Bonus 50% More!

So I have sat in the corner and started to sniff through the Hind design to look for all the T50 within it. There are tailplane spar boom liners, mainplane spar boom liners, aileron spars, elevator torque tubes, mainplane bracing struts. I haven’t finished it all and there is 50% as much material in all of these as in the total fuselage tube requirement. The tailplane raking struts and interplane struts are also T50 but formed into streamline section, and these quantities haven’t been added in yet. So, on the back of the envelope T50 requirements for this biplane design may be 75% more than the previous quantities worked out for just the fuselage, meaning the tube run will be bigger.

I figure that in the monoplane designs there will be a lesser additional requirement the later the design goes, but it is surprising where T50 is found. The gut feel is that real requirements are 50% more than the original total. That’s OK, unless the size required is not already identified. I figure I will go to aerospace tube manufacturers in July 2015 with a definitive list of required dimensions, so if you are interested in a particular aeroplane design, let me know the sizes and gauges you might want, if they are not already on the list.

Last night I read ‘Daedalus’, the Halton Magazine, Christmas 1934,the rag put together for RAF Halton apprentices. It has the article, including “A Visit to Messrs. Hawker Aircraft Ltd” and out of this a a glistening pearl rolls out :

“On our second afternoon we had an hour’s quiet talk with a ‘stress merchant’, who informed us regarding more recent Air Ministry requirements in loading and strength calculations.

[I reckon this may be AP970 May 1935 ‘Design Requirements for Aeroplanes for the RAF’, based on verbatim extracts of the Handbook of Aeronautics published in 1934 by the Society of British Aircraft Constructors]

In his opinion the firm have a general reserve factor of safety of 1.1, that is to say, for example, where a front spar must be capable of standing 7.5 times normal loading, the firm makes it to stand 7.5 x 1.1 or 8.25 times normal loading.”

In AP970 May 1935 ‘Design Requirements for Aeroplanes for the RAF’ there are tube schedules which lay out performance factors for different lengths of tube at different gauges and outside dimensions. So within the Hind design the original manufacturer has incorporated an additional load reserve factor within the structure of 10%. So here is a little nugget to assist in the interpretation of the structural design, whichever tube path you follow.

My gut feel is that T45 metallurgy is at 110% of capacity if tested for T50 values and replaced like for like with the original T50 dimension, while T50 is, if the stress merchant from 1934 is believed, at 90% of its design capacity. Using T45 may not be a conservative position, viewed through the lens of historical Hawker practice. I ruminate on original aircraft still operating with original steel, that are, in good sense, operated conservatively. Without munitions, and with the original reserve factors incorporated in the design, all these factors add up to structures being only used at a fraction of their potential. All this good sense is subject to the opposing factors of corrosion, past, unknown loadings and heavy landings. I wonder if there is a more scientific way to maintain these structures as non destructive testing becomes increasingly sophisticated, faster and cheaper, like hand held ultrasonics that instantly output graphical displays that can show up cracking.

Today recreational fishers use side scan sonar which shows the eyeballs of fishes deep underwater- this digital technology becomes more and more sophisticated and cheaper every year. To an extent the use of original material in antique structures may be the conservative position for a number of decades in initial use, but in structures that may be seventy years old it may be a form of fanaticism. Anyone interested in historic aerostructures is a fanatic, so this is not a negative, but there are interesting tools out there to help defend the position. The truly conservative position is to use new metal. And cheaper. And more relaxing at 20,000 feet. To me it’s about learning how the designers thought, preserving this knowledge and using it to celebrate their achievements by keeping their products safely in the air.

I guess the fanatic part of me wants to unwind the conservative approach to what these structures are allowed to do. New metal with a 825% reserve factor should be allowed to dive bomb a cardboard cut out battleship and sink it in flames, as long as a sufficient number of carbon offsets are purchased.:p

At first I cooked my head over the question of DTD54a-BS88c wing spar material.
Then I boiled my brains over T2 tube.
Then I sizzled my synapses over T50 tube
Now I am almost afraid to raise the topic, but I have ignored,for health and safety, aluminium T4 tube….which is all kinda thin walled in pin jointed structures and scattered here and there, although Westland and Glosters seemed to like it back then.
Can anyone tell me if T4 is available today? What is the spec for modern aerospace aluminium tube ?

