Aoa.Tex

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  • Topic: Aircraft, Aerodynamics, Flight dynamics
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  • Published : February 14, 2013
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\subsection{Survey of Existing Approaches} \label{ssec:existing}

Because few remote control (RC) setups allow for live telemetry, almost all flying is done "by eye," and RC instrumentation and data logging is a poorly developed field. RC gliders especially eschew any projecting elements which could increase drag. The few relevant RC systems the author has found are described in this section, but most considered designs are in practice found only on manned vehicles.

\begin{figure}[!htb]
\centering
\subfigure[\label{fig:f:1}Goodrich Model 0861 swept-vane AOA probe.] {\includegraphics[width=3.05in]{./pics/407AOA.jpg}} % bb=
\subfigure[\label{fig:f:2}Spaceage Control air data probe.] {\includegraphics[width=3.05in]{./pics/airProbe.jpg}} % bb= \caption{\label{fig:f:plain}}
\end{figure}

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\par

\noindent \textbf{Vane Type}

Commercial aircraft typically have leading-edge high-lift devices, making the wing leading edge unsuitable for reliable angle of attack (AOA) sensors. The circulation about the wing in high lift configurations necessitates a probe placed far (one or more chord lengths) from the wing to avoid induced flow or complex calibration and correction software. It's common practice to place AOA and angle of sideslip (AOS) vanes on the fuselage, near the nose to avoid measuring wing circulation. Most probes are internally heated due to the need to fly through icing conditions without loss of data.

Nose-mounted air data probes are commonly seen on experimental aircraft during testing. They combine pitot-static systems with AOA/AOS probes, and frequently temperature, humidity, and other sensors into one probe that flies in front of the aircraft, far from interfering wings and the like.

Vane type probes are one of the few types seen in use by RC hobbyists. Tom Harper designed a balsa vane and potentiometer sensor for logging AOA in flight \cite{harper:vane}. Helmut Lelke designed a hall-effect AOA probe for use on his Actively Stabilized Flying Wing Plank Project, a horizontal stabilizer-less winch-launch glider \cite{lelke:vane}. However, neither of these probes show promise for high-acceleration or highly dynamic applications, and no of the RC instrumentation/data logging manufacturers seem to manufacture any type of AOA sensor, though there are several commercially available airspeed indicators.

\begin{figure}[!htb]
\centering
\subfigure[\label{fig:f:1}Tom Harper's vane AOA probe.]
{\includegraphics[width=3.05in]{./pics/rcVane.jpg}} % bb=
\subfigure[\label{fig:f:2}Aerosonic Corp's actively driven AOA probe.] {\includegraphics[width=3.05in]{./pics/aerosonic.png}} % bb= \caption{\label{fig:f:plain}}
\end{figure}

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\noindent \textbf{Actively Driven}

Actively driven AOA probes use a rotating element which is driven by a servo actuator, commonly to hold a zero pressure differential between "upper" and "lower" pressure taps. Holding these taps isobaric ensures the front of the sensor is directly oriented into the relative wind, meaning these devices can additionally measure stagnation pressure like a pitot system. Examples include the X-15 ball-nose sensor and one-directional probes such as those made by Teledyne and Aerosonic. These probes are often found on military aircraft, as well as some business jets. They are usually heated, allowing operation in icing conditions, and are less mechanically fragile than vane probes. They are well-suited for supersonic or hypersonic operation, and can withstand harsh operating environments, as expected of military aircraft.

The weight and complexity of drive elements is not well suited for small-scale use, and the high-Mach and durability advantages of such a device serve little purpose for experimental glider use.

\par

\noindent \textbf{Multi-Hole}

Multi-hole probes allow directional sensing of relative wind by placing a set (typically 5 or 7) of pitot tubes in a bundle, and shaping the tip into a...
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