leadouts again

I realize that this is an issue that has been debated before and, for some, the passion is almost like starting the pipe verses muffler debate of the past. So I am going to ask you to be kind to each other when stating your preferences or findings.

We, personally, have always used solid leadouts in our planes. It is our preference, and we haven't ever had any problems with .032 size leadouts. In spite of that, Matt has gone to using .039 leadouts in his last several planes "just to be safe". With good wire and good bending techniques these should work with no fear of failure even after a thousand flights or so.

Stranded should also work well, however, if good wire is used and good techniques for finishing them off. The strandeds must be bushed at the belcrank, and care must be exercised that these do not flex at the belcrank end under load. If one bushes the belcrank end with copper or brass tube, and then brings the end of the tube all the way around until they meet, and then the wire is tied off properly (I would prefer wrapping to swaging) then the stranded leadouts should be fine. The key to using either solid or stranded leadouts is to keep it from flexing. If either type flexes under load, it will fail.

So, I am not asking for a vote. Just to report your findings on what works and what has not worked--either with you or with someone else...and why--so we can all avoid the pitfalls of losing a plane to a bad leadout.

I use heavy cable (usually .045 stuff noted). I use my own design bellcrank cut out of 3/16" aluminum or like the last one, a piece of titanium. I've been using a fork end on the ears of the bellcrank for the past 3 or 4 years. I just double wrap the end of the cable ala AMA with an eyelet and shrink tubing over the copper wire and put a 4/40 sockethead screw through the bellcrank fork and the eyelet. I slip on a nut and use some locktite and jimmy the threads on the end of the screw. It's not likely to come out and there isn't much stress on the bolt. The current plane used a 4/40 x 1/2" grade 8 socket head screw that was only threaded a 1/4 of the way so the unthreaded part is riding on the eyelet. Works for me.

Case in point (this is ugly so send the kids to bed). About 4 years ago, on a plane that used a more conventional method of cable hook up at the bellcrank, I had an interesting occurance (this plane is still intact and being flown by Dave Gardner, Scott). I live out in the forests of Kitsap Peninsula, near Puget Sound. The most quickly accessable flying site is an auxillery field at a local junior high. The field is only used for field events during track season and some PE stuff. It's out of the way on the top of a small hill, so it's pretty private and noise isn't too much of a problem. The only real problem is, they only mow the scraggly grass and weeds during the school year. I was flying there on a Sunday over the summer and some of the weeds were getting a bit high. I had resolved to bring my mower the next weekend. I went to take off and just as the wheels left the ground the lines caught a weed. The plane made an unscheduled left turn and came directly at me about 6 feet off the ground. Hey, at least it seemed to be flying straight. Once the plane went past dragging the lines all the way, I tried to move to the left of the place where the plane reach the end of the lines to lessen the cable angle and planted by feet getting ready for a really big jerk. The plane made it to the end of the lines, snapped to the left and the force of it, surprisingly, killed the engine. The plane dropped about 5 feet rather suddenly and landed on the gear. Once I had cleaned my shorts, I put down the handle casually and strolled over the the plane.

The weird part was, I came to the end of the lines with both leadouts still attached about 10 feet before I got to the plane. Other than missing the leadouts, the plane seemed shockingly undamaged. A bit of surgery revealed that both leadout snapped right at the bellcrank in the middle of the tubing they ran through. So, I put in new leadouts and flew the plane for the rest of the season without problems. Gotta love that bellcrank installation, it didn't budge!

Now comes the part that needs to go on the Dumb and Dumber thread on RCOnline. Last year, flying my brand new SV-11 at the same site just after the NW Regionals, I did the exact same thing. It had the forked bellcrank and heavy cable. I didn't see any weeds that could have caught the leadouts. Hey, maybe a gopher jumped up and grabbed them, I don't know, but just as the plane was taking off, the 4th or 5th flight of the day, it jumped, made a left turn and flew right at me. It was a bit higher than the last time at about 15 feet. I wathched it go over my head, draging the lines with it. I didn't move this time and it came to the end of the lines, same unreal sudden snap, made another left turn and proceeded around the circle. This time the engine didn't quit (I guess PA engines are less suceptable to sudden fuel system pressure changes than Stalkers). I couldn't believe the thing didn't just come back at me. The lines went a bit slack for maybe an 1/8 of a lap and the thing just cruised along. I just flew it out at level flight and upon landing, inspected the plane. No damage that I could see and the controls felt fine, maybe a bit smoother. When I managed to plant the poor thing in the pavement at the WOLF contest in August, I inspected the controls on the inside (sigh) and they looked just like they did when I put them in. No apparent damage.

