Why are the modern air crafts made with only two engines as opposed to four?
Two main reasons: One is that jet engines have become much more reliable and more powerful over the years. In the old days, more engines were needed just to get the aircraft flying. The 707 had to dump water into the engines on take-off just to keep them from overheating at take-off power, and the B-52 needed eight engines to get off the ground. Also, while jet engines have always been pretty reliable, they were less so 40 years ago than they are now, and for overseas flights having four engines was insurance against failures. The second reason is that two engines are easier to run and maintain than four. Four engines are still required to completely cover the world, but with increasing engine power and reliability, many overseas routes that were formerly allowed only for four-engine aircraft can now be safely flown by two-engine aircraft, so the need for four engines has diminished. The very largest airliners still have four engines, though (A380, 747), just to be extra sure. Overall
