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Post by silverdragon on May 14, 2014 5:26:34 GMT
Thats a new one to me... you learn something new............
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Post by silverdragon on May 14, 2014 5:44:03 GMT
Blower assisted aerodynamics.
Hmmm.....Putting this forwards....
So you suck the air from in front of the car and blow it out the back....
Wouldnt that make a jet powered car?....
They done that already. as in not the mythbusters, but jet powered drag racing, it already exists, in a form, but I only ever seen one run at a time and they time the run, 'cos two jets running at the same time tend to "steal" each others air and create a vacuum between them... which really sucks... literally... they suck the air out between them and that pressure difference crates its own form of collision?....
Which would be a great example, can two jets alongside each other that are not prevented from moving "Attract" each other by creating a vacuum?...
There are small electric powered jets that could be used for that one.
I suggest strapping some to say a surf board or plank of wood and setting them off side by side to see what happens.
Back on subject....
Would there air jets strapped to a car sucking air through vents, through the vehicle, and out the back, be any good.
Questions raised, as they are fuelled, where does the fuel come from, as extra weight for that fuel will be detrimental to the vehicles performance.
If its electrical, that has to be generated from the vehicle, which is detrimental to horses under the bonnet.
If you have the space for an air duct, projecting this forward into race vehicles and stripped down open wheel racing, if you have space for an air duct, then removing the body work anyway and creating a smaller cockpit would work out more beneficial to weight to horsepower rather that adding in extra weight and an extra motor would.
But that was before the invention of these super small electrical air jets......
However, we have to look at the weight gain issue.
And then at what the vehicle will be used for.
If its just a straight line drag race, sure, strap on extra junk.
If its going to do a corner at any point, you are going to have to brake that weight to make that corner....
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Post by Cybermortis on May 14, 2014 10:30:37 GMT
An electrical system could run off a small battery, after all it doesn't have to be (and isn't intended) to be running continually.
Air could be funnelled from the existing duct system that runs into the compartment. Cut the existing tubing and extend it so it runs to the back of the car.
Weight increases could be countered simply by removing things like the spare tire, or carpeting in the passenger compartment. Heck, you could remove the passenger seat if you had to - after all this rig would be about testing the principle not making it a practical everyday vehicle.
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Post by the light works on May 14, 2014 13:57:40 GMT
It occurred to me today that blower assisted aerodynamics would be different from rocket assisted aerodynamics, because the blower pulls airflow from somewhere else, whereas the rocket manufactures its own volume of gas. they might be able to do a smaller scale test with a pressure tank (and I would expect them to start with water tunnel tests with a supply tube for water) The effect should be negligible. But if you think it might have a significant effect, you could have two intakes arranged so that any force due to suction cancels itself out. even so, it is a different scientific principle. a rocket is not a ducted fan engine. |
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Post by the light works on May 14, 2014 14:00:26 GMT
Blower assisted aerodynamics. Hmmm.....Putting this forwards.... So you suck the air from in front of the car and blow it out the back.... Wouldnt that make a jet powered car?.... They done that already. as in not the mythbusters, but jet powered drag racing, it already exists, in a form, but I only ever seen one run at a time and they time the run, 'cos two jets running at the same time tend to "steal" each others air and create a vacuum between them... which really sucks... literally... they suck the air out between them and that pressure difference crates its own form of collision?.... Which would be a great example, can two jets alongside each other that are not prevented from moving "Attract" each other by creating a vacuum?... There are small electric powered jets that could be used for that one. I suggest strapping some to say a surf board or plank of wood and setting them off side by side to see what happens. Back on subject.... Would there air jets strapped to a car sucking air through vents, through the vehicle, and out the back, be any good. Questions raised, as they are fuelled, where does the fuel come from, as extra weight for that fuel will be detrimental to the vehicles performance. If its electrical, that has to be generated from the vehicle, which is detrimental to horses under the bonnet. If you have the space for an air duct, projecting this forward into race vehicles and stripped down open wheel racing, if you have space for an air duct, then removing the body work anyway and creating a smaller cockpit would work out more beneficial to weight to horsepower rather that adding in extra weight and an extra motor would. But that was before the invention of these super small electrical air jets...... However, we have to look at the weight gain issue. And then at what the vehicle will be used for. If its just a straight line drag race, sure, strap on extra junk. If its going to do a corner at any point, you are going to have to brake that weight to make that corner.... more a ducted fan assisted car, in the power class we are discussing. |
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Post by silverdragon on May 15, 2014 4:59:51 GMT
As much as I am liking the above suggestions, I think we are going too much into race track aerodynamics for the actual suggestion.
