7ECA Wing and Tail Recovering Project

[MarcM]

Earlier this year we came across my dream bird, a floatplane that wasn't going to break the bank to operate. A 7ECA Citabria.



We flew the 300nm out to see it in mid-march, had a good look through all the inspection plates, checked over the somewhat sparse logbooks, agreed on the (very reasonable) asking price, left him a deposit and said we'd be back to pick it up come the spring thaw.

We were told, and the logbooks described it being recovered about 10 years ago, at least as far as I can tell in handwritten scribble, in another language...

The fuselage coverings is in more or less immaculate condition. There is some corrosion in the right horizontal stabilizer, but ACA has been making us up a new one we hope to have in a couple weeks.

Now, the wings.... had a several patches, slight deformation of a couple ribs, the right tip had quite a lot of cracking and that first inboard bay had so much tape in the trailing edge area, obviously something had happened, and in the process of covering it up, there is overspray, everywhere! And worst of all, the white on top, doesn't match the rest of the white on the plane. Despite all of this we got a full summers enjoyment out of it, while keeping a keen eye on these few issues at every preflight.



But now, the air is getting chilly and the trees have lost their leaves. So we figured what better time for a project!

We started by disconnecting a aileron turnbuckles


And then disconnecting the rest of the plumbing and wires in the wing root


...removed the pulleys so the aileron cables may pass..



And the removed the 3 bolts while an assistant supports the wing tip....
and voila



...wash, rinse, repeat for the other side..

Until you end up with something that looks like the short-bus of seaplanes


So we took it for a final flight, got most of the fuel burned out of it, and then proceeded to remove the wings to trailer the whole thing home for the winter so the rehabilitation may begin.
Onto the trailer she goes...

This was definitely the most challenging part of the exercise


So now the left wing is already on my operating table...



Yes, I need to finish organizing the garage and get some of the summer stuff put away!

And later that I evening I couldn't help myself and starting removing the covering....Only messed up one of the rivet holes in the process.



The spars look pretty decent to me...

But could some confirm that this is just the lacquer that looks funny on the rear spar?



Ok, a few questions, if were going to tear it down to replace a few tweaked ribs, should we sand and laquer the spars?
How do you measure tension on the flying wires?
What is that material where the flying wires intersect? It kind of looks like petrified string.

Hope this is as fun for you as it was for us!

 

[Bob Turner]

Spars get varnish, not lacquer. Its sole purpose is to keep moisture constant (mostly out). There are very sophisticated varnishes available, but all you really need is spar varnish.

Find out if you can repair the ribs without removing them. A lot depends on how well they are attached to the spar.

That tape is likely "friction tape." In the olden days they put a coat of shellac over the tape.

 

[MarcM]

So a light fine sanding of that rear spar and brush some varnish on?

 

[Bob Turner]

That's what I would do, unless you are disassembling.

 

[Hiperbiper]

If the wires you're talking about are the ones that run from the front spar to the rear spar in an X pattern then those would be the "Drag" and "Anti-drag" wires and they're purpose is to apply the proper amount of tension to the compression struts (the 4 tubes bolted between the front and rear spars) and keep the spars lined up relative to each other. Without the proper tension between each bay the wing will twist somewhere along its span and you end up with an airplane that flys cockeyed (technical term) and can't be trimmed out...
The process of making sure the wing is straight is called "trammeling" a wing.
If you take the wing apart to replace ribs you will have to trammel the wing to get it straight.
As to the tape used where the wires cross it can be almost anything...it's just there to keep the wires from rubbing.
I used the numbers for a Citabra wing when I built my wings. 40lbs in the root and tip bays and 55lbs in the inner two bays. The trammeling process is tedious and time consuming but the reward is an airplane that flys straight, is simple to rig and one that doesn't change flight characteristics with speed changes.

Chris

 

[Bob Turner]

Trammeling goes easier if you stretch a line along the front spar. Dead straight spars are as important as "square".

 

[Bartman]

@MarcM first of all, you're my new favorite member for posting so many good photos! WE LOVE PHOTOS!!!!!

second, if you haven't already started pulling nails for the ribs, don't! they can really pull a lot of wood with them which will damage the spars and mangle the ribs. I used an old industrial strength soldering iron to heat each nail for maybe 30 seconds before I pulled them so they'd unstick from the wood and come put more easily. Also, the ribs won't slide smoothly off the spars, they'll catch and gouge the spars so be absolutely sure, like 110% sure that you really need to do what you're talking about before you start. If the damaged ribs can be repaired in place, that's a great alternative.

not sure what they used on the spars, probably spar varnish if the spars are original. some clean up with sandpaper couldn't hurt I suppose before putting a fresh coat of varnish on. if the existing coating isn't cracked or otherwise compromised it might not be necessary.

are you the IA that is signing everything off? if not, maybe run it all by that guy before wrenching on it.

