Quote:
Originally Posted by JulianEdgar
Just a point re testing. Some on-road testing can be spectacularly accurate and repeatable eg measuring lift and downforce, measuring surface body pressures. (ie don't throw baby out with bathwater)
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Absolutely!
Even with purely mechanical cable linkages and chart recorders,accurate lift measurements were conducted in the 1960s.
Scanivalves with either Magnehelics or U-Tube manometers have been successfully used to capture static pressure profiles around a body during road testing.
I should have prefaced my remarks with the caveat,that in my own personal situation,I neither had a safe venue,nor instrumentation of high enough sampling rate or resolution,to conduct coastdown measurements which would satisfy the SAE standard procedures and protocols,and deferred to the technical staff of CAR and DRIVER and their equipment at the Chrysler Proving Grounds at East Chelsea,Michigan.
The car was measured an a 4-load cell balance for accurate mass measurement for the calculations.
We had our own scientific-grade weather equipment with us.
Chrysler has a long,straight,level straightaway,perfect for the necessary back-to-back reverse-direction runs.
The Daytron-Messteknik optical 5th-wheel introduced no rolling resistance of it's own,and was state-of-the-art in accuracy at the time.
The surrounding trees offered wind protection,had there been any.
And CAR and DRIVER had their own software program for data reduction,to tease out each road horsepower for drag analysis.
Plus,the 8-mile oval,offered an absolute terminal velocity for comparison.
Between a record at World of Speed at Bonneville,the Chrysler Proving Grounds,and Glenn Scharf's help at the the GM Aero. Lab,we got a good agreement on drag.Cd 0.235 for the modified 1984 CRX HF.
And CAR and DRIVER cut me a little break on their fee.