Steel in aircraft construction, 1935-45?

SaparotRob said:

I can't wait to drop Eutectiferous in conversation!

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Many years ago, I saw a car ad in which they claimed that their engine used a hypereutectic alloy.

Can any you engineering types out there name a hypereutectic alloy suitable for engine blocks?

MikeMeech said:

Hi
Aircraft designers and manufacturers had thought about and even built 'metal' aircraft from the early days of aviation. The merits of using 'steel' and/or 'aluminium' alloys had also been thought about. Here is Sydney Camm's view on the subject from his 'Aeroplane Construction - A Handbook on the various Methods and Details of Construction Employed in the Building of Aeroplanes' published in 1919 but written during WW1:
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Mike

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1919 is a bit early to discuss aluminium. Today, any aluminium alloy suitable for structure is either heat treated or work hardened. The high strength alloys suitable for aircraft structure are brittle and difficult to bend. The strongest alloy available is 7075-T6, which is solution heat treated then artificially aged. It was developed by the Japanese prior to WWII, and used in Mitsubishi A6M Zeros. Aluminium was in decent shape in the 1930s, leading into WWII.


I collect old books. This is from O'Rourke's General Engineering Handbook from 1932. Modern 6061-T6, very popular for machined parts, has a yield stress of around 40,000psi, and an ultimate stress of around 45,000psi. The high strength 7075-T6 is 73,000psi and 83,000psi respectively.

I understand that for the later Yaks the Soviets switched from wood spars to steel once the US began supplying them with quantities of a suitable alloy.

Of course Lockheed made steel drop tanks.

MIflyer said:

I understand that for the later Yaks the Soviets switched from wood spars to steel once the US began supplying them with quantities of a suitable alloy.

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The steel fuselage frame was originally used on the Yak aircraft and remained almost unchanged until the end of their production. Tubes made of 30KhGSA steel were manufactured in the USSR (e.g., in Pervoural'sk). It is a misconception that Soviet aircraft were made of wood—most of them were of mixed construction with a high proportion of metal. For example, the I-16.
The Soviets experimented extensively with steel as a structural material in the 1930s, creating a number of aircraft designs with a very high proportion of steel in the airframe (I have included a picture of one of these aircraft above).

And now for the most obvious fact. Armor parts accounted for more than 15% of the total weight of the Il-2 (957 +/- 20 kg).

re

Howard Gibson said:

Many years ago, I saw a car ad in which they claimed that their engine used a hypereutectic alloy.

Can any you engineering types out there name a hypereutectic alloy suitable for engine blocks?

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A319, A356, and A357 seem to be a common casting alloys for engine blocks in production vehicles (eg Toyota uses A319 and A356, while Ford uses A356 and A357). Cast A357 or machined from billet 6061 series seems to be popular for higher performance racing engine blocks. The above are all non-hypereutectic alloys.

A390 and NASA 398 are both hypereutectic alloys.

At room temperature the mechanical properties of A390 are superior to 319 and A356 alloys, and about equal to A357 and machined from billet 6061.

At room temperature NASA 398 is inferior to A390, A357, and 6061, but superior to A319 and A356.

(For those not familiar, the tensile strength, yield strength, and hardness of aluminum all decrease with rising temperatures.)

The tensile strengths of A357 and 6061 - for example - are rated at about 45 kpsi at room temperature, A319 and A356 are rated at about 34 kpsi, while A390 is rated at 43 kpsi and Nasa 398 is rated at 40 kpsi. At elevated temperatures (above about 300°F) NASA 398 starts becoming superior to the other alloys, gradually increasing in superiority until at 700°F its ultimate tensile strength is about 5x that of the other alloys (tensile strength of NASA 398 is still 16 kpsi whereas it is only 3 kpsi for the others.

A390 is sometimes used for cast pistons and heads, along with other parts that reach high temperatures, while NASA 398 is being used for some large cast pistons in maritime diesel engines.

I do not know if there is any particular reason to use hypereutectic alloys for an engine block, but A390 and NASA 398 are both easily castable, so it could be done easily enough.

I think.

