Automotive Aerodynamics (video series)

[gumby79]

Originally Posted by aerohead

So far,I think that 20-21% drag reduction maximums have been reported for caps.

What were the mpg improvements @20-21%drag reductions??
This is why I am asking for help in finding "facts"about what actually happened to improve FE from 18.237us mpg average up to 23.067 average a 26.458% increase. The only time I've had the cap off in the last 10,000mi I had a load on or severe weather
I anxiously awaiting the specifications for small diesels. As I would like to be able to publish reliable statistics.

Source for 2:1
Secrets of Better Fuel Economy
The Physics of MPG
pg 4 ph2
https://www.google.com/url?sa=t&sour...D_FWTQjBg3_j1A

Thire is a 2:1 drag(drag = Cda correction may be necessary ) to mpg on over the road diesels semi

Originally Posted by aerohead

So far,I think that 20-21% drag reduction maximums have been reported for caps.

I will take this as a compliment that my design is slightly above average especially for a blind shot in the dark with a 18 year old(as in 1998) idea from high school. Thankyou Aerohead.
A 26.458% gain on FE at any raito evan 1:1 is well above 20-21%cda avrage gain ,for a cap.
My last 3 trips to Helena Montana from Anaconda,Mt 200 mi roundtrip over 2 passes Have averaged 25.095mpg. 1 ea. 60mph (27.705mpg) 65mph(24.27) and 70mph(23.11) . With 1200lbs in tools in back under cap (the reason i haven't completed a Terminal Velocity Test the junk in my trunk will yield an invalid test )

Originally Posted by Aerohead

Hucho shows a different CdA/MPG relationship for Diesels compared to gasoline vehicles.I don't have his book with me.Perhaps a member can help us out on this one.
These relationships are predicated upon steady-state highway cruise mpg,not coasting or coastdowns.
Also,we have no idea what the engines BSFC is doing with the modifications,and all the relationships presume a constant BSFC,or gear-matching to achieve a constant BSFC which may not reflect reality.

Agreed gas vs diesel

the cost down( terminal velocity test is what i meant) was in reference to me wanting to do more testing. Mpg alone has been and will always be an unbelievable test hear@ ecomodder and in reality/life .
I am aware that a terminal velocity test will not give me the stock cda. However terminal velocity aba test ,I believe and correct me if I'm wrong, give the % improvement. And will not involve the motor in neutral.
This is my proposed test site
https://goo.gl/maps/ufJoDps6hcN2

stock sealed injection pump
a 16sq cm housing
Exhaust manafuld and turbocharger wrap
End of list
Full list of mods to motor
GraysGarage has showed that he has the necessary equipment to print the correct1:10 modle. Reference. Watch "Automotive Aerodynamics Ep. 7: Spoilers and Gurney Flaps for Racing" on YouTube
https://youtu.be/vzMe1e9fE50
This with the 1:43 model and some basic measurement angle of body ground clearance and I'm shure a couple more. Should be able to gert some reliable specifications. Thank you as your input is helpful

[gumby79]

Also I have refrained from some simpler mods. Moonies , finder, skirts, and not so simple mods ,belie pan, side skirts ,bumper rellocation/redesine entire front end to be more like a vw bug instead of a stack of bricks ,air dam, hood angle, rain gutter delete ect Ect ...
Why most would ask ?
Disbelief. I was expecting a 10-15% improvement and surprised myself with 20%+,haveing stumbled across some thing that would need better proof than simple manipulateable MPG
so what test will be expected as un irrefutable proof and not a gusstament 100%macanical diesel no computer or OBD 2
One major differentance that may have yealded the above average results is the8" past the tailgate. A cap crossed with a camback. A design aspect not seen on other caps . This is affecting the trailing air as well, not just top/sides. This feature I've noticed being implemented on '14 and up full size pick up trucks accrost the top of the tailgate. Also on mini vans, and cars .





How much can this bump help ? And will it work with other cars/trucks as mod?

[freebeard]

When you type do you see red squiggly lines under some of the words?