The average family saloon is aerodynamic as a brick.
If we start doing the major bodyworks and fan assists we are adding weight.
If that is the case, why dont we go forward with the next logical suggestion that we ahould remove the whole body and strap on a light minimal body that is as aerodynamic as it can be.
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Post by the light works on May 15, 2014 5:35:30 GMT
As much as I am liking the above suggestions, I think we are going too much into race track aerodynamics for the actual suggestion. The average family saloon is aerodynamic as a brick. If we start doing the major bodyworks and fan assists we are adding weight. If that is the case, why dont we go forward with the next logical suggestion that we ahould remove the whole body and strap on a light minimal body that is as aerodynamic as it can be. with a jalopy, it would be fairly simple to bundle model rocket engines on the back bumper, or to cut a hole in the trunk bottom and put in a fan - though powering the fan is another story. |
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Post by silverdragon on May 15, 2014 6:17:52 GMT
Be careful where you take the air from.
If you take air from another low pressure zone, you will alter the aerodynamics in that spot as well, and may just end up creating more drag than you solve.
The ideal would be put a pipe where air would flow through anyway without the fan, then fan assist it to boost that process at speed.
The fan is going to have to be powerful.
The aerodynamics of each individual car only start at a certain speed, and by that time, you have a pretty powerful airflow already.
Putting a weak fan in that will just hinder what you already have...
Therefore, you need a real doozy of a fan, and that is going to need a lot of power?....
Now in above, you suggest sucking out the air under the car....
Thus producing downforce.
Great....
But I wonder if that will aid speed?...
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Post by Cybermortis on May 15, 2014 10:52:07 GMT
As I noted above, you could test the basic principle by using the existing air-ducting system that feeds the inside of the car. You could remove the back window and replace it with a sheet of plywood with holes for the tubing. The fan and battery could then sit in the boot or on the rear shelf.
The added weight should not be that significant, probably less than having a passenger in the car. But if you wanted to offset that you could remove the passenger seat, spare tire or other objects from the car without having to cut it up. The air itself would be taken from the front of the vehicle, and would be 'naturally' lost anyway. In the case of some older cars, especially the old Mini, the air ducts are located in the upper rear of the front wheel arches* and tend to blow air into the car even if closed. So this wouldn't have any major effect on the performance of the car in itself.
You are missing that the basic idea isn't about blowing air (or gas) at high speeds out of the back of the vehicle in itself. Rather it is that if you blow air just fast enough it will 'smooth' the airflow at the car of the car - in effect creating a streamlined rear end. In theory this does seem as if it would work, but we need to look at this not just from the physics viewpoint but also in terms of Mythbusters.
MB's car rig needs to be something that can be set up and reused cheaply and quickly. Rockets in this regards are not ideal. They don't burn for that long, any minor increase in performance could be argued to be a result of loosing mass rather than any streamlining effect, they are costly, would need to be taken off and replaced after every test and it would be complex and time consuming to try and see how fast the gasses at the rear would need to be moving to have any effect.
Using some form of air-blower system (especially the kind of design I had in mind) would overcome these problems. The system itself wouldn't require that they wreck the car, could be used as long as they have batteries to power the fans and could be tinkered with to give variable airflow speeds. They could also increase the size of the fans (or alter their position/angle) by removing the plywood window and replacing it with something else - and this is the sort of modification they could do on location themselves. We also have to remember that rockets are basically explosive devices, and as such have to be treated and modified with a sharp eye on safety for all concerned. Something that doesn't apply to fans.
