what is the color characteristic of the SR 71 exhaust?

Answer 1

It's blue. Not red like other jets, but blue. The Blackbird used a binary fuel system that was circulated throughout the plane to cool it in flight. The components were mixed just prior to being pumped into the combustion chamber of the engines. Couldn't tell you what the components were, but when they burned, it was blue.

Answer 2

The SR-71, a black, high-altitude airborne reconnaissance platform that flew at trisonic speed, gave the United States the ability to photograph military sites in hostile countries as well as the opportunity to confirm interpretations of satellite photographs from 1968 until 1990.

The plane was designed to have a very small "radar cross-section" — the SR-71 was an early stealth design. However, the radar signature aspects of the SR-71 design did not take into account the extremely hot engine exhaust, and it turns out that this exhaust can reflect radar. Ironically, the SR-71 was one of the largest targets on the FAA (Federal Aviation Administration) long range radars, which were able to track the plane at several hundred miles.


There were a number of features in the SR-71 that were designed to reduce its radar signature. The first studies in radar stealth seemed to indicate that a shape with flattened, tapering sides would reflect most radar away from the place where the radar beams originated. To this end the radar engineers suggested adding chines (see below) to the design and canting the vertical control surfaces inward. The plane also used special radar-absorbing materials which were incorporated into sawtooth shaped sections of the skin of the aircraft, as well as cesium-based fuel additives to reduce the exhaust plumes' visibility on radar. The overall effectiveness of these designs is still debated, but since the aircraft did not include other elements of today's stealth technologies, it was still easy to track by radar (and had a huge infrared signature when cruising at Mach 3+). It was visible on air traffic control radar for hundreds of miles, even when not using its transponder.[11] This fact is further corroborated by the fact that missiles were fired at them quite often after they were detected on radar.

The Pratt & Whitney J58-1 engines used in the Blackbird were the only military engines ever designed to operate continuously on afterburner, and actually became more efficient as the aircraft went faster. Each J58 engine could produce 32,500 lbf (145 kN) of static thrust. Conventional jet engines cannot operate continuously on afterburner and lose efficiency as airspeed increases.

The J58 was unique in that it was a hybrid jet engine. It could operate as a regular turbojet at slow speeds, but at high speeds it became a ramjet. The engine can be thought of as a turbojet engine inside a ramjet engine. At lower speeds the turbojet provided most of the compression and most of the energy from fuel combustion. At higher speeds the turbojet throttled back and just sat in the middle of the engine, as air bypassed around it, having been compressed by the shock cones and only burning fuel in the afterburner.

here is a link to a photo showing ground test of the engine
http://aerostories.free.fr/technique/J58/J58_01/banc.JPG
the afterburner is redhot and the blue diamond shock waves in the discharge can be clearly seen.

Answer 3

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