4 ms·
If 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.
by idlewords 2y ago
If 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]