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Post by the light works on Sept 9, 2014 13:58:11 GMT
Two vehicles passing head on.... close?...erm.... I think dedicated "Stunt" drivers for that?.... we have a few thousand vehicles in my town - all passing that close to each other. I don't think I live in a town full of stunt drivers.
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Post by wvengineer on Sept 9, 2014 16:50:13 GMT
Some thoughts:
For the truck involved: I wonder of different styles of truck would effect the results? While the truck is having to move the same amount of air, the shape of the truck would effect the angle the air blows off of it and also how turbulent/laminar the flow is. The greater the angle and more turbulent the flow, the more pushing affect the air would have It would be interesting to test if a boxy cab-over tractor would have a stronger side wind than a modern streamlined tractor.
Also how does the rear of the trailer effect things? A lot of trailers these days have those collapsible panels on the back that help aerodynamics (please help me with the name of what those are called)
Thinking about how to measure this, The ultimate effect would be on a bicycle, that is inherently a lot more unstable than a car.
To go along with that, here is an idea for a device you could use to measure the sideways force generate byt he air coming off a semi. A small trailer towed some ways behind a car. On that trailer, mount a silhouette of a small car, made out of plywood. This cutout would be mounted along the long axis of the trailer, parallel with the lane, on spring loaded hinges to hold it upright. You can measure how much force is generated by the wind of a semi by simply measuring what angle the silhouette get push over to. Greater angle, greater force. To try different cars simply use different cutouts. Quick to measure and quick to reset after each test.
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Post by the light works on Sept 9, 2014 17:17:14 GMT
Some thoughts: For the truck involved: I wonder of different styles of truck would effect the results? While the truck is having to move the same amount of air, the shape of the truck would effect the angle the air blows off of it and also how turbulent/laminar the flow is. The greater the angle and more turbulent the flow, the more pushing affect the air would have It would be interesting to test if a boxy cab-over tractor would have a stronger side wind than a modern streamlined tractor. Also how does the rear of the trailer effect things? A lot of trailers these days have those collapsible panels on the back that help aerodynamics (please help me with the name of what those are called) Thinking about how to measure this, The ultimate effect would be on a bicycle, that is inherently a lot more unstable than a car. To go along with that, here is an idea for a device you could use to measure the sideways force generate byt he air coming off a semi. A small trailer towed some ways behind a car. On that trailer, mount a silhouette of a small car, made out of plywood. This cutout would be mounted along the long axis of the trailer, parallel with the lane, on spring loaded hinges to hold it upright. You can measure how much force is generated by the wind of a semi by simply measuring what angle the silhouette get push over to. Greater angle, greater force. To try different cars simply use different cutouts. Quick to measure and quick to reset after each test. I don't think those areodynaimc aids have any common name, yet - I'm sure eventually one manufacturer will become dominant, and then their brand name will become the common name.
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Post by silverdragon on Sept 10, 2014 6:29:33 GMT
Two vehicles passing head on.... close?...erm.... I think dedicated "Stunt" drivers for that?.... we have a few thousand vehicles in my town - all passing that close to each other. I don't think I live in a town full of stunt drivers. I can safely bet at full throttle they miss each other by six feet?.... We are talking "Inches" for that test, we want so close you may take mirrors off.
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Post by silverdragon on Sept 10, 2014 6:33:27 GMT
Thoughts on truck shape, VW has echoed what I said, and now I can go further by suggesting a european style cab-over flat front may produce a bigger bow wave than your american ...here's the bonnet aint she big the rest will be here soon type rigs.
The aerodynamics are named, fluid dynamics, they are the same as air and water react the same way when pushed out of the way. Its just air compresses slightly easier.... but only a little.
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Post by the light works on Sept 10, 2014 14:30:32 GMT
we have a few thousand vehicles in my town - all passing that close to each other. I don't think I live in a town full of stunt drivers. I can safely bet at full throttle they miss each other by six feet?.... We are talking "Inches" for that test, we want so close you may take mirrors off. you're talking inches. the rest of us are talking feet. the myth is whether the the truck affects the car more, or the car affects the truck more.
