Real Metalworking -- Control Line Bellcrank Mount

The "old way" is to mount a plywood plate in the middle of the wing, then mount the bellcrank to the plate by screwing down a bushing to
retain the bellcrank.
The "new way" is to use small plywood plates top & bottom, with an all-thread steel rod mounting that bushing in the middle of the wing. Because the plates are much closer to the strong points of the wing spar, it takes less material to bring the bellcrank forces (which by the rules get tested to ten times the weight of the plane) out to where they need to be.
This is my "new way", just because. The big aluminum post replaces the bushing (I hope Nylon wears well working against aluminum), the little aluminum bushing determines the spacing of the plywood plates, and the post rides in the plates on 1/4" pegs, which gives a lot more area to bear on the plywood than an 8-32 all-thread rod would.
http://www.metalworking.com/dropbox/belcrank_mount.jpg
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Tim "Over Engineered" Wescott
Control system and signal processing consulting
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Nylon LOVES to absorb water. How will this work on damp days when the nylon swells up?
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On 06/17/2010 02:01 PM, Cross-Slide wrote:

This is the problem with design reviews -- the information that's most likely to make you happy (or at least not deeply unhappy) in the long run is the information that in the short run is most likely to make you want to point and scream "you bastard!".
I think the tolerances are open enough that it won't make a difference, although I could thin the post down a bit (as long as I do it _now_) to make sure. If anything I'll have problems when it dries out and gets smaller -- we're having a humid summer here in Oregon.
I am going to chuck the assembly into the freezer in a moment, to see how it'll work at cold -- for which idea I thank you. Presumably at hot it'll just have more slop and it'll work better, although perhaps I should chuck it in a 150 degree (F) oven to make sure. Perhaps to make _really_ sure I should chuck it in that oven & bake out moisture for a while, then toss it into a sealed jar so I know that it's nice and dry at room temperature. Or maybe I'll just go put my damn wing together -- the wood working has been waiting on this part for a while.
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Tim Wescott
Control system and signal processing consulting
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wrote:

When you're ready to go beyond denial, consider acetyl (Delryn) or Noryl.
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On Fri, 18 Jun 2010 01:05:33 -0500, Don Foreman

Tim, I forgot what you were doing here when I posted. If you'd like a bit of Delryn and glass-filled Noryl I would be happy to send you bits. Also bronze. We're talking pissant postage here, not worth worrying about. Say the word and an addy. Tell me what size OD stock would enable you.
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On 06/17/2010 11:05 PM, Don Foreman wrote:

For the pivot, or for the bellcrank?
The bellcrank is a commercial (Sig) unit -- I'm just making a new pivot for it. I think Delrin would be way too flexible for a pivot, although glass-filled might be OK if I didn't mind dulling all my bits.
The materials of choice for the bellcranks in really competitive circles seems to be either aluminum alloy, linen-filled phenolic with brass bushings, or the obligatory CF-epoxy laminate.
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Tim Wescott
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    [ ... ]

    The bellcrank *may* already be natural Acetyl (Delrin). Whatever it is, it was molded, not machined.
    Delrin is stronger and more humidity resistant (thus more dimensionally stable) than Nylon, so it would be a better choice. It comes in your choice of natural (looks like what you have there) or black (more UV resistant).

    It would certainly be more rigid than Nylon would.
    I would not suggest that you make the bellcrank and the pivot of the same material. With metals, you have the problem of galling (pressure welding and then pulling out material from one part and sticking to the other, making a rough surface.)
    One possibility might be the body of the pivot of something low friction like Teflon with a steel core making up perhaps half the diameter of the pin. This would produce some savings in weight yet retain sufficient rigidity.

    :-)
    O.K.
    Perhaps a hard aluminum alloy for the bellcrank with lightening holes scattered around it.
    Good luck,         DoN.
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wrote:

Looks great. Just weigh it relative to the old way to know whether you over-engineered or not.
Pete Keillor (locomotive jack stand weight bench guy)
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On 06/17/2010 02:27 PM, Pete Keillor wrote:

Seven grams, which compares favorably to #10 hardware but probably gains a gram on #8 hardware. If it weren't going into a sport plane I'd use 1/16" plywood instead of 1/8", on the grounds that the larger bearing surface of the aluminum vs. #8 hardware would give better local crush resistance.
But it's a plane to learn stunt on (yes, it's dumb to be doing this much work for that), so I think the "crush resistance" that I'm going to test is going to be the fuselage, the wings, and the vertical stabilizer surfaces.
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Tim Wescott
Control system and signal processing consulting
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wrote:

Yup, my second r/c plane did the figure 9 on the 1st flight. The engine was buried 9" in clay. It still works. I also have the pilot figure, although he's a little banged up where he flew through the bubble canopy.
Pete Keillor
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Yup - used to fly a 2-meter glider. 8 Ni-cad pack and a cobalt motor used to drive it almost upwards. It took a while to understand that up is down and down is up and one day as landing on a blacktop it came in a bit hot and instead of flaring for a stall - I tipped it into the blacktop. bent a 3/8" Stainless propeller shaft. Ugly. got a new gearbox/shaft and worked at it for a while. Now it is long gone. Just stuff here and there for the hobby.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net "Our Republic and the Press will Rise or Fall Together": Joseph Pulitzer TSRA: Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
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Speaking of control line; I just snagged a Testors .049 BD5 on Ebay. SUPER rare. The engine mounts just behind the cockpit, with the same shaft drive setup as the original. Super cool. About 22" wingspan. Unfortunatly, it was displayed in an evironment of heavy cooking fumes and prolly cigars or pipe smoke.The slime etched into the plastic, which I am slowly fixing by careful wet sanding with 1k grit. JR Dweller in the cellar
Tim Wescott wrote:

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On 06/17/2010 03:18 PM, JR North wrote: (top posting fixed)

> Speaking of control line; I just snagged a Testors .049 BD5 on Ebay. > SUPER rare. The engine mounts just behind the cockpit, with the same > shaft drive setup as the original. Super cool. About 22" wingspan. > Unfortunatly, it was displayed in an evironment of heavy cooking fumes > and prolly cigars or pipe smoke.The slime etched into the plastic, which > I am slowly fixing by careful wet sanding with 1k grit. > JR > Dweller in the cellar
If I were at all the collector type I would be absolutely green with envy -- I didn't know they _made_ a BD5. It seems like they would have lost their shirts on it, unless they really jacked the price up.
Kewl -- that would be one to model with an electric, with the engine behind and the battery waaaay out in front.
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Tim Wescott
Control system and signal processing consulting
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wrote:

I just saw this one....COOL!!!
http://cgi.ebay.com/70s-Testors-Galax-IX-Spacecraft-Gas-Powered-Airplane-/400110538904?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5d28725098
Gunner
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Too much. I got my BD5 for $50. JR Dweller in the cellar
Gunner Asch wrote:

http://cgi.ebay.com/70s-Testors-Galax-IX-Spacecraft-Gas-Powered-Airplane-/400110538904?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5d28725098
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On Fri, 18 Jun 2010 13:28:44 -0700, JR North
OMG! What a deal, JR!
http://www.bd5.com/My5JPics/P1020131.JPG
-- Peace of mind is that mental condition in which you have accepted the worst. -- Lin Yutang
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