Make it Happen

A divergence into T50 tubing from S88c sheet material for strip steel construction comes from a nagging feeling that this issue cannot be treated in isolation to strip steel construction; that 3% Nickel alloy tube was as much a part of the school of design thought as the Nickel Chrome roll formed steel strip in the spars. Today’s SAE 4130 tube comes from an entirely different school of design thought

There may be a middle ground in SAE 8630.

So here we have the tiniest, hopeful thread that may make pin jointed tube structures easier to restore in the future. If the original engineering allowed 8630, and it is weldable, you MAY be able to convince a mill to run commercial quantities of 8630 tube for absorption in the larger automotive racing market, allowing sub economic quantities to be diverted into pin jointed aircraft structures, while dealing with certification on the basis of a history of safe use.

Now that the T50 elephant in the room has trodden on my toe I have not been able to put it back in its box. Apart from the unique Bulldog, there is no other 1925 – 35 aircraft made entirely from roll formed strip steel. There was Boulton Paul roll formed tube, but its most significant commercial application was in Airship R101, and that is never going to be rebuilt. The principal application of strip steel construction was in aircraft spars. However the principal mass of these aircraft was T50 3% Nickel tube used in the fuselage, so the two materials, BS S88c and T50 Nickel tube, are joined in the Siamese fashion. The art cannot progress until the issue of T50 tube is progressed.

T50 is no longer available because it was obsolete once the last Hurricane or Typhoon rolled off the assembly lines. It characterised pin jointed tube construction from 1925 to 1945. It was not a weldable material because its alloy composition did not allow it to be successfully welded. It was a high strength material that was also highly elastic, which is the principal difference with SAE 4130. You may heat treat 4130 to achieve the strength values of old style T50 but at a cost to elasticity, as 4130 becomes excessively hard. It is said that T45 manganese alloy tube could be tested to achieve T50 strength values, and I believe it, but not the same elasticity.

So what does this mean ? Think of the bow and arrow. The bow needs to be made of a strong material, so it does not break when it is drawn back. The further it is drawn back, the more potential energy it stores for sudden release. If you have a strong, elastic airframe, it can absorb more energy as it is flung about the sky, without breaking. It’s almost like the fine, pliable, strong bones of a bird’s wing…

You can rebuild a WW1 flyer because you can get spruce and birch ply. You can rebuild a WW2 aluminium monocoque flyer because you can get alclad sheet. But you can’t really rebuild a T50 based fuselage unless you rely on carefully found 80 year old material or patches of 4130 that limit performance factors. Nobody is ever going to commission a run of T50 because the key attribute of pin joint construction was the ability to insert tubes of different diameters and wall thicknesses between each pin joint, according to the local stress requirements. Thus a Hurricane or Hawker Demon fuselage is composed of many, many different diameters and gauges of tube, not one simple tube dimension. A tube maker must tool up and economically run a tube dimension in thousands of metres of production, and you may only want 3 feet of a particular type.

I thought SAE 8630 might be a way to resolve this, but after consulting the tube schedules for Demons and Hurricanes there are so many different permutations of tube dimension that even this now seems too commercially difficult to address. Cue wailing and gnashing of teeth.

So let’s go back to basics and start from what we know and perhaps find a way to what we want.

1. Hawker Aircraft Ltd were not the only users of the pin jointed technique but found a formula through the Hart biplane family of being the fundamental suppliers of service aircraft in the 1930s. The pin joint fuselage technique relied on T50 alloy steel tube with 3.75% Nickel matched with wing spars using DTD 54a/Bs88c Nickel Chrome steel alloy roll formed strip steel. These material choices are common to Bristol Bulldog, Westland Wapiti and other types of the era. By virtue of the technique transferring to the Hawker Hurricane design and ultimately Typhoon and Tempest, T50 3.75% Nickel tube persisted as a characteristic material of these designs.

