Junkers: flattened tube ends and spanwise tubing

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Culleningus

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Probably the easiest way of connecting tubes to form a truss, is to belt the end with a hammer (or :) press), and drill a hole.
Its similarly straightforward with wing construction to use the said tubes spanwise to carry the +ve and -ve loads.

These are methods I think Junkers empoyed in their 'heyday' with the 'J1' etc.

Regardless of modern regs, these aircraft flew ok, didn't they, and if they failed what aspect of these methods was deemed to have contributed to any related failure of which I have no knowledge?

The flattened tube ends were supported by the metal skins, or by something else presumably in other places (but not in all!!) Take a look at the extent that this method was employed on this machine.

I'm not advocating such a method just questioning its validity.

http://www.greatwaraviation.com/forum/index.php?topic=1589.0


Dave
 

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skier

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From what I have heard, Eurocopter uses the same method on the tubes they use for control rods.
 

orion

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Actually it may be light gauge steel. The plane was built around 1917, well before WWII. Around this time there seemed to be a substantial reluctance in Europe to weld, despite the fact that welding was already often employed in the US.

I recently provided engineering support to a classic reproduction of a Bristol Bulldog, which was built about ten or more years after the J1. The documentation the builder has gathered in connection with the Bulldog (including many original documents) goes well back and includes numerous engineering texts that provide some insight into the design practices of the day. I know this plane is British but according to these texts, the same prejudices seem to be spread throughout much of pre-war Europe. As such, steel tube truss structures were built using machined fittings, which were bolted to the other structural members, which in turn allowed the interface of secondary members through simple interfaces. The riveted flattened tubes go right in line with much of what's written in the references.
 

Culleningus

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I guess the hard bit would be forming the brackets from sheet steel on the longeron intersections.
They would need to be tightly wrapped around the longerons.
The tubing is most certainly steel (probably mild steel).
And it looks like most everything is sheet/tube steel here.
Stressing the metal (small stress fractures) would be something only test pieces could determine.
But its interesting how much potentially one can fabricate from steel without resorting to welding.
This pic is one of the same but you can see how the brackets wrap around the longerons.
Blind rivetts is presumably what you refer to..
Strikes me as a bit strange the longerons were not simply 'angle' rather than 'tubing'.
I'm thinking the likely explanation is that the fusalage skinning method did not provide a continuous connection along the length of the longeron. As such 'angle' would then be liable to buckle.
Dave
 
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Culleningus

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This sketch below is an idea to use angle with Correx/Corroplast (fluted plastic sheeting) to provide temporary support for grp skin layup around 'angle' longerons. Does anyone know how well grp would adhere to metal? The Correx sheeting would be removed after layup.
 

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Culleningus

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On second thoughts, if 'angle' is employed the crossmembers might just as easily be made of same. Correx to fill the voids, then grp laid up on exterior. The fibre orientation 45deg to the centreline of the fus. Keying of the metal to form a good bond. Any thoughts please?
 

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BBerson

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Actually it may be light gauge steel. The plane was built around 1917, well before WWII. Around this time there seemed to be a substantial reluctance in Europe to weld, despite the fact that welding was already often employed in the US.

.
That last photo looks like they welded the flattened tube ends. I had considered this also. It makes the tube fitting and welding much easier.
BB
 

Culleningus

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Sadly its not clear.
If it is welded these are spot welds (are there dimples in the flattened tube-ends?), as there looks to be no seam, just rusting of the plates wrapped around the longerons.
The brown rust suggests the plates were ordinary mild steel, but the tubes possibly might be something else.
Dave
 

Culleningus

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Hi yes thanks Jan. Defo rivetts. Not welded.

I found the walk around video which shows the wrap-around brackets are not just flat sheet but more like the battery connector on your car.
This is the J1 biplane like you say I think there was a monoplane.

Here (below) I have 3 different details of the J1 biplane, so take your pick.

This certainly was a heavy weight!


1)The plane was constructed from an aluminium alloy with a front fuselage made of 5 mm chrome-nickel sheet-steel. The metal components resulted in a strong aircraft that was heavy, slow and difficult to maneuver. The physical strength of the Junkers J.I provided substantial protection for the crew and engine against enemy ground-fire and eliminated the need for structural bracing wires to support the wings

2)Like all Junkers aircraft, the J-1 incorporated an all-metal structure. The wing was composed of 0.08-inch corrugated aluminum alloy skin riveted to an internal framework of aluminum alloy tubing.

3)There was a fairly gradual change-over from the use of wood to the use of metal from WWI onwards, though the Junkers J-1 monoplane (1910) was built entirely from metal (steel tubing & thin sheet iron coverings) while theFokker DR-1 triplane (1917) also used steel tubing for fuselage trussmembers.

Dave (Ignore my drawing its wrong!)
 

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jumpinjan

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No. They are riveted. All of those tube members are riveted to the junctures. The junctures are "steel" and are rolled (a complete 360 deg) & welded sheetmetal. The tubing is aluminum.
Also, be careful when referencing the Junkers models. That Junkers biplane in Ottawa CA, has a military designation J.I (roman numeral number 1). The Junkers factory designation for the J.I is the J4. The first all metal airplane, built by Junkers in 1915 was the J1, so these model desiginations can get confusing really quick.
Jan
 

jumpinjan

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Here's a better picture of the spar juncture. The J.I's fuselage was fabric covered, but the very later J.Is had the corrugated aluminum. The wing structure was a "space frame" and so the corrugation covering only added rigidity in the cord direction.
Your first picture posted is the framework of the Junkers D.I (or J9), which is the FIRST all-metal production fighter.
(I have done a lot of research on the Junkers metal working techniques as well as the D.I fighter)
Jan
tubes.JPG
 

Culleningus

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Yes its not all that straightforward. Domed tube ends to spread load, sufficient clearance between rivett holes etc.
This pic is interesting as your tubes are 'sawn off' (showing the wall thickness).
As I understand it, the a/c in the colour pics I have posted should really have the J4 nomeneclature, as you say the real J1 was the 1915 first all-metal monoplane (which think is what Ive got in my B&W pics).
This link below is the most revealing yet I have found of those attachments on the fus (better detail photos). Thanks for that cluster joint pic. The spaceframe wing structure allows the use of more of that sized tubing. I'm inclined to think it also dispenses with spar webs and the like therefore?
Yellow Junkers J.I
The tubing is aluminium alloy of some sort as I think Orion stated earlier in the thread. The 5mm sheet Chrome/Nickel plating up front on the fus must have been hugely heavy. Cant believe it was so thick!

Dave
 
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Culleningus

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More pics of this amazing machine.

Album:Junkers J.I

Designed by Hugo Junkers, the J.1 was the worlds first all-metal aircraft to go into mass production and proved very successful in its intended role as an observation and ground attack aircraft. The sheer strength of its structure and mass of load-bearing struts eliminated the need for bracing wires and the outer portions of the wings were not linked by interplane struts, affording the observer / gunner a clear field. The crew and engine were protected from ground fire with 5mm armour plate, all of which added to the considerable weight of the J.1, which suffered with relatively poor performance as a consequence. It was powered by a 200hp Benz BZ.IV inline engine and well over 200 of this innovative machine were put into service during 1918.

Junkers Fus Close-Up.jpg
 
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