... or better known as "engine test beds".
Wiki: The T38 started life with a 19-stage axial compressor, eight can type combustion chambers, a 4-stage turbine driving the compressor and the extension shaft to the reduction gearbox.
Initially rated at 2,000 shp (1,491.40 kW) the T38 first ran in 1947 and flew in the nose of a Boeing B-17 Flying Fortress test-bed on 19 April 1949, rated at 2,250 shp (1,677.82 kW). Problems with gearbox vibration and combustion were dealt with during the test programme and were mirrored by problems in the Allison T40 programme. The engines fitted to the Convair CV-240-21 Turboliner were rated to 2,750shp.
Although the only aircraft slated to receive the T38 as a production engine, the Convair T-29E, was cancelled, the T38 did power a converted Convair CV-240 (the CV-240-21 Turboliner, a project that would be abandoned due to engine problems), and was fitted in the nose of the McDonnell XF-88B to drive experimental supersonic propellers. Further development of the T38 provided the power sections for the Allison T40 as well as forming the basis for the Allison T56/Model 501 and the projected Allison T39
The Allison T38 (company Model 501) was an early large turboprop engine developed by Allison Engine Company during the late 1940s. The T38 became the basis for the very successful family of Allison T56 turboprop engine.
Lockheed built B-17G with Allison T-38 engine, January 1955. A B-17G with nose section removed and replaced with a strengthened mount for a fifth engine.
This Lockheed/Vega B-17G-105-VE Fortress 44-85747 was loaned to the Navy as BuNo 83999 for engine testbed work.
Lockheed built B-17G with Allison T-38 engine, January 1955.
Lockheed built B-17G with Allison T-38 engine, January 1955.
B-17G as test-bed for Allison T-56 turboprop engine, ca. 1956.
B-17G as test-bed for Allison T-56 turboprop engine, ca. 1956.
B-17 Flying Fortress test bed for the P&W T-34 turboprop engine. Later flown on airshow circuits as "Liberty Belle".
Wiki: The Pratt & Whitney T34 (company designation PT2) was an axial flow turboprop engine designed and built by Pratt & Whitney. Its model name was Turbo-Wasp.
In 1945 the United States Navy funded the development of a turboprop engine. The T34 was produced from 1951 to 1960, but never used in U.S. Navy aircraft production.
The YT34 engine with three wide-bladed propellers was made for two Navy Lockheed R7V-2 Constellation(C-121s) variants, for testing. Flight tests were on 1 September 1954.
In September 1950, a testbed Boeing B-17 Flying Fortress flew with a T34 turboprop mounted in the nose of the bomber. The first application for the T34 was the Boeing YC-97J Stratofreighter, which later became the Aero Spacelines Super Guppy. The next application for the engine was the Douglas C-133 Cargomaster.