Yak-9 Build, part one

RknRusty wrote:I started cleaning up the ribs getting them ready to slide onto the spar. Was hoping to have something that resembled a wing by this time. I wish I knew how some of you guys get so much built, and at the same time keep your other planes in tune and ready to pick up and fly, all the time without raising your wives ire. So no wing tonight. Probably not tomorrow.

A lot of things I crank out in hotels. This isn't always the best setting as it's a pain to be away from my regular tools. No distractions though.

Wife goes to bed earlier than I do so I stay up late and work at home.

Hope you knock the wing out soon. I am ready for some pictures to accompany this thread.

I also have a touch of adult ADD most times it's a PITA. However, it does allow me to hyper focus on the things I really enjoy.

Ron

Boy, modern laser technology is great for kit modelers. This Sterling kit takes me back to the days of building real Goldberg kits. Glad I stocked up on zirconium nitride exacto blades. I got all the ribs popped out and the three square holes in each carved out. Sanded the edges smooth and slid them onto the spar. The next step is supposed to be to glue them to the LE, but some of them don't reach fully into their slots, so I need to take them back off and widen the spar guide holes. But I have it rubber banded in place. I was surprised that the spar is supposed to be bowed closer to the LE at the tips. So I used rubber bands to hold the spar to the LE tight while I coaxed the ribs into place.

And I made my first mistake! Last week I misread the plans and glued the angled butting  ends of the TE together. I found out when I tried to put the rib tips into the TE slots and the angle of the stick is wrong. So, razor saw, and problem solved. When I re-fix it, I'll give it a wrap of fiberglass to make sure it's secure and strong. I have searched all over and can't find that ultra light fiberglass tape that always comes in 1/2A kits. Anyone know where to get that?

Anyway, it's looking like something now. No blood, no broken pieces.
Here's what I have so far:

Well, would you look at that! Looks good Rusty. 

I don't know where to find that tape. All the older kits I have give you just enough to do the job leaving no extra. I am lucky in that my wife likes to make clothes and I have a lot of fabric to choose from and it works just as well.

Ron

Nice work, Rusty. I might be not fully waken up yet, but how did you get those rubber bands on in the middle of the wing?

Lieven

That's what I meant, not fully "woken" up.

Hey, Lieven, now that you're fully awake, did you figure out how I got the rubber bands on there?

Okay here's a question for all you kit builders out there. What's your method of getting the ribs straight and aligned? I could try making balsa jig blocks, a tedious chore to get them all uniform, square and the right height. I suppose a stick that runs the full length of the wing for the ribs to rest on while I try to square them all up. It's tapered, so each rib is shorter than the previous rib. If they had a spar notch in the top or bottom that would make it easier. But this spar goes through punch-outs in the ribs, no two of which are the same size and position. I expect I'll be removing them all and re-threading them onto the spar numerous times to get the spar holes to all fit the same.

Just pondering the best way before I start gluing.

Also, the spar has to be forced into a bow for them to be all fit into the LE. The rubber bands at each tip end accomplish the bend in the spar. There was no mention of angled center butting ends on the two spar sticks to make it parallel with the LE.
Here's the picture again so you can see what I'm talking about:

To be brutally honest I TLAR a lot. Most serious builders use a wing jig though. 

Not sure what to tell you about the bow. Usually the leading edge is angled at the butt joints. My guess is it's supposed to be, but not done by Sterling. That's the problem when you don't have full size plans to refer to. Did you make sure you were using the correct end of the LE for the butt joint? 

If the LE and TE are straight and assuming the notches are cut perfectly vertical the ribs will align straight.

I know Ken has built a couple. Hopefully he will pop on and see this.

If it were me I'd leave the spar out. Problem solved! 

Ron

Hey Rusty, Happy Dads Day!

You guessed right with your first guess, making blocks is really not that hard and I see you already have a glass building board. I've seen guys use  1"x2"soft pine or balsa, say a piece of 1.5"x .5" x what ever length you have and cut crosswise, that way your cut will only alter the widths not the height, use a straight edge to line up blocks, a drop of CA on glass and your building.

