Note from Darin (admin): this installment is part of a series posted by Phil (aerohead) about the effectiveness of various aero mods - usually with quotations and citations to source data.
See the Aero mods data index here.
End note.
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More debris from the library. As always, it's a mixed bag spanning a few decades. The numbers should stand on their own merits, as they come from the big-boys. My own tidbits are courtesy, Southern California Timing Assoc., official timers for all F.I.A. land speed records. Images will come later, sorry! Many of the vehicles can be found through GOOGLE Images.
There's not a lot of info, so this will go pretty quick. Thing is, people have thought about these things and "looked into it". As George Santayana said, "those who refuse to learn from the past are doomed to repeat it." There's no reason why any ecomodder should waste time going down a trail that's been thoroughly flushed out.So here we go,and I hope it helps.
Internal-Drag
1938, windtunnel tests on the Adler/Jaray (on the car lots in Germany) demonstrate that blocking the grille achieves a 15-percent drag reduction, dropping the Cd from 0.38 to 0.32.
Walter Korff, in his recipe for a Cd 0.21 passenger car suggests that an idealized cooling system,with airtight inlet and outlet ducts properly positioned, can cut drag by 7.7-percent.
1963, Kelley and Holcombe, of GM suggest "The ideal circuit for an engine-radiator internal flow system requires a smoothly edged, clean intake opening that leads to a completely enclosed diffusing duct, permitting the velocity energy to be converted to pressure energy with low losses, minimum pressure drop across the radiator, and is directed into a contracting duct that exits the air at a convenient low pressure. It should be possible to accomplish the engine cooling job with little or no net loss in an efficient system."
1973, CAR and DRIVER's Pinto picks up an added 0.40 mpg with an optimized grille-block.
April, 1975, C and D's aerovan Dodge picks up a 3-percent drag reduction with optimized grille-block.
1975, Dr.Alberto Morelli designs all the best features into the cooling system of the CNR "banana-car", cooling system losses are cut to 0.008. Morelli observes losses in production cars up to 0.1. On CNR, an air-tight 4:1 diverging inlet duct, and four, air-tight converging exit ducts are positioned on the car such that air bleeds into surrounding air at same velocity.
1986, Fiat windtunel studies of large-scale models show cooling system drag at 6.9-percent. Sealing the system only cuts drag by 1.2-percent, as upper-body drag increases.
1987, Bridgestone/Firestone Test Track, Fort Stockton, Texas,U.S.A., In closed-course, l and speed record attempt, GM tapes-off cabin ventilation NACA inlet to minimize aero drag. Driver, A.J.Foyt, can only tolerate 5-laps in the car at a time before being overcome by alcohol fuel vapors.
July, 1991, Bonneville International Speedway, Wendover, Utah, the Phil Knox, 1984 HONDA CRX, 1.3-liter experimental streamliner : air-cleaner deletion returns no measurable improvement to top speed ( internal-internal flow).
Hucho publishes that cooling system drag can me minimized to 2-percent,drag as high as 10-percent has been observed.
General note, all NASCAR teams use the Korff/Kelley-Holcombe/Morelli/American Aviation P-51 air-tight divergent inlet duct. Kamm and others, since the 1930s have used critically-cited exit ducts for the exit flow. Ford and GM PNGV cars use rear, quarter-panel heat-exchangers to dispense with front grilles altogether, for sub-Cd 0.17 bodies. The Olds AEROTECH uses "ideal" heat-exchanger inlet and outlet ducts, borrowing from aviation oil-cooler technology and probably has no drag at all due to thrust from expanding air mass.
Cooling system drag constitutes about 12-percent of overall aero drag and its been demonstrated that it can be eliminated. Its under the hood and out of sight, but its something to think about.