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BAE SYSTEMS Nimrod MRA.4

DWG

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WRT was it FBW or not? It was being developed by the Rochester FBW team, mostly ex F-14 guys IIRC. By this time we'd done add-on FBW systems for F-14 and A-6, so the process was pretty well understood. I wasn't involved, busy doing Typhoon and other things, but good friends were. I can't recall whether it used a variant of the F-14 box, or the Typhoon box, but I'd certainly call it an FBW system, even if I can understand the distinction people are trying to draw.
 

PMN1

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Posts raise 3 history issues, 2 mischieviously by CJG whose Nimrod's Genesis covers much.
Q1. Why did UK choose a 4xengined type in 1965? A1: to rule out the NBMR.2 winner, Avro-involved Breguet Atlantic. There were 49 NBMRs: UK took none.
USN too rejected Atlantic for a 4some. Their "need" for reliable power on long overwater sorties was risible: USN/RAF/FN et al flew Lockheed P2V Neptune wet and wide; longest WW2 endurance-type was Catalina. Atlantic happily served R.Neth.AF/Antilles, France/Caribbean/Nouméa.

Interesting question on the two engines and taking the Neptune, could that be more a case of 'beggers can't be choosers' and 'that's what's available with the funding'?
 

Zoo Tycoon

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WRT was it FBW or not? It was being developed by the Rochester FBW team, mostly ex F-14 guys IIRC. By this time we'd done add-on FBW systems for F-14 and A-6, so the process was pretty well understood. I wasn't involved, busy doing Typhoon and other things, but good friends were. I can't recall whether it used a variant of the F-14 box, or the Typhoon box, but I'd certainly call it an FBW system, even if I can understand the distinction people are trying to draw.
A stick bolted to push rods, cables, pulleys, bell cranks and servodyns is not fly by wire. Boeing 737 max is not certified as a fly by wire control system because they bodged on an MCAS.

Fly by wire is whereby a stick producing several electrical outputs which goes into several computers, running software, as samples multiple sensors, which process the inputs and supply a conditioned output down electrical wires running in race ways, the servo electrical actuators that move the control surface. MRA 4 had none of these.

I give up
 
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DWG

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I give up

Ultimately the significant part of fly-by-wire isn't how we crank the control surfaces from place to place, which has always relied to some degree on physical gears, cranks and so on. The significant bit is the decoupling of the direct link between pilot and control surface, inserting an FCS between them which can work out the difference between what the pilot wants to do, and what the surfaces should be doing based on the current aerodynamics of the aircraft in order to achieve that without falling out of the sky, or Dutch-rolling all over the place.

And that's what the Nimrod system was there to do.
 

Zoo Tycoon

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I give up
Ultimately the significant part of fly-by-wire isn't how we crank the control surfaces from place to place, which has always relied to some degree on physical gears, cranks and so on. The significant bit is the decoupling of the direct link between pilot and control surface, inserting an FCS between them which can work out the difference between what the pilot wants to do, and what the surfaces should be doing based on the current aerodynamics of the aircraft in order to achieve that without falling out of the sky, or Dutch-rolling all over the place.

And that's what the Nimrod system was there to do.
There was never a “decoupling of the direct link” on MRA 4. It could only be flown in direct law.

Fitting a yaw damper on say Jaguar to stop it Dutch rolling didn’t make it fly by wire.
 
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DWG

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I give up

Ultimately the significant part of fly-by-wire isn't how we crank the control surfaces from place to place, which has always relied to some degree on physical gears, cranks and so on. The significant bit is the decoupling of the direct link between pilot and control surface, inserting an FCS between them which can work out the difference between what the pilot wants to do, and what the surfaces should be doing based on the current aerodynamics of the aircraft in order to achieve that without falling out of the sky, or Dutch-rolling all over the place.

And that's what the Nimrod system was there to do.
There was never a “decoupling if the direct link” on MRA 4. It could be flown in direct law.

