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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
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Id be interested
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Here are 2 pictures of the prototype male for making the mold. I will have my stuff to make the mold Monday.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144242;image)
I am looking for it to weigh 7 grams.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144244;image)
They will have brass bushings installed Except pushrod locations. That is on the builder
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Looks good.
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Is it 4" hole to hole or 4" overall?
MM
4 inch hole to hole. I will be pull testing each one as well.
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I too would be interested in a couple.
Randy Cuberly
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I'd like 2
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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.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144260;image)
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.
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I'd be very interested.
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Pretty Slick Sparky!!!
How about some light weight line sliders?
Randy Cuberly
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Count me in for two.
Michael Palm
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Here are 2 pictures of the prototype male for making the mold. I will have my stuff to make the mold Monday.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144242;image)
I am looking for it to weigh 7 grams.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144244;image)
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
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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.
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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.
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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.
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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. H^^ Steve
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Sparky, I will be interested in some.
Bill
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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.
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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! LL~ Steve
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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! LL~ 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.
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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.
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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
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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)
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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Well Brett thanks but I will find someone who can do a windows 3D program for CNC
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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
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Thank you Brett. The email in my profile is correct.
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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.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144483;image)
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.
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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. y1
See you in Woodland, Jerry
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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,
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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
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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
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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. HB~> HB~> HB~> HB~> HB~>
Ted
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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.
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How do you identify a self-centering bellcrank?
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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
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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...
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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. ???
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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.
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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. H^^ Steve
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Brett, can you post a simple line drawing showing a centering B/C & lead out configuration & a non centering or unstable example?
Thanks, Gil
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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.
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144632;image)
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).
(http://stunthanger.com/smf/index.php?action=dlattach;topic=34859.0;attach=144634;image)
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.
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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.
That problem comes of having at least one hard-mounted bellcrank to control surface link. If everything is adjustable (which I'm pretty sure Paul Walker's planes are -- I know his flaps are individually adjustable, and with a take-apart tail it'd be hard not to make the elevator separately adjustable), then you could have the control surfaces biased any way you wanted to with respect to the bellcrank.
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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.
One reason to be sure. Until you decide to make the flap pushrod adjustable, you can get stuck having to apply constant pressure in one direction or the other just to fly level and fighting it in the maneuvers.
The other issue is of course control effort. If it self-centers, that adds to the control effort required, and even worse, it changes with airspeed. More line tension leads to more self-centering effort that must be overcome. So it varies around.
This sort of stuff is far more important that exquisitely-crafted arguments over the airfoil shape and tail moment, and the usual design "numbers" that people hold to be magical guarantees of success.
Brett
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Doesn't leadout position change the geometry slightly?
What is your opinion of reverse action bellcranks?
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Doesn't leadout position change the geometry slightly?
What is your opinion of reverse action bellcranks?
Changing the leadout position certainly does change it, slightly. Given that for the first 50 years, we did Case 4 all the time without thinking about it, having it "off" a bit is not fatal. This is why you need to figure out your CG and nominal leadout position (using LineII or LineIII, or hand-calculating it) when you draw the airplane, and build in the correct nominal arrangement. Then tweak from there. The good thing is that if you build everything straight, and trim it correctly, there's not much range of variability in the trim settings anyway.
"Reverse action"? I don't know what you mean on that one.
Brett
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Changing the leadout position certainly does change it, slightly. Given that for the first 50 years, we did Case 4 all the time without thinking about it, having it "off" a bit is not fatal. This is why you need to figure out your CG and nominal leadout position (using LineII or LineIII, or hand-calculating it) when you draw the airplane, and build in the correct nominal arrangement. Then tweak from there. The good thing is that if you build everything straight, and trim it correctly, there's not much range of variability in the trim settings anyway.
"Reverse action"? I don't know what you mean on that one.
Brett
Front up line????
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Front up line????
Yes, that's it. I thought that is what it was called.
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Yes, that's it. I thought that is what it was called.
I don't think it makes much difference, but it does tend put the leadouts and pushrod in a good spot to interfere with each other, particularly if you tilt the bellcrank to reduce the geometric funnies with the flap horn. Putting aside the 30-year argument on which way the torque goes in a corner (nose in or nose out, you pick the turn), you can't rely on nor to you want to try to put additional yaw force into the lines. All it does is get the lines whipping more than they have to. You can see the effect even in Tim Wescott's gyro data. So even if you could figure out which line should be up, it's not going to help you very much.
