The Insane Engineering of the SR-71 Blackbird

It is difficult to explain the

engineering

marvel that is the SR-71 Blackbird, a long-range aircraft capable of flying 26 kilometers above the planet's surface at an altitude so high that the pilots could see the curvature of the planet and the black as The space ink from their cabins flew so fast that engineers had to develop completely new materials and designs to mitigate and dissipate the heat generated by aerodynamic friction. Completely unique engines were needed to run from zero to Mach 3.2, solving a host of problems like cooling. fuel efficiency and supersonic shock waves that interfere with airflow, an aircraft so advanced that when it detected a surface-to-air missile its response was to simply change course and accelerate, although the missiles had a higher maximum speed, they could not Achieving high altitude range and maneuverability the Blackbird was able to This allowed the SR-71 to execute hundreds of missions across Vietnam, North Korea and Iraq without ever losing an aircraft to enemy fire despite multiple attempts, the entire aircraft was built around the propulsion system, which alone was a miracle of

engineering

design for a non-turbine jet engine that can operate with supersonic flow on its list yes, this plane was powered by the pratt & whitney j58 turbojet engine forget about This, these engines could only provide seventeen, six percent of the thrust required for Mach 3.2 flies at a speed that the SR-71 could cruise at for extended periods of time, how did it manage to reach those kinds of speeds?

Typically a ramjet is needed, as you can probably guess from the name it is based on. RAM pressure to operate RAM pressure is simply the pressure that is produced when an airplane crashes through the air, so as the engine moves through the sky it channels this high pressure air inward Before entering the combustion chamber, the speed of the supersonic air flow must first be slowed down. It basically acts like the compressor stage of a normal jet engine, raising the pressure of the air before it enters the combustion chamber. Once air enters the combustion chamber, it mixes with fuel and ignites, expanding and accelerating once again out of the exit nozzle with no moving parts.

This type of engine is capable of flying at much higher speeds than a typical turbine-driven engine, but cannot start from a standstill. It needs forward movement to achieve correct compression of the air in the combustion chamber, so it cannot be dropped from a conventional airplane. They either have a secondary propulsion system or are a hybrid of a conventional jet engine and a ramjet, which is precisely what the SR-71 used. The SR-71's J58 turbojet engine is located inside the nacelle here, in front of and around the J58, it is a complicated airflow management system. These control mechanisms allow the propulsion system to transition from a primarily turbojet engine to a ramjet engine in mid-flight first the inlet peak is capable of moving forward and backward 0.66 meters this adjusts the inlet and throat area which controls the flow of air entering the engine also maintains the position of the shock wave normal in its ideal position between the inlet throat and the compressor.

This is the most efficient position for the shock wave as it minimizes the energy lost due to drag when air flows over the shock wave. The inlet tip remains in the forward position up to Mach 1.6 after this point it begins to move. rearward 41 millimeters for every 0.1 increase in Mach number keeping the shock wave in its ideal position the inlet tip contains perforations that connect to the outside of the nacelle through ducts initially the air flow will come from the outside in to provide additional airflow to the turbojet engines, but once the aircraft reaches approximately Mach 0.5 this airflow reverses as the aircraft accelerates the intake peak develops a significant boundary layer of air A boundary layer is a very slow moving layer of air that adheres to the surface of objects by bleeding this slow moving layer of air from the inlet tip.

Freeing up a larger area of ​​the inlet area for high energy fast moving air and therefore improving efficiency around the engine there is a bypass area that takes air from the inlet and diverts it around the j58 engine. This air was used to cool the j58, which again improved engine efficiency and allowed the aircraft to fly faster after the air passes through the engine to which it rejoins. Airflow just after the engine afterburner adds additional thrust as more oxygen is available for combustion and increases pressure across the ejector nozzle. Air entered this bypass area in several ways.

There was a shock trap, also known as a hood sheet, located here, which again helped minimize boundary layer growth. There were suction doors located here that only opened from Mach zero to Mach 0.5 to add additional air to the bypass to cool the engine. Air from the aft bypass doors located just before the j58 engine also fed the bypass. These together with the front bypass doors venting to the atmosphere were used to control the pressure level at the inlet to the optimum level if it was rising too much, a pressure sensor would trigger the front bypass doors to open allowing more air to escape. of the entrance while the The aft bypass doors were controlled by the pilot.