2. T50 tube was generally incorporated in a formula of large diameter and thin wall. Tube for welding, characterised by steel manganese alloy T45, was characterised by smaller diameter and thicker wall to allow weld purchase. Welded steel fuselages were evolved by Fokker and this school of design found favour in Avro aircraft, British licensee of Fokker designs and in the United States. In the US, SAE 4130 was an alloy that found application in weldable tube and US aircraft designs evolved using this technique rather than British pin jointed techniques. The scale of US industry and the uptake of welded tube designs in the aircraft and later automotive/racing industry saw the development of scale 4130 tube supply, while the demand for T50 declined as Hawker Aircraft, the last scale users of the material, exited from Typhoon/Tempest production. SAE 4130 can attain the same strength values as T50 3.75% Nickel alloy tubes, but not the same elasticity.

3. Using SAE 4130 in T50 designs is possible, with curbs that err on the conservative on original performance factors. Either the material is not hardened/heat treated to high strength values, to retain some elasticity, but more material must be added for strength, ie, tubes with thicker walls. In this case the weight of the airframe will increase. This may be deemed irrelevant as munitions/weapons systems are no longer carried in an airframe, but extensive and costly re-engineering is required. Alternatively thinner walled material is heat treated for higher strength values with the compromise in increased hardness, placing limitations on the stresses an airframe may be subject to, and again necessitating extensive and costly engineering. Unfortunately SAE 4130 tube is not supplied in the ultra thin wall thicknesses that T50 was supplied in. You may find the right OD, but not the right ID. A 4130 fuselage must always be heavier. You can’t bore it out, because you are taking strength away. The only way to avoid this is to use T50 material, but available stocks, whether within an airframe for restoration or salvaged from other airframes, are,at a minimum, seventy years old, subject to corrosion and service stresses that require careful testing and examination prior to use. Fully intact airframes are a rare commodity. Wouldn’t it just be easier to use new T50, like new birch ply or alclad ?!

4. Hawker pin jointed construction anticipated new alloys as an intrinsic advantage of the design approach. Thus in 1930 a fuselage could be composed of some T45 steel, lots of T50 steel and some T4 aluminium. It is not a design sin to therefore use titanium tube in a pin jointed structure, as much as sticklers for historical integrity will wail and pull their hair. So the hypothesis that CCF used SAE 8630 in CCF Hurricanes bears on this flexibility in the design philosophy, and the modern day allows for examination of other contemporary aerospace materials to see if they can provide the same performance factors. So far 4130, from an utterly different design philosophy, has established that is can be used with reservation, but what else is out there ? One modern application of thin walled, cold drawn tube is for the hydraulic ‘shiny’ used in high pressure hydraulic rams from excavators to forktrucks to aircraft landing gear. This would require a detailed sifting though myriad suppliers of commercially available tube and an equally detailed process of certification. You may end up matching 40% of all requirements through this method, or via other applications of high strength, modern cold drawn tube.

5. A major philanthropic effort to commission a conventional mill run of 20 permutations of T50 tube may be a circuit breaker, but this would cost a lot of money and leave much underutilised material after twenty or so fuselages have been serviced. Where would such money be better spent on historic aviation, if the ambit of such generosity is limited to this field only? Building a number of structures to house other historical aircraft rotting in the rain ? Keeping unique, intact aircraft like Vulcans and Comet Racers and Lancasters flying ? Ultimately such an event would require the engineering profession to admit a more elegant solution is beyond its wit. The original structures were the product of engineers grappling with a scarcity of funds, management and shareholder tolerance and the comforting blanket of applying proven technologies. It would be sweeter to take on some risk and try and turn pencil shavings into T50 tube.

6. Really we just need to make new T50 tube for Hawker, and other less known, extinct, pin joint, designs. Not one type, but a range of diameters. All tube types follow the same principle of diameter to wall thickness but the later monoplane types have larger diameters in comparison to the earlier biplane designs. All T50 tubes range from 3/4 inch to 2 inch diameter, a fairly small range. There is another key realization : all tube lengths are generally short, perhaps 2-3 feet in length. The only qualification is in the single length used in the tail section, from the rear of the cockpit to the tail. ALL pinjointed designs have a continuous length of tube in this section, generally no longer than 10 feet. So the manufacturing task is to make T50 tube in a tight diameter range in lengths no longer than 11 feet. Simple.