Brett
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I've been thinking about this for six years since Brett's last post. I always thought "self-centering" bellcranks were silly, but now I'm getting interested in them for a weird reason I'm still working on. Could be another six years before I figure it out.
First, Brett's right about straight bellcranks (his figure 2 above) being destabilizing. I did some ciphering for a 4" bellcrank (2" radius from the pivot to the leadout attach points) 30" from the leadout guide at the wingtip. I assumed both leadouts exit the wing at the same point. The first picture below is the upchuck. For the "self-centering" cases, the moment arm of the bellcrank arm closer to the inside wingtip (the arm being pulled) is less than that of the other bellcrank arm, so it takes more force to pull. The straight bellcrank, 0 on the first picture, is the opposite, so it's self-decentering. That's what I use, so I guess I should move my CG aft to stabilize my airplane (reference to a recent inane Stunthangar thread). Brett's bellcrank (his figure 1 above) is the 3.8 line on the first picture. For the numbers I used for the calculation, his bellcrank arm angle works out to 3.8 degrees. The moment arms aren't the same at big bellcrank deflections, but they are for small deflections and the slope of the curve is zero near zero deflection. As mentioned above, if there's much of a slope in the curve, moving the leadouts at the tip will put a torque on the control handle in level flight. With my straight bellcrank, if I move both leadouts 1/4" at the tip, I would need to move both attach points at my handle up or down .003044 inch. That's with a 5.5" handle spacing. Most people would need to move them less. Brett wouldn't have to move them at all. Despite that absurdity, I think that we should be offsetting the bellcrank arms toward the center of the flying circle at least as much as Brett does. I'll see if I can rework my control geometry program for "self-centering" bellcranks, probably making Brett's case the default.
The second picture maybe looks at the same thing a different way. When a "self-centering" bellcrank is deflected, it pulls the leadouts into the wing a little, thus reducing the distance from the airplane to the pilot. The plot shows the total length of both leadouts inside the wing relative to that for zero bellcrank deflection. I don't know what to make of this.
I calculated all these cases assuming that the bellcrank at neutral was perpendicular to a line from the bellcrank pivot to the leadout exit point at the wingtip. I always try to do that on my airplanes. Just for fun, I compared this case on my current plane to Brett's figure 4: bellcrank aligned with the fuselage axis. I used my control geometry program, which assumes a straight bellcrank (pictures 3 and 4 below). Curiously, it doesn't make much difference. Other stuff about the plots I should mention: 1) elevator is down about 4.5 degrees when the flaps are zero (Impacts are like that), 2) flaps look funny because the airplane has Igor's Logarithmic Device (ILD), and 3) I added a cubic trendline through the elevator deflection so it would have the same mathematical sophistication as government Covid-19 case extrapolation.
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Are you familiar with the 4" SIG bellcrank? That's self-centering...or not self-centering (unstable), depending on which side the pushrod lever is pointing. H^^ Steve
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I made bellcrank from 6061 barstock aluminum with hammer and chisel. 1/8in thick, web thickness is .020 in (.5 mm) Line spacing 100 mm, shoulder 24 mm or 21 mm. Weight is 9 grams. One without web is 8 gram.
Jerry
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All science of geometry and positioning of bellcrank, leadouts and control handle will work perfect in case of the lines to be solid and straight like an arrow.
Jerry
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All science of geometry and positioning of bellcrank, leadouts and control handle will work perfect in case of the lines to be solid and strait like an arrow.
???
Brett
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Brett,
All of configurations of common triangular bellcrank can be replaced with a wheel style bellcrank like in racing models F2C. Pivot point can be anywhere in the trailing end of the wing, the control rod from bellcrank connected to the pivoting lever in the middle distance between flap/elevator hinge line, connecting rod from middle lever back to flaps to have better geometry and more equal movement of flaps. One more control rod from midpoint lever to elevator. Leadouts at the wingtip can be in tubes/guides 1/8 in apart or even in one hole to have better geometry for science and accuracy of performance. Couplers for lines located inside of the wing, it’s popular now to make take apart model. The difference in the line length after adjusting the leadouts position can be easy adjusted at the handle.
What will be the complaint? Extra one or two ounces weight of vital components for the controls precision?
Jerry
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Jerry, an interesting concept. It's been used on occasion here in the states. I personally used it to set up the controls for a Shieks Classic Stagger Wing Stunter as it was the best way to arrange the controls in that particular Biplane. I did not use a circular Bell Crank though.
The drawbacks do indeed include added weight, in the tail. This may help with a nose-heavy airplane. It also may be a bit more complex, and can, depending on the distances and angles used or necessitated, still present some inaccuracies.
