Carbon bellcranks

[RC Storick]

Today I made the plug so I can cast the mold next week. These are the same shape as the BB Bellcrank. Four inch with a bearing support for the 1/8 wire. I will be make a few for myself but I would like to know if there is any pre interest? The lines  will loop through like the phenolic copy's I will post a pic of the plug when coating is dry. These will be all tow.

Cost around $20-25.00

[Andrew Saunders]

Id be interested

[RC Storick]

Here are 2 pictures of the prototype male for making the mold. I will have my stuff to make the mold Monday.

I am looking for it to weigh 7 grams.

They will have brass bushings installed Except pushrod locations. That is on the builder

[55chevr]

Looks good.   

[RC Storick]

Is it 4" hole to hole or 4" overall?


MM

4 inch hole to hole. I will be pull testing each one as well.

[Randy Cuberly]

I too would be interested in a couple.

Randy Cuberly

[Rick_Huff]

I'd like 2

[RC Storick]

This is how I am making the mold. Clay is placed at the bottom and bell crank forced half way in. Pins put in for bushing so no drilling and then the Alumilite High Strength 2 Mold Making Rubber  is pored in and allowed to set 6 hours. Clay then removed and PVA applied and flipped over and re pored. Then the blank taken out and the fun begins.

Acorn nuts are alignment pins. BOM well I guess its just how much you are willing to do for your self. Dan Winship made some good stuff but he's not doing it any longer. So I have to do it myself. I will tell you this I have a new appreciation for bellcrank, landing gear and pipe making. Today is was mentioned to me to pull to 150 pounds and thats what I will be doing as I weigh 155 and that makes it easy.

I will do the first one and when its successful I will make a few more molds so I can make 2-4 at a time. I can make 3 landing gear at a time so I will have many available.

[Gil Mc Millan]

I'd be very interested.

[Randy Cuberly]

Pretty Slick Sparky!!!

How about some light weight line sliders?

Randy Cuberly

[Michael Palm]

Count me in for two.

Michael Palm

[Brett Buck]

Here are 2 pictures of the prototype male for making the mold. I will have my stuff to make the mold Monday.

I am looking for it to weigh 7 grams.

They will have brass bushings installed Except pushrod locations. That is on the builder

   How does the bearing work?  On the original, it has a fairly long (1") brass tube bearing for the pivot. You need that to keep it from tilting when you use ball links. With it that long, 1/8" music wire (supported at the ends) flexes too much under load, and binds it up. There are several ways around that, like support it closer to the bearing with structure, but my solution was to go to 3/16 for the bearing rod. Since music wire is so heavy, I wound up with titanium, so it's a 3/16 ID brass tube bearing on a 3/16 titanium rod, supported at the ends.

   The other anti-tilt alternative is a big washer on either side, but I tried that and it, too, bound up and I ended up with a big aluminum washer that looked like ST prop washer with a teflon self-sticky tape, and it was a lot heavier that acceptable.

   Brett

[RC Storick]

It will look exactly as they are sold by Tom. The only difference is the way the lead outs attach. I have not figured out how to do that in CF.

[RC Storick]

Well the casting material arrived today and I have cast the first half of the mold. About 18 hours from now I can remove the formers and start the second half. This is a very costly and time consuming project. I do hope it worth it. First one out of the mold will have cost around a 100 bucks and too much time. I do know now why they are expensive.

[RC Storick]

I've never tried laying up CF in a flexible mold, can you clamp it shut at all.

I guess only time will tell. What have you made? Maybe some info would help me out.

[Steve Helmick]

I'm looking forward to seeing the mold and layup process. It seems as though the mold will split about on CL of the BC, which then seems like you'd have to fill both mold halves with tow and resin and then slap them together without the "stuffings" running out? Figuring that a runny resin would be desireable, I don't see it working. But I only made molds and layups (epoxy & FG) for Boeing, and it was about two lifetimes ago.

I do hope it works out well for you, Sparky.  Steve

[Bill Little]

Sparky, I will be interested in some.

Bill

[RC Storick]

Yes a CNC mold would be ideal but I don't have the money for it. I know this will work with out a doubt. Here is what George Spar form ACP Composites told me today. He said I can by Epon if I like and pay more to get the same resin made by the same people for him that he's been selling for 25 years under a different label. My Choice. He said the tow is what takes the load and not the binder. I think I will listen to him seeing as that is what he does.

Of coarse he also said why am I wasting my time I could give him a file and he could make them for me. But what's the fun in that? I also don't have a spare 1000.00 laying around.

