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Old 09-02-2012, 11:11 PM   #1 (permalink)
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Simple DIY bullnose add-on, (murky) B-A-B coast-down testing

Edit: I wouldn't have posted this if I had analyzed my data properly in the first place. ...which is publication bias. How much much does the likelihood of posting increase as the improvement magnitude increases? Food for thought...

At least next time I'll know how to do it right.

If anyone wants to look at my coast-down spreadsheet, it's an OpenOffice file in the attached zip file (EM server doesn't allow .ods files). I think it's pretty groovy.

============================

I actually decided once that I would not mod my 89 Corolla, considering how little I drive it (like 1,000-1,500 miles a year). Somehow I got amnesia and started modding it before I remembered my own injunction. Apparently no car is safe when my family is out of town.

This is somewhat Aerocivic inspired - most EM front-end mods consist of air dams and grill blocks, but I felt like the 89 had a particularly poor nose shape to start with (newer models are generally better than this). So I thought it would be good to lower the point of stagnation, smooth the transition to the hood, and block some of the air going to the grill at the same time.

My other design criteria here is to keep it brutally simple. This is an old car, I might not have it 3 years from now, and the mods just aren't going to see a ton of use (well, probably - maybe I'll love it more as it gets better).

Step 1: Bend some metal strips into a frame


Step 2: Pop-rivet coroplast onto frame. I note that steel was not a good choice. Aluminum drills much faster and also won't rust. But I had a bunch of steel strips lying around for some forgotten project.

Step 3: Paint, drill and tap for screws to attach license plate (required in Utah).

Step 4: Zip tie onto car.



This car has a carburetor (no FE instrumentation), so I did a coast-down from 40 to 25 MPH. Since I already had the bullnose on the car when I started, I decided to shake things up and do B-A-B testing, that way I'd only have to remove and reinstall the mod once. I used my GPS (smartphone) to record data, and I processed the data in my own spreadsheet.



Average of all B runs: 0.326
Average of all A runs: 0.358
Improvement -9.7%

Unfortunately, there are some significant caveats for my data. For one thing, I've never been successful in getting a curve fit to give me a reasonable differentiation between Crr and Cd - meaning I have never measured Crr. Instead, I just assume it is 0.012, because I think it's a reasonable number and I think it puts my Cd numbers in the ball-park. But more importantly for this test, I was consistent.

The real problem is I think the error bars on my methodology are large. That should be evident looking at that bar graph. Run A1 in particular had some GPS drop-outs and the resulting choppiness in my chart makes it subject to interpretation. It would be best to drop that test and redo it. Unfortunately - I'm not going to.

In all, when I claim a 10% drag reduction, there is a large error bar that should go with the claim. My gut feel is that my coast-down results are not too far off, but this really isn't hard proof, folks.

I have some improvements I might try on this, even though I've already over-modded:
1) Close the sides. Additionally, I think if I put square sides to enclose it, I imaging extending the sides forward to create a barrier between the air flowing up over the bullnose and the air flowing off to either side. Right now there is probably turbulence around the sides.
2) Duct a cooling inlet from the bullnose to the lower grill.
3) Maybe add another frame member to stiffen the top edge (this would also reduce the chance of my framing members puncturing the radiator in a fender-bender), then add a large weatherstrip or foam tape to close off the upper grill.

Attached Thumbnails
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Name:	2012-08-31 bullnose1.jpg
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Name:	2012-09-01 bullnose2.jpg
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Name:	2012-09-01 bullnose3.jpg
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Name:	Coast-down results.gif
Views:	260
Size:	9.8 KB
ID:	11441  
Attached Files
File Type: zip CoastDown.zip (96.2 KB, 23 views)

Last edited by christofoo; 09-24-2012 at 09:22 PM.. Reason: change in conclusion :(
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Old 09-02-2012, 11:35 PM   #2 (permalink)
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Those open sides mean that you're creating a huge low pressure area on the front behind your addition, and air is certainly rushing into that low pressure area. I would recommend covering the whole front of the car with that shape, and making it all closed off.
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Old 09-03-2012, 12:13 AM   #3 (permalink)
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Quote:
Originally Posted by MTrenk View Post
Those open sides mean that you're creating a huge low pressure area on the front behind your addition, and air is certainly rushing into that low pressure area. I would recommend covering the whole front of the car with that shape, and making it all closed off.
What about the the blinkers (if it isn't clear from the picture, they are under the bumper). Can you think of a solution that doesn't require a compound curve in transparent plastic, or 5 different components? Probably the easiest thing to do is to move them to the bullnose - but even that is too much.