Compare the geometrically adjusted control horns. One short pushrod from the bellcrank to the corrected flap horn. One longer pushrod from the flap horn to the elevator horn, saving weight from the longer pushrod used on the system you describe.
The main change the corrected system uses is what is commonly called the "Hockey Stick" flap horn. It's simple to layout the geometry for this horn from the plans, a drawing, or in Howard's case, an excel sheet. My own testing shows that for many cases, the horn only needs to lean forward 9 degrees to be useful. Since the distance and angles between the flap horn and elevator horn do not introduce a major differential, the elevator horn can stay at 90 degrees and be accurate enough.
There were some, oldtimers "back in the day" who ran the pushrod from the bellcrank to the elevator horn, and then another pushrod from the elevator horn forward to the flap horn. Because of, once again, distance and angle relationships, created rather accurate relatrionships between bellcrank, flaps, and elevators.
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There were some, oldtimers "back in the day" who ran the pushrod from the bellcrank to the elevator horn, and then another pushrod from the elevator horn forward to the flap horn. Because of, once again, distance and angle relationships, created rather accurate relatrionships between bellcrank, flaps, and elevators.
I tried this on something relatively small, because Larry Renger did it on a 1/2a stunt plane. A little flapped clown I think... his looked really cool, and he does very well in leprechaun stunt with it (and other planes)
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You can get a perfectly (almost) linear relationship between leadout travel and control surface deflection with a regular bellcrank and either a straight-up or bent-forward control horn. It's a 3D problem.
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I made my belcrank only for myself, and I’m using it in conventional way: belcrank linkage to flaps and from flaps to elevator.
Whatever I said earlier was just to prove that there are better ways to improve smoothness, accuracy and reliability of control system of stunt ship. It’s sometimes more complicated to make.
Jerry
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Jerry,
Thanks for posting,, that one is a beauty also nice to see a few hammer & file men left on the planet.
John L.
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John,
Wait until I will polish it in the best traditions of stunt pilots! :-*
Oops! It's inside of the wing already)) :'(
Jerry
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To continue the science talk ...
I think it’s possible to make wheel belcrank in the middle of the fuselage ( mid-distance between hingelines of flaps and stub). 4 in diameter wheel will be positioned vertically (pivot pin parallel to hinge lines) Control lines will enter from the wingtip and go to separate pulleys at the typical location of bellcrank. Then each line will turn 90 degrees and go to the wheel belcrank. Each pulley shaft tilted to make cable alignment with leadout points and top and bottom of the wheel. Here is the best part . On the same shaft with wheel belcrank are located two more wheels to do pull-pull to the two more wheels- one at the flaps, one at the elevator. Why it is interesting? Because pull-pull wheels can be made elliptical to have exponential function. Ellipse has same circumference length as circle, so there will be always the same tension in pull-pul. It can be made in any combination - wheel to ellipse , ellipse to ellipse, to achieve the best result in flap to elevator ratio and exponential from bellcrank to elevator and flap. ( Less sensitive are neutral ).
Jerry
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To continue the science talk ...
I think it’s possible to make wheel belcrank in the middle of the fuselage ( mid-distance between hingelines of flaps and stub). 4 in diameter wheel will be positioned vertically (pivot pin parallel to hinge lines) Control lines will enter from the wingtip and go to separate pulleys at the typical location of bellcrank. Then each line will turn 90 degrees and go to the wheel belcrank. Each pulley shaft tilted to make cable alignment with leadout points and top and bottom of the wheel. Here is the best part . On the same shaft with wheel belcrank are located two more wheels to do pull-pull to the two more wheels- one at the flaps, one at the elevator. Why it is interesting? Because pull-pull wheels can be made elliptical to have exponential function. Ellipse has same circumference length as circle, so there will be always the same tension in pull-pul. It can be made in any combination - wheel to ellipse , ellipse to ellipse, to achieve the best result in flap to elevator ratio and exponential from bellcrank to elevator and flap. ( Less sensitive are neutral ).
The topic of circular and other elliptical shapes, and "pull-pull" systems has been discussed several times over the years. An interesting feature of the circular bellcrank is that when used with a conventional control handle, it's "reverse-exponential", that is, it the angle at the handle rotates it faster around neutral than at higher deflections. A straight crank can be either forward or reverse-"exponential", depending on the relative size of the handle and bellcrank.
Brett
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To continue the science talk ...
