Double curvature in aluminium

[Marty_d]

A question for the knowledgeable.

 

My current project, the CH-701, has no double curves in aluminium - every part is curved in one plane only. The wing ribs and other formed parts have relief creases where they're bent over following a curve.

 

However at some stage in the future I would like to scratch-build a Spitfire copy, and this IS going to require double curvature - pretty much every skin on the aircraft is curved in more than one plane.

 

The 701 uses 6061-T6 which is, obviously, already tempered.

 

What would be the best way to do these parts? Does it involve an English wheel and many years of apprenticeship, or shaped moulds to pressure form over? Or another method?

 

Thanks in advance.

 

Marty

 

 

[IBob]

You'd have to wonder about that, no?

 

"We're on the back foot in a war, fighting for our very survival. Hey, what say we invent an aircraft without a single straight line in it???..........."

 

 

[facthunter]

That was never made in large numbers for the reason you highlight. Costly to build and costly to repair. looks good though and every pilot I know who flew them, liked it. Flew off grass paddocks with a waddling U/C and some fairly low hours pilots at the controls. Nev

 

 

[Marty_d]

They had the ones with straight lines (and fabric covering for the curvy bits) - it's called a Hurricane.

 

Nev I recently read a book called "The Silver Spitfire", an autobiography of Tom Neil. Amazingly the Spits had a designed service life of around 40 hours - at that stage they were pulled down and checked over completely before being released for another 30 hours. I can't comprehend the amount of work done by so many people to produce something of such performance (and beauty) with a design life of 40 hours.

 

(Good read, by the way. It appears this bloke had himself a very pleasant war (in relative terms), hobnobbing with the US flyers and tooling around at will in a Spitfire he found abandoned at a French airstrip, which he somehow convinced the maintenance guys to fix up and remove all the paint so it couldn't be identified).

 

 

[Yenn]

If the curve is fairly gentle you could just use 2024T3 and some gentle hammer work. I did this to make the fairings above the wing, fuse joint.

 

When building an RV wing you roll the outer section up to gain access for riveting, it surprised me that this was possible with the wing profile at right angles to the bend.

 

 

[pmccarthy]

You can create double curves with a hammer and a clean flat plate. A systematic pattern of hammer strikes (in lines, like writing) gently curves the plate. I recommend the Bodywork Restoration Tutorial by David Gardiner, a DVD that you can purchase. It has lots of guidance on bending and shaping sheet metal.This DVD is available at: http://metalshapingzone.com

 

 

[facthunter]

I've done some working into old conveyor belt with a soft hammer. A wheeling machine can be obtained fairly cheaply. Nev

 

 

[Marty_d]

If the curve is fairly gentle you could just use 2024T3 and some gentle hammer work.

I was going to ask about the alloy and especially the Temper. According to wikipedia, T3 means "solution heat treated and cold worked" whereas T6 means "solution heat treated and artificially aged".

 

That kind of means nothing to me - is 2024T3 more malleable?

 

Possibly some wheel work will be needed - the most extreme curves would be the wing and tail surfaces leading edges.

 

You can create double curves with a hammer and a clean flat plate. A systematic pattern of hammer strikes (in lines, like writing) gently curves the plate. I recommend the Bodywork Restoration Tutorial by David Gardiner, a DVD that you can purchase. It has lots of guidance on bending and shaping sheet metal.This DVD is available at: http://metalshapingzone.com

Thanks PM, I'll check that out.

 

 

[Riley]

I was going to ask about the alloy and especially the Temper. According to wikipedia, T3 means "solution heat treated and cold worked" whereas T6 means "solution heat treated and artificially aged".That kind of means nothing to me - is 2024T3 more malleable?

 

Possibly some wheel work will be needed - the most extreme curves would be the wing and tail surfaces leading edges.

 

Thanks PM, I'll check that out.

Getting respectable 'pudding' (compound curvature) into any alloy sheet in excess of 500mm square with a shaped mallet and a sand-filled leather bag is a very difficult task for the un-initiated, particularily when there's a need for two items of mirror image. For the large areas of fuselage skinning, you almost have to have both an English wheel and a gas torch for seam welding/annealing/reworking. Above all else, one needs to have the experience and proficiency to use both items of equipment when working with aluminium sheet. This I became aware of (but didn't learn how) when building the body for the Riley Special. Ended up getting lucky and finding an old codger with both a wheeling machine in his shed and +60 years experience in using it. He would allow me to practice wheeling with bits of scrap but wouldn't let me near anything that was going on the car. Good luck (and be mindfull, perseverance pays). cheers

 

 

[bexrbetter]

Marty, use 6061 for the purpose, it's far more pliable than a 2 series.

 

Gentle double curves are quite available to you at home, depends on how severe you want to go, the Morgan turtle deck has a minor double curve that you don't even think about for example and their longerons are even more so as is my current build.

 

Looking at the Spit, as I do often in China, I can't see where you are talking about that will present a big issue, Shirley the nose and wing tips would be f'glass?

 

As for tools, look for a metal edge shrinker/stretcher, cheap and simple, plenty of Youtube clips.

 

 

[Marty_d]

Looking at the Spit, as I do often in China, I can't see where you are talking about that will present a big issue, Shirley the nose and wing tips would be f'glass?

