( POSSIBLE ) Invite to the folks at A2 wind tunnel for a one time Q&A session here.
 

Hey everyone, I'm not sure if they have enough time to drop by the forum, but the guys at A2 windtunnel MIGHT be able to answer a few questions.
Please think of what you would like to ask and post in this thread.
Please limit the number of questions you ask, since their time is limited .
Nothing is set in stone regarding this, since it is just an invite, but I did speak with Geoff earlier today, and he says he will ask his dad about it.

And FYI Gary Eaker ( the dad ) personally worked on the aerodynamics on the EV-1 !
This is the same guy that dropped the cD on a 1981 Camaro to an amazing .201 !

- Thanks !

It's hard to think of something that's not too specific. How about: What are the popular misconceptions?

'questions for Geoff and Gary and Mr. Romberg'
 

Since fuel economy for ICE vehicles and 'range' for BEVs is of much interest, and since low drag factors so strongly into that calculus; in light of Wolf Hucho's comment in 1986 that, Cd 0.09 was 'technologically feasible', I'd be very interested in knowing how they might navigate that magnitude of drag reduction.

Question 1: When cars are being tested in the tunnel, is suspension height locked or left free to react and measured or tested both ways?
Question 2: how much impact does an operating engine at speed have on results, air intake, fan, exhaust, etc?

Here are a few questions I have, since I see there are not that many posted in the thread:
Blunt fronts, versus pointy front ends.
These two cars have the exact same cD ( nevermind cDxA in this example )
https://ecomodder.com/forum/attachme...1&d=1680472072
https://ecomodder.com/forum/attachme...1&d=1680472171
This car you tested had a .201 cD
https://ecomodder.com/forum/attachme...1&d=1680472891
, yet this other one had a .21 cD - so actually higher !
https://ecomodder.com/forum/attachme...1&d=1680472961
Of what importance is a "pointy" front end at normal road speeds ?
How does the increase in pressure on a blunt front effect drag ?
In these examples, the car has a very blunt front :
https://ecomodder.com/forum/attachme...1&d=1680473467
How does the air stay attached with such sharp edges at the corners ? ( in green )
https://ecomodder.com/forum/attachme...1&d=1680473693

And on this other car, how does air remain attached, despite the flat, upright windshield ?
https://ecomodder.com/forum/attachme...1&d=1680473746

On the example Camaro above, there is also a large portion of the tire exposed to the wind ( in green on the image ) Gary tested some side spats that one would think would deflect air away fron this area, yet they did not change the cD.
https://ecomodder.com/forum/attachme...1&d=1680474020
Finally, since the Lexus LS430 had such a good cD ( the .25 example at the start ) yet has a 3 box design, could the car do even better with a boattail ?
( silly looking, yes, but as an example )
https://ecomodder.com/forum/attachme...1&d=1680474279
All these questions have been covered on this forum , but I would like your opinions as well.
- Thanks !

seems like optimal front is the '' indented front'' like teslas, mercedez eqxx, hyundai ioni 6 and so on... feeds air into the air curtans

Hello everyone. I have phone Q&A session with Gary Eaker of A2 tomorrow.

He prefers to speak over the phone, rather than type.
Therefore, I will ask him some of these questions and try and post back to the forum with his reply.

If you have any other questions for him, please post them to this thread.

ask if they do any youtuber collaboration discounts

additional Questions:
#3 what is the max speed they test at?
#4 how many runs per set-up to verify/avg results for each modification?
#5 Is any tuff testing w/video possible during test runs, lighting, thru viewing window, etc?
#6 Are there any general suggestions to give regarding the sequence of items tested, as they are likely to interact with each other, without excessively having to take steps backwards? Like work with the front of the car modifications first, and then start at the back or at both ends of the car alternating modifications?
#7 For best tunnel management, start with all mods in place and test by test remove a modification, as removing is often faster than installing?
#8 what is the time usually allocated for just one test run for one set-up, not including any set-up or modifications or reruns.
#9 If one has as primary objective F&R DF measurements with drag considerations secondary, is there any significant difference in the test programs vs mainly looking for drag reduction?

Awesome thread, somehow, I missed this one?

