The Pratt & Whitney J58 - The Engine of the SR-71 Blackbird

Hello, my name is Arnie Gunderson. I worked for Pratt Whitney for 33 years, 20 of which were on this

engine

and this wonderful program. I started as a young junior test

engine

er. I was chosen to go out into the field and worked at a flight test center. For 10 years, near Edwards Air Force Base, I was able to play with the airplane and the engines for 10 years with a team of very experienced people. It was a great moment. Later I also took charge of the engine overhaul and repair line at Pratt.

whitney

plant in west palm beach florida and eventually became the program director before I got there before the show was canceled and I moved on to other things so I love talking about this show because it was the most rewarding part of my career as an engineer, so the engine, the j58 engine was actually launched before the

blackbird

, the navy was interested in being able to run at mach 3, so

pratt

whitney

drew the basic centerline of this new engine that It could reach Mach 3, but only for a very short period.

For a while when the navy found out how much it was going to cost for the overall program to be able to build a Mach 3 plane they lost interest, their business is obviously making ships and a plane is just an accessory to them so sort of. At the same time, Francis Gary Powers was shot down on May 1, 1960 while flying over Moscow and the US government at that time realized that we needed something that was higher and faster to prove invulnerable to what which we knew were air defenses at the time. Then there was a competition between Boeing Northrop and Lockheed to see who was going to build this new plane.

Apart from that, the CIA approached Pratt Whitney and told him that we had heard about this Mach 3 engine that you built and that we I would like to move forward. We picked up where the navy left off and the j58 was born, so let's talk a little about the basic engine. The basic engine is quite simple. It's a turbojet. A single spool turbojet. Most modern engines today have two spools, one that drives a gigantic fan in front and another that is the core of the engine, so if we think about the parallels between these two, this is like the core of an engine. modern jet, but it is a turbojet, so it does not have a normal bypass as you would like.

Those big fans, we actually have a bypass, but that came a little later, so let's talk more about what happens at Mach 3 and what drove some of the design features of this engine at Mach 3.2 and 80,000 feet, which is the The design point for the airplane is that everything you see here was designed to have its optimal performance at 2,300 miles per hour and 80,000 feet, so our entire design had to do with the heat that also it happens there. crossing a Mach 3.2 shock wave goes from minus 45 degrees at 80,000 feet to 800 degrees Fahrenheit and as it crosses that shock wave it compresses and also goes from 0.4 psi, almost a vacuum, to about 15 psi when crawling inside the gondola.

And so the engine likes to see nice 15 psi high pressure air, but it's also pretty hot, that 800 degree air is our cooling air, so what happens when the metal gets hot? It expands, this engine literally grows six inches in length when cruising and two and a half inches in diameter, so how do you design it to take care of that? Those were some of the challenges we had to overcome to make this engine actually work, so we have some titanium in the front of the engine, the first stage of the compressor the rest of the engine our various iron alloys and nickel alloy wasp mostly some inconel a part that is made of an alloy called asteroid and this is how it works this engine has many new features associated with it, it is the first use of directionally solidified metal, that is, metal in which all crystals grow in the same direction that is right here on the turbine, so as the turbine blades spin, their growth rate is monitored, we know which direction to measure and the stretch that happens over the life of the turbine. turbine can be measured and we can take maintenance measures to ensure that the blades don't break, but they are very, very strong in that direction, which is what we needed.

It is also the first use of self-metering afterburner. spray bars and after the continuous burning that we have to do when we turn on our afterburner, it can run for an unlimited amount of time, as long as we have fuel, we can run the afterburner, so that's another great thing. You may have noticed that there is quite a bit of plumbing in the engine. The engine has 600 plumbing parts. All pipes are made of 321 and 347 stainless steel, which is very easy to work with and resists heat. Please note that all pipes have fuel or oil inside them.

So that it doesn't get as hot as the rest of the engine's exterior, the oil is a pure synthetic called polyphenol ether and is chemically stable up to about 650 degrees Fahrenheit. We try to keep the oil at about 400 degrees with the use of a fuel cooler when the fuel first enters the engine after going through the main fuel pump, the next thing we need to do is go through the fuel cooler because we want keep our bearings cool and lubricated, so I mentioned Computers earlier, when this engine was built digital computers were just in their infancy and they were so large that it was impractical to put them in the engine and how would they stay cool?

Electronic components, as you probably already know, do not withstand high temperatures well. so we ended up having to use hydraulic computers and that's what the control system of this engine is all about, each one of those blocks, one on each side, this one is for the afterburner, the one on the other side is for the main engine, actually They are computers and they have cams and levers and valves and things inside that are driven by the outside temperature, some of the internal temperatures and pressures, but mostly by what the pilot is doing with the throttle, so all of those inputs are As you enter each of these controls, the controls calculate what to do to control the fuel flow as a result and all of those tubes are like the circuits that you find inside any computer type device these days, so those are our cables in addition to the muscle behind. actuators, so let's talk a little bit about how the engine, intake and exhaust work together.