A Thesis in One Day

A Hawker Hind biplane has an all up weight of 5,217 lbs. Within its structure, it has 166 lineal feet of T50 tube. Using an ‘average’ tube member of 1 ¼-16 gauge to calculate the mass of the tube gives a weight of 135 lbs, or 2.5% of the total weight.

So if the structure used T45 with double the wall thickness of the original T50 this would only increase the weight by 2.5% or 135 lbs. Given the Hind was rated to carry a 500 lb bomb load then omitting the bomb load would assist in compensating for the additional weight in the tubular structure. The centre of gravity issues are more complex, but this argument supports the contention that it is not necessary to use the original T50, if T45 can be supplied to the same strength values as T50. Where this T45 is only commercially available in thicker walled tube, then the weight affect of being forced to use thicker walled tube is not difficult to resolve. This, in fact, is the only realistic approach today for dealing with pin jointed T50 structures.

The cost of this approach is in the engineering for material substitution. While T45 may be obtained with a mill certificate setting out adequate ultimate strength values, the substituting of a novel member for the original T50 requires an engineering analysis. Where there are many members of many different diameters and gauges, interacting within a whole design that also must accommodate centre of gravity issues, this engineering analysis must be detailed. The financial and time cost of this analysis is significant.

One budget conscious way of performing this analysis is to be overly conservative and over specify members, resulting in an airframe that is heavier than it needs to be and more restricted in the stresses it may be exposed to.

Performing this analysis in detail will result in a more elegant engineering and performance solution, but the high financial cost places this approach beyond the resources of most participants in historic aviation.

This analysis seeks to examine a path that leverages off the extensive engineering already invested in the original airframe by the original manufacturer, that was further resolved in testing and operational use to be recognized as safe. In this case the approach is based on using materials identical to those used by the original manufacturer. Specifically, to replace T50 with T50 in pin jointed structures.

A further aspect of this approach is to seek to better understand this original material choice, in terms of high strength, aeroelastic performance structures. In this case it is argued that 3% Nickel steel alloy T50 tubes demonstrate performance factors that exceed those of Chrome Moly steel alloy T45 tubes. Both tubes may be treated to the same ultimate strength, but T50 has a higher fatigue life.

So the benefits of this approach derive from lower engineering and time costs and better performance factors for a resultant T50 aerostructure. The assumption is that T50 may be provided at less net cost than the combined material and engineering costs of utilizing a T45 substitute aerostructure. This assumption needs to be tested.

In reviewing the T50 tubes used in four typical pin jointed structures, Hind, Gladiator, Hurricane and Typhoon, four tube sizes ( the 4 size group) constitute 80 -90% of each structure, in simple terms 80 – 90% of the engineering challenge.

In general, a commercial tube mill will seek larger quantities of tube orders for ease of operation and to develop cost efficiencies, generally a minimum run of 2000 pounds per tube size. In order to develop a commercial model, this analysis is based on the assumption of meeting the needs of 28 aero frames in the next 25 years. Where the four principal tube types will meet up to 90% of the engineering challenge, these are pursued in the model to the exclusion of outlying dimensions required in smaller quantities or differing metallurgy.

Strategies for fulfilling the smaller dimension/differing metallurgy demand are :

In the case of T2 and DTD 254 Nickel Chrome members, machining Nickel Chrome round bar to the finished dimension
Or
Providing a billet of Nickel Chrome steel to be run in conjunction with Chrome Moly steel in a standard tube run with the closest dimension to that finally required, then machining to finish or accommodating higher weight in these members.

In the case of T50 members of smaller dimension than the 4 size group, where tube squaring in pin jointed structures allows different diameters to be incorporated into the same joint, using larger T50 members from the 4 size group to substitute smaller T50 members and accommodating higher weight
Or
In the case of T50 members of larger dimension than the 4 size group, providing a billet of 3% Nickel steel to be run in conjunction with Chrome Moly steel in a standard tube run with the closest dimension to that finally required
Or
In the case of T50 members of larger dimension than the 4 size group, using T45 tested to T50 and accommodating higher weight.

In order to resolve a commercial mill run of the 4 size group, two considerations are accommodated :

1. In full pin jointed fuselage structures, the longest and most critical members in the fuselage are the continuous lengths running from behind the cockpit to the tail, generally 11 feet in length, and it is desirable in an engineering sense that these members are included in the 4 size group.
For Hind these are 1 ¼ – 20 gauge
For Gladiator these are 1 1/8 – 22 gauge
For Hurricane these are 1 3/8 -20 gauge and 1 ¼ – 20 gauge

2. Within the 4 size group , are a range of gauges. In order to aggregate the greatest quantity of a particular OD within a single gauge, the thickest gauge is chosen for each OD, to reduce the manufacturing task from 12 tube tooling sets to 4 tube tooling sets. This approach may be reviewed in respect of what tooling may already be available to a manufacturer to use.

