Clean car gets +10% mpg
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Originally Posted By: Gary Allan
Some Mythbusters stuff is just silly. Some is decent, but they do need the entertainment factor.
The one where they tried to disprove a car being blown off the road when a plow came by was just dumb. They could have simply measured the pressure on a like cross section'd sheet and said it was enough or not enough to do the job.
You're missing the point of the show. It's more about actually doing it, rather than theory. I mean, you know for instance the starting force to get that car moving from the snowplow is greater than the force to keep it moving. Kind of hard to predict all that stuff, inc the actual friction under the tires at any give time, sooo....
Some Mythbusters stuff is just silly. Some is decent, but they do need the entertainment factor.
The one where they tried to disprove a car being blown off the road when a plow came by was just dumb. They could have simply measured the pressure on a like cross section'd sheet and said it was enough or not enough to do the job.
You're missing the point of the show. It's more about actually doing it, rather than theory. I mean, you know for instance the starting force to get that car moving from the snowplow is greater than the force to keep it moving. Kind of hard to predict all that stuff, inc the actual friction under the tires at any give time, sooo....
Don't race teams dust the exterior with talc?
We always kept jets washed and waxed when I was in Flight School! In fact if you screwed up big time waxing the jets was one of the punishments for mind numbing stupid mistakes! I am happy to say I never had to wax one of the jets!LOL
Kestas
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AJ just brought up a good point. If dimpling did indeed reduce drag, the NASCAR team would be all over it, considering the efforts they make to gain a 0.1% edge over the competition.
In order to assure that all cars are as aerodynamically alike as possible, all NASCAR teams have to stick to a very tight set of rules regarding body shape. Even the thickness of the body sheet metal is subject to regulation. I have a feeling that if a car showed up with a dimpled body, it simply wouldn't be allowed to race.
Thats what makes NASCAR the Non Racing league.
Whats wrong with innovation that gives one team an advantage over another. I miss the days of winners that are three laps ahead of the losers, thats real.
What we have now is fake and contrived for TV excitement garbage....JMO though.
Whats wrong with innovation that gives one team an advantage over another. I miss the days of winners that are three laps ahead of the losers, thats real.
What we have now is fake and contrived for TV excitement garbage....JMO though.
Originally Posted By: StevieC
I like the one that they did with the mileage of a Pick-Up truck and it's bed.
That was cool.
I'm no mechanic nor do I play one on TV, but they might have one serious flaw in that "study".
They connect a flow meter directly to the fuel line to measure fuel taken in by the engine but isn't there a return fuel line in modern, fuel-injected engines? If so, wouldn't the flow in minus the flow out equal the actual fuel consumption? From what they have told us, they did not do that.
Clark
I like the one that they did with the mileage of a Pick-Up truck and it's bed.
That was cool.
I'm no mechanic nor do I play one on TV, but they might have one serious flaw in that "study".
They connect a flow meter directly to the fuel line to measure fuel taken in by the engine but isn't there a return fuel line in modern, fuel-injected engines? If so, wouldn't the flow in minus the flow out equal the actual fuel consumption? From what they have told us, they did not do that.
Clark
That one probably does have a return line, yes. From my point of view, it looks correct because its changing. I would think if they were only measuring flow going to the engine, it would just show a pretty static number all the time. If it was just on the return you would have a high flow at idle that goes down with more fuel being used.
However, modern engines are going to return-less fuel systems and getting around pressure build up by making the pump variable and computer controlled.
However, modern engines are going to return-less fuel systems and getting around pressure build up by making the pump variable and computer controlled.
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Either way more fuel was pumped to the engine during certain tests than other which IMO has to show an increased usage.
They didn't go into detail about it but this was the second test using a more scientific method because people didn't believe the results on the first test.
They also said they had it calibrated before their test so I would imagine some conversation took place about what they were trying to achieve.
Steve
They didn't go into detail about it but this was the second test using a more scientific method because people didn't believe the results on the first test.
They also said they had it calibrated before their test so I would imagine some conversation took place about what they were trying to achieve.
Steve
Originally Posted By: LS2JSTS
Maybe you know....something I've always wondered. Is it the spinning that the dimples help create that helps or is it the dimples themselves that break up the air around the ball?
I don't think the dimples would cause more spin. They'd probably actually slow the spin of the ball since they increase friction drag. A spinning ball with dimples would hook/slice much more because the surface friction is greater, so one side of a spinning ball would have much more drag than the other side compared to a smooth ball. The dimples are there to cause rougher flow at the surface, which sticks to the surface better. Once the flow separates at the trailing end, it creates a low pressure zone (vacuum effect) at the back of the ball, so a more turbulent (stickier) boundary layer reduces that vacuum effect by holding onto the ball longer and making that low pressure zone smaller.
At low speeds, where flow separation is minimal, the dimples would actually hurt fuel economy by increasing friction drag. However, I don't imagine it takes much speed before pressure drag dominates on a typical automotive shape. The more aerodynamic the shape is, and the lower the speed is, the less a rough surface will help. Aircraft designers only intentionally create turbulent boundary layers immediately ahead of the control surfaces (ailerons, elevator, rudder), since a control surface won't function as anything but a brake if flow separation occurs.
Maybe you know....something I've always wondered. Is it the spinning that the dimples help create that helps or is it the dimples themselves that break up the air around the ball?
I don't think the dimples would cause more spin. They'd probably actually slow the spin of the ball since they increase friction drag. A spinning ball with dimples would hook/slice much more because the surface friction is greater, so one side of a spinning ball would have much more drag than the other side compared to a smooth ball. The dimples are there to cause rougher flow at the surface, which sticks to the surface better. Once the flow separates at the trailing end, it creates a low pressure zone (vacuum effect) at the back of the ball, so a more turbulent (stickier) boundary layer reduces that vacuum effect by holding onto the ball longer and making that low pressure zone smaller.
At low speeds, where flow separation is minimal, the dimples would actually hurt fuel economy by increasing friction drag. However, I don't imagine it takes much speed before pressure drag dominates on a typical automotive shape. The more aerodynamic the shape is, and the lower the speed is, the less a rough surface will help. Aircraft designers only intentionally create turbulent boundary layers immediately ahead of the control surfaces (ailerons, elevator, rudder), since a control surface won't function as anything but a brake if flow separation occurs.
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