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Old 02-17-2012, 12:08 PM   #11 (permalink)
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Quote:
Originally Posted by Cd View Post
My thought exactly.
The airdam most likely just adds frontal area.

A few panels underneath can still make it even better though, and i agree with Basjoos about the pontoons.

I have to wonder about the added frontal area they ( pontoons ) have in crosswinds though, but thats a thread i'll create all by itself.
If you look at all of the ultra-low Cd vehicles such as the solar cars discussed recently, none of them have airdams since you can get lower drag by combining a smooth underside with well faired wheels.

Although the Prius has a cleaner underside than most cars, there's still a lot of room for improvement since it is still fairly rough under them. By smooth underside I'm talking about a panel(s) covering the entire underside, not the scattering of small, sometimes rough, panels seen under most "aero" production cars.

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Old 02-17-2012, 10:11 PM   #12 (permalink)
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Thanks Doax I need to read through that again...

Got the pizza pan wheel covers on and rear wheel skirts on as well today...once I'm sure the wheel skirts are working good I'm going to re-make them out of foam and fiberglass so they look factory. I like the way the coro looks now though.

Was getting dark so I'll probably take some new photos tomorrow in the sunlight.








used this grease to make sure the trim rings would come on and off a little easier.






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Old 02-17-2012, 10:27 PM   #13 (permalink)
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Oh yea wife is going to film a tuft test Sunday...cut all the yarn today and told her the plan...I'm going to try some kind of temporary deck lid to see what angle it needs to be to keep flow attached as well.

I have around a 150 mile trip tomorrow which I have averaged 52 mpg stock with no mods. so I'm curious what if anything these will do?

Double checked the front damn and in the middle where it bowed up it is level or maybe slightly higher than anything under the car so it is not adding to the frontal area but I'm still not really happy with it...I guess it is good for coroplast but ???? when I bust out the foam and fiberglass to make some of these mods more "factory" looking I can shape it exactly how I want. I'll have to draw up something in paint and see what you guys think.

I didn't get the side skirts on yet and those are going to take a minute to get all setup nice and also be able to still get a jack under there when needed...I'm going to plan on doing the belly pan at the same time probably.
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Old 02-17-2012, 10:37 PM   #14 (permalink)
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Basjoos...I'm going to look at those solar vehicles some more and see just how they are setup but most of the ones I've seen really look like an airfoil for all the shapes, body, cockpit, wheel pilons...maybe I can get some more ideas tomorrow.

any thoughts on the angle of the front air dam? does it matter if it is flat or angled to toss the air over the hood...angled under I could see it wedging more air under the car.



like this guy but not as exagerated... Modified Honda CRX HF Wins Fuel Economy Competition with 118 MPG! : TreeHugger

I think that thing would get torn off in no time unless it was spring loaded or something.
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Old 02-18-2012, 02:33 PM   #15 (permalink)
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could be bad

From SAE# 860212,FIAT aero researchers found that a well conceived,fully detailed underside,without bellypan,added only 0.007 to their development models Cd.
They report that an airdam can actually increase the drag of a low drag car.
NASA's research,published in 1981,revealed that a cleanup of a vehicles nose would net less than a 5% drag reduction.Less than 2.5 % mpg for all your trouble and expense.
If you wanted a default design for you airdam,I would have you look at the Aerodynamic Streamlining Template thread.For speeds below 250-mph,it is recommended for low drag .There is a thread for a Prius boat-tail trailer.You can see what I did to the car.
Toyota has done a very good job with Prius.
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Old 02-18-2012, 05:38 PM   #16 (permalink)
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Nice prius! Good job with the dam and the wheel skirts. Subscribed
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Old 02-19-2012, 06:51 AM   #17 (permalink)
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The most important thing is can you see an improvement in the FE or not? Good aero can be felt during coasts -- how does the car feel when you drive? Are you carrying more speed than you used to?

How did you attach the pizza pans to the Prius wheels?
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Old 02-19-2012, 10:42 AM   #18 (permalink)
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[QUOTE=aerohead;287777]NASA's research,published in 1981,revealed that a cleanup of a vehicles nose would net less than a 5% drag reduction.Less than 2.5 % mpg for all your trouble and expense.
QUOTE]

Phil, can you please expand on that statement ?
By 'cleanup' of the vehicles nose, do you mean by adding an air dam, or something like the wedge on the CRX in the picture above ?
In reality, how much of a mileage gain do you think that CRX gained from the ramp at the front of the car ?
Although adding a pointed nose versus a blunt ( and preferably rounded ) nose to a car may lower the stagnation point and reduce A pillar votices on cars with steep transition angles between the hood and windshield, the angle on the Prius is very close between the hood and windshield, and therefore I'm guessing it would not show much benefit to add a wedge shaped nose cone versus a more rounded nose.
Is this assumption wrong ?

