Packard vs Rolls-Royce Merlins

wuzak

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What are the differences?

My understanding is that the initial production of Packard single stage engines differed from the equivalent Rolls-Royce engines in minor details only. Such as the sealing between the head and the block. Which was changed to match the Rolls-Royce engines later.

The two stage engines differed in having a Wright designed epicyclic supercharger drive system, as opposed to the Rolls-Royce Farman type.

Packard engines going to the USAAF had SAE splined prop shafts, those going to the UK/Commonwealth had SBAC shafts.

From another thread:

Packard Merlins were built to Rolls-Royce specs and standards.

No, they were not. There were built to more stringent standards.

Packard Merlins were surely built to Rolls-Royce drawings, even if they had to be redrawn for American conventions. So I can't see why Packard Merlins were "built to more stringent standards".


Parts built by Packard were interchangeable with parts made by Rolls-Royce and Ford UK.

Not all parts in all equivalent engines. R-R still had many hand fit parts and much "File to fit" in their engines.

Apart from the eronious term "file to fit", did Rolls-Royce production Merlins (as opposed to those built in the experimental shop) have parts individually fitted? I have my doubts, especially for engines built by Ford UK.


Now, the Packard Merlins all had equivalent Rolls-Royce engines, and were rated according to the Rolls-Royce ratings.

V-1650-1 = Merlin 28
V-1650-3, -5, -7 were 60 series engines.
V-1650-9 and later were 100 series engines - with strengthened components.

An example of the supposed superiority of the Packard built engine was the V-1650-9. With water injection and +30psi boost the -9 delivered just over 2200hp.

The equivalent Rolls-Royce engine (RM.16SM) was not fitted with water injection, and was limited to +25psi boost and just over 2000hp. With ADI the other 100 series Merlins could, surely, match the 2200hp of the -9?

Just how much engine development did Packard do on the Merlin?


Finally, the RM.17SM was cleared for flight at 2380hp with +30psi boost @ 3300rpm (I assume with ADI). It was to be rated at 2200hp @ 2000ft MS gear and 2100hp @ 15,000ft FS gear. I believe both were at +30psi and 3000rpm.

And the RM.17SM was tested for 15 minutes at 2620hp, +36psi boost, 3150rpm with ADI.
 

Shortround6

Brigadier General
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I think the "file to fit" was pretty much done away with the British Ford involvement. There may have been a lot less "file to fit" than measuring parts and selecting the best fit. As in measuring the bores of the cylinders and picking the pistons that fit the bores best even if not all pistons would fit all cylinders rather than 'filing' the pistons.

There were four UK sources and Packard. The UK sources provided over 100,000 engines

There were Six UK and RAF overseas repair facilities. The UK based repair facilities repaired/overhauled 50,000 engines. The number repaired/overhauled in the overseas facilities is unknown.

That is a LOT of "filing and fitting". :)

According to one source not a single engine from the Ford Tafford works failed or had to be torn down and rebuilt for failure to meet specified performance on test.
 

michaelmaltby

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".... No, they were not. There were built to more stringent standards."

They most surely were built to different standards ..... BSI for the UK builds and American Standard for Packard builds (and De Havilland and AV Roe employment in Canada for Mossies and Lancs).
 

wuzak

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".... No, they were not. There were built to more stringent standards."

They most surely were built to different standards ..... BSI for the UK builds and American Standard for Packard builds (and De Havilland and AV Roe employment in Canada for Mossies and Lancs).

In what way?

If Packards were built to American Standards they would have been fitted in UNC and UNF threads - they, in fact, used BSW and BSF threads.

BSI and American Standards may have had different tolerances - but the Packard engines would have used the tolerances specified on the drawings. Doubtful that they would have changed them.
 

Aozora

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Dec 23, 2012
Packard Merlins were surely built to Rolls-Royce drawings, even if they had to be redrawn for American conventions. So I can't see why Packard Merlins were "built to more stringent standards".

Apart from the eronious term "file to fit", did Rolls-Royce production Merlins (as opposed to those built in the experimental shop) have parts individually fitted? I have my doubts, especially for engines built by Ford UK.

Here is an analysis of the Packard Merlin's construction; it should help answer several questions:

View attachment PackardMerlin.pdf

According to this, Rolls-Royce continually modified the Merlin to make it easier to build on both sides of the Atlantic; Packard helped contribute innovations to the overall design, as well as developing features unique to their version of the Merlin:

During the life of the Merlin almost 1,000 modifications were issued by Rolls-Royce to increase reliability or simplify manufacture. Packard initiated some of these as well as a number which applied only to Packard-built engines....A few of the more significant changes contributed by Packard were: Introduction of the two-piece cylinder block; introduction of a new design water pump with sealed ball bearings; use of a continuously variable ratio supercharger drive....Although it has been reported in some prior publications that the design of the Packard epicyclic two-speed supercharger drive was one derived from on in use by Wright Aeronautical, that is not the case...(page 7)

Also attached is a description of how R-R analysed early Merlin performance.
 