"Brutally simple" is a key requirement for this one, although I may well make a more sophisticated bullnose for the Civic.

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Last edited by christofoo; 09-03-2012 at 12:21 AM..
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Old 09-03-2012, 12:21 AM   #4 (permalink)
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similar to a Geo Metro

i have done /
am doing something similar to a geo metro
only
i removed the front bumper cover and made a steel frame down low that extends forward of the bumper re enforcement
slips into steel tubes
3/4 inch EMT tubeing welded to lower tow eyes on the frame
to support the lower part of three layers of coroplast
alternated the grain for stiffness , and it is very stiff indeed

a definate improvement per seat of the pants
i have tried two versions , currently the version is flat and covers more than you have but corners are open , tilted back slightly about 10degrees
that version has more drag than the
vertical version with no tilt to the rear of the car

i get rude comment s ,
but
it is a work in progress
i can test for drag delta at speed by comparing calculated load values at consistent speed and temperature -
i did not think there was a need as i assumed the 10 degree tilt would be a improvement
now i have to test it to confirm that it is not and then undo version 2 depending on the outcome

do not assume anything
test as best you can , with what you have to work with

in the end google "Meridith effect" as you will need an opening for the radiator , may as well make it do something , how ever slight the contribution will be .
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Old 09-03-2012, 12:59 AM   #5 (permalink)
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christofoo, The blinkers are located in the sides of the headlights, and I believe the lower 'lights' are just reflectors, but I'm not sure.

Moving lights to the bullnose = extending the wires and cutting holes in your bull nose. Just sounds like a Saturday afternoon to me.

Brutally simple: Extend the nose in a straight line to be flush with the sides of the car body, then extend flat panels back to meet up with the car sides.

Simple: Use cardboard to shape out the rest of the nose (for compound curve), then stitch it together somehow and fiberglass it.

Simple: Do the curve the other way around, like an air dam, matching with the sides of the car, and sloping in a way that it would fit the front of the car nicely with some manhandling.

Somewhat challenging: Combine the air dam profile and the smooth nose profile with lots of cardboard and then fiberglass.

Challenging: Do a 3-D model of what you want, make a mold, then fiberglass or carbon fiber.
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Old 09-03-2012, 01:22 AM   #6 (permalink)
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Quote:
Originally Posted by MTrenk View Post
christofoo, The blinkers are located in the sides of the headlights, and I believe the lower 'lights' are just reflectors, but I'm not sure.
...
That's how every other car blinks. On this car, the ones under the bumper blink, the ones on the sides of the headlights are parking lights. I checked, I remembered it right.

Your ideas are good ones, I'll weigh them carefully before I go for v2. It really still depends on how I define brutal.
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Old 09-03-2012, 03:31 AM   #7 (permalink)
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Just gotta decide how bad you want it! =P
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Old 09-03-2012, 09:48 AM   #8 (permalink)
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Data rules

Quote:
Originally Posted by christofoo View Post
I actually decided once that I would not mod my 89 Corolla, considering how little I drive it (like 1,000-1,500 miles a year). Somehow I got amnesia and started modding it before I remembered my own injunction. Apparently no car is safe when my family is out of town.

This is somewhat Aerocivic inspired - most EM front-end mods consist of air dams and grill blocks, but I felt like the 89 had a particularly poor nose shape to start with (newer models are generally better than this). So I thought it would be good to lower the point of stagnation, smooth the transition to the hood, and block some of the air going to the grill at the same time.

My other design criteria here is to keep it brutally simple. This is an old car, I might not have it 3 years from now, and the mods just aren't going to see a ton of use (well, probably - maybe I'll love it more as it gets better).

