WW2: Why was the 9th Air Force given P51 ins6tead of giving them to the 8th Air Force in 1943? (2 Viewers)

[Engineman]

I note that the V-1650-1, with a single stage two speed supercharger, apparently had no such plug problems, or at least none that I have read of. This, despite the P-40F being deployed to locations where maintenance and supply was something of a challenge, like Guadalcanal and North Africa.

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As for the difference between the V-1650-3 and the Merlin 61, Packard used removable heads, unlike RR, which had found them too leaky with their first attempts. Packard also redesigned the supercharger gears, presumably to make them easier to manufacture. The challenge of producing enough of the gears was cited as the main limiting factor for RR production. Packard also had Wright redesign the supercharger impellers, presumably for ease of production. And of course Packard used US made accessories, including most significantly the Bendix Pressure Carb, which eliminated the Merlin's notorious Lean Cut/Rich Cut power loss associated with negative G's.

Sparkplugs were a development issue at several stages of the Merlin developments. In the early Merlin's during the late 1930's the sparkplugs had just developed from versions that used worked natural Mica for the central insulator body of the sparkplugs. Cast and fired ceramic insulators were developed by companies in Germany during the late 1930's and the ceramic varieties of insulator were just establishing themselves at the start of WW2. These early war engines were working up to about 6lb Boost. As 100 Octane fuel was established
in use, Boost levels were raised to around 12lb and sparkplug issues came and went, with problems from internal gas leakage and Harder plugs that suffered more from fowled plugs at lower power settings. The particular sparkplug issues in the early days of the long-range escort Mustang were really just further problems with these issues, that happened to coincide with higher Boost levels, long cruise flights and more exotic fuels in the 2-stage engines. I believe that the rush for certain British sparkplugs for early 2-stage Packard engines was precipitated by the fact that Rolls-Royce had been pushing the sparkplug development with British manufacturers for these higher spec plugs for a while. As soon as the American companies got the details of the later plugs, they tooled-up and made them by the thousands.

Eng