Tow goes in the mold dry and resin is drawn into the mold with vacuum. I will be solid tow and resin.

[Steve Helmick]

Sparky, if you thought our molds at Boeing were CNC'd...you'd be wrong. We made our own molds out of plywood,  sheet aluminum, "hydrocal", plaster of paris, and sometimes "horsehair". I did finish up one mold that was mahogany with a recess machined in (only male/female mold I recall), and the male part was a hunk of aluminum plate with an aluminum disc screwed to it. We made mockup parts, including the cowl LE section for the Boeing proposal for the C-5. The only thing that wasn't mockup parts were "PIE" ("Pride In Excellence") award plaques. They were a girl dog, because they expected them to be really nice. Imagine that!  Steve

[RC Storick]

Sparky, if you thought our molds at Boeing were CNC'd...you'd be wrong. We made our own molds out of plywood,  sheet aluminum, "hydrocal", plaster of paris, and sometimes "horsehair". I did finish up one mold that was mahogany with a recess machined in (only male/female mold I recall), and the male part was a hunk of aluminum plate with an aluminum disc screwed to it. We made mockup parts, including the cowl LE section for the Boeing proposal for the C-5. The only thing that wasn't mockup parts were "PIE" ("Pride In Excellence") award plaques. They were a girl dog, because they expected them to be really nice. Imagine that!  Steve

Well if mine don't work (which I am assured they will) I will try something else until I get it. But the LG worked first try and are strong and light.

[RC Storick]

Second day of mold making. Here you see the 2 test molds and the finished half (pink) I have spread PVA and it drying next I will poor the second half and let sit for 24 hours. After the cure of the second part of the mold I will make the frames. So by the time my carbon and resin arrives I should have them ready to use.

By the way I had to change my phone number so anyone who wants to call me send a PM for number. Sorry but I got tired of telemarketer's on my cell phone.

[Gerald Arana]

Sparky,

From your pictures, it looks like the LO's and the pivot point don't line up. Is there a reason for that or am I blind? Or is this a "self" centering BC?

Just curious, Jerry

[RC Storick]

Sparky,

From your pictures, it looks like the LO's and the pivot point don't line up. Is there a reason for that or am I blind? Or is this a "self" centering BC?

Just curious, Jerry

It's Brett Bucks design and yes its self centering (well almost thats the theory)

[Brett Buck]

Sparky,

From your pictures, it looks like the LO's and the pivot point don't line up. Is there a reason for that or am I blind? Or is this a "self" centering BC?

Just curious, Jerry

  He is using my geometry, which means it is neutral if you put it in a 30" wing with a 3/4" spacing. A conventional "straight" bellcrank is slightly unstable/uncentering when used in conventional models where the leadouts converge towards each other.  The leadouts-leadout hole-pivot angle is nominally 90 degrees.

   See this thread for more:

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=51380&mesg_id=51380

    Bob is leaving the hole for the ball link blank, so you can make that 90 degrees in whatever application you are using by drilling it in the right place.

   Brett

[Brett Buck]

It's Brett Bucks design and yes its self centering (well almost thats the theory)

   It is neutral if you have the same leadout geometry I do. I would never ever recommend a self-centering bellcrank.

    If your leadouts converge more steeply than mine, it is slightly unstable/self-uncentering, if your leadouts converge less steeply than mine, it is self-centering.

     A conventional "straight" bellcrank is slightly self-uncentering/unstable when the leadouts converge towards each other.

    The effect is pretty small in any case, it's not worth worrying about small amounts of variation in the convergence angle.

    Brett

[RC Storick]

 He is using my geometry, which means it is neutral if you put it in a 30" wing with a 3/4" spacing. A conventional "straight" bellcrank is slightly unstable/uncentering when used in conventional models where the leadouts converge towards each other.  The leadouts-leadout hole-pivot angle is nominally 90 degrees.

    Bob is leaving the hole for the ball link blank, so you can make that 90 degrees in whatever application you are using by drilling it in the right place.

   Brett

I am leaving this blank because some like different throws. Mine I will bushed for 3/32 music wire. This design works much better than the Steve Wilk- Mike Pratt design. Sorry Mike

[Brett Buck]

As an aside, I have nothing whatever to do with (and certainly no "cut") of any of the various versions of this, Tom Morris asked if he could make some and I sent him my drawings. He made some changes afterwards, and I did have one comment for him on the original batch, but otherwise I have nothing whatsoever to do with it.

    Anyone is free to make copies in whatever way they want, enjoy!