Wing tips maybe, but even those I'd like to do similar to the originals (see below on the beautiful rendering of a Mark IX from Raymond Ore - see Behance)

 

There would be a fair curvature on the leading edges of the tailplane and tail especially, the leading edges of the wings (particularly outboard sections), and things like the wing root fillets etc.

 

Even the rear fuse and upper wing surfaces would have some small amount of double curvature.

 

 

 

[bexrbetter]

Even the rear fuse and upper wing surfaces would have some small amount of double curvature.

Ally is more flexible than you obviously imagine.

 

What's important is the methodology that you use as you are fitting the panels up.

 

 

[Nobody]

Production forming can be done using either hydroforming or rubber forming. eg

 

 

If the amount that the material has to be worked is small you can do it to an already heat treated sheet (eg -T3) but other times it is done to the annealed material (-O) and then the heat treatment done later. There are companies that will heat treat for you once you have formed the part.

 

Be very careful with a metal shrinker or stretcher on aircraft parts. Most will leave score marks in the aluminum which will crack due to fatigue in the future. On a steel car body this is much less of an issue.

 

 

[pylon500]

As mentioned, the 6000 series is more workable than the 2000 series, even at T6 temper.

 

If you look closely at a Spitfire, it's not unusual to see the odd wrinkle and buckle, they were built quick.

 

The usual trick for 'compound' shapes is to do 'steps' between bulkheads, if you sight along the skins, this becomes apparent.

 

Have a look at a Sullivan Spitfire for some ideas, he solved most of them.

 

In stressed areas like the wing skins, using the multiple skin join steps, requires a bit of thought about number of rivets at the joins.

 

A lot of it depends on how complex you're willing to get...

 

 

[Ultralights]

sadly its English wheel, or Piccalo work, or hydraulic forming.

 

 

[Downunder]

This bloke has some good metal shaping vids.

 

Looks like he knows what he's talking about !!!

 

 

 

[spacesailor]

Yes!

 

You would be well advised to use all the methods at your disposal, if you can make a mould to hammer the shape to, it makes getting the second one looking reasonable much easier,

 

A little hump to clear the engine mount would be a good practice start, as being small takes little scrap, I did three before tackling my cowling, & don't be afraid to seek professional help as most workshops like new things to do.

 

spacesailor

 

 

[spacesailor]

[ATTACH]44924[/ATTACH]Hi you can make molds out of wood / plastic of even plaster-of-paris.

 

spacesailor

 

 

 

[Marty_d]

Ally is more flexible than you obviously imagine.What's important is the methodology that you use as you are fitting the panels up.

Can you expand on that a bit Bex?

 

I'm guessing you mean that the shape of the panels themselves would help minimise the need for forming, eg using several narrower or triangle -shaped skins for the rear fuselage instead of trying to form large sheets... is that it?

 

 

[fly_tornado]

Marty why not try the Mustang?

 

3/4 Scale P-51 Mustang Aircraft Kit, All Metal, Titan Aircraft T-51 Kit

 

 

[Kyle Communications]

Why dont you do FRP or Carbon fibre skins done with molds on the double curve bits and the rest in alu. It would be much easier

 

 

[Marty_d]

Marty why not try the Mustang?

Because it's not a Spitfire. This is the project that will see me well beyond retirement (if I live that long)... I'm not going to waste all that time on something that's not my absolute favourite aircraft.

 

Why dont you do FRP or Carbon fibre skins done with molds on the double curve bits and the rest in alu. It would be much easier

Starting to think that'd be the best way. Especially since I've just found the most incredible resource for anyone wanting to build a Spit (flyable, scale model or just a solid desk ornament!)

 

From another site I found a reference to MONFORTON PRESS - scale Spitfire drawings . I took a punt and bought their PDF e-book for $24.

 

This is fantastic. 429 pages of detailed drawings and photos of the Mark 9 and 16 Spitfires. Every measurement, angle, rivet spacing, panel lines, skin thicknesses etc etc taken from 5 surviving aircraft. (As the book says - manufacturing differences mean that no two Spitfires of the same mark are exactly the same!)

 

Looking at the panels it's obvious that most of them can be manufactured flat instead of needing to be shaped, which is a relief.

 

If you're into Spitfires at all, it's worth the price just to drool over the pictures and marvel at the detail they go into. They sell a hardcover copy for $75 + postage from Canada, but I'm glad I got the PDF version - means I can zoom right into the drawings and print only the pages I need.

 

 

[pylon500]

If you want a Spitfire, and are willing to go the composite route, you should do some serious digging around, and see if you can find the 3/4 scale Mk9 moulds that Scott Winton made for George Markey.

 

They must be out there somewhere?

 

 

[facthunter]

"Favourite Aircraft" is not fixed in stone. Also "Scale" versions often have vices worse than the originals. (Often with the rudder effectiveness as an example) A plane should be "nice to fly" Vice free and controllable hopefully, or you will hate it, even though it looks great in the hangar or in front of the clubhouse. Notice I didn't put stability as you can have too much of that sometimes, at the expense of YOU being able to control it, which I regard as paramount. Nev

 

 

[Marty_d]

That's true Nev. When I was young and silly and knew no better, the P51D Mustang WAS my favourite. Then I went to England and saw Spitfires, heard Spitfires, drooled over them in museums. When you see those perfectly shaped elliptical wings slicing through the sky... you think to yourself "THAT is a real plane."