Ralph Hooper follows up Roy Braybrook’s piece in NL.30, “Iconic Humour”…

Assuming that Roy’s memory is not at fault then Bob Copland had got things back to front.

In Stan (Digger) Fairey’s section circa 1948-50, during the original design of the P.1067 fuselage, work was progressing from the front towards the back. Initially you can only work with confidence on the front end. The centre and rear are dependent on aerodynamic loading on wings and tail surfaces and these are almost certainly still somewhat uncertain, whereas at the front you just bung 7 g on everything and you’ll be OK.

There were just eight people charged with the whole fuselage: Digger Fairey, Jack Simmonds, Teddy Compton, Jack Mills, Peter Jefferson, Bertie Tyrrell, Eric Pacey, and yours truly. Jack Mills was mainly doing engine installation, Bertie Tyrrell concentrated on flying control systems, and Eric Pacey was gradually working up a detailed large scale side view as various bits of equipment settled into position. That left five of us to do the structural work.
The Hunter Main Wing Spar Root
toptop toptoptop toptop top

Digger doled out the frames, longerons, stringers etc as he saw fit. Besides keeping an eye on the rest of us he occasionally contributed a drawing himself. You could always tell a Fairey drawing - it might have the occasional burnt hole in it, but it would certainly have semi-circular swaths where spilt pipe ash had been swept aside!

So, time passing, we worked our way back to the main wing spar frame and I felt flattered that this was allocated to me (up to then the most significant frame I had done was the nose undercarriage frame).

Digger himself undertook the structure to attach the fuselage frame to the wing main spar, it being assumed that the wing breakdown joint would be at the wing end rib.

Now, Digger had been a civil structural engineer working for the Gas Light and Coke Company before finding himself in the aircraft industry, and his solution now was entirely sound and simple. It consisted of two large triangular machined steel forgings, one upside-down relative to the other so that they were pinned together at their apex, with the other two corners of each attached respectively to the fuselage and the wing, thus clearing the intake duct which at this point protruded through the fuselage skinning. They became known as the ‘butterfly’ fittings but unlike that insect they were not light.

Five large pins completed the structure. The butterfly fittings survived the attentions of the Stress Office and any inputs from Harold Tuffen and Frank Cross, or from the works Experimental Department.

Now Digger’s section (at Canbury Park Road) was in the corner of the Experimental Drawing Office (EDO) opposite Mr Camm’s office; and there was a door. So we saw a lot of the Chief Designer. He accepted the butterfly fittings at first but when the weights people came up with their estimate he became critical.

Numerous meetings took place around Digger’s board with Chaplin, Rochefort, Weetman et al being involved. This went on for a week or more. Meanwhile the butterfly drawings were issued and forgings ordered. I never saw Mr Camm (or the later Sir Sydney) solve a problem, but he knew what he did not like, and he would not give up. He continued to grumble.

Eventually, to restore peace, and to my great astonishment, I was directed to seek a lighter alternative. Now, this could have been very embarrassing; I was being asked to ‘show up’ my section leader. But Digger was a super boss and he never showed any resentment. My respect for him increased accordingly.

Meanwhile the butterfly fittings were being manufactured and ‘faute de mieux’ they were built into the first two  P.1067s, WB188 and WB195.(I believe 188 still survives - perhaps someone would like to check its wing attachments? Ed. WB188 is in the Tangmere museum so please report to the Newsletter if you go there).

So, I drew an outline of the main spar, including its extension through the intake fairing, with the outline of the intake duct and fuselage side. So that’s the space available. Great, now fill it! Well, anyone who has seen a Hunter wing free of the fuselage will be familiar with the result; it is rather prominent.

I did my own stressing and weight estimates and it sailed through various approvals unchanged. I can’t now remember the percentage weight saving achieved; perhaps as much 25 or even 30%. It had reduced the number of lugs and pins from five to two and the shear-carrying material was now light alloy instead of steel.

Its simplicity was slightly spoiled by Bill Allan (‘Mister Fuel Systems’) coming along and saying that he needed to carry a fuel pipe through the thick web, so I made an impractical suggestion as to where he should put his fuel pipe! However, it was apparently impossible to get a pipe from the front tanks to the engine in any other way so it had to be accepted. It meant that, even before the Hunter had wing tanks, you had to break down the fuel system in order to remove the wings.

Not quite the end of the story. The ‘bent boom’ forgings were supplied by Firth Vickers. At Kingston these were clamped onto machining fixtures and reduced to final form. Fine - except that on being released from the fixtures there was a ‘sudden twang’ and the booms assumed a graceful curvature! There was much coming and going between the two companies before new heat treatment and machining sequences solved the problem.

Finally - the flanges of the original design tapered smoothly onto the fuselage side lugs. When it came to productionising the Experimental drawings the Production Drawing Office (PDO) was approached by the Works who sought an easement of the machining process whereby a small step, with a radiused root, was introduced at the lug. This was accepted and the Hunters poured forth in this form.

You’ve guessed? Eventually the Hunter fatigue test airframe went bang, with failure at the small step on the lower lug. (I believe Richard Cannon has preserved this lug!) So, all the World’s Hunters had to be inspected, some cracks were found, some wings were scrapped, some were recovered by grinding out the step. It is pleasing to record that Peter Jefferson, then risen to Production Director, accepted that they had been responsible for the problem (even though it was approved by ever-helpful Design!)

So, there we are, we had achieved the weight reduction that the Chief Designer sought, although it may have been more expensive than the butterfly fittings. But then, who had heard of cost in 1949?

From Digger’s section as I joined it, Jack Mills and I survive. So, hello Jack! - hope you are OK!   Ralph.

PS Since writing the above I have looked out all the photos I can find of WB188 in the hope of confirming its wing root structure. No luck. It remains possible that at some stage in its career it may have been refitted with the later design of wing root.