This test rig should give them enough data about how this principle works (or doesn't), which they could then use to fit another vehicle with rockets to see if the theory holds up. The rig would also give them the chance to do a lot of testing (and hence footage) as well as a small but fairly decent build plus a fair amount of small scale testing and the chance to introduce some science to the segment.
In terms of cost and time, this would also be much more practical for MB. Other than the car itself everything they need they will have in the shop. As such it wouldn't cost them anything per test. Maybe just as importantly since the rig doesn't require that they cut the car up they would have the option of either reusing it, or if it is in good condition selling it afterwards. So they might be able to test the idea out for next to nothing.
(*I know the location of the air ducts on the old Mini because I used to drive one. I also know that the ducts tended to 'blow' air into the car even when closed from first hand experience. I had a friend who also drove a mini, and he likewise knew exactly where the ducts were located and that they never really closed. In his case he discovered this when he drove through a deep puddle at speed and was hit by a jet of water that came through the ducts....)
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Post by the light works on May 15, 2014 13:52:33 GMT
don't forget that the original myth was that a kid strapped some rocket engines to his car to win a drag race.
this is part of the reason why I keep pointing out that blower assisted aerodynamics is different from rocket assisted aerodynamics.
but yes, I like the idea of ducting the blower air from the cabin air intakes, rather than from beneath the car. perhaps if they use the right model car, they can fold the rear seats down and remove the taillights to duct the air out the back without cutting up the car. On the other hand, there may be some critical need to render the car a pile of smoldering wreckage at the end of the myth...
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Post by Cybermortis on May 15, 2014 13:58:53 GMT
I'm not forgetting, but that kind of set up is rather similar to the JATO car myth which they have done three times already.
Having a theory they could test using blowers seems a somewhat different and more interesting take on things. Plus they could test the original myth as is, and then use data gained from the blower tests to see if they could fine-tune the placement of the rockets - which will save them a lot of time, money and hassle.
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Post by the light works on May 15, 2014 14:40:00 GMT
I'm not forgetting, but that kind of set up is rather similar to the JATO car myth which they have done three times already. Having a theory they could test using blowers seems a somewhat different and more interesting take on things. Plus they could test the original myth as is, and then use data gained from the blower tests to see if they could fine-tune the placement of the rockets - which will save them a lot of time, money and hassle. I guess there is a superficial similarity - but JATO was centered around the magnitude of the rocket thrust turning the car into a ballistic missile, while RAA centers around whether weak rockets can provide more improvement than their net thrust it will also be easier to test rocketry in the water tunnel than fans - because the rockets can be simulated by adding water from an outside source; whereas for the fans, you would have to actually have fans and ducting in place. another interesting comparison would be testing rockets against high volume smoke bombs - the idea being to get the same discharge volume between the rockets and smoke bombs, without the discharge velocity of the rockets. |
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Post by memeengine on May 15, 2014 17:15:41 GMT
Now in above, you suggest sucking out the air under the car.... Thus producing downforce. Great.... But I wonder if that will aid speed?... Increasing downforce would only increase overall speed if the vehicle was otherwise wasting power through lack of traction or was cornering at high-speed, neither of which is an issue if you're considering modifying a 'normal' car. Racing cars use it because they have large power-to-weight ratios (with the potential for wheel spin) and a requirement for high-speed cornering, the trade-off is that increasing downforce effectively increases the weight of the vehicle which limits straight line performance. |
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Post by memeengine on May 15, 2014 18:33:33 GMT
You are missing that the basic idea isn't about blowing air (or gas) at high speeds out of the back of the vehicle in itself. Rather it is that if you blow air just fast enough it will 'smooth' the airflow at the car of the car - in effect creating a streamlined rear end. In theory this does seem as if it would work, but we need to look at this not just from the physics viewpoint but also in terms of Mythbusters. MB's car rig needs to be something that can be set up and reused cheaply and quickly. Rockets in this regards are not ideal. They don't burn for that long, any minor increase in performance could be argued to be a result of loosing mass rather than any streamlining effect, they are costly, would need to be taken off and replaced after every test and it would be complex and time consuming to try and see how fast the gasses at the rear would need to be moving to have any effect. Using some form of air-blower system (especially the kind of design I had in mind) would overcome these problems. The system itself wouldn't require that they wreck the car, could be used as long as they have