I plan to call this evening, since I missed the early hours that I was given to call ( I was at work )
And just FYI folks, some of these questions posted here are in the FAQ section of their website. A2wt.com

So by all means edit my listed questions, as many are addressed in FAQ.
Thanks

No, I didn't mean it that way. I just added that to inform everyone and not just you.

:)

Regardless, the shoe fit, don't want to waste your efforts/time, and yes the site's FAQ is useful and informative.
Enjoy your chat.

I visited the facility years ago, can't wait till I haul my junk up there, and btw I would welcome any free day of test help doing my set-ups, etc, but mainly with somebody with a similar car and goals, as it should be a learning experience at little expense, and I am not a racer so no need to hide anything learned.

I had a conversation with Gary Eaker late yesterday.
I recorded the conversation so that I could go back and condense it.
I'll post back when I have gone through it.

I think Phil ( Aerohead ) would be the ideal person to do a better job of talking with the guys at A2.
In fact, most of what Gary spoke about has been posted here by Phil.
A lot of the cars Phil has mentioned in the past are ones that Gary did the aero on too, so I know these two guys would have a lot to talk about.




I

Can't sleep with anticipation.
Any update?

Sorry for the delay.
A lot of what Gary mentioned as aero information Aerohead has mentioned in the past here on the forum.

There are a few interesting bits that he mentioned about the EV-1 and such, but again it may be something Aerohead has posted in the past.

I have taken a few notes from the conversation, and will post them here later, but I still have to go through the remainder of the conversation.

I have also been distracted with my car project.

Again, sorry for the delay.

His reply was that people think that factory aero kits work, when in reality, they are designed to just look good and sell the car.
He didn't go into much detail about less obvious misconcetions, such as aero ideas that have been updated with new data.

Phil, I think you might have to ask this question yourself, since you can understand what his reply was. He spoke about how that drag is being reduced each decade, but I didn't understand his answer on how to get to .09 cD.
I'd love to hear a conversation with you two in the future.

1)In the A2 the car is supported by the springs and shocks.
Their Aerodyne facility has electromechanical rams.
He said when you test a car, you wantbcc the car "stiff"; since even minor variations in ride height can have a huge difference.
I got the impression that the car suspension is not test locked and free at the A2.
2) "Not as much as you would think " was Gary's response on the engine aero effect.
He stated that the engine effect is minimal compared to the effect caused by cooling flow.
And the exhaust is "lazy, and doesn't shoot out like a rocket out the back "

Geoff had a comment about this.
There is a YouTube guy 'Cleatus McFarland' that has thousands of followers and brought his car to A2.
Despite having their Facebook page "blow up" with "likes" and followers, they didn't get any business.
So this is not likely to be something they would be interested in.
I also asked Gary if they would be interested in doing aero consulting through email / video chat ( Charging a fee to give aero advice for those that could not test at the tunnel )
Gary said he would pass on the idea, since he would feel resposible if he gave advice that turned out to not be correct .

[QUOTE=j-c-c;682471]additional Questions:
#3 what is the max speed they test at?

I think it is 80 MPH, but thst can simulate over 200 MPH.
#4 how many runs per set-up to verify/avg results for each modification?
sorry - didn't ask

#5 Is any tuff testing w/video possible during test runs, lighting, thru viewing window, etc?
Yes :)

#6 Are there any general suggestions to give regarding the sequence of items tested, as they are likely to interact with each other, without excessively having to take steps backwards? Like work with the front of the car modifications first, and then start at the back or at both ends of the car alternating modifications?
#7 For best tunnel management, start with all mods in place and test by test remove a modification, as removing is often faster than installing?

For both of these questiins, his reply was that it is bestvto start with everthing in place, and then remove each item

#8 what is the time usually allocated for just one test run for one set-up, not including any set-up or modifications or reruns.
Sorry I'll have to look that up.
#9 If one has as primary objective F&R DF measurements with drag considerations secondary, is there any significant difference in the test programs vs mainly looking for drag reduction?
Sorry - didn't get that question in.

