T-6/Harvard wing attach angle manufacturing technique

[Matt]

Hi all,
Was going to make this another post to the thread with the wing attach angle images but thought I'd start a new topic given that the other one has unfortunately deteriorated.

Anyway, I'm wondering if anyone knows how NAA/Canadian Car and Foundry, etc manufactured the wing attach angles originally? I currently believe that they would likely have been stretch formed (the extrusion being formed around a die while stretched beyond its yield point) however this would have had to have been a very time consuming process and I'm not sure if the material would have really been taken to yield.

Although I'm not working on a T-6/Harvard, the Wirraway is from the same family and I was trying to address an attach angle issue for some time prior to the recent accident. One main reason why I want to install new angles on my Wirraway restoration is simply to have confidence in what's holding my wings on.

While Lance have NOS T-6 attach angles, which could be used on the Wirraway, the metal is not 'new' as such, having been made some 50 or so years ago. Ideally I'd like brand new material but this means going through the whole manufacturing process - hence why I'm trying to confirm the original forming technique. I can get the extrusions made up easily and quite economically but initial investigations suggest that the forming of the extrusion will be a very expensive process.

Anyway, I hope to receive some informative responses. Thanks in advance.

Cheers,
Matt

[Firebird]

While Lance have NOS T-6 attach angles, which could be used on the Wirraway, the metal is not 'new' as such, having been made some 50 or so years ago.

Surely it doesn't matter that it's not 'new', as provided it's never been fitted to an airframe, it hasn't therefore been subject to fatigue cycles to reduce it's lifed time, so, as long as it's been stored reasonably well (i.e. not sat in a salt water tank for 50 years or been knocked about and damaged ) then it should be perfectly OK.

Mind you it's been over 20 years since my metallurgy lectures

[snj-5]

The drawings call out an NAA "Standard" extrusion in
"O" (annealed) condition.

They were either stretch-formed over large dies and subsequently
heat-treated, or they could have been roll-formed in annealed
condition, and then heat-treated.

If I were a bettin' man, I'd say the former (stretch-formed) is
the way they were manufactured. Sounds expensive, until
you ammortize the cost of the tooling over 15,000+ units.

Bela P. Havasreti

[italian harvard]

If conserved properly, a metal part is just an inert thing, so there should be no trouble in fitting it on a plane, the fact is that u need to be sure it was never installed on a plane. If u want to rebuild it following the original specs it's fine, but as stated before u need a dedicated workshop to do that, and I wonder what the costs would be like... Did any of u guys ever rebuild/made rebuild the wing attach angles?
If possible I'd like to hear some other opinion about the wing fairings issue too..

Alex

[Cvairwerks]

Matt: I would suggest having a conversation with Tom Reilly?, the B-25 guy in Florida. Tom is about the only one that I know of that has manufactured any attach angles, though his are for the -25. Otherwise consult with a reputable materials/manufacturing engineer ( not mechanics in the Brit vernacular, but real live degreed engineering guys).

Forming in the T0 condition is not hard at all, just finding someone that is competent and has the equipment to correctly heat treat and is willing to do aircraft parts is the biggest problem.

[snj-5]

I use a local heat treat vendor that is a supplier/vendor for
a "major aerospace corporation" near Seattle.

I get cert. sheets for the parts I have heat-treated, and my
parts go on the racks and get heat treated right next to
"major aerospace corporation" parts.

These folks also (on request) put my parts on dry ice so I can
get them home and straighten them before they harden up.

I agree if you're going to have new angles manufactured (perfectly
legal in the States under FAR §21.303(b)2 ("Owner Produced Parts"),
consult an engineer who can evaluate the original parts as-produced and
come up with a safe way to manufacture replacements. I'd then
run whatever said engineer came up with past the feds for concurrance
before I had anything made. For T-6s in the states, it'd be way easier
to just call Lance and buy NOS angles (at least until that supply dries up!).

Bela P. Havasreti

[italian harvard]

Thanks Bela
I was thinking of Flugwerk here in Europe, they are working on several T-6 projects and can redo all components (ah, the german workmanship!)

