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

Always keep towels and alcohol by your side when using. The alcohol quickly cleans off any residue left from epoxy. Until I learned how to use the alcohol, I was making a real mess of epoxy and was very hesitant to use it period. I can do perfect repairs doing so.

Looking Good Rusty! I love these build threads.. I learn so much from them. Looks like the Yak will be flying very soon!   

Roddie

Years ago, one of the big names in stunt had a article in STUNT NEWS (the PAMPA magazine) about installing pinned hinges using Aliphatic resin glue, aka yellow glue or carpenter's glue....wow, after all the fun of epoxy, why try something that sounds so easy?

Well, I did it and it worked, it worked very well!

Mark, that may have been Bob Zambelli. Bob was a member of our club until he moved to the South Carolina. Bob's building skills are just impeccable. Bob to this day still uses yellow glue for hinges. I asked him why in the past and his response was easy clean up and no glued barrels. I did suggest that aliphatic resin and plastics generally don't glue well. His response was, "Did you ever try and remove it from the glue bottle top"? He does scarify the hinge leaf and he does drill additional holes. I've used RC-56 which also worked well. My biggest problem early on was using too much epoxy. Once I place it in the hinge slot, I like to hit it with the heat gun for a second and it just runs right into the mortise. I then work the hing up and down a bit to get the leaf covered . I guess it all becomes personal preference, but your very correct that carpenter's glue works. Ken

Hi Ken,
I'm not sure who it was, I got the impression that its become somewhat of a common option to installing hinges. Like many procedures, there's always several different ways to do the same thing. The glue basically sticks to the wood and locks the hinge in place, any residue on the hinge barrel can be picked off with a xacto knife after drying, if it didn't get wiped off with a damp cloth.

The hinged flaps. The one with the big doubler supports the horn as well as the flap coupler.




The flaps are free moving. Very nice fit for a first timer.

I'm not sure I used heavy enough wire from the bellcrank to the flap horn. I can't make it bend by applying pressure to the flap, but maybe I should sleeve it with CF tube. I'm not sure yet how I'm going to make the transition to a 4-40 clevis. I really don't want to cut the sheeting open.

The stab is just stuck in the slot. Still needs wet sanding, clear coat and sewing, and the engine is rubber banded on, but it looks good. And I haven't dropped an exacto knife through the wing yet.

We're about to get a major ice storm, so I probably won't be painting. In fact I expect to lose power tomorrow night or Wednesday.
Rusty

Looks wonderful, I like the way the lucky boxes and hinges worked out. Very clean.

If you want to transition from wire to to a 4-40 clevis all you need to do is buy a solder 4-40 threaded coupler from the LHS. They work well, just be careful not to dollop any solder balls onto the wing. I use a wet rag for that purpose.

Not much longer to go. Did you decide to ditch the Fox?

Ron

Cribbs74 wrote:Looks wonderful, I like the way the lucky boxes and hinges worked out. Very clean.

If you want to transition from wire to to a 4-40 clevis all you need to do is buy a solder 4-40 threaded coupler from the LHS. They work well, just be careful not to dollop any solder balls onto the wing. I use a wet rag for that purpose.

Not much longer to go. Did you decide to ditch the Fox?

Ron

I have some 4-40 couplers, just that this wire is thinner than their hole. At the time it seemed like the right stuff. One of the perils if my first 35 sized build. I'll think it over in the light of day first. I don't want to weaken the wing's integrity by cutting the sheeting, and I have plenty of assorted hardware that might solve it for me and be trustworthy. It fit the hole in the bellcrank so I assumed it was okay. That was a long time ago. I have all sorts of different sized threaded rod, couplers, CF and brass tubing. I'll come up with a strong and not too funny looking fix.

No, the Fox is just all oily and on an engine mount. That's the fp25 for the new Skyray. I needed some nose weight so I could prop it on its nose to work on it.