    Brett

[RC Storick]

As an aside, I have nothing whatever to do with (and certainly no "cut") of any of the various versions of this, Tom Morris asked if he could make some and I sent him my drawings. He made some changes afterwards, and I did have one comment for him on the original batch, but otherwise I have nothing whatsoever to do with it.

    Anyone is free to make copies in whatever way they want, enjoy!

    Brett

I wish I could figure out how to use your leadout system. But aside from injection molding I have not thought of a way to lay it up. If there are any CNC programmers I will send you a blank and bell cranks for life if you will send me the file. I would do this differently if I had that file.

[Brett Buck]

I wish I could figure out how to use your leadout system. But aside from injection molding I have not thought of a way to lay it up. If there are any CNC programmers I will send you a blank and bell cranks for life if you will send me the file. I would do this differently if I had that file.

   I can certainly send you the original DXF file, but there are no guarantees that you can read it. 

      Brett

[RC Storick]

  I can certainly send you the original DXF file, but there are no guarantees that you can read it.  

      Brett

Oh wait your on a MAC I doubt I can convert it.
Does it look like this one? If not I can tinker with ILL and draw one.
I can and is this what they use in the CNC machine? I have illustrator 11

[Mark Knoepfle]

Robert,
DXF - drawing exchange file. Can be, or should be, able to be opened by any CAD program. If Brett is willing to send me the file I can send you a PDF. Illustrator should be able to measure and manipulate that. Of course I'd also get to check out the drawing too.

Mark

[Brett Buck]

Oh wait your on a MAC I doubt I can convert it.
Does it look like this one? If not I can tinker with ILL and draw one.
I can and is this what they use in the CNC machine? I have illustrator 11

    DXF files are fundamentally ASCII text, so that will not be an issue in and of itself, even rudimentary capabilities of Windows should be able to deal with it.

     Whether it's what you need run a CADCAM machine is anyone's guess. These are 2D line drawings, not a 3d model, so I would guess no.

    Brett

[RC Storick]

Well Brett thanks but I will find someone who can do a windows 3D program for CNC

[Brett Buck]

Well Brett thanks but I will find someone who can do a windows 3D program for CNC

  When I can get it off the other machine, I will send it to you and to Mark, maybe you guys can work something out.

    I would be a little concerned about the forked ends in carbon, it would work, but you would have to be very careful about fiber direction to make sure it wasn't prone to cracking. The carbon/honeycomb versions that Justin Sparr and Jim Aron made look pretty good - they are woven cloth plates with the 1/8 honeycomb that Justin/George/ACP sells.

     Brett

[Mark Knoepfle]

Thank you Brett. The email in my profile is correct.

[RC Storick]

3 days into making a mold and I think I have one that will work.. The ruber molds did not release so I wasted time and money on those. If this one does not work I will wait on Brett's file and I have another solution in motion.

The dowels are to push it out of the mold when cured. My Hinges are on the way from the laser cutter and I will say this once you use them you will never use anything else. Hinges will be 9.95 + 3.95 shipping for 14 enough for horns and elevators and flaps. I will post a picture of those when they arrive.

[Gerald Arana]

Brett,

Thanks for the education! I have always viewed the geometry on the profile side of the fuse...........but, I didn't check out the 90's on the top view! Which I will surely do on my next ship.

See you in Woodland, Jerry

[Monty Summach]

Hello Robert,

I certainly admire the way you jump in and do things. The carbon gear and bellcranks being a prime example. You mentioned you would like to make a forked bellcrank and I think there might be a way to do it with the method you are using. It will require mold inserts. See attached photos. Note - This is just roughed out - may not work - but I can refine it as suggestions are made.
Regards,

[Brett Buck]

Hello Robert,

I certainly admire the way you jump in and do things. The carbon gear and bellcranks being a prime example. You mentioned you would like to make a forked bellcrank and I think there might be a way to do it with the method you are using. It will require mold inserts. See attached photos. Note - This is just roughed out - may not work - but I can refine it as suggestions are made.
Regards,

   It would definitely need to be multi-piece. Or just use premade plates and a honeycomb or end-grain balsa filler and build it up. I do almost nothing you can't do with hand tools and determination.

     With the basic original design, the forked ends are the easy part. The only hard part to make in mine are the leadout bearings. I am modifying mine to use 1/8" tall electronic board "standoffs" just to get away from having to make them myself.