Test
 

Test

• test
• test2

Test
 

So - here are some random bits from the conversation with Gary Eaker :
When asked about how a car with a flat front end, or flat windshield can still have good aero, he replied that you can have good aero if you curve the edges on a "barn door" at 80% flat to 10% curved.
You would end up "Almost as good as a nice round hemispherical nose. It's not the ideal though ".
"A soft plan view desn't really buy you much as long as attached flow is retained ."

• On the roaster image I posted with attached flow, there is indeed a pressure bubble at the base of the flat windshield that is causing air to flow up and over the roof.
  https://ecomodder.com/forum/attachme...1&d=1681864432

The most important factor in that car for good attached flow are the radiused edges. ( The "critical radius" )

He mentioned that when designing the GM Impact ( early EV-1 ) they found that :

• Giving the car a 'sportier' windshield for styling caused more drag, since it sent air over the sides of the car.
• Fender covers ( wheel covers ) - " More wasn't that much better "

• The EV-1 backlight ( rear window ) taper is "too steep" for good attached flow, but only in 2D
• Plan taper angles result in good flow. ( EV-1 ) But the two angles have to be matched just right, or you get trailing vortices, which can really kill your drag.
• Besides the boattail, "fender flares" were added in front of the front tires on the Ft.Stockton 'Impact' car that went 183 mph, and got to .137 cD

• An underbody panel came loose and fell off on the Impact / EV-1 and the drag went down, much the same way a 3/4 toneau cover helps on a pickup, or a box cavity works.

• Gary is most proud of two cars - the Impact at .137, and Bobby Alison's '87 Buick Le Sabre - as raced, the car had a .237 cD

https://ecomodder.com/forum/attachme...1&d=1681867166

• Don't go too long on a design, or viscus drag results in separation

• You want the pressure coefficient at the rear of the car to be as low as possible.

• When the Citation IV was created, the 'shell' tested at .14 - G.M. produced a drivable car, and the cD went to .28 ( " cooling flow,wider tires, exposed wipers, moudings, less efficient wheel covers, etc

The G.M. team then did a coast down test on the driveable car and concluded that wind tunnel testing was not a good way to predict real world cD ( When the opposite was true, and in reality the car now had a .28 cD.
)

• Notch angle is just as important as backlight angle on a design.
• A rear window with perfect attached flow will show a pressure bubble at the base of the window when a rear deck is added. This would have people saying " Oh that must be bad for drag" , but it's not due to the Adverse Pressure Gradient

When trying to get the record for the stock bodied car class at Bonneville on a 1988 Firebird, they couldn't do much besides remove mirrors and lower the car.
Since the car is a "bottom breather" they didn't have to do any grille blocking, but they still got good results by adding ultra fine screen at the entry to the radiator inlet under the nose.
The car ended up with a .23 cD
https://ecomodder.com/forum/attachme...1&d=1681867795
https://ecomodder.com/forum/attachme...1&d=1681867856

Sorry for the delay folks. I recorded the conversation on my laptop, using a program I had never used.
The converation was over two hours long, and trying to pause, and then restart the conversation results in it skipping to the start all over again, so I did my best to scribble some super messy notes.
I know a lot of information I posted is info you guys already know.
I would really like to get someone knowledgeable on aero to do a proper interview.
I appreciate the time that Gary Eaker took to talk with me.
He prefers a phone conversation over email or a forum, so that makes it a bit hard i guess.

My go-to example is always the Beetle. If you compare the contour around the windshled's changes from the 1950s through the 60s, you can see this. The windshield grew but the bootom edge didn't move. The contour radius in the upper corners did.

Well two points combined here makes me wonder. The Bubble at the front windshield base helps smooth airflow over the car. So why is it the drivable car they use that location for engine air intake to reduce that bubble?
I find it hard to believe any power gain from higher intake pressures offsets aero losses/drag/DF from reducing that useful bubble.

.

The pictured Nascar the A2 tech is so impressed with does not have a raised cowl, has no provision to exhaust air into cowl area and seldom runs below 150mph, other than that it all makes sense, really, but ducting air from in front of the radiator would solve the two noted advantages of cowl air and not potentially reduce negatively the cowl bubble at high speed.

aerohead put a lot of work into splashing a fiberglass hood bubble off a Viper windshield, put it on one of his pickups and ran it at Bonneville. [citation needed] Concluded the size of the bubble doesn't make much difference.

