Simviation Forum - Another Mustang question

Jun 16^th, 2010 at 1:17pm

brettt777 Offline
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I have heard people talk about the differences between the Rolls Royce Merlins and the Packard Merlins. Is there any obvious way to tell from the outside the aircraft which version of the Merlin this aircraft has? It is a P-51D, AAF sn 44-74009. Were the Packard Merlins used in the later airframes? The "D" model only? Now, this may be a moot point anyway because I am fairly sure this engine, regardless of which Merlin it is, has been worked over by the folks at Roush Racing.

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Reply #1 - Jun 16^th, 2010 at 1:34pm

Hagar Offline
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I believe that all production Merlin-powered examples of the P-51 were fitted with the Packard-built engine. That would include your P-51D. There's no telling what the racing specialists get up to. I believe they prefer the Rolls-Royce originals if they can get their hands on them.

PS. The two engines were not interchangeable. The Packard version used some US-built accessories like the starter motor, generator, hoses & possibly fasteners with US standard thread sizes.

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Reply #2 - Jun 17^th, 2010 at 9:49am

brettt777 Offline
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Hagar wrote on Jun 16^th, 2010 at 1:34pm:

I believe that all production Merlin-powered examples of the P-51 were fitted with the Packard-built engine. That would include your P-51D. There's no telling what the racing specialists get up to. I believe they prefer the Rolls-Royce originals if they can get their hands on them.

PS. The two engines were not interchangeable. The Packard version used some US-built accessories like the starter motor, generator, hoses & possibly fasteners with US standard thread sizes.

So then the planes that have the Rolls Royce Merlins would have metric hardware, at least for the engine stuff...?

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Reply #3 - Jun 17^th, 2010 at 11:31am

Hagar Offline
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brettt777 wrote on Jun 17^th, 2010 at 9:49am:

So then the planes that have the Rolls Royce Merlins would have metric hardware, at least for the engine stuff...?

I would expect Rolls-Royce to use British standard threads like BSW (Whitworth), BSF & BA. I could be wrong but always thought the Packard-built equivalents used US standard threads. I would also expect ancillary components like starter motors & pumps to be of local manufacture. The pipes & flexible hoses fitted to the Rolls-Royce manufactured engines probably have BSP threads & British components would use BA or BSF bolts & screws. If it's an original engine the information you need should be on the manufacturer's data plate.

This is a typical Rolls-Royce data plate.

Compared with the Packard plate.

I believe the rocker covers on British built engines had the name ROLLS-ROYCE engraved on them (see THIS PHOTO) while the Packard versions were plain. This would not be positive identification as the covers could be easily replaced or modified during restoration. Please note that I've never worked on a Merlin & I'm only going from what I've been told over the years.

PS. Just found this. Scroll right down to the bottom. http://www.enginehistory.org/british_fasteners.htm

Quote:

Packard Built Merlins

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.

« Last Edit: Jun 17^th, 2010 at 1:44pm by Hagar »

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Reply #4 - Jun 18^th, 2010 at 9:58am

brettt777 Offline
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Wow, that is all very fascinating to me. I love historical things like that. So basically Rolls Royce gave Packard the specs for the Merlin and then Packard fabricated or sourced out all the components and built them from scratch or did they get some of the parts (blocks, cylinders, crank, rods, pistons, etc) from RR...? Hmmmmm...

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Reply #5 - Jun 18^th, 2010 at 9:59am

brettt777 Offline
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Oh and by the way, thanks a million for your response and info. Much appreciated.

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Reply #6 - Jun 18^th, 2010 at 3:46pm

Hagar Offline
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brettt777 wrote on Jun 18^th, 2010 at 9:58am:

Wow, that is all very fascinating to me. I love historical things like that. So basically Rolls Royce gave Packard the specs for the Merlin and then Packard fabricated or sourced out all the components and built them from scratch or did they get some of the parts (blocks, cylinders, crank, rods, pistons, etc) from RR...? Hmmmmm...

I believe that Packard produced the complete engine. The idea was to set up a separate production line to increase output. Rolls-Royce was also involved with development & production of other aero engines & did not have the capacity to keep up with demand for the Merlin. There was also the constant threat of the factories being put out of action by enemy bombing.

The history of the Packard Merlin is fascinating. Have a search on Google. It was an incredible achievement by Packard Motors & a fine example of cooperation between the two companies on opposite sides of the Atlantic. The Packard Merlin was fitted to Canadian built Hurricanes & Mosquitoes, the Lancaster B.III, Spitfire Mk XVI and other British types as well as some versions of the P-40 and of course later variants of the P-51.

Quote:

Oh and by the way, thanks a million for your response and info. Much appreciated.

You're welcome but don't take everything I say as gospel. That goes for articles published on the Internet. Also bear in mind that a lot of WWII aircraft flying today aren't all they appear to be, especially if they've been raced at Reno at some point in their lives.

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