Back to the Yak - Yak-9 Build, Part II

**RknRusty** Sat Jul 06, 2013 10:14 pm

Since I got bogged in preliminary questions and then had to undo what I started, let's get a fresh start on the build thread. I intend to avoid over thinking any problems I encounter this time around. If you want to catch up, you can read this thread: Yak 9 Build - Part One

I've never built a wing this size before, so I had to make some jigs to hold it in place to keep it lined up. I was lucky enough to find my old Li'l Jumpin Bean TE jigs fit the trail edge sticks on the Yak pretty well. So all I had to do is measure the height they held the sticks and cut some blocks off of a square balsa log I had and mark the height, and pin the LE in place. After my earlier foul up with the LE angle, I marked a line on the table so I could place the blocks to hold it at a 10 degree sweep back. I test fit the outer and innermost ribs and pinned the TE jigs to hold it in place. The kit cut angle where they butt together turned out to be correct. This causes a gap where the LE sticks join that I can fill later.

Since taking the pictures, I've glued the ribs into one side of the wing. Tomorrow I'll finish the rest of them. I pre-glued with Titebond and then put them in place with a second application. All very neat. I'm happy with how it looks so far.
Here it is before gluing:
Back to the Yak - Yak-9 Build, Part II SAM_2524_zps21c770d6

Back to the Yak - Yak-9 Build, Part II SAM_2524_zps21c770d6

The gap in the LE to be filled:
Back to the Yak - Yak-9 Build, Part II SAM_2526_zps11156ab1

Kee88's Brodak P-51 wing. We've got two builds at one time on the table. His kit has no instruction booklet, but that shouldn't be a problem. The plans are not quite life sized either, slightly reduced.
I think he's going to post a thread about it, so I won't bother with details at this time.:
Back to the Yak - Yak-9 Build, Part II SAM_2529_zpsf6ceb703

Back to the Yak - Yak-9 Build, Part II SAM_2529_zpsf6ceb703

**Cribbs74** Sat Jul 06, 2013 10:24 pm

Well Shoot!

Going to be a good Ol' Sterling Combat Match once you guys are finished.

Looking Good Rusty! Be sure to wrap that Leading and Trailing edge with some glass. Can't wait to see the finished product!

Ron

**RknRusty** Mon Jul 08, 2013 3:03 pm

I got the rest of the ribs glued and added the wingtips too. Some of the rib slots are wider than the ribs, enough that there is a gap on one side or the other. I started using Titebond to try and fill the gaps, but stopped after a couple of ribs. I think I'll peel some thin strips of balsa and soak them in glue and stuff those in the gaps.

The wingtips are just a rounded chunk of 1/4" balsa with front and rear edges angled to fit between the overhanging LE and TE sticks after the last rib. After sanding the angles to fit squarely, they snug into place about a rib bay's width from the last rib. That position makes it a 39-40" wingspan instead of 38" span as stated on the box. Now the rest of the overhanging overhang has to be tapered and shaped to blend into the tips and follow the contour of the flaps. Gotta be very careful here.

It's thunder storming again. I planned to take the night off from building and fly over at the church this evening, but it might be too soggy if the radar is right.

EDIT: I looked at the front doublers on the P-51 when Kee88 showed them to me. Something strange stuck in my mind, so later I had another look. They look like wood but they're paper thin. I measure them at 0.020" thick. I have never seen any doublers made of less than 1/16 or 1/32" plywood. I don't see what these can possibly add to the structure other than the strength of the glue that holds them on. Maybe they offer some tensile strength(terminology?) to prevent flexing?

**Cribbs74** Mon Jul 08, 2013 6:35 pm

It's usually wise to go thinner on the doublers, but those are thin. If this is Kee's first plane then you may want to beef those up some. Maybe you could swap his for yours..... Laughing

Edit: It's no secret that Sterling kits build nose heavy. If I could go back in time I would drill holes in the fuse under the doublers of my Ringmaster. My guess is Brodak is wise to this and decided to use the minimum amount of ply they could get away with.

jhaye Mon Jul 08, 2013 7:04 pm

Rusty,

Great builds. I love the yak 9, definitely on my short list of builds down the line. Like Ron said most of Sterling's kit's were pretty heavy. One of the old fella's in our club claims the leading edges are made with baseball bat wood. LOL! I have a Sterling Mustang. It's my racer, I love flying it. What type of power plant is the Yak going to have?

Jim Hayes

**RknRusty** Mon Jul 08, 2013 8:34 pm

Cribbs74 wrote:It's usually wise to go thinner on the doublers, but those are thin. If this is Kee's first plane then you may want to beef those up some. Maybe you could swap his for yours.....

Edit: It's no secret that Sterling kits build nose heavy. If I could go back in time I would drill holes in the fuse under the doublers of my Ringmaster. My guess is Brodak is wise to this and decided to use the minimum amount of ply they could get away with.