If this system will stand up to that, I'm keeping it. I could tow my car with this. And no, I don't fly at that site much any more. Call me silly, but...

This long winded dissertation by:

>>HAY Randy your Raptor is one of my fav planes. SCOTT <<

It's just a somewhat aesthetically modified Saturn with an Impact tailplane.

Sorry, I went out to the shop and looked. They are .032, seven strand. Had to look on the tag. The aluminum bellcrank weighs about .80 oz. Pretty heavy as things go, I guess. The titanium one ( get small pieces from a friend that works in an industrial plating shop) weighs about .55oz, but the stuff I built it from is a bit thinner. I haven't weighed the cables. I will when I cut the next set. I get the leadout cable from an industrial supply place in Tacoma, WA. They sell pretty much as much as you want.

The interesting thing to me at this point is that the lines didn't snap. Even using .018 braided lines does not leave a lot of margin. But if you were using the .045 stranded leadouts at the time and they snapped and the flying lines didn't, well, now you see why we need heavier leadouts (than the flying lines) in our planes. It is not the straight pull strength that we have to worry about, it is the bends and the curves and the flexing. If there is any flexing going on in the system at all (whether we use cable or solids) it will eventually fail where the amount of flexing is the greatest. And, although we don't think about it too much, when we put the leadouts under tension, we often cause that flexing that eventually leads to failure.

I think one of the reasons we don't see any more leadut failures than we do, is it is often the less experienced builders who are also the less experienced flyers whose systems are most prone to failure. Many of these don't have planes that last too long anyway.

>Now comes the part that needs to go on the Dumb
>and Dumber thread on RCOnline. Last year, flying my brand
>new SV-11 at the same site just after the NW Regionals, I did
>the exact same thing. It had the forked bellcrank and heavy
>cable. I didn't see any weeds that could have caught the
>leadouts...but just as the plane was taking off...it jumped,
>made a left turn and flew right at me....I wathched it go over
>my head, draging the lines with it. I didn't move this time
>and it came to the end of the lines, same unreal sudden snap,
>made another left turn and proceeded around the circle. This
>time the engine didn't quit....I couldn't believe the thing
>didn't just come back at me. The lines went a bit slack
>for maybe an 1/8 of a lap and the thing just cruised along. I
>just flew it out at level flight and upon landing, inspected
>the plane. No damage that I could see and the controls felt fine.
>
>If this system will stand up to that, I'm keeping it...
>
>Randy

Again I find it interesting that your lines didn't snap. But it does point out the difference in strength brought about by proper temination of the leadouts. Your leadouts may be a bit of an overkill with your present system, but I would rather have them too heavy and stand up to whatever we give them, than to have a failure at some point that leads to the loss of a plane. With our lines we can check them before each flight. With our leadouts we don't know what is happening inside until it is too late.

>>The interesting thing to me at this point is that the lines didn't snap. Even using .018 braided lines does not leave a lot of margin. But if you were using the .045 stranded leadouts at the time and they snapped and the flying lines didn't, well, now you see why we need heavier leadouts (than the flying lines) in our planes. It is not the straight pull strength that we have to worry about, it is the bends and the curves and the flexing. If there is any flexing going on in the system at all (whether we use cable or solids) it will eventually fail where the amount of flexing is the greatest. And, although we don't think about it too much, when we put the leadouts under tension, we often cause that flexing that eventually leads to failure.<<

This is a good point. In the plane where they failed, they were standard Pylon Leadout cable. .027 I think, but I don't remember. The leadout was threaded through some copper tube and passed though a conventional design bellcrank, and wrapped with copper wire. Pretty much a standard installation that I've seen on many plans. In the SV-11, the bellcrank was made from some .20" aluminum with the forked end and used the .032 stuff with conventional AMA sort of end wrap with heavy eyelet and heat shrink tubing over the copper wire.

> This is supposed to
>be good quality wire that
>doesn't have these brittle characteristics.
> So I am posting
>this to get other's experiences
>with both solid and stranded
>leadouts.
>

I've used both, and I prefer stranded leadouts. The main reason is that they are much less prone to incidental damage. One twang on solids and some damage has been created. This may be why you have come to the conclusion that you need such heavy wire. Clearly, .032 or larger is greatly excessive to the loads applied even under the large FAI pull test. It's clear that even .024 music wire, undamaged by manipulation, is plenty strong enough, but it may not be given the inevitable damage and weakness created from making the ends and getting tweaked on hotel doors, etc.

