How fast was the SR71 REALLY??

DavidWhite

DavidWhite

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So I know Mach 3 is the listed max speed but I think that's bunk. The XB70 Valkyrie could go that fast. Anyone care to speculate?
 
I know in Brian Shul's books he describes speeds pushing Mach 3.5.
 
The aircraft was not limited to a specific airspeed or Mach speed in cruise ( though it did have a max KEAS limitation for dynamic pressure at lower altitude) - it was limited by maximum CIT (compressor inlet temperature) of 427 Celsius. This depended greatly on outside air conditions at the point of flight, so assigning a "max speed" is not relevant beyond not exceeding that temperature, which was dependent on stagnation temperature increase above ambient. The SR-71 was cleared for a one-time max CIT of 450 Celsius on it's final flight to set to the trans-continental speed record across the US during it's delivery to the museum, but due to atmospheric conditions it was not required on that flight.

I had a conversation one evening with Brian Shul after the Reno Air Races with a group of other aviators where he acknowledged flying in the 3.5 range, but wouldn't say exactly where in the world he was or what the actual mach reading was, nor could he (or would he) say what the CIT reading was. He did say "We were fired at, but we were never hit." It was not clear whether he was speaking about that particular flight or about the program as a whole.
 
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airguy said:
I had a conversation one evening with Brian Shul after the Reno Air Races with a group of other aviators where he acknowledged flying in the 3.5 range, but wouldn't say exactly where in the world he was or what the actual mach reading was, nor could he (or would he) say what the CIT reading was. He did say "We were fired at, but we were never hit." It was not clear whether he was speaking about that particular flight or about the program as a whole.
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Probably his run across Libya when they were shot at. He talks about it in one of his standard speeches. Fastest he ever went in the SR-71.

First hit on Google: http://maggiesfarm.anotherdotcom.com/archives/7821-Major-Brian-Shul-I-loved-that-jet.html
 
We have an SR-71 hanging in the Offutt Space Museum near Omaha. One of the pilots (there were only 85 I think) is a member of a local EAA chapter. He tells amazing stories.

If you ever pulled 2 gs in the Blackbird you will do structural damage to the wings, 1.5 was the max. :eek:

There was no GPS back then and ground navigation aids were worthless at altitude. They navigated by stars using a sextant. :yes:
 
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My friend who flew the SR-71 said the normal 'driving around' speed was M3.0, and it could go a bit faster at a greatly increased risk of a catastrophic compressor stall.

I'm skeptical that it could go M3.5, the declassified -1 says the max mach was 3.2.
 
We have a pitot/static probe off of an SR-71, hanging in our Blackbird Room. It (and a slew of other cool memorabilia and artwork) was donated to us by Bill Fox, who worked at the Lockheed Skunkworks for three decades. He also ran Area 51 for a few years.

The probe is an amazing piece of technology. The front half is titanium, because nothing else could survive the heat at Mach 3.2+. Ours is actually burnt.

The second half is stainless steel. I'm told that the only way those two metals can be joined is with explosive welding.

The probe is hollow, for the first bit. There are tiny holes drilled in from the sides that were the pressure sensors for the autopilot. At three times the speed of a rifle bullet, no human could fly straight and level, so the autopilot kept things on an even keel -- until it didn't. A pitch up at that speed was catastrophic, of course.

At the base of the probe are half a dozen electrical and pressure connectors. The real mystery, to me, is how they were able to drill the length of the probe up to the pressure sensors in the tip. What could drill through titanium? I suppose diamond, but what could drill a precise hole almost three feet long, inside the probe?

And there are quite a few of those holes.

That probe is my favorite piece of memorabilia in our collection. It's an amazing piece of technology. And that's just the freaking pitot static probe! It's hard to believe what Kelly Johnson's boys did with slide rules and ingenuity.
 
Geico266 said:
We have an SR-71 hanging in the Offutt Space Museum near Omaha. One of the pilots (there were only 85 I think) is a member of a local EAA chapter. He tells amazing stories.

If you ever pulled 2 gs in the Blackbird you will do structural damage to the wings, 1.5 was the max. :eek:

There was no GPS back then and ground navigation aids were worthless at altitude. They navigated by stars using a sextant. :yes:
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INS has been around since the 50's. I'm willing to bet they had at least 2 onboard.

TACAN can be received at all altitudes as well as NDB.
 
RotorAndWing said:
INS has been around since the 50's. I'm willing to bet they had at least 2 onboard.

TACAN can be received at all altitudes as well as NDB.
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At that kind of altitude, wouldn't you get into problems with interfering NDBs?
 
