Improve That Design: How Aircraft Could Have Been Made Better

[GrauGeist]

It's possible that the valves were at least packed in straw or set in racks for the journey, but my first thought was what a time consuming process.
Load a batch, wheel across to the other side, unload.
Conduct the hardening.
Load up the finished valves, wheel back to the plant.
Unload and continue with the assembly process.
For custom work, that would be a non-issue, but for assembly line efficiency, that's a critical bottle-neck.

 

[pbehn]

It's possible that the valves were at least packed in straw or set in racks for the journey, but my first thought was what a time consuming process.
Load a batch, wheel across to the other side, unload.
Conduct the hardening.
Load up the finished valves, wheel back to the plant.
Unload and continue with the assembly process.
For custom work, that would be a non-issue, but for assembly line efficiency, that's a critical bottle-neck.

In terms of production it can be done but as you say is very labour intensive and inefficient. The real problems start when you have a quality issue, which Napiers had. Trying to pin down what was done to which sleeve valve to cause the problem and then determine which others are or maybe affected is a huge and maybe impossible task.

 

[swampyankee]

Going across would be no problem I would think as they hadn't been machined yet.

How would bumping across the cobbles effect the machined pieced?

The sleeves were very thin. Indeed, I've read they needed to be stored vertically because they'd become too out-of-round to use if they were laid on their sides.

 

[don4331]

The problem with Napier's sleeve valves starts with the inner and outer surfaces must be concentric (or relatively close) i.e. you can't have thick wall on one side and thin on the other. The craftsmen building the prototypes/initial production could hold the tolerances but when they brought in lower skilled individuals for volume production, they weren't able to maintain it. The solution to the problem is to finish the inner surface using a "center-less" operation - in practise, center-less grinding machines were used at the expensive of American valve being able to be produced. Center-less finishing ensures constant wall thickness.

Then they laid the cylinders 5 or 6 high on a hand cart with steel wheels that was pushed over cobbles from one building to next. Somewhere there's a picture of a "gopher" driving tractor pulling a cart of cylinders. The result was the bottom cylinders were no longer round by the time they got to the heat treatment shop. And oval sleeve valves don't work well. As swampyankee says they needed to be transport vertically.

And you have the standard production line issues: bored employees, rushed production schedules, staff not understanding what they are doing that lead to quality issues.
Rolls Royce Vulture rod bearing issues were example - they needed to be tightened just to certain torque aka tight-enuf. But employees, on the line, gave it an additional tug, just to ensure it wouldn't come loose. The result was the bolts were over-stressed and failed in service. RR changed from measuring tightness via torque to measuring bolt stretch with a no/no-go gage - replacing over tightened bolts and the problem when away. 'Course, by that time, the Vulture already had a "reputation". And it needed a wholesale redesign to be a 2,500hp engine on 100 octane, which RR didn't have time for just then.

Lastly, you need to keep the f Rolls-Royce technicians away. Their "tweaking" of the Napier "black box" to give "a little" more boost, tended to blow up otherwise fine Sabres. They did make Napier look bad, but at the cost of RAF pilots.

 

[MikeMeech]

Some of the machinery at Napier's was Victorian. It wasn't a big factory building it was a collection of relativity small buildings set around a cobbled yard. One of the problems with the sleeve valves they were machined in one building and then taken on a wooden hand cart to another building to be hardened then back by hand cart to the assembly building. So the sleeve valves which had to be perfectly round were bumped across a cobbled yard at least twice.

Napier's factory was a Victorian style small engineering works, the sort that was in common use in the mid 19th Century. There was no production line it was craftsman style production.

Hi
For interest an image of part of Napier's Acton factory during 1924. The engine is the Napier Lion, in 1927 the production of this type was around 50 per month. This was a 'small' factory in WW2 terms which is why MAP 'supplied' the factory at Liverpool aiming to supply 2000 Sabre's per year. Machine tools were also bought in the USA for this and other factories, on top of British machine tools.

Mike

 

[wuzak]

Rolls Royce Vulture rod bearing issues were example - they needed to be tightened just to certain torque aka tight-enuf. But employees, on the line, gave it an additional tug, just to ensure it wouldn't come loose. The result was the bolts were over-stressed and failed in service. RR changed from measuring tightness via torque to measuring bolt stretch with a no/no-go gage - replacing over tightened bolts and the problem when away. 'Course, by that time, the Vulture already had a "reputation". And it needed a wholesale redesign to be a 2,500hp engine on 100 octane, which RR didn't have time for just then.

I find it hard to believe that a trained assembly technician would over-torque bolts just because they felt like it. They would have used torque wrenches to apply the correct torque.

The original Vulture big end had only two bolts on one side of the rod. The other side was kept in place with a transverse pin. This design was problematic.

