If you've ever tried to understand the
SR-71's engines, chances are you've come across these diagrams from
the SR-71's flight manual. Let's face it though: they're not as
clear as they could be. So let's clean it up and simplify. There we go! The whole diagram
is the complete engine nacelle made up of the airflow inlet, the Pratt &
Whitney J58 engine, the convergent divergent ejector, and the airplane body. At speeds below Mach 2,
the J 58 acts like any other after burning turbojet engine. Air flows into the nacelle through the
inlet, where it's allowed to diffuse behind the supersonic shockwave before moving
into the multi-stage axial compressor which looks like this, but bigger. Here,
the air is compressed before heading into the burner where fuel is added for
combustion. The heated exhaust turns the turbine and
provides the engine's forward thrust as its accelerated to high speeds by the
ejector. The turbine turns the compressor and
keeps the engine cycle going. Just after the turbine is the afterburner, where more fuel is
added to the exhaust in order to get as much of the oxygen out of the air as possible. While
afterburners allow for powerful bursts bursts of acceleration, they're really inefficient, costing huge
amount of fuel for the increased force. What makes the J58 engine so different
than all other turbojets are these 6 bypass tubes which you don't find on these diagrams. The
tubes open when the plane is flying at speeds greater than Mach 2.2, moving compressed air from the fourth
stage the compressor directly into the afterburner This allows the engine to act more like
a ramjet, which allows the SR-71's afterburner to operate at a much higher
fuel efficiency, the forward motion aircraft handling
most to the air compression at a ratio of about 39:1 (38.8:1),
with the four turbines ages adding an additional compression about 1.6:1. The combined action of the turbine and
ramjet compression makes the J 58 a very unique type of engine: a turboramjet; and allows the plane to
cruise at speeds that would make a normal turbojet melt. The Blackbird's inlet design is as important
to allowing the J58 to do its thing as the engine itself so let's see how it
works. In the middle of the inlet is this
symmetrical spike, called the inlet spike, or centerbody, and behind it is the diffuser, where
compressed air spreads out before entering the engine. At supersonic speeds the inlet spike
takes the pressure the leading supersonic shockwave off of the engine so that the engine gets
the best airflow. Inside the inlet a second shockwave is formed called the
normal, where the air coming into the nacelle transitions from low-pressure,
supersonic speeds, to high-pressure, subsonic speeds. Where the normal ends up inside the
inlet depends on the speed at which the aircraft is moving and the shape of the inlet and inlet spike. When the aircraft hit's Mach 1.6, the normal ends up in the best place
inside the inlet for pressure recovery, Which is the percentage of the pressure
caused by the plane's supersonic flight forward that gets translated into usable
pressure inside the diffuser for the engine. This ratio is a very high ninety percent,
for the SR-71 when flying at Mach 3.2. So to keep the normal in the optimal
position for pressure recovery, the spike retracts 1.6 inches for each
point-one increase in Mach number above Mach 1.6. This changes the relative geometry of
the inlet, keeping the normal at the optimal position. When the plane
reaches its cruising speed of Mach 3.2, the external shock wave is positioned
directly at the inlet's lip, called the cowl, and the inlet spike has
retracted 26 inches. It's at the speed that the J 58 turboramjet
has its maximum fuel efficiency, with the pressure recovery at the inlet
doing most to the air compression work for the afterburner. Okay! Now that we've seen how the inlet, engine,
and ejector all work together, let's look at the other details found inside the
engine nacelle. Positioned inside the cowl is a cowl bleed, that captures some of the incoming air
and passes it through a ring of circular openings called shock traps, that drop
the air speed to subsonic and guide it through the cell body
around the engine for cooling. The air is drawn out of the nacelle by the
fast-moving exhaust flowing through the ejector. At speeds below Mach 0.5, not enough air
is coming through the inlet for cooling, so more air comes in through suck-in
doors that are position midway along the nacelle. These close at Mach 0.5,
which the plane only hits just after takeoff, and just before landing. Before the
ejector are set up tertiary doors that also open at low speeds to prevent the ejector from creating
places a drag caused by not enough air and exhaust flowing through it. These close at Mach 1.2 and
stay closed for most of the Blackbird's flight, opening only for takeoff, landing, and refueling. Both the suck-in doors and the tertiary
doors allow the powerful J58 to operate at speeds much slower than its high
cruise speed. The engines are so big that each needs two
muscle car motors on the ground to start it, and rev it up to a self-supporting speed.
