Why is the SR-71 Blackbirds' true maximum speed still classified?

Question

The planes' maximum speed at altitude is still claimed to be "Mach 3.3+" ...I saw a show on the discovery channel that interviewed one of its pilots who said he was at cruising speed(Mach 3.2) over Cuba when he noticed a SAM being launched at him and nudged the throttle forward until he began seeing Mach numbers that where getting "scary" and outrun the missle. That sounds to me to be more like Mach 5+. They claimed to have retired the plane in 1998 and is currently only being used by NASA for high altitude research. I understand that some of the planes' technology has to still be classified but if it was retired by the CIA and USAF then why can't they reveil it's true maximum speed and why is 10 pages of its flight manual still classified when its missions are now being done by un-manned stealth aircraft?

Vincent G, the X-15 had an outer skin that consisted of a nickel-chrome alloy called Inconel X which has a melting point slightly lower than SR-71s' titanium alloy(specific type is classified) and it reached a speed of Mach 6.7...And the inlet cones on the Blackbirds' J58 engines moved in and out to compensate for the pressure.

calnickel, I have the flight manual too...Did you not notice all of the missing pages? For instance, on page 5-8 you'll see "Flight Envelope Limits" where it reads: "Refer to figures 5-3 and 5-4 for summarized Mach, airspeed, angle of attack, alititude and bank angle limits and restictions." Now go and look for figures 5-3 and 5-4. And if you'll notice it doesn't say or give any idea of what speed will create a CIT that will exceed 427 degrees. Also, everything in there thats not classified pretains to it's maximum CRUISE speed that can be maintained for hours like where it says speeds of up to Mach 3.3 can be flown if it is authorized by the Commander. These limits are conservative and far from it's flight envelope limits.

Answer 1

Well, it was a SPY plane, after all. Some of the U-2's missions are still classified! MOST of the missions of the SR-71 are still classified.

The Blackbird was designed to fly at incredible altitudes and speeds in order to fly above other countries and look down on them. Violating a nation's airspace for the purpose of espionage is against international law, and can even be considered an act of war. The less other nations know about what that plane did, the better.

Answer 2

Because the classifying authority has not chosen to de-classify the information. That's the very short & sweet answer to the question.

The rules on classification of official information state that only the minimum classification level necessary to protect national security shall be applied. When there is no longer any national security reason to protect the information from disclosure the information shall immediately be de-classified. All well and good, BUT, there is no oversight on the classification and de-classification of information so there is little doubt that there is an enormous amount of information that is still classified for little or no good reason.

Ultimately the President has the authority to classify or de-classify any information he sees fit to without any explanation or justification. The current administration has been on an almost endless campaign to re-classify enormous amounts of previously de-classified information. With that in mind, it's not likely that it will be de-classified until there is a regeime change in January of 2009.

Answer 3

Simple. To give out such information on what is -still- being listed as the world's fastest airplane (not aircraft or spacecraft, mind you, airplane), would date us and show vast research that we've worked too long and too hard to protect. We developed the SR71 Blackbird in the late 70's (supposedly). A lot of times, that factors in, as well as the fact that if I were to say "well, I flew the SR71 Blackbird to a maximum speed of Mach 5.6", i'd have to answer a very interesting follow-up question. "Where?" If the place was classified, well, I can't very well go spouting off about how fast I flew over it in a military aircraft.

Answer 4

This Site Might Help You.

RE:
Why is the SR-71 Blackbirds' true maximum speed still classified?
The planes' maximum speed at altitude is still claimed to be "Mach 3.3+" ...I saw a show on the discovery channel that interviewed one of its pilots who said he was at cruising speed(Mach 3.2) over Cuba when he noticed a SAM being launched at him and nudged the throttle forward until...

Answer 5

It also out ran a missile over Iran in 1979, I don't think it's fully retired, they just say it is, (U2 is still operational, AND IN USE), a Black bird went from California to the east coast in 69 minutes, now thats "BOOKIN" ! There is no caulking on the black bird's fuel tanks, so they weep fuel when re-fueling on the ground, when at speed the metal expands and tightens up, they have not found a caulking that does not turn into melted burnt marshmellow goo from the high temps on the aircrafts skin at mach + speeds

Answer 6

Last I heard they brought it back into service a year or two ago. Do you know everything about the projects that made stealth technology a reality? Probably won't for years either. Until you see devolping countries get any tech like the SR or Stealth you won't see the projects associated with them de-classified.

Answer 7

Its not classified. I have a copy of the SR-71 Pilot Operating Handbook that says the maximum speed limit is based on a compressor inlet temperature of 427 degrees Celsius. With this limt, a speed of Mach 3.3 can be achieved at an Outside Air Temperature of -49 resulting in a True Airspeed of 1925 Knots. This is also listed as the maximum useable speed in the POH. The design Mach number is 3.2.

If you can find a lower OAT, it could go faster. Also you could 'push' the plane faster. My old boss flew CF-104 Starfighters which are also CIT limited and he pushed it to Mach 2.2 when it was limited to Mach 2.0. I also heard of a Russian pilot pushin a Mig 31 to Mach 3.1 instead of Mach 2.7 and cooking his engines.

Can the SR-71 go faster than Mach 3.3, probably, but it would be at the expense of safety and reliablility.

I can email you a copy of the page if you give me an email address, or search for it on the web, that's where I got it.

Answer 8

Even if it was "officially" retired does not mean it cannot be brought back... It is not like all of them were scrapped. In this case, what is being protected is not only the capability of the plane, but the capability of the Lockheed company to still build airplane like that, if there is a need.

As for the speed, MACH 5+ it cannot be. The kinetic heating at such speed would have melted the titanium alloy; also the inlet cone of the engines would not be appropriate for M 5 speed. You can measure the angle of those inlet cones and compare with the Mach angle; as soon as the speed requires an angle smaller than the cone, the isentropic compression of oblique shock that the cone allow will drop in efficiency, and the engine will not be able to produce more thrust (and you do need more thrust to go faster).

To be scared in a SR71 probably means M 3.5 or 3,6; at such speed, the aircraft is likely to start buffeting, and the heat sensors in the aircraft skin and inside the engines will most likely start complaining that something is very uncomfortable.

Answer 9

I can only say that what you have heard here upon specifications of the airplane in question is guess work at best and speculation. There are no facts you have heard here that will ever give you the slightest fact as to the accurate information.

This airplane is classified for a reason, you can guess all you want or build a fantasy world around it and come up with all your own ideas but you will never know in your life time what the truth is.

I will give you something to wet your whistle " sort of speak" The airplane in question was designed at area 51.

Answer 10

Sr71 Speed