wing ribs

[914pete]

I've made 14 ribs using Leonards full page rib plan. I didn't notice that the nose cap strip is not square with the bottom cap strip on the plan until now. I made my rib jig exactly to the plan and laid out the cap strips directly over the drawing. (That left most dotted line on the pic is square with the bottom cap strip.) I built the spars over the past few weeks and was eager to line up some ribs with them. Having the front spar perpendicular to the table with a rib clamped to it, the trailing edge of the rib is 3/4" off the table. The drawing is out of square 1/8" which makes a big difference at the trailing edge. Now I'm wondering if I can use the 14 ribs I made. Any suggestions? Am I missing something?

[jrbirdman47]

I encountered the same thing and discovered it 5 ribs into the build.

After much consideration, I narrowed down my choices to either complete the remaining ribs so that they were all the same "off" angle and just accept that the forward spar would tilt rearward slightly, (And I didn't think it would make a lot of difference aerodynamically, just be a pain to jig and finish the wing as such), or I could "repair" the existing ribs.

I chose the latter and came up with a fix that took less than a day to complete them all.

I built a jig that allowed me to hold the rib on a table saw with the bottom 90 degrees to the (Very fine) blade. I then cut the forward vertical stick at a true 90 degrees, shaving off maybe 1/8" or so at the "thick" end, giving me a true 90 degree surface. Then I glued another 1/4" stick to the face I just cut and when cured I again cut it on the saw to nearly the proper thickness, finishing it up on a sander. The finished product was of proper dimension and angle.

Then I fixed the @$%^* jig so the rest would be 90 degrees!

This worked well and I didn't have to start over.
I could tell no difference in the structural integrity, but for a little peace of mind during gluing them to the forward spar I added a couple of "gusset" strips where the rib gusset now came up just short of contacting the spar. I made them about an inch long, out of 1/4" caps strip cut in half lengthwise across to opposite corners so that they fit in the corner of the rib/ spar.

Hope this helps.

Rick

[Chuck in Indiana]

Oh, man.. that is disheartening. So you are saying on your rib jig, the bottom of the rib and forward vertical member is *not* 90 degrees? (!) The rear spar vertical member isn't 90 degrees, either?
If it is just the front, I would try *carefully* removing the gussets, and making it 90 degrees. That's a lot of work to just throw away.

[EthanP]

I think I would complete the rest of the ribs in the same manner and then square them all up using jrbirdman47's method.  I don't think it would be necessary to glue in a filler strip afterwords though, once bonded to the spar, the spar verticals provide the strength, you'll just be 1/8" shorter than planned.

[Chuck in Indiana]

Sounds to me that it would be 1/8" thinner.. not cool. And.. how about the rear spar opening? is it out, too? We need more info.

I think I would complete the rest of the ribs in the same manner and then square them all up using jrbirdman47's method.  I don't think it would be necessary to glue in a filler strip afterwords though, once bonded to the spar, the spar verticals provide the strength, you'll just be 1/8" shorter than planned.

[EthanP]

If you want to beef it up afterwords, glue in the piece indicated on the drawing for the double eagle

[jrbirdman47]

My rear spar opening was nice and square, so I think the problem was in the printed plans. Like Pete, I simply built my jig using the drawing as a template. Although it seems so obvious now, it never dawned on me to check that angle. Can't remember what brought it to my attention, but I did like he did and set the forward vertical plum and noted the trailing edges were off the table about 3/4 " at the end. The way I fixed the 5 ribs affected was quick and easy, and once the jig was reset, it cranked out 47 more without issues.