Personally, this is one more reason for me not to use that spar. Anything that's bowed has pressure on it is the equivalent of having a loaded mouse trap in the wing in the  event of impact. The pressure that the spar is generating currently is lifting the two outboard trailing edges up and forward or at least trying to. You really want to try and avoid dialing in a unwanted warp into the structure. 

When you sight down the ribs where the trailing edge glues onto, are the ribs following the same bow that the spar is taking? Determine which is incorrect first, the length of the ribs or are the spar cutouts incorrect.

At this stage, I would place the wing on the table and support the two ends blocking them up without forcing them up and weigh the root rib down. If you have two extremely straight spars , I use arrow shafts, lay them from leading edge to trailing edge and tape them with Scotch tape to both members. Come to the side of the wing and get down eye level with the table and sight from tip rip to the opposing tip rib sighting across  the arrow shafts.

The arrow shaft in the front should cancel the one directly behind it. If indeed the wing is twisted, it will be readily apparent as you will see the shafts are scissored. At this point, break any glue joint from the desired rib away from it's dado in the leading edge and reblock the wing until the arrow shafts are aligned and tack glue.

If memory serves me correctly, the Sterling instructions even suggest NOT to glue the rib ripper in the wing until the wing is fully assembled and your satisfied the wing is straight. At that point it's suggested to go back and glue alongside the rib and spar. Ken

Rusty,

I had a look at the picture of the drawing in Ron's thread about the Yak 9.:

https://www.coxengineforum.com/t3584-yak-9

The spar seems to be straight. As sai above, are you sure you didn't swap both LE halves around and ended up with a wrong angle in the middle??

On your Stuka Stunt thread, there is a larger copy of the plan view and here also, the spar seems to be straight.

Here is a picture I've borrowed from the French forum about a wing building set up:



Might give some ideas.

Lieven

I believe SIG has the glass you are looking for.

If a wing doesn't go together "dry" then something is not right.

Glad press-n-seal resists every adhesive I have tried on it. CA, Testors, epoxies, white and wood glues. This over the plan, or a re-drawing of the critical points of the plan, on some foam board allows for "jig free" building that helps provide a straight wing.

Phil

Hey guys, thanks for the input. I'll work it from bottom to top.

Phil, unfortunately there is no plan, just a couple of 10" pictures of the bones on a 24"x36" sheet of text. I could re-draw it at the right dimensions, but I think I can get by without doing that. I agree, I would expect the wing to press-fit together dry without having to force the spar to flex.
I'll check Sig for that glass.

Lieven, outside ends of the LE are flat, 90 degrees, and all four of the spar ends are flat with no angle. Besides there is a cutout in each of the two angled LE ends for a biscuit to join the two halves at the proper angle. All of that seemed to fit perfectly.

Ken, so this is the infamous Rib Ripper, nice to meet it.
With the ribs all inserted snugly in their LE slots, the TE slots fit right into place, with the exception of the three or so ribs that have the spar hole a few mm too far abaft. So the ribs are the correct length, not following the bow. If I leave the spar out it will fit fine.

So fast forwarding to where I either leave the spar out, I like the arrow alignment method. I wonder if bicycle spokes are straight. If I tack glue, I suppose I should already have the wood glue in place? Or should I trust the slightly thinned Titebond to adequately soak in from outside the joints? On the Refried Bean, I applied Titebond and then tacked some parts in place with CA while it set.

Mark, thanks for the Happy FD, hope you and the other guys had one too. Your method of jigging the wing was what I had in mind. But when I botched my first block, I closed up shop and came inside to be air conditioned and post on CEF.

Ron, I've used TLAR too and was determined not to do it too much on this one. I tried the TE in every way I could stick the four ends together. I haven't looked at any of this since yesterday, so I'm going to stop look and re-think before I move on.