RknRusty wrote:

Rusty, I've been following this thread since the beginning with much interest, in particular the flap construction. I was looking at the picture above and wondered if the U shaped piano wire connecting both flaps shouldn't be straight and not bent as on the picture just because it has 2 hinges. That piano wire cannot articulate normally when fixed to 2 different axis unless you have some play in the hinges. Or do I see that wrong?

Lieven

Lieven, I'm not sure exactly which part you mean, so I'll address your question two ways.

If you're talking about the slight bend between in the center of the wire between the prongs, That is so that it mates flush at the vertex of the angle of the TE... at least in neutral. And yes, it won't rock up and down and stay perfectly flush, but considering the small diameter and width of the two surfaces, and the fairly short throw, there only needs to be a small amount of spare room to keep the shoulders behind each prong from binding against the TE.

And yes, there is no good "cheap and easy" way to connect two opposing flaps that follow such a forward swept angular hinge line. With a straight TE, it's easy, plug in the coupler and everything moves freely. But Sterling's mission was to make "cheap and easy" kits and this part was meant to work "well enough." A more sophisticated design would have separate control horns and rods to move each flap independently to prevent them from fighting each other for movement. That's where the Lucky Box sort of grooves I cut in the flaps come in.

I never showed a picture of the finished groove, but this is the rough-out:


The triangular groove is allowing the hinge to have lateral "play" as it swings back and forth. There is no glue in there. The caps on top of it as shown in the above post of the finished flap allows no vertical play. That was the first thing I confirmed with a sigh of relief after I put it together.

I hope this answers your question.
Rusty

Here's the wire I was fretting over last night. It seems to be stiff enough for the job, so I'm leaving it. I may even use a z bend instead of a clevis on the flap horn.

Two things come to mind.

Brass/copper tubing over the existing wire to increase the diameter to have a snug fit with the 4-40 coupler

Or

Solder 4-40 coupler over smaller diameter control wire then wire wrap copper wire overtop of the 4-40 coupler and solder.

Both ways would look clean and give you piece of mind.

Or..... Z bend it and press like you mentioned   

Rusty, my question was in fact about the 2 hinges made of brass shim to attach the coupler on the TE. But looking at the picture posted above, it seems that you didn't fix them. A good thing because otherwise, your coupler wouldn't go up and down.

Lieven

Oh...I say dumbly. Well I blathered on about everything but that, didn't I.

You're right, and for the same reasons as my other essay. Those were to be retainers to prevent wobble and fly-away as was Ron's concern a ways back. I was hoping that if they were positioned out by the shoulders of the coupler they'd be loose enough not to bind within the limits of throw. But they were clumsy and in the way, so I abandoned them.

As it turns out, everything is snug as a bug in a rug, but with enough room to be free moving. And it will be further blocked in by the yet to be added faux profile air scoop that covers that joint. I feel relieved that if I t try to wiggle the flaps up and down in any way there's no evidence it will be floppy and chattering in flight.
Rusty

Regarding the flexy bellcrank to flap wire, it might have worked okay, but less than perfect if I had just ignored it and kept finishing the project like I've done in the past on my little planes. But then I would have missed yet another learning opportunity. Never worked with CF before either, and had at least one foul up that I'll know how to avoid next time. I totally underestimated how fragile the tubes are when the cut ends are not reinforced. So I toiled away for hours today figuring out my solution and implementing it. I'm happy with my solution and it appears to work perfectly and look pretty good too.

The thing that made the link too weak was that I had to jink the wire about a half inch over to meet the horn. This is where it flexed. Had it been straight, it would have been fine.