[ATTACH=CONFIG]237495[/ATTACH]

By aggregating this volume the following tube runs emerge in commercial quantity, an aggregate of 1,454 lineal metres or 4,772 lineal feet.

[ATTACH=CONFIG]237496[/ATTACH]

By using an “average” tube of 1 ¼ – 16 gauge at 0.811 lbs per lineal foot the value of 3,870 lbs or 1,757 kgs is obtained.

To obtain a costing for this production, certain assumptions are applied to these figures. These assumptions must be tested in a commercial tender.

Assumption 1.
Suitable billets or blooms of aerospace grade vacuum furnace 3% Nickel steel alloy or Nickel Chromium steel alloy are obtained at USD30 per kg, being USD52,715 for 1,757 kg.
Assumption 2.
The cost of transforming this material into a cold drawn tube, including the cost of 4 tooling sets, is USD60 per kg, being USD105,430 for 1,757 kg.

This cost includes the cost of material losses, where a policy is pursued of retaining full
lengths of tube where ultrasonics detects flaws. In this case flaws are cut out but short lengths of accept tube are retained, where final requirements may only be 3 feet of tube.

Assumption 3. In this case it is aimed to have 90% utilization of the original billet material.

The combined cost of transformation is USD90 per kg or a USD158,145 funding requirement for 1,757 kg.

What may this cost to an individual subscriber ?

In the case of one Hind, using 61.45 kg of T50, the pro rata cost is USD5,531
In the case of one Gladiator, using 51.41kg of T50, the pro rata cost is USD4,627
In the case of one Hurricane, using 96.44kg of T50, the pro rata cost is USD 8,679
In the case of one Typhoon, using 63kg of T50, the pro rata cost is USD5,706

These costs are indicative for 80 – 90% of the steel tube requirement. Each aeroplane design has further tube costs for undersize and oversize tube not provided from the 4 size group and members made from T2/DTD254 and T4 aluminium.

Accepting error in any of the assumptions, and additional costs of engineering perculiar to individual designs, it may be prudent to reserve the figure of USD10,000 to provide for T50 fuselage tubing for an airworthy project.

In this case, in using T45 which must be proof tested, a significant portion of this USD10,000 allowance may be absorbed in purchasing T45. In addition, an investment must be made in re engineering the aero structure which may, in itself, cost far in excess of USD10,000.

Alternatively, subscribing to a T50 production run may absorb a significant portion of this UDS10,000 allowance, but the costs of re engineering up to 90% of the aero structure for material substitution are avoided. In addition, the benefit of enjoying fuller performance from the aero structure akin to its previous demonstrated history of safe use.

This approach is only as realistic as the willingness of unrelated parties to combine temporarily together to form a buying club for T50 tube. A failure to fully subscribe to a buying project can obviously frustrate the basic object. One way to formalize a buying club that provides prudent regulation and protection for members is in an entity called a Non Profit Incorporated Association, that exists to achieve defined aims, then ceases to exist.

These aims may include :

1. Co-ordinating an accurate quantity survey of T50 & T2/DTD254 tube requirements.

2. Issuing a tender for supply of T50 tube to aerospace certified tube mills.

3. Coordinating with National Aerospace Regulators to ensure that any T50 tube supplied by a certified tube mill is acceptable for use within each jurisdiction.

4. Contracting a certified engineer to perform a body of work on the substitution of say, T50 larger diameter for T50 smaller diameter, T45 for T50, machined Nickel Chrome bar or hollow for T2 and DTD254. Submitting this work to National Aerospace Regulators to assist in the timely evolution of individual projects and reduce the work of Authorities in examining the same question over myriad individual projects.

5. Coordinating the manufacture of suitable billet and tube material and final distribution to subscribers of finished tube product.

Such a process may take two years and incorporate 5 steps :

The first step is to obtain expressions of interest from any party that may wish to subscribe to a T50 production run under the buying club Association model.

The second step is to divide the quantity survey task amongst subscribers intimately familiar with particular designs, to fully identify tube requirements that may be hidden in spar liners, aileron spars, undercarriage members, wing drag struts etc

The third step is to issue an accurate tender from an Association to a range of mills to make tube supply cost assumptions accurate.

