Especially when looking at the Tu-134:
The Tu-134 has no leading edge high lift devices, which makes production and maintenance much simpler and cheaper. When you compare to for instance a DC-9-30, then you will see that the wing airfoil is very different. On the Tu-134 the airfoil leading edge upper surface is almost as half extended slats on the DC-9.
It improves runway performance, but it increases drag at high Mach numbers dramatically. The high sweep-back angle partially counters the high Mach number drag buildup.
You see the same on the Caravelle and the DH Comet (except Comet 1). But instead of high sweep-back angle they were designed with a somewhat lower cruise speed in mind. In fact you also see it to some extent on the 707 wing root. And when the lighter and faster cousin, the 720 was made, then one important change was in fact "leading edge gloves" which modified the airfoil to accept higher cruise Mach numbers without transsonic drag buildup.
The "low hanging" wings" - negative dihedral: No doubt the Tu-134 has its roots from the Tu-16 Badger bomber plane. The Tu-16 was a very hastily designed plane based on German World War II studies. The Germans had early realized that high sweep-back angled planes were prone to dutch roll. The negative dihedral counters dutch roll tendency, but makes it less stable in flight - and of course more prone to tip strike in sidewind landings.
Modern planes use yaw dampers to artificially counter dutch roll tendency. I don't know, but I would gladly bet that the Tu-16 had no yaw damper. Does anybody know if the Tu-134 has a yaw damper?
If my theories are correct, the Tu-134 is a comparatively simple and cheap compromise, while for instance its cousin, the DC-9, is a much more advanced plane with superior runway performance, cruise speed, payload and economy performance.
The Tu-134 runway performance is in fact quite impressive, but that is due to a very low payload performance compared to wing size and installed engine power. Which are some of the reasons for the world record low fuel efficiency.
If we compare the Tu-134 to modern and equally capable regional airliners from Canada or Brazil, then they carry the same pax load over the same distance at half the take-off weight using one third the installed power and burning one fourth the fuel. We have come a long way since Herr Heinkel studied jet bombers in Leipzig 60 years ago.
Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs