Did Biplane pilots turn off their engines before landing?
Did Biplane pilots turn off their engines before landing?


Sometimes--

Rotary engines had rather primitive throttle arrangements, so a pilot would often use a "coup" button or "blip" switch, mounted on the control stick, to "blip" the ignition on and off and give partial power.  

However, an alternative technique was recommended for some rotary engines:


  By 1918 a Clerget handbook advised maintaining all necessary control
  by using the fuel and air controls, and starting and stopping the
  engine by turning the fuel on and off. The recommended landing
  procedure involved shutting off the fuel using the fuel lever, while
  leaving the blip switch on. The windmilling propeller made the engine
  continue to spin without delivering any power as the aircraft
  descended. It was important to leave the ignition on to allow the
  spark plugs to continue to spark and keep them from oiling up, so that
  the engine could (if all went well) be restarted simply by re-opening
  the fuel valve. Pilots were advised to not use an ignition cut out
  switch, as it would eventually damage the engine.[7]
  
  Pilots of surviving or reproduction aircraft fitted with rotary
  engines still find that the blip switch is useful while landing, as it
  provides a more reliable, quicker way to initiate power if needed,
  rather than risk a sudden engine stall, or the failure of a
  windmilling engine to restart at the worst possible moment.


(Source: https://en.wikipedia.org/wiki/Rotary_engine#Monosoupape_rotaries, quoting Nahum, Andrew (1999). The Rotary Aero Engine. NMSI Trading Ltd. pp. 44–45. ISBN 1-900747-12-X.) 

The key here is "rotary", not "radial", and regardless of which technique was used, the concern wasn't to avoid a hazard from engine torque or other related effects per se, but just to control the power output of the engine to allow the aircraft to descend for landing.

Of course, at other times, such as when taking off, the gyroscopic reaction to the whirling mass of the engine was a very significant factor while flying with a rotary engine, and the low ground clearance of the lower wingtips of most biplanes wouldn't have helped matters.

You can read much more here-- 

How are rotary engines controlled?

https://en.wikipedia.org/wiki/Rotary_engine

http://www.theaerodrome.com/forum/showthread.php?t=17121

http://www.theaerodrome.com/forum/showthread.php?t=2302&amp;page=1&amp;pp=10