Author Topic: folded wing (Read 5915 times)

Jim Morris · « **on:** October 08, 2007, 09:54:48 AM »

I was flying the new Avanti this weekend and was going pretty good,getting ready for Huntersvill,well during the triangles the outbd wing folded WHAM! plane is toast. This is the third plane in a row that didnt last long.I blamed the wing vortexes during the last two,but now I am reconsidering because I always join the wings the same way.This is a lesson learned.

Airacobra · « **Reply #1 on:** October 08, 2007, 09:59:10 AM »

Jim, sorry to hear about the Avanti, but I am curious as to how you join the wings. I am assuming the wings are foam? Spar no spar, fiberglass wrap?

Chris McMillin · « **Reply #2 on:** October 08, 2007, 10:50:34 AM »

I am really curious how you build them too.
Could you give a detailed description of the steps, possibly some guys on here can help out.
Chris...

Steve Fitton · « **Reply #3 on:** October 08, 2007, 11:30:50 AM »

Did it fold at the wing root or center section? Was it an Avanti 60 core with spar or Avanti 50 or 54 without spar?

Jim Morris · « **Reply #4 on:** October 08, 2007, 12:06:58 PM »

It was an Avanti 60 core with spar. Glass wrap. What I believe is when I mount the bellcrank.I glue it to the end of the spar before joining the wing.This I thought woul keep the bellcrank from pulling out,thinking the fiberglass wrap would take care of the center halves.All I needed was a plywood splice at the spar joint.

Steve Fitton · « **Reply #5 on:** October 08, 2007, 12:39:18 PM »

Do you have a digital camera? A picture of the wreck would be worth the proverbial thousand words right about now.....

Doug Moon · « **Reply #6 on:** October 08, 2007, 01:03:48 PM »

Dont mount the BC inline with the spar. Mount it infront of or behind it. Then leave excess pivot rod sticking out of the top and botton of the wing. Then after you mount the wing in the fuse you block the pivot rod up to the inside of the fuse with 1/8 plywood. The 1/8 ply should go around the pivot arm and tightly fit up against the inside of the fuse side. Then shear off the left over BC pivot rod that sticks above plywood you just installed. Then cap it with 1/16 plywood as well. If you dont cap it eventually it can move up and down. With a cap in place it will hold until the cows comes hom. Do this top and bottom. This should alos be done up against fuse sides that have the ply formers that go back past the this point. NOT against Balsa only. Makes for a bullet proof BC mount and doesnt get in the way of the spar. Plus it gives you a a great place to pull from on your pull test.

Also when you mount your wing into the fuse on the inside of the fuse you should use a fillet of 5 minute (NOT 15) mixed with milled fiberglass on the inner joint ALL the way around. The wing should but up against F-2 and be blocked in place with balsa and 5 minute. The motor mount beams should go back past F-2 and follow the the front of the LE shape and they should glue to the wing as well. The outside fillet should be strong material as well. I use a small amount of glass around the joint as well About 1.5" wide with 5 minute epoxy heated to run into it. The different glue joints at this point should be strong enough to take the pressure off the main joining joint of the wing. I have built many foam wing and none have had a spar and so far, knock on wood, none have folded.

Also you must have good foam to balsa adheasion. If the balsa skin comes loose from the foam in this area it will snap like a twig every time. Together the two are bullet proof. Alone they are fragile.

You mentioned you thought it was vortecies?? You got any data on that or speculation why or how that could be???

Eric Viglione · « **Reply #7 on:** October 08, 2007, 01:17:51 PM »

Hmmm... Steve is right, a picture would help immensely...

But I think I understand what you mean and why you probably went without it, I too had second thoughts when I built my Avanti because the top block is so thin at the joint and the wing almost protrudes through the top block.

Gives it a cool look, but makes doing a proper suspended BC much harder. I did prevail though, and ended up making my top block a smidgen taller and left the block solid around the BC and just hollowed it out enough to tightly embed the plywood plate. I may gave up a little on the traditional Avanti look, but I dont think anyone would notice, and I'm glad I did it.