Astro-Inertial Navigation System

The USAF sought a precision navigation system for maintaining route accuracy and target tracking at very high speeds, superior to the inertial navigation systems used by the preceding U-2 and A-12.[citation needed] Nortronics, Northrop's electronics development division, had developed an astro-inertial navigation system (ANS), which could correct navigation errors with celestial observations, for the SM-62 Snark missile, and a separate system for the ill-fated AGM-48 Skybolt missile, the latter of which was adapted for the SR-71.

Before each takeoff, a primary alignment brought the ANS's inertial components to a high degree of accuracy. Once in flight, the ANS, which sat behind the Reconnaissance Systems Officer (RSO)'s position, tracked stars through a circular window of quartz glass set in the upper fuselage.[38] Its "blue light" source star tracker, which could see stars during both day and night, would continuously track a variety of stars as the aircraft's changing position brought them into view. The system's digital computer ephemeris contained data on 56 (later 61) stars.[49] The ANS could supply altitude and position to flight controls and other systems, including the Mission Data Recorder, Auto-Nav steering to preset destination points, automatic pointing and control of cameras and sensors, and optical or SLR sighting of fix points loaded into the ANS before takeoff.[50] Former pilot Richard Graham told an interviewer at the Frontiers of Flight Museum that the navigation system was good enough to limit drift to 1,000 feet off the direction of travel at Mach 3.[51]
The original B-1A Offensive Avionics Request For Proposal (RFP) required the installation and integration of an NAS-14 system, but cost-cutting changes later deleted it from the B-1. Some U-2Rs did receive the NAS-21 system, but newer inertial and GPS systems replaced them.
 
Wow...and to think the ANS was created in the in the relative dark ages of electronics. Impressive.
 
LDJones said:
Wow...and to think the ANS was created in the in the relative dark ages of electronics. Impressive.
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I'd love to know that that program cost. I'm sure some of it piggy backed off of the NASA space program, but still, big bucks.
 
That was the dark age of digital electronics. It was to golden age for analog.

A star-tracking INS is equivalent to a gyro stabilized telescope, which is older than the SR71. The spherical trig isn't hard mechanically; that was used in World War II to navigate large ships, and is still used on legacy medium sized ground-based telescopes.
 
Henning said:
OMEGA was around back then as well.
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Any of the ground based stuff can be jammed or spoofed.

Celestial bodies, star tables, and trigonometry are immune to jamming.
 
kyleb said:
Any of the ground based stuff can be jammed or spoofed.

Celestial bodies, star tables, and trigonometry are immune to jamming.
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I've done celestial navigation since back when it was the only way to get across an ocean, I can just imagine what my plotting sheet would look like for a 3 star running fix at Mach3.:rofl: I would bet that hand done celestial at Mach 3 would be right around as accurate as my DR plot(which usually isn't too bad.)
 
Henning said:
I've done celestial navigation since back when it was the only way to get across an ocean, I can just imagine what my plotting sheet would look like for a 3 star running fix at Mach3.:rofl: I would bet that hand done celestial at Mach 3 would be right around as accurate as my DR plot(which usually isn't too bad.)
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Yeah, but we're talking a state of the art 1960 computer (!) performing the calculations, probably based on near simultaneous readings. Apparently it was up to the task.
 
kyleb said:
Yeah, but we're talking a state of the art 1960 computer (!) performing the calculations, probably based on near simultaneous readings. Apparently it was up to the task.
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Oh yeah, probably the same system used in the early space program. I was referring to the earlier statement that the back seater was working the fixes through the glass in the roof.
 
It used an Astro-Inertial Navigation System (ANS). A glass porthole on top of the fuse that tracked up to 300 stars to determine its position. It interfaced with the autopilot as well. RSO was responsible for its operation.
 
Velocity173 said:
It used an Astro-Inertial Navigation System (ANS). A glass porthole on top of the fuse that tracked up to 300 stars to determine its position. It interfaced with the autopilot as well. RSO was responsible for its operation.
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300 stars? HO 249 only has 57, and there are only 41 prime navigation stars of which you'd need 7 to make a hemispheric trip, 11 to make an antipodean trip, in a day.
 
Henning said:
300 stars? HO 249 only has 57, and there are only 41 prime navigation stars of which you'd need 7 to make a hemispheric trip, 11 to make an antipodean trip, in a day.
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I didn't design the thing. That's out of Sled Driver page 69. Excellent book.
 
Velocity173 said:
I didn't design the thing. That's out of Sled Driver page 69. Excellent book.
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Still doesn't sound correct, especially in a day when having that computing power and database required large expensive machines. Sled Driver is a neat book, not sure everything there is fully accurate. Could be a typo meaning able to track 30 stars continuously, at their altitude that would be about right from even past the tropics.
 
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