Hi all, when I look at my 4*60 fuselage area behind the wing mounting block, I can understand why many have reinforced that area. Could I get some detailed information about how the modification was done, what materials I need to get. I hope that this mod is worthwhile and I will not be transferring the weak spot to another area. Thx for the inputs...............

Hmmm... I took the practical easy approach. I just cut off some of the plywood scraps and CA'd them to the skinny sections where the large cut-outs are behind the wing. I made each scrap width a little wider than the existing skinny strip and made the length run from former to former.

The fuse seems to be plenty strong right next to the formers between the cut-outs. The weak links are skinny plywood strips along the edges of the cutouts. I CA'd a strip inside both sides, top, and bottom across the first two cut-out. Can't say that it wont break, but it's gotta be two times as strong now. Who knows where the weak spot is now? If I find out, I'll let ya know.

Someone here re-inforced the first section behind the wing, only to report that the next one back broke. I re-inforced the first two sections behind the wing. Maybe my third section will fall victim?

I would post a photo, but it's already covered.

Note to self: don't smack the four-star down really hard unless I want to repair fuse...

Hi BGI, what is the thickness, width and length of the plywood strips you used. Sorry for the basic question because I need to order the right amount of plywood for this job. Did you use any balsa triangle stocks ? Thx again............

Rajul,

Balsa tri-stock should work, too. I just used the scraps from the plywood sides because it was there (i.e. free). I'm not sure how thick it is - it's the same as the fuse sides. I can't say it's the best thing to use. Be concious of the CG change.

Rajul, I'm currently building a 4*60, too. The fuselage is plenty strong enough as designed. I believe some that have fuselage failure perhaps did not glue the fuse properly. The sections behind the wing do not have the bit of extra gluing surface the fuse doublers provide. Simple butt joints between liteply sides do not give CA enough gluing surface to bite good.

The problem is compounded by the fact that the instructions tells the builder simply to rubber band the fuse together and CA. Well, CA needs a tight fit to yield a strong bond, particularly between plywood pieces. Even though Sig does caution the builder to go back with thick CA to form fillets, this to me is not really enough.

What's worse, if you sand to round off the fuselage corners somewhat, you'll end up with even less glue contact area. Bear in mind that bending and torsional moments on the fuse (e.g. from a hard landing) will subject a good amount of shear stress on the butt joints between the four fuselage sides.

I will be using 3/8" and 1/4" tristock to tie the sides together better. Also, CA the fuselage one joint line at a time and press the parts together tight till the CA bond take set. No need to go nuts with reinforcement, just more gluing surfaces for the fuselage structural members to take hold.

I had the same problem building a 60 Stinger. Fuse sides are lite ply, which I have little respect for. Manual says to "score" the lite ply vertically behind the wing so it will bend to form a distinct angle, rather than bending in a curve. This is necessary in order to make a fit for the abs turtledeck that goes on top of the fuselage from wing te to tail.

So against my better judgment, I scored the sides, then very gently bent them to get the required angle. One side broke right at the score--no surprise! So I broke the other side for perfect symmetry, tacked them back together, reinforced the two butt joints with carbon fiber tape, iron-on variety, stuck them down with thin CA worked in with my finger tip. That was fun. To hide the ugly scar, I ran a sheet of 1/16 balsa down each side and ca'd that to the lite ply.

I have had a couple fuselages fail, and it irritates the goshdarn heck out of me when that happens. My cf reinforcement is not going to fail, no way. If I tried to break it over my knee, it would not break at that joint. The extra weight of 36" of 1/16" sheeting is a small price to pay for the confidence I now have in this fuselage.

I am gradually learning to take all lite ply parts out of any kit and replace them with lighter balsa of maybe the next size in thickness, cf reinforce where it looks like it needs it, and fly with confidence.

Volfy makes some very good points. However, while the four-star 60 fuse failures I've seen may have been caused by the lite-ply butt joints failing, the result was the fuse snapping in half right behind the wing trailing-edge former. This seems to be a result of the cut-outs being too large, not leaving enough wood for sufficient strength. That's what led me to just double-up on the narrow strips behind the wing.

