Just to close this off in case anybody looks at this in 2035 :

1. After looking through boxes of historical Release Notes used in the construction of Australian GAF (English Electric) Canberras from the 50’s, it is evident that great volumes of paperwork, identified by a Release Note number, were retained for each removable structure in the Canberra. It is surprising that these Release Notes remain for RAAF Canberras, as it is reasonable to assume a Constructor or Service would dispose of these once an airframe was obsolete. They take up a lot of room and serve no commercial purpose. A number of boxes of these are, however, to be found in the Archives of ANAM Moorabbin in Australia. For the sake of resolving the Hawker question, the keeping of Release Notes for removable/replaceable structures such as fins, rudders, ailerons AND fuselage is hypothesised to be British Constructor practice.

2. After looking at numerous historic photographs of prewar Hawker biplanes, where sufficient resolution exists, 41Hxxxx numbers are painted on the underside of all removable upper and lower wings and elevators and on the starboard side of rudder, fin and fuselage near the cockpit. It is hypothesised that the 41Hxxxx number is the Release Note number.

3. This hypothesis is supported by the finding of small dataplates on the remains upper and lower wings, elevators, fins, rudders, displaying the 41Hxxxx numbers, example pictured below. Data plates show Release Note and relevant drawing and Issue number, consistent with traceability. These plates have been identified on Hawker biplane remains in the UK, NZ and Australia. Where up to 11 individual, removable structures may be provided on each biplane, all with 41H Release Note numbers, a production run of 2,851 biplanes would require 31,361 Release Note numbers, in between other Hawker products. An Australian Demon Scarff ring exists which shows a 41Hxxx dataplate fixed to the Scarff ring, so there may be more numbers generated. This scale of number helps to reconcile the larger Fuselage dataplate numbering sequences, where sequential numbers are allocated from a Release Note register, but two biplanes built side by side during the same period may have up to 22 numbers of difference on a Fuselage dataplate. In general, a sequential Release Note register would issue numbers or blocks of numbers roughly aligning with blocks of Production. In general a Mk I Hurricane Release Note may be 41H100xxx, a 1935 Hind is 41H56xxx and a 1930 Hart might be 41H18xxx.

4. Within this Release Note system, a Hawker biplane identity may be defined by a list of 11 Release Note numbers, or for simplicity, a Master Release Note number for fuselage, being the Constructor’s Number, repeated in paint on starboard side fabric near the pilot’s position, and on the brass larger dataplate fixed on the portside under the instrument panel, in case of fire.

5. The Hawker Drawing Office handbook, in dealing with the allocation of drawing numbers, rules that a Drawing Number Register be kept, where numbers are allocated ‘first in, best dressed.’ No blocks of drawing numbers are reserved for particular aircraft. Australian Demons were retrofitted as trainers after 1936, with Australian Demon remains showing 1935 some parts as A56xxx while later retrofitted trainer parts show A91xxx, beginning to fall within Henley and Hurricane part numbering blocks, supporting this sequential allocation of drawing numbers. It is hypothesised that Release Note numbers followed the same rule, as it is simple and functional.

6. In order to confirm these theories, the finding of original Hawker Release Notes, and the matching of these to a high resolution, starboard photograph of a Hawker biplane displaying painted 41H numbers would be required. Alternatively a Production Office Book detailing Release Note number allocation practice in the period 1929-1939.

7. High resolution images of Hawker biplanes manufactured for the Persian government show the same Farsi script painted in the positions of 41H Release Note numbers. In this case, for a limited production run, Hawkers seems to have adopted a Release Note system where each elevator, rudder, aileron, wing and fuselage is numbered with the same Persian Service Number, for simplicity. For modern restorations of Hawker biplanes used in some foreign services, marking these components with foreign service numbers appears to be historically accurate.

8. For Australian Demons, based on high resolution images, 41H numbers within a ‘band’ of numbers appears to be historically accurate. A remnant fin, remanufactured by 2 Aircraft Depot in Sydney, has its own 2AD Release Note number in place of the usual 41H number. A remnant Avro Cadet fin, serviced by Clyde Engineering in Sydney, has a painted CECxxx (Clyde Engineering Company) in place of the usual 41H number on a Demon fin. This supports the hypothesis that 41H numbers are Release Note numbers, a system adopted by RAAF 2AD and CEC for traceability.

9. To match a Service identity, with a removable component Release Note Dataplate in remains, would require the finding of an original Service Logbook, detailing a Service number and Release Note numbers listed as being incorporated within that airframe. In Australia, original Service logbooks for a range of WW2 Service Aircraft have been found, which detail the identity of removable components. It is hypothesised that this is British practice, which would have extended to Hawker aircraft, but no Australian Demon airframe logbooks have been sighted to date to support this.

10. No-one will really know, unless they are 130 years old.

Coming together….

