The different Mustang engine configurations

[DaveBB]

The P-51A with an Allison engine, which performed poorly at high altitude:


The P-51B through H, with the high performance Merlin engine:


The twin-engined P-82:


The radial engined P-51 concept:


The tri-engined P-51:



The turbo-prop P-51:

[Ack-Ack]

The pictures of the P-51 with the jets wasn't intended to be a version of the Mustang powered like that, those were just a couple of Mustangs that were used to test, IIRC, captured German jet engines.

ack-ack

[DaveBB]

Roy Marquardt was an aeronautical engineering graduate from Caltech who had worked at Northrop during World War II on the YB-35 flying-wing bomber project. While working on problems cooling the engines, which were buried in the wings, he found that the heat generated by the engines produced useful thrust. This started his interest in the ramjet principle, and in November 1944 he started Marquardt Aircraft in Venice, California to develop and sell ramjet engines. In the late 1940s the company relocated to Van Nuys, California, adjacent to the Van Nuys Airport.

Marquardt's first products were wind tunnels, but by the end of their first year they had delivered an experimental 20 inch (0.51 m) ramjet to the United States Navy for testing. The United States Army Air Forces purchased two of the same design early in 1946, and fitted them to the wingtips of a P-51 Mustang fighter for in-flight testing. By this time the Navy had fitted theirs to a F7F Tigercat and started flight tests in late 1946. Later Navy tests fitted the same engine to a XP-83 and F-82 Twin Mustang.

[skorpx1]

I'd like to know the top speed of that turbo prop 51.

[Ack-Ack]

Okay, it was US jet engines being tested.  The fact remains the tests were for the jet engines, not the feasibility of a jet powered Mustang.

ack-ack

[BnZs]

I'd like to know the top speed of that turbo prop 51.

I believe that is the Piper Enforcer, which itself was derived from the Cavalier Mustang.

http://en.wikipedia.org/wiki/Piper_PA-48_Enforcer

[olds442]

I would fly a radial 51 all day

[DaveBB]

Two different types of jet engines were used on the P-51.  The ones attached to the wing hardpoints were actually German ramjets from V-1s.  While these provided a great amount of thrust and acceleration, it was said to have severely hampered roll-rate of the P-51.

From 43-47, hybrid engine aircraft were abundant in the U.S. military.  I'm not sure why you are so dead-set on saying the jet engines were just for "testing".  The goal was to get a long cruise range from the piston engine, and to use the jet engines during combat.  Wingtip mounted jet engines were certainly not just for testing the ramjets.  This installation was far more complicated and difficult than just mounting them to the inner wing hardpoints like the V-1 jet engines.

A neat note about the turbo-prop PA-48 enforcer, it competed against the A-10 for the air force contract of a ground attack aircraft.  The idea is not as crazy as it seems.  Just within the last few years, the air force has selected a turbo-prop plane very similar to the PA-48 to enter service as a COIN aircraft.