https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&feed=atom&action=historyPressure, Atmosphere and Instrumentation - Revision history2024-03-29T01:54:06ZRevision history for this page on the wikiMediaWiki 1.29.2https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=724&oldid=prevTW463: /* The International Standard Atmosphere */ fix typo2020-10-18T20:44:07Z<p><span dir="auto"><span class="autocomment">The International Standard Atmosphere: </span> fix typo</span></p>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== The International Standard Atmosphere ===</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== The International Standard Atmosphere ===</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The '''International Standard Atmosphere (ISA)''' is a '''model''' for the atmosphere widely used in aviation. It is established based on extensive observations. It is not meant to be exact as the atmospheric conditions can vary actively (especially at low altitudes, <del class="diffchange diffchange-inline">knows </del>as weather). Also, the temperature in the atmosphere at low levels is subject to seasonality as we well understand. Despite these factors, the ISA is a good model and perhaps the most acceptable one to be used if some aviation equipment is to be designed.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The '''International Standard Atmosphere (ISA)''' is a '''model''' for the atmosphere widely used in aviation. It is established based on extensive observations. It is not meant to be exact as the atmospheric conditions can vary actively (especially at low altitudes, <ins class="diffchange diffchange-inline">known </ins>as weather). Also, the temperature in the atmosphere at low levels is subject to seasonality as we well understand. Despite these factors, the ISA is a good model and perhaps the most acceptable one to be used if some aviation equipment is to be designed.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The modelling approach of the ISA is to divide the atmosphere into several layers, within each layer the static temperature is assumed to vary linearly. If \(T\) is known, it is then possible to use the theories as described before to solve for the density and the static pressure simultaneously.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The modelling approach of the ISA is to divide the atmosphere into several layers, within each layer the static temperature is assumed to vary linearly. If \(T\) is known, it is then possible to use the theories as described before to solve for the density and the static pressure simultaneously.</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=723&oldid=prevTW463: /* Compressible effects */2020-10-18T20:43:05Z<p><span dir="auto"><span class="autocomment">Compressible effects</span></span></p>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>In the simplified model, it is assumed that the density of air is a constant. The Equation of State clearly says otherwise: density depends on pressure and pressure depends on density. Here we run into a problem and the problem can no longer be solved by simple algebra: the powerful mathematical tool of calculus must be used.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>In the simplified model, it is assumed that the density of air is a constant. The Equation of State clearly says otherwise: density depends on pressure and pressure depends on density. Here we run into a problem and the problem can no longer be solved by simple algebra: the powerful mathematical tool of calculus must be used.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Even this is under the assumption that the temperature is a constant. The additional complexity is that the temperature in the atmosphere varies greatly, and you can feel this quite easily by climbing onto a hill and note the temperature drop (just make sure you use a thermometer instead of feeling, to isolate the effect of windchill). At low altitudes, as a rule of thumb, the temperature will reduce by <del class="diffchange diffchange-inline">0.6°C </del>for every <del class="diffchange diffchange-inline">100 meters</del>' <del class="diffchange diffchange-inline">raise </del>of altitude.  </div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Even this is under the assumption that the temperature is a constant. The additional complexity is that the temperature in the atmosphere varies greatly, and you can feel this quite easily by climbing onto a hill and note the temperature drop (just make sure you use a thermometer instead of feeling, to isolate the effect of windchill). At low altitudes <ins class="diffchange diffchange-inline">before the cloud base is reached</ins>, as a rule of thumb, the temperature will reduce by <ins class="diffchange diffchange-inline">3°C </ins>for every <ins class="diffchange diffchange-inline">1000 feet</ins>'<ins class="diffchange diffchange-inline">s rise </ins>of altitude<ins class="diffchange diffchange-inline">. This is known as the dry adiabatic lapse rate</ins>.  </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The temperature of the air greatly depends on the heat transfer between the ground and the air: it is the ground that absorbs the radiation from the sun and heats up, the air is transparent so the absorptivity is quite low in the visible spectrum. Generally, the higher the altitude, the less heat the air will get from the ground, and, as a result, the air will become cooler. This applies until the tropopause is reached, beyond which the temperature ceases to decrease and, in fact, starts to increase again at higher altitudes. Gliders almost never reach the tropopause, so we can ignore this complexity.