Wing - Rib to Spar attach problem

I have a partially built wing/empennage that I got for a good price. Now I am finding several issues. Here is the biggest one:

The original builder (now deceased) cut off all of the rib flanges that are supposed to be riveted to the spar. Each rib is now only held onto the main spar by being riveted to the reinforcement angle which is bolted to the spar with 2 AN bolts. The left wing has already been skinned and the right wing is still in the jig ready to be skinned.

I called Van's and did not get good news. They cannot predict how cutting off the rib flanges and riveting them only to the reinforcement angle will affect the strength of the wings.

Has anyone seen this done before to an RV-4 wing? Is the RV-4 wing overbuilt to the point that using the reinforcement angles to hold the rib to the spar is enough? I just am concerned that the only attachment most of the ribs have to the spar is two AN bolts. Of course ribs without the angles have flanges and are riveted to the spar, but these are only the few ribs towards the wing tips.

My frustration is to the point that I have decided to sell the project and move on to a matched drilled RV-8 kit from Van's.

By the way the seller did not know of this problem when he sold it to me.

Branden

Ribs

HI,I think it would be o.k because "correct me if I am wrong" The ribs are not the load bearing part just the airfoil shape and the spar is the carrying the load as well as the skin the rib is just giving the shape.It should hold just fine,but if the plans show something different that would bug me too.I would add a flange if you can and inspect the other wing to see if it is also missing flanges.I am sure you will get some good input from others shortly.Just my 2 cents. Have a better day. Jim

Is the RV-4 wing overbuilt to the point that using the reinforcement angles to hold the rib to the spar is enough?

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Given both RV-3 and RV-8 wings have been redesigned over time after accidents where the wing(s) failed resulting in fatalities, I would be wary of describing any RV wing as "over built"

Yes - in each case the original loadings were rechecked, no definitive fault found - in the RV-3 case(s) it appeared faulty building was lilely the cause, in the RV-8 case a straight overstress. However, as I say, in each case a fairly fundamental redesign resulted.

Whilst there is an argument that "ribs only hold an airfoil shape":
1. Why then are the RV-3 ribs each held to the spar with 5 x AD4 rivets and 2 x AN-3 bolts?
2. Some of the RV-3 issues were atrributed to "Root Rib failure". If the ribs are "not load bearing" how can their failure result in loss of the aircraft and occupant(s)?

Van's gave you the only answer they could, and I would doubt that anyone on this list could give you a better one that you could have any reasonable basis to rely upon.
Build the structure as the plans specify. Ribs can have flanges added, properly riveted as per "Acceptable Methods..." (AC 43.13-1b)., or can be replaced.
It can certainly be repaired.
Bill Brooks
Ottawa, Canada
RV-6A finishing kit.

I agree with Bill and others.

C-GRVT said:

Van's gave you the only answer they could, and I would doubt that anyone on this list could give you a better one that you could have any reasonable basis to rely upon.
Build the structure as the plans specify. Ribs can have flanges added, properly riveted as per "Acceptable Methods..." (AC 43.13-1b)., or can be replaced.
It can certainly be repaired.
Bill Brooks
Ottawa, Canada
RV-6A finishing kit.

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Before you do anything, make sure the distance between the main spar and rear spar are correct per plans.
This is one area you just dont want to mess with. On the wing that is not skinned you can drill out the rivets on the angle, add the flange, and drill to the spar. Put some thought into the process so you can keep everything lined up, assuming it was lined up to start with. The flange needs to fit flush on the spar.
On the skinned wing, drill out the bottom skins. This sounds daunting, but with a little practice, you will get it down and it will move quickly. Research the methods and practice a bit then go at it.
If you find the spar distances are not per plans, you will need new ribs and new rear skins. Still, not the end of the world.

It matters

The front ribs do not just hold the shape of the wing. They also tranfer the lifting force (think 6 G) of the wing in front of the spar to the spar itself. You can think of each rib as a short cantelever spar attached to the wing that has to transfier the lift force of that section of the wing and counteract any moment generated from the force.

I would try to make an angle of the same thickness as the rib and rivet to the skin and the rib. If you had to you could put a few inspection holes along the bottom to help with access.

Alternatively you could try to get Van himself to have a look at your problem. It may actually be that the rib to spar attach is strong enough as it is. But you need to either get Van to tell you that or get an airplane stress engineer involved. They are out there, and may not cost that much.

It does matter. The RV wing is a stressed skin structure. What this means is that not only does the skin and ribs form the lifting surface and transfer the flight loads to the spar, it is also the structure. The skin/ribs/spars combination form a box designed to withstand the torsional loads experienced by the wing. I would take heed of the cautionary advice offered so far.

I purchased a partially completed RV6 empenage kit and have similar challenges. Unless you really want an RV8 and can afford it, I recommend perservering. Put the left skinned wing to one side, sorting out the unskinned wing will be easier. Then use what you have learnt on the unskinned wing to fix the skinned wing.

Really, the easiest way of sorting out the unskinned wing is buy new ribs. If you didn't pay too much for the project, they aren't that expensive. Replace them one at a time, so as to not disturb the wing. The skinned wing may be easiest sorted out by a repair as Bill Brooks suggests per AC43-13.1. Any A&P should be able to help there.

I hope that helps.

Cheers,
Andrew.

Dont think he has a problem there...

N999BT said:

The front ribs do not just hold the shape of the wing. They also tranfer the lifting force (think 6 G) of the wing in front of the spar to the spar itself. You can think of each rib as a short cantelever spar attached to the wing that has to transfier the lift force of that section of the wing and counteract any moment generated from the force.

I would try to make an angle of the same thickness as the rib and rivet to the skin and the rib. If you had to you could put a few inspection holes along the bottom to help with access.

Alternatively you could try to get Van himself to have a look at your problem. It may actually be that the rib to spar attach is strong enough as it is. But you need to either get Van to tell you that or get an airplane stress engineer involved. They are out there, and may not cost that much.

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I believe the front ribs rivet directly to the spar web. Not sure he has a problem with them.

Thanks for the quick replies everyone. I have been mulling over solutions for a few months with this kit and you have confirmed my basic conclusion that I would need to fix this issue among other problems including no matched drilled fuse center section (anwered in an earlier post) and the rear spar attach point has a 1/8" hole drilled in it.

I had originally wanted to get an RV-8, but the price of the RV-4 project swayed me. I thought I would be ahead and get the project done faster. At this point I would like to cut my losses, sell the project and buy a RV-8 from Van's It will be more money for sure, but less stress on me and more enjoyable.

I will definately offer these solutons to a prospective buyer of this project.

Thanks again,

Branden

You are right

JonJay said:

I believe the front ribs rivet directly to the spar web. Not sure he has a problem with them.

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I read the original post as ribs forward of the spar not front of the rear ribs. But it still matters for the same reasons.