Yak-9 Build, part one

As long as I'm cutting parts, I wonder if there are any balsa parts in particular that I could copy with lighter wood. The LE looks like pretty strong grade wood, but I would guess that's what it should be. I'm not really educated in what grades go where.

I'll go to Lowes tomorrow and get some ceiling tiles to use for my working platform. I've read that they make a good work surface. I used drywall before, but it's too firm for sticking pins into. I also have a 30"x42"x1/4" mirror to make a good flat base to lay the tiles on.

In between assembling the Yak and waiting for glue to dry, I'm also going to be rebuilding the T-28 Trojan to mount my MP Jet .061 on. I've already cut out all the parts for it, so It will be an easy side job.

I'll be posting abbreviated updates on Stuka and Stunthanger(do they know it's spelled wrong?), but this thread will be the official build thread.

The fuse wood is usually where the Sterling kits fall short. The ply nose doublers are heavy and crappy as well. I would get some from Martha Stewart as you mentioned, but go down to 1/16 and maybe extend them back to the wing highpoint.

I never paid attention to how they spelled hangar. That's funny.

Hello Rusty, if I'm reading your post correctly, you suggested that you left out the ply biscuit? I would seriously reconsider that option and use it due to it providing the strength to the wing. In addition to the biscuit was another piece of ply that glued directly over top of the biscuit. When these wings break, they break directly at the exit point of the fuse. The biscuit eliminates the stress riser created at that exit point. Many times from hard flying or even a hard landing, the leading edge becomes stressed and breaks or cracks directly at the end of the piece that glues over the biscuit. You then open the sheeting up on the bottom of the wing, break out the piece that glues over the biscuit and install another one that's slightly longer. Ken

No I didn't leave it out. I haven't glued anything yet, just looking at the pieces. I mentioned I noticed, with the biscuit in place, the two LE pieces don't line up exactly. One side is about 1/32" higher than the other. It could either be hidden by sanding or fixed by re-cutting and shimming the groove in one of the LE pieces. It's a tiny mismatch.


EDIT: I re-read my post. Maybe where I said "I cut out the biscuit." casusd a misunderstanding. I meant I cut it out of the plywood sheet holding all of the assorted ply parts. Then I inserted it into the LE pieces and noticed the difference in height. One of the slots in the backside of the LE sticks is cut higher than the centerline of the stick. It's not going to cause any problem, just an observation.

you'll love titebond (aliphatic resin) i even think i like it more than Ambroid, but CA still has its place on the workbench.

http://newtowoodworking.com/aliphatic-resin-glue/

you'll love titebond (aliphatic resin) i even think i like it more than Ambroid, but CA still has its place on the workbench.

http://newtowoodworking.com/aliphatic-resin-glue/

Rusty, anytime you preglue a joint, it will ultimately have more strength. For instance, if you choose to glue you doublers on with Titebond, a thin film is applied and left to the open air to dry. This film would be applied to both pieces. Sand the area firmly to level it after it's dry and reglue with just enough glue to cover the entire area and clamp. It will gain far more strength due to the wood not soaking up the adhesive. Aliphatic resin glue or pva takes a long time to dry when it's covered up in the case of a doubler. I prefer to use it however regardless of what the majority claims. I have many of these models that are nearing 50 yrs old still in flyable condition and that's all they had back then next to Ambroid. Gluing ribs with Titebond gives you workability and sufficient joint strength. I can't use CA due to it screwing with my eyes. I hate the stuff and only use it when I need to. But to answer your question, no it doesn't need to be preglue. Ribs can be joined directly to the leading edge. I myself don't use it on the sheeting. Reason why is that the water in the glue causes the sheeting to warp and buckle. I prefer solvent based glues like Ambroid and Sig Ment. Yellow or white glue can be used, be sure to have strips of tape, pins, and also weights on hand and you'll be fine. The main importance is making sure it's down tight to the center ribs. Ken

Rusty you are heading to Lowe's today...I do not recommend the ceiling tiles as they chunk and deteriorate and create a mess

Go to the dimensional wood isle and look for the pre made boards for small table top or other building projects...soft pine or similar are generally flat enough and not too expensive. I think I paid around $11 for a 24"x 36" panel

I find it funny that we get more answers and general feedback on our CEF site than sites that are dedicated to CL flying.

I am a big Sigment/Ambroid fan and use it in places on all my builds. I absolutely love epoxy and use it anywhere I want granite strength. CA has it's place, but anymore I just use it for tacking.

