Skip to main content

Betrayed by Heat: The SR-71 Blackbird

A couple of friends and I went to the Steven F. Udvar-Hazy Center, part of the National Air & Space Museum near Dulles Airport, a few weeks ago. The museum is home to over 160 aircraft, almost as many spacecraft and missiles, and several thousand smaller aviation-related artifacts. What is perhaps most exciting object on display, though, is the one that greets visitors as they first enter the museum -- the SR-71 Blackbird.

[The view you're greeted with upon entering Udvar-Hazy.]

The three of us were particularly struck with the Blackbird. It's not surprising since the plane is the museum's centerpiece, with the pearly white Enterprise peering over its shoulder from the next room.

[A view from behind shows the Blackbird's Delta-wing shape common to many supersonic airplanes.]

The Blackbird was developed by Lockheed Martin's division for secretive projects called Skunk Works. It was designed to replace another stealth aircraft developed by Lockheed Martin's Skunk Works -- the U-2 . The U-2 was created as a high-altitude reconnaissance aircraft (a spy plane) but it was not capable of flying supersonically, or faster than the speed of sound, making it vulnerable to anti-aircraft weapons. The Blackbird can fly above 82,000 ft. (15 and a half miles) and up to speeds of Mach 3.2, or around 2,400 mph.

[The Lockheed Martin Skunk Works livery.]

Developing a high-flying, supersonic airplane came with one giant problem: Heat. As a supersonic airplane flies faster and faster, the friction from air ramming it results in a lot of heat building up around the airplane. To keep it flying functionally, the designers had to find clever ways to keep the Blackbird cool.

[A man checks out an engine intake on one of the Blackbird's two engines. The cone in the center of the engine retracted while the airplane flew at supersonic speeds to help ensure proper airflow into the engine.]

A special fuel that was stable at high temperatures was developed for the Blackbird. According to the SR-71 manual, the fuel was used both as energy for the engine and also as engine hydraulic fluid - fluid used to power certain engine components.

When the airplane was traveling supersonically, the fuel was also used as part of a heat sink. A heat sink is a device that uses a fluid to wick away heat from a solid object. The Blackbird's manual states that without that heat sinking capability, parts of the airplane and its engines would overheat at high Mach speeds.

[A Blackbird engine from behind.]

Though the airplane was designed to be stealthy, it was fairly easy to detect on radar thanks to the large amount of heat coming out of its engines when it traveled at high speeds. According to, the Federal Aviation Administration could track the Blackbird from several hundred miles away by detecting the airplane's exhaust.

[The Blackbird was officially retired in 1990, though two were brought out of retirement in 1995 and are still used by the U.S. Air Force. This Blackbird set four world records on its March 6, 1990, trip from Los Angeles, Calif., to Washington D.C. on its way to its new home in the Udvar-Hazy. It made the journey in 64 minutes, 2 seconds, with an average speed of 2,144 mph.]

The Blackbird had another quirky heat-thwarting feature: It leaked fuel. According to Lockheed Martin, 93 percent of the airplane is made of titanium alloy. Titanium expands as it is heated. To keep the airplane from crunching up like a soda can when it was flying at high speeds, the designers left gaps between its body panels. Consequently, fuel, stored in the airplane's body, leaked out onto the runway before take off. Once airborne and warmed up by friction, the titanium would expand, the gaps would seal and the Blackbird would be refueled before leaving on its mission.

Skunk Works improved upon the Blackbird when it created the F-117 Nighthawk, their first truly stealth airplane. They also collaborated with Boeing to develop the more conventional-looking F-22 Raptor stealth fighter. And who knows what else is up Skunk Works' sleeve these days. Regardless of what it is, I doubt it could ever have the unique personality of its early predecessor - the SR-71 Blackbird.


  1. Top Pentagon Military Officers are also Top Lockheed Martin Salesmen

    Not sated after sacking the U.S. Treasury, like locusts our Military Industrial Complex is swarming around the globe seeking new sources of sustinance. In the photo linked below we see U.S. Air Force Chief of Staff General Norton Schwartz presenting a model of the C-130J-30 Super Hercules to Indian Defense Minister A.K. Antony at a ceremony at the Air Force Station at Hindon near New Delhi, India on Saturday (5 February 2011) to mark the induction of the first of six Lockheed Martin C-130J airplanes purchased for the Indian Air Force.

    U.S. total debt $55.6 trillion, U.S. federal debt $14.1 trillion, U.S. federal deficit $1.5 trillion, U.S. dollar rapidly losing world reserve currency status, as U.S. politicians bought and paid for by multinational corporations (legalized by Citizens United vs. FEC) cut education, close schools, convert asphalt roads to gravel and accelerate America's descent into oblivion so they can pay Lockheed Martin and other greed- and graft-infested government contractors billions for Rube Goldberg defense systems and myriad non-defense boondoggles as unnecessary, unaffordable and unjustifiable as our unending wars for oil and profit. And with the open support of Pentagon top brass, the debt for death and destruction will grow to plague nations around the world:

    1. Are you calling the SR-71 a Rube Goldberg defense system? The C-130? You'd better not quit your day job as a liberal hack because you seem bereft of technical acumen and logical thinking.

