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vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Advantages_of_high_overall_pressure_ratios"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Advantages of high overall pressure ratios</span> </div> </a> <ul id="toc-Advantages_of_high_overall_pressure_ratios-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Disadvantages_of_high_overall_pressure_ratios" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Disadvantages_of_high_overall_pressure_ratios"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Disadvantages of high overall pressure ratios</span> </div> </a> <ul id="toc-Disadvantages_of_high_overall_pressure_ratios-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Examples" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Examples"> <div class="vector-toc-text"> <span 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<div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Proportion of air "heaviness" before to after passing through a jet engine</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output 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print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a></b>.<span class="hide-when-compact"> Please help <a href="/wiki/Special:EditPage/Overall_pressure_ratio" title="Special:EditPage/Overall pressure ratio">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a>. Unsourced material may be challenged and removed.<br /><small><span class="plainlinks"><i>Find sources:</i> <a rel="nofollow" class="external text" href="https://www.google.com/search?as_eq=wikipedia&q=%22Overall+pressure+ratio%22">"Overall pressure ratio"</a> – <a rel="nofollow" class="external text" href="https://www.google.com/search?tbm=nws&q=%22Overall+pressure+ratio%22+-wikipedia&tbs=ar:1">news</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?&q=%22Overall+pressure+ratio%22&tbs=bkt:s&tbm=bks">newspapers</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.google.com/search?tbs=bks:1&q=%22Overall+pressure+ratio%22+-wikipedia">books</a> <b>·</b> <a rel="nofollow" class="external text" href="https://scholar.google.com/scholar?q=%22Overall+pressure+ratio%22">scholar</a> <b>·</b> <a rel="nofollow" class="external text" href="https://www.jstor.org/action/doBasicSearch?Query=%22Overall+pressure+ratio%22&acc=on&wc=on">JSTOR</a></span></small></span> <span class="date-container"><i>(<span class="date">May 2009</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <p>In <a href="/wiki/Aeronautical_engineering" class="mw-redirect" title="Aeronautical engineering">aeronautical engineering</a>, <b>overall pressure ratio</b>, or <b>overall compression ratio</b>, is the ratio of the <a href="/wiki/Stagnation_pressure" title="Stagnation pressure">stagnation pressure</a> as measured at the front and rear of the compressor of a <a href="/wiki/Gas_turbine" title="Gas turbine">gas turbine</a> engine. The terms <i>compression ratio</i> and <i>pressure ratio</i> are used interchangeably.<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> <b>Overall compression ratio</b> also means the <i>overall cycle pressure ratio</i> which includes intake ram.<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> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History_of_overall_pressure_ratios">History of overall pressure ratios</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Overall_pressure_ratio&action=edit&section=1" title="Edit section: History of overall pressure ratios"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Early jet engines had limited pressure ratios due to construction inaccuracies of the compressors and various material limits. For instance, the <a href="/wiki/Junkers_Jumo_004" title="Junkers Jumo 004">Junkers Jumo 004</a> from <a href="/wiki/World_War_II" title="World War II">World War II</a> had an overall pressure ratio 3.14:1. The immediate post-war <a href="/wiki/Snecma_Atar" title="Snecma Atar">Snecma Atar</a> improved this marginally to 5.2:1. Improvements in materials, compressor blades, and especially the introduction of multi-spool engines with several different rotational speeds, led to the much higher pressure ratios common today. </p><p>Modern civilian engines generally operate between 40 and 55:1. The highest in-service is the <a href="/wiki/General_Electric_GEnx" title="General Electric GEnx">General Electric GEnx</a>-1B/75 with an OPR of 58 at the end of the <a href="/wiki/Climb_(aeronautics)" title="Climb (aeronautics)">climb</a> to cruise altitude (Top of Climb) and 47 for <a href="/wiki/Takeoff" title="Takeoff">takeoff</a> at <a href="/wiki/Sea_level" title="Sea level">sea level</a>.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Advantages_of_high_overall_pressure_ratios">Advantages of high overall pressure ratios</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Overall_pressure_ratio&action=edit&section=2" title="Edit section: Advantages of high overall pressure ratios"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1251242444"><table class="box-Disputed plainlinks metadata ambox ambox-content ambox-disputed" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><span><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/17/System-search.svg/45px-System-search.svg.png" decoding="async" width="45" height="45" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/17/System-search.svg/68px-System-search.