MFLOOD3800

My Feedback: (51)

Ollie
Is that a YS70 in the pic or larger engine?

Iron Dog

This 409 square-inch version of the CzechMate is designed for the YS .70. However, to me, the drawing incorporated into the plans looks more like the YS .63S, than the YS .70. I would expect that Tim has had the 63S drawn for some time now, and it just didn't make sense to waste a bunch of time to draw a YS70 in CAD just for this one model, when the two engines are almost exactly the same (in regards to external dimensions). Besides, the basic 70 and the DZ70 have minor differences, as well.

I'm sure Tim will chime in with the specifics to set us straight.

tdstaf

My Feedback: (11)

Yes Ollie is correct on both counts!
The YS manuals specify the same width height, and length for all three engines so why spend time on drawing the different variants. I have more important things to draw other then engines.

Iron Dog

Here is a very low resolution screen-shot of an early, incomplete version of the plans. It is enough to give you an overview of the scale planform of the design, and will give you a better perspective of the engine in relation to the fuse; without having to worry about Tim getting mad at me for giving away all his secrets.


Please note that these are NOT a final version of the plans. They lack the construction notes and finer details that his finalized plans include.

airraptor

My Feedback: (66)

Roy you coming out to race in the next event?

Iron Dog

Tim, Eric, and I met up again last Sunday to continue our builds.

While I helped Eric finish his vertical fin, Tim brought his new Bearcat and began building the stab for that model. I mention this here because Tim decided to use the same modification to reinforce his stab that I decided to incorporate in my Czechmate. I guess shaming Tim about not taking pictures worked, because he took pictures, this time. I edited the post that detailed this process with one of his pictures. If you are interested, you might wish to re-read that post. (I believe it was post #16.)



Here is Eric beveling the TE of the fin with a razor plane to contour it to the shape of the airfoil.

Iron Dog

After contouring the framing of the first half of the vertical fin on the building surface, Eric glued the sheeting down. After sheeting, the laser-cut Vertical Saddle is inserted below-, but flush against-, vertical rib 3, and then pressed/contoured against the sheeting and glued. Afterwards, all but about the last inch of the rear section of the sheeting is trimmed away, matching the same airfoiled shape as the vertical saddle.

Iron Dog

Eric's two vertical fin halves, ready to be glued:




After gluing the fins halves together with medium CA, Eric glued the leading edge piece on, and rounded it with a sanding block.



Alright, now Eric is caught-up with Tim and I.

Iron Dog

Now the top block is CA'd to the rest of the fin assembly.




I had already tapered my rudder and hinged it to my fin. I reinserted the assembly and sanded the top block to match the airfoiled shape of the fin and rudder.


Note that the rudder of my assembly fits flush against the fin and remains straight, as the bevel at the LE of the rudder has yet to be sanded. This bevel will be sanded last.

Iron Dog

With the tails sections largely completed, the next stage is preparing for our wing assemblies.

I began by taking the patterns for the shear webs, and trimming them precisely at the lines, by using a metal ruler and an Exacto knife.

Iron Dog

The patterns are then tack-glued to balsa sheet using either light dusting of spray adhesive and waiting a couple of minutes to get "tacky"; or, a glue stick. Stack this piece on another to cut and sand two identical pieces at the same time. (As I was prepping for all three of our wings, I had a stack of 6 balsa sheets.)






Here some shear webs are cut and sanded, and the last set of templates are glued to sheet stock.

Iron Dog

Wing plans are pinned down to our worksurfaces; and, I just had to take a sneak peak at the wing ribs!

Iron Dog

While I was prepping all the shear webs, and showing Eric how I do stacks of them at once, Tim was busy making patterns for the wing sheeting.



Now I must admit that because I was in my small workshop with Eric sanding stacks of shear webs on my belt (and disc) sander, I wasn't there in the main workshop to watch Tim at work. But, I believe he used the dimensions of the wing as drawn on the plans nearly exactly (just very slightly oversized to allow for slight misalignments when gluing) for the bottom sheeting. The top sheeting requires a little more allowance in size (beyond the dimensions as drawn on the plans) because the airfoil is semi-symmetrical; therefore the top sheeting must curve around this airfoil. This requires a little more allowance for length from front to back.



(Please chime-in, Tim, if anything I am assuming is in any way inaccurate; or, you can offer some extra details that builders need to consider in these steps.)

Iron Dog

Here is the leading edge (in the foreground) and trailing edge pieces that were cut from the orignal patterns Tim made in the prior pictures.



The trailing edge is a basic piece of sheet. This pic shows it trimmed at an angle, matching the joint at the wing center section.

