|This article, X-13 Series, was written by Ajax 013. Please do not edit this fiction without the writer's permission.|
The X-13 Series engine is used as the primary engines on all UNSC transatmospheric aircraft. It allows the vehicle to operate both in atmospheric conditions and in exoatmospheric conditions without separate engines or fuels.
The engine is a pulsed detonation jet feeding a variable ramjet engine featuring a variable inlet spike and optional turbine. During low speed, atmospheric flight, the engine inlet opens to its widest setting and the inlet doors close around the internal turbofan spools up, using multiple high grade titanium composite compressor and turbine fan blades. This gives it excellent thrust to power ratios at lower speeds, being used from taxing to mach 3. At higher speed, the internal gates open up, the turbine shuts down and closes inlet and the forward inlet spike is left open, allowing air into the engine, where fuel is injected under pressure and combusted in the chamber. The inlet spike can move to make the inlet narrower or wider, conversely making the speed higher or lower. The combustion chamber's airflow can be modulated to allow it to achieve scramjet capabilities, allowing most engines to achieve speeds upwards from Mach 7 to Mach 13 in atmosphere, giving it sufficient ability to escape atmosphere. However, to achieve transatmospheric travel, where air is not available, it closes the inlet spike then adds a oxidative to the fuel, turning the jet engine into a rocket engine. The performance of both configurations are roughly similar it both the atmosphere of a planet and in space. In addition the X-13 can be fitted with afterburners to give it additional thrust. The resulting engine has high super cruising speeds, good fuel efficiency and the power necessary to preform transatmospheric flights. The engine is entirely computer controlled, allowing it to be adapted to changing conditions and airspeed in seconds, letting the engine maintain maximum thrust power for its current speed.
This engine has been in use for almost 100 years, with its powerful design being unlikely to be replaced for another twenty years.