system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't we have jets that travel faster?

I was wondering what are the physical limitations that make the passenger carrying planes travel only as fast as they do?
EDIT:  Thank you all for the response. Reddit really comes through when answers are both accessible to novices and authentic at the same time! Thank you all!
gpt
Aerospace Engineer Here.

It's really all about efficiency. Once you start going faster than Mach .8-.85, small shock waves begin to form on your wings (this is why most passenger jets have wings that sweep back towards the tail; to reduce the airspeed perpendicular to the wing itself, allowing you to fly faster). These shock waves cause large total pressure losses, which can decrease the lift force of the wing while increasing the drag force it experiences.

Another problem here is that jet engines don't really work too well when the air coming into them is supersonic. If the air is traveling too fast, the blades of the compressor will experience small shock waves, not only causing pressure losses (which are bad in a compressor, whose objective is to *increase* the pressure), but also causing material issues, as shocks cause the air behind them to get very, very hot, which can really do a number on small, thin metal sheets (such as compressor blades).

Modern jet engine intakes are designed to slow down the air coming into them, to allow them to operate at higher speeds. Most engines in fighter aircraft are designed like this.

More viable supersonic engine options include the ramjet and the scramjet, which feature no moving parts, but are extremely inefficient up until around Mach 3. These engines use shock waves to compress the air coming into them instead of the standard rotary compressors found in traditional jet engines.

In short, traveling supersonic means increased ticket costs and heavier aircraft that need to carry more fuel. It's a really inefficient way to go.