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And for that matter, what were RR Merlins?

According to Robert Neal's superb book on the Packard aircraft and marine engines and paraphrasing a bit from it, the British RR Merlin used 4 different threads, British Association (BA), British Standard Fine (BSF), British Standard Whitworth (BSW), and British Standard Pipe (BSP), plus a few that RR modified themselves. About 140 different external threads were used on the engine. One of Packards' significant problems with the contract was duplicating these threads, finding vendors to make the necessary thread tools, etc.

If the topic interests you, buy Mr. Neal's book, it's reviewed in the "Packard Bookshelf" on this website.

O_D, very good reply.

The contract required that the Packard-built engines be able to replace the RR-built engines with no modification to make them fit. Packard did make many improvements to the engine, mainly to accomplish precision mass production.

I don't know what the fastening convention was for the Merlins fitted to the Mustangs (and a few P-40s), but they probably were built using U.S. measurement fasteners, and with some design features that differed from the ones Packard supplied to the RAF. Did Packard run two production lines, one for RAF and one for US AAF?

Also, the Automobile Quarterly book, "Packard a History of the Motor Car and the Company" (edited by Beverly Ray Kimes) discusses the Packard - Rolls Royce connection.

Later, Continental and Ford of England also produced the Merlins.

Great story.

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The Rolls Royce Merlin is a liquid cooled V-12 aircraft engine. It was widely used in a variety of RAF military aircraft. The better known types that were fitted with Merlins included the Spitfire and Hurricane fighters, the Mosquito fighter bomber, and the Lancaster bomber.

Probably the most famous aircraft fitted with a Merlin was the North American P-51 Mustang (Model B and above). I wrote a short article about this (The Car that Won the Air War Over Europe) and it is available on this site in the Literature and Manuals section.

The Packard-built Merlins were designated V-1650 for the cylinder arrangement and displacement.

Read Neal's book and the AQ book for more info.

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Edit: Here is a photo of a nicely restored Merlin showing the rear or supercharger end. It is on exhibit at the Cavanaugh Museum of Flight.

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Anybody ever put Merlins in a P-38? Would be interesting to see what that would do, although in its day it was a very expensive plane......thus a somewhat unlikely candidate for major improvement...

Anybody ever written much on the Allison engines, which were supposed to have been useless for high altitude work of any kind?

Supposedly the fasteners were not modified and the British systems were kept. Any good machinist can move from one system to the next. The problem is in tooling.

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Actually, the US AAF had the answer to its question (before settling on the North American P-51s with their supercharged Merlin engines) of how to escort the bombers from England to their targets deep in Germany, while protecting them coming and going at the high altitudes and long ranges. The Lockheed P-38 with its turbo supercharged Allison engines could have done the job. But, their then superiority in range and altitude was not used.

Having just written this, it brings up a good question: Why? I need to research the reason for not considering the P-38s early on, and get back to the site. Think of all the air crews that could have survived with this protection.

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Hello All,

As a follow-up to my above posting, I went to my favorite aircraft historical source (brother Tom whom just retired from a long-time career at Sikorsky).

I asked him why the AFF did not use the Lockheed HP-38 Lightening as a long-range high altitude bomber escort in the early day of the bombing campaign.

He said the AFF did use them, initially, but experienced a problem in the high altitude cold air over Europe. When the airplane would be in a high speed dive the air flow over the stub wing portions between the engines and the fuselage pod would go supersonic. When this happened the plane could not be controlled and would crash. Pilots would try and maneuver the airplane, but could not get it out of the condition. If the pilots would have stayed in the dive and waited out this condition until they got down into warmer air the supersonic condition would disappear, and control of the plane would return.

Lockheed came up with a solution to install air brakes on this portion of the wing to disrupt the air flow and keep it from going supersonic. The company made up a supply of kits to retrofit the aircraft in theatre. However, the DC-3 crashed enroute and all the kits were lost. After this the AAF lost faith in the P-38 as a bomber escort, and ceased to use them in this role.

The Lightening had a good record in North Africa and the Pacific, where the air is warmer than over Northern Europe.

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Pat, et al: Interesting Packard war time ad is now appearing in the Recent Photos just to the right of this. A few Packard-built Roll Royce Merlin engines were fitted to the Curtiss P-40 Warhawk. The P-40s were mostly fitted with the Allison V-1710 engines. The Merlin equipped Warhawks can be easily identified because the snorkel used on the Allison is missing and the intake below the prop is larger.

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