Author: David Estrada

4/6 discussion notes

 

• Going over how to edit the class website – join as admin
  • Adding a post is momentarily down
• Recap
  • Vanessa (wheel group): priming the front wheel hub
  • Aynslie (clutch): fixed pin attached to real, adjusted carburetor
  • Ben (engine group): cutting out gaskets for engine
  • Aminatou (electrical group): put kickstarter on the motorcycle
  • Eugene (engine group): in machine shop, widened barrel with a “hone” tool after measuring barrel with a telescoping gauge
  • Prof Littman: painted the hub, got it ready for the wheel group
• Photo of Prof Littman and Bill at Railroad Hall in Franklin Museum which Bill designed
  • They built a visitor operated mini railroad to allow visitors to dispatch trains and change tracks via remote control
  • They used the controls of a real Conrail locomotive, visitors saw what an engineer would see operating the train
  • Prof Littman shows video of the engineering model of the train exhibit

• Prof Littman posted Bill’s wheel talk and Prof Ferris’ engine and fuels talk
• Discussion of Chapter 4 in Shopclass as Soulcraft
  • Chloe (discussion leader): anyone have any thoughts about the first section of the chapter
    • Emily: It was interesting that the author says personalities should dictate career choices
    • Prof Littman: The two personalities were commanding and careful. In selecting a career, disposition is important, whereas in choosing a college you essentially take an iq test
    • Aynslie: I thought it was interesting that the author talked about the rise of medication in schoolchildren and high schoolers. Maybe this comes from a decline in recess and breaktime as people get older.
    • Vanessa: Kids are all pushed to sit down in class and be serious all day. Maybe some kids don’t learn best that way and need ways to release their energy that are different from seated concentration. Included anecdote about her brother who was diagnosed with ADHD
    • Prof Littman: In early America, there was discussion about boys beginning school when they are 10 years old
    • Vanessa: Scientifically we can understand when kids are best tailored to study and work (based on circadian rhythms) but society doesn’t always listen to these scientific findings.
    • Nate: Schooling is often crafted to serve an institutional purpose rather than our own personal development.
    • Aynslie: It’s interesting that later in college you aren’t made to sit all day, but earlier on in elementary and high school you are made to sit and concentrate more often and for longer periods

• Chloe: what did people take away about the story in the repair shop from section 2
  • Aynslie: I noticed he talked about packing a wheel bearing…
  • Vanessa: I packed a wheel bearing. We put a sticky grease lubricant in the bearings before putting them into the hub.
  • Bill: If you pack a bearing full of lubricant, the grease can’t move around in order to cover more of the bearing surface. This can cause a bearing to wear down or overheat.
  • Abby: Motorcycle term from later in the chapter
  • Prof Littman: It also mentions a transaxle. It’s the combination of a transmission differential and an axle, which some cars like Porsches have. He also mentions a flat 6.
  • Nate: A flat 6 gives lower rev but more output.
  • Bill: In a Porsche, a flat 6 is horizontal but not vertical.
  • Prof Littman: We are also introduced in this section to Lance. What is his deal?
  • Rashmina: Lance is the operator of the Porsche facility who the narrator works for, but he only gives the narrator busy work.
• Chloe: In the next section, the narrator talks about seeming like you know what you’re doing but not actually knowing. This was the string theory section.
  • Prof Littman: He talks about practical vs theoretical. The narrator’s physicist father talks about the theoretical shoelace which if you pull hard on one side it tightens. The narrator talks about the practical side, which would hold that pulling hard would cause the shoelace to break.
  • Chloe: Would anyone like to explain String Theory
  • Prof Littman: It’s called String theory because it is a way to understand particles in the universe. Scientists imagine matter is made up of strings that have resonances. The concept is that particles in nature are made up of “harmonics” like a string that is pulled. The big message in this section, however, has to do with the theoretical vs the practical. There is also another motorcycle term: gas shocks. A gas shock is a piston in a cylinder that is filled with air. 
• Chloe: The next section is called The Mentor and we meet a new hippy character named Chas who the narrator says introduces him to the “pleasure of metal”. It is quite a long chapter, but I wondered what you guys thought about the idea of metal as a complex theoretical material and about the idea of “selling” craftsmanship
  • Ben: People wanting to buy cars or items understand that they spend more for better craftsmanship and more speed. 
  • Prof Littman: Customers already know what they want, but maybe they need to be instructed to achieve it. Unrelated: I posted a resource about how head markings on bolts affect tensile strength and yield strength. The author also talks about ways of improving the engine on page 87.
    • He talks about tuning the engine to about 80 horsepower. What causes an engine stroke?
    • Nate: the revolution of the crank would be the full stroke
    • Prof Littman: If you wanted to increase the stroke, you would put the journal further away from the flywheel within the crankshaft
    • Also Prof Littman: You also want air to come in and out of the engine at high speed. 
    • Bill: A muffler is usually at the end of the exhaust pipe and it is a chamber that sound coming out of the exhaust pipe goes into so that when it comes out it is not as loud (it gets dissipated by physics in the muffler)
    • Prof Littman: Yes, the muffler affects the rate at which air comes in and leaves from the engine, which itself affects the power of the engine. If you wanted a more powerful car you would remove the muffler to get better car breathing.
    • Eugene: why would you want a light and fast flywheel. Isn’t the point of a flywheel to store energy so wouldn’t you want a lot of mass?
    • Bill: If you are starting and stopping cars quickly for racing, you want a lighter flywheel so that the mass doesn’t affect breaking as much. 
    • Prof Littman: The author also shows an image of and talks about match boarding. What is that? It is when you make certain that going from one piece to another piece of the engine, it is a smooth and compatible connection (from tube to tube for example).