Do you have, or know anyone who has an iPhone? There exists an iPhone app called Autodesk 123D Catch. With that you could walk around the pickup and take 32-100 pictures of it from various angles and distances (close-ups of the wheelwell, etc.) and recieve a high-resolution triangulated polygonal model of the truck as it exists to a higher level of precision than a typical 18th scale model.

Then there's some mumbly hand-waving to get to a 3D printable file.

Then the 3D printing is available as a service over Internet and probably as a walk-in service in major cities.

[gumby79]

Android no spellchecker

[freebeard]

123D is available on the Android platform. Possibly through the Google Play store?

[aerohead]

Originally Posted by gumby79

What were the mpg improvements @20-21%drag reductions??
This is why I am asking for help in finding "facts"about what actually happened to improve FE from 18.237us mpg average up to 23.067 average a 26.458% increase. The only time I've had the cap off in the last 10,000mi I had a load on or severe weather
I anxiously awaiting the specifications for small diesels. As I would like to be able to publish reliable statistics.

Source for 2:1
Secrets of Better Fuel Economy
The Physics of MPG
pg 4 ph2
https://www.google.com/url?sa=t&sour...D_FWTQjBg3_j1A

Thire is a 2:1 drag(drag = Cda correction may be necessary ) to mpg on over the road diesels semi

I will take this as a compliment that my design is slightly above average especially for a blind shot in the dark with a 18 year old(as in 1998) idea from high school. Thankyou Aerohead.
A 26.458% gain on FE at any raito evan 1:1 is well above 20-21%cda avrage gain ,for a cap.
My last 3 trips to Helena Montana from Anaconda,Mt 200 mi roundtrip over 2 passes Have averaged 25.095mpg. 1 ea. 60mph (27.705mpg) 65mph(24.27) and 70mph(23.11) . With 1200lbs in tools in back under cap (the reason i haven't completed a Terminal Velocity Test the junk in my trunk will yield an invalid test )


Agreed gas vs diesel

the cost down( terminal velocity test is what i meant) was in reference to me wanting to do more testing. Mpg alone has been and will always be an unbelievable test hear@ ecomodder and in reality/life .
I am aware that a terminal velocity test will not give me the stock cda. However terminal velocity aba test ,I believe and correct me if I'm wrong, give the % improvement. And will not involve the motor in neutral.
This is my proposed test site
https://goo.gl/maps/ufJoDps6hcN2

stock sealed injection pump
a 16sq cm housing
Exhaust manafuld and turbocharger wrap
End of list
Full list of mods to motor
GraysGarage has showed that he has the necessary equipment to print the correct1:10 modle. Reference. Watch "Automotive Aerodynamics Ep. 7: Spoilers and Gurney Flaps for Racing" on YouTube
https://youtu.be/vzMe1e9fE50
This with the 1:43 model and some basic measurement angle of body ground clearance and I'm shure a couple more. Should be able to gert some reliable specifications. Thank you as your input is helpful

*At the time Texas Tech did their research,the metric they were using was that a 2% drag reduction would relate to a 1% hwy mpg improvement (not EPA HWY,just constant-speed 55-mph cruising on a straight,level,dry,windless stretch of highway after a full warm up.Based upon that,the 20-21% delta Cd would mean about a 10% mpg improvement.And they are assuming a constant BSFC for the engine.
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*As to the coasting,the Society of Automotive Engineers does not recognize 'coasting' as a reliable means to ascertain drag information.
*They do allow 'coastdown' testing which requires rigorous data acquisition/accounting and very precise measurements for validity on a road course which also satisfies rigid specifications.
*Also,top speed remains an avenue for which to reverse-engineer drag coefficients based upon 'new' top speeds attained after streamlining.I've attempted top speeds twice at Bonneville,however it was a bust,as it created more questions than answers.I wouldn't recommend top speed testing for any U.S.-spec car,since their 'top speeds' aren't really their actual top speeds unless great expense is paid to modify the power train to enable them to actually reach their top speed potential first before beginning any modifications.Euro-spec cars would be a different story.

