8th Scale Aviation's, "CzechMate" Short-kit, Group build
 

This is a group build-log for one of the new offerings from Tim Stafford’s Eighth Scale Aviation. Five prototype laser short-kits of Czech Mate, race #86 are in-hand, and we are excited to start building them!

http://www.rcuniverse.com/forum/atta...mentid=2132270


This 1/8th scale kit features a 409 square inch wing area; and, is designed for Scale Warbird Racing, using a YS .70 engine. And, “Yes” scale officionados, it is an exact-scale planform, at 1/8th scale. Tim has one kit; “The Young Gun”, Eric has another; as does his grandfather, who will build his later; one of Tim’s friends, Mark, has the fourth; and, I have the last of the five prototypes ordered.

The Reno racer, Czech Mate, has long been one of our favorite full-scale racers; and, Eric has been “chomping at the bit” for some time now to get his hands on a kit of this plane. His only concern is that he has nearly no building experience. My father-in-law began showing Eric some construction basics when he built the Stiletto that Eric flew to a 2nd place finish at the Warbird Championship Event a couple weeks ago. I promised that when Tim finished designing the kits, that I would teach Eric how to build from a kit. But Tim, living up to his reputation of offering great support with his kits, offered to make it easier for both of us, by demonstrating first-hand his construction techniques for building this kit, as designed. (I’ve watched these threads for some time now as he’s helped Jake and Airraptor with construction of their Me209 and Tsunami kits, helped Jim A. with his Ta152, and posted construction support videos, and assisted me with my P-51 “Speed Wing” design.) This also serves to give Tim some immediate feedback on his design, to ensure it is perfect prior to wider release.


So, Tim and “The Young Gun”, Eric, came over to my place on Saturday and we began construction on three of the kits . . .

Even though they are prototypes, the kits are beautifully organized. Unlike many other kits, each assembly comes pre-packaged in its own bag. This is a quality touch that shows the amount of thought that went into the design. It means that the builder can start with whichever assembly desired (stab, vertical fin, wing panels, or fuse), open the bag, and have all the parts needed -- and without risk of losing parts to a different assembly in the process.

Unfortunately, we were so enthusiastic about getting started, that we tore into the baggies and started popping out the laser-cut parts, prior to taking a picture of the entire kit, first. The following picture shows the parts that remained, after I finally thought about it, and after we had already removed the stab and vertical fin assemblies. (Sorry, you'll just have to try to mentally picture two more bags of assembly parts, and a two-page set of CAD-drawn plans.)

http://www.rcuniverse.com/forum/atta...mentid=2132326

We set up a workspace where all three of us could work together. In my main shop, I have a counter that would allow us to work on the assemblies, pretty much side-by-side. Here is Eric unrolling one of the two pages of plans for a "sneak peek."

http://www.rcuniverse.com/forum/atta...mentid=2132338

We began the construction process with the horizontal stab assembly.

The first picture shows the laser-cut airfoiled stab pieces and the stick stock cut to shape. The assembly towards the front is mine, and to the rear is Eric's.

Tim would model the construction process first; I would model it for Eric a second time, if needed; then Eric would assemble his.

The stab is built flat on the building surface, with both top and bottom halves.

http://www.rcuniverse.com/forum/atta...mentid=2132339

Here are the top stab halves framed-up:

http://www.rcuniverse.com/forum/atta...mentid=2132341

Prior to sheeting, the stick stock is then razor-planed and sanded because the kit features scale, airfoiled surfaces. Here is Tim demonstrating the procedure:

http://www.rcuniverse.com/forum/atta...mentid=2132342 http://www.rcuniverse.com/forum/atta...mentid=2132343 http://www.rcuniverse.com/forum/atta...mentid=2132344

After the halves are sheeted, they are removed from the building surface and glued together. In the first picture, I have glued my two halves together, and am sanding the trailing edge flush. Eric is removing his second half, preparing to glue his two halves together with medium CA.

http://www.rcuniverse.com/forum/atta...mentid=2132346

Here is Eric holding the stab pieces together tightly, as the CA sets:

http://www.rcuniverse.com/forum/atta...mentid=2132347

With the stab assemblies completed, we turned our attention to construction of the vertical fin assemblies.

They are built in the same manner as the stab. I pulled a "rookie move", however . . . I got too comfortable with the process of the stab, building two identical halves, that I forgot to reverse my second half of the fin, accidentally building two right halves. And, of course Eric had already glued his right half. So, I had to disassemble mine, cutting the airfoiled pieces from the sticks, then having to re-cut new stick pieces.

Here is Eric's completed stab, and the first half of his vertical fin being framed:

http://www.rcuniverse.com/forum/atta...mentid=2132348

Tim's completed stab, and nearly completed vertical fin and rudder:

http://www.rcuniverse.com/forum/atta...mentid=2132349
Tim and Eric tack-glued their rudder and elevators to their respective main assemblies, and then sanded the control surfaces to match the airfoil shape of the main assembly. They will later taper the leading edges of these control surfaces and install CA hinges.



My completed stab, and nearly completed vertical fin and rudder:

http://www.rcuniverse.com/forum/atta...mentid=2132350
I chose to hinge mine, using 1/8" Robart Hingepoints, first. I then slid my control surfaces together, with the hinges installed (but not yet glued) and sanded the airfoil shape into the control surfaces. In this manner, I hope to avoid any possible mis-alignment of the two surfaces due to incorrectly cutting/aligning the hinge slots/holes. I will taper the leading edges, glue the top block of the vertical fin, and sand to shape once we meet up again to continue the group build process, this Saturday.

