kb/data/en.wikipedia.org/wiki/Glossary_of_aerospace_engineering-24.md

title	chunk	source	category	tags	date_saved	instance
Glossary of aerospace engineering	25/27	https://en.wikipedia.org/wiki/Glossary_of_aerospace_engineering	reference	science, encyclopedia	2026-05-05T07:50:15.292303+00:00	kb-cron

== P == Parallel axis theorem – also known as Huygens–Steiner theorem, or just as Steiner's theorem, named after Christiaan Huygens and Jakob Steiner, can be used to determine the moment of inertia or the second moment of area of a rigid body about any axis, given the body's moment of inertia about a parallel axis through the object's center of gravity and the perpendicular distance between the axes. Parasitic drag – also known as profile drag, is a type of aerodynamic drag that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of form drag and skin friction drag. It affects all objects regardless of whether they are capable of generating lift. Total drag on an aircraft is made up of parasitic drag and lift-induced drag. Parasitic drag is so named because it is not useful, whereas lift-induced drag is the result of an airfoil generating lift. Parasitic drag comprises all types of drag except lift-induced drag. Perpendicular axes theorem – states that the moment of inertia of a planar lamina (i.e. 2-D body) about an axis perpendicular to the plane of the lamina is equal to the sum of the moments of inertia of the lamina about the two axes at right angles to each other, in its own plane intersecting each other at the point where the perpendicular axis passes through it. Define perpendicular axes

    x
  

{\displaystyle x}

,

    y
  

{\displaystyle y}

, and

    z
  

{\displaystyle z}

(which meet at origin

    O
  

{\displaystyle O}

) so that the body lies in the

    x
    y
  

{\displaystyle xy}

plane, and the

    z
  

{\displaystyle z}

axis is perpendicular to the plane of the body. Let Ix, Iy and Iz be moments of inertia about axis x, y, z respectively. Then the perpendicular axis theorem states that

      I
      
        z
      
    
    =
    
      I
      
        x
      
    
    +
    
      I
      
        y
      
    
  

{\displaystyle I_{z}=I_{x}+I_{y}}

This rule can be applied with the parallel axis theorem and the stretch rule to find polar moments of inertia for a variety of shapes. If a planar object (or prism, by the stretch rule) has rotational symmetry such that

      I
      
        x
      
    
  

{\displaystyle I_{x}}

and

      I
      
        y
      
    
  

{\displaystyle I_{y}}

are equal, then the perpendicular axes theorem provides the useful relationship:

      I
      
        z
      
    
    =
    2
    
      I
      
        x
      
    
    =
    2
    
      I
      
        y
      
    
  

{\displaystyle I_{z}=2I_{x}=2I_{y}}

Pitch Angle – Plasma (physics) – (from Ancient Greek πλάσμα 'moldable substance') is one of the four fundamental states of matter. It consists of a gas of ions – atoms or molecules which have at least one orbital electron stripped (or an extra electron attached) and, thus, an electric charge. It is the most abundant form of ordinary matter in the universe, being mostly associated with stars, including the Sun. It extends to the rarefied intracluster medium and possibly to intergalactic regions. Plug nozzle – is a type of nozzle which includes a centerbody or plug around which the working fluid flows. Plug nozzles have applications in aircraft, rockets, and numerous other fluid flow devices. Pogo oscillation – Prandtl–Glauert singularity – Precession – Pressure – Pressure altitude – Pressure-fed engine – Propeller – Proper orbital elements – Pulsed inductive thruster – Pulsed plasma thruster – Propulsion –

== Q ==

== R == Radar – system using the reflection from transmitted electromagnetic waves to detect the distance and rough shape of an object, working even in outer space, unlike sonar Radio direction finder – Railgun – Ram accelerator – Ramjet – Rate of climb – RCS (Reaction control system) – set of rocket thrusters used for spacecraft maneuvers over the craft's three rotation axes in outer space Reentry – Reflection – Relativistic rocket – Remote Manipulator System – Resistojet rocket – Reusable launch system – Reynolds number – RL-10 (rocket engine) – Rocket – Rocket engine – Rocket engine nozzle – Rocket fuel – Rocket launch – Rogallo wing – is a flexible type of wing. In 1948, Francis Rogallo, a NASA engineer, and his wife Gertrude Rogallo, invented a self-inflating flexible wing they called the Parawing, also known after them as the "Rogallo Wing" and flexible wing. NASA considered Rogallo's flexible wing as an alternative recovery system for the Mercury and Gemini space capsules, and for possible use in other spacecraft landings, but the idea was dropped from Gemini in 1964 in favor of conventional parachutes. Rudder –