I am still here in this padded room. I do sessions with handheld XRF on various remains and as more questions are answered, more new ones appear.

The Mond Nickel company of Canada had 90% of the world’s supply in 1939, and as Re-Armament and the US Military machine expanded, Nickel became a scarce material indeed. Even the US was forced to create National Emergency low nickel compositions, like NE8630. Just the need for stainless steel exhausts on aero engines was a critical application that drew on limited supply. Strangely enough wartime Allied examination of Japanese aero engines showed no under salting of nickel alloys. Probably the only other source of Nickel in the world at that time was New Caledonia, where the French administration chose to go with the Free French after 1940, and the US occupied as a priority of after 1941, on the way to Guadalcanal, ultimately giving us the musical ‘South Pacific’.

All this time I have been staring at Nickel as the key alloy focus, but now my eyes drift down to the more humble manganese. The problem is that NO 1930’s Hawker biplane T50 tube remains seem to have enough Manganese in them to meet the chemistry laid out in the original historical material standards. This is a scandal ! The mills were under salting the manganese in 1935 ! I can’t believe it ! In the 1930’s there should be 1.7% Mn but I am consistently getting 0.4% Mn from known Hind and Australian Demon remains. This is a big difference in specification. In other words, these tubes would fail the T50 standard of the day. They would also fail the later 2T50 standard, which has a later concession to go down to 1.2% Mn.

I have to go back and re-test later UK and Canadian Hurricane T50 tube remains check the Mn. In 1935, alloys were generally over salted and the pressures of later wartime scarcity where not in force – what could be going on ? Less alloy would make a tube material cheaper to constitute. Less Mn would make a softer tube, in other words more cold drawing with less annealing – cheaper and faster to make. I can understand why a tube mill would be attracted.

Now I am starting to realize that all the pin jointed tube structures I have been looking at are Hawker designs – Hart biplanes, Hurricanes etc. This is not so much a T50 issue as a Hawker Tube issue. Surely Hawker QC would pick up a significant difference in chemistry, even with the time consuming chemical testing methods of the day. Surely no mill would dare to pull the wool over the eyes over it’s major customer ? Surely there would have had to be a conversation about ‘making tube cheaper to buy’. But this must have been balanced with either no compromise on performance, or better performance….

Much of this relates to the function of manganese within an alloy. It has a role in purifying iron, ‘allowing’ more mechanical performance. But if you were using the finest Swedish ore, would you need all the manganese? Now if you had less manganese you would have more ductility, more capacity to work harden if you wished to manipulate the tube. This is what brings me back to Hawkers. ALL the business ends of Hawker tubes were squared. The pin jointed structure is constructed around a work hardened square portion of a round tube. This portion is mechanically different to the unmolested round portion. So maybe Hawkers REQUESTED low Mn T50, to accomodate tube end squaring, where excessive hardening around the pin joint could lead to premature failure…The issue of work hardening had an initial focus around streamline tube, as a known phenomenon around shaping round tube.

After the War, “Reynolds 531”, basically manganese alloy T45, became the bees knees for bicycle racing frames. The big trick was to stretch tube so that the middle section became thinner than the ends, but work harden to develop a desired mechanical strength. I have talked to an old racer who saw many frames badly bent, but never cracked. I wonder how much aeronautical knowledge from the 1930’s passed into the working of Reynolds 531. I will have to put the XRF onto this material to see if it was low Mn.

Another 1935 Hawkers works method was oven baking in black enamel, at 170 degrees C, for a number of hours, square ended tubes, to stress relieve. There was a lot of thought put into the material and the design method.

Things orbit around my mind like loose electrons : Hawker Australian Demons were crashed and repaired time after time after time – surely a testament to a carefully resolved and applied materials technique. Were low Mn, higher ductility T50 tubes part of the magic?

The problem is that modern T50 tubes, made to the approved recipe of T50 or 2T50 would have ‘too much’ Mn, in comparison to known Hawker remains.
The ideal thing to find is a bit of original ‘Hawkers’ T50 that is not corroded, has never been stressed within an airframe, and MEASURE what it’s actual mechanical attributes are, as distinct from the published mechanical attributes of ‘Standard T50.’

For clarification, commercially available modern 4T50 or T45 is chrome -moly, a different material.

Probably the only way any scientific conclusion could be arrived at is to cast a test rod of “Hawker Low Mn T50” and “Standard T50” and do some real life mechanical testing.

Why bother ? I understand that later on, during WW2, material performance was compromised due to scarcity and the reality of a ‘short and brutish’ aircraft life. XRF reveals some great material selection crimes in WW2 aircraft structures. Who knows how much was flak or an in flight structural failure ? I guess today we may want a restored aero structure to last 100 years, so the most highly resolved material selections can facilitate this.

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