Is it possible to use a pigtail patch antenna on the RX to increase the range?
Yes and no.
Yes, you can mount patch antenna to anything, as long as they are tuned for the frequencies and have low SWR ratios.
Yes and no, to range increase.
I would suggest you do a Google on antenna design for range increase and read up on it.
In essence, you get range increase at the expense of directionality.
So if you put patch antenna on your craft you had better make sure they always point towards your Rx.
OK.
One more thing i want to know I want to use Duck style antenna so i can use Interface Cable SMA to mount the antenna outside of the body for better reception is it possible? for example, take the Flysky FS-X6B it has a pigtail connector will it be possible to use an SMA to U.Fl Interface Cable and mount duck antenna? how much i select the correct length duck antenna?
yes something like this but i want to do it on the RX side instead of Tx