Here is the Hawker Typhoon fuselage and the Hawker Hurricane fuselage, with the key 10 foot length of continuous tube highlighted between the jaws of the calipers. Of course the hybrid pin joint monocoque structure of the Typhoon and Tempest requires only shorter lengths, but these are generally of the largest diameter.

[ATTACH=CONFIG]236133[/ATTACH]

Here is the Hawker Demon biplane fuselage, identical in principal to the later Hurricane.

[ATTACH=CONFIG]236134[/ATTACH]

Here is the forgotten Hawker Henley fuselage, illustrating the wonderful flexibility of the pin jointed technique to arrive at utterly different aircraft types from the same Meccano mix of components. To change the shape, change the length of the tubes. To increase the strength of the structure, use thicker walled or larger diameter tube.

[ATTACH=CONFIG]236135[/ATTACH]

Here is the Gloster Gladiator, after 1935 Glosters were owned by Hawker Aircraft, and utilised Hawker techniques and materials, even though they were old hands at pin jointed tubular fuselages. The key dimension is the single length of continuous tube in the tail section, 126 inches or 11 feet. This characteristic of pin jointed structures is common across designs from the Bristol Bulldog to Hawker Hurricanes, defining the maximum length of tube required. It is not necessary to run thousands of feet of T50 material, just 11 foot lengths.

[ATTACH=CONFIG]236136[/ATTACH]

Now we need to put our minds to a process that can run 11 foot lengths of T50 tube.

Let her go

4. Upon setting of calculator wind the clockwork arm anti clockwise to the start position. The Air Force understands that your aircraft may be subject to turbulence and musketry from the ground. Do your best. Remove the panel allowing you to sight the ground and take aim. The course setting bomb sight is equipped with a foam rubber eyepiece but the Air Force accepts no liability for eye injuries sustained in squinting through the sight. In generality the effect of bombs dropping within 100 yards of the target is sufficient for Police Action.

[ATTACH=CONFIG]236128[/ATTACH]

Smartly lift the release toggle on the bottom centre of the panel to allow the clockwork arm to rotate clockwise and make contact with the electrical striations of the calculator.

[ATTACH=CONFIG]236129[/ATTACH]

Tally Ho !
In an emergency, when you need to immediately jettison all bombs, you may depress the short circuit arm on the upper portion of the panel. Doing so above Headquarters will result in you being subject to Air Force disciplinary action.

[ATTACH=CONFIG]236130[/ATTACH]

Step by Step

Ed,
There’s no better description than that given in AP1095 dated 1935. I’ve copied the relevant paragraphs from a PDF I have into a Word document, but at 1.1Mb it’s too big to attach. If you PM me your email address I’ll send it.
Andy

Compliments of AndyY herewith step by step instructions for the operation of the bombing system on a 1935 Hawker Australian Demon. I think that any well rounded individual ought to know how to hop into a one of these fine aircraft or its contemporary Hind in case it is necessary to straddle some recalcitrants in Waziristan.

[ATTACH=CONFIG]236115[/ATTACH]

Step 1 : Enter into the pilots cockpit. On the upper centre of the panel is the bomb system master switch. Activate this in flight by a prompt and resolute flick.

[ATTACH=CONFIG]236116[/ATTACH]

To the left of the Master Switch is the Pilots Jettison release. It is not the pilot’s task to release bombs, but the Air Gunner/Bomb Aimer in the aft seat. However, if the Air Gunner is incapacitated, or, for the safety of your aircraft you need to jettison bombs, you may do so using this switch.

[ATTACH=CONFIG]236117[/ATTACH]

Lift the safety cover on the switch and press the globe smartly to release bombs.