Jamesshaw89 - I'm really looking forward to that tuft test I cant wait to see the airflow around the A pillar area and around the wheel area .
Another interesing area is going to be at strakes just behind the rear wheels .

Can you throw some on the back of the car as well ? I'm wondering how large the vortices are back there compared to an average car such as my hatchback Civic.
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Old 02-19-2012, 07:27 PM   #19 (permalink)
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Just finished tuft testing, first time doing this and it was a blast! My daughter filmed this with my iphone 4 and I think she did a great job. My wife was driving the chase vehicle her ,2009 Dodge Charger, and we were on the phone so she knew what I was doing and when to pass me etc.

I didn't read in time to put tufts on the very back of the car I put them all over the side and part of the rear window, wiper blade, and fin.

Hopefully you guys can analyze these and give me some input...

I took the front air damn off after driving to Cincinnati and back and not seeing much of an improvement followed by a coast down test on a local hill I went from 40-56 on Friday without the damn, skirt or wheel covers! but today I went 40-53 with the dam/skirt/wheel covers and 40-52 without the dam but with the skirt/wheel covers. I was getting pretty annoyed after not going faster but maybe today I had a head wind and Friday I had a tail wind? I had driven the car for 20 minutes to make sure everything was warmed up...

OK some Numbers from the last couple days off the SG II

-home-school 55mph cruise control 12.1 miles car started trip fully warmed up 68.5 mpg
-school-coffee-home 55 cruise, 9.7 miles 53mpg - stop/coffee - 4.3 miles 72.5mpg - home...I need to figure out how to average this trip as SG split it into 2 trips with an average for each so average for the 13 miles is ??

-trip to flea market 55 and 65 mph cruise control 34.8miles 61.5mpg
-trip back from flea market-stop/subway-home 55 and 65mph cruise control 35miles 56.9mpg...note subway is the same place as getting coffee only subway home there was traffic and I could not use the electric much at all which cost me about 16mpg average for that last 4.3 miles!

I can get some insane mpg if I can get some rolling hills and stay under 40mph...this is why I'm REALLY looking forward to trying out a stick shift Metro sometime as I won't be limited to 40mph with EOC, and the prius engine randomly stays running sometimes even when your coasting under 40mph.

Tuft testing links...















While the front air dam was still on...


A clear shot of the rear skirt...there is very little clearance between the 1/2"x1/8" aluminum bar I used at the bottom of the skirt to keep the coroplast from rubbing on the tire, maybe 1/2" clearance from the tire.

I ended up using 3/4" #4 stainless steel screws from Lowes to mount the aluminum pizza trays on the trim ring...5 screws leaving one out where the fill stem thing is so when I pry the cover off hopefully that will be OK. So far maybe 200 miles on them and nothing is coming loose. NOTE look at where your trim ring is mounted to make sure the screws will not hit the rim when you try to put the trim ring back on. I also cleaned and put that marine grease where the trim rims snaps on so hopefully they will come off a little smoother next week when I check my tire pressure.

Front Air dam...I think I might need to put more effort into making it perfect instead of just getting it on there like making the shape like the front of a NASCAR and filling in the bottom of it instead of leaving it open. Integrating or adding wheel splitters in front of the front tires like on Basjoos car as well.

I think this is going to be a pretty good tank of gas as I was at 250 miles as it clicked to 1/2 tank left...I need to re-calibrate my SG II s well since it seems a little optimistic now compared to how it turns out after I fill up...I'll be filling up in the next couple days so we will see.
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Old 02-19-2012, 07:32 PM   #20 (permalink)
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CD how long of string do you want on the back of the car? is yarn big enough? I was thinking of taping some balsa wood sticks on there to extend the sting out a little farther on the back? would that help see anything?

Did I do the A-piller like you were looking for? I can add more and test again tomorrow.

I've got over a sheet of coroplast left so I'm seriously thinking of putting together some kind of short cam back on there for the trip to St Louis this weekend. Maybe I'll get it together tomorrow and do another tuft test before I go to school AND I'll be able to see what kind of MPG I get on the to school trip.

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