Main rib alignment

[eric_marsh]

I've got my spar in the jig with the main ribs clamped to it and am ready to start drilling the ribs to the angles and then the spar. Looking at SK-33 (I can't seem to find SK-3) and reading the instructions I see that I should be aligning the ribs vertically before I start drilling. I'm finding that there isn't enough vertical play to get all the rear indexing holes to within less than a quarter of an inch of each other. The flanges are square where they attach to the main spar. My kit was made in 1995 or prior to that. I'm wondering if manufacturing variation would account for what I'm seeing.

After coming to the conclusion that I'm not going to get the indexing holes lined up by moving the rib up/down in relation to the spar and wondering how to deal with the situation I laid the rear spar onto the ribs and clipped the spar and ribs together. That seemed to more or less pull the trailing edge of the ribs into place. Looking things over it occurred to me that I might do well to drill and cleco the ribs to the rear spar and then do the same to the front. It will put some tension on the ribs but I don't see another way around it.

Actually, trying to move the front of the rib so that the rear lines up doesn't seem like such a hot idea anyway. Some of them are shoved all the way in one direction, others in the opposite direction (as per the last photo which I'll admit is a little hard to make out). That, in turn, is bound to have an effect on how smooth the skin is from rib to rib.

Is there anything that I'm overlooking here? Does that seem like a reasonable approach?

I don't want to go messing anything up so I'm going to spend a little time pondering this to see if I can come up with any other ideas.

 

[OneCharlieKilo]

work one spar at a time - follow the plans

Eric,
It's been a while since I was at that stage but I also built with kit from that time frame (no pre-punched ribs or spar/rib holes) and this advice is from what I can remember on that process. I recommend following the plans and don't drill the rear spar to the ribs before getting them all located, faired, and drilled to the main spar. If you drill the rear spar first, you might have a hard time lining things up in the jig later without a twist or something built into the wing.

Just get the position/spacing correct, make sure it is square to the main spar, and fair the rib on top and bottom by clamping a long trim strip to the rib and spar flange to simulate the wing skin. If I recall correctly, rather than clamping all in place at once and going back to drill to the main spar, I started at inboard end and drilled each one in place, including angle where specified, working outoboard.

Any variations at the aft end of the ribs are fairly easy to resolve when you fit the aft spar with the wing in the jig leading edge up. You'll line the spars up with plumb bob through carefully located/drilled small holes in main and rear spars, per plans, and any problems you have with the aft rib flanges lining up flush to the rear spar can be adjusted at that point with slight bending, shimming, or even cutting rib flange off and riveting new one on with custom fit (probably won't have to do that, but easy to do if necessary).
Everything seems pretty flimsy and hard to believe you'll make it all work at the point you're at, but it'll work out.

Here's link to page showing setup I used and a couple pictures of one of my wings at that point:

http://rv6aproject.ckhand.com/Wings/wings_pg1.htm

You're on the right track, so just keep at it. Good luck!

Chris

 

[az_gila]

These instructions...

...from Frank Justice might help.

http://www.matronics.com/rv-list/hovan/wingribs.html

Do it in the order specified in the plans and, as Chris said, it will work itself out...

One thing that might help is to rig up a strong, fixed "zero" reference at the root that is exactly vertical. You can then use this to measure along the main spar and aft spar to mark the rib locations.

 

[DickDe]

Rib alignment

Eric...

I am relying on my memory from about 1999 but I used an aluminum strip about 1" wide and a couple feet long to lay fore & aft along the rib and over the spar to determine how the skin would fit over the junction of the rib and the spar. You want a nice smooth fit so as not to either crease the skin in event of a rib being too low or causing a "bump" with a rib being too high so fit the rib accordingly.

My wing kit was about a 1998 vintage and the skins only were prepunched but far from the matched hole kits which Van's produces today. The holes in the skins determined if the side to side (inboard or outboard) location of the rib was correct. If you don't have the prepunched skins then the dimensions are on the prints to locate the ribs and you have to drill everything from scratch. As I recall, after the ribs are located on the main spar, than the aft spar is clamped in place.

Two plumb bobs on fish line are hung through very small holes drilled at locations specified in the builders manual (at least as I remember it), one at the root and the other at the tip end of the wing. With this assembly tight in the jig, these plumb lines must pass through the center of the holes in both spars and over 2 ink spots on the floor while the skins are being drilled to the spar/ribs to keep twists out of the wing. If something did not align up work stopped until it was determined what was wrong. When the leading edge and one side of the wing is riveted the wing becomes very stable and the jig process is not needed any longer. That is how I remember the process and hope it helps.

Dick DeCramer
RV6 N500DD flying since 2004
RV8 Fuselage canoe stage
Northfield, Mn

 

[az_gila]

I found...

Eric...

I am relying on my memory from about 1999 but I used an aluminum strip about 1" wide and a couple feet long to lay fore & aft along the rib and over the spar to determine how the skin would fit over the junction of the rib and the spar. You want a nice smooth fit so as not to either crease the skin in event of a rib being too low or causing a "bump" with a rib being too high so fit the rib accordingly.
....

...that cheap metal yardsticks from the hardware store worked perfectly for this application, they had just the right stiffness.

There are a lot of holes that need drilling right in a spar flange that are hard to get to even with a right angle drill adapter.