.029 stranded is much weaker in ultimate strength, but is less prone to damage due to making the ends, and essentially immune to accidents. It also requires much less space to pack, meaning the model box can be 6" smaller, which is a significant factor. The one mitigating factor is that you have to be careful to put bushings on the ends that go through the bellcrank.

Windy's new carbon/epoxy bellcrank, with the forked ends instead of the vertically drilled holes, suggests a much better and easier way to go. A great idea - all you need now is a smooth steel pin with a Ti bolt, and a thick brass or aluminum grommet. No more bent copper tubing teardrops. While I typically make my own hardware, I may make my next bellcrank an homage to Windy's. Homage sounds so much better that rip-off.

A few points about handling high tensile steel in any form. Scratches, nicks, inclusions or voids (voids are unlikely) at a bend can all cause hard sheet steel or wire to break at a bend. A mark on the wire from the grip grooves on the jaws of standard pliers can do the damage.

When designing high tensile steel (550 MPa or 40 tons/sq in) building products, we always used minimum bend radii of 2T (twice material thickness). That is .031 wire, .062 radius; .045 wire, .09 radius. Cracking was never a problem.

I've always used multi-strand cable and will continue to do so. However, has anybody tried nylon coated fishing trace wire? It appears to me that using the coated multi-strand would allow the plastic covering to be melted with a heat gun to bind the whole assembly without glue, copper wire, solder, etc. I intend to conduct some tests real soon.

I have read 2 times or 3 times the radius recommendation before for steel wire, and agree that this would be best when making the radius around the belcrank, or looping the ends that attach to the lines (which have to be larger, anyway, to accomodate the clips). But I have often wondered, how do you wrap the wire around itself at the end terminations and still use a radius that is 2 times the radius of the wire when you have to wrap it around the wire, itself? I suppose one could spral the wrap down the line more, but it sure doesn't look pretty that way.

Bob Hunt lost a couple of models because of poor quality wire..one as leadouts and one when a pushrod failed, and I would bet dollars to donuts that he treated the wire correctly at all times!

Windy had some 4' long pieces that he was using for leadouts, and used, I believe, 1/16th"? He broke that once, explaining his move to the saddle/braided solution.

See Ya

When Bob lost his, he was using .025 wire. This is way too small even for a classic size plane simply because of the flexing that takes place at the belcrank when we put it under tension. (And he was using it on a pipe ship.) It is not that the wire won't take the straight pull, it is that bend around the belcrank and the flexing that will do it in.

Windy was using 1/32 wire (.031). This should be adequate in size for most planes when properly terminated. It is stiff enough to prevent the flexing. Again, we don't know the exact cause of failure in Windy's plane. There could have been a slight nick, a too sharp bend, whatever, but the plane did have over 2000 flights on it with a multitude of higher power engines and a multitude of different flyers at the handle before it suffered its failure. He went to .039 leadouts after that on his large ships, and it was his experience that led Matthew to go to that size, too.

We went that .025 route once ourselves. Matt lost his number 2 OT Stuka at a contest in Indy using .025 leadouts that, to our knowledge, were properly terminated. The plane was powered by an OS 35S, had passed the pull test, and yet both leadouts broke at the belcrank in the middle of the overhead eight. The autopsy afterwards led us to the conclusion that they were flexing--ever so much--at the belcrank under tension. The constant flexing at that point, maneuver after maneuver, led to failure. With flexibles it is possible to see them breaking a strand at a time (if it were possible to look inside the wing.) With solids they will simply let go at once.

The moral: A little overkill is OK. And I think a few of the ideas expressed here are good for all of us to ponder. Perhaps these new belcranks allowing flexible cables to be terminated in an eyelet with a bolt through it for attachment to the belcrank will prove to be a good solution for the more serious entries (read this as those willing and able to put a little more money into their ship.) But my main concern is still for those building less expensive (and more expendable) planes for sport. We need to stress the importance of a simple, inexpensive, method of choosing and attaching leadouts that will last through the life time of the airplane.

>When Bob lost his, he was
>using .025 wire. This
>is way too small even
>for a classic size plane
>simply because of the flexing
>that takes place at the
>belcrank when we put it
>under tension. (And he
>was using it on a
>pipe ship.) It is
>not that the wire won't
>take the straight pull, it
>is that bend around the
>belcrank and the flexing that
>will do it in.

