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

[Cd]

Originally Posted by Phase

ask if they do any youtuber collaboration discounts

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 .

[Cd]

[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.

[Cd]

Test

• test
• test2

[Cd]

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.
  

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

• 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

[Cd]

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.

[freebeard]

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.

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.

[j-c-c]

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.

[freebeard]

https://www.summitracing.com › search › part-type › hoods › hood-style › cowl-induction
Cowl Hoods | Summit Racing
A cowl induction hood is raised in the middle, allowing for a taller intake manifold, and has an opening at the trailing edge. At high speeds, the cowl takes advantage of the higher air pressure in front of the windshield to draw in more power-building cool air. At lower speeds, the cowl lets hot air out to help keep high-horsepower engines cooler.

.

[j-c-c]

Originally Posted by freebeard

.

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.

[freebeard]

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.