That's the magic of the sr-71 and its ability to cruise at 2,300 miles per hour for about an hour at a time as the air cruises by. The primary shock wave coming out of the nose of the plane we pick up another flow with that tip. The tip of the tip at the front of a cell is a very sharp conical device and then it also has a small conical shape at the back. and at about mach 1.6 1.6 that tip begins to settle back into the nacelle, the inside of the cell is also conical in shape and therefore as the larger part of the tip or cone of entrance moves behind the throat of the device, in other words the narrower portion starts to recede and also gets smaller, that is where compression occurs and the temperature increases, it is right at the throat, so it regulates the air coming in when it gets to the front of the engine, the air is actually split, we have a series of doors around the outside of the engine right in this area here and a lot of air, about half of the air is diverted around the outside of the engine but inside the nacelle, the most modern aircraft that can go supersonic f14 uh f-15 F-16 F-18 all do the same thing, they throw that air overboard that creates drag.

We don't want resistance. We want to be efficient at mach 3.2, so we keep all that air in and let it flow. the outside of the engine and then in the back behind the afterburner we let the air join again with the engine exhaust and then we extract all the energy that we put into that air when we compress it and heat it we run both the engine exhaust and that secondary air flow through a convergent diverging nozzle and expand it again. I'm going to do a little bit of engineering here if I haven't already blown your mind with that to achieve supersonic flow from an exhaust stream or anything, you have to have a pressure ratio across that convergent diverging nozzle of at least eight to one to get a Mach 3.2 flow out of a nozzle, you have to have that pressure ratio of at least 40 to 1.

So at sea level, that's pretty hard to do because the one at that ratio at sea level is about 15 psi, so what is 40 times 15? It's 600, not 6000 psi. So how do you get 6000 psi inside a duct? It's very, very difficult. with a rocket engine, but you can't do it with a jet engine, if we put 6000 psi back in here, it would fly out the front of the engine, which goes against why we have the jet engine to begin with. , but when you're at 80,000 feet, here we only have 0.4 psi, so we only need to carry about 20 or 21 psi into that conduit and when we cross the convergent diverging nozzle, lo and behold, we have a gas velocity of exhaust from mach 3.2 and we are very very happy just cruising once you get past Mach 1 the drag of the plane drops significantly and at Mach 3.2 it's not significantly higher so it turns out you don't need much thrust in those conditions and the engine is adjusted accordingly.

We get about half the thrust we need from the engine and the other half comes from recovering the energy that was around the outside of the engine when we put those two streams back together. This is the most amazingly efficient device. We actually recover 88 of the energy that we put into the air at the front of the engine and then it all comes out the back, there's only a 12 percent loss and that's due to thermal energy. What else can I tell you about the engine and the plane and how our propulsion works? The system works. I will be happy to answer any questions you have.

Let's talk well. Let's talk a little about fuel. Fuel is another big problem. It was another thermal obstacle we had to overcome. This system uses something called jp7, which is a highly refined kerosene very similar to the jp4 jp5 or jet that you may have heard or seen written on a fuel truck when you went to the airport. The same basic substance kerosene as ours is refined, it has an extremely low vapor pressure, what that means is that it is very difficult to light, you can hold a match over a container of jp7, it will not burn what it actually burns now with gasoline, obviously you wouldn't do that because you know as soon as you did that, you would have this gigantic flash. with jp7 it doesn't happen, jp7 has to be above 135 degrees before that phosphorus does anything to the fuel, so the part that actually burns is vapor and that's why we worry about vapor pressure, so jp7 is also used as hydraulic fluid in our engine, so we add lubricity additive, antioxidant additive and anti-coking additive.

These three additives allow the fuel to be stable inside the engine. In reality, the fuel reaches the burner or afterburner. The fuel is around 600 degrees and then when we spray it, it burns pretty easily, so starting the engine was a big deal, it wasn't so much starting for Pratt. We had giant air starters that we used in our test cells, but on the plane there were no portable air starters at the time that were large enough to do the job. Today it's a different story. Now we have portable air starters and on the other side of this airplane there is something known as a Buick starter cart and that's what we came up with to start the engine when it was installed on the airplane, it's a pretty low cart and some of the guys They were hot rodders back then, I think there are still some around and it was decided to use a v8 engine a right angle gearbox to start the engine here is the main gearbox and there is a starter pad on the bottom, It's an open gear cup and on the starter carriage there is a positive gear that fits into that cup and then rotates through the force of the v8.

It turned out that one v8 wasn't enough so we ended up putting two v8 engines side by side. from the other and the engine we chose was the 1960 to 1962 Buick 400 cubic inch wildcat engine, it seemed to be the best choice. at that time that's how we ended up with the buicks and since we had jp7 as our fuel and occasionally it can leak it turned out to be safe and fine because we had these very short pipes on the buicks you may have seen them and we when we were driving the Buick car, we literally had flames coming out of the exhaust pipes, but the other part that was great is that the sound that came out of those Buick engines at high revs was just incredible, it was like music to a gearhead's ears, so they did it.