Howard Gibson said:

1919 is a bit early to discuss aluminium. Today, any aluminium alloy suitable for structure is either heat treated or work hardened. The high strength alloys suitable for aircraft structure are brittle and difficult to bend. The strongest alloy available is 7075-T6, which is solution heat treated then artificially aged. It was developed by the Japanese prior to WWII, and used in Mitsubishi A6M Zeros. Aluminium was in decent shape in the 1930s, leading into WWII.

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I collect old books. This is from O'Rourke's General Engineering Handbook from 1932. Modern 6061-T6, very popular for machined parts, has a yield stress of around 40,000psi, and an ultimate stress of around 45,000psi. The high strength 7075-T6 is 73,000psi and 83,000psi respectively.

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Hi
I am not sure why "1919 is a bit early to discuss aluminium", it was already being used in aviation. For example the ill-fated Vickers 'Mayfly' airship of 1910 had a Duralumin structure as did many of the Zeppelins used during WW1. 'The Aviation Pocket-Book' of 1918, by R. Borlase Matthews, includes the following on 'Metals':


The late 1930s part work 'Aero Engineering' Volume 1 includes a chapter on 'Materials for Aircraft Construction' which has a table showing the 'Strength-Weight Ration' of materials used, which may be of interest:

Mike

A few notes by the Germans:
- bombers (not including the Ju 87*), as well as the Ju 52 are noted as having the aluminium (IOW light) alloys representing 50% of the empty equipped weight; the coversion to the greater steel usage was hoped to make that down to 35%
- fighters, like the Bf 109 and Fw 190, were with 36% of light alloys weight; conversion was hoped to bring that down to 235 for the 109, and, if the fully-steel wing is made for the 190, the % of light alloys can be brought down to just 12% of the empty equipped weight
- fighters might even be made completely from steel



* Ju 87 was at almost 50%

One of the changes from the Ju 252 to the 352 was the implementation of teh mixed construction vs. the light alloys predominant on the 352.
The switch towards steel was supposed to make a huge impact on the manhours requirement for an aircraft. They stipulated that, on just ten Si 204 aircraft, 11.2 tons of the light alloys can be saved with, presumably, implementation of steel where possible, and with that, 500 000 (!!) manhours.
(my guess is that the manhours saving came both from the easier manufacturing of iron/steel/etc, as well as the production of the aircraft itself)
The change from the Al to Fe was to supposed to cost 1 million of manhours - basically, by 20th A/C, the investment in manhours required to switch has paid off.
Weight increase was judged to be 2% for most of these conversions, with Fw 190 being at 3% if the steel wing is also included.

Germans hoped that they will be able to keep the aluminium alloy use for aircraft production same between the late 1942 (when the plans were dated) and early 1944, despite the plans to much increase the production of aircraft. They were also plans to reduce the % of light metals in the engine production, but these were much more modest, at least the ones for the time between the late 1942 and early 1944.

Light alloys were more than double the price than steel, ratio of 1.5 vs. 3.2 per ton of material I've seen mentioned;. Obviously, a lot more of sheets and other semi-finished products can be made from a ton of steel than from a ton of light alloys, further increasing the price difference between the two materials in aircraft building.
Arado was asking less money for an airframe for a heavy transport aircraft if it is made with 1200 kg of light alloys' semi-finished products per unit, vs. what they asked for a 30% lighter Ar 432 airframe that used 4265 kg of light alloys' semi-finished products per unit. Arado disagreed on the manhours required, though, the 'light alloyed' Ar 432 was supposed to require a lot less of manhours per a kg of airframe; their math does not include the savings amounted before the material is shipped to them.

tomo pauk said:

A few notes by the Germans...

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My problem with all this is that you don't build a steel airframe the way you build an aluminium one. You can build an aluminium space frame, but why would you? In World War II, monocoque frames were state of the art, in aluminium or wood. Steel sheet metal must be way thinner and/or way heavier. Thin sheet metal is weak in buckling. A space frame out of steel tube is light and functional, especially if you do not need absolute maximum performance out of the aircraft. Cover it in fabric, or in very lightweight (i.e., non structural) aluminium panels.