What is the advantage of Titebond? I have used Sig Bond in the past and wasn't impressed. I assume it's similar.

Ron

I have used Elmer's Wood glue with a small paint brush to good success. The large applicator bottles are a waste of time (but nice price/volume), but a syringe applicator might be a good thing. Careful application seems to build a stronger joint than Testor's wood and metal cement (celluloid) at the same weight. No scientific research done by me though.

Buying a gallon is not a good idea unless you really use that much, since glues go bad after a while. If a water based glue smells sour then it is likely "spoiled". It will still work, but it won't be as strong as fresh glue. I don't know the mechanism of how it spoils, whether it is a age/light breakdown of the compounds or a contamination like bacteria or fungus. When bottles of glue turn colors like purple, black, green, or red they get tossed (yes I have seen all these colors, and threw out some of my favorite containers over it).

Phil

I keep all my glues (cyano, white, yellow, epoxy, loctite, PU) in a fridge - don't freeze it. I have an old (but good working order) small(ish) fridge in my workshop. Ensure that they're all sealed well and it'll last almost forever. I still have and use 10 year old cyanos, epoxys and yellow glues which all work as well and as strong as the day I bought them.

Ron, to answer your question, as far as advantages. The first thing due to us control liners being the cheapest on the planet, cost. Another factor is weight. Wood glue is comprised of more than 50% water. When it evaporates, your left with a minimum amount of solids. Epoxy weighs a lot, it's also very unnecessary in certain places. Many times we overemphasize the glue which just compounds the weight. A properly fitting joint is going to be just as strong regardless of glue type. I'm sure you've heard this, a properly glued joint will break fore and aft of the actual glue joint if done properly due to the glue being stronger than the wood itself. White glue mixed 50/50 with yellow will ultimately result in the strongest joint you can achieve using aliphatic glue. The problem is the sandability. It will not sand and don't expect it to do so. It will peel rather than cut. Aliphatic resins however over time will become brittle. This can sometimes save your model as the glue joint just fails and the piece just comes apart and this makes for an easy repair. I like this type of glue for that factor. Again a downside is the water in the glue. It can warp pieces of too much is used especially sheeting. A thin film is all that's needed with just enough to cover the part to be glued is all that's in order. This can work like contact adhesive and will stick immediately. Too much and the piece soaks up the moisture resulting in it wanting to curl the opposing direction of the work your gluing it too. This can happen when gluing up a D tube style wing where you have sheeting from your leading edge to the spar. If too much glue is used, the sheeting buckles between ribs causing what is known as "Horse starved" look where you can see the sheeting buckled inwards between the members. To avoid this look, one can preglue the ribs with white PVA glue and let it dry. You can then prefit your sheeting and iron your sheeting onto the wood framing with a Monokote iron.

Ambroid and solvent based adhesives sand readily and smoothly. They sand better than ANY other adhesive. Another thing that is a known fact is that they provide flexibility to the joints. For instance, I know many freeflight builders that will use a toothpick and yellow glues to build the wing structure but when it comes to dihedral braces and wing joints, they would rather use Sig Ment or Ambroid. This is due to the adhesive providing enough strength to hold the parts but they can be put into a rigorous amount of flexing due to the adhesive flexing just like the wood itself. CA glues wicks into the wood, therefore that area becomes extremely compromised becoming very hard and causing a stress riser directly in that area and the next place it will break is just outside of that glued area. Ambroid however, is constantly drying . It never stops. It will eventually shrink back from the parts you glued resulting in a failed joint. This of course is over a long period of time.

Epoxy will sand, not easily and it carries the same weight that it did when you mixed it. Try weighing your epoxy sometime and you will surprised how many grams it weighs. 7 grams being approx a 1/4 oz., it doesn't take much to easily gain up to 3/4oz. in weight just in epoxy on a .35 size model.Choose your epoxy areas to be glued wisely. Full strength epoxy in bellcrank landing gear blocks areas, modified epoxy for fillets If you choose to use it for fillets as well, this can add an additional 1/4-3/8 oz. Mixing microballoons in with your epoxy can give you twice the amount of material. It will compromise strength, but it will still have enough strength to do it's job. It will cut the weight in half as well. Ken

Amen to all that Ken has written there. However, there is another glue type rising up the ranks of popularity. I've seen "Titebond" (http://www.titebond.com.au/) mentioned in various threads, but "Titebond" is a brand name, not a glue type, or genre. They do a whole range of glues, but I particularly note their Polyurethane glue. This is my new favourite. Easy to use, slightly gap filling, ultra strong, waterproof, sands and paints beautifully and is light. Also, check out the link I've provided and have a look at "Titebond Cold Press for Veneer". Looks like the answer for the problem of thin sheet warping.

