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I see these Blackbirds sitting in museums and airparks and it seems kind of a shame to me that we restore and keep, for example, B-17's and P-51's flying and not an SR-71 when they are just as much a huge part of aviation and military history. Which got me wondering what it would take to bring an SR-71 back into flying condition. Not for active missions, but for air shows, historical flights, and so forth.

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Short Answer: everything related to the aircraft that is not currently in a museum has been destroyed by the airforce including all the tooling to build the parts. It would not be logistically possible to bring one back to airworthy condition without effectively recreating the whole program.

TLDR;

I'll preface this answer with a note; I think everyone can agree it would take a large sum of money to get an SR-17 flying again and I will discuss mostly logistics below under the assumption that money is not really the problem.

Most of this answer comes from the following sources:

I consider all of these sources to be primary sources and there is some incorrect information out there about these plans so I will try and stick to information from these sources. Below is a list of things you would generally need to get an SR-71 flying again

I will generally only address the flight portion of these aircraft. They also carried a lot of sophisticated wet film cameras that could be brought into action but let's ignore that for now.


You're going to need an airframe to at least start this endeavor and its unlikely you're going to get one easily.

The first hurdle you will have is simply convincing companies to produce small batch parts they have not made in a long time. The SR-71 was a sophisticated plane and was designed for a flight regime that no other aircraft ever really flew in. Everything on the aircraft from the wheels to the pilots had to survive the extremes the aircraft operated in and I'm confident that every part made for that aircraft is no longer made and the tooling has been destroyed. This is basically your limiting factor and the hardest to overcome. It took close to half the time of the original Lockheed project just to figure out how to work with titanium to the point the project could even be a reality. Any notion you could produce some of these parts yourself is foolish at best.

Engines

All of the SR-71's I know of on display no longer have their engines in them (although most still have the critical inlets). You will need to find a way to source two, good condition, flightworthy J-58's which are long since out of production. There is one on static display.

Fuel/Fluids

You're going to need a tanker support plane. There were a lot of concerns that a blowout on take-off would disable the aircraft so the SR-71 took off with a minimum fuel load and almost immediately refueled in air. To operate it by the book you will need a support tanker aircraft.

Once you have the tanker you need to fill it with JP-7 which is not exactly for sale at your local airport. The fuel not only powered the engines but served as a heat-sink as well (see page 22) to pre-cool the bleed air used in the cockpit which was hot even with all the cooling applied. On top of that due to panel expansion and a wet tank configuration (even with 10,000 Ft of sealant) the aircraft leaked a considerable amount and the panel expansion was an important part of the operation. So you're going to need the right fuel and you're going to need to fly it fast.

The fuel and hydraulic fluids are still commercially available and would not be a limiting factor to get one flying.

Mechanics and Manuals

The SR-71's were maintained by huge crews of highly trained mechanics. It took almost 24 hours to prepare one for a flight. Some missions were as short as 58 minutes and still required as much prep. To operate the plane you will need a full team of these people and these are people who need knowledge that may very well be gone (although this guy might be able to help).

It's highly likely that there is a full set of maintenance information still stashed away with the remaining NASA spares but you will need, at minimum, access to this documentation to confirm a given airframe you are looking at even has all the parts it needs to fly.

Pressure Suit/Cooling System

Operating at extreme temperatures means the pilots themselves were subject to higher temperatures than was typical. At the altitudes at which they flew, ejection was basically impossible with regular equipment, so they needed to wear cooled pressure suits. To actually fly a Blackbird you would need 2 suits that fit the pilots.

Training

There was one double-cockpit trainer airframe built to train the pilots, which might not be a bad first plane to bring back since even if you got one operational you would need to train people to actually fly the thing. It might be best to do this before all the living pilots are gone. The trainer was acquired by NASA along with their two SR-71A's and now resides in the Air Zoo museum.


All that remains

After its second retirement by the US Air Force most of the SR-71 parts were consolidated to a single location and two remaining airworthy airframes were given/sold to NASA with all the spare parts left. Ultimately the airframes were test beds for experiments at the end of their lives and presumably the remaining spares are still held in some capacity by NASA. These were (as far as I have found) the last remaining flightworthy airframes. One is now on display.


Destruction of the spares

According to this lecture the spares that were not given to NASA were destroyed if they could not fit in the NASA warehouse. According to that lecture none of the stuff ever actually belonged to NASA as the Airforce remained the "owner" of the aircrafts and spares and NASA simply had custody of the test beds allowing the Airforce to call them back at any time if they wanted. Ultimately after NASA stopped using them the remaining spares were destroyed at the behest of the Airforce.

Sadly all the stuff was shredded, melted, cut up, chop shopped into destruction including the tooling so you could not even re-build the parts if you wanted to. All this seems to indicate it really would not be viable to bring one of these aircraft back.

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The main thing would be to de-tune or replace the engines, so they can run on a standard aviation fuel. At least you wouldn't need to get the ramjet bit working; besides the laws against sonic booms, high Mach numbers would be neither achievable with the de-tuned engines and low-thermal-tolerance fuel, nor the accompanying tendency to unstarts acceptable!

There is also the endemic problem of fuel tank leakage, which is not really acceptable in an everyday environment. You'd have to line enough of them to get the plane to your airshow and back. Easy enough, as there are plenty of them.

Possibly some components would have to be removed/substituted or paint-stripped, to remove any materials or items which might still be classified. Maybe that's already been worked through on the available airframes.

And your sponsors would be asking themselves how many B-17s and Sabres they could keep flying, or flying cars they could be investing in, for the same money. The UK struggles to get its lone subsonic Avro Vulcan back up there any more, and when they do it soon heads back to the maintenance hangar for a very expensive overhaul.

Still, a Blackbird and a Hustler roaring along beside each other would be a sight to behold.

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