I would convert any and all ARC/ARF's to a suspended BC too, the platform BC or other schemes I see just wouldn't cut it for me in any ship larger than a .35 size.

Got a backup ship handy?

EricV

Ron King · « **Reply #8 on:** October 08, 2007, 02:02:55 PM »

Quote from: Doug Moon on October 08, 2007, 01:03:48 PM

Also when you mount your wing into the fuse on the inside of the fuse you should use a fillet of 5 minute (NOT 15) mixed with milled fiberglass on the inner joint ALL the way around.

Doug,

I am curious why you recommend 5 minute epoxy instead of 15 minute. Over the years we have learned that the 5 minute epoxy becomes much more brittle than the slower epoxies, so we no longer use anything faster than 15 minute epoxy for our UAVs. Thus, I don't use 5 minute epoxy on my models.

I agree with your other construction tips and do my wings the same way.

Thanks,

Ron

Doug Moon · « **Reply #9 on:** October 08, 2007, 02:29:57 PM »

Ron,

I have found over the years that hobby epoxy like 15 or 30 is a much more thin material. It has very little gap filling quality. Also it is a finish cure and doesnt seem as strong. I found finish cure to mean just that. You can finish on it and strength is not the main goal. At least that is what I have found. I am strictly talking hobby stuff here. Not the more advanced stuff you would build boats or composite parts with. Just your plain old run of the mill off the shelf $8 dollar stuff from HobbyTown or the likes. 15 will fool you. It dries up nice and hard and you think you have a good bond. But it is very thin and wicks into the wood. Using it on a butt joint like wing halves will leave gaps and that creates weak spots. In my personal experience I stay away from it. 5 minute has always worked better for me. In the areas where I will use slow stuff, for carbon or glass, I use West or Pro-Set.

Hope that helps let you know where I am coming from.

Doug

phil c · « **Reply #10 on:** October 08, 2007, 02:37:39 PM »

You really need something more than a ply cap over the bellcrank pivot. I've seen the pivot rod in a couple of these grind its way through the plywood, allowing the bellcrank to pull out. Notch the ends of the pivot rod for set screws and put on wheel collars. Then glue them in place with thin CyA.

Doug Moon · « **Reply #11 on:** October 08, 2007, 03:09:31 PM »

Phil,

That works well. I have done it that way too.

The main goal of blocking the thing up to the fuse side gets the BC supported by the fuse and the wing.

Jim Morris · « **Reply #12 on:** October 09, 2007, 07:44:35 AM »

Doug, the vortecies question is that hear at Hobby Park in NC we are surrounded by trees and the air is terrible alot of times.You MUST back up during calm days. When the wing folded it was at the bottom of the menuver.Its hard to tell between vortecies or folded wing unless your outside the circle. They act the same and it happens in a split second. The plane rolls violently and slams into the ground.

Doug Moon · « **Reply #13 on:** October 09, 2007, 09:23:52 AM »

Jim,

You are saying that the Vortecies slam planes to the ground all the time? Sounds like an awful site.

But from what you are saying sounds like you have an issue in the wing contruction as well. If you are getting folded wings three times in a row there is somehting missing. Hope some of the tips helped.

Give us a low down on what you are doing... Contruction and glue types....

Bill Little · « **Reply #14 on:** October 09, 2007, 09:57:53 AM »

Hobby Park is VERY turbulent!

It's one of the only two C/L sites I know of in NC. The site is a combination R/C, Soap Box Derby, C/L facility. Two paved circles and a large grass area. The paved circles are in the corner against the trees, with two sides open and the grass area is elevated. There is just no way of telling what the wind will do. Sometimes you can be in the center circle and hit tree limbs! The worst part is, there is a bike trail that comes out through the edge of the best paved circle. Just waiting for one of the bikers to get hit in the face by a .60 powered stunt plane at 55 mph.............. Then there are the fly overs by the R/C guys. Saturdays are pretty much impossible according to Tommy Luper. When we had our "Fly IN" there a month or two back, at least one combat plane was hit by an R/C car while it was sitting on the ground (A dirt track for R/C cars is on one side).