Kee's kit is a 25" w/s 1/2A model, so I'm thinking I'll copy them and either cut some 1/16" ply or buy some 1/32" ply, and and extend over the wing a little farther back. If it weighs in nose heavy, that's the easiest balance to fix.

jhaye wrote:Rusty,

Great builds. I love the yak 9, definitely on my short list of builds down the line. Like Ron said most of Sterling's kit's were pretty heavy. One of the old fella's in our club claims the leading edges are made with baseball bat wood. LOL! I have a Sterling Mustang. It's my racer, I love flying it. What type of power plant is the Yak going to have?

Jim Hayes

Haha, it is like baseball bat wood. It's 1" stock and hard as a rock. I'll be powering it with a model EJC-49 Fox Stunt .35 from 1958. I found it listed in an old thread by G_Willie that got bumped yesterday over at Stuka.

For Fox Stunt owners, this is an informative thread:
http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=323889&mesg_id=323889&page=

**Cribbs74** Mon Jul 08, 2013 8:49 pm

Does yours have the bottom casting web?

**RknRusty** Mon Jul 08, 2013 9:06 pm

Cribbs74 wrote:Does yours have the bottom casting web?

Yep.

Back to the Yak - Yak-9 Build, Part II 05191310

jhaye Mon Jul 08, 2013 9:33 pm

Nice engine Rusty, will go well with that build.

Jim Hayes

**RknRusty** Mon Jul 08, 2013 9:55 pm

I think so, Jim. This thing has by far the highest compression I have ever felt flipping the prop over on an engine. Granted, I'm not very experienced with bigguns yet, but it's a serious finger buster. Much more than my Thunder Tiger .25 on the Shoestring.

For your viewing pleasure here is my only test run so far. Once it was running I couldn't turn the needle so I leaned it by pinching the vent.
https://www.youtube.com/watch?v=bF6kVne_dzg&feature=c4-overview&list=UUgYkP8ZpK_AtOfDvWYCANyA

**RknRusty** Thu Jul 11, 2013 7:24 am

What size bellcrank should I get for the Yak, 3 or 4 inch? I can look at the Shoestring to see what size horns. I assume the flap horn is the same as the elevator horn.
I could make them out of ply, but I think nylon would be better for the crank and the horns.

duke.johnson Thu Jul 11, 2013 8:52 am

It most likely calls for a 3 or 3 1/2" bellcrank, but if you can put a 4" bellcrank in it will handle better. Smoother.

**Cribbs74** Thu Jul 11, 2013 9:24 am

3 inch is what I use, I have no experience with anything larger. Use the nylon control horns and try and find the longest possible. You want less flap movement than the elevator.

duke.johnson Thu Jul 11, 2013 10:25 am

The big boys over here run big controls for smoother stunting. Big bellcrank and control horns and 1:1 ratio for the flaps to the elevator. And I'm only one of the big belly guys, not one of the big boy plane guys.

**RknRusty** Thu Jul 11, 2013 10:48 am

Haha, no comment, but I did I see you in a pic. As for me, I'm a human stick. I'll put a 3-1/2 or 4 incher on it. Thanks, dudes.

I did some more sanding and shaping on the wing this morning. I was worried about the wide gap between the flap and the fuse, but I've got it down to about 3/8" now, so I'm feeling good about it. It takes a lot of sanding to shape the overhanging LE and TE sticks, blending it into the tip blocks. I love sanding, it's like sort of a Zen thing.

The bellcrank platform and flaps are next. I need to make something to give the control wire free lateral movement, a necessary mod to keep the forward swept hinge line from binding. It took me a while to wrap my head around that problem. There's something called a Lucky Box(named after its inventor) that allows a non-binding linkage on this type of design. I'm getting better at building, kits at least. This is going to be the best build I've done.

Kee88 and I worked in my shop last night on opposite sides of the table. His baby P-51 wing is coming along nicely, but not without some modifications.

duke.johnson Thu Jul 11, 2013 12:37 pm

And do like they suggested you do on stunthanger, use the inside hole on the bellcrank and the outside hole on the control horns. You'll be happy you did. I have a friend how just built this kit and converted it for carrier and we have the kit on the shelf for a future build. I'm also STILL building the P-51 version as a carrier plane.