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wuzak

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Here is an analysis of the Packard Merlin's construction; it should help answer several questions:

View attachment 246126

According to this, Rolls-Royce continually modified the Merlin to make it easier to build on both sides of the Atlantic; Packard helped contribute innovations to the overall design, as well as developing features unique to their version of the Merlin:



Also attached is a description of how R-R analysed early Merlin performance.

Thanks for those files Aozora.

A couple of things I would take issue with:

Introduction of the two-piece cylinder block

That's all good, but they didn't design or develop the 2 piece cylinder block. Rolls-Royce did, and the only reason RR didn't introduce it earlier was because they were busy building engines for the war effort. RR waited until they started 60-series production before they went to the two piece block.

use of a continuously variable ratio supercharger drive

Packard Merlins did not have a continuously variable supercharger drive. They had two distinct ratios.
 

GregP

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I believe there were some "fitted" parts in British Merlins that ran just fine but were not interchangeable. The Packard Merlins were interchangeable throughout.

I have not heard that Packard or Rolls-Royce Merlins had significantly different time-between-overhaul if operated in similar climatic conditions.

I HAVE heard the quality of the Packard Merlins surprised the British, who expected they would not be "good," but found out they ran just fine. That is no knock on the British at all. It is rather a natural expectation ... expect the worst and be happy if you are incorrect. At that time, the British had not had a lot of recent things to be "happy" about, and lower than the highest expectations seems quite natural. Hopefully they were pleasantly surprised.

I wonder how many Rolls-Royce Merlins versus Packard Merlins are running today but really have no idea myself. It isn't a subject that matters a great deal either. Whoever has a running Merlin is probably happy with it if he or she can find parts at all, regardless of the source. Whoever has a FLYING Merlin these days is largely happy to just keep it running well, and hopes the next parts he of she gets won't be even MORE expensive ... but they probably will be.
 

Aozora

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Dec 23, 2012
Thanks for those files Aozora.

A couple of things I would take issue with:

...they didn't design or develop the 2 piece cylinder block. Rolls-Royce did, and the only reason RR didn't introduce it earlier was because they were busy building engines for the war effort. RR waited until they started 60-series production before they went to the two piece block.

This is explained in the article (page 4):

On 2 August 1940 three representatives from Rolls-Royce came to talk to Vincent about the engine and "almost immediately after their arrival they raised the question as to what type of engine block we were prepared to tool up for. Up to that time we had never heard of the two piece block....They showed us drawings of the two-piece cylinder block and stated that in their opinion we should tool up for this improved two-piece construction....(Actually the two-piece cylinder design was modified by Packard to facilitate manufacture and was used only in engines made by Packard. Rolls-Royce continued to use single-piece construction for some time before they were able to switch...when they finally did it was one designed by themselves and somewhat different from Packard's. For the sake of uniformity Packard switched to the Rolls-Royce design at that point.)

Packard started Merlin construction from the outset using their own version of two-piece cylinder block, before switching to the R-R version once R-R had changed to two-piece construction with the introduction of the 61 (from memory the 60 still used single-piece blocks?).

Packard Merlins did not have a continuously variable supercharger drive. They had two distinct ratios.

Not sure what the author was referring to, unless he was describing the Simmonds automatic supercharger control; he was also incorrect in implying that the British 60/70 series all used manual supercharger controls - most also had automatic, barometrically controlled clutches.
 

michaelmaltby

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".... BSI and American Standards may have had different tolerances - but the Packard engines would have used the tolerances specified on the drawings.

You are correct. I misspoke.

"An often asked question is; “did Packard replicate the British thread system when they built Rolls-Royce Merlins under license during World War II?” The answer is yes; all threads that were used on the Merlin were accurately replicated by Packard. This would include BSW (British Standard Whitworth), BSF (British Standard Fine), BSP (British Standard Pipe) and BA (British Association). Having said that, however, Packard Merlins> used U.S. built Bendix injection carburetors; PD-16 for single stage engines and PD-18 for two stage engines, both of which used U.S. Unified threads. British built Merlins employed S.U. carburetors using Whitworth threads. The job facing Packard when they undertook manufacture of the Merlin was daunting to say the least. It’s bad enough having to build a complex product like the Merlin but exacerbating the situation was the fact no tool maker in the U.S. made Whitworth taps or dies. Therefore, Packard were forced into making their own. Although this created a significant hurdle to overcome, the effort was well worth it, Packard and Rolls-Royce components were interchangeable.