If it breaks because of flexing, then the obvious fix is to keep it from flexing. Instead of treating it like a rigid piece, we should instead use grommets and other strain-relieving devices, and wrap or swedge the ends, instead of just bending it through the hole and then twisting it to terminate. That's what I mean when I refer to damage through end treatments. You wouldn't treat a set of solid flying lines that way. Treat it like stranded. .025 is then more than adequate.

The grommets, in either case, shouldn't be round. They need to be teardrop shaped. On flying lines, a round grommets with a nylon "golf-tee shaped" spacer on the line side provides better strain relief. No reason that wouldn't work for leadouts, solid or stranded. Even better for leadouts, would be to hack them out of 3/32 brass with a jeweler's saw and a file. Use a Zona saw or a needle file to cut the groove around the outside.

> Perhaps these new
>belcranks allowing flexible cables to
>be terminated in an eyelet
>with a bolt through it
>for attachment to the belcrank
>will prove to be a
>good solution for the more
>serious entries (read this as
>those willing and able to
>put a little more money
>into their ship.) But
>my main concern is still
>for those building less expensive
>(and more expendable) planes for
>sport.

You don't actually have to buy Windy's bellcrank, although it's easier. Just cut out a couple of pieces of bellcrank-shaped .050 2024 T4 Aluminum (McMaster-Carr), glue/bolt on opposite sides of some 1/8 aircraft ply, leaving the ends open in a "fork". Cut the holes where they need to go for the pivot, etc, and some lightening holes. $5 bellcrank suitable for 91 4-strokes. Note that the plywood can also be sized to allow the ball of the ubiquitous Rocket City ball link to fit between, thus capturing the ball as well. This has the very desirable effect of keeping all the forces in one plane, avoiding the necessity of an elaborate bearing to keep the crank from tilting from side to side.

> We need to
>stress the importance of a
>simple, inexpensive, method of choosing
>and attaching leadouts that will
>last through the life time
>of the airplane.
>

Couldn't agree more.

I, also, agree that if we are going to use the finer solid type leadouts that we need to use grommets or bushings as on stranded. The beauty of solids, however, is their simplicity, if one can simply bend them around and have them work effectively. (Notice the "if"). The heavier solids only weigh a couple more grams, and you save that if you don't have to use the other hardware. The flexible cables have their attraction, too, if done right.

One more question, how do you keep the cables from sawing through the leadout guide? We have been making ours out of plywood with brass eyelets for the guide. That may work. The slider on the Brodak guide is made out of nylon and I question that holding up with the flexible leadouts that he supplies in his kits.

It depends. If the eyelet doesn't rotate in the bellcrank hole, the leadouts will saw through the eyelet pretty quickly. Packing it with heavy (wheel bearing) grease will make it last longer. If the eyelet is loose in the bellcrank, the leadout will eventually break where it gets bent around the sharp corner. Mode 2 will last longer, if it makes it past the first pull test.

I sleeve stranded leadouts with close-fitting brass tubing. For a regular plane, I use about 6" of 1/16 od copper tubing, with the ends tapered. Slide the leadouts into the tube, leave about 6" free end to make the end fitting. Find the exact center of the tube, and slide it into a loose 1/16 hole in the bellcrank and center it. Bend the tube/leadout assembly towards into a teardrop shape until the ends meet. Then wrap as normal with #28 copper magnet wire, all the way up onto the tubing. This locks the whole thing together wo there's no abrasion where the wire comes out of the tube. It will be a bit tight to start with, but as soon as you do a few pull tests and manipulate it a bit, the point contact of the nylon bellcrank to the tube will cold-flow to conform, and it will be free.

This would hypothetically work with solid leadouts, too.

I know of no source of teardrop shaped grommets. but a little work with 1/16 or 3/32 brass, nylon, or teflon shouldn't take too long.

I beleive that they were heavier.

I believe that we must rely on the law of averages and emphasize the fact that solids work a ton more frequently when they are bent with round pliers.

I would disagree about .025 being too small: Bob flew that aeroplane on .012 solids and they didn't break. I believe, too that the break was downstream from the bend.

I'm preferring braided of late because they don't bend when I try to cram the plane into too small a space. I have my friend wander over and wrap the exposed ends, because it's sexier, although I have no problem crimping the bellcrank end.

See Ya

Leonard

I think we might be talking at crossed purposes on bend radii. I was referring to solid high tensile steel, sheet or wire. Do you actually wrap solid wire tight on a single piece of itself? I've not seen that since my return to the sport but I would expect some spring-back.

If you are talking about binding stranded wire with itself, I would expect at least two pieces in the core so the bend radius would vary between 1 and 2 times the thickness of the stranded cable, which is much greater than the thickness of each strand.

