Editing Lockheed SR-71 Blackbird (section)

====Complete powerplant====
The SR-71 used the same powerplant as the A-12 and [[YF-12]]. It consists of three main parts: inlet, J58 engine and its nacelle, and ejector nozzle. "Typical for any supersonic powerplant the engine cannot be considered separately from the rest of the powerplant. Rather, it may be regarded as the heat pump in the over-all system of inlet, engine, and nozzle. The net thrust available to propel the aircraft may be to a large extent controlled by the performance of the inlet and nozzle rather than by the physical potentialities of the engine alone."<ref>https://apps.dtic.mil/sti/citations/ADB183548,'Inlet-engine matching considerations', Obery and Stitt, NACA Conference on Turbojet Engines for Supersonic Propulsion, AD B183548, Section VII, Paper 2.</ref> This is illustrated for the Blackbird by the thrust contributions from each component at Mach 3+ with maximum afterburner: inlet 54%, engine 17.6%, ejector nozzle 28.4%.<ref>Campbell, David. [https://arc.aiaa.org/doi/10.2514/3.60402 "F-12 Series Aircraft Propulsion System Performance and Development"], "Table 1 Propulsive thrust distribution"</ref>

When stationary and at low speeds the inlet caused a loss in engine thrust. This was due to the flow restriction through the inlet when stationary. Thrust was recovered with ram pressure as flight speed increased (uninstalled thrust {{cvt|34000|lb(f)|kN}}, installed at zero airspeed {{cvt|25500|lb(f)|kN}} rising through {{cvt|30000|lb(f)|kN}} at 210&nbsp;knots, unstick speed).<ref>{{cite book |url=https://www.sr-71.org/blackbird/manual/1/1-7.php |title=SR-71 Flight Manual |via=SR-71 Online |section=Section 1 |pages=1–7}}</ref>

At supersonic speeds not all the airflow approaching the inlet capture area entered the inlet. At supersonic speeds an intake always adapts to the engine requirements, rather than forcing air into the engine, and the unwanted air flows around the outside of the cowl, causing spillage drag. More than half the air approaching the capture area had to be spilled at low supersonic speeds and the amount reduced as the design speed was approached because the inlet airflow had been designed to match the engine demand at that speed and the chosen design point ambient temperature. At this speed the spike shock touched the cowl lip and there was minimal spillage (with its attendant drag) as shown by Campbell.<ref name="Inlet development">{{cite journal |url=https://www.jstor.org/stable/44657533 |title=F-12 Inlet Development – Fig.4 – Inlet airflow |first=David H. |last=Campbell |journal=SAE Transactions |volume=83 |year=1974 |pages=2832–2840 |publisher=SAE International|jstor=44657533 }}</ref> The inlet and engine matching was also shown by Brown,<ref>Brown, William. "J58/SR-71 Propulsion Integration, attachment to CIA-RDP90B001170R000100050008-1, Fig. 3 'Inlet and engine airflow match'".</ref> who emphasized the benefit of increased engine airflow at higher Mach numbers that came with the introduction of the bleed bypass cycle. These two authors show the disparity between inlet and engine for the Blackbird in terms of airflow and it is further explained in more general terms by Oates.<ref>"Aerothermodynamics of Aircraft Gas Turbine Engines", Oates, Air Force Aero Propulsion Laboratory, Figure 13.1.17 'Elements of Inlet Airflow Supply Determination', (a) and (b).</ref>

Engine operation was adversely affected when operating behind an unstarted inlet. In this condition the inlet behaved like a subsonic inlet design (known as a pitot type) at high supersonic speeds, with very low airflow to the engine. Fuel was automatically diverted, by the fuel derich system, from the combustor to prevent turbine over-temperature.<ref>A-12 Utility Flight Manual, 15 September 1965, changed 15 June 1968, Fuel Derich System.</ref>

All three parts were linked by the secondary airflow. The inlet needed the boundary layers removed from its spike and cowl surfaces. The one with the higher pressure recovery, the cowl shock-trap bleed, was chosen as secondary air<ref name="Inlet development"/> to ventilate and cool the outside of the engine. It was assisted from the inlet by the pumping action of the engine exhaust in the ejector nozzle, cushioning the engine exhaust as it expanded over a wide range of pressure ratios which increased with flight speed.<ref>https://www.sae.org/publications/technical-papers/content/740832/, "J58/YF-12 Ejector Nozzle Performance" pp. 1, 2.</ref>

Mach&nbsp;3.2 in a [[standard day]] atmosphere was the design point for the aircraft. However, in practice the SR-71 was more efficient at even faster speeds and colder temperatures. The specific range charts showed for a standard day temperature, and a particular weight, that Mach&nbsp;3.0 cruise used {{cvt|38000|lb/h|kg/h}} of fuel. At Mach&nbsp;3.15 the fuel flow was {{cvt|36000|lb/h|kg/h}}. Flying in colder temperatures (known as temperature deviations from the standard day) would also reduce the fuel used, e.g. with a {{cvt|-10|C|F|order=flip}} temperature the fuel flow was {{cvt|35000|lb/h|kg/h}}.<ref>{{cite book|url = https://books.google.com/books?id=6svmtOFa1JIC| pages=165, 166| title=SR-71 Revealed: The Untold Story| isbn=978-1-61060-751-3| last1=Graham| first1=Richard H.| publisher=Zenith Imprint}}</ref> During one mission, SR-71 pilot [[Brian Shul]] flew faster than usual to avoid multiple interception attempts. It was discovered after the flight that this had reduced the fuel consumption.<ref name="Shul">Shul and O'Grady 1994</ref> It is possible to match the powerplant for optimum performance at only one ambient temperature because the airflows for a supersonic inlet and engine vary differently with ambient temperature. For an inlet, the airflow varies inversely with the square root of the temperature, and for the engine, it varies with the direct inverse.<ref>https://archive.org/details/sim_journal-of-aircraft_november-december-1968_5_6/mode/2up Design and Development of an Air Intake for a Supersonic Transport Aircraft, "Effect of Ambient Temperatures", p.518</ref>

<gallery widths="270px" heights="203px" mode="packed" class="center" caption="Powerplant">
File:1 - Seattle.jpg|The inlet extends from the spike tip to the four sets of three louvers that vent the spike boundary layer bleed overboard through four spike support struts. The more-forward louvers vent the forward bypass bleed. The engine extends from there to the ejector nozzle blow-in doors (shown open) and the nozzle extends from there to the ejector flaps (shown closed).
File:SR71 J58 Engine Airflow Patterns.svg|Diagrams show operation of the air inlet, flow through the engine (primary air), nacelle flow past the engine (secondary air), and flow into the ejector nozzle (primary, secondary and tertiary air).
File:Pratt & Whitney J58 ground test.jpg|This picture of an uninstalled engine being tested illustrates the need for cooling air around the exhaust duct. The engine, when installed as part of the powerplant, has secondary cooling air at {{Convert|1200|F|C|round=50}} passing over the afterburner duct which is heated internally by combustion up to {{Convert|3200|F|C|round=50}}. The heating, followed by the primary nozzle restriction, accelerates the exhaust to sonic speed as it leaves the primary nozzle (shown). The ejector nozzle (not shown) surrounds the primary exhaust with secondary and tertiary air to cushion its expansion in the ejector nozzle.
</gallery>