These gates played a critical role in maintaining the position of the normal shock wave. If this was managed poorly, the engine would lose control of the normal shock wave and could even spit it out of the inlet, causing a sudden loss of power called on the stairs, causing the plane to veer violently into the air. Faulty motor steering. If this happened, the forward bypass doors would open fully and the tip would move to the forward position to reduce back pressure and return the shock wave to position. Normal position In addition to this bypass area that took air from the inlet and dumped it into the ejector, there were also six bypass ducts that took air from the compressor and dumped it directly into the afterburner.

These ducts were the main mechanism that transformed the engine into a turbojet. on a ramjet afterburners are great, they significantly increase thrust without needing a lot of extra waste, they basically just inject fuel into the jet engine exhaust and ignite with the remaining oxygen to provide additional expansion and so so much, push, but they are really inefficient. However, as speed increases they are the only feasible way to generate thrust and gain efficiency due to the forward motion providing the air compression needed to run them rather than needing to feed the turbine to spin the stage. of the compressor. the sr-71 is that the engineers could have gotten more thrust from this engine to increase the top speed, even more ram jets can reach Mach 5, so why did they stop at three point two?

They would have run out of fuel. in terms of cost it doesn't mean much for a military plane like this, the military doesn't care about cost, but the more fuel you carry, the heavier and bigger the plane gets, increasing the fuel it uses, there is a breakeven point . and the range of the plane will be limited, but the engineers managed to fill the plane with an astonishing amount of fuel with some clever engineering. The aircraft was strictly a surveillance aircraft, so no internal volume was used for weapons, freeing up space for fuel. I've heard that the SR-71 leaks fuel on the runway because there were holes in the fuselage, but that's a simple fact that ignores much of the engineering that caused it.

The SR-71 used something called the west wing total fuel tank system, which meant that the fuel was not contained within a separate fuel bladder, this was a weight-saving measure. Separate metal fuel tanks would add too much weight and lighter plastic ones would melt due to the intense heat generated by aerodynamic friction, so the fuel was contained in the aircraft's skin. Engineers applied sealant to every gap the field could exit, but because the plane's titanium skin expanded and contracted with each flight, it gradually deteriorated over time, allowing fuel to escape. Because of this, the SR-71 had to do it regularly. go to maintenance and reapply sealant, but it usually came back still leaking, but not that much, the amount of labor hours required to get it down to zero was simply too great to put it in between flights, so they only had a limit of allowed fuel leak that looked like this, this rocket-like plane was mostly fuel, its dry waste, depending on the sensor, payload was between 25 and 27 tons, its wet waste was between 61 and 63 tons, making it converted by weight to 59% fuel to feed those hungry engines, even then without the ability to refuel in mid-air, this plane would have had terrible range for what was supposed to be a long range spy plane.

The range varied greatly, for example the engines became significantly less efficient when the outside temperature was higher, a fully loaded SR-71 could burn. almost 13 metric tons of fuel accelerating from Mach 1.25 at 30,000 feet to Mach 3 at 70,000 feet if the outside temperature was 10 degrees Celsius above standard, that is, 36% of its fuel capacity, if it was 10 degrees Below standard, the fuel burned almost half as much at 7.2 tons and of course the range was severely affected by its speed and the use of afterburner, but on average the SR-71 had a range of about 5,200 kilometers , enough for a one-way trip from New York to London, which is not very useful for the US.

It was not going to land on its target to deliver a top secret plane to the enemy, however, with aerial refueling the plane could staying in the air more or less indefinitely as long as there were no mechanical problems, in reality the range was completely determined by the pilots. The longest operational sortie occurred in 1987, when the US flew the SR-71 from Okinawa to observe developments in the Iran-Iraq War. This mission lasted 11.2 hours and probably required at least five x' aerial refuelings along the way, so if it wasn't fuel or engines that limited mr. The stall speed of -71, which aimed at Mach 3 in the nose of the SR-71, reached 300 degrees Celsius, while the engine nacelles could reach 306 in the front and 649 in the rear, that is which really limited the top speed of the sr-71.

Without careful selection and design of materials, the aircraft would simply overheat and fail, even the fuel needed to be specially formulated to solve these overheating problems. This was a specially formulated fuel called jp-7 which has a very low volatility and a high flash point. This was partially necessary because fuel was leaking onto the runway and they needed fuel that would not ignite or evaporate easily and make ground crew sick, but mostly they needed fuel that would not vaporize in the tanks and cause pressurization problems. and fuel supply. -7 was so stable that it actually functioned as a coolant for the entire plane.

