Why do modern aircraft tend to have angular tails? In the WWII-era and earlier, many (most?) planes had rounded tails, even high-speed and high-performance fighters such as the Bf 109 K, Ta 152 (though it is more square-ish), P-38, Hawker Typhoon, and even the F-80. A notable exception to this trend is the P-51.



Modern aircraft, on the other hand, tend to have very angular tails. High speed fighters, to airliners, even relatively slow aircraft like the Cessna 152 or Piper Archer have very angular tails.



What is the reason for this change in trend?
The rounded or elliptical design was found to be the cleanest aerodynamically in non-compressible subsonic airflow, which is why it's very common on aircraft of that era.  While the design is very slippery for speeds of Mach &lt; 0.6 or so, it is more difficult to manufacture, which is why, near the end of the war, Spitfires had the 'clipped' wingtips as opposed to the original pure elliptical planforms.

The modern low aspect, sweptback, trapezoidal tail design is a better choice for higher airspeeds and supersonic flight ie Mach > 0.8 and mitigating flight control flutter due to compressibility effects, the same reasons we use sweptback wing.  Note as well that modern fighters use the same kind of planform for their wings and tail planes as they offer a compromise between acceptable supersonic aerodynamics and good trans sonic maneuverability.