You Got to Be Kidding Me!

Dean Kamen Has Another Idea That’s Not As Good As He Thinks It Is

Posted in Engineering by Stacy McMahon on October 29, 2008

Remember when the Segway was “IT”, the miracle something-or-other that Jeff Bezos embarassingly predicted was going to change human society forever? This time IT’s a hybrid car powered by a Stirling engine.

The internal combustion engine, as we’ve known it for over a century, is what’s known as an open cycle device. That is, the so-called working fluid flows into and out of the engine and is constantly circulated. A closed cycle engine keeps the same working fluid contained within the device and heat is generated externally rather than from combustion inside the cylinder. The best known example of the latter is the stirling cycle engine.

Well actually the best-known closed-cycle reciprocating engine would be the triple-expansion steam engine that powered most of the world’s powerplants and steam ships until the late 1940s. But anyway…

The theoretical thermodynamic efficiency of the stirling cycle is 100 percent although creating a 100 percent efficient mechanism has proved elusive.

Of course being 100% efficient would make it a perpetual motion machine, but don’t worry, there’s no doubt the inventor of the Segway can repeal the laws of physics.

What makes the Stirling engine cool is that it can work ‘backwards’ i.e. you can make it run by feeding it a cold material just as well as a hot one. Perfect for geothermal power, or vehicles that travel into hostile environments where the ability to use whatever resources are available is more important than ultimate horsepower. Good for a hybrid car? Maybe, but as a general rule external combustion isn’t as efficient as internal combustion – that’s why steam disappeared off the scene rather quickly between 1925 and 1945.


Engineering Break: Thoughts on The ME 109 Versus the ‘Spit’

Posted in Aircraft and Flying, Engineering by Stacy McMahon on June 5, 2007

One of my very minor hobbies is reading “period” pilot reports about WW2 fighter planes. The other day I Googled up a dour and uncomplimentary review of the Messerschmitt 109, written by Kit Carson for Airpower Magazine in the mid-70s, and based on some apparently incomplete and selectively reported data from wartime reports page. Shortly after, I found an anonymous response. Diplomatically titled “Why Carson was an Idiot”, it’s an astute, sarcastic and occasionally quite humorous point-by-point rebuttal (italics are quotes from the Carson article):

Intention of this page here is to correct serious errors in this particular article, which happened due to a serious lack of knowledge about the 109 technics and design history. It begins right here (quotes from the article in “italics”):

“But another household work, the highly propagandized Me-109G, was obsolete when it was built and was aerodynamically the most inefficient fighter of its time. It was a hopeless collection of lumps, bumps, stiff controls, and placed its pilot in a cramped, squarish cockpit with poor visibility.”

The nameless author, who does not appear to be a native English speaker, follows up this opening shot with some fairly devastating comparisons of Carson’s quotes to data on competitive planes, especially the Spitfire.


More on Green Buildings

Posted in Engineering, Environment, Home Improvement, Urban Planning by Stacy McMahon on February 14, 2007

Some of my friends and associates are probably a little bemused by my fascination with “green” buildings, green roofs, and sustainable development. Really though, it all makes perfect sense. Jim Bede once introduced his BD-10J personal supersonic jet with the tag line that he was “tired of 60 years of 130-mph airplanes”. Housing and building is, if this is even possible, even more stuck in the “because we’ve always done it this way” mentality than general aviation, and with even less economic justification.

And that is while the gains in efficiency and savings in utility bills from so-called green design are such low-hanging fruit that it’s silly not to avail yourself. I’ve already replaced most of my light bulbs with compact fluorescents, and I plan to install LED lighting. It’s hard to do more than that since I live in a condo, but if I had a house there are lots of things I could do–everything from a green roof (no more drainage problems in your yard) to placing windows and vents to take advantage of sunlight for heating. Whenever I do have a house, I will do all that stuff. Aside from the financial benefits (I’ve always believed in spending more upfront if it means lower recurring costs in the future) it’s just too appealing as an engineering project.

Anyway, I started this post as a way to link the Green Building Council as well as this Popular Mechanics list of top “green” technologies available today. Forget the hair-shirt version of environmentalism, I prefer this cool-toy version instead 🙂