High mach straight wings
 

"Advances in airfoils over the last 20-30 years have been able to get the same benefit without the sweep, at least up to Mach numbers in the 0.8-range. The later straight-wing Citations have Mmo's in the 0.8 range, if I remember correctly."

That is what I read from someone else's post today. So what exactly are those advances?

Supercritical airfoils?

Not a 21st century invention. Perhaps on the short span airplanes some of the effects can be tolerated and you reap the structural benefits of simple design?

Ain't that the truth....(thinks F-104 and of course the Bell X-1)...

F-18, filler

The X 3 Stiletto, but I'm not sure it actually qualifies as a high mac aircraft!

I am just asking myself where you got that quote from.

Advances in Airfoils can differ from higher stiffness in the profile itself to qualify such a Jet as the Citation for higher altitude stable flight, where such numbers can be reached by nearly every jet propelled aircraft with highest efficiency.
Or it could be even a lighter wing, which leaves the Power of your Airplane obtaining less weight to lift, increasing speed (Less lift needed, less induced resistance)
Or latest advances in aerodynamics and modeling airflow. Swept wings have benefits, for shure but you can even simulate a lightly swept wing on a straight one if you vary the profile over the length.

As the Citation is a Business Jet operating at FL40 I would assume it is more meant stability-wise, just keep in mind that nearly every high altitude airplane operating at speeds under mach 1 had more or less straight wings ever since. U-2 is a great example for that.

But it depends on the source of the quote after all.