Dc8jet From United States of America, joined Feb 2004, 321 posts, RR: 0 Posted (9 years 4 months 3 weeks 3 days 1 hour ago) and read 3256 times:
Suppose one of the airlines operating 737-300s wanted to sell them. Say NW was interested in them but all of the others have RR engines as opposed to NWs P&Ws. Would it be possible to re engine them with P&Ws? If so would it be worth it from a cost standpoint?
CitationJet From United States of America, joined Mar 2003, 2319 posts, RR: 3 Reply 2, posted (9 years 4 months 3 weeks 2 days 23 hours ago) and read 3200 times:
Like Grease said, it is possible, but not economical.
I worked at Boeing Wichita as a structures engineer when the CFM-56 were added to the KC-135 to make the KC-135R model.
It is a lot of work.
Some of the items required to certifiy a new engine on an airplane include: updated aircraft loads analysis (flight maneuver loads, dynamic gust loads, dynamic landing loads), updated flutter analysis, updated mass properties to support flutter analysis, ground vibration test (to validate dynamic model for flutter analysis), flight flutter testing (envelope expansion), fatigue analysis, flyover noise certification. Not to mention designing the hardware to accomodate the new engine.
Dl757md From United States of America, joined May 2004, 1560 posts, RR: 18 Reply 4, posted (9 years 4 months 3 weeks 2 days 18 hours ago) and read 3133 times:
A couple of years back when DL 757s were having bad problems with 10th/11th stage stator cracks there was talk of re-engining all 121 of DL's PW 757s with RR. The cost I believe was estimated at 12 million dollars per plane.
Broke From United States of America, joined Apr 2002, 1322 posts, RR: 3 Reply 6, posted (9 years 4 months 3 weeks 2 days 13 hours ago) and read 3039 times:
Another kicker on re-engining the 757; P &WA engines rotate clockwise, RR engines rotate counterclockwise (anticlockwise in the UK).
Pylon problems (and there are some) that are related to the torque on the pylon and wing result in problems occurring on one side on a Pratt powered airplane and on the opposite side of the Rolls powered airplane.
Swapping engines would result in an airplane that has been torqued in both directions and would likely give you long term problems that would be unique to the modified airplanes.
JeffDCA From , joined Dec 1969, posts, RR: Reply 10, posted (9 years 4 months 3 weeks 2 days 8 hours ago) and read 2965 times:
Yes you are correct. In an effort to keep costs down the 7E7 will have a common pylon that can mount both the RR or the GE engine.
Not only that, Boeing are also looking at the ability to have 1 GENX and 1 Trent 1000 on the same aircraft, making it a lot easier for airlines when an engine goes tech, and they have one available from a different manufacturer.
LMP737 From , joined Dec 1969, posts, RR: Reply 11, posted (9 years 4 months 3 weeks 2 days 7 hours ago) and read 2920 times:
That will be interesting to see. An airline would have to be preety desperate to fit another type engine on it. Changing an engine twice costs money so my bet would be on them waiting for the same type engine to show up. But like I said before it would be fun to see it.
JeffDCA From , joined Dec 1969, posts, RR: Reply 12, posted (9 years 4 months 3 weeks 2 days 6 hours ago) and read 2914 times:
I think the idea of it is that if a RR operator has an aircraft with a bust up engine somewhere and there's no replacement, but there's a GE operator at that airport with a spare GE engine, then rather than delay the flight and wait for a RR engine to be flown in, they can fit the GE and carry on with the flight.
Thrust From United States of America, joined Sep 2003, 2686 posts, RR: 10 Reply 13, posted (9 years 4 months 3 weeks 2 days 6 hours ago) and read 2916 times:
Of course you can reengine, but that don't come cheap, cookie
AA wanted to retrofit TWA's 757s with RR engines, but again, the excessive costs made it inefficient and uneconomical to do so. My one question to you is...why was it much cheaper to retrofit the 707s with turbofans over turbojets rather than do an engine change today? Why were many more airlines willing to do this with their earlier 707s? Obviously to maintain engine consistency in the fleet, but AA didn't seem to have a problem operating TW's 757s for 4 years. Please help me out. Thanks.
LMP737 From , joined Dec 1969, posts, RR: Reply 14, posted (9 years 4 months 3 weeks 2 days 5 hours ago) and read 2888 times:
AA never wanted to reengine the TWA 757's with Rolls Royce motors. The cost of doing so on leased aircraft that were eventually going to be returned anyway would not have made sense. As we speak AA is in the process of returning all the TWA 757's to the lessors.
QantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 34 Reply 15, posted (9 years 4 months 3 weeks 2 days 4 hours ago) and read 2875 times:
In the case of four-holers, something else needs to be checked out before re-engining: resonant vibration. Depending on the engines' vibration frequency and the spacing between the engines on each wing, the vibration could be resonant and start shaking the wings with increasing amplitude, possibly to the extent of structural damage (like flutter). If it happens that the frequency of the new engines to be fitted are resonant at the spacing of the old engines on the wing, the whole engine hardpoints, fuel lines, systems, etc., would all have to be moved to rectify that - a big expense. Better just to stick with what you've got!
Broke From United States of America, joined Apr 2002, 1322 posts, RR: 3 Reply 16, posted (9 years 4 months 3 weeks 1 day 10 hours ago) and read 2766 times:
The early 707-100's and 720's were converted to the "B" version by exchanging the JT3C turbojet engine for the JT3D turbofan engine. The reason was the dramatic improvement in fuel consumption, with an increase in take-off thrust, and a reduction in engine noise (not very noticeable).
Both engines used the same mounts, as they are variants of each other.
The down side of the conversions was an increase in engine weight, an increase in frontal area (more drag), modifying the pylon to accommodate the fan portion of the nacelle, and a loss of thrust at higher altitudes.
Turbofan engines suffer a greater percentage loss of engine thrust than turbojet engines as ambient pressure decreases (altitude increase).
Korg747 From United States of America, joined Mar 2003, 549 posts, RR: 6 Reply 17, posted (9 years 4 months 3 weeks 22 hours ago) and read 2675 times:
It's a great idea with the 7E7 to have changeable engines. It would be a bad idea though to have on GE on a side and one RR on another side. I'm sure there will be weight differences and thrust differences too. How would one deal with that? Unless GE and RR agree on one specific numbers for every thing on both engines, I can see problems with that.
Techspec From United States of America, joined Sep 2001, 70 posts, RR: 0 Reply 18, posted (9 years 4 months 3 weeks 8 hours ago) and read 2585 times:
Do not get too carried away with the idea of "interchangeable" motors on the 7E7. This is driven by the leasing companies for "marketability issues" not a maintenance convenience. I highly doubt you will ever see a 7E7 flying with a mixed set of motors.
JeffDCA From , joined Dec 1969, posts, RR: Reply 19, posted (9 years 4 months 3 weeks 6 hours ago) and read 2562 times:
I've seen the idea discussed on the interent somewhere (i believe it was the Boeing website), also, i found this from www.airmech.co.uk (an Aircraft Mechanic forum):
"Yes, the aim is to be able to have a mix of both engines on one aircraft. No need to have a double engine change because brand GE or brand RR is not available at the airport where an engine failure occurs. Hook up the available brand, EGR, Alles!!
It is all being worked out at the design stage, to ensure that it goes as easily as other interchangeable parts we are currently familiar with."
Whether or not we will ever see a 7E7 with both engines attached at the same time remains to be seen, but it is certainly being discussed as a possibility.