However, we have a weak point when the Buicks reached about 6000 rpm, we finally reachedapproximately 3000 rpm on the engine and at that moment, when the pilot accelerated to idle, the engine started and picked up speed. Going up the last thousand rpm to our idle speed, which is four thousand, sometimes the guys driving the cars got a little carried away by the noise and wouldn't leave the engine speed at 3,000 rpm and blow up the Buicks. and that vomits all over the floor during the first years. Oh, maybe in the first 15 years of the program we broke enough Buicks that we sold out the entire United States.

Every junkyard in America doesn't have a single cubic inch of 400. We were left with the Buick engine, we got all of them and we broke them into this program, so we still had to be able to start the engines, so at that time it was made a decision on what we are going to go with and we ended up going with the 454 chevy engine because they were more of those around than almost anything else, it had the power and torque we needed to get going but it never sounded as good as the buicks for everyone Those of us who were in the program, the Buicks were the best, so another little story you might enjoy when I was on a test flight in Palmdale, California, very close to Edwards Air Force Base.

We flew test missions in the plane before the rest of the Air Force understood what we were testing, so one day we were testing a radar system and the mission was to fly from Palmdale to Las Vegas, turn north. Over Utah and north of Logan Utah there is a radar range, so we were supposed to shoot down some radar targets on the ground. Go back, refuel, get back up and do the same thing and then come back. Turn right. over Las Vegas and landed back in Palmdale, so that was the mission pretty simple, so the pilot and the back seat on the plane finished the mission a little early and the pilot said, well, I wonder how fast it's really going this thing and that's why it's going down. the route from Utah to Las Vegas and pushes the throttle to the firewall and the plane begins to accelerate as expected.

It got to a little above Mach 3.4 and swallowed both shock absorbers and killed both engines. at about 2,400 miles per hour and 80 thousand feet it's flying like a hot rock at that point, so it started descending pretty quickly. The guy in the back seat is responsible for pulling out the emergency checklist and reading to the pilot what he needed to do to get things back to normal. He restarted an engine at about 65,000 feet so we knew we were going. to return home safely at that point and then restored the second engine at about 25,000 feet and re-entered. Palmdale landed, taxied, stopped and took off, that in itself we knew something was going on at that moment because normally when the guys came back from a mission, where we were in Palmdale, the place next to us was where the bomber b -1. was being built and there was an intense rivalry between our guys who flew the sr-71 and the guys from Rockwell who flew the b1 bombers and after each mission, after each of their acceptance flights, they would come and buzz our building in max a b and of course we had to return the favor too, we would buzz his building with our max a b, so this time when he came in and landed and opened the parachute we said okay something is up there we put up the ladder. next to the plane, the crew came down and said there will be no information today, guys, they got in the truck and left, we didn't find out until the next morning, when we received the tapes from the recording system of our mission from Burbank.

It had actually happened, we didn't know, so I went to work early the next morning to read my tapes. The Lockheed flight test engineer, my counterpart did the same thing with his tapes and I called him, said Larry, you see what I do, he said. Yes, he says, let's go see the colonel. I'm not going to say the name so I can protect the guilty, so we went into his office. He says, come on, guys. I was waiting for them to close the door so that the crew and this plane can't lie about anything we record everything there are voice recorders there are heart rate monitors every parameter that is on this plane is recorded there is a series of about 15 different tapes and each tape has about 15 parameters in and the data is taken every three seconds so there's no lying about what's happening so what really happened was that it moved fast enough to exceed the capacity of the input so it could regulate where it ended up the shock wave. was sucked back enough to interfere with the flow in the front of each engine, each engine then caught fire, it literally stopped running like a jet engine, we now have procedures in place to fix it, obviously restarted the engines again, but in A Side Note of Humor, we knew they were very, very surprised because the voice recording of the guy in the back seat his voice went up an octave while he was reading the checklist items, so our adventures on the show some are fun, some not at all.

It's funny, but for the most part we all had this incredible esprit de corps and loved going to work every day. I couldn't believe they paid me for this other story. I would tell it in a more personal way. I finally knew what it was going to be that I was working on because I didn't know when I first hired Pratt. I said you were going to work here and I said what is it used for and they said you're not authorized. I can't tell you, so they even told me I couldn't tell my wife what he was doing.

I had to tell her that she was working on water heaters. If you can believe such a silly thing, they finally told me that I'm going to go to California and work directly with the air force with Lockheed Skunk Works and I'm going to be on a flight test, so I was very excited about that, so I traveled to California, I got to Palmdale and the next morning I got to work and they walked me to the hangar and I know if you remember the scene at the beginning of the Star Wars movie where Luke Skywalker goes into the gigantic cave or whatever and sees all the x - Wing fighters are being worked on and he is amazed.

That's the exact feeling I had walking into the Skunk Works hangar and seeing the

blackbird

for the first time and I've been in love with it ever since.