A342 From Germany, joined Jul 2005, 4655 posts, RR: 4 Posted (5 years 11 months 3 weeks 17 hours ago) and read 4581 times:
had just thought about this and decided to start a thread.
IMO, there were some strange engine choices on certain military aircraft, and it would be nice to hear something about the respective backgrounds.
First example: The C-5B. From what I know, they rolled off the assembly line between 1986 and 89. The GE CF6-80C had already entered service in 1985, yet those aircraft were equipped with the obsolete TF39. Had the CF6 been chosen, the RERP program would have been unnecessary.
Why was the TF39 used? Did Lockheed or the USAF not want to spend additional development costs? Was the CF6 line too busy? Was the schedule too tight? (But then again, the CF6-80A could have been used.) Did the USAF want maximum commonality with the A-models?
Next example: The last USAF KC-135s rolled off the line in 1965 (or at least the vast majority). The JT-3D turbofan engine was available from 1961, but to my knowledge, all aircraft were equipped with the JT-3C turbojet (correct me if I'm wrong!).
Why? Same reasons as with the C-5?
I'd like to hear your thoughts on this topic, and feel free to name additional examples!
FlyingClrs727 From United States of America, joined Apr 2007, 621 posts, RR: 0 Reply 1, posted (5 years 11 months 3 weeks 16 hours ago) and read 4566 times:
Quoting A342 (Thread starter): Had the CF6 been chosen, the RERP program would have been unnecessary.
Perhaps, but the CF6 uses a different pylon, plus the AMP has to be installed first before the digital engine controls will work. The C-5B was built with minimal modifications to the original C-5A. Installing CF6-80's back in the 1980s would have required as much reengineering as the RERP program is requiring now.
KC135TopBoom From United States of America, joined Jan 2005, 11708 posts, RR: 52 Reply 3, posted (5 years 11 months 2 weeks 6 days 16 hours ago) and read 4350 times:
Quoting A342 (Thread starter): Next example: The last USAF KC-135s rolled off the line in 1965 (or at least the vast majority). The JT-3D turbofan engine was available from 1961, but to my knowledge, all aircraft were equipped with the JT-3C turbojet (correct me if I'm wrong!).
That is correct, the last 12 KC-135s (1964 models) rolled off the line in late 1965 and early 1966. They were equipped with the J-57 (JT-3C) engines as the USAF contract called for these 12 airplanes to be KC-135As. There were some 49 KC-135Bs built in 1961, 1962, and 1963 budget years. These never flew as KC-135s but became EC-135Cs and early versions of the RC-135. They were Boeing designation B-717-139s, and were equipped with TF-33-P-7 or TF-33-P-9 engines (two versions of the JT-3D). These airplanes were also receiver refueling capable.
The JT-3D was available to the USAF since 1959, as the VC-137B had them, the VC-137A had JT-3C engines (both were B-707-120, except the JT-3D version was a B-707-120B). Later, both VC-137As were reengined to the VC-137B configueration. Of course the later, larger, (B-707-320B) and longer range VC-137C had the 19,000lb thrust JT-3D-7 engines (USAF designation TF-33-P-9)