Thanks again, I'll update when I get some more work done,
Rusty

Okay, here's the latest scoop. The spar holes in the ribs are positioned so that if I add an angle to the center joint of the spar sticks, the spring loaded bow is gone, and the ribs all line up with their respective slots in the LE and TE. So now I'm faced with two choices. Build it with the spar or build it without the spar. This is the one that's famous for destroying the whole rack of ribs in a nose in crash. So I need to think it over seriously before I whip out the glue. I feel like it needs the vertical support. But on the other hand, the two main pieces are made from pretty tough looking balsa. I think the spar is bass wood or something harder than balsa.

Rusty,

Think Bean.

Apart from that if you really want to, you could notch the ribs top and bottom and run spars that way. It won't rip the ribs on impact and will weigh less than the original thick spar.

It now appears the LE sticks were cut at the wrong angle. Of course that's the only piece I glued.  And since the new birch ply doubler was so stiff that it had to be tightly clamped in the bend, I epoxied it, the sticks, the biscuit, and the doubler. It fits perfectly together at a 5 degree angle. The drawings show closer to 9 degrees with my plastic protractor. Cutting it apart and digging the biscuit out and redoing it would be a pain, and I think these other options are easier.

Option #1: Regardless of whether I use the spar, there will have to be a greater forward sweep of the TE angle in order to mate with the ribs. If I abandon my fancy of using the hinged flaps, I can proceed and just build and fly with an un-Yaklike wing. Sounds tempting, and I'm sure it'll fly fine. And Ken might be happy that I wasn't pestering him with questions every day.

Option #2: As y'all may have noticed, I have a hard head and usually avoid the best plan for a much more entertaining adventure in amateur experiments. When I come back from vacation with a clear head, I'll decide which way to go. Right now, I'm thinking of cutting new TE sticks with a trapezoidal shape that mates with the ribs and also returns the forward sweep of the TE to its original angle... or maybe even less. Less would allow for easier flap hinging. I don't think this will be a difficult modification. And I would also end up with a few extra square Inches of wing area.

I cheated on y'all and posted over at Stunthanger.com. I just couldn't pass over such a vast collection of stunt ship builders. If anyone is interested you can read about it here.
It gets interesting with post #12. That's where I learned the LE was the culprit.:
http://stunthanger.com/smf/index.php?topic=31789.0

The saga continues. Thanks for humoring me,
Rusty

If it were me I would cut the joint. Soldering iron work great for breaking epoxy bonds. Just dig out the biscuit, install a new one and start again.

Just to be sure wrap the split with fibreglass tape soaked in epoxy. Easy peasy........

Saw it apart carefully, then saw the biscuit out, but only saw the biscuit.

The soldering iron is an interesting trick, but could produce some...unique...smells.

Phil

Yeah Phil,

Hold your breath! It's foul and probably causes cancer in the state of California. If you don't live there you should be ok.

It does work really well though.

I sealed all the Yak ribs in a ziplock bag, all the other parts that would fit, into the box, and it awaits a clearer thinking Me when I return from vacation. I promise to leave ten pounds of stupid in the ocean.
I spent the rest of my shop time today giving all of my engines a glug of air tool oil and making sure I had two planes pre-flighted for a quick Friday evening excursion.

The heat gun de-bonded the epoxied LE sticks with no problem. I didn't even have to do any digging. Now I have all the wing parts laid out on the table loosely fitted together. I've propped the LE and TE sticks on some pieces of 3/8" square dowels to hold it off the board and some square blocks to hold the mating sides vertical while I test fit all of the ribs. It's sort of precarious and hard to know when it's squared up. So I'm going to draw a grid on the board to help me eyeball it, and then pin the big parts down when I feel it's aligned and ready to glue. I think the rib ripper can be a helpful tool to hold it all in place. Then when the ribs are glued to each end, I'll cut the spar and remove it, and finish the wing without it.

Smart thinking! guess that trip cleared up all the bad mojo......