Differences between engines on a real plane?

[Guest nandrzej]

Hello EveryoneWith the up and coming release of 747-400 Queen of the Skies I thought I would post a question about why an airline would choose one engine type/manufacturer over another?The differences in FS are a different discussion, I am wondering what happens when an airline buys a plane, what factors do they weigh up? I assume things like initial cost, fuel efficiency, maintenance costs, life cycle and so on but what else. Are some better suited to short hops and others to long hauls.For instance you can get the 747-400 with three engine manufacturer flavours, namely Pratt and Whiteney, Rolls Royce and General Electric, but you can't get the Rolls Royce engines on the 744ER. Is this because they are not powerful enough, or because no one would by them, or because no one has bought them?Apart from the obvious differences like how an engine looks on wing and thrust rating, what other factors influence engine selection?Input from industry people greatly appreciated.regards, Nick

[CF104 0]

Hi Nick,Probably the two most influential points of engine choice are fleet commonality and regional support. If an operator is already running a specific type of engine on type 'A' aircraft and has the opportunity to match that engine on type 'B' aircraft, the spares and maintenance costs will be far lower than if the operator had a mixed engine fleet. There is also the regional support issue. How close to the operator is the nearest parts/overhaul centre and it's a plus if it's in their country as it keeps locals employed.Cheers, JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[Guest Hawkeyeted]

John,You hit the nail on the head. If, lets say United for sake of argument, has all of it's mechanics certified on GE engines, then there is considerable cost savings in training/certification of their mechanics, as well as spare parts procurement.All of these issues are taken into consideration during the contract negotiation.

[Guest nandrzej]

Ok so if I understand correctly it is the support costs that govern engine selection most, based on personel experience, skills and training, and parts availability on the flown routes.So for instance when British Airways opted for GE engine on the first batch of 777's and snubbed their traditional and local big Boeing engine supplier RR, it was primarily because they thought they could save money (It could have also been the timing, my understanding is RR anounced an engine for the 777 and several days later BA announced it was going with GE and could not back out). Now they are buying a second batch of aircraft they are opting for RR engines this time, would this be because they have found this not to be true, or some other reason?much thanks for the replies, cheers, NickPS can you re-engine an aircraft with a different make of engine, or is it prohibitively expensive?PPS I know this is not quite PMDG related but it was the only example I could think of .... and it shows the passion for the 777, that I would be delighted if PMDG were to make!

[Qavion 19]

"PS can you re-engine an aircraft with a different make of engine, or is it prohibitively expensive?"It can be prohibitively expensive, Nick, as the modifications required are very extensive.Examples...Engine mounts (attach system) may not be the same. E.g. On GE and RR-powered 747-400's the fuel tanks are not the same size because one type of mount requires more wing area.Some engines require different fire extinguishing systems (including different bottle location, number of bottles, different indications in the cockpit).Different engines will require different fuel system logic, different FMC software, different display logic/indications, etc...Some 744 engines have hydraulically opererated reversers (P&W), some are pnuematically operated (GE and RR). I'm sure you can imagine the hydraulic and electrical changes involved. The extra load on the hydraulic system will have to be considered. 4 high powered Air Driven Hydraulic Pumps may have to be fitted instead of 2 lower-powered electric and two Air Driven types.One engine may be more efficient than another, but it may weigh more. As said above, one type might take up fuel tank space.... so the aircraft range will be reduced as a result. On the case of engine choice, engine manufacturers have been known to offer large subsidies (some call them "bribes") to airlines which are large enough to offset any losses in fuel efficiency. This may only be an interim solution until the engine manufacturer can improve the efficiency of their engines.Hope this helps.CHeeers.Ian.

[Guest Hawkeyeted]

Ian, you are correct to. I am a mechanic on the Rolls Royce/Allison T56-427 turboprop. In short, it's a piece of crap. There is a problem with the T-1 disc rubbing the inside of the turbine casing due to heat warp from the combustion section. Rolls Royce are experimenting with different solutions and right now it looks like a ceramic pad is the answer. The T-1 disc will wear a grove in the ceramic pad, and therefore mitigate any "wobble" in the turbine.Short story, Rolls has a reputation (and contract) to uphold.