Why would the blackbird fly so high? I looked it up and it says they can fly up to 90,000ft.

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Why would the blackbird fly so high? I looked it up and it says they can fly up to 90,000ft.

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It was a spy plane used for very, very, *very* sensitive operations and the government could not afford to lose them by being shot down or intercepted. So they were designed to fly really fast and really high to help keep them safe.

It flew so high not only to save fuel, but so it didn’t get blown out of the sky by enemy missiles or planes. Weaponry (and usually radar) of the time wasn’t good enough to fight or track at that altitude. Even if they somehow detected the plane being there, the enemy didn’t have a weapon or plane they could use to shoot it down.

Well it’s a plane that should make photos from high above enemy territory.

The higher you are the less likely it is someone stops you.

The project was stopped once satellites could do the same job from even higher above.

As I remember in the late 1950’s an U-2 spy plane had been shot down over the Soviet Union. Causing a big international incident, so the SR71 was created to fly higher and faster than the Soviet missiles.

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ELI5 – the air up there is less dense, it’s easier to fly faster at 70,80 or 90K feet above the ground. [Flying high and fast put it out of the reach of Soviet Surface to Air Missiles (SAMs) for decades.](https://theaviationgeekclub.com/even-if-it-was-faster-than-the-blackbird-the-sa-2-sam-was-never-able-to-hit-the-sr-71-heres-why/) If when they could climb that high, systems weren’t that accurate or the missiles were never fast enough to catch the SR-71.

When missiles were introduced that could pose a threat ([starting with the SA-5](https://en.wikipedia.org/wiki/S-200_(missile))) the Blackbird wasn’t allowed to fly over the USSR and some of it’s client states that got those missiles.

There are two main reasons.

Firstly, the altitude made it difficult for foreign nations being spied on to counter the SR-71. No fighter/interceptor could fly high and fast enough, and no missile could climb fast enough and track well enough to hit it.

Secondly, the air up there is thinner allowing the plane to fly with less friction. Even so, due to its immense speed, the Habu heated up so much in flight that almost the entire plane had to be made of titanium, which at the time (late 50s) was a very exotic material.

The Blackbird and the U-2 that came before it were spy planes that flew over the Soviet Union and warzones where the enemy would would try to shoot them down.

The Soviet Union managed to shoot down a U-2 that could fly at 70,000ft.

The Blackbird solved this problem by flying higher and faster making it more difficult for it to be shot down.

Because these planes were photographing Soviet airfields, factory’s, nuclear facilities, test site, aerial defences and everything in-between the Soviets really wanted to stop them.

Flying at mach 3 at 90,000ft was the best way to keep them safe. The enemy air defence did not have enough time or energy to detect the plane then get a missile that high and fast to shoot it down.

I was just at the Airforce museum this weekend and they had one there. It is a really cool looking plane.

Antiaircraft and air defense missiles that they had to worry about were mostly on the ground having been warned that it is coming. The aircraft could fly far above and far away from these while doing it’s mission of taking pictures. If they detected incoming missiles they had time to hit the gas and outrun them once their automated warning system alerted them even if they were flying a bit slower from turning.

The SR-71’s cruising speed was just above mach 3 so was going faster than 2,223 mph normally when going mostly straight and even faster if a missile is inbound. While the exact top speed it flew hasn’t been released it is speculated to be about mach 3.5-4 with the fuel they used as the plane had been theoretically designed to go mach 6 on paper. Another reason you want to fly far above the ground when flying at such insane speeds so you don’t get distracted and crash into the ground.

85,000 ft is 16 miles above the planet’s surface. If the pilot looks down at his dashboard for just 5 seconds at mach 3 you have traveled 3 miles! That means if they were to all of sudden to pitch straight down it would only take roughly 30 seconds to crash into the Earth at it’s cruising altitude.

200 aircraft tried to intercept it and 4,000 missiles were fired at the SR-71 and none of them ever hit them, not a single SR-71 was taken out by enemy forces. During the SR-71’s lifetime we developed a missile that could go mach 5 ourselves that might have been in the bay of a few experimental SR-71 variants but when outrunning enemy missiles it didn’t have to go faster than their top speed even just stay ahead long enough for them to run out of fuel. I know it outran Soviet SA-2s SAM missiles fired by North Korea which could go mach 3.5 but maybe even some that were faster and this is great reason to stay far away from the ground.

