Desert Rat Wing Spars

[bdk]

Tapered chemical milling is a somewhat common process on aluminum aerospace components, both wing skins and extrusions. There is no issue neutralizing the solution. C-17 used a lot of parts processed in this manner.

So, how do you make an internally tapered tube? Enquiring minds and all. Acid milling process or???

[/quote

Good to know, thank you!!

https://www.misumi-techcentral.com/tt/en/surface/2010/01/031-chemical-milling---2.html

[Spitty]

Would Waterjet milling work?

[BigGrey]

Wire EDM and waterjet are not suitable due to the length. Attempting to machine the inside taper would be tough to get it right and any oops or bad mark left by the tooling would make it susceptible to cracking due to stress risers.
The aircraft companies in WWII came up with many innovative designs in tooling and processes. It would be nice if the tooling survived all these years but that was not to be for a multitude of reasons.

[Kyleb]

It was suggested that the original tubing was tapered using a mandrel.

How would that be accomplished? I can't picture it.

[bdk]

It was suggested that the original tubing was tapered using a mandrel.

How would that be accomplished? I can't picture it.

I would think a drawing process with rollers on the outside that push the tube against the tapered die. Many ways to skin a cat though. Bulge forming might also be possible using a female die. That can be done either hydraulically or explosively.

[BigGrey]

It was suggested that the original tubing was tapered using a mandrel.

How would that be accomplished? I can't picture it.

I would think a drawing process with rollers on the outside that push the tube against the tapered die. Many ways to skin a cat though. Bulge forming might also be possible using a female die. That can be done either hydraulically or explosively.

Bdk is right in his thinking. Without knowing all the details and dimensions on the part it is hard to know how they did it.

[dhfan]

Many years ago I when I worked in aluminium stockholding, I toured British Aluminium's works at Redditch. The main business there was extrusions, using some presses that went back to WWI I think.
They also had a section on site that manufactured solid-drawn seamless tubes. We did stock a few but they were fearsomely expensive and used mainly in aircraft I believe which wasn't our business so I didn't take a great deal of notice.
There was a discussion about yacht masts, which are/were also tapered, but all over not, just internally, and we basically said 'how?'
Bear in mind this was 45 years ago, but I'm pretty sure I remember they said they drew the tube through an aluminium die, which wore away and got bigger as the tube was pulled through.

[menards]

For all the airframes that have survived, including bits and wrecks that are out there....many of which are destined to stay grounded, none are willing to part with spar tubes for a bird destined to be a flier? I always remember hearing stories of restoration teams getting hard to find parts from other sources.

[Chuck Giese]

What makes the B-17 spar tubes really interesting is that not only is the taper internal, but there are two different rates of taper over the length of each tube. And, of course (being Boeing), the upper spar tubes are different internal thicknesses than the lower spar tubes. All in all, a ton of fun!

[RyanShort1]

What makes the B-17 spar tubes really interesting is that not only is the taper internal, but there are two different rates of taper over the length of each tube. And, of course (being Boeing), the upper spar tubes are different internal thicknesses than the lower spar tubes. All in all, a ton of fun!

Seems every time I look at it that we seriously underestimate the genius of our forefathers and overestimate our own with computers and such...

[marine air]

That's an interesting thought about the yacht masts. Considering the 1930's wasn't that many years past the sailing ships era.
I bet you are onto something about the technology. Boeing got the idea from somewhere.

[menards]

Found this cool vid...applicable to the discussion of trying to make parts 75 years later. All that tooling cost more to dismantle than it was worth in parts.

https://m.youtube.com/watch?v=XoAsDmTnh ... e=youtu.be

[JimH]

This video popped up on my feed, sad to see Mike so dejected. Seems the machine shop should be liable for the poor machinging?

https://youtu.be/9kN7ItnIT-U

[Spitty]

Many years ago I when I worked in aluminium stockholding, I toured British Aluminium's works at Redditch. The main business there was extrusions, using some presses that went back to WWI I think.
They also had a section on site that manufactured solid-drawn seamless tubes. We did stock a few but they were fearsomely expensive and used mainly in aircraft I believe which wasn't our business so I didn't take a great deal of notice.
There was a discussion about yacht masts, which are/were also tapered, but all over not, just internally, and we basically said 'how?'
Bear in mind this was 45 years ago, but I'm pretty sure I remember they said they drew the tube through an aluminium die, which wore away and got bigger as the tube was pulled through.

A lot of British stuff is done that way.Spitfire main spars are round tubes pulled through a die to be square then bent.Hawker aircraft from the 30,s and 40,s use different shape dies to produce their tubes.

[menards]

This video popped up on my feed, sad to see Mike so dejected. Seems the machine shop should be liable for the poor machinging?

https://youtu.be/9kN7ItnIT-U

Interesting when he said they may receive some parts from "909" because "they don't need them anymore".