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It is a shame to go all that way and release bombs without some attempt to straddle the yelling tribesmen. You may use the pilot’s remote release, holding the control column in your right hand, the release button in your left and looking over the side.

[ATTACH=CONFIG]236119[/ATTACH]

Test pieces

Attached are images of very useful material for metallurgical testing that would not otherwise be practical for any other use. These pieces of Hurricane fuselage were purchased on ebay, and while this is not a particularly scientific source, the information around the description is credible and the pieces themselves, after measurement, agree with the tube schedule dimensions for Hurricane I. Additionally, a remnant piece of stainless steel pin joint fishplate is consistent with the Hawker construction technique, featuring tube spacers, S80 hollow rivet ferrules and hollow rivets. A small included remnant of an aluminium instrument case includes a 1939 production date and the aircraft was reported to be shot down in 1940.
I do not have details of the excavation of this material, which would provide a lineal record.

[ATTACH=CONFIG]236040[/ATTACH]

[ATTACH=CONFIG]236041[/ATTACH]

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One thing I would also love to get for metallurgical testing is a postage stamp piece of stainless steel (DTD 42H) from the longitudinal tubes of Airship L101, which crashed in France. From time to time a framed display comes up on ebay, but someone pays top dollar for bits of spoons and buttons and no doubt historic interest, but I just want a tiny chunk of the stainless !!

The Hurricane pieces themselves are 1 3/8 OD X 17 G T50 tube that should be 3.75% Nickel alloy tube, different from weldable T45 Manganese tube used in Avro airframes and ubiquitously for engine mounts. In matching these dimensions to the Hurricane I tube schedule, these could only come from the engine mount or cockpit area. It was reported the aircraft dove into the ground, so these may be from the cockpit area. Of interest is the remnant coating of stove pipe black enamel, overlaid by silver dope. I understand the standard finish was black stove pipe enamel for the tubes, but it seems as if the whole structure was overlayed with silver.

A divergence into T50 tubing from S88c sheet material for strip steel construction comes from a nagging feeling that this issue cannot be treated in isolation to strip steel construction; that 3% Nickel alloy tube was as much a part of the school of design thought as the Nickel Chrome roll formed steel strip in the spars. Today’s SAE 4130 tube comes from an entirely different school of design thought, the welded tube Fokker school. As Sir Winston Churchill described Ghandhi as a “half naked Fakir” so strip steel/pinjointed construction described Anton as a “mad Fokker.” These materials and their application in contending schools of design thought never met then and probably should not now.

There may be a middle ground in SAE 8630. It would be good to get samples of Canadian Hurricane tube to see if it was made from 8630, which is SAE 4130 with a bit of Nickel and a bit of Chromium. 8630 was weldable but also took on some of the attributes of fine grain structure that 3% Nickel T50 pin jointed tube boasted. The US aero industry switched from 4130 to 8630 in 1940 as a War Emergency Standard. Why would you make 4130 more expensive by adding alloys if it was already ‘good enough’. The hunch is that it was halfway between British T50 and Fokker 4130, the “best for the boys” and Canada would have relied on North American material rather than import scarce material from the UK to support CCF Hurricane production.

So here we have the tiniest, hopeful thread that may make pin jointed tube structures easier to restore in the future. If the original engineering allowed 8630, and it is weldable, you MAY be able to convince a mill to run commercial quantities of 8630 tube for absorption in the larger automotive racing market, allowing sub economic quantities to be diverted into pin jointed aircraft structures, while dealing with certification on the basis of a history of safe use.

So bring in those bits of CCF Hurricane for testing. Even better, who has the metallurgical information on CCF Hurricane structures and materials ?

Wow

Evenin P&P and all,

starting these old aero engines by hand is not difficult, as seen here,

https://www.youtube.com/watch?v=Ihb8_STa3GE&list=PLDRCGAMcnKEgf4AV_Cm0lEC4vXsQEoz8f&index=1

The Lion starting handle takes 12 revs to 1 crankshaft and the engine usually starts after about 8 or 9 rotations, I don’t remember the sprocket ratio I used but it must be about 4 to 1, it seems the starter mag must be turning fast enough at that.

