'68 Citabria 7ECA Milman Spar Conversion

[Bartman]

It's a long story but this past fall it was decided to convert the wood spars in my 7ECA to aluminum using the Milman Engineering STC. I'm also using their D-cell leading edge STC. So far the first wing is about halfway done. It is taking forever because each little step involves some problem solving or a tool or piece of equipment that I don't have. Things are picking up though and we're still hoping to have it flying this summer!

Like any project, first come a lot of photos to document how it was. I figured I'd dump them here for whomever else might need them sometime. They're a good reference for scale modelers too, fwiw.

 

[Bartman]

More before pics

 

[Bartman]

Removing the wings.

 

[Bartman]

Inside the first wing

 

[Bartman]

more before photos from inside the wing

 

[JimParker256]

Bartman, did you find cracks in your spar that triggered the replacement, or are you doing it just "because"?

 

[Bartman]

Hi Jim and welcome to the site.
I bought the plane, spent six months clearing squawks, and then hit a hawk which damaged the left leading edge. Rather than add more damage history to the logs, it was decided to put the insurance money towards the conversion. So far I think it was the right decision and I'm really looking forward to the end product. No cracks in the right wing spars. Left is still in the hangar with covering still on.
I'll post photos showing my progress as soon as I can get caught up but I should have mentioned it's been slow also due to the insanely crappy weather we've been having in NJ since about the first week of December! I thought it would go more quickly but I also didn't think we'd have snow and sub-freezing temps week after week.
Feel free to ask any questions, I'm happy to share what I've learned from all of this.
Bart

 

[Bartman]

Last batch of before photos

 

[Bartman]

Using the Stewart System you know you're getting close to something happening when you bring home a carriage full of distilled water!



It was cold outside so I opted to clean and prime the spars in the basement. I ended up only doing the first set, the second set is still bare. I used Stewart EkoPrime, a single part water-borne primer that went on pretty well with a sponge brush.

 

[Bartman]

Quick status update.....I'm holding on the delivery of a container of resorcinol glue. The fuel tank support panel for the right wing has some sag in it so I decided to replace it. It's not available from the factory so we ordered materials to make one and included in that is a container of the right glue. It should be here tonight and if it gets here early enough I'll be able to make up my support panels and then get back to work assembling the right wing. Both aluminum spars are in place and as soon as the tank support panel is ready I'll be able to put it in, the fuel tank, and then the drag wires. With all of that in place we'll trammel the wing, install the new leading edges, reassemble the old trailing edge pieces (the trailing edge piece inboard of the aileron is new), and then work on getting the aileron and wing tip back in place.

I'll post updates and photos for the left wings as it goes so all y'all will know what's involved with the Milman conversion from start to finish.

Trying to decided now if we want to do the fabric on the right wing before converting the left wing or if we'll wait and do them both together.

Getting anxious to see this start moving along again.

 

[Bartman]

So, to understand this project so far you have to just look at this photo



Three straight years of mild winters led me to believe I'd be out in the unheated garage Dec, Jan, and Feb getting my wings ready to be flying in the spring. It's spring, I'm not flying but at least it isn't snowing anymore (I hope).

After what feels like eons that spanned trips for work, a two week head cold, shipping delays and more shipping delays, not to mention sub-freezing temps and snow (snow!! doh!) we finally got a warm day in NJ which I took advantage of to make two new fuel tank support panels.

The original panel didn't look too bad but it had some fuel damage from a small leak and it was sagging a bit. She's served valiantly and in her final hours served once more as a template for the new panels.


Spruce and plywood finally arrived and were cut to size


Materials to assemble were a brush that I cut short to make it nice and stiff, Cascophen (Resorcinal) glue from Aircraft Spruce, a scale to measure the glue 5:1 by weight, and my trusty Senco stapler.


The glue starts out with the consistency of unmixed brownie mix (5 parts liquid resin to 1 part powdery hardener) which slowly transitions to a thick consistency like a good barbeque sauce. It's weird stuff, it's slick in the mixing pot but once it's spread out it really starts to tack up quickly. Within the few minutes it takes to lube up a joint and get it pressed together it gets really sticky, like a thin rubber cement. I started out trying to be super neat because I knew I'd be taking photos but ended up just getting it done so I'll take the downgrade for being sloppy. My garage is a mess at the moment because the warmer weather has me scrambling to get our kitchen project (from last year) done and a garden roughed out in the back yard for us and the kids.



So the panels each need a 2" hole for the drains and a couple of coats of sealer and they'll be ready to be screwed into place. I'm using the Stewart System for covering so the panels will get clear coated with EkoCrylic.

That's it. Gotta fly a trip tonight so these will be finished up and the first one will be laid into place early next week. A little progress gets me smiling.

 

[Clifford Daly]

Awesome thread with a lot of information! I’m in the process of doing my spars as well, so you want me to start a new thread or post some stuff in this one? I’m happy with the kit so far!

 

[Bartman]

Hi Clifford, thanks for the reply. Feel free to join in the conversation here or go ahead and start a thread with your own photos/experiences/comments. I'd think it's better all around to have multiple threads demonstrating multiple builds.

Me too regarding the kits from Milman, the fit has been excellent and the quality is top notch. A hardware list would have been nice but I've got a spreadsheet I'll publish once I've got more confidence in it.

 

[flyingdakota]

COOL! That is what we'll be doing with 06S! Everything is primed just need to start the assembly process!

 

[Bartman]

COOL! That is what we'll be doing with 06S! Everything is primed just need to start the assembly process!

looking at your avatar, I'm jealous you're doing a full rebuild project, that'll be beautiful when it's done. maybe another build thread?

 

[Bartman]

I've got a spreadsheet I'll publish once I've got more confidence in it.

I mentioned elsewhere an OS upgrade to Win10 wiped out my laptop's harddrive.....apparently the hardware list was lost in that little accident but I've got a hard copy so I'll type it in again when I have time. Just ordered more hardware to fill in the gaps left from the first order.

 

[Bartman]

A few examples of the spacers used to mount the old ribs & fittings to the new aluminum spars. The wood spars had a rectangular cross section, the aluminum spars are an I-beam so the spacers make the thickness of the I-beam match the wood. There are both wood and aluminum spacers. The wood ones come pre-sealed and the aluminum spacers are primed.

Ribs (nuts are not tightened yet on this one)


Rear wing attach fitting


Front strut attach point


Compression strut

 

[Bartman]

Finally opened up the box with the leading edge sections yesterday. Not much to see but just the fact that the box is in play means we're back to making progress which feels, sooo good.

 

[Bartman]

@Clifford Daly & @flyingdakota Would you guys mind posting photos of the front & rear of your wing attach fittings? I'm trying to figure out what the correct orientation is for the mounting hardware since my two wings are different from each other. I think the scheme is to be able to remove the hardware with the tank in place so the fwd hardware goes in from the front and the read hardware goes in from the back? Not sure but want to get it right. The parts manual doesn't quite show that though.

Thanks!

 

[Clifford Daly]

Funny, I just installed these two fittings last night! I only have pictures on my phone from when I took it apart. My wing had them as you described, front ones in from the front and rear ones in from the rear with all nuts and washers on the inside of the spars. Also if you look very closely at the diagram it appears to be that way too.