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The temperature of the air greatly depends on the heat transfer between the ground and the air: it is the ground that absorbs the radiation from the sun and heats up, the air is transparent so the absorptivity is quite low in the visible spectrum. Generally, the higher the altitude, the less heat the air will get from the ground, and, as a result, the air will become cooler. This applies until the tropopause is reached, beyond which the temperature ceases to decrease and, in fact, starts to increase again at higher altitudes. Gliders almost never reach the tropopause, so we can ignore this complexity.</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=531&oldid=prevTW463: /* Setting */2019-03-17T18:46:53Z<p><span dir="auto"><span class="autocomment">Setting</span></span></p>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>QFE means the datum level is at airfield elevation. In this setting, the altimeter reads zero on the ground at the airfield where it flies from. In local circuit training and local soaring, the QFE is normally used. However, when the terrain surrounding the airfield is not level, the QFE setting does not guarantee a correct indication of the height above the ground. QFE is also useless if a circuit and land is planned at locations other than the home airfield, which is the reason you must be comfortable to circuit and land without reference to the altimeter. In addition, if a very long soaring flight is being made, the QFE levels at the take off time and the landing time can be different.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>QFE means the datum level is at airfield elevation. In this setting, the altimeter reads zero on the ground at the airfield where it flies from. In local circuit training and local soaring, the QFE is normally used. However, when the terrain surrounding the airfield is not level, the QFE setting does not guarantee a correct indication of the height above the ground. QFE is also useless if a circuit and land is planned at locations other than the home airfield, which is the reason you must be comfortable to circuit and land without reference to the altimeter. In addition, if a very long soaring flight is being made, the QFE levels at the take off time and the landing time can be different.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>QNH means the datum level is at the mean sea level. This is a useful setting for cross country flights, because all the altitude values given on a chart are above mean sea level (with some exceptions such as obstacles above the ground, in which case a height above the ground is also quoted). It is possible to circuit, approach and land with QNH, which power pilots do, but the usefulness is limited in gliding as all operations are supposed to be under visual flight rules, and visual approaches rely little on knowing the absolute height above the ground.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>QNH means the datum level is at the mean sea level. This is a useful setting for cross country flights, because all the altitude values given on a chart are above mean sea level (with some exceptions such as obstacles above the ground, in which case a height above the ground is also quoted). It is possible to circuit, approach and land with QNH, which power pilots do <ins class="diffchange diffchange-inline">(their standard instrumental terminal procedures involve checkpoints with altitudes prescribed in QNH)</ins>, but the usefulness is limited in gliding as all operations are supposed to be under visual flight rules, and visual approaches rely little on knowing the absolute height above the ground.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>STD is the setting where the sub-scale is adjusted to 1013hpa or 29.92in Hg. This setting shows flight levels. For example, FL55 is 5500ft when the altimeter is at the STD setting. This is useful if navigating at great altitudes or if attempting to avoid airspace.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>STD is the setting where the sub-scale is adjusted to 1013hpa or 29.92in Hg. This setting shows flight levels. For example, FL55 is 5500ft when the altimeter is at the STD setting. This is useful if navigating at great altitudes or if attempting to avoid airspace.</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=530&oldid=prevTW463: /* Altimeter */2019-03-17T18:44:22Z<p><span dir="auto"><span class="autocomment">Altimeter</span></span></p>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Altimeter ===</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Altimeter ===</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">==== Function ====</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">An altimeter is an instrument that displays the vertical distance between the aeroplane and a reference datum, which is defined by the sub-scale setting on the altimeter.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">An altimeter is a compensated instrument, which means the density variation in the atmosphere is automatically corrected for. An altimeter, therefore, gives reliable readings at all altitudes with the exception of readings very close to zero, in which regime the absolute errors become significant.