I use to get up there quite a bit, but it is becoming more difficult.

Bradley Walker · « **Reply #15 on:** October 09, 2007, 11:16:38 AM »

Quote from: phil c on October 08, 2007, 02:37:39 PM

You really need something more than a ply cap over the bellcrank pivot. I've seen the pivot rod in a couple of these grind its way through the plywood, allowing the bellcrank to pull out. Notch the ends of the pivot rod for set screws and put on wheel collars. Then glue them in place with thin CyA.

HAHHAHHAHAHAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAHAHAHAHA

Man, you are not kidding Phil!!! That wire can bore through just about anything, it can also oversize the hole too.

Ask Doug!!!

Chris McMillin · « **Reply #16 on:** October 09, 2007, 02:02:48 PM »

Quote from: Jim Morris on October 08, 2007, 12:06:58 PM

It was an Avanti 60 core with spar. Glass wrap. What I believe is when I mount the bellcrank.I glue it to the end of the spar before joining the wing.This I thought woul keep the bellcrank from pulling out,thinking the fiberglass wrap would take care of the center halves.All I needed was a plywood splice at the spar joint.

Jim,

Putting the bellcrank wire in between the spar ends makes a void in the structure, even with a good scarf/splice. It will be weak to start with.

Add to that the bellcrank pivot using itself as a pry bar to loosen the joint every flight.

After so many flights the stress, with stresses added from the rough air conditions at your field, cause the spar splice to open. Now there is a spar with a void, which lets energy get a wind-up before the foam and glass gets tension , and wham, it overloads that part of your structure and the wing fails.

I don't use lite ply spars in foam wings because it acts as a stress riser, in my opinion. I use the technique Doug outlines as far as the bellcrank installation. Then I make sure I have a very precise mating suface when I glue the wing halves together so there are no voids. I use masking tape span wise to add tension to the center joint, top and bottom, to get it tight and aligned level, then trap it in the saddles to dry. Then I make some elliptical spar caps from .05 fibreglass top and bottom, double layered. This is to hold the foam and balsa together in tension while inflight.

One can use the 1 or 2 inch strip of glass down the middle OK, and a light ply spar OK, as long as you don't have the bellcrank wire in the middle of the spar. This is a structural void and a stress riser that is the cause of your failures.

It is also OK to NOT use a lite ply spar and a strip of glass, as long as the bellcrank pivot is mounted into the fuse structure after the wing is mounted, again as Doug describes.

Many of us have thousands of flights at fields with lots of turbulent air, and the models are just as sound as when new, using the bellcrank mounting where the vertical wire is integrated into the inboard fuse side. Making sure the structure is sound to start with is the key, and the wood spar, as well as the mating sufaces of the foam/balsa wing halves, cannot have spaces between them. In your case you not only had the space, but a metal pry bar to make sure it eventually was pried apart!

Now you know. Change this and you won't have anymore failures, I'd bet.

Good luck.

Chris...

Eric Viglione · « **Reply #17 on:** October 09, 2007, 02:25:31 PM »

I'm probably going to get some strange looks over this... but I suspend my BC with fuel tubing from inside the wing... which holds it nicley centered until I solder washers over the plywood plates. Otherwise I do it pretty much like Doug.

Also, I make sure the plywood touches both sides of the fuse, not just the inboard side that we pull against. I never put the BC on the stub spar, it creates a disconnect and leverage effect there. Also usually sneak in a partial vertical former somewhere on BC mount plate top and bottom of the wing, even if the plans dont show a former there. It's a tiny amount of weight added, so I just try and make up for the extra weight by dremeling a little thinner on the blocks somewhere else where structure is not critical.