Drilling #50 pilot holes in the rib flange, clamping the rib in place, and then drilling through the #50 pilot hole with a 12 inch long #50 drill bit worked well. You will be amazed at how much bend you can put in a thin 12 inch drill bit while it is running. Once the #50 holes are in, the same trick can be used with a #40 drill and cleco each holes as it is enlanged. When all of the holes are in, the rib can be removed and all holes enlarged to the final size of #30.

Takes longer to type this in than to drill...

 

[F44evr]

It's been a long time

Here's some pics from those days long ago. Kit circa 1992 that I bought from the original owner. He paid for the "Phlogiston" spar.

Here I'm using a couple of the trimming strips from the kit to set alignment:

Here's my version of one of the plumb bob lines:

And the left wing skeleton with jack in center to keep it from sagging (plumb bob line barely visible between far left ribs:

 

[eric_marsh]

Gentlemen,

Thanks for the input. I'm going to go back through the docs again and see if I can find that SK-3 drawing. I think that looking at SK-33 got me off on the wrong foot. It shows the front ribs being lined up with a string. In retrospect that doesn't seem to be the right strategy for the main ribs. I had one builder suggest drilling the ribs at each end and then using string to line up the indexing holes in the ribs between them.

I'm going to sit down and review all the docs again before I go any further.

Thanks,

Eric

 

[az_gila]

Send me your...

Gentlemen,

Thanks for the input. I'm going to go back through the docs again and see if I can find that SK-3 drawing. I think that looking at SK-33 got me off on the wrong foot. It shows the front ribs being lined up with a string. In retrospect that doesn't seem to be the right strategy for the main ribs. I had one builder suggest drilling the ribs at each end and then using string to line up the indexing holes in the ribs between them.

I'm going to sit down and review all the docs again before I go any further.

Thanks,

Eric

...e-mail address and I will send a scan of SK-3.

I don't think it will help though - it only talks about fluting the forward ribs and filing off the protrusions/bumps at the slots.

One thing a lot of folks did for the forward ribs was to use a length of 3/16 threaded rod through the upper (in the jig) rib reference holes. A nut on each side of every rib will allow the ribs to be spaced correctly and not move when you pull the leading edge skin over them.

PS SK-3 is page 6-22 of my oldest manual and is in the group of sketches dealing with the horizontal tail.

 

[eric_marsh]

Here's what I ended up doing.

After concluding that I would not be able to use the indexing holes - they were simply too inconsistent - I aligned the ribs to the main spar using clamps and aluminum stock to simulate the skin. Once the ribs were all clecoed in place I mounted the spar onto my jig, clamped the rear spar to the main ribs and again I used the "fake skin" method to align the ribs to the spar and then drilled them in place.

I was working with the assumption that even though my kit is old (~1992) any variation in the main ribs after they were properly prepared would average out and pull the spar in line and that I would be in worse shape if I were to adjust them individually in an attempt to get the indexing holes to all be the same.

One I'd drilled and clecoed the rear spar I used a self leveling laser to check my work. I set it to be parallel to my jig and then using the laser I adjusted the main spar so that it to was parallel to the jig within a 1/32". I then used the laser to check the alignment of the rear spar. As far as I can see it's extremely close to being in perfect alignment with the main spar. Close enough for military work, as they say.

So I think that's going to do the trick. Now on to skinning the wing.

 

[chriscencula]

Sounds like you're on the right track with your technique for rib mounting...
In some ways, you are probably better off not having the pre-punched skins because you don't need to accurately position the ribs to match the positions of the (not yet installed) holes in the skins...

Even though I made some holes for 'plumb bobs', I didn't use them 'inside' the structure as described in the plans as much as I used some 'outside' the structure... You can hang plumb bobs off the top edge of the main spar, then measure the horizontal distance between the top edge of the rear spar and the plumb line... The distance should be the same on the inboard and outboard ends of the wing...

When it comes time to create the hole in the rear spar for the aileron pushrod, DON'T just follow the dimensions & location given in the plans... You will regret the mess that leaves when you have to enlarge the hole for the 'actual' pushrod clearance... I have on hole that looks pretty good and another that has 'extra' clearance due to following the dimensions on the plans! (It would have been OK if there were no dimensions, then I would have just 'figured it out', however the dimensions were WRONG...

Chris

 

[vtfast]

I just finished drilling my wings up finally after 3 years of work. Will be disassembling this next week to start the deburing and dimpling process. My wings were the vintage kit as well. I can say for sure the pre-punched skins and the dimensions called on the plans do not match. If I had to do this again I would by new skins with no holes and back drill my own holes. In the end everything has kinda of worked itself out.

Drilling and using the plumb bob alignment holes seemed to be a futile fight for me, all it did was give me a general idea of how things were changing depending on temperature that day, seemed to always change in the jig. Had I built them in my temperature controlled living room instead of a hangar in Georgia, maybe this would not have been a problem. Hanging the plumb bob over the spar and measuring is also a good idea. I opted to go to LOWES and get a long Sheet Rock square and used that instead. Just be sure to take a known square item with you to find find the truest square though, they are not all manufactured to exacting tolerances as I found out.

I did not drill my rear spar up on one wing and only clamped the ribs to the spar to drill the ribs up for alignment issues with the skins and ribs, this allowed me to move some of the ribs as required to get proper alignment. Once I had one side done I checked the alignment of the pre-drilled skins on the the other side before drilling the ribs to the rear spar and the skins to the spar. I did it this way to split the difference between the the alignment of ribs and upper and lower skins. Other than this I followed the the instructions as outlined.

I used a machinist square to insure my ribs were vertical to the front and rear spars.

Good luck and happy building.

Tom