WW2: Why was the 9th Air Force given P51 ins6tead of giving them to the 8th Air Force in 1943? (4 Viewers)

[skyking1]

But "real" RR Merlins were sometimes used in USAAF P-51's. One of my college professors said the P-51 he flew had a RR engine and that they were much smoother than the Packard Merlins because it was a RR practice to sort through the available pistons and select ones that were as close as they could get to the same weight, leading to lower vibration.

The Packard built Merlins were different in numerous ways from the RR version, both due to a need to adapt the design for true mass production and to make some improvements that RR had not gotten around to doing yet.

Spitfire Mk XVI usually had Packard built Merlins.

they likely did that with the connecting rods too. It takes a little time and another operation to do that but it is otherwise a 'free' way to improve the balance overall.

 

[MIflyer]

they likely did that with the connecting rods too. I

True! I guess you have read of the conversation the Packard people had with Stanley Hooker, saying they could not make the V-1650 components to the same tolerances as those used by RR? Hooker replied, "Are the RR tolerances that much tighter than yours?" and the Packard guys replied, "NO! They are TOO LOOSE for us to build engines!" The American way was to build the components to tolerances so tight that it did not matter which parts the used when engines were assembled on a production line. The RR way was to build them to looser tolerances and have their craftsmen hand select them. Packard had to tighten up the tolerances so that they could run a typical automotive style production run.

One interesting thing that occurred was that the RAF followed the usual government practice of buying the airframes and the engines under separate contracts. When they agreed to give the AVG 100 Tomahawk I's, to be replaced by P-40D, they did NOT agree to give them the engines. Faced with no engines for the AVG Tomahawks, Allison stepped up to the plate and provided a solution. They had plenty of non-compliant out-of-tolerance Allison C series V-1710 engine parts. So they got some engineers together and used them to build 100 engines for the AVG out of "left over" parts. They did special machining or added shims and bushings to get the formerly unusable parts in acceptable condition. As a result they produced 100 "blue printed" engines that produced more power while using less fuel than any other C series V-1710. The Flying Tigers confirmed that their Tomahawks were noticeably faster than any other early P-40 around.

A friend of mine who was working with an airline on some RR engine problems in the 1960's said he saw RR custom build fan blade assemblies by making little tweaks to them, even marking them specially.

And the USAF used the TF-41 version of the RR Spey engine in the A-7D, with horrible results. The engine overhaul line at Tinker AFB just dismantled all the engines and sent the parts out for cleaning, inspection, and repair. But the TF-41's had been custom assembled in RR fashion, using match drilled assemblies and just would not go back properly.

 

[MIflyer]

There were a number of changes internally and externally, which required the swap out and replacement of a number of ancillary items if you wanted to change from a R-R Merlin to a Packard Merlin or vice versa.

I read where in early 1944 a P-51B went down, ditching in a French river, when the engine failed. Problem was that the standard spark plugs used by the USAAF were not suitable for the V-1650. I wonder what those spark plug differences were?