So I cut it off and soldered this brass tube that will fit the ID of a CF tube. The remaining length of 1.5" to the crank will be plenty stiff enough now. But the next problem is that it's still offset 1/2" to the side of the horn. Here's the first step:


Another problem is that not only does the control rod move front to back, it also moves side to side because of the bellcrank motion. So if I just put a z-bend and wire through the hole in the horn, it may have added some stiffness. So I cut a 5/32" long piece of the same brass that I sleeved the end of the bellcrank wire and soldered it into the top hole of the horn, giving the pushrod some side to side capability. This is the new pushrod passing through the 3/16" brass tube that's soldered into the horn. Notice the 1/2" of play it has for the side to side motion of the rod.:


Now to get to the horn with a straight angle of input. I cut a piece of CF tube that will fit over the above connection. While roughing up the inside I split it with ease. I learned that the ends must be reinforced before doing anything else with it, so brass around each end to hold it together, and then rough up the interior to accept glue. Another brass sleeve just like the one on the crank wire goes on the end of the pushrod and fits into the other end of the CF tube. And here it is all together. Note; this is prior to gluing, and after adjusting for neutral, there is only 1/8" of wire protruding from the end of the CF tube. I should have waited until then to take the photo, because it looks much sturdier that way. I don't think there will be any flex:


I wanted it to be adjustable length, but there is just not enough room to do it without being clunky. I was starting to knock things over. And when I cut the pushrod to length, the end I cut off flew up and punctured the wing, so I postponed JB Welding and aligning neutral for the next visit to the shop. This all looks easy, but it wasn't for me. I fiddled and fooled with it before I fully grasped what I wanted to do, and had a couple of misfires while i was making it up. So that's what I spent my last 5 hours during the great ice storm of 2014 doing.
Rusty

I like the way you did the CF tube, very nice. To be honest and because you are my pal I am not keen on the "Z" bend.

It will work, but a ball link would be tighter to the control horn and allow the bellcrank to swing through it's range of motion without binding the link.

I consider you a much better builder than myself so please don't think I am being all high and mighty.

Ron

I wanted to avoid the z-bend too. I don't have any ball links and didn't know if they would work with the offset I was dealing with. I've never seen one and just wanted to get past this. It seems to work smoothly, so I'm going to leave this corner cut. If I had a ball link, would there be room for another one to connect to the next hole and go to the elevator? Or do you connect both rods to one link?
If I'd had an HS I could get to, I would have investigated the idea.

Don't consider me a better builder. By now you have as much experience as I do, at least with this size model. I sure hope I don't run into any other glitches. Hopefully it's just gluing and painting from here on out. I do need to make an adjustable fuel tank mount, but I don't think that'll be a problem.

I have a serious case of Oriental on my mind, with a speed plane and a Skyray between me and it. At least when I get to the Ray, I've already learned some good lessons from the Yak. Just not looking forward to making the rib set, but like everything else, it looks easy.  
Rusty

EDIT: I did notice that it is not using that whole half inch of sliding room through the horn bushing, so if I see that it just stays in one happy spot, I may very well end up cutting some of it off and soldering a retainer on the end.

The offset is the killer here. I can send you a ball link if down the road you want to mess with it again. Like I said it will work fine as is.

There is enough room to connect 2 ball links to the same horn. That horn looks to be made for a ball link because the holes are such a good size.

I learned something through this build. Bellcrank final placement is critical.

Anyway, the Oriental will have you flying intermediate in no time. You are a lucky dog!

Cribbs74 wrote:I learned something through this build. Bellcrank final placement is critical.

Anyway, the Oriental will have you flying intermediate in no time. You are a lucky dog!

Yes it is critical. The main reason I have offset is because the flap coupler leg is in line with the bellcrank. I located it all where the plans had it, but now I know I could re-engineer some of those things. When I was building the wing, flap hardware wasn't on my mind, never having had them before. If I had used heavier wire, I wouldn't have had flex at the adjustment bend either. That was my main mistake, underestimating the strength needed for a plane this big.