Alex

[HarvardIV]

Hey Guys:

As was discussed on the earlier thread. I think the angles could be milled if they were made from a higher yield strength material. THe only problem would be that the grain direction wouldn't follow tangent to the attach angle's surface. Would a Titanium angle hold up?

I am aware that Titanium is harder on milling equipment, and has a different thermal expansion coefficient. With that aside, would the angle hold up?

Chris

[snj-5]

You'd have a way harder time getting a titanium replacement
angle pass the feds than you would an aluminum one.

A properly engineered (and N/C programmed) replacement part
could be hogged out out of a block of aluminum, but it would take
knowlegeable folks to make it happen (not to mention access to
an N/C controlled, 5-axis milling machine). You'd have to hand-blend
all the machining mis-matches, the stress relieve / shot peening schedule
would have to be addressed.... It would have to be engineered by
someone who knew what they were doing from womb to tomb.

We're talking about a bunch of nothing however, since (for the time
being anyway), NOS attach angles are available. If it were me and there
were no NOS angles available, I'd look into fabricating some roll forming
dies and roll-form "O" (or annealed) extrusions, and subsequently heat
treat them to T-42 condition.

In one of the sheet metal shops I used to support, we had an N/C
roll-forming machine (cool little contraption...). It would readily
roll-form you a pretzel if you programmed it to do so....

Bela P. Havasreti

[bdk]

I am aware that Titanium is harder on milling equipment, and has a different thermal expansion coefficient. With that aside, would the angle hold up?

My last post on this subject... Yes it would hold up. Would the adjacent structure? Titanium is much stiffer than aluminum. It could cause a stress concentration in the wing skins and stiffener attachments because the attach angle would not flex as much (be as soft) spanwise. Why keep trying to reinvent the wheel?

IF the problem is with the radius, increase the diameter of the fillet radius slightly and use a large radius on your counterbore cutter as Glenn W. suggested.

I still see no evidence that there is ANY problem with the attach angle design. This could have been a fatigue fracture, but again, I have no information as to any damage history or to how the aircraft was operated over its entire lifetime. There could have been a flaw in the original part, who knows?

And finally, without seeing the blueprint (anyone have a copy?), I suspect the extrusion was annealed, stretch formed, heat treated, straightened (hot or cold?), routed to shape, and then drilled.

Is the original part 2024 or 7075? If 7075 you might be able to make it from 7050 which is much more resistant to stress corrosion cracking. But why? A new part from Lance is much cheaper and will last another 60 years. What more do you need?

[jcw]

none of the t-6 structure is 70 series, it is all 2024 1100 or 5052 as wel as forgings and castings. 70 series came after the war

[HarvardIV]

JCW:

I am aware that most of the T-6 has 24St AL aka 2024T-3 throughout. Where is there 5052 H AL?

[warbird51]

5052 can't be heat treated. 6061 can.

[snj-5]

bdk wrote:

"And finally, without seeing the blueprint (anyone have a copy?), I
suspect the extrusion was annealed, stretch formed, heat treated,
straightened (hot or cold?), routed to shape, and then drilled"

I have a complete set of blueprints, and I've re-reviewed a
"typical" attach angle drawing. I concur with your observation on
how they were manufactured. Based upon the "excepted norm"
in industry, my guess is subsequent to heat-treating, they were put
on ice (in W condition) and hand-straightened before they hardened (it
typically takes 96 hours for a 2000 series aluminum part to naturally
(room temp) age-harden up to "full strength). I also agree making the
attach angles "stronger" (substitution of materials, whatever) will only
transfer a potential point of failure elsewhere. The airplane is designed
well/correctly from the get-go (the original design is sound, and there is
no need to "strengthen" the area in question).

You will find 5052 (back then they called it "half-hard") used on stuff
like electrical / power junction boxes, electrical switch boxes,
empennage / wing fairings, etc. In other words, 5052 is (was)
typically used in "non-structural" applications where good formability
was more of a requirement than over-all strength.

Bela P. Havasreti

[vanguard]

The hydraulic lines in a T-6 are 5052.