well ............ all things naval in one boat?

Preparations continue: Navy’s smallest ship paves way for maiden voyage of its largest

caught a news clip on BBC Scotland where the proud shipyard worker was showing the mis-alignment between the carrier sections. The 2 sections were marked with a chalk reference line and it was "only a few millimeters out". Looked more like at least 3cm, possible more to me. If we are 'proud' of that margin of error (I realise the percentage is small given the scale of the vessel) - isn't that a worrying attitude? I cannot imagine that would be acceptable in a German shipyard?

British shipyards are where they are today because of that sort of thing............

Before starting on a critique of British engineering, I think one would need to know what's the best accuracy achieved elsewhere.

HH, a broad, sweeping generalisation there. Please could you provide the evidence to support that statement? Or do you know little about such things, yet felt the need to pull the proverbial pin and throw a hand grenade of "bolleux" into the discussion anyway?

Having spoken to ex Harland & Wolf employees who worked there back in the day the engineering mismatches were horrific. When two large sections of ships hull or superstructure were offered up together they were out by considerable margins, the solution large chains and powerful winches to bend the two sections to fit and then a welding team would go in and weld the thing together. That was SOP perhaps 30 yrs ago not sure about today.

I had the pleasure of visiting Scotstoun some years ago with a group including aviation engineers. The practice described was pretty much the SOP for matching ship sections together. Its difficult to avoid noticing it as the sections are held in place for welding by what look like substantial telegraph poles braced against the floor. The shipyard escorts were asked about this and they said that the practice had been in use forever and our worries about building stresses into the structure were not causing any issues in practice during the ships' life. From memory (not very reliable these days, I admit) up to a foot mismatch was readily capable of correction.

As an aside, one of our number (an Engineering Director) asked why there were so few drawings scattered around assembly areas. Apparently as soon as they can get access to the basic structure, a few trusted employees go in with drawings and mark locations of major items with chalk on the floors, ceilings, walls and bulkheads. The fitters then come along afterwards and fit the ship out using the chalk marks. This seems extremely odd to anyone with an aerospace background but it works.

I've no idea whether other nation's shipyards have better ways of avoiding a mismatch in the first place but if anyone here knows how, I'm sure the shipbuilding industry would appreciate the advice.

EAP

Further to the comment(s) above about the quality of British shipbuilding, there was documentary following the building of one of the US Navy's Arleigh Burke class destroyers, the shipyard was the Bath Iron Works, in Maine. During the programme two large sections of hull were offered up together and when the 'marriage' was complete there was a considerable gap/mis-match between the two sections, low and behold, large brackets were welded to the sections and substantial winches, chains etc were used to 'finesse' the sections together for final welding. So, despite the sneery comment about British shipbuilding, it seems it's not just British shipyards that employ brute force when required...

-RP

I did hear (about 40 years ago), that a Trident (airliner!) under construction for the Chinese had a bit of a problem when it was discovered that sub-assemblies didn't fit...

The reason being that they were for different marks of Trident...

Probably an urban myth, but who knows?

Hope these few snippets might inform some readers - apologies for boring those who already know this.

It would be an understandable assumption that aircraft structures are manufactured to exacting tolerances and built with precision to ensure that they fly properly. However, I can say with some confidence that in some areas of the UK aviation industry, this was most definitely not the case.

Just one example (there are others) was the Hawk 'production' assembly operation at Kingston and Dunsfold. I put production in commas because, in truth, the operation was often more like one huge experimental shop rather than assembling aircraft in a prosecution manner. It was fairly common to see standard car jacks being used to 'ease' (that was the term used, 'ease') the lugs connecting wings to fuselages into alignment so that the bolts could be pushed (or more normally hammered) through.

The Hawk aft fuselages were also things of variable beauty. When the job was moved to Warton as part of the T-45 programme, new jigging methods were designed - we found that the drawings had been 'adjusted' to cope with problems experienced at Hamble in getting the port and starboard sides to line up - the result was a 50 thou difference between two supposedly symmetric longerons. Hamble's old fashioned build methods were the reason behind the well known problems in moving Hawk upper fuselage panels and canopies between aircraft.

I am sure that many people contributing to PPrune could join in with tales of how badly many UK military airframes were built, and the problems that caused out on the front line. Tornado was no exception, either.

Let me say that these comments aren't meant to criticise the BAE design teams, especially Hawkers, who were sheer geniuses in developing good, affordable aircraft that also sold overseas. But our 'design for manufacture' skills were way behind those used in the US, and the quality of work on the shop floor was sometimes well below what you might have expected.

