Ben Kransow builds a unique rocket engine in his workshop. This rocket engine is a hybrid that uses solid fuel (acrylic) as well as oxygen gas. The clear body allows you to see the combustion take place, as well as the changes that occur when the throttle is changed. Another feature of the hybrid rocket engine is that you can decrease the throttle or turn off the engine if desired, versus a solid fuel rocket that will continue to burn once lit until no more fuel is present.
Quote from Ben's youtube: I built a small rocket engine for demonstration purposes. The engine is built from a 2" diameter acrylic rod through which I drilled a 0.5" hole. The oxygen at 80 psi or less is passed through the hole and then is forced through a convergent-divergent nozzle at the tail end. The nozzle's throat is about 0.25" and expands to 0.625". I lit the engine by inserting a burning cotton swab (with wooden stick) while a small amount of oxygen was flowing. The acrylic catches fire very easily in a pure oxygen environment. The engine can be throttled and shut off completely, which is a major benefit to hybrid engine designs. Solid-fuel rockets cannot be throttled or shut off, which makes them difficult to control.