I am a lucky dog. I so want to jump on that thing now. I've read the instructions a couple of times. There are some things to bolster and modify, but with Ken advising me, I'll be in good shape. Wayne has a Smoothie that is similarly constructed and he's been asking me questions I already know some answers to because Ken has already given me a primer on it.
Maybe I'll work on both projects at the same time. I don't think the little Speed Reedy will consume too much time. I can do 1/2A in the dark now. Yeah, right.  
Rusty

I went to the LHS today and got some Lustrekote clear for the fuse. Silkspanned the rudder and cheek block and finished stitching the hinges, so the stab can be mounted any time after I paint the fuse. It's pretty much all built except for the rear control rod. I picked up a pack of a dozen or so Dubro ball links. They didn't sell pairs or singles. When I went to check out, they were over $20 bucks. Damn. I left them there and will use 4-40 clevises against recommendations, at least for now since it's what I've got. With a CF rod.

The flaps work great, they move by way of gravity when I tilt the plane, so I'm happy with that. It'll be ready for paint tomorrow, so paint and decals go on soon. And the rack of aluminum exhaust pipes.

This low wing allows for any fuel tank I choose. I want to use the Brodak wedge that gave me fits on the SS, but not before I open it up and fix it. It's a 3oz uniflow. Do y'all think that's big enough for the Fox Stunt 35, or should I go with a 4oz tank? I have to ad some adjustment tabs for it. I also have a 4oz clunk like the one on my Skyray, but they're so unsightly, I'm thinking not. I wish I could find a way to snag some exhaust pressure from this muffler-less engine.

I'll have good pictures soon. I see no reason to show more pics of unassembled bits.
Rusty

3.5oz is what I was told for a Fox .35. Depends on what you want to do with it I suppose. I you think it will fly well enough to do a pattern then you may want to up your tank size. 3oz will work for sport.

4oz will surely give you some breathing room.

You could always tap the backplate, but to be honest the Fox will do fine with standard vent. They have been doing it since the 40's.

Ron

Cribbs74 wrote:You could always tap the backplate, but to be honest the Fox will do fine with standard vent. They have been doing it since the 40's.

Ron

I have a 4oz metal tank, it's just ugly. But paint will fix that.

One reason I run pressure is where we fly, the dry winter grass gets powdered by the prop and fills our tanks through the open vent. Hooking the uniflow vent (or normal vent) to the muffler is a convenient way to keep it clean. I could filter it though.
Rusty

I feel that there's nothing wrong with Z bends. The Z bend should be terminated with a washer and the music wire should have a groove filed on it to assist holding the washer and also the solder. Seeing we fly counterclockwise I always place the bend in the direction that centrifugal force is going to pin the bend into the hole. This is my thinking anyhow, as it may just give you a fighting chance to recover the plane if the solder joint failed. What I see here however is the side to side play due to the Z being extended. I would personally avoid Z bends that allow for that side to side movement as this can cause the wire to jump back and forth giving up control and wearing horns and bushings out quickly. Soldering a washer on the one side would fix that. I use perfectly square cut fuel tubing on the pushrod and lay the washer on the tubing to solder. When soldered, the tubing can be cut off or slid off if possible leaving a washer nice and square. A little tip, only clean the side of the washer you want soldered. This would be the opposing side that doesn't mate against the horn. Use a #11 blade and bevel out the inside of the hole of the washer to remove plating as well.  Many times when needed, the spring coil retainers work excellent when you discover how they thread onto the wire and around the horn. I used to bend them out of the way and then try to re bend them which resulted in a not so tight fit. This application only requires a L and not a Z.

You may make the beginner pattern with 3 oz. of fuel. However, it would be far better to use a larger tank due to your advancement in flying the pattern. It won't be long before you start flying the PAMPA pattern. That being said, 3.5 oz's will not make the PAMPA pattern. Fuel will pretty much be depleted in the overhead 8. You don't want to be running short here as this is where I've witnessed the demise of many planes. It's better to over run then to come home with a Monokote bag of balsa. The 4 oz. tank would benefit you in this situation as you don't have to top it off or you could fly and discover exactly how much fuel is required and withdraw a .25 oz or more if needed.   Muffling a old non eared Fox is simple to do. I can provide pictures of strap mufflers I made for them. The Fox case is very fragile and therefore you run the risk of binding the piston if overtightened. Some of the non -eared 50's Fox's don't like mufflers and it will let you know it.