Fitting a yaw damper on say Jaguar didn’t make it fly by wire.
[/QUOTE]

Most FBW aircraft have direct law as a reversionary mode. But when the system isn't in reversionary mode, the FCS sits between pilot and controls and decides what they really want to do. And that's true whether you're only controlling one surface, or all of them. I fully understand the difference between a Stability Augmentation System and a full flight control system, but the technology is identical and the same team that did the Typhoon FCS, the 777 PFCS and F-14's drop-in replacement DFCS also developed the MRA.4 SAS.
 

alertken

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CJG #80. Dunno, but I can help you. There's a bloke publishes rather good monographs, who's brewing an RAF companion to Admiralty & Heli, which might offer you food for Pumas.

My own feeble story is of my bright idea to assign 2 Buccaneer S.1 front ends to Redifon Air Trainers for RN S.2 sims. I was presented with a higher bill to cobble and grind, than Brough's to supply 2 new bare shells.

Boeing does use LEGO. HKG had an overrun 747F, nosegear collapsed into lower 41. HAECO's price to cobble and splint a splendid sheet metal repair was > a Boeing team on site, replacing with a new (Convair-built) lower 41. After the Dan-Air Lusaka 707 tail loss there was a mod on the cast-iron cross-bar joining vertical: horizontal stab. HKG bought from Boeing such a new-build lump, then ran 24 swaps, thus reducing airframe downtime. No prob. Try doing that on, well, anyone else's prime load-bearing structure. Agriculture can be good in aviation, too.
 
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Zoo Tycoon

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So let’s kill one of the common myths around MR4;- at original Nimrod build, the wing to fuselage joins where made without jigs.

Please find below pictures of one part of the wing to fuselage alignment jig. I’m not completely sure if the picture shows Comet or Nimrod, but as I’ve said before Nimrod has its own tooling set which was in principle the same.

This jig was a two piece affair which could be assembled together. One part was then used to align the fuselage pick up and the other the wing. Only the wing part is shown in these pictures, it’s the triangular tube structure over the top of the wing and wing centre box alone.

In 65 HSA claimed that every single Nimrod wing was interchangeable with every fuselage. The figures I saw in the 96 measurement survey suggested this claim was probably correct given a little bit of shimming and hole reaming. 91D0D14F-0422-439A-927A-3199438FAFB9.jpeg 5C117CB8-23BB-4A19-8B36-8CABF28BF909.jpeg
 
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DWG

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Maybe this will help readers understand the difference between an SAS and an FBW .


By the definitions detailed in the attached link, MRA 4 was not FBW.

That's a pretty basic history lesson on the evolution of flight control systems from a basic SAS to a full authority DFCS, it's not a definition of how we do add-on stability augmentation systems nowadays.

And let's be clear, at no point have I claimed the entire aircraft is FBW, merely that the SAS is functionally an FBW system, because that's what we build.
 

CJGibson

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Zootycoon - where did this no-jig myth first appear?

Chris
 

Mike Pryce

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Zootycoon - where did this no-jig myth first appear?

Chris
And why was it not rebutted at the time? It's a pretty damning allegation, and is repeated even by those involved. At Woodford people giving me photos said ' here it is, the actual moment', and they were on it.

Earlier this week I talked to the engineer given the task of sorting out the 28 deficiencies identified in early 2002. He just snorted when I asked him if this wing thing was true. Some interesting comments on the handling and SAS though. Lots of Harrier knowledge used in the fixes.
 

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The info originated In 2002, April I think, when BAe Systems put out a press release targeted at their share holders claiming three things;-
1 - the wings wouldn’t fit on production A/C *
2 - the wings would have to be redesigned prior to entering service due to a structural issue
3. - despite these difficulties the first MRA4 would fly by the end of the year.

All three were nonsense (today it would be called Fake News), unsupported by the National Audit Office review which are a matter of public record and in my opinion a fair assessment.

* at this time I think they had completed three join up without any significant issues.

To understand the reason for the press release you need the background on how the original MRA4 fixed price contact worked, the position BAe Systems was in with regards to it share holders after announcing the biggest loss in their history, various movements of project responsibilities within BAe Systems and what was going on with the MRA4 follow on production contract with the MOD.

At this point, you should be asking, how was it that in 1996 a fixed price contact was placed for 21 aeroplanes, only for a follow on contact to be placed in late 2002 for only 9 production A/C + 3 flight test A/C conversions?

So Harrier are you really expecting anyone to believe that a picture of a persons face with a caption as undisputed proof that a jig aligned fuselage didn’t fit to a jig aligned (CNC manufactures) wing?
 
