SR-71 J-58 Powerplant (2024)

Specifications:

Model: Pratt & Whitney J-58JT11D-20

Compressor: 9-stage, axial flow, single spool Turbine:two-stage axial flow

Thrust: 32,500 lbs. with afterburner

Weight: approx. 6,000 lbs.

Max. operating altitude: above 80,000 ft.

The SR-71 Blackbird is powered by two Pratt & WhitneyJ-58 turbo-ramjets, each developing 32,500 pounds of thrust with afterburning.The critical problems concerning supersonic flight with air breathing enginesare concentrated in the air inlet area. The circular air intakes of theSR-71 contain a center body tipped with a conical spike. The spike is movable,forward for takeoff and climb to 30,000 feet after which, as speed buildsup, it moves rearward, controlling the amount of air entering the engine.As it does so, Air Inlet Bypass Doors in the side of the nacelle closeto establish the correct flow of air through the engine, holding the supersonicshock wave in it's critical position within the inlet. The engine itselfoperates at subsonic speed. At Mach 3+ the spike is three feet to the rearof it's takeoff position, slowing down the incoming airflow, establishingan area of pressure within the nacelle, which is now pushing the engine.This action is so powerful that it accounts for 58 percent of the totalthrust, the engine providing only 17 percent, and the ejectors (surroundingthe nacelle near the afterburner) is responsible for the remaining 25 percent.Should the shockwave be expelled from the inlet, a condition known as an"Unstart" occurs. Unstarts have been known to be so violent as to crackthe pilots helmet from the severe yaw of the aircraft. If unchecked, theresulting yaw is described by SR-71 pilots as though the nose and tailare trying to swap ends. However, an automatic control system senses thisproblem and repositions the Spike in milliseconds, doing so with greataccuracy even though air loads of up to fourteen tons are acting on thespike, dealing with the difficulty before the human brain becomes awareof the problem, and the Blackbird cruises on....faster than a rifle bullet.

A correction to the above paragraph isneeded. Ken Hall, a retired Astro/Aero/Electronic engineer states: It appearfrom this description that FREE thrust is being generated by the pressurized airbehind the inlet shocks. Not true.A portion of the"pressurized" incoming air flow was/is piped and valved around therotational core to the afterburner section where fuel is added and combustedwith this, so called by-pass, air thus producing thrust. An engine thatfunctioned as you have described would be a free energy machine.

KenHall kenjack@hughes.net

Editors Note: Thankyou for the clarification.

I recently came across yourwebsite an enjoyed it immensely. I did notice the picture on the J58 pagecaptioned as “J-58 Engine Testing in Afterburner at Lockheed MartinCorp.”. This is incorrect. The picture actually shows test cell A-1 atPratt and Whitney’s West Palm Beach facility. I had the pleasure of workingthis test cell in the mid 1980’s. This test cell was actually an altitudesimulation cell used for testing purposes. (We had a additional cell used forsea level runs for motors which were overhauled onsite also.) It used anon-afterburning J-79 as a slave motor. The exhaust of the slave was introducedto the inlet of the J-58 through a series of valves thereby simulating thespeed, temperature, and density of the air at the inlet normally seen duringflight. In this particular picture the motor is running at sea level asindicated by the inlet screen. I spent many hot and humid nights servicing,mounting, and running this particular cell. I was one of a crew of five. Some ofthe greatest co-workers I have ever had the privilege to of worked with. Sadly,the cell is no more. It didn’t go without a fight though. The contractor hadto repeatedly repair his demolition equipment saying it was the hardest concretehe had ever had to remove. Sincerely,

Kurt Schmidt

Sun 5/3/2009 8:30 AM, John Evans adds this information to the above photo: Kurt Schmidt's article with the J58 test photo appears to be accurate with some exceptions. The photo of the sea level engine test stand looks more like stand A3 as the engine is fitted with an inlet screen. Stand A1 had a J75 engine just ahead of the J58 engine (J75 in stand A1A) with the J75's exhaust ducted through a mixing valve into the J58 inlet. The mixing valve had a fresh air inlet on the bottom and a hot exhaust stack on the top. A butter-fly valve in the mixing valve was positioned to control the J58 inlet temperature to simulate HIGH MACH NUMBERS AT SEA LEVEL, not high altitudes.

The first J-58s delivered to the blackbird program, all three models,had all stainless steel lines and the oil tank gold plated, the reasonwas for better heat dissipation. After a couple of years, and the subsequenttear down of engines, it was noted there was an abnormal amount of corrosioncaused by dissimilar metal electrolysis. The gold plate was removed becausethe heat dissipation properties did not out weigh the cost of replacinglines as they started leaking.
Side note: When #957 crashed off the North end of the runway atBeale AFB and pictures were published, the hew and cry that came from thecivilian segment about all the gold that was on the engine caused quitea commotion, even when it was explained why the gold was there. (Info courtesyRon De Lozier)

AnIn-Depth Article on the J-58 Engine Lineage

byPhilippe Ricco

Fri, 19 Jul 2002 08:18 Philippe Ricco Writes: 15 years ago, when I wasa student and very impressed by the beautiful Blackbird, I wrote some personal notes aboutthe Pratt & Whitney J-58. Years after, as Aeronautics Engineer, I found some moreinformation to add to these notes. Recently, I gave the first part of these notes to one of my friends for publishing on theWEB, at the following address:http://aerostories.free.fr/technique/J58/J58_01/page8.html

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