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Old 02-24-2009, 09:10 AM   #1 (permalink)
aero guerrilla
Piwoslaw's Avatar
Join Date: Oct 2008
Location: Warsaw, Poland
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Svietlana II - '13 Peugeot 308SW e-HDI 6sp
90 day: 58.1 mpg (US)
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Other incarnations of Pulse & Glide

I've been thinking about the Pulse & Glide technique lately, about why it works etc. One of the things I've read is that when P&G'ing between, say, 50 and 70 (speed units) your average speed is 60. Now, I've been repeating that to my family and friends even though I know it's not really true, it's only approximately true. Why? Aerodynamic drag increases with the square of velocity, so the drag between 60 and 70 is greater than between 50 and 60. In other words, above 60 the force which is slowing you down is greater than below 60, so the time it takes to slow from 70 to 60 is shorter than from 60 to 50. This means you're spending more time below 60 than above.

I noticed something similar with the heating in my house: The day temperature is 19.5C while the night temp is 17.5C. When the thermostat switches from day to night I can see that the house cools down to 19.0C pretty fast, like under an hour. After 2-3 hours it's down to 18.5C. It takes 5 hours to get to 18.0C. I think I remember from long long ago that cooling is an exponential function of the temperature difference, but maybe I have it wrong. Anyway, my thermostat seems to use the P&G method. Instead of adjusting my furnace to constantly keep the house at 19.5C, it warms up to 19.75C, then "coasts" down to 19.25C and back again. I'm all exited about this because:
(1) Until a few months ago we didn't have a thermostat. The furnace would keep the water in the system at a constant temperature, meaning the radiators were always warm.
(2) We are saving money and, more important, natural resources. Even though it's been colder than last year and prices have gone up since then, our bill is about 10% less than a year ago. I have yet to check how much less Russian gas we've used.

So these are two incarnations of P&G. Yesterday I read in Bearleener's signature:
You ever notice that birds pulse & glide, too?
I decided to post this thread to discuss other ways of how P&G shows up.

e·co·mod·ding: the art of turning vehicles into what they should be

What matters is where you're going, not how fast.

"... we humans tend to screw up everything that's good enough as it is...or everything that we're attracted to, we love to go and defile it." - Chris Cornell

[Old] Piwoslaw's Peugeot 307sw modding thread
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