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laser cut ribs, what would you do?

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Old 12-23-2012, 10:37 AM
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kenh3497
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Default laser cut ribs, what would you do?

I have a laser cut short kit with the wing ribs that are inconsistent in their cut. The wing has quite a bit if taper. The ribs do match the plans so I find the fault with the plans and not the kit cutter.

I'm considering cutting a foam wing but it needs to be grafted onto a ply center section that houses the retracts and attached to the fuse. When complete the wing is intended to be a 83inch span one piece wing. Here are some photos of the wing ribs.
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Old 12-23-2012, 11:29 AM
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Default RE: laser cut ribs, what would you do?

Which plans?
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Old 12-23-2012, 12:48 PM
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Default RE: laser cut ribs, what would you do?

Whats actually wrong with them?
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Old 12-23-2012, 01:26 PM
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Default RE: laser cut ribs, what would you do?

Line the spar slots up straight and see what you get. From what your pictures show, I can't see anything wrong with them.

Frank
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Old 12-24-2012, 07:45 PM
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Default RE: laser cut ribs, what would you do?

I have a friend that just built a Cessna 170 from some old plans he bought through AMA. He cut the ribs himself and when I saw them I figured he had really screwed up, they looked just like yours. Some flat bottom, so concave, some convex and virtually none of the spar notches lined up. While we were trying to piece it all together I took a look at the plans and turns out he had cut them exactly as shown on the plans, unfortunately the plans sucked. In the end, he's the kind of builder that doesn't really care and basically made the pieces go together whether they fit or not. If it was me I would have thrown them out, but once it's done I'm sure it will fly just fine.
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Old 12-26-2012, 08:24 AM
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Default RE: laser cut ribs, what would you do?

The thing to do is to trial fit everything together and then custom-make pieces where the laser parts are bad. It's no big thing to fix a single wing rib or bulkhead. Many plans have discrepancies that show up because they were hand-drawn. You live with them and make new parts as needed that fit properly. Sometimes, you only have to sand/cut the existing part and you're done. Other times, you project what the part should be and make a new one. It's all part of plans building.
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Old 12-26-2012, 08:28 AM
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Default RE: laser cut ribs, what would you do?

I think that those ribs are quite good as it looks like they are cut with wing washout in mind at least in refrence to the cuts of the bottom surface. Do the plans mention wing washout?

JM
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Old 12-26-2012, 11:10 AM
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Default RE: laser cut ribs, what would you do?

The wing was dry fit and there was issue with the size of the spar slots being to small. (good thing). The next issue was the location of the spar slots. Some were so badly misaligned as to leave a gap when the slot was enlarged to fit the spar location. After the dry fitting, a strait edge on top of the wing would rock and not lay flat touching all the ribs. With 17 ribs, how do you determine which are OK and which need replacing. The center section of the wing also had some of these same issues but they were minor and easily corrected as it is more or less without taper

Again, and I emphasize, it is not the fault of the kit cutter. The ribs match the plans well.

OH, the wing had 6 degrees of washout and 4 degrees of positive incidence if that helps.

Ken
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Old 12-26-2012, 01:07 PM
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Default RE: laser cut ribs, what would you do?

What aircraft are you building?
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Old 12-26-2012, 02:02 PM
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Default RE: laser cut ribs, what would you do?


Quote:
ORIGINAL: FlyerInOKC

What aircraft are you building?
Zlin 526. It is a bit of an odd wing. The root is semi-symmetrical and the tip is under cambered.
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Old 12-26-2012, 03:34 PM
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Default RE: laser cut ribs, what would you do?

Ken, if you want to switch to a foam wing, flying foam.com can help. I have received about 20 of their wings in the 50cc size that were perfect. Dan.
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Old 12-27-2012, 01:04 PM
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Default RE: laser cut ribs, what would you do?

Its a good looking airpane! If you look at my avatar you will see one of my ongoing projects. It has a bit of a tapper and then the tip ribs are cut to allow a 3/8" washout. The root rib is 17.75" and the tip is 4.75" long. Now that is a tapper!
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Old 12-28-2012, 08:50 AM
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Default RE: laser cut ribs, what would you do?


Quote:
ORIGINAL: kenh3497

The wing was dry fit and there was issue with the size of the spar slots being to small. (good thing). The next issue was the location of the spar slots. Some were so badly misaligned as to leave a gap when the slot was enlarged to fit the spar location. After the dry fitting, a strait edge on top of the wing would rock and not lay flat touching all the ribs. With 17 ribs, how do you determine which are OK and which need replacing. The center section of the wing also had some of these same issues but they were minor and easily corrected as it is more or less without taper


Ken
If you project a straight line from the root rib to the tip rib, you can usually find the bad ribs. If there are too many that are high or low, then you build the wing and then use a long bar sander to true-up the ribs. Ribs that are undersized must be replaced. You also use a bar sander on good-quality kits, where the ribs need to be sanded smooth before covering or sheeting.

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Old 12-29-2012, 06:32 AM
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Default RE: laser cut ribs, what would you do?

It seems there may be a fix in the works for these ribs. When the solution gets a little closer I'll post something. I'm not sure of the time table though.

Ken
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