This was redesigned to use 4 bolts - 2 long on one side and 2 short on the other. These did not allow the normal pre-tensioning to Rolls-Royce's normal standards. This design still had bearing issues.

Had the Vulture continued, the master rod would have been a new design, which may have been done but not made it to production.

Lastly, you need to keep the f Rolls-Royce technicians away. Their "tweaking" of the Napier "black box" to give "a little" more boost, tended to blow up otherwise fine Sabres. They did make Napier look bad, but at the cost of RAF pilots.

Rolls-Royce technicians? Do you mean RAF technicians, who were used to working on Merlins?

 

[don4331]

I find it hard to believe that a trained assembly technician would over-torque bolts just because they felt like it. They would have used torque wrenches to apply the correct torque.

This was redesigned to use 4 bolts - 2 long on one side and 2 short on the other. These did not allow the normal pre-tensioning to Rolls-Royce's normal standards. This design still had bearing issues.

If you believe the assembly line workers are all there because they want to do a perfect job, you've never worked in a manufacturing environment. For most people, it was a job, not a career. And when worker were putting in 6 x 12 hour + 8 on Sunday for an 80 hour week - week after week, the job gets old real fast. And with 100% employment, you can't fire people, because you can't replace them.

And it doesn't have to be deliberate - 2 individuals competing to see who can get their 3 rods done fastest - so, you're overshooting the torque wrench because you're pulling so fast that you don't stop right when the torque wrench clicks. And we aren't even discussing that the individuals have foregone the correct tightening sequence which can result in warped parts.

The long and short bolt of the Vulture rod are the problem. The issue with pre-tensioning is the longer bolts need to be tightened to a higher value than shorter so that bolt stretch under load is equal. Any designer/manufacturers prefers that all 4 be the same length, so they can be tightened the same. The easy to do mistake of tightening the short bolts to the long bolts value results in the short bolts being over-tighten and failing in service. Hence, the implementation of a gauge to check bolt stretch.

Rolls-Royce technicians? Do you mean RAF technicians, who were used to working on Merlins?

Manufacturers representives, might be better name for them; individuals for whom RR paid their checks, and knew better but were being malicious. The RAF fitters weren't the worst problem.

 

[wuzak]

If you believe the assembly line workers are all there because they want to do a perfect job, you've never worked in a manufacturing environment. For most people, it was a job, not a career. And when worker were putting in 6 x 12 hour + 8 on Sunday for an 80 hour week - week after week, the job gets old real fast. And with 100% employment, you can't fire people, because you can't replace them.

And it doesn't have to be deliberate - 2 individuals competing to see who can get their 3 rods done fastest - so, you're overshooting the torque wrench because you're pulling so fast that you don't stop right when the torque wrench clicks. And we aren't even discussing that the individuals have foregone the correct tightening sequence which can result in warped parts.

The long and short bolt of the Vulture rod are the problem. The issue with pre-tensioning is the longer bolts need to be tightened to a higher value than shorter so that bolt stretch under load is equal. Any designer/manufacturers prefers that all 4 be the same length, so they can be tightened the same. The easy to do mistake of tightening the short bolts to the long bolts value results in the short bolts being over-tighten and failing in service. Hence, the implementation of a gauge to check bolt stretch.

The design of the joint was the problem, not assembly errors.

When did Rolls-Royce start using bolt stretch to measure pre-tension?

Manufacturers representives, might be better name for them; individuals for whom RR paid their checks, and knew better but were being malicious. The RAF fitters weren't the worst problem.

Do you have specific instances that you can share?

That sounds like a conspiracy theory, an excuse to explain the poor reliability of the Sabre in its early service.

 

[MikeMeech]

It's possible that the valves were at least packed in straw or set in racks for the journey, but my first thought was what a time consuming process.
Load a batch, wheel across to the other side, unload.
Conduct the hardening.
Load up the finished valves, wheel back to the plant.
Unload and continue with the assembly process.
For custom work, that would be a non-issue, but for assembly line efficiency, that's a critical bottle-neck.

Hi
For interest, here is a short overview (from 'British Piston Aero-Engines and their Aircraft' by Alec Lumsden, p.175) of Sabre sleeve valve problems and Bristol's involvement:

Also reference to Napier's and the Sabre, with Hives (Rolls-Royce) commercial worries about Napier (from 'Industry and Air Power, The Expansion of British Aircraft Production, 1935-1941' by Sabastian Ritchie, p.140):

Also from an on-line source the Acton factory of Napier from the air:

Mike

 

[don4331]

The design of the joint was the problem, not assembly errors.

When did Rolls-Royce start using bolt stretch to measure pre-tension?

RRHT No. 16 p.139 - special care being taken during assembly to obtain the correct stretch of the bolt during tightening by means of a direct measurement of sttetch of the bolt

p.142 The condition was slightly improved by a rigid tightening order.

Do you have specific instances that you can share?

