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The aircraft pitch axis is the transverse body axis about which the nose rotates upward or downward. In the convention used by NASA Glenn Research Center, it passes through the centre of mass and points toward the right wing tip; the aircraft roll axis points toward the nose and the aircraft yaw axis toward the underside. These are body-fixed directions, so their orientation relative to the ground changes with the aircraft.^[ref]

Choose right-handed body coordinates $x$ forward, $y$ right and $z$ down. A force $\mathbf{F}$ acting at displacement $\mathbf{r}$ from the centre of mass produces torque $\mathbf{\tau }=\mathbf{r}\times \mathbf{F}$. Its pitching moment isFor an original tail-load example, $\mathbf{r}=(-4,0,0)\mathrm{m}$ and $\mathbf{F}=(0,0,100)\mathrm{N}$ give ${\tau }_y=+400\mathrm{N}\mathrm{m}$. The downward tail load lifts the nose in this convention. If the aircraft pitch axis is a principal axis, the motion is initially pure pitch and the corresponding moment of inertia is $I_y=2000\mathrm{kg}{\mathrm{m}}^2$, then the instantaneous angular acceleration is $\dot{q}={\tau }_y/I_y=0.20rad/{\mathrm{s}}^2$. Coupled three-axis rotation requires the full Euler's equations.

The axis is a geometrical reference, not necessarily a physical hinge. Changing a control-surface load changes both forces and torques; a zero net translational force does not establish zero pitching moment. A balance measurement therefore needs the reference point and sign convention alongside its reported moment.^[ref]

By NASA Glenn Research Center.

Publisher: NASA Glenn Research Center.

Online text: www1.grc.nasa.gov/beginners-guide-to-aeronautics/bernoullis-equation/

Cited passages: NASA Glenn, Bernoulli's Equation: restrictions and Common Assumptions.

By NASA Glenn Research Center.

Publisher: NASA Glenn Research Center.

Online text: www1.grc.nasa.gov/beginners-guide-to-aeronautics/dynamic-pressure/

Cited passages: NASA Glenn, Dynamic Pressure: definition and use beyond incompressible inviscid flow.

Online text: www.grc.nasa.gov/www/k-12/rocket/machang.html

Issued and hosted by NASA Glenn Research Center. The footer credits Tom Benson as editor and NASA official; no individual author byline is established. Last updated 13 May 2021, an online revision date.

Cited passages: wavefront geometry and displayed angle equations.

Online text: www.grc.nasa.gov/www/k-12/airplane/mach.html

Issued and hosted by NASA Glenn Research Center. The footer credits Nancy Hall as editor and NASA official; no individual author byline is established. Last updated 13 May 2021, an online revision date.

Cited passages: speed-ratio definition; gas and temperature dependence; flight regimes; disturbance propagation and wind-tunnel similarity.

By NASA Glenn Research Center.

Publisher: NASA Glenn Research Center.

Online text: www1.grc.nasa.gov/beginners-guide-to-aeronautics/pitot-static-tube-speedometer/

Cited passages: NASA Glenn, Pitot–Static Tube–Speedometer: pressure connections, Solve for Velocity, Limitations.

Online text: www.grc.nasa.gov/WWW/K-12/airplane/tunvschlrn.html

Issued and hosted by NASA Glenn Research Center. The footer credits Nancy Hall as editor and NASA official; no individual author byline is established. Last updated 13 May 2021, an online revision date.

Cited passages: slit source, two concave mirrors, knife edge and recording device; density-gradient contrast; dimensional interpretation.

Institutional educational slide issued and hosted by NASA Glenn Research Center. Its footer identifies curator and responsible-official roles, without establishing a personal author. No publication or revision date is established.

Official text slide: www.grc.nasa.gov/WWW/k-12/WindTunnel/WTExpKids/tsld027.htm

Cited passages: slide 27, partially filled Tygon tube with water; total and static pressure connections; direction of water displacement and height-difference readout. The slide documents an experimental method and qualitative prediction, without supplying measured results.

By Raymond S. Castner, as credited on the PDF cover and title page. NASA/TM-2010-216259, April 2010; issued by NASA Glenn Research Center and hosted by the NASA Technical Reports Server. The associated conference occurred in August 2009.

Report: ntrs.nasa.gov/api/citations/20100019443/downloads/20100019443.pdf?attachment=true

Cited passages: §II, printed p. 2; §§IV–V, printed pp. 8–9; Figures 7–10; concluding remarks, printed p. 10.