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CJGibson

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Am I being thick here? (Shut it, Pryce) The myth was (apparently) that the wings were fitted without a jig. Your answer (Items 1-3) doesn't mention jigs at all, basically saying the wing fit issues are bolleaux (as I already knew). So how do items 1-3 translate into the no-jig myth?

If all was rosy in the MRA.4 garden, why were they grounded and gas-axed with indecent haste?

Chris
 

Mike Pryce

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The info originated In 2002, April I think, when BAe Systems put out a press release targeted at their share holders claiming three things;-
1 - the wings wouldn’t fit on production A/C *
2 - the wings would have to be redesigned prior to entering service due to a structural issue
3. - despite these difficulties the first MRA4 would fly by the end of the year.

All three were nonsense (today it would be called Fake News), unsupported by the National Audit Office review which are a matter of public record and in my opinion a fair assessment.

* at this time I think they had completed three join up without any significant issues.

To understand the reason for the press release you need the background on how the original MRA4 fixed price contact worked, the position BAe Systems was in with regards to it share holders after announcing the biggest loss in their history, various movements of project responsibilities within BAe Systems and what was going on with the MRA4 follow on production contract with the MOD.

At this point, you should be asking, how was it that in 1996 a fixed price contact was placed for 21 aeroplanes, only for a follow on contact to be placed in late 2002 for only 9 production A/C + 3 flight test A/C conversions?

So Harrier are you really expecting anyone to believe that a picture of a persons face with a caption as undisputed proof that a jig aligned fuselage didn’t fit to a jig aligned (CNC manufactures) wing?
The version I was told was that the wings were digitally designed based on measurements taken from a Comet airframe that was used in early Nimrod development, found on the fire dump at Farnborough! That part always stretched credulity.

These super fine tolerance wings were then offered up to actual Nimrods which may have been jig built but had been bent in service. Even the original build had, I was told, a four inch tolerance (across what was never said. Fuselage? Wing root?).

The pictures I was given, hundreds on a CD, were mostly of the wing/fuselage join. The old ones coming off look tired, the new ones are shiny and machined. But no picture shows a big glaring gap. The pictures of people I was asked not to show at work as they identify people and that one in particular, up a step ladder, has a look of 'blimey'. I was told this was 'the moment', but my own selfies often look dreadful when I feel sunny inside!

Without documents to back things up I seldom trust talk alone, but your mention of the press release explains why all the talk lined up in this case. But very little evidence for the myth exists, although governance issues seem to be raised by it.
 

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January 2001 and the wings not fitting are mentioned here:


Hard to believe an article quoting senior BAE execs would say such a thing if it was nonsense, or that BAE would not respond to say so if that was the case.

Also, if the press release mentioned above really did say it, and it was untrue, then BAE would have lied to shareholders. Hard to see that happening, or not being discovered. It would be a very serious matter.

EDIT: from BAE Annual Report 2002 - "The first flight of the Nimrod MRA4 aircraft has been delayed as a result of design issues identified late in the year. Modifications occurred late in the build and equipping of the development aircraft, resulting in significant impact to the overall programme. A substantial increase in the overall cost of completion of the development, testing and initial manufacturing work has subsequently been evaluated. " (p.10) https://www.marketscreener.com/BAE-SYSTEMS-75568/pdf/8944/BAE Systems_Annual-Report.pdf

2nd Edit: https://www.telegraph.co.uk/news/uk...ng-the-Nimrod-but-now-the-wings-dont-fit.html As before, if not true, a company on the ropes at the time, as BAE was, with famously combative execs (I interviewed Mike Turner and 'abrasive' is a term others have used that I will not demur from), would surely have come back fighting at such a slur, surely?
 
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Zoo Tycoon

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Am I being thick here? (Shut it, Pryce) The myth was (apparently) that the wings were fitted without a jig. Your answer (Items 1-3) doesn't mention jigs at all, basically saying the wing fit issues are bolleaux (as I already knew). So how do items 1-3 translate into the no-jig myth?

If all was rosy in the MRA.4 garden, why were they grounded and gas-axed with indecent haste?

Chris
The myth originated from the first bullet point of the press release. BAe Systems just said there was a big unforeseen issue. All the armchair experts/keyboard idiots filled in the rest with whatever fantasy they could dream up.... original built without jigs, CNC matched to holes drilled to chalk marks, fire dump measurement or 4 inch frame pitch tolerances.

