Jet Life with Maggy Blog/Vlog Series

Hey guys! I'm Maggy, and I'm here to teach you all about general electric J-85 engines and my life here at Larsen Motorsports! Check below for my blogs, and stay tuned for more videos!

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Jet engines take in a great amount of surrounding air through their inlet. Behind the inlet is the compressor section. The compressor section, as you may have already guessed, compresses this incoming air. The compressor’s job is to increase the pressure of the incoming air before it reaches the combustion section.


There are two main types of compressors: axial and centrifugal. Many modern turbojet and turbofan engines have axial compressors because of their performance efficiency. Centrifugal compressors can increase the total pressure of the air by a factor of 4, and axial-flow compressors can only increase the pressure by a factor of 1.2. So, how do axial compressors become more efficient? They’re made to be multi staged, therefore, the pressure increase is multiplied row by row. Axial compressors have an advantage over centrifugal compressors because of their ability to have multiple stages. These advantages are ideal for an application where the thrust of the engine itself is the driving force of the aircraft, or in our case the driving force of the vehicle.


A J85 engine is made up of 8 stages, and uses an axial-flow compressor. If you multiply the 8 stages by the factor of 1.2, that makes for an overall pressure increase factor of 4.3. In an axial-flow compressor, the flow enters in an axial direction, which means it is parallel with the axis of rotation. This compressor first compresses the incoming fluid by accelerating it and then diffusing it, which creates that increase in pressure.


A fluid is anything that flows, so do not be confused with the term “fluid” in referral to air. Although liquids are most commonly known as fluids, anything that is loosely held together by gas particles is in fact a fluid. Since air is a gas, it does flow and it will take the shape of its container.




Figure: General Electric J85 Cutaway


“Stages” within the compressor refers to the rotors and stators. Rotors are the blades that rotate and accelerate fluid, and stators are stationary blades that do the diffusing. In axial flow compressors, the air flows from stage to stage. The pressure increases in the direction of flow, and the stages allow for incremental increase in pressure to eliminate the risk of the engine stalling. Incremental pressure increases also allow for higher engine efficiency. Throughout the compressor, the flow area decreases. The blades get smaller and smaller, and this compensates for the increase in fluid density, creating a constant axial velocity.


Through the front of the engine, at the inlet, air enters the compressor at about 14.69 psi, which is the standard atmospheric pressure. Standard atmospheric (air) pressure at sea level is 14.7 psi, give or take. Air pressure is simply the force exerted against a surface by the weight of the air. Once the air reaches the back of the compressor, its pressure can reach around 70 psi. This is a very high pressure for air that is coming through a wide open inlet and exiting through another wide open area. Along with a pressure increase of the air within the compressor, there is a velocity increase too. Air entering the inlet is flowing at speeds higher than 200 mph, and once it reaches the back of the compressor it can reach speeds close to 700 mph!


The back of the compressor leads to the combustion section, which will be covered in the next segment of the jet engine breakdown. Check back next time to see how the combustion section of the engine works!




Have you ever wondered how we take jet engines out of planes and put them into our jet dragsters? To take these engines from an airplane and make them fit into a racing application, we “put the engines on a diet.” A handful of changes are made to the engine to lighten up the weight and make it more efficient for drag racing.


J-85 engines weigh just a little under 400 pounds when they are taken straight off of the plane. We place our own custom afterburner on the jet engine. Starting from the exhaust flange back, we remove the original exhaust in order to apply our custom racing afterburner. The new afterburner adds about 60% more power to the engine itself.


Some other parts that we remove from the engines when they come off of the plane are the engine anti-ice system, bleed air plumbing components, factory engine mounts, the exhaust gas temperature probes and harness, and any rear components that must be removed to place our custom afterburner on.