#4, 8, and 9
 

[QUOTE=Cd;682913]#4 there would just be a 'run' per configuration. Repetition would just reproduce drag and lift data already captured. The load cell strain gauges are that accurate.
#8 Once a configuration is attained, you'd have your result within 7-minutes.
( with 'tear-off' modifications, you're within a minute of re-starting the fans to measure your next configuration ).
#9 With each configuration, you'll receive overall drag, plus lift/downforce over each axle, at zero-yaw condition. The velocity-squared, and velocity-cubed relationships allow extrapolation to 200-mph conditions, since all we're talking about are frontal area-based coefficients.

ask yourself
 

Thanks.
Geoff thought I ought to talk with his dad on the phone, but I figured his, and Mr. Romberg's time was too valuable to burn on the phone, and I could wait until I got there with Spirit and the newest mods before pestering them to death.
Geoff did share some extremely powerful info regarding A2, AeroDyne, and Windshear ( Gene Haas Racing ) collaboration studies, which I should leave to Geoff or Gary talk about, if willing, as I interpreted the data as confidential.
--------------------------------------------------------------------------------------
The Cd 0.09 WILL be an interesting 'story.'
During all the hoopla over Sunraycer, one automotive journalist mentioned that Sunraycer , with it's full wheel fairing package ( not raced with ), measured the lowest Cd ever experienced for a 4-wheeled vehicle, at Cal Tech's GALCIT tunnel (below Walter Korff's 'Goldenrod, Cd 0.1065 ), in the neighborhood of Cd 0.089. If factual, this would place Sunraycer below HONDA's 1993 Dream.

'Bubble'
 

1) the 'bubble' dates to the ( Ludwig )Prandtl 'surface of discontinuity' reported on by Frederick Lanchester in 1907. Air will 'figure out' how to get around an object which is attacking it by forming a perfectly streamlined phantom shape ahead of the actual structure ( seen in all wind tunnel smoke flow, and water-table flow images).
2) The flow attachment is due to a 'critical radius' at the leading edge at the windshield header and A-pillars.
3) On NASCAR racers, if you relied on the forward stagnation point for engine air you'd be screwed during a two-car, or three-car draft. By moving the combustion-air inlet to the cowl 'bubble', you get some fraction of stagnation pressure, and it's further away from the track surface, which might be 140-F on a summer race day, providing higher charge density than at the radiator inlet.
4) And even at 220-mph at Daytona, ram-air isn't as impressive as one might think. The volume of air which the engine is ingesting from this 'bubble' is miniscule compared to volume available from the oncoming flow.
This stagnation bubble travels along with the car, and the kinetic energy robbed from the free-stream to maintain it isn't remarkable, compared to the wake.

I don't know what the relative air temp distribution is above a race track surface based on elevation. I suspect its mimical above 6" in all but the stillest of air for the first car, and likely nonexistent for every car thereafter in the pack. I also suspect because of drafting the lead car is the car producing the most power output in a pack over time and the one car most dependent on every single hp any cooler air or ram effect provides, and the car that aero slickness is most beneficial. My suspicion, cowl intake air location in NASCAR is more just a holdover from the 60's. On a slightly related note, I do know that rear center exhaust exit location (David Pearson) was banned in the 60's in NASCAR because it prevented anyone drafting the lead car due to engine overheating.

'NASCAR'
 

1) from Chrysler's Romberg et al's reporting in 1971, the lead car receives a 30.1% drag reduction from the car behind them, while the trailing car picks up a 37.1% drag reduction.
2) From Gotz' commercial vehicle 'drafting' research we know that the car in a three-car draft would experience even lower drag ( 71% in the case of buses ).
3) rear exhaust outlets were banned because of carbon monoxide poisoning to the trailing drivers.
4) with respect to cooling, during the draft, the Cd of the second car has fallen from 0.315, to 0.198 ( in 1971), and because of the velocity-cubed power law of aerodynamics, the trailing car's engine is actually 'loafing', and it's heat rejection requirements extremely reduced. They could race 500-miles like that without event.