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Building Tips and technical articles. => Building techniques => Topic started by: Donald R Olson on June 20, 2023, 09:54:13 AM
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I’m going to machine a nice wing jig out of aluminum. I usually build my own designs from scratch. I like to base them on older plans from the 60s and 70s. I usually can make the rod diameter and center to center space whatever makes sense for the particular plane. But if there is a standard diameter and center to center spacing used for the rods from one kit to another that would be helpful to know. I can design the jig to accommodate those numbers. Short of looking at multiple kits to see if it is the same, which I don’t have access to, I was wondering if anyone here might know. Thanks in advance for any help you can provide.
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I have built all of my planes on this type of jig and I don't recall ever having the same hole locations between designs.
Ken
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The Brodak jig and kits fit together OK.
There's nothing trick about these rod jigs. Brodak gives you holes to fit all of kits.
You don't even need a precision surface. You can simply level the knife edges with a carpenter's level.
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Thanks Ken and Paul. I didn't think there was any standard for this type of jig, but I thought I would bunce it off you guys here. The Brodak kits use 5/16" rods so I will do the same. I will post a pic when I'm done with the jig. It will be over kill for this type of building but I like playing with the Bridgeport mill.
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Donald:
You are on the right track. I use a similar jig whose origins date back to the 60's. It is simply two wooden blocks sandwiching the rods between them held down by a butterfly nut. I use this for two reasons. I don't have a "shop" so there is no place to put a "permanent" jig and second, you can take the wing out and flip it over in seconds. It has no limits on wingspan. I build my wings in halves then join them on the jig. I use arrow shafts which are a bit smaller but they have a threaded (6-32) end for the arrow head. For joining the wing I put two together with a short piece of all thread. So far the cheap set I am using now has produced 4 straight wings.
Ken
This is very far from an original idea, I copied it from the guy that copied it from the guy, you know, the thing...
https://www.bing.com/images/search?view=detailV2&ccid=1A6uzT%2fD&id=90B4C125D590CDD41BFFD499B346A18C9065E54B&thid=OIP.1A6uzT_Dg7KZ6EWIcP5RZgHaFj&mediaurl=https%3a%2f%2fi.servimg.com%2fu%2ff76%2f18%2f50%2f45%2f90%2frcm_wi10.jpg&cdnurl=https%3a%2f%2fth.bing.com%2fth%2fid%2fR.d40eaecd3fc383b299e8458870fe5166%3frik%3dS%252bVlkIyhRrOZ1A%26pid%3dImgRaw%26r%3d0&exph=600&expw=800&q=Model+Airplane+Wing+Jig&simid=608025893394713147&FORM=IRPRST&ck=4A45A24EDAF0B963CA5BAEC3528E9343&selectedIndex=45&ajaxhist=0&ajaxserp=0
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Depending on the rigidity of the two rods that go thru the ribs, you will likely need some support blocks (under the rods) at mid span to prevent dipping of the rods from their own weight.
As to distance between the two rods they can be quite small and still provide a stable, accurate building platform. I do most of my balsa framed wing building on a legacy A Justo Jig and the distance between the notches -supporting the rods- is easily less than 3 inches.
Michael in Ontario, Canada
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Dennis Nunes gives some nice detail on the wing jig he uses for his Circulas designs in the article linked below (See Part 2 - Wing Construction).
http://flyinglines.org/nunes.circulas.article.pdf
The approach is similar to the Pat Johnston/Brodak style jig but instead of the 2016 arrow shaft/5/16 tubing, Dennis uses slightly larger/stiffer 3/8th stainless tubing.
https://www.zoro.com/zoro-select-38-od-x-6-ft-seamless-316-stainless-steel-tubing-5lvr8/i/G1545686/
At the end of the day, you just need to hold the rods parallel/equidistant, and have a good system to make the holes consistently in your ribs. The latter being a bigger challenge, I think.
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My self I quit using rods and went with aluminum tubing. Easy to join tubing together when wing is over 36 inches. Also doesn't sag. D>K
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If there's a "standard" diameter it's 5/16" / 8mm. I got myself a couple of five or six foot carbon fiber tubes, 8mm diameter, from GoodWinds kite shop. My "jig" is just chunks of 1/2" square aluminum extrusion that I've glued up. Put the ribs on the rods, set the rods on the blocks, all on a dead-flat surface, and you've achieved what a jig should achieve.
If you fear (or observe!) the rods not sitting firm on the blocks, a bit of masking tape or weights will hold things down.
I've used 1/8" music wire rods -- the 8mm CF tubes are much more rigid, and make it easier to build a straight wing.
(https://stunthanger.com/smf/open-forum/legacy-build/?action=dlattach;attach=157806;image)
Or just block up the trailing edge and be happy:
(https://stunthanger.com/smf/scale-models/ercoupe-build-(slow)/?action=dlattach;attach=282121;image).