The nice thing about space frames is that you can get at all the stuff inside. Just make the panels removeable. This may be one of the things people liked about the Martin Baker MB5. The Fokker D.VIII frame above has nice thin steel tubes, and bracing wires by the looks of it. These aircraft crashed because the wooden wings came apart due to Fokker's crappy workmanship. Look at all the space in the fuselage behind the pilot for radios, radar controllers, beer coolers...

Crimea_River said:

Hawker Hurricane fuselage backbone was steel tubing

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I wonder if that resulted in corrosion on Sea Hurricanes.

MIflyer said:

Of course Lockheed made steel drop tanks.

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And many parts of the later P-38s themselves were made from steel - possibly/probably because it was easier to form the shape in steel than alloy as steel segments can be welded to create the whole.

For example the chin cowl on the later P-38s is steel and the same may apply to the earlier ones.

The Keystone BT-12 was spot welded stainless and therefore saved the weight of rivets and a spot welding machine could make dozens of spot welds in the time it takes to fit one rivet. Using spotwelds very close together also increases the strength of the joint whereas trying to fit 20 rivets per inch would create a tear along the dotted line structure so there are pros and cons to both sorts of structure. I expect that repairs on the Fleetwing would not be easy.

Regarding tubular frames I prefer the welded steel type usually used by the Americans. Fokker in some, maybe all, steel tube frame aircraft included diagonal wire bracing in some areas which results overall in a lower weight but complicates maintenance and probably makes them more prone to damage. Avro in Britain used the Fokker system in parts of the Anson.

The Hawker bolted steel tube frames with diagonal bracing wires and round tube rolled square or rectangular at joints is easy to repair in theory and does not require welding expertise but I detest it. There are several Hind and Hurricane pubs on this site that cover that.

The Vickers steel tube frames are just as bad. To me a solid welded frame is faster to build and easier to repair - even if it involves replacing a cluster like this which, naturally, on a welded frame does not need all the bracing wire attachments because it is far more rigid.

I am not qualified to comment upon the methods of joining steel tubes but there may be some insight into the choice of rolled or square fabricated tubes with bolted mechanical joints by Hawkers when I think of the issues found by the early Formula One welded space frame Lotus racing car space frames. Lotus made ones had a marked tendency to crack around the welded joints as the basic gas welding puddling of the joints caused cracking at the joint between the remelted weld and the unmelted solid tubing. The subcontracted customer racing space frames, of the same design, were lower temperature brazed by the sub contractor and these proved free of such cracking. The bronze brazing metal was stronger than the parent mild steel of the joints.

There may be also some clue in that the Hawker Hurricane was licenced and built in Yugoslavia and Belgium. So, once the capital cost of the forming machinery had been paid out, the assembled labour costs might be lower through needing skilled labour? The cost of making the forming machinery was a barrier to refurbishing historical Hurricanes until, IIRC, some old originals were found in South Africa.

Modern welding can easily form steel tube joints of reliable standard but mass production welding was with simple basic kit which was subject to air contamination unlike modern MIG and TIG welders. I have only practiced welding with a small arc welder myself and gas brazing with which I get a neater finish but harder work to clean off the hard flux residue.

yulzari said:

I am not qualified to comment upon the methods of joining steel tubes but there may be some insight into the choice of rolled or square fabricated tubes with bolted mechanical joints by Hawkers when I think of the issues found by the early Formula One welded space frame Lotus racing car space frames. Lotus made ones had a marked tendency to crack around the welded joints as the basic gas welding piddling of the joints caused cracking at the joint between the remelted weld and the unmelted solid tubing. The subcontracted customer racing space frames, of the same design, were lower temperature brazed by the sub contractor and these proved free of such cracking. The bronze brazing metal was stronger than the parent mild steel of the joints.

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Welding is sensitive to workmanship. The medium carbon chrome molybdenum steel is prone to hydrogen embrittlement. All aluminium extrusions and a lot of steel grades are heat treated, until you weld them. There is a lot to be said for screwing stuff together.

yulzari said:

I am not qualified to comment upon the methods of joining steel tubes but there may be some insight into the choice of rolled or square fabricated tubes with bolted mechanical joints by Hawkers when I think of the issues found by the early Formula One welded space frame Lotus racing car space frames. Lotus made ones had a marked tendency to crack around the welded joints as the basic gas welding piddling of the joints caused cracking at the joint between the remelted weld and the unmelted solid tubing. The subcontracted customer racing space frames, of the same design, were lower temperature brazed by the sub contractor and these proved free of such cracking. The bronze brazing metal was stronger than the parent mild steel of the joints.