But you guys are right. Lite-ply is fairly brittle. I think it's made from poplar in many cases - very brittle wood. I think that tri-stock would have been a better choice.

To those of you who replace the lite-ply pieces with balsa: You have my respect! No way would I have time to do that on a plane such as the four-star 60!

I agree. I am trying hard to stick to the original design when building this bird. Afterall, I bought this kit thinking it is about the only kit I can afford to build given what little time I have these days.

Having built a Kadet Seniorita, I know just how strong a properly designed lightweight structure can be. I also realize that even the toughest airframe has its limits in terms of survivability. Hit the ground hard enough, and even a (s)Turdy Birdy will break. Striking a proper balance between lightweight and strength is a delicate task, and I believe the original kit design has put a heck of a lot more thought into it than I could ever muster.

The 4*s are deisigned relatively light to fly right. A little reinforcement here and there at key places won't hurt it. The landing gear area is one perfect example. I will be fliberglassing mine, but only enough to strengthen an area otherwise substantially weaker than the rest of the fuse. Rajul has a genuine concern about not overbuild one area - only to transfer the failure point to the next weaker spot.

Practically every aspect of a model plane design is a compromise, nnowhere more common than in strength vs weight. Same is true of full scale. I try to build for light weight with adequate strength for good performance.

However, I gained a little perspective on this topic at a recent club weight-lifting event. The object was to lift more weight than the other guys, flying one full minute, taking off and landing in one piece, with power limited to stock two-cycle engine of no more than .46 displacement. The winner was a very ingenious 17' polyhedral wingspan, glider type wing, on a v-tail boom fuselage made from a composite surf-fishing rod blank, powered with an OS 46 FX turning through a 5:1 belt-driven gear reduction to swing a 26X10 prop. The plane itself weighed 23 pounds, before any payload was added. It flew slow, but steady, sorta like an albatross, if you've ever seen an albatross in the air. I couldn't stay for the very end, but they were up to 3009 grams at the time I left--that's close to seven pounds of payload on a 23 pound plane, so the OS .46 was flying 30 pounds around the field.

The other contestants had smaller planes, one of which was not way different looking from a standard 40-size trainer with maybe a little more wing area than typical, scratch design but conventional kind of airframe. I had the opportunity to heft this bird with its payload, and it was heavier than any Thanksgiving turkey I ever lifted. This plane was in second place when I left, and not far at all behind the albatross, in the neighborhood of 3000 grams payload as well. So what I learned from this was that a standard size model and standard size power will fly at two or three or even four times the five-pound weight we would aim for on a .40-.50 size engine. It won't loop, and it won't roll unless you start five hundred feet high, but it will fly.

The other end of perspective comes from watching a Yellow Sukhoi fly. I don't know its exact weight, but it was definitely light (and strong) for its size. I was amazed how it floated like a feather in low-speed maneuvers. So that showed me the benefits of light weight.

I am a sport flyer, out for a good time, not looking to win any trophies. So while I am not reckless about adding weight, it doesn't bother me to add a little weight when I think the added strength will pay off. My planes are usually within 10% of what might be considered light for their size, and there are no maneuvers of which I'm capable that they will not do, and in decent form depending on who's flying. If I think a particular model is more sluggish than I would like, I have no qualms about swapping in a bigger engine.

So on my Stinger as mentioned above, the stock design imho is clearly defective. The fix I came up with was carbon fiber reinforcement, at negligible added weight; plus 1/16" hard balsa sheeting on both sides of fuselage, certainly less than an ounce of added weight; and finally wrapping the fuselage in 2 oz fiberglass and painting instead of covering. The glass/epoxy/paint vs monokote covering maybe cost me another couple ounces. On the strength side, I have a very solid fuse, stress distributed via the balsa sheeting and fiberglass wrapping, and I can get a better looking fuse by painting vs covering. On a .60 size plane (powered with a .75), I think I'm way ahead of the stock kit.

All this extra fussing does take extra time, but to me that's the attraction of kit-building and bashing vs ARFing or bowing down to the original design. When I crash through my own stupidity, I accept it and build again. But when a plane fails in "normal" usage because of less than adequate strength in the design or manufacture, it takes me a long time before the urge to kill goes away.