Andy

How good is that ! Thank you for sharing the starting info and video. Seems like these ratios were the ‘accepted wisdom.’ Looks like BTH SC12 magnetos so the trailing contact for the starter magneto on the rotor, 30 odd degrees, would be the same. When does the Lion fire BTDC ?

Now you have to build a Supermarine Schneider Trophy Racer…..

The Skysport Bulldog group made a rolling machine and rolled out pieces for the rear fuselage which for some strange reason dissapeared. Two different tubes were made. A 180^ and a 270/90^ tube. The early Bulldog tubes (as well as spar) were riveted together (on the longitudinal flange) and later had the edge folded over with the occasional rivet at a junction. In the case of the fuselage ‘tubes’, they were not round shaped, but ever so slightly egg shaped. Very smart. Very strong for that little bit of extra forming. The metal used in the rebuild was not the original call out. In the immortal words of Tim, ‘not even God has enough money to make this thing fly’. Thus the original premise was to make a flying machine, but money got in the way. I do understand that Guy Black’s group has made original steel (from Switzerland) for his Hawker series. We are talking mill run. Normal man translation: if you ask, you can not afford.

Ed, thank you for illuminating some of the achievements and tribulations of the Skysport rebuild. I wish you had a PA who could also help share some of the extraordinary stuff you are doing with your Bulldog. Go find some young aero tragic who can do some facebooking for you ! Part of the pleasure of the whole thing is showing what CAN be done without being ultra rich. I am fairly confident that you may have started rich, but your Bulldog has fixed that up for you now !

Money certainly helps, but not if it becomes an agent of discouragement to others interested in a subject. Hiram Maxim had money and built an aeroplane. The Wright Bros had no money and built an aeroplane. One of them worked ! I would certainly encourage anybody to look into steel strip construction, because it is under represented, and while the construction techniques were remarkable in 1930, they are unremarkable today and certainly within the capacity of any industrial community capable of making house guttering or a folding clothesline.

[/QUOTE] The U.S. Navy did a lot of testing with the material used in the Bulldog, and was not terribly impressed. This could very easily have been “not made here” syndrome. [/QUOTE]

I have found one US reference to the use of “British type high tensile strip steel” in a Curtiss flying boat, with a discouraging commentary on the difficulty material spring back posed for the builders. The key attribute of this material was its strength and elasticity, so spring back would have been discouraging for unsupported users. Certainly US steel was absent from the promotion of this technique in contrast to the integration of the UK steel industry with UK aircraft firms. It seems the US was more enamoured of Fokker type welded tube construction, which may have offered more volume sales.

[/QUOTE]Interesting comment about not being able to use 4130 today.[/QUOTE]

I wish I could ! Assuming the identical structure, going 1:1 on weight, I might end up with a hardened, brittle structure that would be prone to crack when manipulated through some of the strip rolled geometry. Or I could go for a softer, more flexible structure at double the weight. I may be entirely wrong and am happy to debate the point over a bottle of wine, or two.

[/QUOTE] This leads to the question of what size (and weight penalty) would you use today, and if you had period steel, would anyone pay the extra million quid for that satisfaction under the fabric and paint. Which is more important seeing the machine fly or know that it is 100% original? Knowing the acceptable substitute for todays rebuilds IS worth knowing, so yes Ed2, you are doing us a great service. Keep up the good work. Ed1[/QUOTE]

In trying to understand the period steel it has exposed me to schools of design thought and metallurgical alleys of excursion that I would have no reason to wander down otherwise. The further I wander in the less fearful it all becomes. I do think it is more and more possible. This does not subtract from the usual challenge of building any structure. There are plenty of kit builds and IKEA furniture that come in their totality but never get built. Finding the material ain’t the problem. Money ain’t the problem. If you can do what you have already done, nothing is impossible !