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Why are the modern air crafts made with only two engines as opposed to four?

Aren’t the four engine air crafts safer?
p.s. I know about the latest A380 but how come boeing stopped manufacturing four engine air crafts after 747?

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10 Responses to “Why are the modern air crafts made with only two engines as opposed to four?”

  1. Matthew said:

    Because the engines have become more reliable, and more powerful. When is the last time you heard about a jet going down because of both engines failing?

  2. MichaelS said:

    The modern engines have enough thrust to keep the plane aloft with just two. As a matter of fact, the plane can fly on one engine in case one goes out. They are tested this way.

  3. FN-GM said:

    They are more reliable for one and another point is that it is cheaper to run (fuel wise) an aircraft with 2 engines as apposed to 4 by more than a 3rd. This makes it work buying brand new aircraft with 2 engines to replace the 4 engined ones. they will save money by doing that.

  4. JAGUAR said:

    its cheaper to use 2 plus lighter these engines are £2 millon each and newer engines produce more thrust

  5. Dan W said:

    2 passenger are flying across the country when the Pilot announces that “1 engine has trouble and will be shut down,there is need for alarm, the plane is safe with 3 engines but speed will be reduced and they will arrive late.
    Another engine develops a problem ” no need for alarm we will continue at a slower speed”
    1 passenger says to the other if another engine dies we’ll be up here all night.

    Todays engines are better than yesteryear’s, but economy and design allow for better aircraft.

  6. Doggzilla said:

    The FAR/AIM states that all new jets must have enough trust to be able to CLIMB at 500 feet per minute with one engine out.
    Modern engines are roughly 2-3 times more powerful than the turbojets that originally equipped jets like the DC-10 and 707. Think 45-80k plus lbs of thrust compared to 8-15k for the older jets. They have become immensely powerful. They can climb on one engine, they dont need 3 engines to stay up anymore.

  7. Techwing said:

    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 chances of unacceptable engine failure diminish with an increasing number of engines. With four engines instead of two, the chances of a single engine failing go up, but the chances of too many engines failing (two or more) go down, so overall the chances of losing an aircraft because of engine failure are lower for aircraft with more engines. But more engines are more expensive to operate and fuel and maintain, so they are not often used except for routes over water (or for aircraft so big that they need the extra power or a diminished risk of failure).

  8. richard b said:

    as engine power and reliability increased the need for four engines in most aircraft has diminished. two engines are more economical to run, are lighter, and since the aerodynamics are better with two engines as opposed to four engines, less power is required to overcome drag, which also improves fuel economy.

  9. Bardic said:

    Jet engines are now substantially more powerful and almost boringly more reliable than the early ones. For instance, the four P &W engines on the 707 developed about 18,000 lbs thrust each, for a total of 72,000; Rolls Royce are now getting 95,000 lbs out of the Trent -each!

    Big twins now are so over engined that, as already mentioned, they are capable of continuing a take-off and climb away on just the one, should the other fail.

  10. Rick said:

    Engines are more reliable, produce more power, two are cheaper than 4, the risk of engine failure is just about cut in half because you have half the number of engines. Also, because a certain amount of fuel is lost for cooling and just general engine overhead, two engines burn less fuel. The systems (electrical, hydraulic, fuel, pneumatic) are easier to design and require fewer parts with fewer engines.

    I forget the exact numbers, but a jet airplane must be able to climb at about a 2.4% climb gradient up to about 800 feet, and 1.2% thereafter, assuming a failure of the most critical engine at V1—the go/no go decision point. Further, a jet must be able to safely land with the failure of 1/2 of the available engines rounded up. Lastly, in approach configuration, a jet aircraft must be able to climb with the failure of the most critical engine, in the approach configuration. With the more powerful engines, these climb requirements are fairly easy to attain.

    Because the loss of an engine on a two engine airplane causes more asymmetric thrust, you might notice that two engine jets have larger rudders to provide for proper control when in the low speed take off regime after takeoff with an engine failure.

    Also, very importantly, the airplane manufacturers and airlines have convinced the FAA and ICAO that Extended Twin Engine Overwater Operations (ETOPS) are safe—-and they are.

    The acronym also stands for Engines Turning Or People Swimming!


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