P51 with Allison turbo

[fastmongrel]

I would have to qualify and say yes and no but ultimately claim that it could have been done.

The Merlin engine P-51B took nearly 2 years to get into production. Surely in that time the turbo Allison could have been fitted. Now in terms of the space issue.
1 Q: Where would the intercooler be fitted?
A: The same place the Merlin had its water cooled intercooler: behind the engine.
2 Q: Where would the turbo supercharger be fitted?
A: The same place the Merlin had its mechanical supercharger: behind the engine and underneath the supercharger.

Of course the assembly would have been somewhat larger, but its hard to imagine that it would be so much that it could not be dealt with by a slight nose extension of the P-51.
The twin Mustang was for instance some 18 inches longer. The P-51B had nearly every panel redesigned compared with the P-51A so given the redesign this was not much to go a little further.

The problem may have been that the NACA's advice to the Army Air Corps which was that the turbo supercharger should be kept separate from the engine connected by ducting. Integral turbochargers, which were integrated into the engine and shipped in a single package would have to be used with such a P-51 turbo Allison.

The advantage would likely be
1 The same top speed, likely higher speed at high altitude, say above 25,000-30,000ft
2 Much better cruise fuel consumption and therefor escort range.
3 Higher service ceiling and climb rate at high altitude.

Have a look at the size of the Turbo and associated piework on the P38 not forgetting the intakes under the prop for intercoolers. Its a lot to squeeze in not saying it couldnt be done but by the time it has been fitted in the growth in size is possibly going to absorb any preformance benefit.

Clickable link that zooms in http://thehuwaldtfamily.org/jtrl/vehicle_data/Fighters/Lockheed%20Martin/Lockheed%20P-38%20Lightning%20Cutaway.jpg

 

[Shortround6]

Putting the turbo close to the engine may present problems. Exhaust gas temperature going into the turbine blades was a problem and the existing turbos and engines may have been just below the critical temperature with several feet of exhaust pipe exposed to cooling air before the the hot gas hit the turbine blades. Hotter gas may mean turbine blade failure and turbine blade failure does NOT mean the turbo stops working, it means turbine blades (or pieces) leave the turbine at very high velocity (many US aircraft had steel "scatter" shields installed near the turbines), at some point the turbine becomes un-balanced and the turbine bearing/s can fail. Please remember that the turbine is operating at 1200-1300 degrees F and spinning at around 22,000 rpm at/near full throttle.
The exposure of the turbine blades to the slipstream air in "most" installations ( the P-47 being one of the few exceptions, and how much of the airflow through the ducts was was cooling purposes?) is another indication that cooling the turbine was more important than the last degree of "streamlining/drag reduction".

 

[wuzak]

Also, if the turbo is right behind the engine you will need space to duct the air to the compressor inlet, and you also have to have the space to dump the exhaust overboard.

I am visualising the turbo's axis being parallel to the crank.

If it was positioned perpendicular, then its the diameter of the turbo that is adding to the length, and you will be dumping exhaust into the air headed for the radiator.

 

[drgondog]

Major redesign of P-51 to accommodate a turbo - front or back. CG trade off issues and ultimate performance degradation of a drag compromised fuselage to accommodate intake inlets is probably the reason no prototype contracts were ever secured.