Like a real jet, these radio controlled versions do not have propellers and instead use a ducted fan to produce the power. These ducted fans produce a jet of air providing more thrust than a propeller powered plane and, coupled with the streamlined design of the jet, this makes them capable of extremely high flight speeds. Some of them are capable of flying at over 100km/h! RC jets are usually not categorized by the size of the wingspan or length, but rather by the diameter of the ducted fan (known as the EDF), although generally speaking the larger the fan the bigger and faster the jet will be. The trainer jets are easier to fly than the scale replica ones which are all about the same in terms of flying difficulty (although the larger ones fly a little quicker making them a little more difficult) so the decision on which to choose comes down to budget and design preference.