Ending the Argument

[pbehn]

That's more than likely: according to Morgan & Shacklady, the new "...oleos were lengthened and strengthened to cope with the large diameter propellers...". The F. Mk XIV & XVIIIs used a 10ft 5in diameter Rotol R19/5F5/1, whereas on the F. Mk 21/22/24s, the propeller was a Rotol R14/5F5/2 of 11ft 10in diameter. The maximum speeds of the 20 series Spitfires increased by about 10-15 mph over the XIV/XVIII using the same Griffon 61/65s.

Thankyou, I pick up "stuff" from many sources but cant quote them. One of the "tricks" of the original Spitfire design came to haunt it later was the undercarriage set up it limited the prop diameter and made the later versions tricky on take off and landing, just like its only adversary the Bf109 which was also designed around a circa 1000BHP engine.

 

[drgondog]

Bill,
As a CROT (crude rule of thumb) could one compare the equivalent Spitfires with Merlin / Griffon engines for fuel flow differences to get a "rough" hack at what a Griffon Mustang would have burned? And from that extrapolate a "rough" hack at it's range with or without external fuel tanks?
Cheers,
Biff

Maybe. Because a.) the drag co-efficient is higher on a Spit XIV than a B Mustang, and the Griffon, as geared, dropped Hp delivered rapidly above 22K+ feet at equivalent RPM/Boost it would be hard to extract SFC at 25K+ where the Mustang was king for 8th AF escort. The RAF flew very few mission types above 15,000 feet, so the gearing was designed for a lower altitude peak performance.

If Flight tests for range, clean, existed for the Griffon/Spit accompanied by Hp as function of altitude and boost a CROT could be extracted

 

[drgondog]

The Griffon had similar power at 20-25,000ft with 100/130 grade fuel and +18psi boost (67inHg MAP) as the V-1650-9 did with 90inHg MAP and ADI.

The Griffon-Mustang discussion was occurring when the Mustang X and P-51B programs were in their initial stages. The Griffon Mustang would have predated the P-51H by a year or so. Certainly the 100 series Merlins (of which the V-1650-9 was one) had yet to be developed at that time.

The Griffon Spitfire (XIV) was 30-40mph faster than the equivalent Merlin Spitfire (VIII), depending on the sub type (F, LF, HF) and the Merlin variant used (63, 66, 70). Certainly the Mustang was as fast as the Griffon Spitfire, but it was quite a bit faster then the Spitfire with the same engine.

Wuzak, I don't believe that a Griffon could have been adapted for first flight on or around the February 1944 timeframe without a major disruption of P-51D airframes. The XP-51F was first flying with 1650-3 in mid Feb and the first series production D also first flew in February. The modified Merlin 145 (SM 14) type was installed in the same airframe for the XP51G (with cooling and engine mount mods flew August 1944 - Just six months before production P-51H

 

[wuzak]

Wuzak, I don't believe that a Griffon could have been adapted for first flight on or around the February 1944 timeframe without a major disruption of P-51D airframes. The XP-51F was first flying with 1650-3 in mid Feb and the first series production D also first flew in February. The modified Merlin 145 (SM 14) type was installed in the same airframe for the XP51G (with cooling and engine mount mods flew August 1944 - Just six months before production P-51H

The original discussions relating to putting a Griffon in the Mustang were taking place in late 1942.

Any effort on that project would likely have detracted from the P-51B program.

The main issue for production would be the supply of Griffons. There wasn't enough production historically to supply NAA as well as Supermarine and Fairey. So it would need a licence version built in the US. Maybe at the Continental plant which was originally to build the IV-1430, but ended up building Merlins (in small numbers?) instead.

Changing over to a Griffon variant would also have cost time and reduced the numbers of P-51Bs built.

I think in reality the only way a Griffon P-51 would have emerged is if they committed to it from the start, instead of the Merlin P-51. But it would have required Packard Griffons, or similar.

 

[drgondog]

The original discussions relating to putting a Griffon in the Mustang were taking place in late 1942.

Any effort on that project would likely have detracted from the P-51B program.

The main issue for production would be the supply of Griffons. There wasn't enough production historically to supply NAA as well as Supermarine and Fairey. So it would need a licence version built in the US. Maybe at the Continental plant which was originally to build the IV-1430, but ended up building Merlins (in small numbers?) instead.

Changing over to a Griffon variant would also have cost time and reduced the numbers of P-51Bs built.

I think in reality the only way a Griffon P-51 would have emerged is if they committed to it from the start, instead of the Merlin P-51. But it would have required Packard Griffons, or similar.

I pretty much agree Wuzak. That said, the gating factor that delayed delivery of P-51B-1-NA to ETO was the gestation period at Packard to tool up for the 1650-3 changes from 1650-1, then pass bench tests at Wright Pat, and subsequent production. I suspect that a.) concluding negotiations to build Griffon in US, particularly with political forces arrayed (MC/GM/Allison) against yet another Brit engine - then convert drawings, and tool up for production for Griffon, then direct NAA to redesign the P-51B/D for Griffon - would heve never made it past the sniff test when 8th AF was getting Hammered.