batteries to power the fans and could be tinkered with to give variable airflow speeds. They could also increase the size of the fans (or alter their position/angle) by removing the plywood window and replacing it with something else - and this is the sort of modification they could do on location themselves. To be effective, you'd have to move a significant volume of air from the front of the vehicle to the rear. At 40 mph a car is moving at 58.6 feet per second. A typical car is about 4.5~5 ft high and 5~6 ft wide. So if we take the smaller dimensions and knock off 6 inches for ground clearance, the car is displacing a volume 58.6 ft long by 4 ft high by 5 feet wide or 1172 cubic feet of air per second. Even if you simply try to vent 20% of that into the area at the back of the car, that's still 234 cubic feet per second. I suspect that a car's cabin intakes aren't designed to handle that volume of air. So they would have to design their own intakes, which is something that I suspect is easy to get wrong. Mounted in wrong place or having the wrong shape, they might easily increase the car's drag or fail to draw in sufficient air. There's also the problem of tuning the fans to the vehicle speed. If the fans push to little or too much air into the area behind the car, the effect on performance is going to be inconsistent or possibly even detrimental. Another consideration is how the vented air is introduced into the space behind the car. If it's not done carefully and uniformly, it could easily increase the turbulence behind the vehicle which in turn could make the overall aerodynamics worse. |
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Post by the light works on May 16, 2014 1:34:08 GMT
You are missing that the basic idea isn't about blowing air (or gas) at high speeds out of the back of the vehicle in itself. Rather it is that if you blow air just fast enough it will 'smooth' the airflow at the car of the car - in effect creating a streamlined rear end. In theory this does seem as if it would work, but we need to look at this not just from the physics viewpoint but also in terms of Mythbusters. MB's car rig needs to be something that can be set up and reused cheaply and quickly. Rockets in this regards are not ideal. They don't burn for that long, any minor increase in performance could be argued to be a result of loosing mass rather than any streamlining effect, they are costly, would need to be taken off and replaced after every test and it would be complex and time consuming to try and see how fast the gasses at the rear would need to be moving to have any effect. Using some form of air-blower system (especially the kind of design I had in mind) would overcome these problems. The system itself wouldn't require that they wreck the car, could be used as long as they have batteries to power the fans and could be tinkered with to give variable airflow speeds. They could also increase the size of the fans (or alter their position/angle) by removing the plywood window and replacing it with something else - and this is the sort of modification they could do on location themselves. To be effective, you'd have to move a significant volume of air from the front of the vehicle to the rear. At 40 mph a car is moving at 58.6 feet per second. A typical car is about 4.5~5 ft high and 5~6 ft wide. So if we take the smaller dimensions and knock off 6 inches for ground clearance, the car is displacing a volume 58.6 ft long by 4 ft high by 5 feet wide or 1172 cubic feet of air per second. Even if you simply try to vent 20% of that into the area at the back of the car, that's still 234 cubic feet per second. I suspect that a car's cabin intakes aren't designed to handle that volume of air. So they would have to design their own intakes, which is something that I suspect is easy to get wrong. Mounted in wrong place or having the wrong shape, they might easily increase the car's drag or fail to draw in sufficient air. There's also the problem of tuning the fans to the vehicle speed. If the fans push to little or too much air into the area behind the car, the effect on performance is going to be inconsistent or possibly even detrimental. Another consideration is how the vented air is introduced into the space behind the car. If it's not done carefully and uniformly, it could easily increase the turbulence behind the vehicle which in turn could make the overall aerodynamics worse. I think you are severely overestimating the necessary airflow. and, of course, that is why this is an interesting topic |
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Post by memeengine on May 16, 2014 6:19:03 GMT
I think you are severely overestimating the necessary airflow. and, of course, that is why this is an interesting topic The dead-air that you're aiming to eliminate is kept trapped there by the air flow coming around the car. Once you eliminate the pressure difference trapping the dead-air, that air is free to move away from the car (or, more accurately, the car can move away from the air). Therefore you'd have to constantly replenish that air or a new dead-air pocket will form. Obviously the exact rate will vary depending on the speed of the vehicle and the original size of the dead-air pocket. My numbers might be wrong but I haven't seen anyone else even attempt to get a grasp on the magnitude of what's required. So if you think that my numbers are "severely overestimating the necessary airflow", show me your calculations. |
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Post by the light works on May 16, 2014 14:06:43 GMT
well, the hood to side door vents Ferrari uses on their newest (gentleman's sausage) extender to improve the laminar airflow around the car are about 9 square inches on a car that goes 200 MPH.
