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They are not; the 707 flew noticeably faster than modern airliners (525 knots cruise, compare to 485 knots for the Boeing 787).
by idlewords 2y ago
They are not; the 707 flew noticeably faster than modern airliners (525 knots cruise, compare to 485 knots for the Boeing 787).
- WalterBright 2y agoThe cruise speed is selected for maximum fuel efficiency. The airplanes can fly faster, and do under special circumstances. Your gas car's maximally efficient speed is about 35 mph.
- idlewords 2y agoIf you want to go by top speeds, for the 787 (entered service 2011) it's Mach 0.9, for the A-350 (2015) it's 0.89, while for the 707-120 (1958) it's Mach 0.91. The 747 (1970) can go Mach 0.94. Modern jets are built to fly slightly slower than early jetliners, both in normal operation and at top speed. The reason is fuel economy, but the difference is real.
- TylerE 2y agoMach really isn't an appropriate unit here as it is highly depended on altitude and atmospheric conditions.
- AnarchismIsCool 2y agoNo, try again. Not correct in any way.
- TylerE 2y agoMach is highly depended on altitude and atmospheric conditions. It is a ratio, not a speed.
- idlewords 2y agoA specific Mach number is what airliner airframes are designed to fly at; it's absolutely the correct unit to talk about in this context. If airplane A is designed to cruise at 0.94 mach, it is faster than airplane B that cruises at 0.89 mach. I don't understand the need for all the smoke and din in this argument thread. Old passenger jets flew a little faster than modern ones and that's okay!
- TylerE 2y agoMach 0.94 at 40,000ft is slower than Mach 0.89 at sea level. That’s my point. It. Is. Not. A. Measurement. Of. Speed.
- AnarchismIsCool 2y agoStill no... It's dependent on the speed of sound, which is only dependent on temperature, not specifically altitude contrary to popular belief.
- jjk166 2y agoTemperature varies by altitude. Mach 1 at 30,000 ft is 677mph, mach 1 at 35,000 ft is 663 mph.
- AnarchismIsCool 2y agoPer ISA yes
- WalterBright 2y agoThat doesn't disagree with what I wrote.
- idlewords 2y agoYou're saying planes have a top speed faster than their cruise speed; I'm saying it doesn't matter which of the two metrics you compare on, older jets are faster on both.
- deleted 2y ago[deleted]
- AnarchismIsCool 2y agoThey're not faster in any absolute sense, look at the wing sweep angle of new vs old jets or the fact that early low bypass ratio jets have a much higher exhaust velocity, the old jets are marginally faster by every metric.
- WalterBright 2y agoThe airplanes can fly faster than their cruise speed. It's just not economic to do so.
- AnarchismIsCool 2y agoModern airplanes can exceed their cruising speed in a relative sense but older planes have a higher absolute maximum speed, as well as cruising speed. Why is everyone trying to ackshewally this? The stat's are publicly available. Aircraft are optimized for a particular speed range and that impacts the designed cruising speed as well as Vs and VNE.
- jjk166 2y agoMax cruising speed of 707-121 was 593 mph at 30,000 ft. Max Crusing speed of 787 is 593 mph at 35,000 ft.