But, I digress. The last three details found in the
nacelle are required for keeping the normal shockwave in place in the inlet. The first is the centerbody bleed, which
connects agrill on the outside the nacelle to set of slits on the spike through
the hollow centerbody middle. At low speeds, the centerbody bleed allows
the engine to pull additional air into the inlet, while at higher speeds
the bleed wicks away the boundary layer a layer of low-pressure turbulent air
that normally sticks to the spike and reduces pressure recovery. Inside the inlet is a series of slots
that run between the shock tubes that lead directly out of the plane. These are the forward bypass doors, which
allow an analog computer to lower the pressure inside the diffuser by sending
some of it outside the aircraft. But if the pilot wants to reduce drag
during acceleration, or provide additional cooling to the engine, he or she
can open the aft bypass doors, which route the additional pressure
through the nacelle and out the ejector. And that's it! That's how the J58 turboramjet
inside the Blackbird engine nacelle, works! Now when you look at these diagrams been
on scene so complicated after all! Don't forget to like this video and
subscribe to Tech Laboratories for more mind-blowing videos on science and
technology! I'm Tech Adams saying Keep Thinking and
thanks for watching!
It's amazing that this engine was designed in about 1960.
Can we take a moment and appreciate the fact that a small army of mathematicians and scientists made this engine with not much more than rulers and calculators? Probably human calculators at that as well...
Damn, when a video says it's going to show you how something works it rarely does like this! This was a lot of information to take in and honestly, I still don't fully get it but I get it more than I would have from most big-name documentaries that chew up an hour of your time with beautiful pictures and nothing of substance.
Easy peasey. The thing make a fire for to go fast.
Slow plane, how fast?okay fast. Army plane, how fast huh? Pretty fast? How cool are we huh? Yes pretty fast. Blackplane, oh yeah what about our fast? Oh yeah, easily most fast way faster than army plane. Army plane embarrass.
There were a lot of things we couldn’t do in an SR-71, but we were the fastest guys on the block and loved reminding our fellow aviators of this fact. People often asked us if, because of this fact, it was fun to fly the jet. Fun would not be the first word I would use to describe flying this plane. Intense, maybe. Even cerebral. But there was one day in our Sled experience when we would have to say that it was pure fun to be the fastest guys out there, at least for a moment. It occurred when Walt and I were flying our final training sortie. We needed 100 hours in the jet to complete our training and attain Mission Ready status. Somewhere over Colorado we had passed the century mark. We had made the turn in Arizona and the jet was performing flawlessly. My gauges were wired in the front seat and we were starting to feel pretty good about ourselves, not only because we would soon be flying real missions but because we had gained a great deal of confidence in the plane in the past ten months. Ripping across the barren deserts 80,000 feet below us, I could already see the coast of California from the Arizona border. I was, finally, after many humbling months of simulators and study, ahead of the jet. I was beginning to feel a bit sorry for Walter in the back seat. There he was, with no really good view of the incredible sights before us, tasked with monitoring four different radios. This was good practice for him for when we began flying real missions, when a priority transmission from headquarters could be vital. It had been difficult, too, for me to relinquish control of the radios, as during my entire flying career I had controlled my own transmissions. But it was part of the division of duties in this plane and I had adjusted to it. I still insisted on talking on the radio while we were on the ground, however. Walt was so good at many things, but he couldn’t match my expertise at sounding smooth on the radios, a skill that had been honed sharply with years in fighter squadrons where the slightest radio miscue was grounds for beheading. He understood that and allowed me that luxury. Just to get a sense of what Walt had to contend with, I pulled the radio toggle switches and monitored the frequencies along with him. The predominant radio chatter was from Los Angeles Center, far below us, controlling daily traffic in their sector. While they had us on