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Apr 09, 2018, 06:09 PM
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Build Log

PuRES V2 Re-Tooled: Back Again

As was most everyone else involved with F3RES airplanes, I was disappointed when Josef Gergetz had to discontinue production of the Slite and PuRES. However, he has transferred both designs to Hollein, and the PuRES is now available. Mine arrived (via Zeller Modelbau) just this past weekend. I promised some one that I would re-do the first build thread, and we will see how this version stacks up to the very nice original.

I discovered the original PuRES on YouTube, watching some guy in far-off Germany hand toss a nice-looking, built-up 2-meter airplane across a field of what looked like young corn - and it just didn't come down! There was enough information on that video I was able to make contact, and he (Josef Gergetz) agreed to send me a kit. I thought the price at the time was too good to be true, but like all else that has gone on with F3RES, it has been a wonderful journey for me. While Josef designed the Slite to be a "better" PuRES, I did not at first find it so, and it took a while for me to adjust my ways before the Slite began to truly perform. Even so, for contest work, I still found that some days, I flew the Slite better, and some days I flew the PuRES better. I know that others thought the same, mostly because both airplanes keep showing up, both stayed in production together, and I even saw a Slite fuselage with a PuRES wing. So, when I lost my own last PuRES to a radio incident, I was pretty disappointed. No longer, the PuRES is back.

I ordered a new PuRES on a Monday morning, and within fifteen minutes, I had a tracking number for shipping. Supplier response was that fast: minutes. Shipping was not, involving some customs, and no one can help that.

The airplane arrived last Friday, right after I had departed for a contest in Phoenix, so I did not get to see it until last night. Opening the box was a treat. Both the shipping box and the contents arrived in immaculate condition, well-packed. Contents included a lot of German-language material, including a publicity sheet for what looks like an Alpine Soaring Meet, several versions of customs and shipping documents and a nice, color-printed instruction booklet with lots of illustrations.

There is a full-sized drawing rolled up as part of the contents. It appears as a revised edition of Josef's original, supplemented with lots of notes. I wish I could read them. As before, all parts are color-coded - for instance, pale green denotes a part in 2mm balsa sheet, Gray-scale denotes carbon, and so forth. Servos that will fit are called out, and the use of the enclosed jigs is shown.

Materials are the same as for the original PuRES, and conform to the established F3RES rule set. The balsa and plywood both are of superb quality: the ply is almost polished and without apparent warp of any discernment. The grain in the balsa is almost invisible. This version includes the tapered tail boom that you guys who got their PuRES late already enjoy - and, it is already pre-drilled for the tail posts and control slots.

Hollein is known for laser-cut kits, and now most of the PuRES is laser cut as well, instead of CNC-routed. Note that I said "most". Some parts are still CNC-routed, where that process makes more sense such as 3-dimensional parts. Trailing edges are still routed, and that makes a lot of sense when you see them. The laser-cut sheets, though, are jewel-like. I have no knowledge of how laser cutting really works, but I imagine there is a unit to describe the width of cut, and a unit to describe the burn power. Here, I'd have to estimate the cut width as about 2 nano-frog-hairs, and the power as about twenty-two gazillion Erg-Zapps. Part numbers are etched on parts big enough to show them. In addition, sheets are etched with numbers that match the drawing call-outs. If you are missing a sheet, I imagine that you could order one separately. Parts include Josef's jigs for ensuring that all ribs are straight, all dihedral angles are proper and the boom is properly aligned with the pod. I am anticipating the extreme satisfaction of a very precise build.

There is no strip wood or uncut sheet: every single part is cut-to-fit. If it doesn't fit, you've got the wrong part in your hand, buddy.

There is a suggested sequence, and I will be following it: tail surfaces, fuselage then center wing panel. Finish with outer wing panels. I will also be using all the enclosed parts with this exception: Hollein includes the usual steel push rods, but I will be using pull/spring, just because I am comfortable with them. So, I hope this build thread will function as an adequate substitute for German-language instructions, if that has put you off buying one of these really nice airplanes.
Last edited by glidermang; Apr 09, 2018 at 06:15 PM.
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Apr 09, 2018, 07:53 PM
An Original!
Gliderguy's Avatar
Looking forward to another nice build thread.
Apr 09, 2018, 08:06 PM
Registered User
mdickey's Avatar
Good luck on the build. I'm excited to see how the updated kit turns out and how it flies vs the other planes you have built up this winter!
Apr 09, 2018, 10:32 PM
Registered User
Watching intently.
Apr 10, 2018, 02:32 AM
DLG Bug Bit Me
Tim Harbour's Avatar
Thank you for your thorough and methodical approach once again Greg. Will be watching.
You got me motivated to get my PuRes a couple of years ago with the original slab tail surfaces.
Only flown it a couple of times due to family commitments but will be enjoyed in the future I have no doubt.

Keep up the posts.
Apr 10, 2018, 01:00 PM
Registered User
Hi Greg,
Looking forward to your build! Really like that Pures and hope to order one soon.
Apr 10, 2018, 01:22 PM
Pro Bro #829
steener's Avatar
I was on the list for a Slite for about a year when I got the email he was closing up. Glad to see theres still a possibility.
Apr 10, 2018, 07:03 PM
Registered User
Thread OP
Glad to see there is real interest. Sometimes, a thread is like shouting down a dry well.

Today, I prepared the tail surfaces. Total time working was roughly two hours, start to finish. The tail surfaces provided are sheet balsa only - there is no longer (for the time being) the option of built-up, profiled tails. Still, what is provided is very high quality, and I enjoyed myself very much.

