On the Bell 47 model the pilot sat on the right. On the 47-J series he sat in the middle. On the Sikorsky S-51 the pilot sat in the middle but on the S-55 and S-58 series the pilot sat on the right to allow him to monitor ingress and egress of the passengers and to maintain visual contact when using the hoist which was on the right side. To be different the S-51 mounted the hoist on the left side. I believe it was the same as the Bell models got bigger. Initially there was only one door and the hoist was on the right side.