GOOD LUCK! Looking forward to seeing your progress.
Bart

 

[MarcM]

If the wires you're talking about are the ones that run from the front spar to the rear spar in an X pattern then those would be the "Drag" and "Anti-drag" wires and they're purpose is to apply the proper amount of tension to the compression struts (the 4 tubes bolted between the front and rear spars) and keep the spars lined up relative to each other. Without the proper tension between each bay the wing will twist somewhere along its span and you end up with an airplane that flys cockeyed (technical term) and can't be trimmed out...
The process of making sure the wing is straight is called "trammeling" a wing.
If you take the wing apart to replace ribs you will have to trammel the wing to get it straight.
As to the tape used where the wires cross it can be almost anything...it's just there to keep the wires from rubbing.
I used the numbers for a Citabra wing when I built my wings. 40lbs in the root and tip bays and 55lbs in the inner two bays. The trammeling process is tedious and time consuming but the reward is an airplane that flys straight, is simple to rig and one that doesn't change flight characteristics with speed changes.

Chris

Hi Chris,
Thanks for the fantastic information. I found a reference to a tensionmeter for those drag wires on the internet, but the link was old and no longer works. Its not the same tensionometer that we use control cables correct? Would you have a link to the correct tensiometer?

 

[MarcM]

@MarcM first of all, you're my new favorite member for posting so many good photos! WE LOVE PHOTOS!!!!!

second, if you haven't already started pulling nails for the ribs, don't! they can really pull a lot of wood with them which will damage the spars and mangle the ribs. I used an old industrial strength soldering iron to heat each nail for maybe 30 seconds before I pulled them so they'd unstick from the wood and come put more easily. Also, the ribs won't slide smoothly off the spars, they'll catch and gouge the spars so be absolutely sure, like 110% sure that you really need to do what you're talking about before you start. If the damaged ribs can be repaired in place, that's a great alternative.

not sure what they used on the spars, probably spar varnish if the spars are original. some clean up with sandpaper couldn't hurt I suppose before putting a fresh coat of varnish on. if the existing coating isn't cracked or otherwise compromised it might not be necessary.

are you the IA that is signing everything off? if not, maybe run it all by that guy before wrenching on it.

GOOD LUCK! Looking forward to seeing your progress.
Bart

Hi Bart!
Thanks! I was trying to get some good shots... Got a few videos that I would like to make a series out of the project too, if I can find some free time.

We haven't done any further disassembly yet, It was my wife's birthday this weekend so the focus was on her.
Before we go any further we want to bring the other wing in and remove top covering and inspect it to ensure that the spars are all a-ok. That'll probably be tomorrow or wednesday evening.

Re: spar varnish, I was just kind of concerned by the look of the varnish on that rear spar, it doesn't appear to cracked or compromised, just kind of splotchy and discolored.

and finally, re: IA... yes, I effectively am, this aircraft is registered in a special category here in Canada, Owner-Maintenance, so we're allowed to do just about anything and everything, short of installing a turbine, according to our best judgement. My experience comes from being an A&P at a flying school for a half dozen years, but it was all Cessna's and Piper's, so these wood and fabric beasts are a little outside my comfort zone... But I'm eager to learn in intricacies of them!

I'm going to have to have a good read of the 43.13 about repairing those ribs in place! Unless there's another resource you could recommend?

Thanks for your advice

 

[Bob Turner]

Occasionally you can find a manufacturer service bulletin - they are usually approved data in the U S. Often they allow simpler repairs than those in 43-13.

I would think a simple riveted doubler would work on Champ ribs - a good guy to check with would be Bill Pancake or Paul Agaliotis. Both are quite friendly, and are experts.

 

[Hiperbiper]

Believe it or not a $10.00 pull type fish scale works great for trammeling...hook the scale near the center of the X, pull until the wire is displaced a measured distance (I used 2" for both the 40 and 55 lb. pull) and check what the scale reads.
The idea is to make sure both the drag and anti drag wires within each bay are the same value.
There are lots of good videos on the web that show how to do this properly.

Chris

 

[Hiperbiper]

Keep in mind that with the Citabra type wing you have the option of replacing different pieces of the ribs.
In the Case of my Champ one wing was in good shape except for the trailing edge from the fuselage to the aileron bay...over the years of recovering the rear edges of each rib were like swiss cheese and way to flimsy to use.
Instead of pulling the whole wing apart I went to the Wag Aero catalog and found the complete trailing edge part of the rib. The old rib trailing edges were carefully trimed off and the new ribs pieces were lined up and nailed in place to the rear face of the rear spar.
A new trailing edge piece (also from Wag) and the wing was good to go. BTW, the Wag Aero airframe parts are the same as the factory part numbers...
They list trailing edge, leading edge and rib doublers.

