On 3-engined prop aircraft like the Ford Trimotor and the Junkers Ju-52, did all three props turn in the same direction?
Yep, clockwise, as seen from the cockpit.
Seehere for details.
English engines turned CCW as seen from cockpit.
Would have to check if all German engines were CW.
P-38 had CR engines as did the Piper Senaca. Just that the P-28 was ( down blade outside while the PA-34 id down blade inside) see picture on this page. You can see that they are CR ( counter rotation )
http://www.flybernhard.de/ueb_eng.htm?http://www.flybernhard.de/pa34_e.htm
ME-109 seems to have been CW from cockpit judging by these pics.
Also, the last flying example of this tri-2ngine aircraft crased on takeoff from TUL. Real rare bird.
http://www.wpafb.af.mil/museum/outdoor/od15.htm
http://www.cavanaughflightmuseum.com/Aircraft/Me-109/Page1.html
Yes, I fly better than I spell and type. 
P-38
tri-engine
crashed
etc…
::::: sheesh ::::
*::: preview is my friend ::: *
Correction: English engines turn ACW (anti-clockwise)!