Step 1: Bend some metal strips into a frame

Step 2: Pop-rivet coroplast onto frame. I note that steel was not a good choice. Aluminum drills much faster and also won't rust. But I had a bunch of steel strips lying around for some forgotten project.

Step 3: Paint, drill and tap for screws to attach license plate (required in Utah).

Step 4: Zip tie onto car.

This car has a carburetor (no FE instrumentation), so I did a coast-down from 40 to 25 MPH. Since I already had the bullnose on the car when I started, I decided to shake things up and do B-A-B testing, that way I'd only have to remove and reinstall the mod once. I used my GPS (smartphone) to record data, and I processed the data in my own spreadsheet.



Average of all B runs: 0.326
Average of all A runs: 0.358
Improvement -9.7%

Unfortunately, there are some significant caveats for my data. For one thing, I've never been successful in getting a curve fit to give me a reasonable differentiation between Crr and Cd - meaning I have never measured Crr. Instead, I just assume it is 0.012, because I think it's a reasonable number and I think it puts my Cd numbers in the ball-park. But more importantly for this test, I was consistent.

The real problem is I think the error bars on my methodology are large. That should be evident looking at that bar graph. Run A1 in particular had some GPS drop-outs and the resulting choppiness in my chart makes it subject to interpretation. It would be best to drop that test and redo it. Unfortunately - I'm not going to.

In all, when I claim a 10% drag reduction, there is a large error bar that should go with the claim. My gut feel is that my coast-down results are not too far off, but this really isn't hard proof, folks.

I have some improvements I might try on this, even though I've already over-modded:
1) Close the sides. Additionally, I think if I put square sides to enclose it, I imaging extending the sides forward to create a barrier between the air flowing up over the bullnose and the air flowing off to either side. Right now there is probably turbulence around the sides.
2) Duct a cooling inlet from the bullnose to the lower grill.
3) Maybe add another frame member to stiffen the top edge (this would also reduce the chance of my framing members puncturing the radiator in a fender-bender), then add a large weatherstrip or foam tape to close off the upper grill.

(I was going to attach my spreadsheet, but apparently the OpenOffice file type .ods is not allowed. I would convert it to Excel, but I used a "multiple-operation", which I know doesn't convert automatically.)
Thanks for sharing your data. I agree about measurement error being a big grain of salt. I think an interesting plot would be all 6 coast-down curves together. Use two colors for A and B runs. (I'm a data geek - shrug.)
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Old 09-03-2012, 11:28 AM   #9 (permalink)
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I agree that moving the blinkers would fall under the category of simple. A little fiddly and an afternoon of time, perhaps, but simple. Go ahead and extend that bullnose to the width of the car. You're in this deep, go for it!

And, if you score the coroplast between the flutes, about every 3 or 4 flutes apart on the backside of the curve, it will follow that curve nicer.
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Old 09-03-2012, 04:59 PM   #10 (permalink)
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I realized the reason my data seemed subjective is because it used the first data point as the initial speed for the model. But since the GPS exhibits noise, there is some error in the first data point. And since I can slide my starting point around, that adds a subjective element. Error in starting speed will translate into an error in Cd.

I made the model initial velocity a fit parameter instead. The subjectivity in my data analysis disappeared.



This data is garbage. Probably my bullnose has no effect, at least in this incarnation.

I have always felt like the drag in my car goes down after it's run 5-10 miles, especially in cold weather. One day I jacked all the wheels up to figure which breaks are dragging, and I found that the front wheels are at fault. But I don't think it's the breaks. I can't hear any rubbing or sliding at all. It must be a differential or the transmission. (Yes, it was in neutral.)

I think what we're looking at in this chart is a change in temperature and viscosity of an oil that needs to be changed. The manual transmission is the most likely candidate. This car has 222k on it, there's a decent chance is has the originial manual transmission, and there's a decent chance the transmission oil has never been changed.

The only thing this chart suggests to me is that my impressions were correct and until I fix it there is no point in doing any drag testing on this car. (Or maybe it would work out okay if I did a warm-up drive first, but it would still be a wild-card.)

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Last edited by christofoo; 09-03-2012 at 05:20 PM..
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