**RknRusty** Sun Jul 14, 2013 7:11 pm

Still building at a snail's pace. Here's the wing. I packed the gaps in the LE rib slots with Titebond soaked balsa strips on the ones where the slot was wider than the rib. I'll do the final taper on the corners of the TE after the flaps are on it, so they blend in.
Back to the Yak - Yak-9 Build, Part II SAM_2531_zps979eae02

Back to the Yak - Yak-9 Build, Part II SAM_2531_zps979eae02

The right wing is 5mm longer so I had to add the extra length to that flap. I cut a new one and sawed the wrong line at the end, wasting my only 1/8" sheet, so I added a short piece to the end. That's how I know it's time to call it a day.
Here you can see the blending that still needs to be done.
Back to the Yak - Yak-9 Build, Part II 0714131933a_zpsd8e3fe06

Back to the Yak - Yak-9 Build, Part II 0714131933a_zpsd8e3fe06

Doubled #1 rib. I put a small strip of fiberglass on each side of the center TE joint. since the above picture was taken
Back to the Yak - Yak-9 Build, Part II SAM_2532_zps03079bd8

Back to the Yak - Yak-9 Build, Part II SAM_2532_zps03079bd8

Tomorrow I sew the flap hinges. I just realized I don't yet have the control horns so I'll have to find those. The bellcrank is on it's way in the mail.

**RknRusty** Sun Jul 14, 2013 9:37 pm

Someone at Stunthangar recommended 1-1/8" control horns for the Yak. Looks like my LHS has them. This seems large. Any opinions on this? Keep in mind, the biggest bellcrank that will fit looks like 3".

Back to the Yak - Yak-9 Build, Part II S557n01

Back to the Yak - Yak-9 Build, Part II S557n01

**Cribbs74** Sun Jul 14, 2013 10:26 pm

Yep, go large. You are going to need the spacing to mess with the movements. It doesn't look bad. I use an 1 1/8" on the flaps for the clown.

Ron

Edit: Ken sent me the large Control Horns and I was not sure if I would ever use them. Then I built a flapped stunter.

jhaye Mon Jul 15, 2013 10:00 pm

Rusty, I had a conversation one time with one of the older fellow's in the club here about Sterling kits. If I remember correctly the Yak 9 has about the same wing surface as a Ringmaster or your Shoestring. I'm thinking a 3" bellcrank will be perfect for that plane.
Nice build so far.....
Jim Hayes

**RknRusty** Mon Jul 15, 2013 10:28 pm

Hi, Jim. I got my 3" Sig bellcrank today, and also an adjustable leadout guide. I don't yet know if the guide will fit in the wingtip without making a bump in the covering. If it's too big, I'll make one out of plywood.
I bid on a 3" crank on e-bay 5 minutes before someone at Stunthangar gave me one. Now I'm the only bidder, so it looks like I'm going to have 2 of them. Rolling Eyes

Here it is, if anybody wants it for another 25 cents. lol!

http://www.ebay.com/itm/321161643754?ssPageName=STRK:MEBIDX:IT&_trksid=p3984.m1431.l2649
It comes with a leadout guide too.

I did a little sanding on the Yak today, not much else. I need to get some Monokote before I can sew the flaps on. I think I'll take a little time off of building sometime this week to preflight the Shoestring in case Sunday brings nice weather. Gotta put my new fuel tank on and find out what it is inside the wing going tickety tickety tick when I tip it back and forth. Hopefully it isn't something critical, but I don't like it.

**Cribbs74** Mon Jul 15, 2013 10:44 pm

Rusty,

I hope Sunday pans out for you, I have almost finished a gallon jug of fuel in the past 3 weeks. Flying most every night. Wish you were here! The Yak wing looks great really good BTW.

Can't help you on the Ebay Bellcrank......Sorry

Ron

**RknRusty** Thu Jul 18, 2013 9:45 pm

Got back to the Yak tonight.
I'm having to lengthen the slot in the #1 rib to allow the bellcrank to swing fully in both directions. It took me some time of fooling around and test fitting before I finally realized the crank platform mounts on the outboard side of the #1 rib. Back to the Yak - Yak-9 Build, Part II Slaphead

Back to the Yak - Yak-9 Build, Part II Slaphead

There is no picture of the bellcrank actually mounted in the instructions. Boy, I'm learning one thing about Sterling... assume nothing!

The leadout holes in the ribs follow parallel straight lines from the crank connections all the way to the #9 rib with no sweep. They apparently are meant to exit at the same distance apart as the connections at the crank. That's pretty wide, and the front leadout will be pretty far forward. I suppose it's because of the amount of sweep back of the LE. I guess it's like this because it works, but before I cover the wing, I'll hang it from the leadouts and make sure it's slightly nose down. I'm trying not to get bogged in over complicating things, some of the stuff on this plane is just different from what I'm accustomed to.

If I can get this wing out of the way, I'll feel like I'm finally making some progress. And hopefully get this thing built before y'all decide I'm a hopeless doofus.
Rusty

**Cribbs74** Thu Jul 18, 2013 10:22 pm

Yeah the instruction like plans leave out quite a bit. Glad you got it sorted though. I bet the leadout positions will be just fine.

Ron

pkrankow Thu Jul 18, 2013 10:46 pm

The Super Ringmaster is supposed to balance at the front lead out....read your instructions carefully. They are a wall of text, so it may take several times through to comprehend... Been there.

Phil

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