Never tried RoF online for all the time I've had but wondered whether you can have 2 players in one plane? One as pilot, other as the gunner?

Yes. All positions on a plane can have seperate players (i.e. heavy bombers).

Not only that, but you can occupy a gunner station on any aircraft (even the ones you did not pay for) in multiplayer.

Cheers,

Fafnir_6

You can also lock the gunner positions out so no one can join them. Unfortunately, I know there's a least one idiot out there that likes to jump into your O/400 after you've spent 20 minutes climbing to bombing height just to shoot your own wings off. Thankfully the gents here pointed out the locking-positions switch.

Spoon

Not only CAN YOU, but your gunner can play FOR FREE!

...super fun part of ROF is to put it on a spare machine (doesnt need a joystick or anything!) download the free-to-play, and have a blast with your friends!