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">An altimeter needs to be read in the same way as a clock: ask an instructor to demonstrate this if you are not fluent at this. Altimeters come with 100ft and 1000ft hands, and most of them found in gliders also have 10000ft hands.</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Setting ====</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Setting ====</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">A datum level must be defined for the altimeter, and it is important to remember at all times that the altimeter reading is relative to the datum '''you''' the pilot have chosen. Depending on the situation in flight, the datum used may or may not be helpful.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">Three settings are relevant to general aviation, they are QFE, QNH, and STD respectively.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">QFE means the datum level is at airfield elevation. In this setting, the altimeter reads zero on the ground at the airfield where it flies from. In local circuit training and local soaring, the QFE is normally used. However, when the terrain surrounding the airfield is not level, the QFE setting does not guarantee a correct indication of the height above the ground. QFE is also useless if a circuit and land is planned at locations other than the home airfield, which is the reason you must be comfortable to circuit and land without reference to the altimeter. In addition, if a very long soaring flight is being made, the QFE levels at the take off time and the landing time can be different.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">QNH means the datum level is at the mean sea level. This is a useful setting for cross country flights, because all the altitude values given on a chart are above mean sea level (with some exceptions such as obstacles above the ground, in which case a height above the ground is also quoted). It is possible to circuit, approach and land with QNH, which power pilots do, but the usefulness is limited in gliding as all operations are supposed to be under visual flight rules, and visual approaches rely little on knowing the absolute height above the ground.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">STD is the setting where the sub-scale is adjusted to 1013hpa or 29.92in Hg. This setting shows flight levels. For example, FL55 is 5500ft when the altimeter is at the STD setting. This is useful if navigating at great altitudes or if attempting to avoid airspace.</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Vertical speed indicator (power) ===</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Vertical speed indicator (power) ===</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=529&oldid=prevTW463: /* Final remarks */2019-03-17T18:25:54Z<p><span dir="auto"><span class="autocomment">Final remarks</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 18:25, 17 March 2019</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Final remarks ===</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Final remarks ===</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>All aviation instruments are precision instruments. While they are normally very reliable, it is important to check their functionality regularly and certainly check for obvious damage before each take-off. Pressure instruments must be airtight, otherwise they will cease to function. It is, therefore, unacceptable to <del class="diffchange diffchange-inline">fly </del>with instruments with broken glasses. When getting into and out of a glider, make sure you pay due attention not to damage the instruments by kicking the instrument panel or allow the metal buckles on your parachute to swing around.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>All aviation instruments are precision instruments. While they are normally very reliable, it is important to check their functionality regularly and certainly check for obvious damage before each take-off. Pressure instruments must be airtight, otherwise they will cease to function <ins class="diffchange diffchange-inline">accurately (or may not function at all)</ins>. It is, therefore, unacceptable to <ins class="diffchange diffchange-inline">launch </ins>with instruments with broken glasses. When getting into and out of a glider, make sure you pay due attention not to damage the instruments by kicking the instrument panel or allow the metal buckles on your parachute to swing around.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>[[Category:Theory]]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>[[Category:Theory]]</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=528&oldid=prevTW463: /* Total energy in gliding: a more interesting quantity */2019-03-17T18:24:45Z<p><span dir="auto"><span class="autocomment">Total energy in gliding: a more interesting quantity</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<col class='diff-content' />
