Practical ways to measure lift, downforce and drag on a 996TT (?)
#16
Three Wheelin'
The best and most accurate method to measure the drag on a vehicle is to measure the decrease in speed over time while coasting. Do the math on it and you can come up with a value for the total drag on the vehicle (aero, rolling and mechanical). Needs to be well controlled for comparison runs (same MPH range, location, no wind, aprox same temp). But if you wanted to measure actual drag change between aero setups this would do it accurately.
#18
Regarding the sensors I posted, it says on the website that they output a certain voltage depending on what position they are in. So I'm guessing that they would read say 0 volts when fully open and say 5 volts when compressed (then various voltages in between) that is what the logger will interpret. If that is how the sensors are setup then you could maybe use a universal datalogger like the AEM AQ-1 (under $400). It has tons of possible inputs to log, including four 0-5V inputs and four 0-16.5V.
http://www.uspmotorsports.com/Engine...FUVBhgodtzsLbQ
http://www.uspmotorsports.com/Engine...FUVBhgodtzsLbQ
So about $1000 for all four corners. That's about what I expected. I also expect the rest of the hardware to cost about $5k, which is a lot more than I'm aiming to spend, though maybe advantage will have some surprises. There's also installation cost, not to mention the need to find someone who can do it. (It may be easy, but it isn't something the average Porsche specialist will have done before.)
My preferred method would be to use the height sensors which the car already has. Someone posted in a 991 thread that they are working on a datalogger that would do just that. Hopefully it will also work with 996s, and won't be sold at 991 prices ... .
There's also a bit more detail in the thread in the performance mods forum mentioned in the original post.
My preferred method would be to use the height sensors which the car already has. Someone posted in a 991 thread that they are working on a datalogger that would do just that. Hopefully it will also work with 996s, and won't be sold at 991 prices ... .
There's also a bit more detail in the thread in the performance mods forum mentioned in the original post.
#19
Regarding the sensors I posted, it says on the website that they output a certain voltage depending on what position they are in. So I'm guessing that they would read say 0 volts when fully open and say 5 volts when compressed (then various voltages in between) that is what the logger will interpret. If that is how the sensors are setup then you could maybe use a universal datalogger like the AEM AQ-1 (under $400). It has tons of possible inputs to log, including four 0-5V inputs and four 0-16.5V.
http://www.uspmotorsports.com/Engine...FUVBhgodtzsLbQ
http://www.uspmotorsports.com/Engine...FUVBhgodtzsLbQ
We just need to figure out how to hook it up to these sensors ... .
#20
I had a chat with AEM. The first question is whether the sensors communicate via OEM cambus. If so, it won't work.
If no, then we also need the harness ($276) and a GPS sensor. (They think it won't work with the car's GPS sensor - I forgot to ask about using a smart phone for GPS.)
Then the software will display the volts coming from the sensor. (It just might be possible to set up the software to display height in mm or cm - they're not sure.)
However, either way, we'd need to figure out how to translate between volts and height. This would require adding/removing weight from the car and quite precisely measuring the resulting height. And the result might not be linear. Not a problem to estimate a function that fits well - Excel can do it. But if there is any way to have the software display not volts but, e.g. milimeters, plugging such a function into the software might be a problem (don't know, didn't discuus it with them).
The ideal solution would gather height data from the car's senors in mm, not in volts, and would be inexpensive. So this isn't ideal. But if the ideal does not exist, then if it works, it could be good enough.
Anyone have any idea if these sensors communicate using cambus (spelling?)?
If no, then we also need the harness ($276) and a GPS sensor. (They think it won't work with the car's GPS sensor - I forgot to ask about using a smart phone for GPS.)
Then the software will display the volts coming from the sensor. (It just might be possible to set up the software to display height in mm or cm - they're not sure.)
However, either way, we'd need to figure out how to translate between volts and height. This would require adding/removing weight from the car and quite precisely measuring the resulting height. And the result might not be linear. Not a problem to estimate a function that fits well - Excel can do it. But if there is any way to have the software display not volts but, e.g. milimeters, plugging such a function into the software might be a problem (don't know, didn't discuus it with them).