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/17/System-search.svg/90px-System-search.svg.png 2x" data-file-width="48" data-file-height="48" /></span></span></div></td><td class="mbox-text"><div class="mbox-text-span">This section's <b>factual accuracy is <a href="/wiki/Wikipedia:Accuracy_dispute" title="Wikipedia:Accuracy dispute">disputed</a></b>.<span class="hide-when-compact"> Relevant discussion may be found on the <a href="/wiki/Talk:Overall_pressure_ratio#Disputed" title="Talk:Overall pressure ratio">talk page</a>. Please help to ensure that disputed statements are <a href="/wiki/Wikipedia:Reliable_sources" title="Wikipedia:Reliable sources">reliably sourced</a>.</span> <span class="date-container"><i>(<span class="date">November 2021</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <p>Generally speaking, a higher overall pressure ratio implies higher efficiency, but the engine will usually weigh more, so there is a compromise. A high overall pressure ratio permits a larger area ratio nozzle to be fitted on the jet engine. This means that more of the heat energy is converted to jet speed, and energetic efficiency improves. This is reflected in improvements in the engine's <a href="/wiki/Thrust_specific_fuel_consumption" class="mw-redirect" title="Thrust specific fuel consumption">specific fuel consumption</a>. </p><p>The <a href="/wiki/GE_Catalyst" class="mw-redirect" title="GE Catalyst">GE Catalyst</a> has a 16:1 OPR and its <a href="/wiki/Thermal_efficiency" title="Thermal efficiency">thermal efficiency</a> is 40%, the 32:1 <a href="/wiki/Pratt_%26_Whitney_GTF" class="mw-redirect" title="Pratt & Whitney GTF">Pratt & Whitney GTF</a> has a thermal efficiency of 50% and the 58:1 <a href="/wiki/GEnx" class="mw-redirect" title="GEnx">GEnx</a> has a thermal efficiency of 58%.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Disadvantages_of_high_overall_pressure_ratios">Disadvantages of high overall pressure ratios</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Overall_pressure_ratio&action=edit&section=3" title="Edit section: Disadvantages of high overall pressure ratios"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>One of the primary limiting factors on pressure ratio in modern designs is that the air heats up as it is compressed. As the air travels through the compressor stages it can reach temperatures that pose a material failure risk for the compressor blades. This is especially true for the last compressor stage, and the outlet temperature from this stage is a common <a href="/wiki/Figure_of_merit" title="Figure of merit">figure of merit</a> for engine designs. </p><p>Military engines are often forced to work under conditions that maximize the heating load. For instance, the <a href="/wiki/General_Dynamics_F-111_Aardvark" title="General Dynamics F-111 Aardvark">General Dynamics F-111 Aardvark</a> was required to operate at speeds of Mach 1.1 at <a href="/wiki/Sea_level" title="Sea level">sea level</a>. As a side-effect of these wide operating conditions, and generally older technology in most cases, military engines typically have lower overall pressure ratios. The <a href="/wiki/Pratt_%26_Whitney_TF30" title="Pratt & Whitney TF30">Pratt & Whitney TF30</a> used on the F-111 had a pressure ratio of about 20:1, while newer engines like the <a href="/wiki/General_Electric_F110" title="General Electric F110">General Electric F110</a> and <a href="/wiki/Pratt_%26_Whitney_F135" title="Pratt & Whitney F135">Pratt & Whitney F135</a> have improved this to about 30:1. </p><p>An additional concern is weight. A higher compression ratio implies a heavier engine, which in turn costs fuel to carry around. Thus, for a particular construction technology and set of flight plans an optimal overall pressure ratio can be determined. </p> <div class="mw-heading mw-heading2"><h2 id="Examples">Examples</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Overall_pressure_ratio&action=edit&section=4" title="Edit section: Examples"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable"> <tbody><tr> <th>Engine </th> <th>Overall pressure ratio </th> <th>Major applications </th></tr> <tr> <td><a href="/wiki/General_Electric_GE9X" title="General Electric GE9X">General Electric GE9X</a> </td> <td>60:1 </td> <td><a href="/wiki/Boeing_777X" title="Boeing 777X">777X</a> </td></tr> <tr> <td><a href="/wiki/Rolls-Royce_Trent_XWB" title="Rolls-Royce Trent XWB">Rolls-Royce Trent XWB</a> </td> <td>52:1 </td> <td><a href="/wiki/Airbus_A350_XWB" class="mw-redirect" title="Airbus A350 XWB">A350 XWB</a> </td></tr> <tr> <td><a href="/wiki/General_Electric_GE90" title="General Electric GE90">General Electric GE90</a> </td> <td>42:1 </td> <td><a href="/wiki/Boeing_777" title="Boeing 777">777</a> </td></tr> <tr> <td><a href="/wiki/General_Electric_CF6#CF6-80C2" title="General Electric CF6">General Electric CF6</a> </td> <td>30.5:1 </td> <td><a href="/wiki/Boeing_747" title="Boeing 747">747</a>, <a href="/wiki/Boeing_767" title="Boeing 767">767</a>, <a href="/wiki/Airbus_A300" title="Airbus A300">A300</a>, <a href="/wiki/McDonnell_Douglas_MD-11" title="McDonnell Douglas MD-11">MD-11</a>, <a href="/wiki/Lockheed_C-5_Galaxy" title="Lockheed C-5 Galaxy">C-5</a> </td></tr> <tr> <td><a href="/wiki/General_Electric_F110" title="General Electric F110">General Electric F110</a> </td> <td>30:1 </td> <td><a href="/wiki/Grumman_F-14_Tomcat" title="Grumman F-14 Tomcat">F-14</a>, <a