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<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 18:24, 17 March 2019</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l304" >Line 304:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>\[ C_{pX} = -1 \]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>\[ C_{pX} = -1 \]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>This is a remarkable result. This implies that if we can monitor the pressure at a location X on the aeroplane such that \( C_{pX} = -1 \), we can track the total mechanical energy change of the aeroplane. This is the fundamental working principle of a "total energy compensated variometer". When installed on a glider, <del class="diffchange diffchange-inline">this is known without ambiguity </del>as <del class="diffchange diffchange-inline">the '''variometer'''</del>.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>This is a remarkable result. This implies that if we can monitor the pressure at a location X on the aeroplane such that \( C_{pX} = -1 \), we can track the total mechanical energy change of the aeroplane. This is the fundamental working principle of a "total energy compensated variometer". When <ins class="diffchange diffchange-inline">a "variometer" is </ins>installed on a glider, <ins class="diffchange diffchange-inline">it usually refers to a compensated instrument </ins>as <ins class="diffchange diffchange-inline">described above, although other types of compensation that shows other quantities of interest are available</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== How to measure total energy ====</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== How to measure total energy ====</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=527&oldid=prevTW463: /* Stall speed and \(V_{NE}\) */2019-03-17T18:21:56Z<p><span dir="auto"><span class="autocomment">Stall speed and \(V_{NE}\)</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<col class='diff-marker' />
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<tr style='vertical-align: top;' lang='en'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 18:21, 17 March 2019</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l205" >Line 205:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>A rule of thumb for calculating TAS corrections is, for every 1000ft above mean sea level, the TAS is 2% higher than the IAS. For example, if you fly at QNH 5000ft, your TAS will be 10% higher than your IAS.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>A rule of thumb for calculating TAS corrections is, for every 1000ft above mean sea level, the TAS is 2% higher than the IAS. For example, if you fly at QNH 5000ft, your TAS will be 10% higher than your IAS.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==== Stall speed and \(V_{NE}\) ====</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==== Stall speed<ins class="diffchange diffchange-inline">, performance airspeed </ins>and \(V_{NE}\) ====</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Just like the altimeter, it is possible to correct for the density variations with altitude in an ASI, but this is not done for a very important reason: the stall speed (\(V_S\)).</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Just like the altimeter, it is possible to correct for the density variations with altitude in an ASI, but this is not done for a very important reason: the stall speed (\(V_S\)).</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>An aeroplane stalls when a critical angle of attack is reached (''See also: [[Aerofoils and Wings]]''). There is a one to one mapping between the angle of attack (\(\alpha\)) and the lift coefficient (\(C_L\)), which is defined as:</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">'''</ins>An aeroplane stalls when a critical angle of attack is reached<ins class="diffchange diffchange-inline">''' </ins>(''See also: [[Aerofoils and Wings]]''). There is a one to one mapping between the angle of attack (\(\alpha\)) and the lift coefficient (\(C_L\)), which is defined as:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>\[C_L=\frac{L}{\frac{1}{2} \rho V^2 A} =f(\alpha)\]</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>\[C_L=\frac{L}{\frac{1}{2} \rho V^2 A} =f(\alpha)\]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Where:</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Where:</div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>*\(L\) is the lift force, <del class="diffchange diffchange-inline">usually </del>equal to the weight of the aeroplane</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>*\(L\) is the lift force, equal to the weight of the aeroplane <ins class="diffchange diffchange-inline">when flying unaccelerated</ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>*\(A\) is the wing area, which is fixed</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>*\(A\) is the wing area, which is fixed <ins class="diffchange diffchange-inline">unless devices such as flaps are in the process of deployment</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>*Note that \(\frac{1}{2} \rho V^2\) is the dynamic pressure</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>*Note that \(\frac{1}{2} \rho V^2\) is the dynamic pressure</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>If the angle of attack is to reach a critical value, the lift coefficient is also to reach a critical value. Because the weight of the aeroplane (equal to the lift) and the size of the wings are fixed, we conclude that the aeroplane needs a minimum amount of dynamic pressure to fly: any less and the aeroplane stalls.