[914pete]

Thanks for the feedback.  I thought it would be bad to leave the front spar not square thinking there would be issues with the attach points and the rest of the assembly. So I tried to carefully remove the front gussets and 1/4" cap strip on one rib, and replace it square. Well that didn't go well. The cap strip wood broke out all around the glue joint on the gussets. Fix that one later or scrap it.  I grabbed another rib and just sanded it square which left the bottom of the front cap only 1/8" and the overall rib 1/8" shorter. I don't think that's an issue other then adjusting the jig to match for the rest of the ribs. Yes/no? I would just add a cap strip behind it for strength. Not too much added weight and I would use 7 of these ribs for each wing. I'll try jrbird's method next week with a rib too.

[Chuck in Indiana]

Well, needless to say, this airfoil isn't rocket science.  Personally, I would do what Rick did. Whatever you do.. they all need to be the same..and..they need to be square. Assuming you beef up the 14 (!) ribs as necessary, you'll be fine.
I should keep quiet, but I won't. These wings are inordinately difficult to build.
(donning flame suit) I talked to the guy that sold me his plans this week, and he said he just couldn't quite get his head around how they were built. I mentored him back in the day, and he has a Lindy from Oshkosh on his mantle, so I'm not just saying that.

[scottiniowa]

Well, needless to say, this airfoil isn't rocket science.    These wings are inordinately difficult to build.
(donning flame suit) 

Not flaming you Chuck or anyone.  Just things to ponder.

 I have been around a lot of aircraft builds and almost always I find that "if" during the build, the builder has built jigs to "hold" various parts of the main build exactly where wanted, then all the rest of it goes better.  That is not to say, that building based on starting in spot A and then building everything to that starting place doesn't work, but it certainly puts pressure that spot A had better be correct and that you don't get into "additive mistakes"   Even adding 1/32" here and there starts to add up if there is a enough of them

Working very hard to get a known correct item duplicated exactly- many times over seems to the most effective method. That is why I have pushed for  making good router jigs, rib jigs, excreta.

This goes clear back to shop class in high school, where we had 20 boys all build exactly the same dustpan. Generally having 2-3 perfect ones, and then quality on down from there.. they all did the job, but some looked so much better.  Attn to details would seem to be in order.   The process of sharing (what works well)  on this forum I'm sure has greatly helped on getting the details on the fore front.

Best of success.

[914pete]

Just got back to the shop. Ok so I sanded one of the ribs front cap strip so it is now square with the bottom cap and will be square with the front spar. You can see down by gusset A1 I'm left with only 1/8" thick cap strip. Still surprisingly strong but I think I'm going to add a cap strip behind it as in the pic. This way I won't have to mess with the gussets, it adds a little weight, but be very strong and only takes a few minutes. It does shorten the rib by an 1/8". Can anyone see issues going forward with the build before I go this route? The rear spar is square. I pulled out IronDesigns rib plan and that's actually 1 1/4" shorter then Leonards ribs and the top cap strip is 1/2" lower. So I'm thinking squaring up the 14 ribs, adjusting my rib jig and making the rest to the same length isn't going to be a problem aerodynamically, just wondering if its going to cause problems going forward by following the rest of the plans.

[Kamcoman77]

Your solution looks fine. Just make sure all the remaining ribs match in length and airfoil.

[jrbirdman47]

Looks nice! I agree and think you have a nice solution that will work and is safe.

And as if it hasn't said enough, if you're about to start building your ribs, don't assume the angles are correct on paper! Make darn sure the foremost vertical strip is jigged at 90 degrees from the bottom!

[Chuck in Indiana]

Agreed, it shouldn't be an issue.. just make the rest of them the same.

[RobMoore]

914pete, thanks so much for pointing this out. My drawing is exactly the same and TBH, had it not been for this post, I'm pretty sure I would have made exactly the same mistake. To the naked eye it looks like a right angle - on my drawing its about 88 degrees to the horizontal but this 2 degree difference is ample to cause a large error over a distance.

I'm expecting the arrival of a full size wing rib drawing soon and it will be interesting to see if that is the same. If it is I'll be reaching for my set-square and a heavy Biro!

This forum is such a useful resource - I've only been a member for a couple of days but I reckon it's already saved me money, time and hair.