IS-4 Jastrzab

[mlachow]

A little sanding and cleanup is still needed on the webs after gluing. Check if all of them look like they are glued OK and sand anything that extends beyond the spar. After that is done, I added a kevlar wrap to the spar, wet it out with laminating epoxy. Excess epoxy gets blotted off and finally it is all wrapped with electrical tape to hold it tight against everything and compress it all a little more. The wing gets put back down on the table and weighted just to make sure things stay straight. Even without the sheeting the wing is starting to get into good shape torsionally. When I add the top sheeting it should pretty much lock things in place.

I wind up the tow on some thin "spools" made of room key plastic. This way I can keep the tow flat on the plastic and unwind it flat while wrapping the wing.

[Steve P]

Great tip!

[Soarntz]

Looking good, thanks for posting....

[gunny11]

Super strong! Nice job!

[mlachow]

Time for a lot of edge joining of the sheeting. Lots of wing to sheet and a whole bunch of sheets. I have a nice long straightedge and a new blade in the knife. Also a long strip of sandpaper attached to a piece of door to make a long sanding block. I edge glue with Duco or other model type cement. It sands well. If there is any minor ridge in the joint, fill and sand that before attaching it to the wing.

Trimming the length of the sheets for the inner panel you get some extra pieces. These are just right for the sheeted areas on the ailerons. The other pieces get spliced into the top sheets to make them long enough On the top I work forward from the trailing edge to the spar. Then one final piece from the spar forward. I also used a few scraps on the back of some of the joints in the center panel. The rib spacing in the back is pretty wide

The leading edge of the tip area almost makes the top and bottom from three sheets with a diagonal cut.

The middle of the tips works well if you angle the sheet and cut off a triangle half the length of the sheet which you edge glue to make use of all of the sheet.



Top of the wing is now sheeted. Time to turn it over and work through the servo access holes and servo mounts.

[mlachow]

I wish there was a sheet cut list on how to best optimize the sheeting. Kind of make it up as you go. Here are some tips if you build one.

On the center panel sheeting behind the spar. Stagger the sheets as you edge join them based on the root rib angle. On the one rear sheet, cut a triangle half the sheet length and about 15mm on the end and glue that back onto the sheet. It helps fill the area with minimal waste.

On the tip panels behind the spar, using the full 1000mm sheets, cut a triangle half way and 47mm at the end and glue that onto the sheet.

Don't cut the top front sheeting way oversize. If you trim it close to the correct size, the leftover piece will nicely make the front sheeting for the bottom of the wing.

Save all the cutoffs from the center sheets. Use those for aileron parts and the tip sheeting on the last one or two ribs.. I think you could also save a few pieces to use on the tail. I am using my own sheeting on the horizontal tail since I wanted to make sure the tail was light and I had one or two 2mm sheets that were pretty heavy. Typically they were around 27g a sheet but the lightest ones were under 20g and I had a few close to 40g.

I used some of the harder sheets on the bottom of the wing panel and in the center.

[mlachow]

With all those balsa sheets joined, time to glue all the sheeting. I worked from the TE forward adding the pieces. I did the outer panel first and then trimmed the end on the ribs at the panel break. Then I sheeted the inner part of the wing. When it was time to do the bottom in the middle, I cut the sheet but did not glue it. I used it to align the rest of the sheeting. The reason is I have still not glued the tube for the rear wire on the wing. That will wait until I can assemble things and make sure everything is in alignment. The wing tip required another few small pieces. On the leading edge, the tip requires laminating a few pieces for the curve. The lamination was done after hard balsa LE was glued to the panel.




Everything all sheeted. It still needs more sanding and I need to make templates for the LE shaping. I also need to make servo covers for the wing.

At this point I also have a stack of strips and some joined sheets ready for the second panel.

It is definitely not a high aspect ratio bird.



The wing panel will require a little filling. The wide spar creates a flat spot. That will require a little work to shape it into a nice airfoil.

The biggest changes from the stock kit so far are:

1) Block in the joiner box and do a spar wrap.

2) Split the ailerons into two pieces and relocate the servos.

[mlachow]

With all that sheeting work, sometimes you just have to wait for things to dry. Fortunately the fuselage provided a few things to fill in the time. The entire kit is 3mm light ply parts. Sometimes you need thicker pieces. When that happens you have to laminate two pieces together. The main two fuselage formers that tie the wing joiner through to the landing gear is one example. Other parts include the canopy frame.



