Speed is divided up into different engine capacity classes and a Jet class (using pulse jet engines) As the name suggests, the idea is to have the model go as fast as possible. The model is timed over a number of laps, and the pilot must hold the handle controlling his model in a yoke on top of a pole in the middle of the circle. This is in order to stop the pilot from assisting the model to go faster by increasing the line tension and leading the model (known as whipping). Monoline control systems are common in the US, but international classes require the use of two-line control. Speeds of the fastest models – Class D 0.60 cubic inches (9.8 cm3) and Jet – have in the past exceeded 220 mph (350 km/h). Current US rules limit the speeds to <200 mph (320 km/h) by requiring the use of larger lines if 200 mph (320 km/h) is exceeded. Speed models are usually launched from a “dolly” – a cart that permits a lengthy ground roll for takeoff, but drops away in the air to reduce drag. The airplane lands on a skid or belly pan.