[Source]
 
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fastmongrel

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My Dad was an instrument fitter on a Coastal Command squadron post war in Malta. They operated Lancaster mkIIIs which originally came with Packards. By 1946 the Packards where in short supply in Malta so RRs were fitted in there place apparently they slotted into place just fine and aircrew could never tell which engine was fited.

Also time expired Merlins were broken for parts for Meteor tank engines when there was a shortage of crankshafts and Packard and RR parts were used interchangeablely without any problem.
 

beitou

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Jun 14, 2012
Did they sound any different or would that be a product of their mountings and exhaust systems?
 

GregP

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V-12's with similar firing orders have very similar sounds, but the actual sound depends on the exhaust stack fitted. A P-40 exhaust stack sounds different from a P-38 or P-39 (all Allison) and the stacks used on several British planes using Merlins are different-souding from one another, but the basic firing sound and frequency is the same. One particularly noticeable different sound with the Griffon is a normal Griffon Spitfire compared with a Griffon Firefly that has the nigh-fiighter shelves over the stack. It deflects the sound outward and the Firefly with these is VERY loud to an observed compared with a Griffon Spitfire.
 

Aozora

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Did they sound any different or would that be a product of their mountings and exhaust systems?

Youl'd be hard pressed to tell the difference between the engine sounds but there were differences depending on the aircraft they were in

View: https://www.youtube.com/watch?v=a3eBD6tLVOQ

The P-51D had a distinct whistle, almost a howl...


View: https://www.youtube.com/watch?v=HPTIe30hr1E

The Griffon was altogether gruntier...


View: https://www.youtube.com/watch?v=3EcCYA68m_w

and the Allison V-1710 was smoother, more mellow than either the Merlin or Griffon...


View: https://www.youtube.com/watch?v=CjZoWU5R9dA

according to pilots who flew both the Allison engined and Packard Merlin P-51s the Allison was a smoother engine, particularly at lower cruising revs and it could be leaned out more.
 

OldSkeptic

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Thanks for those files Aozora.

That's all good, but they didn't design or develop the 2 piece cylinder block. Rolls-Royce did, and the only reason RR didn't introduce it earlier was because they were busy building engines for the war effort. RR waited until they started 60-series production before they went to the two piece block.

No the 2 piece clock was introduced in the XX series (2 speed, single stage) engines. Later versions of the 45 (Spit 5, single speed, single stage) had it to.

The Merlin 60 (prototype 2 speed, 2 stage) had a single block but all the production 60 series engines were 2 piece blocks.

The Merlin 28 (Packard version of the RR XX) used their own 2 piece construction, from the Merlin 33 (Packard version of the RR 23) onwards they used the British 2 piece construction.
 

wuzak

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No the 2 piece clock was introduced in the XX series (2 speed, single stage) engines. Later versions of the 45 (Spit 5, single speed, single stage) had it to.

If that were the case then the 2 piece block would have been in production in the UK from 1940. Which predates Packard's use of a 2 piece design.

I am sure that early XXs used the 1 piece block, while later ones got the 2 piece design - around the time they were stting up 60-series production.
 

OldSkeptic

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True the XX (and 21) were 1 piece blocks. All the later were 2 piece. That's why I said XX series, should have made myself more clear.
 

wuzak

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True the XX (and 21) were 1 piece blocks. All the later were 2 piece. That's why I said XX series, should have made myself more clear.

According to Lumsden the 22 and 23 were also single piece block engines, while the 22A and 23A had 2 piece blocks, but were otherwise the same as the 22 and 23.
 

OldSkeptic

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According to RR the 22 was a 2 piece block and the 22A a XX conversion. The 23 was reversed cooling for the Mosquito and was 2 piece, the 22A was a 21 conversion.
The conversions were to a 2 piece block.
 
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asma18

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Jul 23, 2014
1. The Merlins and Packards differed little, Magnetos, supercharger drive and in fact the Bendix Carb was on the Merlin before Packard
2. It took Packard 12 monthes to convert the Rolls drawings to American convention
3. Two piece cylinder heads suggested by Packard manufactured by Rolls and were fitted to both
4. Rolls/Royce tolerances and specifications were followed to the letter by Packard. Spurious statements have been made that Packard had closer tolerances.
5. Someone has said the Packard engine achieved over 2000 hp ,from Rolls Royce Merlin Variants V-1650-9 1710 hp combat. And that was the most horsepower from a Packard in WW2
6. 1 to 4 from Rolls Royce Heritage Trust Derby U.K.
 

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