href="/wiki/McDonnell_Douglas_F-15_Eagle" title="McDonnell Douglas F-15 Eagle">F-15</a>, <a href="/wiki/General_Dynamics_F-16_Fighting_Falcon" title="General Dynamics F-16 Fighting Falcon">F-16</a> </td></tr> <tr> <td><a href="/wiki/Pratt_%26_Whitney_TF30" title="Pratt & Whitney TF30">Pratt & Whitney TF30</a> </td> <td>20:1 </td> <td><a href="/wiki/Grumman_F-14_Tomcat#F-14A" title="Grumman F-14 Tomcat">F-14</a>, <a href="/wiki/General_Dynamics_F-111_Aardvark" title="General Dynamics F-111 Aardvark">F-111</a> </td></tr> <tr> <td><a href="/wiki/Rolls-Royce/Snecma_Olympus_593" title="Rolls-Royce/Snecma Olympus 593">Rolls-Royce/Snecma Olympus 593</a> </td> <td>15.5:1/80:1 supersonic<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </td> <td><a href="/wiki/Concorde" title="Concorde">Concorde</a> </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="Differences_from_other_similar_terms">Differences from other similar terms</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Overall_pressure_ratio&action=edit&section=5" title="Edit section: Differences from other similar terms"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The term should not be confused with the more familiar term <a href="/wiki/Compression_ratio" title="Compression ratio">compression ratio</a> applied to <a href="/wiki/Reciprocating_engine" title="Reciprocating engine">reciprocating engines</a>. Compression ratio is a ratio of volumes. In the case of the <a href="/wiki/Otto_cycle" title="Otto cycle">Otto cycle</a> reciprocating engine, the maximum expansion of the charge is limited by the mechanical movement of the pistons (or rotor), and so the compression can be measured by simply comparing the volume of the cylinder with the piston at the top and bottom of its motion. The same is not true of the "open ended" gas turbine, where operational and structural considerations are the limiting factors. Nevertheless, the two terms are similar in that they both offer a quick way of determining overall efficiency relative to other engines of the same class. </p><p><a href="/wiki/Engine_pressure_ratio" title="Engine pressure ratio">Engine pressure ratio</a> (EPR) differs from OPR in that OPR compares the intake pressure to the pressure of the air as it exits the compressor, and is always greater than 1 (often very much so), whereas EPR compares the intake pressure to the pressure at the engine's tailpipe (i.e., after the air has been used for combustion and given up energy to the engine's turbine wheel(s)), and is often less than 1 at low power settings. </p><p>The broadly equivalent measure of <a href="/wiki/Rocket_engine" title="Rocket engine">rocket engine</a> efficiency is chamber pressure/exit pressure, and this ratio can be over 2000 for the <a href="/wiki/Space_Shuttle_Main_Engine" class="mw-redirect" title="Space Shuttle Main Engine">Space Shuttle Main Engine</a>. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Overall_pressure_ratio&action=edit&section=6" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Brayton_cycle" title="Brayton cycle">Brayton cycle</a></li> <li><a href="/wiki/Carnot_cycle" title="Carnot cycle">Carnot cycle</a></li> <li><a href="/wiki/Compression_ratio" title="Compression ratio">Compression ratio</a></li> <li><a href="/wiki/Engine_pressure_ratio" title="Engine pressure ratio">Engine pressure ratio</a> (EPR)</li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Overall_pressure_ratio&action=edit&section=7" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">"The aircraft Gas Turbine Engine and its operation" P&W Oper.Instr.200, United Technologies Pratt & whitney December, 1982, p.49</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external free" href="https://www.ulb.tu-darmstadt.de/tocs/210525592.pdf">https://www.ulb.tu-darmstadt.de/tocs/210525592.pdf</a> p.695</span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFBjorn_Fehrm2016" class="citation news cs1">Bjorn Fehrm (October 28, 2016). <a rel="nofollow" class="external text" href="https://leehamnews.com/2016/10/28/bjorns-corner-turbofan-engine-challenges-part-1/">"Bjorn's Corner: Turbofan engine challenges, Part 1"</a>. <i>Leeham News</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Leeham+News&rft.atitle=Bjorn%27s+Corner%3A+Turbofan+engine+challenges%2C+Part+1&rft.date=2016-10-28&rft.au=Bjorn+Fehrm&rft_id=https%3A%2F%2Fleehamnews.com%2F2016%2F10%2F28%2Fbjorns-corner-turbofan-engine-challenges-part-1%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOverall+pressure+ratio" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBjorn_Fehrm2019" class="citation news cs1">Bjorn Fehrm (June 14, 2019). <a rel="nofollow" class="external text" href="https://leehamnews.com/2019/06/14/30405/">"Bjorn's Corner: Why hybrid cars work and hybrid airliners have challenges"</a>. <i>Leeham News</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Leeham+News&rft.atitle=Bjorn%27s+Corner%3A+Why+hybrid+cars+work+and+hybrid+airliners+have+challenges&rft.date=2019-06-14&rft.au=Bjorn+Fehrm&rft_id=https%3A%2F%2Fleehamnews.com%2F2019%2F06%2F14%2F30405%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOverall+pressure+ratio" class="Z3988"></span></span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text">Concorde: story of a supersonic pioneer By Kenneth Owen</span> </li> </ol></div></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: 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