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>If the angle of attack is to reach a critical value, the lift coefficient is also to reach a critical value. Because the weight of the aeroplane (equal to the lift) and the size of the wings are fixed, we conclude that the aeroplane needs a minimum amount of dynamic pressure to fly: any less and the aeroplane stalls<ins class="diffchange diffchange-inline">. This amount depends on the cockpit weight which is significant for a glider</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Recall that an ASI actually measures the dynamic pressure, so <del class="diffchange diffchange-inline">we </del>can <del class="diffchange diffchange-inline">mark a critical value (this marking is best fixed) on </del>the <del class="diffchange diffchange-inline">ASI at which </del>point <del class="diffchange diffchange-inline">the aeroplane stalls</del>, <del class="diffchange diffchange-inline">known as the stall speed</del>. <del class="diffchange diffchange-inline">It </del>is <del class="diffchange diffchange-inline">'''very important''' </del>to <del class="diffchange diffchange-inline">understand that </del>the <del class="diffchange diffchange-inline">aeroplane stalls at a </del>critical dynamic pressure.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Recall that an ASI actually measures the dynamic pressure, so <ins class="diffchange diffchange-inline">it </ins>can <ins class="diffchange diffchange-inline">be used to indicate </ins>the point <ins class="diffchange diffchange-inline">of stall</ins>, <ins class="diffchange diffchange-inline">i.e</ins>. <ins class="diffchange diffchange-inline">it </ins>is <ins class="diffchange diffchange-inline">possible on each occasion </ins>to <ins class="diffchange diffchange-inline">calculate </ins>the critical dynamic pressure <ins class="diffchange diffchange-inline">and mark its value on the ASI. In practice the markings on the ASI are typically based on the maximum all-up weight</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>We want this stall speed to be a well defined value that the pilot can easily compare a cockpit reading to. In other words, the stall speed should be a function of the critical dynamic pressure and nothing else. Therefore, the stall speed defined for an aeroplane is an indicated airspeed. If the ASI does not correct for the density variations and read the IAS all the time, the pilot can conveniently compare his flying to the stall speed. In other words, the ASI shows the stall margin correctly.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>We want this stall speed to be a well defined value that the pilot can easily compare a cockpit reading to. In other words, the stall speed should be a function of the critical dynamic pressure and nothing else. Therefore, the stall speed defined for an aeroplane is an indicated airspeed. If the ASI does not correct for the density variations and read the IAS all the time, the pilot can conveniently compare his flying to the stall speed. In other words, the ASI shows the stall margin correctly.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Note that the reasoning above applies to other flying conditions apart from stalling: the mapping between the angle of attack to a wide range of aerodynamic performances is one to one. Therefore, other speeds such as the speed of minimum sink (best glide) are also best defined as indicated airspeeds. It, therefore, makes a lot of sense that the aeroplane keeps track of its indicated airspeed even if, with the aid of modern computers, calculating the TAS is a piece of cake. On larger aeroplanes with sophisticated avionics, the TAS is displayed real-time for navigational reference.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Note that the reasoning above applies to other flying conditions apart from stalling: the mapping between the angle of attack to a wide range of aerodynamic performances is one to one. Therefore, other speeds such as the speed of minimum sink (best glide) are also best defined as indicated airspeeds<ins class="diffchange diffchange-inline">. In other words, the '''polar''' of the glider is invariant when expressed in terms of IAS</ins>. It, therefore, makes a lot of sense that the aeroplane keeps track of its indicated airspeed even if, with the aid of modern computers, calculating the TAS is a piece of cake. On larger aeroplanes with sophisticated avionics, the TAS is displayed real-time for navigational reference.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>However, the never exceed speed (\(V_{NE}\)) has nothing to do with angle of attack or dynamic pressure: it is the speed that, when exceeded, the aeroplane may fail structurally. The failure of an airframe is dominated by aeroelastic effects, the most notable one being the flutter of the wings (there are videos on YouTube that shows this phenomenon). These horrible things occur when the '''TAS''' reaches a critical value. Recall that, at high altitudes, the TAS is higher than the IAS. Therefore, as you fly higher, '''your \(V_{NE}\), expressed in terms of IAS, will reduce.''' Failing to understand this can lead to serious consequences of overspeeding.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>However, the never exceed speed (\(V_{NE}\)) has nothing to do with angle of attack or dynamic pressure: it is the speed that, when exceeded, the aeroplane may fail structurally. The failure of an airframe is dominated by aeroelastic effects, the most notable one being the flutter of the wings (there are videos on YouTube that shows this phenomenon). These horrible things occur when the '''TAS''' reaches a critical value. Recall that, at high altitudes, the TAS is higher than the IAS. Therefore, as you fly higher, '''your \(V_{NE}\), expressed in terms of IAS, will reduce.''' Failing to understand this can lead to serious consequences of overspeeding.</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l230" >Line 230:</td>
