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

[aerohead]

[QUOTE=Cd;682913]

Originally Posted by j-c-c

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.

#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.

[aerohead]

Originally Posted by Cd

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.

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.

[aerohead]

Originally Posted by 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.

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.

[j-c-c]

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.

[aerohead]

Originally Posted by j-c-c

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.

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.