Nice.... I love the Czech Mate as well. Always wanted to build a round cowl where the engine would totally be hidden in the cowl. No drag.
Keep the posts coming Ollie.

Nicely done Ollie.
I think we forgot to take pictures on how the carbon fiber tube was installed.

I can't wait to get this scale czech mate done, by far one of my most favorite warbirds of all time. Plus with this bird under my radios control she should live up to her legacy! Lol.

Whether this one will fit entirely within the cowl remains to be seen. The CAD views show that it just barely fits within. However, I am worried about it being so close that the heat might distort the cowl if we don't allow some clearance around the valve cover.

Hey, I was busy constructing that racing mod -- so recording it was your job! ;)
(Just kidding, Tim.)

Yeah, I was thinking about that when I was driving home from RC Country this evening. I guess all I can do is describe the process:

I had a scrap length of 1/8" diameter Carbon Fiber tube, and decided to use it to reinforce the stab to ensure it would absolutely withstand the Gs affecting it during tight pylon turns. I had just enough to cut two pieces that would extend to all but the outermost rib of the stab. I used one length in my stab, and gave the other piece to Eric. Sorry Tim, but you're S.O.L.! (You said it shouldn't need it; guess you'll find out! Sucks to be the guinea pig, huh?)

So before gluing the two stab halves together, I measured 2" forward across the length of the trailing edge of both stab pieces, and placed a pencil mark on each of the ribs. I placed my metal ruler on the marks and cut a shallow "V"-shaped notch out of them, towards the LE, nearly 1/16" deep. I then wrapped sandpaper around my length of CF rod and sanded the notches to accept just barely more than half the depth (diameter) of the rod. I used 30-minute epoxy, very slightly thickened with just a tiny bit of microballoons to help fill any gaps, to glue the rod into the grooves of one half. Next, I put some of this thickened epoxy to the slots in the other half, as well as applying medium CA to the ribs and stick stock of the other half. I then carefully- but quickly- aligned the two halves together, and pressed them together until the CA set.

http://www.rcuniverse.com/forum/atta...mentid=2132399
This is me holding the halves of the vertical fin together until the CA sets; NOT the stab. But beings it is the only picture Tim took with my camera, and is also the only one I have left that I haven't already posted, it will have to do. (You also have to read into that last sentence a sarcastic tone, jokingly giving Tim a hard time.)

Revision:

Tim posted a picture of the stab he built for his Bearcat, using the same process for reinforcing the stab that Eric and I used in our Czechmates. Tim stated he measured up about an inch from the TE on his stab. Other than me measuring 2" from the TE, and the shape of the stabs, this picture is very accurate to help you see what I described, above.

http://www.rcuniverse.com/forum/atta...mentid=2133839
A couple further notes:
- Any tube extending beyond a rib into an open bay is dead weight (not that it ways much).
- Note the slightly thickened epoxy in the grooves of both halves of the stab.
- Upon reflection, thickening the epoxy with fibers from chopped (scrap) fiberglass cloth may have contributed slight additional integrity, compared to micro-balloons.

Hi Ollie

I have an unrelated question and your the first person I thought of that might be able to answer my question. Related to the YS 115 WS engine.

Do you know where I can find or make a ring compressor for the crankshaft ring on this engine. I hate shopping. Especially on line so any info you
have would be extremely appreciated. Looked on central hobbies, YS engines and finally gave up. Even a crumb in the right direction would help.

Thanks Ollie.

Ray Brindos or Sergio Vario could probably answer that engine question for you.
I believe they machined a ring compressor from a thin piece if stainless tubing.
It slides over the crank ring and is then displaced as you install the crankshaft into the case.
We used it to convert my old original 115 to a WS.

TommyGun nailed the response for you, Dan. Thanks Tommy.

Very cool! Looks like I am going to have to "happen to be in the neighborhood" and check on your progress.....

Steve Nickerson

Marty,

Here is a shot of what Tim's CAD drawings show regarding engine/cowl clearance:

http://www.rcuniverse.com/forum/atta...mentid=2132771

As you can see, it is going to be close.

I guess "shaming" Tim about not taking pictures of the stab reinforcement worked . . . well sort of. I didn't get any pics of the modification Eric and I made to our stabs, but Tim did share some other pictures that he took. So now, I will share them with all of you.

http://www.rcuniverse.com/forum/atta...mentid=2132774
The iPhone shots always seem to load onto RCU sideways, and when rotated and saved, still do. I'm tired of trying to fix 'em, so here is a nice sideways shot of Eric and I, early in the process, gluing the frame of our first stab halves.


http://www.rcuniverse.com/forum/atta...mentid=2132782
I believe this is Tim's completed stab and ailerons, after contouring everything to an airfoiled shape.


http://www.rcuniverse.com/forum/atta...mentid=2132784
Eric contouring the leading edge of his nearly completed stab.

http://www.rcuniverse.com/forum/atta...mentid=2132799

Tim's two halves of the vertical fin. The laser-cut Vertical Saddle piece is inserted against the bottom of the lowermost half-rib, after sheeting. Then, the sheeting is trimmed to match. (Note that we left some of the sheeting towards the trailing edge to later be trimmed more precisely, after fitting the fin both around the trailing edge of the horizontal stab, and to be glued to the rear of the fuselage.)

We'll be continuing the build this Sunday, if you want to come by at your convenience, Steve. We'd love to see you, and talk to you face-to-face!

You've got plenty of room in that cowl.
Most you'll have to do is cut a small slot to prevent the front bottom of the rocker cover vein chafing.
Your biggest benefit will come with proper restriction of the cooling air coming into the cowl as well as proper sized outlets for the hot air.