Thanks for the Glue tips. Most of my questions answered in one nutshell of a thread. Not that Ken and Dins are nutshells. I'll reserve that title for myself.

RknRusty wrote:Thanks for the Glue tips...

WOW! An unintended pun. :-)

George

Haha. I need more than glue tips. I can look pretty skilled while I'm working... until the glue comes out. Then I would appear to be a complete retard. But since nobody's watching, I generally get it done fine. Right now, the LE and the spar are drying.

I thinned a half ounce of Titebond and put it in a syringe and went to work today. I cut new ply parts for the wing assembly. My scroll saw and tabletop belt sander are lifesavers. My plywood is much stiffer than the kit supplied wood. I got the biscuit that joins the LE cut out and glued those two sticks together. Thankfully, they are straight. I also got the spar and its ply joiner glued but it's going to need straightening as well as the TE sticks. I guess I'll spray them with some Windex and weight them and hopefully they'll true up. The warps aren't bad and they are symmetrical between the adjoining sticks, so I hope by mid week I will have a nice straight wing built.

The fuse needs straightening too. It only has a slight bend along its length so I hope it cooperates. I don't think it has any twist. I'll double check, and if it is twisted, I'll get a new plank to cut out. As soon as I straighten it, I may go ahead and glue the doublers on and shape it and paint its sides to hopefully prevent any re-warping. Is that a good idea, or should I just scrap it now?

Well, it's really up to you. If you think the wood is light and of decent quality and worth saving then keep it. You may find lighter wood may be better. You can save a good bit of nose weight by going thinner on the doublers. The 1/8" ply is not really needed. Up to you though. I am finding that these older kits come out too nose heavy and wish I had reconsidered using thinner ply.

Don't forget what Ken said about the spar aka "rib ripper" another weight saver if you leave it out. The thick LE is what provides the strength.

Ron

You're not the first to recommend 1/16" doublers, so I I'll definitely do that. And also make them longer, over the top of the wing.

Balsa is cheap and I don't see any reason to fight a too-heavy fuse piece anyway. You did tell me that the Sterling fuse was not the best, so I will just replace it with a new one. Should I get medium grade with not too tight, not too wide grain?

In reality, nothing about a Sterling kit is good other than the price at the time. The instructions leave a lot to be desired and the die cutting was typically bad. Carl Goldberg kits really blew the doors off the Sterling kits as far as fits and engineering were concerned. But, Sterling kits were inexpensive and there was some really neat offerings. I would look again at your fuse and see how exactly it's warped. This could be in your favor. If the fuse is bowed to the outside of the circle I would certainly use it. One more thing to take a peek at, Sterling was notorious for using poplar for motor mount stock. The box and instructions claim hardwood, and poplar is a hardwood just not a hard one. If you have maple on hand it will certainly prevent your nose from crushing. Seeing that the kit provided ply is failing, I wouldn't use the bellcrank platform even if it looks like it's intact. The ply Sterling used was poplar core with birch skins. Between the glue that was used and the different species they pretty much had a tug of war with each other until they failed. If this kit still offers the wood control horn, I would not use it. That part is responsible for many wrecks. It either fails due to fatigue or the glue joint comes undone usually at the top of the circle. When using a modern nylon control horn, you should always use a piece of ply 1/64"-1/32" under the top and bottom of the elevator to prevent crushing and spread the load. It can easily pull right through the elevator or start a crack.

One feature that I always liked about the Sterling kits was the music wire that was used for the gear. No current music wire is like the wire they used. It's tough stuff. It can take repeated abuse and bending. The crap that's offered today either breaks or bends. Ken

I've had the LE and spar glued since Sunday, and am going to start assembling the wing today. I was wondering if I should make a thick #1 center rib for it, like Ken suggests for Shoestrings that are going to have a Fox shaker up front.

I'll study the plans more closely before I start, to make sure it won't interfere with anything else, but I'm strongly considering that modification.

I don't think it will hurt anything. I did it to my Super Clown and it doesn't call for it. As long as the bellcrank does not hit it all should be OK. The weight is very minimal.

Ron

Also, to jump on what Ken mentioned about the music wire. I have flattened the LG on my Ring twice and I just bent it back and all is well. The LG looked to have been tweaked really good before I ever got a hold of it as well. It's a pain to bend though.

Ron