planemad2,
Using your 100 engines on an aircraft means you have a higher chance of an engine failure train of thought, it would also follow using your logic that if you had one engine installed on the aircraft you would have less chace of an engine failure....or if we narrow it down to talking about entire population of CFM56 engines...are we saying that somewhere out there installed on aircraft x which may have 1, 2, 4, or 100 CFM 56 engines out there we would expect one failure every 100 000 hrs ?
Does it really mean, a MTBF of 1:100 000, that you would expect mathematically an aircraft with 100 engines to fly for 1000 hours without a failure, an aircraft with 2 engines 50 000 hours without a failure, and an aircraft with one engine 100 000 hours without a failure? or is it really saying that out of the total population of engines you would expect a failure after 100 000 hours, but you don’t know when or where ?
What happens to the aircraft with 100 engines when it reaches 1000 hours of flying ? The MTBF for that aircraft has just jumped from 1:100 000 to 1:200 000 after 1000 hrs, and the two engine aircraft the MTBF would go from 1:100 000 to 1:102 000 after 1000 hrs.
Realistically...this maths is just that, maths. If you can tell me which aircraft if going to have the next engine failure, you are doing better than anyone else out there in industry.
The real reason for the number of engines installed on an aircraft is to do with design parameters, not predicted engine failure rates, when the 747 was designed, you could not get two or three engines big enough to power it, even now the A380 has a limited payload as the 4 large engines it has cannot produce the thrust required for the full design load. Give it time, engine technology will improve, and target thrust ratings will be achieved.
This might actually surprise you....the original 747 layout
Tri jets were designed also to meet design parameters. Before ETOPS you could not fly greater than 60 minutes from a suitable aerodrome in a twin, now with ETOPS introduced, you can do the Atlantic in a twin with ETOPS concessions, so there is no longer a requirement for Trijets.
Why has Airbus gone for the long range quads...could it be as simple as there is not enough ground clearance to put a 777 size engine on the wing without redesigning the landing gear ? You know the aircraft would have ground clearance to put 4 A330 size engines out there….without a big redesign, which is simpler, quicker to bring to the market, cheaper to design, and easier to manufacture ? And of course…lots of punters still like 4 engines…