The fourth step is to engage with Regulators and Engineering resources to resolve certification and acceptance of tube and substitution solutions.

The fifth step is to make the tube.

🙂

After you collect the lottery

As for your idea about the concrete mould: I looked at using this about 15 years ago, and although it is a nice relic of the original production process, it is incomplete and not useable without extensive repair. This would only detract from its originality.

I’ve got all the necessary drawings to re-construct a Hornet from scratch, including the co-ordinates for the fuselage moulds. Throw enough money and time at it, and I could produce a wooden fuselage mould the same as Glyn Powell has done with the Mosquito in NZ.

The difference between the types though, is that enough parts and interest in the Mosquito exist to justify a potential investors input – there is not for the Hornet.

The fact that the concrete formers exist makes your project far more realistic than if you had to loft from scratch and make wooden formers. I understand a significant issue with timber formers is shrinkage/movement of the timber, apart from the lofting task. Far easier to fix a stable concrete form. I respect your attitude to the formers as relics in themselves : I would be more aggressive and offer to reface them before they crumble, and in the meantime run off a few fuselages… One option if you wanted to retain the formers in their current condition is to cast a polyurethane female around them; with lots of release agent, their appearance would not change. The poly would shrink a certain percent, meaning a new concrete male poured in the poly female may would be oversize in the wet, but will shrink itself. Some experimentation may result in a faithful copy. All easy to say, but lots of work. But the fact that concrete formers do exist is astonishing, and makes your dream, forgive me, far more concrete.

I know a bit about Mosquito timber construction, but wasn’t the Hornet (and Vampire) a mix of timber and aluminium, in the sense that the aluminium formed the stressed surface and the timber the spacer between surfaces ? Do you need to press aluminium into shape before a fit over the former/sandwich ?

Aren’t the engines the issue ? How many engines could you rustle up ? Rumour of one in Oz….

Get a Hornet going in Reno and I’m sure you will get some orders for a few more…..

In what I have read of Wrightons they shut in 1979 in the face of competition from West German furniture manufacturers who were outputting products of the same high quality. Germans infected with the spirit of rebuilding their nation. Customers were not opting for something far cheaper, just a little more affordable and of the same high standard. I associate the 1970’s with a period of malaise in British manufacturing, a crisis of spirit, the last hurrah of a proud tradition drifting into oblivion. Here in Australia the odd surviving Wolseley and Austin and Leyland surprise today in the same way as a duck billed dinosaur ambling down the street; once the only thing, now curiosities that astonish twenty year olds by their rheumy persistence. A car today is a German thing or an Asian thing, it is surprising to think of a British car.

I do enjoy engineering books from the 1930’s. I do enjoy books that show the bridge over the Firth of Forth and Schneider Trophy winners and the Golden Arrow. Plenty of spirit. Those formers rotting away have thousands of man hours of engineering in them. I would re face them, coax them back into life, blow the ember into flame. A Hornet made on original Hornet formers, now that’s a story !

ID prop

While I was trying to figure this out I was poking and prodding all sorts of props and dug out this thing which is supposedly from a Walrus-Seagull amphibian. It looks like a four bladed wind generator prop, but I have never seen a windmill generator like it anywhere. It has a 1940 production date stamped on it and the following codes :

Drawing No D29908/
2986
Dec/40

I would be grateful if anybody can positively ID it.

[ATTACH=CONFIG]237448[/ATTACH]

[ATTACH=CONFIG]237449[/ATTACH]

The forger’s panto

In order to stop thinking about this I needed to take it to the bitter end. So off to Rod’s Junk Emporium to look at a pantograph. The nearest thing to hand was a box of pick axe heads, so one became a RH tractor forging blank with text marks denoting the leading edge and one became a LH tractor blank. This old pantograph was good for copying banknotes onto printing plates Rod said, but I wasn’t buying the sales pitch, because we have moved to polymer notes. Maybe Spitfire fuel gauge dial faces, or Dambuster signatures, but not my preferred line of work.

Anyway, with this particular shape, it looked like I could turn the pick axe head 180 degrees and copy a leading edge from RH to LH tractor.

[ATTACH=CONFIG]237443[/ATTACH] [ATTACH=CONFIG]237444[/ATTACH]

But doing this to a rusty pick axe head didn’t mean it could be done to a prop forging blank… time to go bother someone who would really know, the pattern maker.