With the plane to race car transformation also comes maintenance differences. The biggest difference between the two applications is how the engine is cooled after being shut off. Airplanes equipped with jet engines can fly for almost 1,000 hours before having to stop for major maintenance routines. This involves an inspection of the hot section of the engine. This time frame is not the same for our racing application. We inspect the hot section of our engines for every 90 seconds of full power. A race run takes about 6 seconds, so it takes about 15 runs down the track until the dragster reaches 90 seconds of full power. For a hot section inspection, the combustion section goes through a disassembly in order to look for cracks inside from shock cooling.


So let’s talk about engine reliability, because you obviously cannot make these changes to a jet engine without making sure that it is still going to be reliable. To answer this question in short, yes, the reliability of the engine is affected. Take a plane with a jet engine, for example. When a plane lands its engine is still running, but it is running at a lower power setting while taxiing into the gate, all while cooling the engine. Once our jet dragsters reach the end of the drag strip, the engine is fully shut off. Cold air goes down the inlet which shock cools certain parts of the engine. These parts require additional maintenance attention.


Taking engines from planes and putting them into jet cars is not necessarily hard, but it is important to keep safety, efficiency, and reliability in mind. Here at Larsen Motorsports, we do a very good job at keeping our engines in top shape so we can continue racing as often and as successfully as we do!



Jet engines came to fruition in the 1930s and 40s, originating within the military, becoming a strong rival in the world of technology and engine design. Isaac Newton’s laws of motion were the basis for propulsion theories, and in as early as 1872, the first gas turbine engine was invented by a German engineer, Franz Stolze.


Dr. Hans von Ohain is considered the first designer of what we today consider to be the turbojet engine. His jet was the first to fly in 1939, however, a man named Frank Whittle received a patent first for his prototype. These two men had no idea of each other's work, but today we recognize them both as inventors of the jet engine.

The Heinkel He 178: world's first aircraft to fly under turbojet power.

These engines were originally used in aircraft, like the Heinkel He 178, Caproni Campini N, T-37 Tweet, and much more! I got to speak with Ted Morgan about his experience flying these types of aircraft. Jet engine planes were used in the military, and Ted talked about the different planes he flew, which included the T-37, T-38, F-4, and the F-16.


The Cessna T-37 plane first flew in 1954, and it was used as a trainer aircraft for the military. This aircraft was referred to as the “6,000 lb dog whistle” because of the high pitched screech it omitted during flight. This loud sound came from the small turbojets that propelled it. The max speed of this aircraft is about 425 miles per hour!


The T-38 is powered by J-85 turbojet engines, the same kind of engine used in our jet dragsters. This supersonic jet trainer was used in many roles within the military because of its safety and high performance. The AT-38B included a gun sight and practice bomb dispenser, and this jet aircraft has a max speed of over 800 miles per hour. Fast!


Meanwhile, upon creation, the F-4 became the U.S Navy’s fastest fighter jet at it’s debut. Just the prototype itself set the world altitude record at 98,556 feet! Then, it set the world speed record at 1,604 miles per hour! This jet had many improvements as well, one of them being it was equipped with cameras and surveillance gear. By 1978, 20 years after being created, 5,000 of the F-4 jets were built and in use.


Finally, our last fighter jet covered was the F-16. This is a single seat model, making its first flight in 1976. Advanced aerospace science was applied greatly to the invention of the F-16 to reduce its size, weight, and cost without reducing its strength. The F-16 can withstand up to nine G’s with a full load of internal fuel. That is nine times the force of gravity! Additionally, this fighter jet has a max speed of 1,500 miles per hour.


Whether a jet engine is placed inside of a dragster or an aircraft, the adrenaline rush is present. Jet engines made their way from military aircraft all the way to commercial airlines, and of course our jet dragsters. So now that we know the history of how these jet engines made their way into our technological world, stay tuned to see just how they make things go so fast.



Fast Facts

Role at Larsen Motorsports: Aerospace Engineering Intern

 

Major: Aerospace Engineering

Age: 20

Favorite Subject:  Math

Hobbies: Running, Photography, Art 

Dream Job: Rocket Propulsion Engineer

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