Skin for Blanik wing

[Ernst]

We need to replace a section of wing skin on our L-13 Blanik. Any idea
where we can find the material, other than Blanik America?

Thanks,
Ernst

[Bob Kuykendall]

On Apr 20, 9:36*am, Ernst > wrote:
> We need to replace a section of wing skin on our L-13 Blanik. Any idea
> where we can find the material, other than Blanik America?

Is there any particular reason you can't just use 2024-T3 alclad of
similar thickness? Its probably close enough to the original aluminum
alloy as makes no difference. If you had to, you could send a chunk of
the original skin out for analysis of the alloy and temper.

Thanks, Bob K.

[[email protected]]

Bad idea - The Blanik wing skin alloy is the same soviet era material
used on early MIG's. Not even close to 2024, probably stronger than
7075-T6, and anodized, not clad.

Assuming you can identify the major alloying elements of the factory
skins, how will you determine the aging tempering process used, and
show compliance/conformance with the design material properties as
required by the FAR's? Do you think the factory will give you all the
design allowables for this material? Or perhaps you will develop your
own per Mil-Hnbk-5?

See if you can get a piece from a scrapped ship, I know someone that
has several.

Aerodyne

[Bob Kuykendall]

On Apr 20, 4:44*pm, wrote:

> Bad idea - The Blanik wing skin alloy is the same soviet era material
> used on early MIG's. Not even close to 2024, probably stronger than
> 7075-T6, and anodized, not clad.

I'd like to see some data on that, can you point me towards a citation
or resource?

Regardless, it's easy enough to test; just snip out a coupon and pull
it to failure. I've done similar tests many times and often posted the
results to YouTube. There's a broken Blanik between my work and home;
I might try and get a pull coupon off of it to compare with 7075-T6,
2024-T3, and 6061-T6.

> Assuming you can identify the major alloying elements of the factory
> skins, how will you determine the aging tempering process used, and
> show compliance/conformance with the design material properties as
> required by the FAR's? *

Once you've demonstrated that the strength of the replacement is equal
or better that of the original material, most of the other stuff is
pretty much irrelevant. The alloying and temper will mostly affect the
yield and ultimate strength respectively, and you would already have
demonstrated that.

Of course if the replacement alloy is drastically different than the
original there could possibly be a galvanic issue between the original
and replacement material. But in my direct experience, that's more an
issue of taking appropriate anti-corrosion measures and monitoring the
repair in subsequent inspections.

Anyhow, what you really need to do is demonstrate to an A&P or IA's
satisfaction that the substitute material is of equal or better
strength than the original, to the degree that they would feel
comfortable executing the repair and signing it off. I've seen a few
Blaniks with locally-fabricated repair panels, so I know that such a
thing is not unheard-of.

Thanks, Bob K.

[Bob Kuykendall]

On Apr 21, 6:11*pm, "Stephen!" > wrote:

> * Is this the Bob Kuykendall of the Bob and Ellen crew from CCBR?

No, sorry. What is CCBR?

Thanks, Bob K.

[Bob Kuykendall]

On Apr 21, 8:27*am, Bob Kuykendall > wrote:

Just a quick update on this: I've arranged to obtain a coupon of wing
skin material from a local L-13 wreck, and arranged for a lab to do a
chemical assay to identify the primary alloy components. I'll also do
a static pull with my tensile test machine to get basic physical
properties.

Thanks, Bob K.

[Dave Nadler]

On May 6, 6:34*pm, Bob Kuykendall > wrote:
> On Apr 21, 8:27*am, Bob Kuykendall > wrote:
>
> Just a quick update on this: I've arranged to obtain a coupon of wing
> skin material from a local L-13 wreck, and arranged for a lab to do a
> chemical assay to identify the primary alloy components. I'll also do
> a static pull with my tensile test machine to get basic physical
> properties.
>
> Thanks, Bob K.

Thanks Bob !
Best Regards, Dave

PS: Are you going to do an analysis of the rivets as well ?
Composition, taper, hardness, etc ? For the hopelessly
curious...

[Bob Kuykendall]

On May 7, 3:43*am, Dave Nadler > wrote:

> PS: *Are you going to do an analysis of the rivets as well ?
> Composition, taper, hardness, etc ? For the hopelessly
> curious...

Dave, I'm not going to do that at this time. The wreck that I'm
getting the skin sample from doesn't have any riveted parts that are
so badly smunched that their removal would have zero impact.

If somebody out there does have a bit of flush-riveted Blanik wing
wreckage, I'd be glad to cross-section a couple of the rivets so we
can get an idea of the joint geometry.

Thanks, Bob K.