Stringers

[svyolo]

I didn't measure the wall thickness of the kit stringers. I will check tomorrow. If they are the same as the Univairs .032, I don't see much difference in volume of material used. Still leaning towards spruce.

I was just about to start installing the aluminum ones, and I picked up the whole bundle. Got me thinking.........

[Battson]

I was just about to start installing the aluminum ones, and I picked up the whole bundle. Got me thinking.........

Yeah it's a heavy bundle alright.

[svyolo]

.048 wall for the kit stringers. Univair website calls theirs .032.

[Mark Goldberg]

FYI - these stringers are extrusions made of 6061. Mark

[Battson]

.048 wall for the kit stringers. Univair website calls theirs .032.

That is good information, that would explain the weight saving.

FYI - these stringers are extrusions made of 6061. Mark

That is worth considering too, as the 5052 which Bearhawk Aircraft supplies does not need painting and will not corrode. The 6061 can definitely corrode, particularly if it gets wet - think bottom stringers. I believe 5052 is also a softer metal, which means fatigue resistance in the most general terms. They probably use a thinner walled 0.032 because they are using a stiffer metal.

[svyolo]

Univair got back to me about their stringers, but I only asked about the "small" ones that are 1/4 X 1/2. They said .66 lbs for a 13 foot section, which is .05 lbs/ft. I didn't ask the alloy.

[Nev]

If using the supplied kitset stringers, is it the norm to spray them with a corrosion inhibitor before mounting them ?

[PaulSA]

As with everything, it's a personal choice. However, in cold, damp NZ I would ...... Simple 1k etch primer would do.

[Nev]

Thanks Paul.

[svyolo]

I ended up using spruce stringers, with a thin coat of epoxy. I can't say I every thought of priming the aluminum stringers. I would have let aluminum oxide do its job. I have had my kit stringers sitting in my shop for 2 years, in an environment identical to the south island, including being 1 mile from the ocean. They are, as new.

[Battson]

If using the supplied kitset stringers, is it the norm to spray them with a corrosion inhibitor before mounting them ?

No need, they are 5052 and will never corrode. They will passivate as svyolo suggests.

I would recommend taking the outside edges off with a file though, to smooth the edges for covering and prevent cracking the paint in the fullness of time.

[svyolo]

I did't remember that they were 5052. That is marine grade. Good to go. I did look to see if they were anodized, they don't appear to be.

[Nev]

Thanks - well I’ve taken the burrs off (and applied corrosion proofing before I checked here !)

[Mark Goldberg]

The stringers are actually 6061. I had thought they were 5052 for many years, but when I ordered a mill run of them a couple years back learned that they are 6061 and not 5052. I have not primered mine on any of my planes. Mark

[Ryan Koeneke]

This is prolly dumb... But I appreciated the other data folks provided which made me consider other stringer materials. But as a first time builder I'm trying not to get side tracked and just build a "stock" model 5.

I took an 1/8" roundover bit to the standard kitset stringers. Hitting one side (front and back) I lost 0.10 oz/ft... Only a half pound over the ~73 feet of stringer materials.. when rounding over all 4 sides I'd lose a little over a pound out of the tail. I tried crushing and bending the stringer and it didn't seem to lose strength so I upped the ante and decided to shave the bottom edge of the stringer off. Which would result in losing 2.5 pounds. I checked the 1 foot piece and it still had a decent bit of resistence to bending but when it let go it did so spectacularly lol. I turned it around in the vice and hit it with a hammer ~5 inches away and it didn't budge. All anecdotal things but maybe interesting to someone lol.

I think I will use the 1/8 roundover bit, not for weight savings but just to not have a hard 90° edge pushing into the fabric unless someone here wants to talk me out of doing that.

[Ryan Koeneke]

2.23 oz/ft as it came from the factory
2.13 oz/ft after 1/8" roundover one side
1.99 oz/ft after roundover both sides (not sure why I got an extra 0.04 oz on the second pass)

1.7 oz/ft with the bottom cut off and top rounded over

[Daniel]

Has anyone thought of adding lightening holes to the factory provided stringers? Perhaps as Mark mentioned, for the underbelly only?

If introduced on the longer side, depending on hole size and spacing I'm curious if they would remain ridged enough.

[marcusofcotton]

Has anyone thought of adding lightening holes to the factory provided stringers? Perhaps as Mark mentioned, for the underbelly only?

If introduced on the longer side, depending on hole size and spacing I'm curious if they would remain ridged enough.

I very much plan to, but it will be awhile before I get there. Planning to do lightening holes after shaping, using a Unibit carefully to reduce deburring effort.