     Brett

[Mark Scarborough]

having dabbled in manufacturing,,
it would appear if you want to mold the forked type bellcrank,, you could cast a top and bottom then after moulding, join them,, I think it would be a lot more repeatable than trying to cast one peice,, with inserts,, which would be prone to seepage ,,

just my thoughts

[Ted Fancher]

   It is neutral if you have the same leadout geometry I do. I would never ever recommend a self-centering bellcrank.

    If your leadouts converge more steeply than mine, it is slightly unstable/self-uncentering, if your leadouts converge less steeply than mine, it is self-centering.

     A conventional "straight" bellcrank is slightly self-uncentering/unstable when the leadouts converge towards each other.

    The effect is pretty small in any case, it's not worth worrying about small amounts of variation in the convergence angle.

    Brett

It's worth mentioning that purposely making a b/c significantly self centering at "neutral" can, in the final analysis cause noticeable flight trim problems.

Almost every airplane I've built I've tied the leadouts even at neutral during the building and bench trimming process.  A significant number of them, however, have ended up (after flight trimming) to have one leadout longer than the other at "flight test/trim determined" neutral.  IOW, I've ended up modifying the flap/elevator neutral setting for equal inside outside turn, for instance.

By definition, if you've had to do something similar and had installed a significantly self-centering bellcrank it now will self center at something other than the bench trimmed set-up and could be attempting to make flat exits from corners more difficult.  I believe that is at least one reason that Brett states he doesn't advocate or use self-centering features in his control systems.

Of course, when my ships end up trimmed like that the carefully angled B/C at bench trim is no longer at that careful angle!  This, by the way, is probably a good theoretical reason for employing a circular bell crank with the cables running in a groove and always exiting tangent to the groove.

Of course, the cable thus unrestrained for most of its "wrap" around the groove lends itself to some of the same issues we discuss regularly about cabled handle, mildly compromising the "plane attached to your index finger" feel we are constantly seeking.

I guess this stuff isn't all that simple.  

Ted

[Mike Haverly]

   It would definitely need to be multi-piece. Or just use premade plates and a honeycomb or end-grain balsa filler and build it up. I do almost nothing you can't do with hand tools and determination.

     With the basic original design, the forked ends are the easy part. The only hard part to make in mine are the leadout bearings. I am modifying mine to use 1/8" tall electronic board "standoffs" just to get away from having to make them myself.

     Brett

     I think the CF bellcranks would be great but with careful consideration to what these guys are saying with regard to construction.  I know of at least one locally manufactured CF bellcrank that failed because the leadout connection was not well thought out.  A nice airplane was lost but, at least, the design was corrected.
 
     At the risk of "piling on", I was recently asked about how I hook up my take apart system.  Coincidentally, it uses Brett's bellcrank design.  The leadout bearings took no more than ten minutes to make. Material is 1/8 Phenolic, cut on my scroll saw.  The little groove for the leadout to wrap around is was done with a dremel tool and abrasive (not that dangerous) wheel.  The attachment is bulletproof and as smooth as any you'll find.

     Also, don't disregard the part about the length of the pivot bearing.   

   

[Dick Pacini]

How do you identify a self-centering bellcrank?

[Brett Buck]

How do you identify a self-centering bellcrank?

    Draw a line along the leadouts. Take a right angle from that line with the leadout connection point as the vertex, draw a line along that angle. If that line passes on the leadout/inboard  side of the pivot, it is self-centering. If it passes right through the pivot, it is neutral. If it passes on the outboard side of the pivot, it is self-uncentering/unstable.

   Note that if the answer is not the same for the "up" line and the "down" line with the flap at neutral, it is also biased, so a continuous force will be required to hold the airplane level.

    Brett

[Brett Buck]

     At the risk of "piling on", I was recently asked about how I hook up my take apart system.  Coincidentally, it uses Brett's bellcrank design.  The leadout bearings took no more than ten minutes to make. Material is 1/8 Phenolic, cut on my scroll saw.  The little groove for the leadout to wrap around is was done with a dremel tool and abrasive (not that dangerous) wheel.  The attachment is bulletproof and as smooth as any you'll find.

   The teardrop eyelet, I have no problem with either. I use 1/8 teflon-impregnated delrin, cut it with a scroll saw, and use a Zona saw and a needle file to make the groove.

    The hard part in mine is the aluminum spool that the bolt goes through and forms the bearing "shaft" for the eyelet. It has to be exactly the right length, AND, exactly square on each end, or when you tighten it down, it will rack the end of the bellcrank out of plane. I was making them from 3/16 thick-wall tubing, and carefully cutting and filing the ends to a perfect fit( after polishing it, of course).  What I am going to do now is use electrical circuit board standoffs with a 1/4" OD and 1/8" high that I can get for about 1/2 cent a piece at the local electronics supply house*. My eyelet and the hole in it needs to be larger but that's no problem. This all to avoid the issue of not having a proper lathe to make them myself easily.