A good friend (yeah, you know who, Hi Eddy!) gave me the "bullet proof controlls" speach when I was a kid, and I've tried to adhear to it ever since... so I use tweak-unfriendly 1/8" horns, tubular pushrods with the wire all the way through not just the ends, bushed leadouts, little plywood doublers around the horns, etc. If I remeber it went something like this: (he can correct me if I botch this)

"It doesn't have to survive a crash, but it does need to survive heavy flight loads in high winds and the occasional ham fisted pull test. Most planes will fly fine on a calm day, but when the wind comes up or your engine gets off the ground with the needle set a little fast, the ship with bullet proof controlls will get you through the day and still do precision stunts and ones with the spongy controlls are the one most likely to see the loops opening up, soft or bobbled corners or worse case scenario, crash from lack of control authority."

This philosophy has saved my planes bacon on many occasions down here in the hurricane state where the entire flight can sometimes feel like a pull test.

Oh yeah, as long as we're at it, a different set of lines and handle for every plane you own, and toss your lines and get a new set every year, especially if you fly a lot or use crimps.

Thanks again Eddy!
EricV

Jim Thomerson · « **Reply #18 on:** October 09, 2007, 03:01:39 PM »

Some years back, someone showed me a sheeted foam wing airplane with a folded wing. The wing had been covered with carbon veil after being installed in the fuselage. It broke at the edge of the carbon veil. Thought was that the vail stiffened the wing outboard and created a stress riser at the end of the carbon veil.

Clint Ormosen · « **Reply #19 on:** October 09, 2007, 03:19:43 PM »

Quote from: Eric Viglione on October 09, 2007, 02:25:31 PM

I'm probably going to get some strange looks over this... but I suspend my BC with fuel tubing from inside the wing... which holds it nicley centered until I solder washers over the plywood plates. Otherwise I do it pretty much like Doug.

Also, I make sure the plywood touches both sides of the fuse, not just the inboard side that we pull against. I never put the BC on the stub spar, it creates a disconnect and leverage effect there. Also usually sneak in a partial vertical former somewhere on BC mount plate top and bottom of the wing, even if the plans dont show a former there. It's a tiny amount of weight added, so I just try and make up for the extra weight by dremeling a little thinner on the blocks somewhere else where structure is not critical.

BINGO!! That's exactly the way I do it minus the vertical former. Once the wing is in the fuse, I put a plywood plate the width of the fuse over the pivot rod and then solder on a washer. then epoxy the plate down and to the fuse sides. Top and bottom the same.

Jim Morris · « **Reply #20 on:** October 09, 2007, 06:30:31 PM »

hey thanks Chris, I never thought of the BC acting like a pry bar.And yes I screwed up in the past but it was a lesson learned.I will bet that in the past it was wing failure and NOT the vortecies I thought. I have lost two planes on the bottom of the triangles and one on the outside squares at the bottom of course.It all happens so fast its hard to tell what really happened.Since it is hobby park I always assumed it was from the bad air.Thanks everyone for the info. Steve,I do have a camera but I sure dont know how to get anything on here.

Doug Moon · « **Reply #21 on:** October 09, 2007, 07:56:26 PM »

Quote from: Bradley Walker on October 09, 2007, 11:16:38 AM

HAHHAHHAHAHAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAHAHAHAHA

Man, you are not kidding Phil!!! That wire can bore through just about anything, it can also oversize the hole too.

Ask Doug!!!

Ah yes I remember cutting the canopy off the Mr Hyde, I think it was that one red and green beast!. What did we find? Loose BC. It was blocked up real nice to the fuse but nothing holding that bad boy down and it was sliding up and down. We capped that dude with ply and 5 minute. Same on the bottom and I think Joe Gilbert still flys it today. That was years ago......

I have a photo of the plane with the knife sticking out of it. If I can find it will scan it in. Made Brad crazy to see his plane with a #11 slicing off the canopy. Made me crazy to have to do it. BUT Brad made a finish repair on it and you never could tell it was ever even touched. NICE WORK MY BUDDY!!!

Oh yeah, use glue on the BC mount. I once built a perfect Skyray 35. Had a tiger 35 on it. It went super sonic on the first flight and the BC pulled out the inboard wing and the plane went straight in at 80 MPH! It was AWESOME!!! After inspection it was easy to see I had tacked in the BC mount and forgot to come back and finish it up with epoxy! It was a split second disaster!! Tore to motor up real good! I was glad because then I didnt have to fight it anymore.