I think it’s possible to make wheel belcrank in the middle of the fuselage ( mid-distance between hingelines of flaps and stub). 4 in diameter wheel will be positioned vertically (pivot pin parallel to hinge lines) Control lines will enter from the wingtip and go to separate pulleys at the typical location of bellcrank. Then each line will turn 90 degrees and go to the wheel belcrank. Each pulley shaft tilted to make cable alignment with leadout points and top and bottom of the wheel. Here is the best part . On the same shaft with wheel belcrank are located two more wheels to do pull-pull to the two more wheels- one at the flaps, one at the elevator. Why it is interesting? Because pull-pull wheels can be made elliptical to have exponential function. Ellipse has same circumference length as circle, so there will be always the same tension in pull-pul. It can be made in any combination - wheel to ellipse , ellipse to ellipse, to achieve the best result in flap to elevator ratio and exponential from bellcrank to elevator and flap. ( Less sensitive are neutral ).
Jerry
Cool. Even better is if you can fit different wheels to try different functions. Keep us informed.
Good thing you are proficient with that chisel.
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I didn’t claim to be the wheel inventor !))
And life is too short to read all thousands pages of this forum reading material))
But I think it’s manageable to build concept model with elliptical and circular control components from the plywood , plastic or carbon sheet layers. All of components can be made in mold, and now we finally got to the topic of this particular post!
Jerry
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The topic of circular and other elliptical shapes, and "pull-pull" systems has been discussed several times over the years. An interesting feature of the circular bellcrank is that when used with a conventional control handle, it's "reverse-exponential", that is, it the angle at the handle rotates it faster around neutral than at higher deflections. A straight crank can be either forward or reverse-"exponential", depending on the relative size of the handle and bellcrank.
Brett
Brett,
If, for example, straight handle line spacing is 4 in, and straight bellcrank line spacing is 3 in. It’s a linear ratio 4:3
If handle is moved 30 degrees, then belcrank linearly will move 40 degrees.
Exponential movement is not linear. It’s a curve.
Jerry
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Brett,
If, for example, straight handle line spacing is 4 in, and straight bellcrank line spacing is 3 in. It’s a linear ratio 4:3
If handle is moved 30 degrees, then belcrank linearly will move 40 degrees.
Exponential movement is not linear. It’s a curve.
Jerry
Right around zero, yes, but you are not considering sine and cosine effects.
Brett
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Right around zero, yes, but you are not considering sine and cosine effects.
Brett
Linear movement around neutral can be replaced by exponential movement by adding the ellipse to the control system.
Jerry
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Linear movement around neutral can be replaced by exponential movement by adding the ellipse to the control system.
Jerry
It's not really linear around zero, either, it's just very close, so you can adjust how fast it moves the elevator to put you anywhere in the sine/cosine effect, within reason. The "within reason" part is a limiting factor, because while you can pretty easily make the bellcrank angle to handle angle do what you want, similar effects are happening with the other connections at the same time.
What sort of response you want is another endless debate. I am pretty convinced that I don't want it soft around neutral, actually, I want the opposite, so that's why it is a never-ending argument.
Brett
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We will never fully understand the bellcrank or the venturi.
Both are plenty well-enough understood in terms of physics or geometry. The problem is that no one can actually agree what the desired outcome might be. This defeats almost all attempts at model airplanes as an engineering endeavor, and if you can't accept that, it can be very frustrating. There are no "figures of merit" that would allow you to tell which parameters to optimize.
And besides, go look at the list of NATs winners, for the most part, the answer to almost any question as to who is closest to right can be found there. Scoreboards tell you *exactly* what you need to know about any stunt topic. People find that very hard to accept.
Brett
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Yes, using a properly oriented mild elliptical-shaped bellcrank would deliver a softer neutral, much like certain styles of devices in vouge today. Two large questions come readily to mind concerning such devices.
The circular bellcrank has been used in the past, most notably by Ted Fancher in the '70s. For several reasons, he, and others, stopped using them. They added a bit of complexity and concern should the cable jump from the groove. At best, they were very linear as long as the handle and bell crank spacing was the same. You mentioned the ratios that occur when the spacings differ. The exponential systems, as well as your suggested elliptical bellcrank will deliver some form of differential movement near neutral. The question in my mind is, why is that desired? What are we really trying to cure with soft neutral systems? The elliptical bell crank was considered and rejected by myself and others, back in the 80s. for most of the same reasons the circular bellcrank was dropped earlier.