  2. Pertaining to physics, some of your data is not quite accurate. Of course this is not your error, but like dozens of myths that surround the Blackbirds, disinformation and the secret classifications under special access required and need to know basis not many people know any of the facts.

    As far as the SR-71 skin expanding to seal the fuel tanks, that's a myth. When the airframe heats up, I does not seal the fuel tanks. The tanks are manually sealed using a special blend of 3M brand high temperature sealant. It is applied at certain locations depending on the measured drip per minute rates. When the aircraft flies and reaches operating temperature the fuel still leaks at the same rates, there is just no way the measure it in flight. The amount is so small that the effect is negligible. As the airframe heats up the titanium expands and causes the seems to get bigger.

    The stealthiness of the SR-71's was fantastic for it's time. The proof is that none were ever shot down by the thousands of MACH 5 missiles fired at it. The fact is that the tremendous exhaust would have emitted detectable heat for hundreds of miles if it weren't for one clever trick. This little trick was a material that the Skunk Works had nicknamed "Panther Piss".

    After they retired the Blackbirds, Ben Rich, the SR-71's co-designer and also the Director of Lockheed Skunk Works boasted in his book (memoir) titled "Skunk Works" on page 240.

    "We at the Skunk Works believed that the airplane's height and speed, as well as its pioneering stealthy composite materials applied to key areas of its wings and tail, would keep it and its crew safe, but we fortified that belief by adding a special additive, which we nicknamed "panther piss", that ionized the furnace-like gas plumes streaming from the engine exhaust. The additive caused enemy infrared detectors to break up incoherently."

    This little trick gave the Blackbirds enough advance lead time giving it a reduced intercept reaction factor.

    By now your wondering what the hell is "Panther Piss"?

  3. In 2007, the CIA released the History of the OXCART Program, written by Kelly Johnson, the Blackbird's Chief Designer.

    In that document around 1959, Johnson states-

    Page 4.
    " By this time we were working with P&W on a J58 engine. To overcome the afterburner problem of a large radar cross section return from the aft quadrant, we proposed the use of cesium additive to the fuel. This was first brought up by Mr. Ed Lovick of ADP, and its final development was passed over to P&W. It was eventually a basic part of our cross section reduction methods."

    Page 9.
    "We were able to prove by 1 January 1960 that our concept of shape, additive, and loaded plastic parts had enough promise to warrant going forward with the project."

    Dr. Abernethy was an engineer for P&W (Pratt & Whiney) the Blackbird engine builder. Notice the statement is dated nearly 2 years prior to Kelly Johnson's statement in the OXCART document.

    Below it a quote from Dr. Bob Abernethy's web site, a presentation to the Roadrunners and the J58 Reunion.

    "In late 1957 PW had two top secret, black, engine projects that were to use poison fuels! Not a good idea in the middle of Connecticut, how about the middle of the Everglades?? So I was invited to move to Florida. I was assigned to the J58, a Mach 3 Navy engine. To scrub the poison out of the J58 exhaust we built a huge swimming pool with a tall tower to centrifuge the poison out of the exhaust… If it didn’t work, we might wipe out the Palm Beaches so we were a little nervous. The Navy canceled the poison fuel just before we ran the first test. thank heavens!"

    Dr. Abernethy never knew about about the use of cesium in the jet fuel and to this day the Air Force has no record or information about it's use as it was classified top secret as well as a manufacture trade secret of the fuel suppliers.

    For more information about the phenomenal Blackbirds and to request an authentic sample of it's magnificent heat resistant and extremely rare Beta Titanium, check out

  4. I volunteer at the Udvar-Hazy portion of the Air & Space museum. Whenever I run into a former SR-71 pilot they will just smile when you ask them how high and how fast. Keeping the secrets, sure.

