in the position shown in fig1 considering for the moment only the lower chamber for ease of presentation it is seen that the roller 53 is at the lowest point of the cam 27 so that the flaps are opened up or expanded to form a chamber of maximum size this is the intake position in this position the chamber is in communication with an inlet or intake port 61 and as the chamber was expanding in size shortly before reaching the position illustrated in fig1 the fuel mixture was sucked into the expanding chamber as the rotor continues its clockwise rotation beyond the position shown in fig1 the aft flaps 45 and 49 forming the trailing edge of the chamber pass the fuel intake port 61 and so the chamber is now cut off from all external communication as rotation continues the rollers 53 ride up a rising portion of the cam 27 so that the roller 53 is forced radially outwardly folding the flaps to decrease the size of the chamber as the roller 53 approaches the high point of the cam 27 this high point being indicated by the numeral 63 this action may be likened to the compression stroke of a conventional cylinder and piston engine the fuel mixture within the chamber that is confined between the flaps the cross member 32 and the end walls 31 of the rotor is compressed during this part of the rotation to a relatively high compression just as the roller 53 reaches the high point 63 of the cam and is ready to start its descent on a downwardly sloping portion of the cam the chamber has come around so that the.