I also created a board to hold the fuselage for building. Once that was cut I dry fitted the formers to make sure there would be no problems clamping things when things get glued together.

[Soarntz]

Looks very nice mike, you're really cruising along with the build!

[mlachow]

No big rush. Now if I was trying to build fast, there would be more completed on the fuse and the tail. With the wing I am bench constrained

[mlachow]

The wing joiner area and tail area are assembled first in the fuselage. Lots of clamps and blocks to make sure that things are clamped square.


Also assembled the pieces for the stab mount.

[mlachow]

Not much building this weekend. I did get two days of F3b flying in at my local field. Some of the tail parts go together real quickly if you have 20 minutes to glue and clamp them. I did add a few extra pieces to some of the ribs. They are all routed out on the inside.



Not sure why the front of the rudder is rounded on the bottom. All the photos I found show the bottom of the rudder is basically flat.

[mlachow]

More work on the tail surfaces. Time to plan for hinging and control horns. The rudder needs 3 hinges. I picked the bottom one based on the fuselage structure and where the control cables could exit the fuselage. The top one is just above the top rib and the middle one is half way between them,


The next issue is making the holes all in line on both sides. I make up (reuse) strips of ply with some drill bushings mounted in them to take care of things. I mark the spacing and then drill the holes for the inserts using a fence to keep them all the same distance from the edge. Then the threaded part gets pushed into the ply.


The last part is drilling some holes for dowel pins to align the part with the drill guide. If you are careful to align the guides with the middle of the ply. Drill one hole for one edge. Flip the board over and drill the one for the other edge. Hopefully its all centered and aligned. The pins can be used on either side and the bushings can be screwed in either side. This way the fixture aligns with both sides. One for the rudder and one for the elevator side,,

[mlachow]

And after you get the framework glued, it is time for cap strips. One elevator and the rudder are complete. The second elevator needs more work. Fin is ready for the fuselage build. THe fin will bee sheeted along with the rest of the fuselage. The surfaces are also ready forhinging and control horns. They are nice and stiff with all the ribs. The stab will be the next part to build. I am waiting on some tubing for the alignment tubes for the stab.

[mlachow]

The horizontal is another straightforward build. The attachment is two pins at the back and two bolts. I have two M4 bolts set up in the plate. With the basic frame setup I also did a trial fit with the fuselage and fin to make sure that things fit OK and that they are adjustable when I get around to gluing and sheeting the fuselage.

The stab is going to get two MKS6130's inside it. One for each side of the elevator. Wiring hookup will require some preplanning. The stab slides under part of the fin. The hole into the fuse for the wiring is also located at that point. I need to decide what connector to use for the hookup and how it will slide in I might use a 4-pin deans plug It's easier to test fit things before the sheeting..

[Sinkhappens86]

Really impressive, enjoying following this.

[mlachow]

Thanks. Steady progress along with the usual stuff like leaves this time of year,,,, Colder weather has reduced the number of golf days too.

[mlachow]

The wing mount pieces and tail mount pieces were previously glued together. The next step is fitting all the parts to the top and bottom ply pieces. The slots help to align things some. And the building support has an outline of the bottom of the fuse on it for some alignment. The top of the fuse for about 18 inches in front of the stab mount is also straight. That lets you clamp some steel there to keep things straight when gluing that section. I also made a few pieces to fit vertically to be able to clamp the top fuse part while the glue cured,

The most important thing is making sure you can slide the bulkhead in and clamp it flush with the edge of the fuselage during glue up.

After fitting everything, I glued things in stages. About 5 to 6 pieces at a time. I also cut some scrap 3/4 ply to help with spacing and aligning the bulkheads. I also pushed in a few of the stringers to help hold things in place. I found I had cut my stringers about 6.3mm so they were a little oversize. I used a long piece of 3/4 ply placed through my planer and feed a few strips at a time through that to get them down to thickness.



The pieces around the canopy area all interlock. That was nice for gluing up that area. I will have to do a little fettling of the slots before I glue the stringers in. They generally hold the stringer in a nice curve but one or two wiggle a little. The area that is going to take a little time involves a few pieces near the wing intersection. There are ribs for that area but there are also a few strips of machined ply parts that fit along the wing intersection. They aren't flat.

Time to get the wing workbench ready for the second wing panel.