Unforeseen issues (Force Majeure) was the key mechanism in the 1996 fixed price contract for converting PA4 to 21 into delivery delays. You see, the fixed price contract only mandated the delivery of just three aircraft and the rest were negotiable. (Note the steady decline in the total to be delivered between 96-02) In 2002 the whole thing came to a head, because there was no money to continue. A deal was done whereby BAe Systems took a degree of the liability, I.e the big loss, but was awarded a follow on contract for the production aircraft, now just nine of em, plus the a few prototype conversions to operational aircraft. It was therefore essential to make everyone aware of the Force Majeure that justified this arrangement. The real reasons behind the slip up at that time were a collection/build up of more mundane dysfunctional management issues as I’ve mentioned before;- at this time, key components were just not being delivered to support the build which was all firmly within BAe Systems sphere of influence.
 
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Mike Pryce

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Am I being thick here? (Shut it, Pryce) The myth was (apparently) that the wings were fitted without a jig. Your answer (Items 1-3) doesn't mention jigs at all, basically saying the wing fit issues are bolleaux (as I already knew). So how do items 1-3 translate into the no-jig myth?

If all was rosy in the MRA.4 garden, why were they grounded and gas-axed with indecent haste?

Chris
The myth originated from the first bullet point of the press release. BAe Systems just said there was a big unforeseen issue. All the armchair experts/keyboard idiots filled in the rest with whatever fantasy they could dream up.... original built without jigs, CNC matched to holes drilled to chalk marks, fire dump measurement or 4 inch frame pitch tolerances.

Unforeseen issues (Force Majeure) was the key mechanism in the 1996 fixed price contract for converting PA4 to 21 into delivery delays. You see the fixed price contract only mandated the delivery of just three aircraft and the rest were negotiable. (Note the steady decline in the total to be delivered between 96-02) In 2002 the whole thing came to a head, because there was no money to continue. A deal was done whereby BAe Systems took a degree of the liability, I.e the big loss, but was awarded a follow on contract for the production aircraft, now just nine of em, plus the a few prototype conversions to operational aircraft. It was therefore essential to make everyone aware of the Force Majeure that justified this arrangement. The real reasons behind the slip up at that time were a collection/build up of more mundane dysfunctional management issues as I’ve mentioned before;- at this time, key components were just not being delivered to support the build which was all firmly within BAe Systems sphere of influence.
"Armchair experts/keyboard idiots". One of the RAF desk officers told me that they knew about the Nimrods being a different size, but BAE had never asked.
 

galgot

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Am I being thick here? (Shut it, Pryce) The myth was (apparently) that the wings were fitted without a jig. Your answer (Items 1-3) doesn't mention jigs at all, basically saying the wing fit issues are bolleaux (as I already knew). So how do items 1-3 translate into the no-jig myth?

If all was rosy in the MRA.4 garden, why were they grounded and gas-axed with indecent haste?

Chris
The myth originated from the first bullet point of the press release. BAe Systems just said there was a big unforeseen issue. All the armchair experts/keyboard idiots filled in the rest with whatever fantasy they could dream up.... original built without jigs, CNC matched to holes drilled to chalk marks, fire dump measurement or 4 inch frame pitch tolerances.

Unforeseen issues (Force Majeure) was the key mechanism in the 1996 fixed price contract for converting PA4 to 21 into delivery delays. You see the fixed price contract only mandated the delivery of just three aircraft and the rest were negotiable. (Note the steady decline in the total to be delivered between 96-02) In 2002 the whole thing came to a head, because there was no money to continue. A deal was done whereby BAe Systems took a degree of the liability, I.e the big loss, but was awarded a follow on contract for the production aircraft, now just nine of em, plus the a few prototype conversions to operational aircraft. It was therefore essential to make everyone aware of the Force Majeure that justified this arrangement. The real reasons behind the slip up at that time were a collection/build up of more mundane dysfunctional management issues as I’ve mentioned before;- at this time, key components were just not being delivered to support the build which was all firmly within BAe Systems sphere of influence.

Sorry, I'm trying to understand here (not good in english…)…
What you're saying is that BAe blew up that "wing not fitting" problem to get a revision of the original fixed price contract, which they knew would be at loss for them ?
 