Iron Dog

Views of the bottom sheeting pieces, for both the right and left wing panel halves:

Iron Dog

The top sheeting pieces have also been cut. The two pieces making up the leading edge have been glued together on all four pieces needed for both the top and bottom of both the right and left wing panels.




All four of the trailing edges of the sheeting must be beveled so they mate well, when glued together. This accomplishes a couple of purposes:
- Helps to maintain the efficiency of the airfoil, because the TE better forms a near perfect "razor-edge" (>);
- Doesn't distort the airfoil at the trailing edge (such as by introducing undercamber);
- Increases the surface area for gluing, which also serves to make the TE a little more rigid.

We measured 5/8" from the TE, then used a long straight-edge to draw lines parallel to the TE. I placed the sheets on the very edge of my workbench and angled my sanding bar every so slightly, so that I sanded an even and consistent bevel across the last 5/8" of the trailing edge. When you start cutting into the line you drew, you know you are done.

Iron Dog

Here, Tim is giving Eric some tips towards ensuring his bevel is accurate/consistent across the entire surface of each sheet, as Eric works on finishing up the prep of his sheeting pieces (in the back, right corner of the bench). Tim's completed pieces are in the foreground; and, mine are in the middle (on the left). If you enlarge the photo, and look closely you'll see that we have all four sets of sheeting prepared -- the tops are on top of the bottoms.

So, now sheeting and shear webs are all prepped. We are now ready to actually frame up the wing when we get together again, this Sunday.

tdstaf

My Feedback: (11)

Sounds good to me! Great documentation on this so far Ollie..

Iron Dog

There was actually one more piece of prep we completed with the wing sheeting. We CA'd thin carbon fiber reinforcement along the trailing edge of the right and left bottom sheeting pieces.



Tim cut thin strips of carbon fiber veil about 1/2" wide, the length of the sheeting. They are positioned in alignment at the TE, and held in place with a long straight edge. Thin CA is run along at the front edge only. This is just enough to tack it in-place. The majority of the cloth/veil will not be wetted-out until the trailing edge sheeting pieces are mated together, later.

These pictures show Tim tack-gluing his two pieces.

Iron Dog

While Tim was Bogarting the ruler, I thought a long level would be easily as good to use as a straight-edge to ensure my sheeting was pressed tightly against the building surface to keep it straight and warp-free.




Here I am thin tacking mine to my sheeting.

Iron Dog

Now that Eric has seen Tim and I do it, it is his turn (with a little assistance from Tim):

Iron Dog

We turn our attention to making the 4 wing spars needed for both wing panels, of each of our wings. Two 1/8" x 1/4" sticks are laminated together with medium CA.

Here, Tim is laminating his two balsa pieces. First apply CA to one piece:




Then, carefully align the second piece over the top of the first. Start by depressing them together at one end, and carefully work your way methodically towards the other.

Notice how he flexes the top stick to ensure it does not unintentionally make contact at the opposite end, until he wants it to. The sticks need to be lined up perfectly, it they are to fit properly in the slots of the wing ribs.




While Tim used balsa for his spars, Eric and I chose to use spruce, instead. I've always felt that having the hardwood spars butting-up against each other at the center joint gave just a little more insurance against compression and eventual failure at wing center when the wing is subjected to those high G-forces during pylon turns, and makes the wing just a little less apt to fold.

Iron Dog

The bag of all the wing parts is now opened.




Here are all the parts, as laid out on each sheet:



With a #11 Exacto blade, cut through the couple of (approximately) 1/32" wide tabs that hold each of the ribs to the stock, and the ribs fall out of the sheet stock they were laser-cut from.

Iron Dog

Position some waxed paper over the wing plans to protect them from CA, and pin the spars in-position, over the plans.



Because my spars are spruce, I cannot pierce through them with T-pins, so must criss-cross them tightly over the top of my spars to hold them in-place over the plans.

Iron Dog

Place each rib in postion directly over the bottom spar, where its outline is drawn on the plans, one at a time. I started with Rib 2 and worked my way towards the tip. (I recommend saving Rib 1 for last, as it must be glued in at an angle to match the dihedral of the wing. More on that, later.) Use a builder's square at the high-point of the rib (a little bit away from the spar so you don't accidentally glue the square and the spar together) and ensure that the rib is square to the building surface. When satisfied that all is aligned perfectly, apply a couple drops of thin CA against the rib, at the top of the spar. Install ribs 3 - 8 in the same manner.



In the picture above, Ribs 2 -8 are all glued in-place. Rib 1 (far left) is merely setting on top of the rib, being trial-fit, leaning against the dihedral gauge which will be detailed in the next step.