BAE had to improve, got better with Typhoon and the lines at Salmesbury for F-35 are up there with anything else in the world. But it wasn't alway that way.

Best regards as ever to all those working the lines,

Engines

well we're only building two carriers so they're essentialy bespoke anyway I guess................

As a shipbuilder, tolerances of a couple of inches or less when joining unit butts are pretty good and right up there with the other European yards - even the boxheads. Particularly when you consider that that tolerance represents about 1000th of the length of the block.

Welding puts an incredible amount of heat and stress into a structure, which is why most blocks of that size have a small amount of "green" (ie excess plate) at each end. You tend to find that the last couple of feet of sections are only tack welded so that the final alignment can be made easily. The impact - usually a few hundred manhours when a frigate will take between 2 and 3 million manhours, a carrier perhaps an order of magnitude above that.

Shipbuilder welded structure can be millimetres out. One of the Resolution class Polaris boats had a bulkhead in the torpedo stowage compartment that was inches out of position. With one European submarine builder, we had to explain our equipment interface drawings to them as they'd never seen anything like it before. "What do all these dimensions in boxes mean?".

That's fascinating Engines.
Here I was thinking that air-frames were a thing of Swiss-Watch precision, otherwise they'd lose structural integrity.
Had always thought that they were a bit like origami in aluminium, strength deriving from careful shaping, uniform torquing of fastenings etc.
By contrast - I remember the chap who rebuilt the Mossie fuse in Auckland telling me that it was possible to achieve very high degrees of accuracy in wood, which I always thought was pretty amazing considering you were lofting from drawings by hand, and wrapping wet ply and balsa around concrete moulds.

Every Concorde in the BA fleet required a bespoke set of tank liners during the post crash mod programme.

BAe were caught out by the non similarity of the Nimrod fuselage to wing joints during the MRA4 saga.
It is all hardly surprising as until recently the techniques used for building large aircraft would have been familiar to a 1940s shipbuilder.
Engineering fitters work to the nearest thou, carpenters to the nearest eighth and dockyards work to the nearest ship!
N

Engines. The only misaligned Tornado I know of was one that got back after an A to A, that was bent alright and was somewhat "high drag" with a left intake full of, er, Tornado!!

Had a F3 hybrid that leaked quite a lot if left out in the snow f8000 break point connectors found with a nice meniscus of water on their backing rings once @ Sola.

Certainty knew of a F4 that would meander gently if it was clean. Of course the answer was to keep it in the Q sheds as much as possible !!

Packard v. RR-built Merline Engines
 

This may be an apocryphal tale but I heard that the US built Merlin engines were built to much finer tolerances than the UK-built counterparts.


Is there any truth in this? Do current warbird operators have a preferred engine to mount in their prized Spitfire/Hurricane/Mustang?


MB

Engineers at Packard soon discovered that Rolls-Royce did not design the Merlin for mass-production. The manufacturing tolerances were much looser than Packard’s standards. This was because Rolls-Royce had never implemented mass-production techniques to their assembly lines. Rather, they employed highly-trained “fitters” to assemble the engines. The fitters filed or otherwise massaged individual parts to achieve a precise fit. They even tightened critical bolts by trained feel, rather than with calibrated torque wrenches. In effect, each Rolls-Royce-manufactured Merlin was a hand-built engine that reflected the company’s traditions of premium quality and craftsmanship.

While Rolls-Royce’s manufacturing techniques churned out very high quality engines, they simply didn’t jibe with Packard’s way of doing things (or Ford in Manchester for that matter). In his book “Not Much of An Engineer”, Rolls-Royce engineer Sir Stanley Hooker recalls his introduction to the matter with Ford:

“One day their Chief Engineer appeared in Lovesey’s office, which I was then sharing, and said, ‘You know, we can’t make the Merlin to these drawings.’
I replied loftily, ‘I suppose that is because the drawing tolerances are too difficult for you, and you can’t achieve the accuracy.’
‘On the contrary’ he replied, ‘the tolerances are far too wide for us.’ We make motor cars far more accurately than this. Every part on our car engines has to be interchangeable with the same part on any other engine, and hence all parts have to be made with extreme accuracy, far closer than you use. That is the only way we can achieve mass-production.’”

LINK

Even today, most aircraft fuselage structures have their fastener holes match machined at assembly. This makes the structural parts non-interchangeable. The reason for match machining the fastener holes is to ensure a perfectly aligned and precise fit of all the shear fasteners.