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Space Shuttle: Difference between revisions
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→Longitudinal Dynamics
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Since the elevons supply both pitching and roll control, at high hypersonic Mach numbers roll controls are close to being saturated with elevons deflected near full up. To open up better roll control, below Mach 10 the speedbrake is opened to provide a pitching moment relieving the elevons, and the Shuttle's body flap can also be trimmed upward. | Since the elevons supply both pitching and roll control, at high hypersonic Mach numbers roll controls are close to being saturated with elevons deflected near full up. To open up better roll control, below Mach 10 the speedbrake is opened to provide a pitching moment relieving the elevons, and the Shuttle's body flap can also be trimmed upward. | ||
=== Lateral stability === | |||
As mentioned above, during most of the entry phase, the Space Shuttle has no rudder action and the yawing moment as a function of sideslip angle beta is negative, indicating instability. This means that the FCS has to manage yaw stability by commanding yaw thrusters to maintain near zero beta, which is increasingly more challenging as the Shuttle penetrates deeper into the atmosphere and aerodynamical forces grow while thrust is reduced as compared to nominal vacuum values. This implies that a sizable amount of RCS propellant (about 1/3 of the capacity to be on the safe side) needs to be available before atmospheric entry. | |||
Below approximately Mach 6, the rudder starts to contribute to yaw stability and from Mach 3.5 down to Mach 2 where the yawing moment finally becomes positive only the rudder is used. | |||
The real Shuttle has in addition a <b>NO Y JET</b> mode to stabilize the orbiter during entry in which the elevons are used to control yaw. This leads to significantly reduced roll control since roll then needs to be driven by adverse yaw till the rudder picks up sufficient airflow. Currently this mode is not yet available in FG. | |||
== Glossary of acronyms == | == Glossary of acronyms == | ||