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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Specific thrust</span></span>
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<p><b>Specific thrust</b> is the <a href="Thrust" title="Thrust">thrust</a> per unit air mass flowrate of a <a href="Jet_engine" title="Jet engine">jet engine</a> (e.g. <a href="Turbojet" title="Turbojet">turbojet</a>, <a href="Turbofan" title="Turbofan">turbofan</a>, etc.) and can be calculated by the ratio of net thrust/total intake airflow.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
</p><p>Low specific thrust engines tend to be more efficient of propellant (at subsonic speeds), but also have a lower effective exhaust velocity and lower maximum airspeed. High specific thrust engines are mostly used for supersonic speeds, and high specific thrust engines can achieve hypersonic speeds.
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<div class="mw-heading mw-heading2"><h2 id="Low_specific_thrust_engines">Low specific thrust engines</h2></div>
<p>A civil aircraft turbofan (with <a href="High-bypass_turbofan" class="mw-redirect" title="High-bypass turbofan">high-bypass ratio</a>) typically has a low specific thrust (~30 lbf/(lb/s)) to reduce noise, and to reduce fuel consumption, because a low specific thrust helps to improve <a href="Thrust_specific_fuel_consumption" class="mw-redirect" title="Thrust specific fuel consumption">specific fuel consumption</a> (SFC).<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> This is usually achieved with a high <a href="Bypass_ratio" title="Bypass ratio">bypass ratio</a>. Additionally low specific thrust implies a relatively large cross-sectional engine area given its net thrust. Consequently, such aircraft engines are normally located externally, in a separate nacelle or pod, attached to the wing, or the rear fuselage.
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<div class="mw-heading mw-heading2"><h2 id="High_specific_thrust_engines">High specific thrust engines</h2></div>
<p>By contrast, low-bypass ratio military turbofans often feature high specific thrust (45-110 lbf/(lb/s)), which reduces the engine's cross-sectional area, which more easily accommodates a narrow fuselage, which minimizes drag. A high specific thrust usually results in higher noise levels.
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<div class="mw-heading mw-heading2"><h2 id="Maximum_airspeed">Maximum airspeed</h2></div>
<p>Specific thrust has significant bearing on thrust lapse rate: the low jet velocity associated with a low specific thrust engine implies large reductions in net thrust with increasing flight velocity, which can only be partially offset by throttle changes at rated conditions (e.g. maximum recommended climb rating).
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<div class="mw-heading mw-heading2"><h2 id="Supersonic_aircraft">Supersonic aircraft</h2></div>
<p>Supersonic aircraft require high specific thrust engines to reach a high exhaust speed.
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<div class="mw-heading mw-heading2"><h2 id="Afterburners">Afterburners</h2></div>
<p>Specific thrust has impact upon the performance of afterburning turbofans.
</p><p>A low (dry) specific thrust engine has a low tailpipe temperature, which means that the temperature rise across the afterburner can be high, boosting thrust. Nevertheless, the afterburning specific thrust is still relatively low. The total fuel flow (main combustor plus afterburner) is fixed by the temperature rise from air intake to nozzle and, for a given airflow and changes little with dry specific thrust. Consequently, the low afterburning thrust implies a high afterburning SFC. However, the dry SFC is low.
</p><p>The situation is completely reversed for a high (dry) specific thrust.
</p><p>Consequently, engine designers must select a level of dry specific thrust that is suitable for the application
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<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>
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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.grc.nasa.gov/www/k-12/airplane/specth.html">"Specific Thrust"</a>. <i>www.grc.nasa.gov</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2016-04-25</span></span>.</cite></span>
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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.grc.nasa.gov/www/k-12/airplane/sfc.html">"Specific Fuel Consumption"</a>. <i>www.grc.nasa.gov</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2016-04-25</span></span>.</cite></span>
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<div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2></div>
<ul><li><a href="Specific_impulse" title="Specific impulse">Specific impulse</a>/<a href="Exhaust_velocity" class="mw-redirect" title="Exhaust velocity">exhaust velocity</a></li>
<li><a href="Thrust-to-weight_ratio" title="Thrust-to-weight ratio">Thrust-to-weight ratio</a></li>
<li><a href="Jet_engine" title="Jet engine">Jet engine</a></li></ul></div><!--htdig_noindex--><div><div class="zim-footer">
This article is issued from <a class="external text" title="Last edited on 2024-03-02" href="https://en.wikipedia.org/wiki/?title=Specific_thrust&oldid=1211491369">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.
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