The ideal solution would gather height data from the car's senors in mm, not in volts, and would be inexpensive. So this isn't ideal. But if the ideal does not exist, then if it works, it could be good enough.
Anyone have any idea if these sensors communicate using cambus (spelling?)?
#21
affect the aerodynamics, but there is rarely any information
There can't be too many threads that include it.
#22
Drifting
i believe this is what you want if you want something that is accurate.
http://www.windshearinc.com/services...s.htm#Services
From what I can tell after scoping around, its about 2k/hr. two hours should suffice id think.
http://www.windshearinc.com/services...s.htm#Services
From what I can tell after scoping around, its about 2k/hr. two hours should suffice id think.
#23
RL Community Team
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#24
Note however that all of them may increase a car's downforce by reducing lift. As I posted previously, you can definitely decrease drag and reduce lift at the same time.
#25
Which is not to say anything bad about them. But since I'm just one person, and would test the car as is, then test it after making a mod several hours later, then test it again after my next mod a month later, etc., I'd quickly blow through 4k!
No, gophaster's post has given me hope that this can be done for under 1k. And once it's done, I can test again whenever I want for nothing. And as a bonus, even if my results aren't precise, I'll know that they are accurate in the real world.
(it seems pretty clear it can be done for 2k plus setup costs - using both the AEM data logger and the height sensors mentioned earlier. With luck, 1k can be saved by using the OEM sensors.)
#26
RL Community Team
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Not necessarily. In fact, flat floors generally reduce drag. And I believe a good diffuser can do the same. Lip spoilers are another example. The wheel well vents on a 991 GT3RS or a Pagani Zonda (and probably several other street cars and lots of race cars) are another.
Note however that all of them may increase a car's downforce by reducing lift. As I posted previously, you can definitely decrease drag and reduce lift at the same time.
Note however that all of them may increase a car's downforce by reducing lift. As I posted previously, you can definitely decrease drag and reduce lift at the same time.
Basically anytime you displace air by moving an object through it some drag is produced. Even a rain drop, the prefect natural aerodynamic shape, produces some drag.
In order to produce downforce air speed and pressure must change and with any air speed/pressure change there is some increase in drag. All downforce generating devices produce some drag. Devices like ground effects and diffusers just happen to work in ways that produce a lot less drag than wings and spoilers.
Reducing lift negates the lifting forces of the air flow which allows the gravity to do its job that is not the same as manipulating air pressure to producing downforce.
#27
Three Wheelin'
A flat floor may reduce drag but it will not by itself produced downforce. Diffusers do produce downforce but also increase drag a little bit. Lip spoiler absolutely produce drag while also increasing downforce. Wheel well vents do reduce lift but that is not the same as producing downforce and there is still drag produced.
Basically anytime you displace air by moving an object through it some drag is produced. Even a rain drop, the prefect natural aerodynamic shape, produces some drag.
In order to produce downforce air speed and pressure must change and with any air speed/pressure change there is some increase in drag. All downforce generating devices produce some drag. Devices like ground effects and diffusers just happen to work in ways that produce a lot less drag than wings and spoilers.
Reducing lift negates the lifting forces of the air flow which allows the gravity to do its job that is not the same as manipulating air pressure to producing downforce.
Basically anytime you displace air by moving an object through it some drag is produced. Even a rain drop, the prefect natural aerodynamic shape, produces some drag.
In order to produce downforce air speed and pressure must change and with any air speed/pressure change there is some increase in drag. All downforce generating devices produce some drag. Devices like ground effects and diffusers just happen to work in ways that produce a lot less drag than wings and spoilers.
Reducing lift negates the lifting forces of the air flow which allows the gravity to do its job that is not the same as manipulating air pressure to producing downforce.
#29
RL Community Team
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All reducing lift does is enable gravity to function unencumbered by the air flow and pressure.
Producing downforce uses air flow and pressure to literally push the car into the ground. Sometimes with a force exceeding the car's actual mass. Current F1 and LMP1 cars produce so much downforce they can be driven upside down at speeds above 120mph.
Reducing lift negates airflow and air pressure. Producing downforce utilizes air flow and air pressure to do work.
#30
RL Community Team
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