Fuel was pumped around the fuselage to cool critical components such as the engine oil hydraulic systems and control electronics. When the fuel got too hot, it was simply sent to the engines. For combustion, the fuel was so stable that the plane actually needed to carry injections of triethyl, a fuel that ignites spontaneously in the presence of oxygen to initiate the combustion and afterburner cycle. The plane usually only carried around 16 injections of this, so pilots needed to manage them carefully, especially when slowing down to refuel and managing departures. A big question I had about the sr-71 was why it was painted black.

Passenger planes are all white to reflect heat and prevent the plane from overheating, if that applies to a passenger plane why not? The SR-71 The SR-71's predecessors were unpainted, which saved waste, and areas exposed to higher temperatures were painted black. Why would this black surely absorb more heat? The Concorde was once painted blue for a Pepsi advertising campaign and had to slow down as it absorbed too much heat from the Sun, however the Concorde did not fly as high or as fast as the SR-71 and when the Sr-71 71 Rose, the energy he absorbed from the Sun decreased byCompared to the heat you got from aerodynamic friction for this we have to refer to something called Kirchoff's radiation rule which tells us that a good heat absorber like a black object is also an equally effective heat and Mitter, so black paint It helped the SR-71 radiate heat away from the aircraft.

Because it allowed the plane to radiate more heat than was provided by radiation from the Sun, these efforts helped keep the plane cool, but the airframe still needed to be incredibly heat stable. Aluminum is typically the go-to material for aeronautical engineers. used for the Concorde, but as we saw it also had its speed limited by heat to a much lower Mach 2. Aluminum is cheap, has a high strength or ratio and is easily machinable. Titanium, the material that made up 93% of the sr-71. Just one of these properties: its strength-to-weight ratio, also known as specific strength, is fantastic, but titanium is incredibly expensive despite being the seventh most common metal in the Earth's crust.

The refinement process is incredibly long and requires expensive consumables. It is also not easily machinable as it reacts easily with air when welding or forging becoming brittle. For these reasons titanium is rarely used in structural parts in aviation, however the real benefit of titanium is its ability to resist heat. The reasons for this are complex and we will explore in depth in the future, however, The bottom line is that titanium alloys have an incredibly strong bond within their crystal lattice that resists heat upon breaking them. Titanium alloys can withstand temperatures of up to 600 degrees Celsius before their atoms begin to diffuse and slide past each other significantly, allowing them to retain much of their strength.

Even at 300 degrees it also has a very low thermal expansion, so the expansion and contraction we mentioned above is minimized, reducing thermal stresses on the aircraft, but titanium has its limits and for the sr-71 this was about 3, 2 Mach. Today, engineers have made great progress. In materials science, the SR-71 used heat-resistant Compsat materials as radar-absorbing wedges between the structural frame located in these locations. The manufacturing techniques necessary to manufacture composite materials as load-bearing structures did not yet exist, but that has changed. The SR-71's successor, the SR 72, now in development, will take advantage of new high-performance composites that will allow it to reach speeds of up to Mach 6.

Engine components will likely be 3D-printed titanium with directly printed cooling ducts. in the part. Its range will also not be determined by the pilots, since it will be an autonomous drone. The incredible engineering that makes planes like this possible fascinates me and I recently watched an excellent trivia documentary detailing the construction process of the world's largest airliner, the a380, chronicling the enormous sheet metal cutting machines that cut through the skin of aluminum, the vacuum molds that form it and the largest oven in Britain that fixes the shape in place. This is just one. step in the process and the documentary lasts almost an hour.

This is just one of thousands of documentaries from award-winning filmmakers available on Curiosity Stream right now and a subscription costs just 1199 for a full year. With that subscription you will get free access. Nebula, the streaming service created by me and my fellow YouTube creators. Here you can see my logistics of the D-Day series detailing the planning and technology that made D-Day possible. The first episode is available for free on this channel if you want it. A taste of what you're signing up for By signing up for Curiosity Stream and Nebula, you're helping not only me but the entire education community as we work together to build a place where we can create a unique experimental series like Tom Scott's new game. show money as always thanks for watching and thanks to all my Patreon followers.

If you want to see more from me, the links to my Instagram subreddit, Twitter, and my Discord server are below.