Zoo Tycoon

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Am I being thick here? (Shut it, Pryce) The myth was (apparently) that the wings were fitted without a jig. Your answer (Items 1-3) doesn't mention jigs at all, basically saying the wing fit issues are bolleaux (as I already knew). So how do items 1-3 translate into the no-jig myth?

If all was rosy in the MRA.4 garden, why were they grounded and gas-axed with indecent haste?

Chris
The myth originated from the first bullet point of the press release. BAe Systems just said there was a big unforeseen issue. All the armchair experts/keyboard idiots filled in the rest with whatever fantasy they could dream up.... original built without jigs, CNC matched to holes drilled to chalk marks, fire dump measurement or 4 inch frame pitch tolerances.

Unforeseen issues (Force Majeure) was the key mechanism in the 1996 fixed price contract for converting PA4 to 21 into delivery delays. You see the fixed price contract only mandated the delivery of just three aircraft and the rest were negotiable. (Note the steady decline in the total to be delivered between 96-02) In 2002 the whole thing came to a head, because there was no money to continue. A deal was done whereby BAe Systems took a degree of the liability, I.e the big loss, but was awarded a follow on contract for the production aircraft, now just nine of em, plus the a few prototype conversions to operational aircraft. It was therefore essential to make everyone aware of the Force Majeure that justified this arrangement. The real reasons behind the slip up at that time were a collection/build up of more mundane dysfunctional management issues as I’ve mentioned before;- at this time, key components were just not being delivered to support the build which was all firmly within BAe Systems sphere of influence.
"Armchair experts/keyboard idiots". One of the RAF desk officers told me that they knew about the Nimrods being a different size, but BAE had never asked.
One of the RAF officers I worked with caused a load problems when he insisted that there was an in built safety feature on one system on MR2 which we had deleted on MRA4. After spending quite a bit of time in the Chadderton archive I was able to prove the original MR2 had no such protection system. He went white when the penny dropped because he had banked on that protection a few times.

Don’t get me wrong, they were decent, intelligent skilled maintenance people, but they lacked the deep knowledge you gain when you have design something from scratch.

As I’ve said now numerous times, we measured the airframes in 1996/97;- we didn’t need to ask. I personally attended the part of the measurements exercise at Hurn. You’re RAF officer like many others is just repeating hearsay. Not to be too disingenuous to him, again as I’ve said before, the front and rear upswept portion of the fuselage had very wide tolerances. This alone resulted in inches of difference between the smallest and largest fuselage lengths. Which when embellished a little turns into a 4 inch frame position tolerance on each frame.
 
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Zoo Tycoon

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Am I being thick here? (Shut it, Pryce) The myth was (apparently) that the wings were fitted without a jig. Your answer (Items 1-3) doesn't mention jigs at all, basically saying the wing fit issues are bolleaux (as I already knew). So how do items 1-3 translate into the no-jig myth?

If all was rosy in the MRA.4 garden, why were they grounded and gas-axed with indecent haste?

Chris
The myth originated from the first bullet point of the press release. BAe Systems just said there was a big unforeseen issue. All the armchair experts/keyboard idiots filled in the rest with whatever fantasy they could dream up.... original built without jigs, CNC matched to holes drilled to chalk marks, fire dump measurement or 4 inch frame pitch tolerances.

Unforeseen issues (Force Majeure) was the key mechanism in the 1996 fixed price contract for converting PA4 to 21 into delivery delays. You see the fixed price contract only mandated the delivery of just three aircraft and the rest were negotiable. (Note the steady decline in the total to be delivered between 96-02) In 2002 the whole thing came to a head, because there was no money to continue. A deal was done whereby BAe Systems took a degree of the liability, I.e the big loss, but was awarded a follow on contract for the production aircraft, now just nine of em, plus the a few prototype conversions to operational aircraft. It was therefore essential to make everyone aware of the Force Majeure that justified this arrangement. The real reasons behind the slip up at that time were a collection/build up of more mundane dysfunctional management issues as I’ve mentioned before;- at this time, key components were just not being delivered to support the build which was all firmly within BAe Systems sphere of influence.

