also believe that a composite pod is not allowed but that is academic with the YJ because it isn't a composite pod/fuselage. Composite/CF booms are allowed.

Excellent build thread Greg ! I've built 3 YJs , 1.5 M, 2M RES, 2M electric, wood fuselages and I still get good tips from your build threads. One 'tip' I use is to always use wood glue, not CA, or epoxy, on any parts /joints that will require sanding. Makes it much easier to shape the nose block and 'round off' the corners of the fuselage.
Jan 10, 2020, 02:24 PM
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plane_tech's Avatar
What is the span on this version?

As far as the composite fuselage... I m not sure where it is stated that you can not use one.
I have flown at several woodie / RES events with a Bubble Dancer and it is well within the allowable specs.

RES/ NOS might be an issue.

Maybe you are thinking of the F3RES regs?
2. Model:
2.1. A model normally consists of wings, fuselage and tail. Flying wing models that do not have a fuselage and rudder or vertical stabilizer, or none of these components are also allowed if they have a total of only two (2) control surfaces. Each of these control surfaces must be actuated by only one servo. Otherwise, the building codes for a conventional model described herein apply. The model shall be fabricated primarily from wood. This means:
a) For the wings, GRP/CFRP/Kevlar tubes or shapes may only be used for spars, wing leading edge and joiners.
b) The tail boom for the tail unit may consist of a GRP/CFRP/Kevlar tube or shapes. The composite tube or shape may not extend forward of the middle of the root chord of the wing.
c) The wood parts of the fuselage may be reinforced on their surface with GRP/CFRP/Kevlar.
d) Control rods are exempted from CFK/GFK constraint.
2.2. The following Are Not allowed:
a) An all-GRP/CFRP/Kevlar or other plastic fuselage or fuselage pod
b) GRP/CRP/Kevlar monocoque construction wing or tail leading edge, also no GRP/CRP/Kevlar DBox
Jan 10, 2020, 02:47 PM
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Crashbound's Avatar
Thanks for taking this on. These very useful build threads tend to get clogged up like a belt line at rush hour with all manner of things not specific to the build, and become cumbersome to wade through. Received the new 3.5 yesterday, new 2m delivered today. Ready to start building!
Now, I'm not going to comment further unless I have a question or something specific to the build to contribute. Just again, thank you!
The other Greg
Last edited by Crashbound; Jan 10, 2020 at 02:58 PM.
Jan 10, 2020, 02:51 PM
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Jan 10, 2020, 04:02 PM
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banjo328's Avatar
"Maybe you are thinking of the F3RES regs? "

Yes, as stated in your post.

All of the F3RES kits presently on the market conform to those rules. The fact that the FAI has yet to adopt F3RES as an 'official' class doesn't help with the confusion.

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