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Old 01-08-2021, 02:27 PM   #11 (permalink)
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pressures

* So, at the end of the day, after we've accumulated all our pressures, how does that inform how we proceed to modifications, if any?

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Old 01-08-2021, 05:02 PM   #12 (permalink)
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Quote:
Originally Posted by aerohead View Post
* So, at the end of the day, after we've accumulated all our pressures, how does that inform how we proceed to modifications, if any?
I must admit my mouth just fell open when I read that.

That's just like saying, sure you've got a dyno but how does that help us in our modifications?

Or, sure you're using a stopwatch but how does that help us in our modifications?

In short, measuring pressures actually allows us to see what panels are causing lift, what panels are causing drag and what panels are causing thrust. It then allows us to measure how our modifications are changing any of the pressures causing those four forces.

No guesswork, no blindly following rules of thumb, no pretending that modifications that don't achieve anything are actually doing a huge amount.

Here is a list of modifications I have developed on my Insight in the last 12 months using pressure testing to give best results:
  • Front external air curtains
  • Rear separation edges
  • Longitudinal, curved strakes on the undertray
  • Rear spoiler
  • Rear fins

...so in fact every single aero modification I have done in that period!

I've been measuring aero pressures on my road cars since 2004 (then I used it in siting bonnet vents, developing a front air dam, developing a front undertray, improving intercooler flow), so I have real difficulty in getting my head around the idea that someone can't immediately see the worth of testing aero pressures. (It's like the old nightmare of trying to tune air/fuel ratios before wideband air/fuel ratio meters were available.)

Along with tuft testing, pressure testing is the most useful tool available to amateur aerodynamic modifiers.

Last edited by JulianEdgar; 01-08-2021 at 05:33 PM.. Reason: typo
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Old 01-08-2021, 06:37 PM   #13 (permalink)
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modifications

Quote:
Originally Posted by JulianEdgar View Post
I must admit my mouth just fell open when I read that.

That's just like saying, sure you've got a dyno but how does that help us in our modifications?

Or, sure you're using a stopwatch but how does that help us in our modifications?

In short, measuring pressures actually allows us to see what panels are causing lift, what panels are causing drag and what panels are causing thrust. It then allows us to measure how our modifications are changing any of the pressures causing those four forces.

No guesswork, no blindly following rules of thumb, no pretending that modifications that don't achieve anything are actually doing a huge amount.

Here is a list of modifications I have developed on my Insight in the last 12 months using pressure testing to give best results:
  • Front external air curtains
  • Rear separation edges
  • Longitudinal, curved strakes on the undertray
  • Rear spoiler
  • Rear fins

...so in fact every single aero modification I have done in that period!

I've been measuring aero pressures on my road cars since 2004 (then I used it in siting bonnet vents, developing a front air dam, developing a front undertray, improving intercooler flow), so I have real difficulty in getting my head around the idea that someone can't immediately see the worth of testing aero pressures. (It's like the old nightmare of trying to tune air/fuel ratios before wideband air/fuel ratio meters were available.)

Along with tuft testing, pressure testing is the most useful tool available to amateur aerodynamic modifiers.
How does a modification proceed from the pressure profile?
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Old 01-08-2021, 06:45 PM   #14 (permalink)
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Quote:
Originally Posted by aerohead View Post
How does a modification proceed from the pressure profile?
I don't think I understand.

It seems to me that's like saying: How does modification proceed from the base dyno run?

Just like doing a base dyno run, it gives you the starting point from which you can:
  • decide which modifications are likely to give the best improvement, depending on what you are trying to achieve
  • once you have trial fitted them, assess what those modifications are doing.
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Old 01-08-2021, 06:55 PM   #15 (permalink)
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understand

Quote:
Originally Posted by JulianEdgar View Post
I don't think I understand.

It seems to me that's like saying: How does modification proceed from the base dyno run?

Just like doing a base dyno run, it gives you the starting point from which you can:
  • decide which modifications are likely to give the best improvement, depending on what you are trying to achieve
  • once you have trial fitted them, assess what those modifications are doing.
I ask because I haven't clue how one would initiate a modification which would resolve an issue from a pressure profile on the first try? Second? Thousandth?
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Old 01-08-2021, 07:00 PM   #16 (permalink)
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Quote:
Originally Posted by aerohead View Post
I ask because I haven't clue how one would initiate a modification which would resolve an issue from a pressure profile on the first try? Second? Thousandth?
Mmm. Well if you never done it (making modifications based on measured pressures), it would all be new to you. I suggest that you watch some of my YouTube videos where I cover making specific mods, with pressure testing used as part of that development process.
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Old 01-12-2021, 03:51 AM   #17 (permalink)
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Originally Posted by jojokoko View Post
my god,so cool
Thank you! And it's not hard or expensive.

Just have to throw off the idea of guessing aerodynamic mods, rather than doing some test and development.
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Old 01-12-2021, 04:52 AM   #18 (permalink)
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How much of the drag at the base of the windshied is caused by a sharp kink there ?
Does a Honda Fit or Prius have less drag at the windshield base because there is less of a kink ?

If I create a curved ramp at the base of the windshield, would that help ? ( One that actually touches the windshield and completely seals the kink )
I'm thinking of a sloped windshied wiper cover.

If it begins to rain, I can simply pull it off.
Since airflow is recovered a few inches further past the wipers, is it even worth it ?

I think this sort of question has been discussed a thousand times here, but can't recall what the answer was.
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Old 01-12-2021, 05:15 AM   #19 (permalink)
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Quote:
Originally Posted by Cd View Post
How much of the drag at the base of the windshied is caused by a sharp kink there ?
Does a Honda Fit or Prius have less drag at the windshield base because there is less of a kink ?

If I create a curved ramp at the base of the windshield, would that help ? ( One that actually touches the windshield and completely seals the kink )
I'm thinking of a sloped windshied wiper cover.

If it begins to rain, I can simply pull it off.
Since airflow is recovered a few inches further past the wipers, is it even worth it ?

I think this sort of question has been discussed a thousand times here, but can't recall what the answer was.
Another good question.

Look, I think that such an approach would reduce drag, but it would depend on so many factors. I haven't done any personal testing of this, and the tech stuff I've seen has been fairly generic in this area.

Can't do throttle stop testing?
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Old 01-12-2021, 07:53 AM   #20 (permalink)
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Quote:
Originally Posted by JulianEdgar View Post
Another good question.

Look, I think that such an approach would reduce drag, but it would depend on so many factors. I haven't done any personal testing of this, and the tech stuff I've seen has been fairly generic in this area.

Can't do throttle stop testing?
Aerohead built up the area around his cowl.
Perhaps he can share the results here. I can't recall what sort of results he got.
Aerohead, you out there ?

As for my personal testing, I do plan to do throttle stop testing for sure one of these days.
I have yet to try it.
I think it's a brilliant technique if I can make it work.

I asked about the Prius and Fit cowl pressure because I thought you might know that off hand.
I went looking for CFD images of a Prius to see if there was indeed less cowl pressure because there is less of a dramatic kink in angles at the cowl, but I'm not finding any at the moment.

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