Ted Fancher · « **Reply #22 on:** October 09, 2007, 08:14:40 PM »

Quote from: Doug Moon on October 09, 2007, 07:56:26 PM

Oh yeah, use glue on the BC mount. I once built a perfect Skyray 35. Had a tiger 35 on it. It went super sonic on the first flight and the BC pulled out the inboard wing and the plane went straight in at 80 MPH! It was AWESOME!!! After inspection it was easy to see I had tacked in the BC mount and forgot to come back and finish it up with epoxy! It was a split second disaster!! Tore to motor up real good! I was glad because then I didnt have to fight it anymore.

Oh, boy, Doug.

I can go you one better (literally)!

Back when I was a boy and still thought combat was fun, I built the then new "double Voodoo" kit. Two Voodoos in one box. I guess they new more about combat attrition than I did at the time ... although I soon learned.

Built both of those puppies side by side; installed a couple of high zoot Johnson .35s (modified per Riley Wooten's advice at the '59 Nats) and took 'em out to the field to raise a little cane.

Lit off the first one, brother Gary let it go and about two seconds later it was in the dirt with the never glued in bellcrank protruding through the inboard wing. Dang it! I hate it when that happens.

Moved the lines to the second ship, lit it up and ... oh, why bother. You've already guessed it,

Ted

john e. holliday · « **Reply #23 on:** October 09, 2007, 08:36:56 PM »

If you think Hobby Park is bad, come to Topeka, KS at Gage Park when the wind is out of either the North or West. I have yet to have a foam wing fail, so far(now I've jinxed myself) in turbulent air. Even took the landing gear out of number two SIG Mustang on one flight without hurting the foam wing. Nobody mentioned sheeting the center section after the panels were joined. I do run a bolt far enough thru the wing so a plywood plate can be glued top and bottom. Sometimes I put a nut on the bolt top and bottome, but, most times I just J-B Weld a washer over the bolt. Also I have never glassed the center section. Have fun, DOC Holliday

Curare · « **Reply #24 on:** December 09, 2013, 09:38:19 PM »

Hey guys, I thought I'd dig up this long decaying thread, as I just had a wing fold on my latest dog, at the bottom of the first wingover.

This was a double foam spar 48" span model that had a little damage prior to this incident, and i fear that this may have lead to the fold.

Considering this wing was merely a tester I just added a 1 1/2" strip of glass to the centre section, the sheeting appears to have broken just outside of it.

I would hazard a guess that the straight line of the glass created a stress riser along the wing, and when I did a low pullout the day before I may well have touched the ground hard enough to crack the sheeting.

At the time I was umming and ahhing over doing my usual glassing method which is two layers of concentrically smaller diamonds (at different bias angles) with the lateral points lining up with the foam spar in the wing.

Next time I think I will listen to my own advice!

PJ Rowland · « **Reply #25 on:** December 10, 2013, 12:24:45 AM »

2 Stunt ships ago - I decided to reduce weight and looked at all sorts of ways to reduce weight. One bright idea was not putting in a ply stopper on the top of the bellcrank pivot bar - I remember thinking " How is it possibly going to wiggle vertically when all the stress and force is lateral.

Like Ted said " Why bother telling the rest you guessed what happened to that one..... "

Curare · « **Reply #26 on:** December 10, 2013, 12:32:17 AM »

Yeah, P.J. I regularly make rods for my own back, this was just one of them

With that said though, for a set of wings that were just a tester they werent bad till they got divorced.

Next one may have a bit more central reinforement

SteveMoon · « **Reply #27 on:** December 10, 2013, 07:17:34 AM »

What Doug said; and Eric too. I suspend my bellcrank mount with fuel tubing
before putting it in place in the wing and then do all the steps Doug does
exactly the same way.

Ted: The bellcrank on Doug's Skyray pulled out also. After the very short flight
was over Doug was holding a handle with lines running out to a bellcrank and
platform laying there on the flying circle everything else was scattered all over
the place. It was hilarious! I still give Doug grief over that. Use glue!

