'68 Citabria 7ECA Milman Spar Conversion

[flyingdakota]

I would post some pics but the wing is disassembled at this point....

 

[Bartman]

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.

Thanks for the pics! Right away I see you have a channel over the tank for the fabric to attach to, I don't have that. I see your attach point also for the tank strap is on the lower bolt so I'll have to take a look at that too. What year is your airplane and which Citabria is it? I have what Milman refers to as the "rare" 3/8" filler strip behind that nose rib between the root and 1st ribs.

 

[Bartman]

I would post some pics but the wing is disassembled at this point....

no sweat, got it under control for now...........thanks anyway.

 

[Clifford Daly]

Thanks for the pics! Right away I see you have a channel over the tank for the fabric to attach to, I don't have that. I see your attach point also for the tank strap is on the lower bolt so I'll have to take a look at that too. What year is your airplane and which Citabria is it? I have what Milman refers to as the "rare" 3/8" filler strip behind that nose rib between the root and 1st ribs.

It’s a 1967 Citabria 7GCAA. I have the 17 gallon tank so its spread across the the three rib seconds. Definitely a pain in the neck when drilling the holes for the leading edge ribs!

 

[Bartman]

That would make sense, I've only got the 13 gal tanks

 

[Citabria.pt]

Bart, have you considered adding a fuel gauge to your LEFT wing while it's not assembled? You will find it usefull the first the damn bird empties RH tank faster than you expect. Then you'll land ASAP for unsure fuel, and on the ground you'd find all your fuel migrated to your LH wing...

 

[Clifford Daly]

Trammeling the wing.... anyone have any suggestions or pointers? I have my adjustable trammels coming tomorrow as long as a fisherman scale to test the tension. Not much info on doing it on these wings, just lots of Cubs!

 

[Bartman]

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.

Was just looking at the parts diagram again, the front attach fitting has two bolts coming in from the back and two coming in from the front. the lower rib attach bolt enters from the front.
that isn't the way mine was done originally if you look at the photos above. so do we defer to the parts diagram or put it back the way it was?

 

[Bartman]

Bart, have you considered adding a fuel gauge to your LEFT wing while it's not assembled? You will find it usefull the first the damn bird empties RH tank faster than you expect. Then you'll land ASAP for unsure fuel, and on the ground you'd find all your fuel migrated to your LH wing...

that might not be a bad idea Pedro, will have to look into it. thanks for the suggestion. still trying to work out the details of rerouting the vent lines so we can do the skylight one day.

 

[Bartman]

Got the tank back in and should be ready for trammeling tomorrow. It is taking me forever! It took all day to get the tank in and I still think I might have to undo part of it tomorrow since the straps stick up a good bit above the neighboring rib tops.

 

[Citabria.pt]

Hi Bart, consider opening some round holes on the wood base of the tank to make things lighter, still strong. I've done it on mine. Holes about the same size as the one for the fuel drain. Save as much weight as you can, as Milman conversion adds around 20lbs total, as per papers.

 

[Bartman]

Pedro, I would but that thing has been in and out about five times already so it's in for good this time! I haven't seen a reference to the conversion adding twenty pounds but I am committed to putting the plane on scales when it's done so it will be whatever it will be. I need to lose 15 pounds so that will be a net gain of five overall maybe?

 

[Clifford Daly]

My stuff is showing adding 10 pounds added with the spar kit. Wish I had put the wing on scales before I took to fabric off to see the true weight difference. What does your leading edge kit add?

 

[Bartman]

My stuff is showing adding 10 pounds added with the spar kit. Wish I had put the wing on scales before I took to fabric off to see the true weight difference. What does your leading edge kit add?

I have nooooo idea Cliff. I was told by Milman that the leading edges improve airflow so are possibly responsible for a few mph improvement in airspeed. I'm trying not to sweat the weight and will just see how it ends up.

I need to find or make a set of those nifty cuffs for where the fwd lift struts bolt to the underside of the wing. there's another .25 mph right there waiting for me!

 

[Bob Turner]

Re: trammeling.

Have you guys considered a string along the forward spar? Trammel one bay for squareness (important) then make sure that front spar stays dead-straight?

I always check all bays, but think straightness is the most important thing for strength. My trammel bar is a light wood strip, two pointers, and two small C clamps.

 

[Clifford Daly]

Re: trammeling.

Have you guys considered a string along the forward spar? Trammel one bay for squareness (important) then make sure that front spar stays dead-straight?

I always check all bays, but think straightness is the most important thing for strength. My trammel bar is a light wood strip, two pointers, and two small C clamps.

Good point. My trammel bar is a piece of square aluminum and then I bought a set of trammel points from amazon for 20 bucks. I squared every bay so they are all dead on, then I set the points for the distance between the front and rear spar perpendicular to them and measured all 5 dots. All straight!

I did just lay string out to try what you said, it’s straight as can be but a little hard to eye ball it. Both ways work!

@Bartman just something to look out for, there is no set number for the tightness of the drag wires. I made all of mine a 1/2 deflection at 15 pounds. It actually pulled the fuselage attachment fittings on the wing in 1/8 of an inch. Loosening the drag wire half a turn brought it back to the exact demension of the fuselage attachments.

 

[Bartman]

Hi Cliff,
Thanks for the info. I made a bar to keep the fuselage attach fittings at the correct spacing. It's made of steel square tubing and I welded a piece of plate in each end to drill/tap for 1/4" on one side and 3/8" on the other. I can post a photo when I'm back home. In theory, when the wings are being mounted I'll remove the bolts on each end, place the wing of the attach fittings on the fuselage side and then tap the bar out while dropping the wing into position. Milman says to leave the inboard drag wires loose since there is no compression member at the root so I made a temporary compression member to work with.

Just thinking about this, it might make covering the root rib more difficult so maybe I'll have to loosen the inboard drag wires, cover the root rib, and then reinstall the temp brace so I can tighten up the wires before laying out the wing covering.

Regarding the wire tension, the wires shouldn't really be pre-loaded to a large degree. Milman recommends hand tight followed by 1/4 to 1/2 turn. If your standard, 15 lbs per 1/2", is a similar standard then you're all good!

 

[Bartman]

My trammel bar is a light wood strip, two pointers, and two small C clamps.

Mine is homemade too, wood strip, wood blocks with wood dowel pointers and 1/4" nylon RC plane wing bolts!

 

[Clifford Daly]

@Bartman interesting. I have 3 tank mounts that run between the spars and are bolted tight to them. In my eyes it is another compression member. The 1/8 inch difference came from the drag wires pulling the ends in ever so slightly. I just didn’t want too much tension on those wires because WHEN these wings eventually have to come off... they may never go back on.

The tension of 15 pounds at 1/2 inch deflection is the number used for all the cub stuff. The drag wires are similar and they have actually made a standard to follow. It’s weird that American Champion never did that. This way just enables each bay to be the same. Some bays took a lot more than hand tight to actually square which is when I started calling all my cub builders haha

 

[Bartman]

Was going to spend all day fitting new leading edges sections but got redirected to mulching duty! What???

Managed to media blast and prime the jury strut attach fittings after dinner and did some test fitting of the first leading edge section. Should make some progress tomorrow, I hope!.