    Brett

*Halted Electronics, the single greatest electronics supply store in the world. I have heard of people in the vintage radio world making pilgrimages to there from as far away as Japan. That seems a little much but they seem to have managed to squirrel away more old parts than any humans should be permitted. It's 4:45 on a Friday and you desperately need a 1LC6 vacuum tube? No problem, $4, in that box over there...

[Dick Pacini]

    Draw a line along the leadouts. Take a right angle from that line with the leadout connection point as the vertex, draw a line along that angle. If that line passes on the leadout/inboard  side of the pivot, it is self-centering. If it passes right through the pivot, it is neutral. If it passes on the outboard side of the pivot, it is self-uncentering/unstable.

   Note that if the answer is not the same for the "up" line and the "down" line with the flap at neutral, it is also biased, so a continuous force will be required to hold the airplane level.

    Brett

Somehow, my mind's eye isn't seeing this.

[GGeezer]

This is an exaggeration but take the capital letter "A" and hang it on a nail with the nail (pivot) at the crotch. If the legs are equal in weight, the A will remain upright even if you deflect it to the side, it will seek to be upright.

Now take that same "A", turn it upside down and balance it on it's tip. It will want to fall over if it is deflected sideways.

In the first instance, the "A" (or a bellcrank) is stable or self centering. In the second example, the "A" is unstable and there will always have to be some force to hold it in this condition.

I can't demonstrate neutral with this example. In the case of a bellcrank, the holes for the leadouts and the pivot hole are lined up.

Orv.

[Steve Helmick]

If I did it right, there should be a picture of a SIG 4" Bellcrank attached, snatched from the Brodak site after a Googling. That's the first non-neutral BC I ever saw. If you install it with the LO attach points outboard of the pivot, it's self-centering, but if you install it "reversed", then it is self-uncentering, which is what the designers intended, from what I've read.

I believe this self-uncentering might push the "Netzeband Wall" back a bit, but I'm not at all certain about that, and would look forward to learning more about the reasoning.    Steve

[Gil Mc Millan]

Brett, can you post a simple line drawing showing a centering B/C & lead out configuration & a non centering or unstable example?
Thanks, Gil

[Brett Buck]

Brett, can you post a simple line drawing showing a centering B/C & lead out configuration & a non centering or unstable example?
Thanks, Gil

    Top is my bellcrank, with my leadout convergence angle. The line perpendicular to each leadout passes through the pivot at neutral.

    Second is a "straight" bellcrank, note the line normal to the leadouts passes behind the pivot, which means it is unstable and wants to move away from neutral.

    Third is a bellcrank with an exaggerated inboard sweep, it self-centers (as the designers intended, but I discourage (because of Case 4, among other reasons). This is a less-extreme version of the SIG self-centering bellcrank.

    Fourth is a "neutral" bellcrank (same as the first) with the bellcrank mounted right in line with the centerline of the airplane with the flap presumably at neutral. It wants to always give you "down" elevator. You are going to end up with the leadouts about 1.5-2.5 degrees aft of the CG.

    Interestingly, this is a case where moving the pivot (and blindly lining up the bellcrank on the centerline) actually does have an effect - but everybody knows not to line it up on the centerline at this point, no matter which way you set up your bellcrank (stable, neutral, or, for most people using pre-made bellcranks, unstable). In this case, since the key alignment of the leadouts is the CG, not the pivot, you will get better geometry for the "centerline" alignment of the bellcrank if you move the pivot well behind the CG. Of course that makes the errors and varying angles in the flap pushrod much messier, so you can't make a blanket statement about it. Moving it forward and leaving it aligned with the centerline exaggerates the scenario in the last drawing. It's drawn about how most people did it before the 90's and before anyone ever thought it through carefully (and is actually on the Infinity CAD plans that way because I lost my interest in publishing it, I never tried to fix it).

  
Brett


p.s. BTW, I will freely admit that I hadn't realized that Case 2 ("straight" bellcrank) was unstable until maybe 2003 - while analyzing someone else's SSW post. I and many others had realized that Case 4 provided a torque bias a long time ago. I think both were missed in Larry Cunningham and John Miller's seminal work on control geometry in SN. And people say we never learn anything new, it wasn't long ago that we habitually used Top Flite 3" bellcranks and bent wire pushrods, and just lived with what we got.