So, those of you using (or seeing others use) solid wire...how do you terminate the ends?

I now understand what you are doing but, with springback, I will be amazed if the real bend radius is not 2T+. Also, in this instance, regardless of the bend rad, the bend in question performs a low-stressed, locating function. It is not really carrying the load or the bending stresses induced by flight loads. Solid wire leadouts of the form that you describe should be totally reliable provided the bends on both sides of the bellcrank are not too tight or scratched in any way.

It seems to have done the trick and it will be interewsting to see how it turns out in the new year when I get a chance to fly it.

Vernon

OK, I give up. WHAT rigs does YOUR local "rigging shop" deal in? I'm not at all sure there is such a thing in South Texas. Is it something dealing with Maritime Industries? There is not much of a "Commercial Fishery" around here, you know ..

On my Big Fry I used soft solid wire leadouts about 4 in long to get outside the fuselage (the wing rubber-bands on) and run the lines in through the leadout guide. After more than 200 flights, there is no wear on the 3 in perfect bellcrank or the soft wire leadouts. However, I had to bush the pushrod as it had worn out a large hole in the bellcrank. This is a 15 size airplane with a not very powerful 15.

I've got a Sig nylon bellcrank with flexable leadouts in its fourth 35 - 40 size airplane, which means about 3000 flights on it. There was no wear on the bellcrank, but I cannot remember if I put tubing over the leadouts or not.

I doubt that nylon leadout sliders will wear. If you are getting leadouts cutting the guides, that means that your guide is not in the right place.

Kiwi, I'll bet you can find a "rigging shop" in San Antonio. I'm guessing that we are talking either sailing, or serious marine fishing, or both.

The only incident I've ever had with leadouts was when the plywood bellcrank on one of my 1/2A's cut through 018 CL being used as leadout.

Stranded catches on weeds because of a lack of Viagra. Solids stand right out there above the weeds, and are more aesthetically appealing. Stranded leadouts give a droopy, depressing look to a plane.

Hard core engineers are probably right, and the arguments for stranded are powerful.

But if we are to pursue this hobby with passion, we need to be poets and dancers. Anyone can be an engineer.

False.

>>>But if we are to pursue
>this hobby with passion, we
>need to be poets and
>dancers. Anyone can be an
>engineer.

False.<<

Not true, Brett. Anyone CAN be an engineer. Just not necessarily a good one. Based on how some of the intersections around here are designed, the county hires a lot of pass/fail engineers. I often tell people that anyone (just about) can graduate college. You need to be bright or dilligent. If you're both, you should do well, but you don't have to be both to graduate.

OK, maybe not ANYONE, but just about. Says something about the standards in colleges these days.

Randy (that's Dr. Randy to you )

LAST EDITED ON Jan-02-01 AT 07:43 AM (EST)

They will also send you a free catalogue, they sent me a free one to Australia.
I did say I'd use their stuff for my work ( which is true )
Look on page 347 for Bellcrank bushing etc.
Under " Cable and cable accessories "
In fact if you spend less than an hour looking through the catalogue saying " wow i'll have to get some of these, and these, and these......" I'll be most surprised.
I think Iskandar mentioned them, are they on the Suppliers list ?

Dave Moffitt

Edited in later,
yes they are in Iskandar's supplier's list ( of course......)
PPS, what are these belcrancks with forked ends, I may be showing my stupidity here ( AGAIN.....) but I can't envisage it, pictures, anyone ???

Imagine two thin sheet bellcranks, identical in size and shape, stacked on top of each other but spaced apart and the spacer cut back at the ends where the lead-outs connect. Like a clevis, if you like.

Instead of a loop through the lead-out, a small screw goes through both bellcranks and the loop in lead-out wire.

The screw is in double sheer and the lead-out pivots around the bolt. Mechanically, this arrangement should remove all bending forces from the lead-out.

Check Windy's web site and if you still need more info, email me.

What I am going to test is a lead-out of 100lb trace wire with one end formed like a hangman's knot using the trace wire. Because I have been unable to devise a way to pull the ends tight with hangman's knots at both ends, I intend binding the other end using 20lb nylon covered trace, again tied in a hangman's knot. Theoretically, both bindings should hold strong without melting the nylon but I will apply the heat gun to melt the nylon anyway but I will not use a match as I do not want to burn th enylon off the trace wire. I will be genuinely surprised if this arrangement will not carry my 14 stone without failure. That's going to be the test anyway.