A word on general issues, here: For wood-to-wood joints, I use only TiteBond wood glue. There are other wood glues, and I am sure they all work. Titebond is easy for me to get, water soluble and thinnable, and sets up quickly. It can also be used to laminate sheets, and can be very quickly set with heat. CA (either thin or medium) could also be used, but I am now allergic to CA, and must limit my exposure. Even so, I use medium and thin CA for wood-to-carbon and carbon-to-carbon joins. Nothing else works. I just make sure to have lots of air moving by, wear a mask, and get it done quickly. Occasionally, I use 1-hour epoxy for specific joins, but limit its use because of its weight. I regard epoxies that set up quicker as too brittle.

On to building.

I first isolated and brought together all the parts associated with the tail, including the 2mm carbon posts that the tails will mount on. Everything wood has the part number etched on it, including a suffix of either "L" or "R" to denote left or right. The only preparation I did at this point, was to remove the spacers in the "PURES" logo, and the lightening holes in the elevators. Do trial-fit the tail posts into the 3mm carbon tubes - I bet they won't go, at first. Don't panic, but round off one end (only!) of a post, until it fits into the tube. It only takes a few seconds, using fine sandpaper or an emory board. You are removing fuzz left over from the cutting operation. Only shape one end.

I glued the end pieces on each elevator and fixed surface, then weighed them down flat. While they were flat on waxed paper, I inserted the carbon tubes and used a couple of drops of medium CA to fix them in place. After a few minutes, it was possible to pick up each fixed tail, and use more medium CA to really fill any gaps between the tube and balsa. The tubes on mine were a couple of millimeters too long - we will deal with that later.

After the glue set on the tubes, I used a sanding block with an aggressive grit to sand the tubes flush with the tail root. That took only minutes, and I was careful to keep everything square. I used a fine sand paper block to clean up the trailing edge of the fixed tails, and the leading edge of the elevators.

Some more wood glue with a toothpick, and the plywood end pieces found on plywood sheet 75.09 went onto the root ends of all fours surfaces. I made sure the triangle pieces on the elevators were even along the bottom edge of the elevators. Be aware that the end pieces of the fixed surfaces are NOT IDENTICAL! Neither are the two surfaces. The carbon tubes are offset from each other, to allow room for mounting on the boom. The right side should have the word "PURES" facing up, and the carbon tubes are off set aft, from the tubes on the left surface.

When that glue had set, I polished all four surfaces, top and bottom, with fine sandpaper. All excess glue that had spilled out of the end pieces was now gone, and the surfaces are ready for shaping. I marked the center of the leading edges of the fixed surfaces from root to tip. We want to do more than just round off the leading edge; we want a sort of oval shape, and the ply root end gives us the desired profile. I used a coarse block to taper the leading edge, then did final rounding with a fine block. It only took minutes.

For the elevators, all shaping is guided by the root ply pieces. I decided to only shape the top. I started with a razor plane, and took about five strokes the length of the elevator. That got me about half way home. I used a coarse block next, and took care to always stroke the entire length of the elevator. When it got close, and all the divots from the razor plane were sanded away, I finished up with a fine block. The outer tip was shaped to match the outer tip of the fixed surface.

The leading edge of each elevator was then sanded to a roughly 45 degree bevel, to allow hinging.

I did another trial fit of the tail posts, and had to use a 2mm drill to re-open one of the tubes. The tails are ready to cover.
Apr 10, 2018, 09:17 PM
Registered User
Thread OP
I thought these pictures might be interesting. Without glue, I mounted the finished tails onto the boom.

The posts are a bit too long, and stick out the bottom. When I'm ready to finalize the tail mounts, I will apply a drop of CA to the bottom of the posts, then remove the tails and glue the top. The tails go back on to help align the boom to the fuselage in the roll axis. The excess posts will be removed with a Dremel cut-off wheel.

Please note that there are two slots on the TOP repeat TOP of the boom, where the controls emerge to connect to the elevators.

Yours, Greg
Apr 11, 2018, 09:56 AM
Hates Palm Trees
Hey Greg...............Is there a built up option for the tail still or only the solid balsa version shown?

Apr 11, 2018, 10:13 AM
Registered User
gliderguide's Avatar
Solid only at this stage.
Apr 11, 2018, 12:46 PM
Afflicted with DDD
Soarhead00's Avatar
Originally Posted by SteveK123
Hey Greg...............Is there a built up option for the tail still or only the solid balsa version shown?

Do you think the original PuRES built up tails could be retrofitted?
Apr 11, 2018, 10:18 PM
Registered User
Thread OP
Steve, Bob:

GliderGuide is correct: only sheet balsa tail so far. However, the spacing is such that either the Slite or original PuRES built-up tail is a slide-on replacement.

I cut out all the parts for the fuselage today, but other affairs kept me from actually doing any building. Look for it tomorrow.

Yours, Greg
Apr 12, 2018, 02:30 PM
Registered User
banjo328's Avatar
I'll be interested in seeing how the 'new' Pures flies compared to all the other 'Pureses' here. Is the price for one kit and shipping reasonable compared to old pricing and multiple kits in one shipping ?
Apr 12, 2018, 04:31 PM
Registered User
Thread OP

The price is creeping up, but still entirely reasonable. I have had inquiries about shipping multiple kits; I know Zeller Modellbau would be willing to do so.

Yours, Greg

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