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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This was one that's been bashed around a bit and early on, I took the loose position that I thought most current rear spoilers were nothing more than styling gimmicks. Darin has generally defended them, and now, I believe I'll go "girly" on you all, and reverse myself. I've looked around in traffic and realized that some of today's carmakers are going to have to be dragged, kicking and screaming into at least the 20th-Century,if not the 21st.And I won't be targeting my frustration where you may think.
Current fuel prices are pushing some folks into entry-level economy-cars for the sake of stretching their petro-dollars,euros,yen,lira,piasters,and the like. And its these entry-level cars which seem to distinguish themselves as having some of the lousiest body shapes in the back,exactly where it does them the most harm. Kinda like eating a habinero pepper to take the heat of a jalapeno out of your mouth.
Anyway,it looks like decklid and rear hatch spoilers if properly conceived,could really help these mediocre shapes.Kind of like "Crisis-Fighter Rio" or"Crisis-Fighter Accent".So here's some more flotsam and jetsam thats accumulated around my place :
1961, ex-airman,U.S.Air Force,and American test-driver for Enzo Ferrari, Richie Ginther "invents" lips,spoilers,and flaps,and introduces them to the automotive racing world.
June,1962,HOT ROD Magazine:" If there is no lift there will be no induced drag."
January,1963,SAE Paper#649A
(Induced drag) from aerodynamic"lift results,owing to lower average pressures developed on the upper surface than on the underbody...In general,modifications to a body that will reduce areas of accelerated flow and the corresponding low pressures on the upper surface and areas of decelerated flow and the corresponding high pressures of the underbody will reduce aerodynamic lift."
June,1969, CAR LIFE Magazine:"SHOWDOWN FOR SPOILERS": AMC Javelin,roof-mounted spoiler produces no effects whatsoever,at velocities up to 115-mph. Pontiac GTO "JUDGE",tail-mounted,elevated spoiler: added front lift and fails to produce rear downforce.Chevrolet Camaro Z/28 flip-up rear spoiler alone,creates pitching-moment at 115-mph,lifting nose with 400-lbs ( 180-Kg ) force,and 125-lbs ( 56.5-Kg )downforce at rear.Best performance is from front airdam alone."Don't expect much from any of these spoiler designs at highway speeds,unless it's a front spoiler.....consider their function simply for looks."
March, 1974,CAR and DRIVER picks up 1.1-mpg with cobbled-up 6-inch-by-54-inch aluminum rear spoiler,angled back at 30-degrees.The Pinto's 26-degree hatch slope becomes a virtual 20-degree slope with the spoiler.
May, 1974,CAR and DRIVER's Crisis-Fighter Z-Car nets only a 0.2-mpg increase with 30-degree spoiler.They LOOSE 0.60-mpg with spoiler angled at 50-degrees.The Nissan 240-Z,18-degree rear-slope goes to 11-degrees (close to Kamm's recommended angle).
April, 1975,CAR and DRIVER's Project Aerodynamic Van: roof-monted spoiler @ 0-degrees angle-of-attack costs them 15 % in drag and aloss of 2.0-mpg.The same spoiler at 32-degrees increases drag 52 % with a fuel economy loss of 6.93-mpg.
Lotus Car's Lotus 78 Formula-1 car's ground-effects kit produces 550-lbs (248-kg) downforce at 60-mph,and 3,500-lbs (1583-kg) at 150-mph.F-1 cars have Cds of 0.80 to 1.40 due to induced drag of wings and tunnels.
1978, Ford Capri III rear spoiler good for 5% drag reduction.
1980,Citroen GSA rear spoiler good for 8.49% drag reduction.
June, 1982, Ford Motor Co. discovers that 19-24 inches of plywood,laid across the rails of a pickup,ahead of the gate,cuts drag.
1981, Pontiac J-2000 decklid spoiler good for 0.015 drag reduction (3.82%).
1981, Can Am cars,Cd 0.50.
1982, Ford applies for U.S.Patent,for bi-wing spoiler.
August,1982,ROAD & TRACK Magazine tests four different airdam/rear-spoiler combos at VW,Germany: results give 7% drag reduction and 2.3% better mpg at 55-mph.
Pontiac Firebird Trans Am wind tunnel development: decklid spoiler gives 1.26% drag reduction,
1983, patented bi-wing spoiler gives Ford Sierra/Merkur XR4Ti a 5.882% drag reduction.
May, 1984, General Motors makes patent application for half-tonneau cover.
1988, Texas Tech,publishes results of pickup truck aero mods,with drag reductions of up to 20 %(SAE Paper# 881874 [ aero shell ]).
July, 1990, Sport Truck Magazine publishes Texas Tech aero mods.
July, 1990, Larry Mansberger files patent application for an aero shell.
Speed Week,Bonneville Int'l Speedway, Wendover, Utah,U.S.A., July,1991,Day-1, RUN#3: 6-inch-30-degree,cardboard and racer's-tape,boattail- mounted rear spoiler costs Phil Knox 2.053-mph,with 82-cubic inch CRX experimental streamliner.
1992, NASCAR Winston-Cup Ford Thunderbirds,with 35-degree spoiler, crashing in practice-laps. Spoiler angles are raised to 48-degrees.Ford sweep 1st four positions in race.
Ford Escort RS Cosworth, 3-door hatchback, with up-kick bi-wing rear spoiler eats 11.76% in drag,and 5-mph in top speed for 43-pounds of downforce at the rear wheels.
2006, BUGATTI VEYRON 16.4: rear wing alters it's angle-of-attack at high speed to aid in breaking. At 230-mph,the wing generates 1,100-lbs (497-kg) of downforce, and as much as 2,500-lbs(1131-kg) of drag ( an adaptation from a 1950s Turboflite,Chrysler Dream Car ).
It appears that spoilers offer an array of tools,depending on application. I've seen no low-drag concept cars which use any form of lip,spoiler,or flap.Since Dr. Morelli's work with the CNR car, it looks like zero-lift low-drag cars are already in the bag, as suggested by Korff back in 1963.So it looks like spoilers may no longer be necessary for stability, however they may come in handy for ecomodders trying to cheat a gallon or liter of fuel out of some of the late model econoboxes. Just don't put them on a boattail!