Modern control systems start with the handle. For competition use, it should be adjustable, and lately, solid point attachment rather than flexible, adjustable cable, has become the favored style. The handle should be lightweight so you barely feel it in your hand. Heavy handles can make a poor showing as they will slow down your responses. The lines must be sized to prevent the stretchy soft feeling that can cause problems. Line length is used to set and maintain lap time, along with the throttle whether IC or E. Next comes the bell crank itself. As discussed it can be where some real help begins in our desire for help and better patterns.
First, let me address the thoughts of mounting the bell crank aft of the wing and routing the lead-outs through some form of pulleys to make the turn in direction. Way back in the early days of control lining, a similar system was produced to get around Jim Walker's patent for the bell crank. At the time, a royalty had to be paid to Walker when his (?) bellcrank was used in a kit, or even on a drawing. A side note: Many old plans do not show a bell crank. Where one would be there was text to the equivalent, "Use your favorite control here." Back to the aft of the wing discussion.
The design in question routed the lead-outs through pulleys, tubes created too much drag, making a 90-degree turn and then attaching to horns mounted top and bottom of the elevator thus eliminating the bell crank completely. It apparently didn't work well as it's the only one I've ever seen that used this workaround. Imagine what would happen if the lead-outs, either singly or both, jumped from the pully.
For modern PA, the use and understanding regarding longer 4-inch bell crank over the then standard 3-inch lengths was a turning point of some significance. The reasons for and use of "Corrected geometry" control horns were known as far back as the 50s. Knowledge of them was held in secret by most of those who were aware of them. I've come across at least one old set, of plans, drawn by one o0f the early greats, that clearly show such corrected horns from the 50s. Back in the day, it was common to keep some elements of design secret from general knowledge. ("Detroit Stunter" comes to mind.) Getting rid of the small dia. (1/8") flexible pushrods in favor of larger dia. dowels, and later, CF tubing along with the use of adjustable ball links helped make our control systems more "bulletproof".
Add to the list, adjustable lead-outs, tip weight boxes, openings in the tail to allow adjustable elevators neutral and throw, neutral stable, and unstable bellcranks. All developments to tune our control systems.
We've come a long way since it all began.
The questions at this time, at least for me, is. What are we attempting to achieve when making it slower around neutral? I have some ideas, but I would like the opinions of others before offering them.
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John,
My reply #63 and #70 describes my opinion on my model.
My reply #66 was to answer on reply #54.
If you have solid balsa thin wing for racer or for speed model , then circular ( or wheel) belcrank is the best option. Circular belcrank is always neutral ( not stable, not unstable) because lines are always tangent to circle no matter where leadouts positioned. Of course if you make circle center as pivot point. If you move pivot point away from center, then wheel belcrank become eccentrical, and can be stable or unstable. Typically wheel belcrank is sitting in the “cup” with guiding openings for lines exits and clearance between wall of cup and the wheel is less than cable diameter to prevent cable from failure.
If exit leadouts spacing is the same distance as belcrank line spacing - then straight belcrank ( line holes and pivot hole are in line) become neutral. It was common in old models with small bellcrank.
John, to answer your question about soft neutral at control handle - it’s everybody’s own preference. Main reason- to have better level flight. It’s more difficult to perform at much higher speeds than 50 mph of stunt level flight. In CL speed all bellcranks are stable or very stable, and response of model is “retardered” like in helicopter swash plate , ))because of small elevator.
Exponential movement is optional . Some pilots prefer precision movement of their own hands and fingers to always be at control. Some 3D pilots have soft ( less sensitive movement )in the end of maximum travel just to have better control precision at crazy moments))
Jerry
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Both are plenty well-enough understood in terms of physics or geometry.
Control system geometry is understood. although what some folks understand is not true. Control system physics is less understood, despite efforts by Bill Netzeband, yourself, and others to explain it.
The problem is that no one can actually agree what the desired outcome might be.
Not surprising, given that folks (I'll be generous and assume that agreement takes more than one person) can agree on neither the geometry nor the physics.
This defeats almost all attempts at model airplanes as an engineering endeavor, and if you can't accept that, it can be very frustrating.
I can't accept that.
There are no "figures of merit" that would allow you to tell which parameters to optimize.
I'm working on them.
And besides, go look at the list of NATs winners...
I'd include a another contest series, too.
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I made bellcrank from 6061 barstock aluminum with hammer and chisel. 1/8in thick, web thickness is .020 in (.5 mm) Line spacing 100 mm, shoulder 24 mm or 21 mm. Weight is 9 grams. One without web is 8 gram.
Jerry
That's a very precise chisel.