Sorry, I'm trying to understand here (not good in english…)…
What you're saying is that BAe blew up that "wing not fitting" problem to get a revision of the original fixed price contract, which they knew would be at loss for them ?
Yep, really to save the whole project, because the fixed price contract was now outside of its spending limit, was out of time, had delivered nothing and had even exceeded BAe Systems overdraft limit.
 
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CJGibson

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Ah, all clear now. Cancelled purely on cost grounds because the longer the project went on the fewer Nimrods the RAF would have received until the point was reached when the only way BAE could make a profit was to call in Mssrs Steptoe and Son. Fair summary?
PicSteptoeAndSon.jpg

Chris
 

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The origin of the wing myth now makes more sense, though I suspect it may have originated from conflation of tales within the BAE workforce itself and others involved in the programme but outside the company itself. I find it harder to believe BAE management would have created that story as a contract renegotiation ploy, specially with the concurrent Astute issues. It would hardly of convinced the government, or the shareholders, that they were a reputable company. The media stories though were probably a convenient smokescreen.

As a trained historian I find this a fascinating case study of how myths are formed and perpetuated, quite beyond the technical issues discussed here. There are obviously a number of people who were involved who do believe this myth and perpetuate its telling. Like Chinese whispers it changes its form as its retold with new layers of anecdote added and 'evidence' like the photos with glum faces being brought out or reinterpretated as 'proof'.
 

Zoo Tycoon

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The origin of the wing myth now makes more sense, though I suspect it may have originated from conflation of tales within the BAE workforce itself and others involved in the programme but outside the company itself. I find it harder to believe BAE management would have created that story as a contract renegotiation ploy, specially with the concurrent Astute issues. It would hardly of convinced the government, or the shareholders, that they were a reputable company. The media stories though were probably a convenient smokescreen.

Hood
BAe Systems didn’t have to create the fleet variation myth, that was already well embedded in the MR2 community, heavily embellished over the years , but no one in that community really understood the details. We were aware of it at the start, so it was marked as one of the projects biggest risks which was mitigated with a fleet wide measure campaign using portable Zeiss laser trackers (state of the art at that time). I only made two trips to Hurn, the first of which was to make sure the guys doing the measurements had captured the full set required on PA1-3 fuselages which we’re then in residence. When we got hold of the measurements set, together with the original build records, we (a pretty small group) could work out the picture of what happened, and what this meant.

The press releases and info leaks in the 2001-2 period really played on the fact that the majority, knew of a problem but didn’t have access to the measurements or have any kind of idea as to how Nimrods or any other aeroplanes were built.
 
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RLBH

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Which when embellished a little turns into a 4 inch frame position tolerance on each frame.
I've heard quite a few versions of 'what went wrong with MRA4', to the point where I stopped believing any of them verbatim a long time ago, but this one is new on me. The tolerance-based one that I was familiar with was that dimensions for each frame were measured from the previous frame, so that (perfectly ordinary) tolerances stacked up. Whilst each measurement was within tolerance, and therefore individual items would fit locally, the entire aircraft could vary considerably in length if it got all 'long' or 'short' measurements.

4-inch frame tolerances would be so clearly ludicrous that each aircraft would be completely different from the others. I don't think that anyone could build an aircraft that badly without actively trying, and even then I'm not sure.
 

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Being in the steel fabrication industry, I've been quite familiar with that happening, especially when the industry standard was 'well - it's in the 1/4" tolerance' That was for each separate measurement BTW --
 

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Where did Flight Refueling Limited fit into this farce? Lower bid than BAE no doubt, but as soon as the last Condor had lifted from Hurn there was a collective 'Ooooer!'. Did they bite off more than they could chew?

Chris
 
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Zoo Tycoon

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Where did Flight Refueling fit into this farce? Lower bid than BAE no doubt, but as soon as the last Condor had lifted from Hurn there was a collective 'Ooooer!'. Did they bite off more than they could chew?

Chris
After this happened.
No, I think Chris is referring to FRA initial involvement in MRA4 final assembly between 96-99.

FRA Hurn;- Spread the project work around the U.K., plus the (Not so) Smart Procurements race to the bottom mentality = ruthlessly exploitation of the lack of any partners knowledge , their necessity to survive, all done with an ignorance that commercial organisation need to make something. (Not so) Smart Procurement was suppose to bring the advantages of competitive tendering the purchasing of computer paper to massively complicated projects;- what could possibly have gone wrong?
 