<td colspan="2" class="diff-lineno">Line 230:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The point where the stall speed (IAS) corresponds to the never exceed speed (TAS) because of a decrease of density gives the theoretical ceiling. This is the theoretical maximum altitude at which the aeroplane can fly. If you fly at this altitude, you must fly at this speed precisely, or you will either stall or overspeed.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The point where the stall speed (IAS) corresponds to the never exceed speed (TAS) because of a decrease of density gives the theoretical ceiling. This is the theoretical maximum altitude at which the aeroplane can fly. If you fly at this altitude, you must fly at this speed precisely, or you will either stall or overspeed.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The Lockheed U-2, which flies at very high altitudes, have very notable problems when the ceiling is reached. For a U-2 in cruise, the stall speed and the never exceed speed is less than 10 knots apart on the ASI. This calls for very accurate handling by the pilot. The same applies to glider pilots who wish to fly at high altitudes: you must remember that the airspeed window in which you can fly is reduced, and, by flying higher, the red mark on the ASI must gradually move inwards.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The Lockheed U-2, which flies at very high altitudes, have very notable problems when the ceiling is reached. For a U-2 in cruise, <ins class="diffchange diffchange-inline">the difference between </ins>the stall speed and the never exceed speed is less than 10 knots apart on the ASI. This calls for very accurate handling by the pilot. The same applies to glider pilots who wish to fly at high altitudes: you must remember that the airspeed window in which you can fly is reduced, and, by flying higher, the red mark on the ASI must gradually move inwards<ins class="diffchange diffchange-inline">. Such a feature is available on a jet airliner in the 1960s: there is a \(V_{NE}\) flag on the ASI which is driven by the air data computer</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Altimeter ===</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Altimeter ===</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=526&oldid=prevTW463: /* Errors: TAS & IAS */2019-03-17T18:14:19Z<p><span dir="auto"><span class="autocomment">Errors: TAS & IAS</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class='diff-marker' />
<col class='diff-content' />
<col class='diff-marker' />
<col class='diff-content' />
<tr style='vertical-align: top;' lang='en'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 18:14, 17 March 2019</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l202" >Line 202:</td>
<td colspan="2" class="diff-lineno">Line 202:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Most of the times the instrument designers are not completely stupid, so the constant density hard coded into the ASI is not a random number. It is actually the average density of air at sea level, which the airfields and airports are usually not far away from. Therefore, at low levels where the density is quite close to the sea level density, the ASI is reasonably accurate. The problem most commonly arises when aeroplanes are flown at high altitudes: as we have discussed in the atmosphere section, the density of the air decreases with altitude. Therefore, the higher the altitude, the larger the difference between the IAS and the TAS. For example, a jet airliner that operates at FL360 can read an IAS of 280kts, but the TAS is actually around 450kts. For flying in wave lift which can take a glider to high altitudes, this is an important point to understand: you will travel faster than the ASI tells you.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Most of the times the instrument designers are not completely stupid, so the constant density hard coded into the ASI is not a random number. It is actually the average density of air at sea level, which the airfields and airports are usually not far away from. Therefore, at low levels where the density is quite close to the sea level density, the ASI is reasonably accurate. The problem most commonly arises when aeroplanes are flown at high altitudes: as we have discussed in the atmosphere section, the density of the air decreases with altitude. Therefore, the higher the altitude, the larger the difference between the IAS and the TAS. For example, a jet airliner that operates at FL360 can read an IAS of 280kts, but the TAS is actually around 450kts. For flying in wave lift which can take a glider to high altitudes, this is an important point to understand: you will travel faster than the ASI tells you.</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">A rule of thumb for calculating TAS corrections is, for every 1000ft above mean sea level, the TAS is 2% higher than the IAS. For example, if you fly at QNH 5000ft, your TAS will be 10% higher than your IAS.</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Stall speed and \(V_{NE}\) ====</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Stall speed and \(V_{NE}\) ====</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=525&oldid=prevTW463: /* Air speed vs. ground speed */2019-03-17T18:12:07Z<p><span dir="auto"><span class="autocomment">Air speed vs. ground speed</span></span></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class='diff-marker' />
