musang From United Kingdom, joined Apr 2001, 793 posts, RR: 7 Reply 6, posted (10 months 2 weeks 3 days 7 hours ago) and read 1974 times:
I see where you're coming from, lower thrust = longer time to reach the same rotate/climb speeds, which would be true all things being equal. However.....
Reduced thrust take-offs are typically done (assuming a long enough runway) combined with higher speeds, in "Improved Climb" take-offs. The benefits include reduced engine wear, reduced noise, better climb rate, better climb gradient, reduced fuel burn. I guess the increased tyre wear is insignificant or outweighed by the benefits.
Given a long runway, for a typical load in a 737, a full power launch may use, say, 92% thrust (N1) with a Vr (rotate speed) of about 135 knots. Improved climb take-off in the same situation might use only 86% thrust with Vr and V2 (rotate and initial climb) speeds typically 15 knots higher.
Mir From United States of America, joined Jan 2004, 20464 posts, RR: 56 Reply 7, posted (10 months 2 weeks 3 days 5 hours ago) and read 1917 times:
Quoting musang (Reply 3): What Mir means is that it gets off the runway sooner
Quoting musang (Reply 3): An increased take-off flap setting would reduce the rotate speed even more.
Unfortunately, we're not allowed to take off with flaps extended if anti-ice fluid has been applied to the aircraft (which is a possibility if the runway is contaminated), so we can't take advantage of that.
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