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Zoo Tycoon

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Which when embellished a little turns into a 4 inch frame position tolerance on each frame.
I've heard quite a few versions of 'what went wrong with MRA4', to the point where I stopped believing any of them verbatim a long time ago, but this one is new on me. The tolerance-based one that I was familiar with was that dimensions for each frame were measured from the previous frame, so that (perfectly ordinary) tolerances stacked up. Whilst each measurement was within tolerance, and therefore individual items would fit locally, the entire aircraft could vary considerably in length if it got all 'long' or 'short' measurements.

4-inch frame tolerances would be so clearly ludicrous that each aircraft would be completely different from the others. I don't think that anyone could build an aircraft that badly without actively trying, and even then I'm not sure.

Ah no, the fuselages were all jig built (see picture below), all in the same jig and no they didn’t make the school boy error of tolerance accumulation by measuring from frame to frame. Please read my previous posts concerning the problems of building the compound curves panel sections in the nose section frames 1-12 and frames 48 to X in the tail section. This alone accounted for the differences in fuselage lengths within the fleet.

The four inch frame pitch tolerance claim is a fairytale dreamed by a clueless individual with an unknown agenda.

This is not the steel fabrication business so quarter inch position tolerance is irrelevant. 8A1321B5-67C9-4337-B278-D6D0C94A0C61.jpeg
 
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Ah no, the fuselages were all jig built (see picture below), all in the same jig and no they didn’t make the school boy error of tolerance accumulation by measuring from frame to frame. Please read my previous posts concerning the problems of building the compound curves panel sections in the nose section frames 1-12 and frames 48 to X in the tail section. This alone accounted for the differences in fuselage lengths within the fleet.
As I said - healthy skepticism about all the stories. A lot of the claims I've heard are totally impossible to belive, but MRA4 seemed to attract such stories.
 

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One thing being missed from the discussion of why the project was axed is the wider political dimension, with the new ConDem coalition eagerly looking for targets for the Austerity Juggernaught. Scrapping MRA.4 allowed them to both save the acquisition costs, at the cost of the already sunk costs (which could be blamed on Labour), and to close Leuchars, which would be a not inconsiderable saving in its own right. Other MoD decisions of the era had major political oars inserted, such as the brilliant idea of converting the carriers to CATOBAR and buying F-35C. Outside of MoD other government departments were outright resorting to lies and black propaganda to justify Austerity cuts; searching for engineering logic in the decision may be a lost cause.
 

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Which when embellished a little turns into a 4 inch frame position tolerance on each frame.
I've heard quite a few versions of 'what went wrong with MRA4', to the point where I stopped believing any of them verbatim a long time ago, but this one is new on me. The tolerance-based one that I was familiar with was that dimensions for each frame were measured from the previous frame, so that (perfectly ordinary) tolerances stacked up. Whilst each measurement was within tolerance, and therefore individual items would fit locally, the entire aircraft could vary considerably in length if it got all 'long' or 'short' measurements.

4-inch frame tolerances would be so clearly ludicrous that each aircraft would be completely different from the others. I don't think that anyone could build an aircraft that badly without actively trying, and even then I'm not sure.

Ah no, the fuselages were all jig built (see picture below), all in the same jig and no they didn’t make the school boy error of tolerance accumulation by measuring from frame to frame. Please read my previous posts concerning the problems of building the compound curves panel sections in the nose section frames 1-12 and frames 48 to X in the tail section. This alone accounted for the differences in fuselage lengths within the fleet.

The four inch frame pitch tolerance claim is a fairytale dreamed by a clueless individual with an unknown agenda.

This is not the steel fabrication business so quarter inch position tolerance is irrelevant.View attachment 616596
The 4 inch claim I heard (and saw in writing somewhere) was never stated as frame pitch. I always assumed it was either the aeroplane overall or the 'spectacle' engine mounts' range of possible movement after years in service, or some such. That said, a desk officer was clear 'one was a foot longer than the rest'.

The claims are all pretty non specific; hard to rebut without knowing what they really are. Finger on a drop of mercury stuff. Any idea where the 4 inch claim came from (the now notorious and possibly illegal BAE press release?), and if it was specifically 'frame to frame'?
 