[aerohead]

Originally Posted by gumby79

Also I have refrained from some simpler mods. Moonies , finder, skirts, and not so simple mods ,belie pan, side skirts ,bumper rellocation/redesine entire front end to be more like a vw bug instead of a stack of bricks ,air dam, hood angle, rain gutter delete ect Ect ...
Why most would ask ?
Disbelief. I was expecting a 10-15% improvement and surprised myself with 20%+,haveing stumbled across some thing that would need better proof than simple manipulateable MPG
so what test will be expected as un irrefutable proof and not a gusstament 100%macanical diesel no computer or OBD 2
One major differentance that may have yealded the above average results is the8" past the tailgate. A cap crossed with a camback. A design aspect not seen on other caps . This is affecting the trailing air as well, not just top/sides. This feature I've noticed being implemented on '14 and up full size pick up trucks accrost the top of the tailgate. Also on mini vans, and cars .

Attachment 19745
Attachment 19746
Attachment 19747
Attachment 19748Attachment 19749
How much can this bump help ? And will it work with other cars/trucks as mod?

As to what will pass muster as scientific proof,we may be looking at wind tunnel data.After 40-years,I'm not confident that Cd vs mpg relationships can be taken as gospel due to a myriad of variables which can affect on-road testing.
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*As to your 'over-length' cap,mine's the same way.I ran a verification run a few months ago at 55-mph and showed a 23.2% improvement over 'naked',but along with the cap,I also had a nose,4-skirts,most of a belly pan,and hood blister.
With the whole kit,I've seen a 59.6% mpg improvement on three occasions at this speed.

[gumby79]

https://www.aa.washington.edu/AERL/KWT/rateguide

Originally Posted by aerohead

As to what will pass muster as scientific proof,we may be looking at wind tunnel data.After 40-years,I'm not confident that Cd vs mpg relationships can be taken as gospel due to a myriad of variables which can affect on-road testing.
--------------------------------------------------------------------------
*As to your 'over-length' cap,mine's the same way.I ran a verification run a few months ago at 55-mph and showed a 23.2% improvement over 'naked',but along with the cap,I also had a nose,4-skirts,most of a belly pan,and hood blister.
With the whole kit,I've seen a 59.6% mpg improvement on three occasions at this speed.

Based on this your short ancer is 500usd per hr Times 9hr min. [4500usd] and this is the only non phd acceptable meteod
How many hr in the tunnel to get 23% or is this # just as bosga as my 8000mi TEST

[aerohead]

Originally Posted by gumby79

https://www.aa.washington.edu/AERL/KWT/rateguide

Based on this your short ancer is 500usd per hr Times 9hr min. [4500usd] and this is the only non phd acceptable meteod
How many hr in the tunnel to get 23% or is this # just as bosga as my 8000mi TEST

*Mercedes-Benz has a supercomputer CFD package that is within 1% accuracy.That's a really good agreement with empirical measurements in their wind tunnel.It requires over 24-hours of run time to calculate a single iteration of body change.
*The DARKO tunnel is $500/hr.
*The A2 tunnel offers a 1st-time users discount at under $500/hr for the 1st 2-hours.
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*Once the vehicle is inside the test section,centered, and strapped down to the load cells,you can accomplish one complete data acquisition run in 4-minutes.
*If you have taped-on mods,you can get quite a few runs in within an hour.
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*there is tunnel-to-tunnel variability as far as drag coefficients go,but we're slowly compiling a comparison list for some of that.
*my truck measured Cd 0.268-0.267 at DARKO.It might have shown Cd 0.244 at A2.Cd 0.218 without the mirrors.
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*my 23% mpg number is just tank mileage.It compares to previous non-boat-tailed highway runs.I have a 22-year, 392,000 mile fuel log database for the truck.
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*I feel like the tunnel data offers the best science we can get.Sure we can learn something from down-hill,or flat-land coasting,and mpg variability,but to really pin it down we need a lab environment like a wind tunnel.
*If you'll read the SAE Handbook requirements for coastdown testing you'll have to catch your breath when you realize what's expected to achieve meaningful results.

[freebeard]

3D capture your aerocap and truck, pay for a commercial print, and suspend it upside down in a flowing river (with a flat white plate for a photo backdrop) and generate your hydrogen bubbles with a laptop battery.

When it's all done you still have the model for a lawn ornament.