Volfly:

I always use some epoxy. The fuse broke when it went into low weeds on the side of the runway while still on the ground and not rolling very fast(too fast obviously). It broke behind the reinforcement. Absolutely no other marks anywhere and after only a couple of flights. People have been flying into those weeds without damage for a long time. The lite ply broke. Just remember all ply has voids, especially lite ply and especially in 2002. It is not what it was a few years ago. I sheeted the leading edge, reinforced behind the wing and a few other things. With the YS 91 FS the CG came out bang on, so it is great. I now have reinforced further down the fuse and I am happier with it. BTW my landing gear and the fuse above are strong enough without any mods. Whatever one wants to do they shoulld do. Rajul if you build it you can fly it, if you ponder building it you can't!!

Hi Volfy, could you possibly show some pics of your reinforcement areas? Hopefully you have not covered yet. Did you apply the tri-stock in the first and second sections behind the wing, or only in the first section ? Why do you need two sizes of tri-stock ? Thanks again................

Rajul, I started this project not long ago and so far I have just glued the fuse doublers onto the sides and trial fitted the fuse parts together. I'm putting together a WM Super Stunt 60 at the same time so it might be awhile till I get back on the 4*60. I'm terrible about having too many projects going at the same time, but sometime it works to my benefit. If I'm waiting on some parts for one project, I can proceed with another.

BTW, if you want to see some skimpy liteply fuse construction, you ought to see how the WM Super Stunts are built. I have both the 40 and 60 size and compared to them, the 4*60 fuse is stout! Then again, the Super Stunts are funfly planes with extremely light wingloading. Coupled with quad flaps, one can do some amazing flying otherwise impossible.

Back to the tristock, the idea is very simple. Just glue the fuse together, and add the tristock to the four corners of the fueselage in sections from former to former. 3/8" is for right behind the wing; 1/4" goes to the very rear of the fuse.

Thanks Volfy. Quad flaps ? Hmmm, I must check out the Super Stunt. What engine do you plan to use ?........ )

I assume you meant the 4*60? I have several engines on the shelf I could use, but I have settled on my just broken-in Magnum 1.08. So far, I have it mounted on the firewall with a Hayes motor mount - inverted, at about 1/4" higher than the thrust line drawn on the plans. This way, I can use a fully enclosed cowl if I choose, and the carb would be high enough to mount a 16Oz. tank centered to it.

The 1.08 is a little heavy for this plane, and even with it almost butt up against the firewall, I expect the plane to come out quite tail heavy. I'll be sheeting the turtle deck and mounting the rudder servo (and elevator servo, if necessary) in the back to compensate. I don't want to add lead.

I have replaced the stock landing gear with a larger heavy duty aluminum one I bought at a swap meet, so prop clearance shouldn't be a problem. I didn't know it at the time, but two of the three holes on the gear actually matched the 4*60 LGM perfectly.

BTW, to answer some of you guys' comments, I didn't mean to imply that reinforcements are not a good idea. As a matter of fact, I'm doing it to several parts of this kit. I could never resist the temptation to bash a kit. Every kit and ARF I put together, since I got back to RC about a year ago, has not escaped without at least some kind of embellishment on my part. Some of them are functional (taildragger conversion, flaps addition,etc.), others are structural (wing sheeting. fiberglassing, etc.), still others are plain unabashed cosmetic touch-ups (prettier cowl, rounded tail feathers, etc.).

I know if f I don't pull the reigns on myself, I can easily get carried away with bashing an otherwise perfectly good design. That was what I was cautiioning. I believe we bash a kit often not because it's necessary, but because it's fun! There is nothing wrong with that, so long as we are honest about it.

Someone mentioned kit bashing the 4-Star. Here is a photo of my bashed 4-Star 60. Removed 2 ribs and added curved wing tips. Moved gear to the wing & added wheel well doors. Angled engine over and cowled. Added tips to vert & Horz tails & re-shaped. OS .91FX power.

Ed: Where? Where? Sounds like I'd like to see it!