Also beware of making too many repairs to each rib...especially if the rib is cracked at the spar attachment area. You'll end up with a rib that won't stand up straight after covering.

Chris

 

[Bartman]

(I used 2" for both the 40 and 55 lb. pull) a

2" or 1/2"???

 

[Hiperbiper]

2" or 1/2"???

As I recall I pulled to 2" and measured the lbs. On the scale...
You can use any displacement distance you want to within reason. Just use the same deflection for all your measurements.
Oh yea, your going to need a way to measure the distance between the spars...a 3 foot straight edge with nails glued in place worked great for me.
I know it sounds confusing but look at a few videos online...you'll see how to do it.

Chris

 

[MarcM]

Look at this fantastic discussion we’re having already.
I noticed one rib had already been repaired, that should be an easy repair for the one rib that’s kinked at the rear most lightening hole…. Going to go have to spend some time discovering all the other goodies that Wag has to offer and hopefully we can avoid the full tear-down

 

[MarcM]

Alright! Update Number 1,
Some good news, some.... well, we'll get to that.

So as far as the Left Wing goes, everything seems to be in pretty good shape, we've come up with a short list of parts consisting of just two of the rear rib sections from WagAero and the trailing and leading edges. The leading edge isn't really that bad, but for $150 from Spruce, it would be silly to not put a new one on. Our's our unprimed, and have quite a bit of surface corrosion and some character marks.



Getting all those screws out are going to be fun tho as they're all rusted.

Now, The right wing... The first thing we found, was that there was sooo much moisture underneath the plywood under the fuel tank..



But absolutely nothing else inside the wing was the least bit damp.... It had been stored outside my house for the last week or so, and it had rained, but I suspect this was longer term judging on the condition of the wood. The fabric was well sealed up are the fuel filler, so it has to have been coming from the wing root area. The spar appears slightly discoloured, and also has a doubler glued to it to it there, so some of the discoloration is just the excess advesive.



So as we carry on assesing the situation, we notice that this wing has been reassembled once already, due to the second set of nail holes in the spar. but also finding some cracking emanating from the nail holes.



And then we start to see some more horizontal marks (cracking? I sure hope not) throughout much of the length of the length of the main spar




It certainly doesn't appear to be a compression fracture the way the AD pictures it, but, i think the next job is to finish removing the leading edge to be able to inspect both sides.... Hopefully these are just markings from sliding the ribs into place! I've been talking to the IA who does our work on the partnerships Cessna and he's going to try and get over this weekend to see it and offer his advice, Hopefully its good or we'll be making a road trip to Wag-Aero for a new spar pretty soon!

 

[MarcM]

Update 2!
Got some more of the covering pulled back off the leading edge to expose the gap under and none of the markings on the aft side are visible on the front! Maybe just assembly marks after all!

 

[Big Ed]

I don't have any expertise or experience in this area. But IMO, if you have the wings that close to nekkid, I would seriously consider pulling the spars out and replacing or refinishing. Rainbow Ron sells full sets for $3300 that are supposedly better because of the larger doubler plate.

If yours are still in good shape and you don't want to incur the expense, then pull them out and refinish them with a modern polyurethane varnish so you don't have to look at hairline scratches every annual and wonder if they are cracks.

Again, I have no experience, so maybe I am FOS. But you are unlikely to have the wings uncovered again in the next 20-30 years. If you were ever going to replace the spars, now is the time.

 

[MarcM]

I don't have any expertise or experience in this area. But IMO, if you have the wings that close to nekkid, I would seriously consider pulling the spars out and replacing or refinishing. Rainbow Ron sells full sets for $3300 that are supposedly better because of the larger doubler plate.

If yours are still in good shape and you don't want to incur the expense, then pull them out and refinish them with a modern polyurethane varnish so you don't have to look at hairline scratches every annual and wonder if they are cracks.

Again, I have no experience, so maybe I am FOS. But you are unlikely to have the wings uncovered again in the next 20-30 years. If you were ever going to replace the spars, now is the time.

Hi Ed,
Thanks for the heads up, I thought my only options were Wag or Millman, and the Millman’s are quite pricey, and then add a considerable shipping charge to the great white north.
I guess the third option is new blanks from Spruce, And then I could get them longer and add another rib, I bet that would help the seaplane performance… but that’s a pipe dream I think if I want it back in the air for the spring,
I think if we’re going to need new spars we’d be looking for gcbc wings with the flaps to Frankenstein together because lord knows it’s a struggle to get her off the water on a hot summer day.

 

[Bob Turner]

Look a bit more carefully. On Cubs, when sliding the ribs on and off you routinely get scrape marks from the nail holes, and they look like cracks until you do a little sanding. Cracks do not usually start at nail holes.