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Unread postPosted: 22 Sep 2010, 03:09
by mustang65
Obviously the Blackbird isn't flying now good observation Gunsmiley. All I wanted to know was how long usually it could fly at mach 3.2 because it is the design speed of the airframe. Also why was mach 3.17 the max scheduled cruise speed for the Blackbird?

Unread postPosted: 23 Sep 2010, 00:22
by That_Engine_Guy
mustang65 wrote:why was mach 3.17 the max scheduled cruise speed for the Blackbird?

MAX is beyond which things become damaged or begin to break.
CRUISE is where you get the best speed versus fuel consumption, versus altitude, versus range.

Max is what you COULD do, Cruise is what you SHOULD do for the best mission profile.

Give up on the 'what if' thing concerning the periscope. If it had needed one, it would have had one.


Unread postPosted: 23 Sep 2010, 03:03
by mustang65
I didn't mention the periscope in the last post, but I thought that the Blackbird was capable of safely flying at Mach 3.2 since that was the design speed, but 2110 mph is really fast too especially for 90 minutes at a time. I'm sure you would not get as much range at that speed but it could fly at that speed relatively safely (with all of the unstart problems and such) for a descent amount of time even thought the Blackbird is not flying anymore.

Unread postPosted: 23 Sep 2010, 22:58
by aaam
For non-operational and regular missions, the normal recommended cruise was M3.17, @ 24,384m/80,000 feet based on the normal Compressor Inlet Temperature limit of 427C. For non-operational missions, there was no point in going any faster. On operational missions, higher speeds could be authorized by the Commander. Speeds of M3.2 to 3.31 were not uncommon. Of course, the crew could use its own discretion (those were the days!) should the operational situation require. Higher speeds also required a change in the descent profile to dissipate excess heat.

The fastest USAF has ever officially acknowledged SR-71s have traveled was M3.5. The aircraft suffered no problems or damage, but that was pushing the absolute limit and was not ordinary. Of course atmospheric temperature comes into play and since there was variation between each bird, that would come into play as well.

Unread postPosted: 26 Sep 2010, 22:23
by mustang65
Yeah but were speeds between mach 3.2 and 3.31 sustained for a good part of the mission if the crew needed to operate at those speeds? The CIT problem only happened after they exceeded mach 3.31.

Unread postPosted: 26 Sep 2010, 22:53
by That_Engine_Guy
The CIT limit was reached depending on atmospheric conditions versus altitude versus speed.

At a lower altitude, higher density, the CIT would raise faster than 'up high'. To get the real high MACH 3.2+ speeds the Blackbird's altitude would be near or at limits as well. Thinner air is better for the speeds involved and keeping CIT from being exceeded.

IE an SR-71 can't reach MACH 3 at lower altitudes, the air is too thick.

So again it depended on where, when and why the pilot was operating a Blackbird as to his maximum MACH for a particular sortie.


Unread postPosted: 28 Sep 2010, 05:16
by mustang65
Wasn't 85000 ft the altitude for the max Afterburner profile?

Unread postPosted: 02 Oct 2010, 08:45
by TC
The max altitude of the SR is still classified.

Unread postPosted: 02 Oct 2010, 15:11
by mustang65
I wasn't talking about max altitude I was saying that 83000-85000 ft would be the altitude for the SR to travel at mach 3.2 to mach 3.3 safely so the CIT does not get to high and they can maintain that speed. If the situation called for it how long could the Blackbird fly at mach 3.2 or a little above so the CIT does not get to high?

Unread postPosted: 06 Oct 2010, 03:19
by mustang65
Has the blackbird really been to mach 3.5?

Unread postPosted: 06 Oct 2010, 05:48
by TC
Re: My last post Mustang. Same goes for airspeed. Hence, the + in "Mach 3+".

However, I will reference Brain Shul's story about making "feet wet" in the SR over the Gulf of Sidra. They were exiting Libyan airspace, following Operation El Dorado Canyon. Just before leaving the threat area, they received a mud spike, likely from an SA-2, or SA-5.

Already knowing that we had lost one of the 'Varks on the airstrike (Maj. Ribas-Dominici and Capt. Lorence), they pushed up the throttles to full afterburner to get out of range before the Libyans could take a shot and down another American jet.

Several years later, Shul said, "The Mach meter started reading off numbers we'd never seen before!"

He never stated an actual speed, as it is still classified, but make of that what you will.

Unread postPosted: 06 Oct 2010, 23:06
by That_Engine_Guy
Most of us can't talk about the Blackbird's actual high-end numbers...

...unless you're around when that 'don't talk about any of this for the next 99 years' is up... :))

When they say MACH 3+, the PLUS is there for a good reason.


Unread postPosted: 07 Oct 2010, 20:30
by singularity
There was the one mission where the pilot says they were flying a mile every 1.6 the blackbirds altitude the mach number is incredibly high.

Unread postPosted: 07 Oct 2010, 21:26
by mustang65
What was the altitude that the SR usually operated at. I guess your right though but what was the typical "unclassified" mach number that the Blackbird flew at? They must have usually operated at Mach 3.17 a lot though for mission purposes since that is the speed that the engines are most efficient.

Unread postPosted: 08 Oct 2010, 01:07
by TC
Folks, several of the conversations on this thread have been about other models of the Blackbird, so I've changed the title to this thread to reflect the entire family of Lockheed's Blackbird aircraft. Feel free to discuss the A-12, M-21/D-21, YF-12A, and SR-71. This thread is now all-inclusive. Enjoy!


@ Mustang: The unclassified speed is usually said to be 3.2 Mach. Again, the operating altitude remains classified. As TEG said, anyone who's "in the know" wouldn't be able to talk about it anyway.