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One thing being missed from the discussion of why the project was axed is the wider political dimension, with the new ConDem coalition eagerly looking for targets for the Austerity Juggernaught. Scrapping MRA.4 allowed them to both save the acquisition costs, at the cost of the already sunk costs (which could be blamed on Labour), and to close Leuchars, which would be a not inconsiderable saving in its own right. Other MoD decisions of the era had major political oars inserted, such as the brilliant idea of converting the carriers to CATOBAR and buying F-35C. Outside of MoD other government departments were outright resorting to lies and black propaganda to justify Austerity cuts; searching for engineering logic in the decision may be a lost cause.
Mark Francois was muttering about Nimrod being terrible and a sensible cancellation at the House of Commons defence budget debate today.
 

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Ah no, the fuselages were all jig built (see picture below), all in the same jig and no they didn’t make the school boy error of tolerance accumulation by measuring from frame to frame. Please read my previous posts concerning the problems of building the compound curves panel sections in the nose section frames 1-12 and frames 48 to X in the tail section. This alone accounted for the differences in fuselage lengths within the fleet.
As I said - healthy skepticism about all the stories. A lot of the claims I've heard are totally impossible to belive, but MRA4 seemed to attract such stories.
Well the MRA4 story in general is almost impossible to believe were it not for the fact it happened. 10 years late, billions overspent and scrap metal output.
 

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Ah no, the fuselages were all jig built (see picture below), all in the same jig and no they didn’t make the school boy error of tolerance accumulation by measuring from frame to frame. Please read my previous posts concerning the problems of building the compound curves panel sections in the nose section frames 1-12 and frames 48 to X in the tail section. This alone accounted for the differences in fuselage lengths within the fleet.
As I said - healthy skepticism about all the stories. A lot of the claims I've heard are totally impossible to belive, but MRA4 seemed to attract such stories.
Well the MRA4 story in general is almost impossible to believe were it not for the fact it happened. 10 years late, billions overspent and scrap metal output.
Yes. I feel the need to dig out the old documents and notes my three slides on MRA4 from years ago were based on. The story makes one doubt every source at each re-telling. Perhaps posting such things as PDFs etc. here might be useful. The 'truth' that is documented is some form of truth. As is the money wasted.

EDIT: Some files from an old USB drive attached (Folder 'Nimrod - web pics'!). Old article but showing some being built, Nimrod1 image: old wing coming off; Nimrod 2: XV147, the alleged fire dump Comet/Nimrod hybrid that was supposedly measured; Nimrod 3: loading/unloading at FRA Hurn I have lots of images of new wings going on but these are copyright BAE and only usable for teaching. They all show a much shinier structure, clearly made using more modern technology, but no 'smoking gun' with holes mis-aligned etc. Old structure looks well worn/repaired, but not 'bodged' together.
 

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Mike Pryce

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Looking at the structure of Nimrod, if any area was going to have 4 inches of wriggle room it is the 'spectacles'. Jig built wings, fuselages and centre wing boxes, all connected by these, that hardly seem to be monocoque structures amenable to jig assembly.

With root bending in low level turns, thrust loads, endless maintenance over decades, it is hard to imagine they were not supposed to 'give' in some way and at some time. As I understand it, this was also the area that caused various problems on the MRA4. Were the new, bigger 'spectacles' designed to be too stiff or something similar? Maybe that is the source of the 4 inch myth - maybe they did not 'give' like the old ones? Too stiff and stress would develop.
 

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Zoo Tycoon

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Looking at the structure of Nimrod, if any area was going to have 4 inches of wriggle room it is the 'spectacles'. Jig built wings, fuselages and centre wing boxes, all connected by these, that hardly seem to be monocoque structures amenable to jig assembly.

With root bending in low level turns, thrust loads, endless maintenance over decades, it is hard to imagine they were not supposed to 'give' in some way and at some time. As I understand it, this was also the area that caused various problems on the MRA4. Were the new, bigger 'spectacles' designed to be too stiff or something similar? Maybe that is the source of the 4 inch myth - maybe they did not 'give' like the old ones? Too stiff and stress would develop.
Utter nonsense. As is the fire dump measurements fairytale as is the fuselage to wing attachment were drilled to chalk marks.

Just repeating over and over again won’t make it real
 

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