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Post by the light works on Sept 10, 2014 14:33:16 GMT
Thoughts on truck shape, VW has echoed what I said, and now I can go further by suggesting a european style cab-over flat front may produce a bigger bow wave than your american ...here's the bonnet aint she big the rest will be here soon type rigs. The aerodynamics are named, fluid dynamics, they are the same as air and water react the same way when pushed out of the way. Its just air compresses slightly easier.... but only a little. well, there IS a reason why boats and airplanes aren't flat across the front... but how that affects the bow wave, I can't say off the top of my head.
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Post by silverdragon on Sept 11, 2014 8:44:27 GMT
Speed. Flat fronted ferries are very economical, unless you want to get there in a hurry. Flat fronted trucks are below the road speed where aerodynamics get to being a right pain in the tailgate.Both create a bow-wave, but its manageable. If you want fast, you have to do the aerodynamic things.
Inches and Feet....
How close do you have to get before the aerodynamics that are in play on a moving truck start playing merry hell with your own aerodynamics.
I suspect there is a distance that is finite for certain speed where passing a truck at that distance will give you no actual interference, I also suspect that the researchers down at the TRRL road transport research labs know that exact distance, and use it in road design to give the lane widths for overtaking lanes and the like, and motorway/freeway lane spacings..?....
I also suspect that its used when trucks in different directions pass, to minimise the effect of passing air disturbance, hence on may dual carriageways, the lanes are separated by a central divide, ...
Question, is it as much to do with air disturbance as it is with safety?... I dont know the answer yet, but I have suspicions.
Therefore, passing within 6ft, I expect a little wobble. How close before that becomes a serious wobble. How much closer can you get, and how much does it change...
I was expecting several passes getting gradually closer to see what the "Butter zone" is for disturbance.
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Post by the light works on Sept 11, 2014 14:38:35 GMT
Speed. Flat fronted ferries are very economical, unless you want to get there in a hurry. Flat fronted trucks are below the road speed where aerodynamics get to being a right pain in the tailgate.Both create a bow-wave, but its manageable. If you want fast, you have to do the aerodynamic things. Inches and Feet.... How close do you have to get before the aerodynamics that are in play on a moving truck start playing merry hell with your own aerodynamics. I suspect there is a distance that is finite for certain speed where passing a truck at that distance will give you no actual interference, I also suspect that the researchers down at the TRRL road transport research labs know that exact distance, and use it in road design to give the lane widths for overtaking lanes and the like, and motorway/freeway lane spacings..?.... I also suspect that its used when trucks in different directions pass, to minimise the effect of passing air disturbance, hence on may dual carriageways, the lanes are separated by a central divide, ... Question, is it as much to do with air disturbance as it is with safety?... I dont know the answer yet, but I have suspicions. Therefore, passing within 6ft, I expect a little wobble. How close before that becomes a serious wobble. How much closer can you get, and how much does it change... I was expecting several passes getting gradually closer to see what the "Butter zone" is for disturbance. if the dolts at the tire center think that "Max pressure 65PSI means you should inflate the tires to 28 PSI, then the widh of the space between lanes is too close. the division in divided freeways is more to allow people space to fall off the road without taking other people with them, than to keep aerodynamics from interfering with each other.
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Post by silverdragon on Sept 12, 2014 6:12:33 GMT
I leave that open to speculation, but, I gather the faster the road the greater the gaps is not just for space to fall off, but for allowing a little extra room to dissipate wind sheer.
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Post by the light works on Sept 12, 2014 14:24:54 GMT
I leave that open to speculation, but, I gather the faster the road the greater the gaps is not just for space to fall off, but for allowing a little extra room to dissipate wind sheer. you are crediting highway departments with more intelligence than I give them credit for. particularly when the US has plenty of high speed freeways where the only division between the directions is a concrete barrier.
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