I love the sr71. This is my favorite YouTube of a “speed check”. Not about the altitude but gives a since of the over US soil speed and you can expand that to cold war spy needs.

https://youtu.be/8AyHH9G9et0

In addition to what others have said about air speed defense, because the SR-71 is a reconnaissance aircraft, the aircraft is able to collect a lot of reconnaissance data very quickly and a board area.

There were three main reasons. First, you simply can’t fly that fast unless you’re up high enough that there’s practically no air. Your aircraft would heat up and burn. Even so, they got pretty hot at 80,000 feet. Second, the SR-71 was faster than any missiles of the time, but if someone fired a missile in front of it, they still might hit it before it could turn away. At 90,000 feet (that’s 17 miles up), it was beyond the range of a lot of missiles, and even the few that might reach it were slow enough that they could turn and run away long before the missile reached them. Third, at 90,000 feet, the horizon is 368 miles away, so if you have the proper cameras, you can take pictures pretty far inside the Soviet Union without actually crossing into their airspace (or maybe just crossing over a little bit, due to “navigation errors.”)

That all combines to let you know the locations and capabilities of their aircraft and missiles, as they try intercept you. You can also see what kind of air defenses they’ve sold to places like Libya by watching what kind of missiles they fire at you as you fly past.

A couple reasons:
It was a spy plane. Not only are they designed to be hard to pick up on radar, flying so high made them VERY difficult to see, and if they were detected, they were so high up, it was really hard to get to them to do anything. (Very very expensive planes, not to mention, don’t want to lose whatever intel they gathered)

Second, wind resistance. The higher in the atmosphere you go, the “thinner” the air is. If you wanna go SUPER DUPER fast, you want as little air to push against as possible. The top speed of the SR71 Blackbird was 2,193 mph (3,529kph), or at least that’s what I can find. To go so fast, high altitude, while not a requirement, REALLY helps.

Altitude is just another means of defense for a warplane. The combination of being able to fly that high in addition to being able to fly well beyond three times the speed of sound means that to have any chance at all of intercepting such a plane, you have to know it’s coming and what route it will take.

Soviet interceptors had to sit on the runway and launch inside very short windows of time to have a *chance* of making the Blackbird deviate from its flight plan and perhaps fail its mission by getting in its way or into a position where they might have been able to shoot at it. Similarly, the higher you fly, the more time you have to react to a missile launched at you, and the air is very thin up at 80-90k, making it much harder for a missile to maneuver to hit you.

Also, height played a very big *offensive* role in the plane’s mission as well – the higher they flew, the more their high-definition cameras captured. The SR-71 never officially penetrated Soviet airspace, but by flying close to it (international airspace starts 12 miles off a country’s coastline, but the Soviets claimed far more) at extremely high altitudes, they could take pictures inside the Soviet Union several hundred miles inland.

Look up the Brian Shul “speed check” story on YouTube, you won’t regret it. In it, he talks about how over Arizona, he could see Downtown LA and all the way up the Rockies into Canada, as well as a whole host of other amusing recollections.

Heating of fuselage necessitated a special fuel with higher flashpoint. You could toss a lot match into a catch tray full of fuel and it wouldn’t ignite.

Oooo I love SR-71 related stuff. The reasons why it flew high are easy. They flew so high because it generally put them above most active radar. In addition to that no other planes could fly as high so it’s hard to intercept an aircraft that’s flying much higher than you. Another reason is the air is less dense up there, so less wind resistance.

Basically that aircraft was designed to fly high and fast with an incredibly small radar profile so that nothing could really contest it to take it down. If you managed to get something to lock onto it, the SR-71 will just speed up and out run it. With its difference in distance from anything launching at it and how fast it could fly, anything shot at it even if it was faster wouldn’t be able to catch up to the SR-71 before running out of fuel and falling to the ground.

Long ago soviet rockets don’t have enough accuracy and range to hit anything flying 9x the sped of sound at 90,000ft. let alone chase it with their own aircraft