the rear spoiler on a NASCAR car that goes 200 MPH is less than 4 inches tall. (to improve the laminar airflow)
certainly an engineer could calculate out an optimum airflow through the blower assisted aerodynamics system as well as the optimum inlet and delivery points - but I strongly believe that 120CFM (which can use 2 4" diameter ducts) will be sufficient to make a discernable difference in performance. this would be inserted in the boundary between the dead air pocket and the airflow around the car to produce a buffer zone.
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Post by silverdragon on May 17, 2014 5:14:43 GMT
Technically this is what I was trying to get at... at speed, thats an awful LOT of air being displaced, and a but more than a couple of drainpipes passing through the cabin with the cooling fan from a PC?....
A LOT more.
This is what I thought as well.
So taking air out under the bonnet or under the floor of the car will increase downforce effectively, which will be a waste.
What would be needed to effect a smooth transition negating aerodynamics....
The holy grail.
If you could design a system that sucks ALL the air out from in front of the vehicle, pressurises it, then chucks it out the back.....
Wait, they did that already, its called a jet engine?.....
Thrust two, and thrust three, a little project someone in my greater family (Distant cousins on the Scottish side of the border) namely Richard Noble, have a great experience with.
He just took it a stage further and used the jet as the main thrust.
I agree with the ideas above of creating a system that will be ducted fans, but, to be effective, the fans will have to be rather powerful, and although you can get very powerful fans, running a separate battery is going to be heavy if they are to be used on a repeated basis.
And I believe you are severely under-estimating the airflow required.
Look at how drag increases with speed.
There is a reason why the Veyron requires 1,000 hp.... the later veyrons have increased that as well, 200 extra hp at top speed only gave them an increase of 5mph..... why?, because drag at that speed is (almost) like hotting a brick wall, to go 5mph faster is the square of a very large number extra horse power per mph...
This is on an already aerodynamically designed car.
In F1, they will spend a million quid sterling to get one hundredth of a second lap time in aerodynamic design.
Ok, so we are not talking that kind of speed here, but what we are talking is the design problems of "An average family car" who's average life time speed is well under the speed where aerodynamics actually matter....
Until the boy racer decides to go fast.
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Post by the light works on May 17, 2014 6:28:27 GMT
Right. you are talking about a car that has the relative aerodynamic properties of a brick.
consider: add 5 HP to your F-1 car. or add 5HP to a Dacia Sandero. on which car is it going to make more difference.
similarly, displacing 80 less CFM of air will make more difference on an old jalopy at 60 MPH then it will an F-1 car at 60 MPH. Although, as I said, it is less about not displacing the air as it is directing it in such a way it makes the low pressure one less obnoxious. consider - by adding a truncated boattail to s standard car, it makes it more aerodynamic WITHOUT any sort of blowers. the car doesn't displace one cubic inch less air - but because of the improved laminar airflow, it still has less aerodynamic drag.
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Post by the light works on May 17, 2014 6:29:13 GMT
Are you sure you guys aren't secretly Americans - you are approaching this puzzle from a brute force perspective.
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