• Chloe: The next section talks about blueprinting an engine. I think this means identifying the wear and tear of an engine and making sure the parts you put into an engine are usable and strong. To get us started in this section, it is interesting that my perception of why wheels changed by working with the motorcycle wheels and thinking about their alignment.
  • Bill: I teach a course on watercolor painting, and I go around and comment on other people’s paintings. I usually tell people to go walk around the room and then come back to their painting to look at it again with a different perspective.
  • Aynslie: In flying, you have to put complete faith in your flying instruments to see the bigger picture and not freak out or just focus on one thing while flying.
  • Prof Littman: I was thinking of the drawing of the skeleton. There is an exercise in painting where beginner painters are made to paint a face right side up and upside down. It usually looks better starting upside down because in that case you are thinking about the relationship between lines and angles without bias of thinking you know what a face looks like.
  • Abby: We also drew a skeleton in my high school.
  • Prof Littman: This section also talks about patterns of wear and mushrooming in engine valves and stems
• Chloe: The next section is on personal knowledge.
  • Nate: I really like the new definition and interpretation of what an “idiot” is. It talks about how mechanics who don’t really care about their craft are idiots because they aren’t embracing their public role.
• Chloe: The next section thinks about stopping to make sure you understand what problem you’re solving before moving to actually solve the problem. It is the issue of metacognition.
  • Emily: I think it was interesting to see the vulnerability involved in accepting you could be wrong in some way.
  • Chloe: Yes, I think this is something that I sometimes get stuck in, not wanting to admit a mistake. I like the way he framed this problem in honesty and humility.
• Chloe: Last section talks about how our perception of service workers as automated script readers should inform our decisions as consumers to seek out more authentic and dedicated service.
  • Nate: I thought about this when I worked at a restaurant. It seemed like pushing people to follow a script undermined the intellectual integrity and expression of the service workers.
  • Bill: I’m worried about this issue especially in the context of AI.
  • Prof Littman: Yes, I also think an understanding of the big picture of systems and applications could also get lost in the context of AI, because AI just seems to care about the minutiae.

• We also have to start to talk about the final presentation. Presentations should be group powerpoint presentations on small but interesting details of each motorcycle group.

 

4/8 Discussion Notes

 

• Class introductions to Professor Martinelli (guest speaker today)
• Prof Martinelli – originally from Rome, Italy – came to Princeton for grad school, never left (began teaching here), is an expert in fluid mechanics and locomotion
• His talk:
  • Computational fluid mechanics is at the intersection of engineering and computational mathematics
  • Fluids are usually opposing motion (Drag force)
    • A fluid flow goes from a laminar (organized) motion to a more disturbed and chaotic motion after coming into contact with an object in motion
  • Lift (force)
    • Keeps airplane in the air – generate lift by making use of fluid flow on the wing surface
    • Flow field behind the wing of an airplane is very messy (turbulent regime of fluid flow)
      • Lift is generated by the most turbulent, tornado-like fluid flow on the wings
        • This also generates drag
    • Professor Littman query – it is often taught that lift is generated by suction
      • Prof Martinelli says this explanation is not actually true
      • The control volume approach (that Prof Littman tends to use) is in the long-run accurate, but the more correct explanation comes from the vortexes of fluid generating lift by spinning in a certain direction
    • Other question about aspect ratio
      • Aspect ratio is fixed as a function of how the airplane is made – need stronger engine to overcome induced drag which is inevitable
  • Reynolds number
    • As you increase the Reynolds number, the drag in the wake of an object in motion becomes a far more turbulent regime and the drag’s diameter decreases
    • Adding dimples to a golf ball for example accelerates the process of increasing friction drag, creating more turbulence in the wake, and having the induced drag go down
  • In supersonic or subsonic speed fighter jets, the plane wings must be narrow to stay within the shock angle – less lift so stronger engines
  • Acoustic Field
    • Lots of interaction between the fluid dynamic structure and the acoustic field that is generated
      • Speech is the result of a very very small pressure disturbance that the listener detects and can decode as language

 

• Integrated resistance – propulsion – control
  • Sail boats with hydrofoil wing in the water with very large aspect ratio
    • This lifts the boat out of the water
  • Aerodynamic forces at work – two important parameters at work within Reynolds number (ratio of inertia over viscous forces)
• Venturi Effect
  • FOR AN INCOMPRESSIBLE FLOW, A REDUCTION OF AREA CAUSES AN INCREASE IN LOCAL FLOW VELOCITY AND A CONSEQUENT DECREASE IN PRESSURE
• Engine Cooling
  • Heat is dissipated through convective heat transfer
• External Aerodynamics
  • Wheel spraying water at passerby – the vortex structure behind the wheel as it moves forward picks up water off the ground and moves it laterally
    • This can be mitigated by changing the structure of the wheel hub to bend the vortex force and make the water’s spray not as problematic
• To make his models and simulations, Prof Martinelli uses GPU processing to visualize and compute forces on objects
  • There is some bottlenecking because with GPUs, getting data in and out takes a really long time
  • You have to maximize operation and minimize the translation with the GPU
  • The measurements of the simulation are accurate to a magnitude of a fifth order polynomial
• Stall
  • Bird flapping wings when it lands allows for a very large stall margin
  • If you want to do this in an airplane, you have to start flapping very fast
  • An airplane stall is an aerodynamic phenomenon where wings lose lift because the angle of attack (AoA) exceeds a critical point, disrupting smooth airflow
• Professor Martinelli also teaches the flight design course and the aerodynamics course at Princeton