Steve

Steve Fitton · « **Reply #28 on:** December 10, 2013, 07:59:39 AM »

I never heard of soldering keeper washers OVER the plywood plates top and bottom. I guess my planes are doomed......

john e. holliday · « **Reply #29 on:** December 10, 2013, 10:32:44 AM »

Well, I lost my Sheeks Spitfire, because I didn't secure the bell crank rod from moving vertically. Had J-B Weld on the wheel collars like Tom Morris showed at the time. Now I put a ply wood pad top an bottom to make it doesn't have any where to go.

Brett Buck · « **Reply #30 on:** December 10, 2013, 11:00:23 AM »

Quote from: Curare on December 09, 2013, 09:38:19 PM

Hey guys, I thought I'd dig up this long decaying thread, as I just had a wing fold on my latest dog, at the bottom of the first wingover.

This was a double foam spar 48" span model that had a little damage prior to this incident, and i fear that this may have lead to the fold.

Considering this wing was merely a tester I just added a 1 1/2" strip of glass to the centre section, the sheeting appears to have broken just outside of it.

I would hazard a guess that the straight line of the glass created a stress riser along the wing, and when I did a low pullout the day before I may well have touched the ground hard enough to crack the sheeting.

At the time I was umming and ahhing over doing my usual glassing method which is two layers of concentrically smaller diamonds (at different bias angles) with the lateral points lining up with the foam spar in the wing.

Next time I think I will listen to my own advice!

   Mine have all had ~1" wide glass and epoxy, with no issues - spar or no spar, assuming they were not damaged.

   This spate of wing folding started with the ST60 planes, which finally had enough power and speed control to keep the speed in the corners. Then tuned pipe engines came along, and it got much worse, for the same reason.

   The mistake with a lot of ST60 airplanes was that they built the airplane, then covered it after it was assembled. Do that, and the wing folds near the fuse side because of the stress riser from the tissue ending near there. The New Jersey solution was to put large elliptical fiberglass patches under the sheeting, in many cases, several layers worth of 1.5 oz glass. The correct solution is to cover the wing completely, including the center section, before assembly, so the covering is in one piece. This solves the problem and is far lighter than large amounts of glass and epoxy it takes to beef it up on the inside.

   Ted pointed this out back in the "Pro Stunt News" era, endearing himself to the Jersey crowd no end.

   The only fold our little group has had was mine, right before (like, a day and a half before) the 1994 NATs. The problem there was different - it was sparless, and Monokote, so no significant stress riser was formed. Many of them were built that way and all are still working, at least those I made, 25 years later. My problem was that, due to incorrect circle markings at a contest in Sacramento, I hit Paul Isenhower in the shoulder with my wingtip. He was OK. The airplane was less OK. The whip of the fuselage cracked it right at the wing root on the inboard side, so I fixed that and kept flying it. I also noticed, over the next few years, that I would have chordwise wrinkles in the Monokote near the root on the top of the outboard wing. I would shrink them out, but they kept coming back. It flew OK, so I kept at it. Then, in the last practice session before the NATs, the wing folded in the outside square loop. After that, I figured out what happened was that the hit on the wingtip probably cracked the LE and some of the sheeting, and a few hundred flight later, it finally propagated to the high point, and gave up the ghost.

   Brett

RC Storick · « **Reply #31 on:** December 10, 2013, 11:39:17 AM »

I have built many airplanes as a mater of fact I lost count but its in the hundreds. I personally have never had a wing fold. I was taught that tight fits and spreading the load out over at least 2 bays on each side for built up wings (with hard wood). I have built many foam wings with and without spars and again make sure the center joint is tight. I quit with all the glass cloth in the center and only use 2 layers of .02 CF applied with dope. I have done it both ways cover before the wing is installed and after. I like after. The biggest problem I have seen in others airplanes is sanding the sheeting in the center too thin.

Try to imagine you are spreading the load out all over the wing and keep that in mind when building and sanding. Sorry about your loss its always hard to loose a plane but learn from your mistake.