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Building Tips and technical articles. => 1/2 A building. => Topic started by: jim gilmore on November 22, 2010, 01:10:36 PM
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For you guys flying 1/2a models that do the whole pa pattern. What size bellcrank do you use? And would a bellcrankk made with 1/32 ply and foam be strong enough ?
I'm thing 1/32 top and bottom and egg box foam to provide a little thickness. and bush all 4 holes with brass tubing.
Maybe 1/8" for the mounting bolt and thimbles for the leadouts and whatever has a 1/16 hole for the pushrod.
Scaling down larger a model does mean I have to adjust the belcrank size and position.
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That sounds overly complex but cool. Sig 1/2-A bellcranks work fine for me -- but I've never had a 1/2-A plane that could do the full pattern.
You can get 1/64" ply; with your foam and bushings I think it'd be enough, and lighter.
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For 1/2A stunt I use 3" bellcranks, slows the action down enough to pretty much eliminate the 1/2A "twitchies". I cut mine out of 3/32" ply. Use a very short pushrod arm and let the BC pivot as far as it will (mine are about 170 d.)--makes 'em handle much more like the larger planes.
For sport planes the nylon 1/2A bellcranks work fine. Speaking of that, I'm in need of a supply of those little one-bolt horns that come attached to those nylon bellcranks. I know a lot of guys just throw them away; if you could throw them my way I could sure use them!
Maybe I'll put a note in the "classifieds" section too...
--Ray
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I can use them too, Ray. I use them on our R/C planes - they are a better size for the small planes. I have lots of bellcranks with the control horns, I'm selling them for 10 cents each.
Larry
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I used up all my little plastic control horns years ago, on 1/2-A RC. Too bad Sig never just molded the horns separately.
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Speaking of that, I'm in need of a supply of those little one-bolt horns that come attached to those nylon bellcranks.
I've had very good luck bending up one-screw control horns out of sheet aluminum. Cut out a blank, drill in the obvious places, bend in the obvious place, then turn the sharp corners of the mounting tab toward the elevator side to give it some "bite".
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I can use them too, Ray. I use them on our R/C planes - they are a better size for the small planes. I have lots of bellcranks with the control horns, I'm selling them for 10 cents each.
Larry
10 cents? That for the nylon BC/elev. horn I'm paying $1.79 ea. for at the LHS? I'll have to order some from you if so!
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A 3" bellcrank made with a plywood & balsa sandwich works good for me. For a control horn I just use a small off-the-shelf 2-bolt nylon horn.
My TeeDee-powered Clown will do both the OTS and modern stunt patterns on one tank of fuel, well within the FAI 7 minutes.
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No, Ray, that is just the Bellcrank but I can beat the heck out of the hobby store price. Call me (562-728-5661).
Larry
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RSM includes a 2-1/2" bellcrank made from 1/16" ply in their 1/2A kits for the SkySport. It is bushed with brass eyelets. I have used these for years with no problems. 2" bellcranks are way too small. 2-1/2" is the minimum, but often the largest one you can cram into the model. My control horns usually use a hole about 1-1/4 times as far out as the hole in the bellcrank. And I use my exponential handles with spacing about 2/3 the bellcrank line width.
It is amazing how slow the controls on a 1/2A need to be, but they still corner perfectly. y1
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I make four inch 1/2A bellcranks out of 1/32 ply and a Popsicle stick. One piece of the stick goes along the line side edge of the bellcrank, the remainder goes on the other side making an overlapping T, so that the pivot bolt goes through two pieces of stick and the 1/32 ply. And yes, bush them, as raw wood will cut through leadouts :o; pretty quick in my experience. One of my bellcranks withstood a 30 lb pull test with no problem. There is a picture in the MA Cheap Thrill construction article.