Engineered for Speed – Part 2 (The Gearhead Report)

by Mary Martialay on April 4, 2011

 

I tagged along with Michael Mullaney at the unveiling of the 2011 Formula SAE car purely because I like engines and I wanted to take a look. After standing back for a while, I buttonholed a few of the students on the team to go over the car, and here’s a bit about what I learned. I didn’t take notes, and my knowledge of cars is spotty, so if I make any mistakes, I apologize. Some of the parts that I mention are shown in the above photo. You will find the corresponding description for each numbered part in this post.

For starters, the students told me that they build the car from scratch each year. The rules that govern the competition actually limit the top speed of each car – for safety reasons – and the race course is very curvy, so the name of the game is quick acceleration, tight suspension, and light weight.

This year’s car will weigh about 410 pounds (including fluids), the engine will put out about 80 horsepower, and speed will top out at around 75 miles per hour.

In case you were wondering how you build a custom car from scratch (as I was), I can tell you that the team starts with an off-the-shelf engine block and pairs it with custom-fabricated parts and a few off-the-shelf parts. The design of the chassis is all theirs, and they did all the TIG (tungsten inert gas) welds on the steel frame, as well as all the welded suspension components, themselves. They built many of the systems, although they had some of the more complicated components professionally fabricated to their specifications. They also programmed the chip that governs the air-to-gas intake of the engine at various RPM.

First, let’s repeat a quick mantra from my high school driver’s-ed class. The internal combustion engine works on a repeating cycle of four elements:

  1. Intake – air and gas enter the cylinder.
  2. Compression – the piston compresses the air and gas inside the cylinder.
  3. Ignition – the spark plug emits a spark which ignites the air and gas, causing an explosion which propels the piston away from the head of the cylinder and, in the process, rotating the cam shaft thereby providing motive power,
  4. Exhaust – the spent air/gas mixture is flushed out of the cylinder.

This year the team worked with a four-stroke, four-cylinder Honda motorcycle block (part #1).

They – of course – bored the cylinders for custom pistons. The pistons they designed come really close to the head of the cylinder, which gives them (literally) the most bang for each intake of air and gas. Since they don’t have the in-house manufacturing capability to meet the tight tolerances for the pistons, those are made to their specs elsewhere.

One of the most critical rules from a design standpoint is a requirement that – at some point during the air intake system – the air intake be reduced to about the diameter of your pinky. Since an engine can only run as hard as it can breathe, that severely limits horsepower. The students knew they could’ve gotten a lot more horsepower out of the Honda block if it weren’t for that rule, but, since they weren’t going to be running at the max capacity for the block, they made several design decisions with that limitation in mind.

The Rensselaer team’s custom-designed air intake (part #2) is a triumph. Even with the diameter restriction, they managed to get the air inside that pinky-diameter space (which you can see at the very top of the main chamber) to move at a speed just below mach one. Any faster, they said, and the moving air would begin to flow in a cone shape inside the intake, which would actually decrease air speed. Just past the gauntlet, their custom-built air intake balloons into a large chamber, after which air is separated and channeled to each cylinder.

Knowing that the race is more about acceleration and maneuverability than speed, they removed the fifth and sixth gears from the 6-speed transmission of the Honda (with plate clutch).

Another rule specifies that the oil and coolant systems on the engine be “open,” which means that they had to include overflows for oil (part #3) and coolant (part #4) – again for safety reasons. If for any reason either the oil or coolant systems overheat, they will vent through hand-built overflow chambers.

The car is rear-wheel drive, and it’s chain-driven (as opposed to a drive shaft) like a motorcycle. They were able to put the differential (part #5) only inches away from the transmission, which meant they could reduce several inches off the length of the car (a factor that they said vastly reduced weight).

They do have CV joints in the rear, but the front suspension only required hand-welded tie rods and what I think is a strut assembly (but I could be wrong!).

Another neat suspension element were the TIG welded wheel mounts (part #6). One student told me that many other teams make such components out of billeted aluminum, in which the desired shape is carved out of a larger block. While that takes less labor than welding a part, it usually means more bulk and weight. Rensselaer’s welded wheel mounts alone took 50 hours of labor.

And they used carbon-fiber body panels (part #7) which they made themselves by scoring off-the-shelf carbon fiber sheets, bending them to the correct angle, and then using an epoxy glue to weld each seam. The panels stiffen the frame, increasingly torsional rigidity in turns, and allowing them to do away with two welded supports with no loss in rigidity.

Finally, I’d like to mention that I really admired the rotors which were both slotted and drilled. Which, let’s face it, just looks cool.

I really enjoyed speaking with the team members, who were both knowledgeable and enthusiastic about their work. It goes without saying that come race day, I’ll be rooting for Rensselaer!