<col class='diff-content' />
<col class='diff-marker' />
<col class='diff-content' />
<tr style='vertical-align: top;' lang='en'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 18:12, 17 March 2019</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l183" >Line 183:</td>
<td colspan="2" class="diff-lineno">Line 183:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>An '''air speed indicator (ASI)''' is used to measure the '''airspeed''' of an aeroplane. The airspeed measured from an ASI is known as "'''indicated airspeed'''".</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>An '''air speed indicator (ASI)''' is used to measure the '''airspeed''' of an aeroplane. The airspeed measured from an ASI is known as "'''indicated airspeed'''".</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==== <del class="diffchange diffchange-inline">Air speed </del>vs. ground speed ====</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==== <ins class="diffchange diffchange-inline">Airspeed </ins>vs. ground speed ====</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Airspeed is the aeroplane's speed relative to the surrounding air (contrasted with '''ground speed''', which is the speed relative to the ground). The reason <del class="diffchange diffchange-inline">air speed </del>can differ from ground speed is because the air itself can move, known as wind. If you fly at an airspeed of 40kts directly into a 40kts headwind, your ground speed will be zero, i.e. looking from the ground you will not be moving. This is because you move forward relative to the surrounding air, but the air is itself moving backwards relative to the ground, so the two effects cancel each other.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Airspeed is the aeroplane's speed relative to the surrounding air (contrasted with '''ground speed''', which is the speed relative to the ground). The reason <ins class="diffchange diffchange-inline">airspeed </ins>can differ from ground speed is because the air itself can move, known as wind. If you fly at an airspeed of 40kts directly into a 40kts headwind, your ground speed will be zero, i.e. looking from the ground you will not be moving. This is because you move forward relative to the surrounding air, but the air is itself moving backwards relative to the ground, so the two effects cancel each other.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Function ====</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>==== Function ====</div></td></tr>
</table>TW463https://wiki.cugc.org.uk/w/index.php?title=Pressure,_Atmosphere_and_Instrumentation&diff=524&oldid=prevTW463: /* How to measure pressure */2019-03-17T18:11:14Z<p><span dir="auto"><span class="autocomment">How to measure pressure</span></span></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 18:11, 17 March 2019</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l116" >Line 116:</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The difference between the pitot tube reading and the static port reading is the dynamic pressure.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The difference between the pitot tube reading and the static port reading is the dynamic pressure.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Note that there are restrictions on both of these regarding the relative direction with respect to the flow. <del class="diffchange diffchange-inline">Given that most of the times an aeroplane flies straight and level, the designers will use this attitude to design the </del>pitot tube and the static port. If a significant amount of yaw is present, or if the angle of attack is extreme (such as when an aeroplane is stalled), these pressure readings will be unreliable.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Note that there are restrictions on both of these regarding the relative direction with respect to the flow. <ins class="diffchange diffchange-inline">The </ins>pitot tube and the static port <ins class="diffchange diffchange-inline">are designed to function correctly when the aeroplane is flying unaccelerated with zero yaw and small angle of attack</ins>. If a significant amount of yaw is present, or if the angle of attack is extreme (such as when an aeroplane is stalled <ins class="diffchange diffchange-inline">or flying inverted</ins>), these pressure readings will be unreliable<ins class="diffchange diffchange-inline">. In case of intentional inverted flight, additional devices may be fitted to the pitot tube to improve the accuracy</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>For reasons that should be obvious by now, it is important that the pitot tube and the static port are not blocked. This should be a part of the daily inspection of an aeroplane. Furthermore, there is a chance that the pitot tube may ice up in flight, for example, if the aeroplane is flown in rain at low temperatures.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>For reasons that should be obvious by now, it is important that the pitot tube and the static port are not blocked. This should be a part of the daily inspection of an aeroplane. Furthermore, there is a chance that the pitot tube may ice up in flight, for example, if the aeroplane is flown in rain at low temperatures.</div></td></tr>
</table>TW463