Nakamura-san -
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I could not do better than Chris Scott's explanation given to you, which is very accurate.
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The only thing I would like to add about the reversers, is that they block most of the residual thrust of the jet engines. Residual thrust is quite sizeable on modern high-bypass fan engines, and being able to cancel the idle thrust after landing is a further help, to the use of wheel brakes and (spoilers) speed brakes. Many airports request not to use reversers for noise reasons, obviously, and carbon brakes are excellent at doing their job... but I never fail to use reversers, even if only at idle, to block the residual thrust.
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In the 747s that I fly (the old ones), the reversers are installed on the fan. In the initial 747 airplanes, with JT9D-3As, there were turbine reversers as well, installed on the exhaust of the engine, but they were a source of problems, so these were eventually removed.
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Bear in mind that a typical 747 engine has amost a 5:1 bypass ratio. By deflecting the fan exhaust air, you deflect quite a bit of the residual thrust. The remaining "core thrust" accounts for very little of the idle thrust.
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Happy contrails