Just curious, why would it be easier to test two engines? The crew of flight engineers already have their hands full testing one engine, why complicate things by adding more engines?
During flight test the job of the other 3 engines is to keep the aircraft flying. This allows the crew of flight test engineers to focus on the one test engine. On the first couple flights, the test engine may not even be used at critical phases (i.e. during takeoff) until it demonstrates that it can operate safely in the air.
Also, throughout an engine development test program, unexpected things can and will happen. That's the point of engine testing, you want to find problems and fix them before your customers start flying your engine. So no matter how much time and effort is put into engineering design before testing, engines will break. The goal is to find all the big issues during ground test and fix them before flight test. However, Murphy's Law still governs in the air, so if something can go wrong, it will. The flight crew needs the capability of shutting down the test engine if needed.
CF188A From , joined Dec 1969, posts, RR: Reply 6, posted (6 years 9 months 6 days 1 hour ago) and read 2363 times:
back in the day I dont think they cared as much about efficiency. It was pretty cool just to get your feet off the ground and use the fuel gauges as a clock to determine how much longer one could remain airborne... hence... efficiency!
Starlionblue From Greenland, joined Feb 2004, 16340 posts, RR: 66 Reply 7, posted (6 years 9 months 6 days 1 hour ago) and read 2348 times:
They once hung a JT9D (I think) from one of the pylons on a B-52, replacing the two existing engines. This was during testing for the Boeing C-5 proposal. There's a picture in "Boeing - Planemaker to the World". IIRC, the engine had as much thrust as three of the original B-52 engines.
KELPkid From United States of America, joined Nov 2005, 6147 posts, RR: 4 Reply 9, posted (6 years 9 months 5 days 21 hours ago) and read 2236 times:
Quoting Starlionblue (Reply 7): They once hung a JT9D (I think) from one of the pylons on a B-52, replacing the two existing engines. This was during testing for the Boeing C-5 proposal. There's a picture in "Boeing - Planemaker to the World". IIRC, the engine had as much thrust as three of the original B-52 engines.
IIRC, this is how the JT9D was tested for the 747 program. There was simply a lack of other aircraft at the time with the required wing clearance
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
Starlionblue From Greenland, joined Feb 2004, 16340 posts, RR: 66 Reply 12, posted (6 years 9 months 5 days 17 hours ago) and read 2138 times:
Quoting KELPkid (Reply 9):
IIRC, this is how the JT9D was tested for the 747 program.
I looked it up and we are both right. B-52s were used for both the C-5 and the 747 engines.
Two B-52Es were modified for use as engine test beds. One aircraft (B-52E-55-BW, S/N 57-0119) was used to test the General Electric TF-39 for the Lockheed C-5A Galaxy program. The TF-39 was mounted on the right inboard engine pylon in place of the two J57s normally installed. The single TF-39 turbofan, rated at about 40,000 pounds, had as much thrust as four J57 turbojets on a standard production B-52E.
Another aircraft (B-52E-85-BO, S/N 56-0636) was similarly modified to test the JT9D turbofan engine for the Boeing 747 program.