There may be also some clue in that the Hawker Hurricane was licenced and built in Yugoslavia and Belgium. So, once the capital cost of the forming machinery had been paid out, the assembled labour costs might be lower through needing skilled labour? The cost of making the forming machinery was a barrier to refurbishing historical Hurricanes until, IIRC, some old originals were found in South Africa.

Modern welding can easily form steel tube joints of reliable standard but mass production welding was with simple basic kit which was subject to air contamination unlike common MIG and TIG welders. I have only practiced welding with a small arc welder myself and gas brazing with which I get a neater finish but harder work to clean off the hard flux residue.

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Hi
Looking at the technical publications of the period gives info on welding during the period, The 1937 edition of 'Metal Aircraft Construction' by M Langley, has details of tubular construction and the use of welding and other joint methods. Below extracts from the book relating to British firms and 'welding' for information on the subject:





This is a very useful book for information on aircraft construction using metals in the period before the outbreak of war.
Mike

yulzari said:

I am not qualified to comment upon the methods of joining steel tubes but there may be some insight into the choice of rolled or square fabricated tubes with bolted mechanical joints by Hawkers when I think of the issues found by the early Formula One welded space frame Lotus racing car space frames. Lotus made ones had a marked tendency to crack around the welded joints as the basic gas welding piddling of the joints caused cracking at the joint between the remelted weld and the unmelted solid tubing. The subcontracted customer racing space frames, of the same design, were lower temperature brazed by the sub contractor and these proved free of such cracking. The bronze brazing metal was stronger than the parent mild steel of the joints.

There may be also some clue in that the Hawker Hurricane was licenced and built in Yugoslavia and Belgium. So, once the capital cost of the forming machinery had been paid out, the assembled labour costs might be lower through needing skilled labour? The cost of making the forming machinery was a barrier to refurbishing historical Hurricanes until, IIRC, some old originals were found in South Africa.

Modern welding can easily form steel tube joints of reliable standard but mass production welding was with simple basic kit which was subject to air contamination unlike common MIG and TIG welders. I have only practiced welding with a small arc welder myself and gas brazing with which I get a neater finish but harder work to clean off the hard flux residue.

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Cracking of welded joints indicates a welder who is not properly trained in that type of welding.

One of the reasons Hawkers did not use welding was that their primary structural steel was classified as non weldable. These days modern techniques probably make it weldable but there are modern weldable steels with similar properties to the old T series steels and these would probably be a better material to use.

Welding in aviation, in most countries, is or was a specialised trade. These days many countries allow welders who are qualified in welding other critical structures like gas pipelines to weld aircraft parts.

Admiral Beez said:

I wonder if that resulted in corrosion on Sea Hurricanes.

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This is why things like paint and aircraft inspections exist. Aluminum is also subject to corrosion, especially around salt water.

Admiral Beez said:

I wonder if that resulted in corrosion on Sea Hurricanes.

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Hi
Aluminium Alloys used for aircraft construction can also be prone to corrosion when sea water is involved, which is why all metals have to be protected by various means to avoid/reduce the chance of it when at sea.

Mike

Hi
For those interested some more info on Tube welding, these extracts are from the 1940 edition of 'Materials of Aircraft Construction' by F T Hill, Chapter III 'Steel Tubing':



Plus details on materials used:


Mike

Admiral Beez said:

I wonder if that resulted in corrosion on Sea Hurricanes.

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The one and only Hurricane I worked on (in Canada) had all the tubular steel parts stove enameled so external corrosion was non existent. I do not know how the internals of those tubes was protected.

MiTasol said:

The one and only Hurricane I worked on (in Canada) had all the tubular steel parts stove enameled so external corrosion was non existent. I do not know how the internals of those tubes was protected.

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I suppose the life of a Sea Hurricane is measured in months, so it may not matter. HMS Indomitable, for example operated Sea Hurricanes in summer 1942 before switching to Seafires in 1943 and later Hellcats.