That sounds like a conspiracy theory, an excuse to explain the poor reliability of the Sabre in its early service.

Looking for the reference for the Sabre mods. But it was late Sabres operating with 2nd TAF.

Why is it so hard to accept that workers RR added to during the war were human?

 

[wuzak]

Looking for the reference for the Sabre mods. But it was late Sabres operating with 2nd TAF.

Why is it so hard to accept that workers RR added to during the war were human?

Being "human" implies a mistake or mistakes.

But you said they were being "malicious" - which is a deliberate act.

Manufacturers representives, might be better name for them; individuals for whom RR paid their checks, and knew better but were being malicious.

 

[Thumpalumpacus]

But you said they were being "malicious" - which is not a deliberate act.

This appears to be a typo?

 

[wuzak]

This appears to be a typo?

Thanks. Fixed.

Should have read "But you said they were being "malicious" - which is a deliberate act."

 

[Reluctant Poster]

The problem with Napier's sleeve valves starts with the inner and outer surfaces must be concentric (or relatively close) i.e. you can't have thick wall on one side and thin on the other. The craftsmen building the prototypes/initial production could hold the tolerances but when they brought in lower skilled individuals for volume production, they weren't able to maintain it. The solution to the problem is to finish the inner surface using a "center-less" operation - in practise, center-less grinding machines were used at the expensive of American valve being able to be produced. Center-less finishing ensures constant wall thickness.

Then they laid the cylinders 5 or 6 high on a hand cart with steel wheels that was pushed over cobbles from one building to next. Somewhere there's a picture of a "gopher" driving tractor pulling a cart of cylinders. The result was the bottom cylinders were no longer round by the time they got to the heat treatment shop. And oval sleeve valves don't work well. As swampyankee says they needed to be transport vertically.

And you have the standard production line issues: bored employees, rushed production schedules, staff not understanding what they are doing that lead to quality issues.
Rolls Royce Vulture rod bearing issues were example - they needed to be tightened just to certain torque aka tight-enuf. But employees, on the line, gave it an additional tug, just to ensure it wouldn't come loose. The result was the bolts were over-stressed and failed in service. RR changed from measuring tightness via torque to measuring bolt stretch with a no/no-go gage - replacing over tightened bolts and the problem when away. 'Course, by that time, the Vulture already had a "reputation". And it needed a wholesale redesign to be a 2,500hp engine on 100 octane, which RR didn't have time for just then.

Lastly, you need to keep the f Rolls-Royce technicians away. Their "tweaking" of the Napier "black box" to give "a little" more boost, tended to blow up otherwise fine Sabres. They did make Napier look bad, but at the cost of RAF pilots.

Is this a true story or urban legend? I have never seen a factual account.

 

[Reluctant Poster]

I the Rolls Royce story true or urban legend? I have never seen a factual account.

 

[DarrenW]

Yes I really do wonder. Half of them went to the Soviets where they won the war and the other half were used as trainers here. And ANY combat plane would be a major step up from an AT-6 Texan.

You can keep grasping for any straw and rumor to somehow make the P-39 a deathtrap, but in reality it was a very serviceable combat plane. Do you consider the F6F Hellcat to be a good plane? Scourge of the Japanese and kings of the Pacific. Shot down more Japanese aircraft than any other plane. Look at the attached graph (wwiiaircraftperformance.org) with P-39N performance overlayed in red. Pretty competitive, no? And consider that the P-39N was out of production before the Hellcat had it's first combat with the USN.

The graph you posted displays the performance of the F6F-3 in a "combat" condition, meaning with underwing bomb racks and fuselage bomb shackles. The points you added display the speed of the P-39N in a "clean" condition with no racks or pylons mounted. Not really an apples to apples comparison.

Sure the P-39N had a decent enough top speed and climb rate but there are other qualities needed in a fighter in order to make it competitive in it's designed role and area of operation.

 

[P-39 Expert]

The P-39N only had one external store, a belly shackle. Deduct 10mph for the shackle with braces. Still very comparable to the F6F in speed and very much better in climb.

 

[DarrenW]

The P-39N only had one external store, a belly shackle. Deduct 10mph for the shackle with braces. Still very comparable to the F6F in speed and very much better in climb.

How did you come up with that speed loss figure? But even if that's true at the end of the day what does that really get you? It had a mediocre bomb carrying capability and range suffered even more because it couldn't carry a drop tank at the same time to help overcome the extra drag and weight of the bomb being carried.

 

[DerAdlerIstGelandet]

How did you come up with that speed loss figure? But even if that's true at the end of the day what does that really get you? It had a mediocre bomb carrying capability and range suffered even more because it couldn't carry a drop tank at the same time to help overcome the extra drag and weight of the bomb being carried.

 

[GrauGeist]

Still very comparable to the F6F in speed and very much better in climb.