  5. A lot of things not quite right here. First, the writing is lacking; a lot of awkward phrasing and word choices. Then, friction is not caused by "air ramming the object". That's like something you'd tell a little kid. This is supposed to be a physics page? Next, the "special fuel" was not only meant to be stable at higher temperatures, but it also was designed with a very high density, meaning much more energy could be stored per given volume of fuel tank, which was important, given the incredible fuel consumption in full afterburner. Which brings me to the fuel being used as a hydraulic fluid: t says that it was used to power "engine components"? By this I take it you mean it powered the variable inlet cone and exhaust nozzle, because there is nothing hydraulically powered in a jet engine. All of the engine accessories, including the hydraulic pump, are mounted to the jet engine, and mechanically driven by the spinning compressor spool, like a power-steering pump or air-conditioning unit on an automobile. In some instances, a few accessories can be mounted remotely from the engine and powered by the hydraulic system, but the main purpose is to provide pressure for the flight control hydraulic system (i.e. elevons, slats, rudders), and landing gear, etc. Right after this, it claims that a heat sink "wicks away heat using liquid". That's partially true; however, a heat sink can also take the form of a large mass, such as metal, which absorbs the heat as it is created. Liquid radiators also "wick away heat" with liquid, but the difference is that a radiator runs the fluid through a heat exchanger, dissipating it. A liquid heat sink wicks the heat away, and transmits it into a reservoir of fluid, which slowly heats up as more energy is added to it. An SR-71 has hundreds of small tubes running through the skin of the aircraft, which circulate fuel to absorb the heat, which is then returned to the fuel tank, which stores the heat (with the added benefit that the heat is recycled to the engine, like a steam locomotive pre-heater). It is basically a REVERSE radiator, necessary because there was no way to actually dissipate the heat due to the aerodynamic heating. A radiator would not work.
    Next, the aircraft was fairly easy to detect on INFRARED SCANNERS, due to the heat generated by the engines. Radar systems do not detect heat. The heated air returns a different radar signature than cooled air, meaning that a radar could detect the AIR changed by the heat, but not the heat itself. More important was the presence of chemical compounds and heavy metals in the exhaust, the particles of which reflected a lot more radar, on a different wavelength, than the relatively pure atmosphere at 80,000ft. This is how meteorologic radars can track cold fronts and cloud systems.
    Next, "leaking fuel" is not a heat defeating measure. The fuel leaks BECAUSE of a heat defeating measure. The phrasing is important. The fuel leaks because the fuel tanks have to be designed with expansion gaps to cope with the heat, not because leaking fuel somehow helps with heat control. As for the person who claims that heat expansion had nothing to do with sealing the fuel tanks: bull. First, leaking fuel in flight is dangerous, especially in a superheated aircraft at Mach 3.2. Second, a loose-fitting metal object DOES fight tighter as you heat it up and the metal expands. That's just how it works. The gaps are (somewhat) sealed with sealant, but the main effect comes from the gaps tightening on the sealant after the tanks are heated. Think of it as a gasket. If all of the sealing comes from the sealant, why didn't they just apply enough to stop leaking at all times? The sealant is merely to HELP the sections seal as they squeeze together.

    1. Yay! Finally a person that knows what they are talking about, AND can articulate the facts CLEARLY in such a way as to deliver all relevant information in a concise and legible manner. Thank you for being both literate enough to convey highly technical information, and technical enough to convey it to those who do not yet understand it. Thank you. You cleared up all the confusion created by this article and the other comments.

    2. Thank you just justforever96, I'm glad you let that jackass squawking all that BS know he that he's a damn idiot that stayed up to late watching Nat Geo and got everything completely wrong about the SR-71 leaking fuel and how the heat did seal the gaps and it was intentional,and they would refuel shortly after takeoff. I read the comment about the "special 3M" product applied and the "drip per minute bullshit and almost laughed out loud @ 3am in bed next to my wife. I hope you have a good night and thank you for correcting the dumbass Sir.����

    3. Yeah, the SR-71 gets people excited about planes the way a 12 year old kid gets excited about ninjas. It's easy to get caught up in the mystique and lost in the technical aspects.

  6. How come no one talked about how the cones worked on the engines? Don't they create a plasma ball that per-ignites the fuel outside the engines or some such cool innovation that the Skunk Works boys came up with?

    P.S. The special fuel had a higher ignition point, hence what made it special... density, stability, and consumption aside.

  7. Cones were adjustable air shockwave devices used to compress air at the higher altitudes to achieve combustion.Gave Ben Rich many sleepless nights over a year till he got them to work.

  8. I'd like to know how the air conditioning system worked. If the skin is 1000F or so, how do you keep the guys in the seats from burning up after a few hours? Anyone know this one?

  9. i never know the use of adobe shadow until i saw this post. thank you for this! this is very helpful. Warmtepompen


Post a Comment

Popular Posts

How 4,000 Physicists Gave a Vegas Casino its Worst Week Ever

What happens when several thousand distinguished physicists, researchers, and students descend on the nation’s gambling capital for a conference? The answer is "a bad week for the casino"—but you'd never guess why.

Ask a Physicist: Phone Flash Sharpie Shock!

Lexie and Xavier, from Orlando, FL want to know: "What's going on in this video ? Our science teacher claims that the pain comes from a small electrical shock, but we believe that this is due to the absorption of light. Please help us resolve this dispute!"

The Science of Ice Cream: Part One

Even though it's been a warm couple of months already, it's officially summer. A delicious, science-filled way to beat the heat? Making homemade ice cream. (We've since updated this article to include the science behind vegan ice cream. To learn more about ice cream science, check out The Science of Ice Cream, Redux ) Image Credit: St0rmz via Flickr Over at Physics@Home there's an easy recipe for homemade ice cream. But what kind of milk should you use to make ice cream? And do you really need to chill the ice cream base before making it? Why do ice cream recipes always call for salt on ice?