their scope (albeit briefly), we were in uncontrolled airspace and normally would not talk to them unless we needed to descend into their airspace. We listened as the shaky voice of a lone Cessna pilot asked Center for a readout of his ground speed. Center replied: November Charlie 175, I’m showing you at ninety knots on the ground. Now the thing to understand about Center controllers, was that whether they were talking to a rookie pilot in a Cessna, or to Air Force One, they always spoke in the exact same, calm, deep, professional, tone that made one feel important. I referred to it as the “ HoustonCentervoice.” I have always felt that after years of seeing documentaries on this country’s space program and listening to the calm and distinct voice of the Houstoncontrollers, that all other controllers since then wanted to sound like that… and that they basically did. And it didn’t matter what sector of the country we would be flying in, it always seemed like the same guy was talking. Over the years that tone of voice had become somewhat of a comforting sound to pilots everywhere. Conversely, over the years, pilots always wanted to ensure that, when transmitting, they sounded like Chuck Yeager, or at least like John Wayne. Better to die than sound bad on the radios. Just moments after the Cessna’s inquiry, a Twin Beech piped up on frequency, in a rather superior tone, asking for his groundspeed. Twin Beach, I have you at one hundred and twenty-five knots of ground speed. Boy, I thought, the Beechcraft really must think he is dazzling his Cessna brethren. Then out of the blue, a navy F-18 pilot out of NAS Lemoore came up on frequency. You knew right away it was a Navy jock because he sounded very cool on the radios. Center, Dusty 52 ground speed check Before Center could reply, I’m thinking to myself, hey, Dusty 52 has a ground speed indicator in that million-dollar cockpit, so why is he asking Center for a readout? Then I got it, ol’ Dusty here is making sure that every bug smasher from Mount Whitney to the Mojave knows what true speed is. He’s the fastest dude in the valley today, and he just wants everyone to know how much fun he is having in his new Hornet. And the reply, always with that same, calm, voice, with more distinct alliteration than emotion: Dusty 52, Center, we have you at 620 on the ground. And I thought to myself, is this a ripe situation, or what? As my hand instinctively reached for the mic button, I had to remind myself that Walt was in control of the radios. Still, I thought, it must be done – in mere seconds we’ll be out of the sector and the opportunity will be lost. That Hornet must die, and die now. I thought about all of our Sim training and how important it was that we developed well as a crew and knew that to jump in on the radios now would destroy the integrity of all that we had worked toward becoming. I was torn. Somewhere, 13 miles above Arizona, there was a pilot screaming inside his space helmet. Then, I heard it. The click of the mic button from the back seat. That was the very moment that I knew Walter and I had become a crew. Very professionally, and with no emotion, Walter spoke: Los Angeles Center, Aspen 20, can you give us a ground speed check? There was no hesitation, and the replay came as if was an everyday request. Aspen 20, I show you at one thousand eight hundred and forty-two knots, across the ground. I think it was the forty-two knots that I liked the best, so accurate and proud was Center to deliver that information without hesitation, and you just knew he was smiling. But the precise point at which I knew that Walt and I were going to be really good friends for a long time was when he keyed the mic once again to say, in his most fighter-pilot-like voice: Ah, Center, much thanks, We’re showing closer to nineteen hundred on the money. For a moment Walter was a god. And we finally heard a little crack in the armor of the HoustonCentervoice, when L.A.came back with: Roger that Aspen, Your equipment is probably more accurate than ours. You boys have a good one. It all had lasted for just moments, but in that short, memorable sprint across the southwest, the Navy had been flamed, all mortal airplanes on freq were forced to bow before the King of Speed, and more importantly, Walter and I had crossed the threshold of being a crew. A fine day’s work. We never heard another transmission on that frequency all the way to the coast. For just one day, it truly was fun being the fastest guys out there.
Easy peasy. I just engine swapped a J58 into my mustang last month
https://www.youtube.com/watch?v=Ccoj5lhLmSQ
That's it?