State of the RTS pin
You can configure RequestToSend to be on or off. If RequestToSend is on, the Request to Send (RTS) pin is asserted. If RequestToSend is off, the RTS pin is unasserted.
In normal usage, the RTS and Clear to Send (CTS) pins work together, and are used as standard handshaking pins for data transfer. In this case, RTS and CTS are automatically managed by the DTE and DCE. However, there is nothing in the RS-232 standard that requires the RTS pin must be used in any specific way. Therefore, if you manually configure the RequestToSend value, it is probably for nonstandard operations.
If your device does not use hardware handshaking in the standard way, and you need to manually configure RequestToSend, configure the FlowControl property to none. Otherwise, the RequestToSend value that you specify might not be honored. Refer to your device documentation to determine its specific pin behavior.