It’s rather long, dense and technical, but if aerodynamics is not a drag for you, you might want to peruse this. It’s a good complement to my own three-part series on the history of Automotive Aerodynamics.
Vintage R&T Tech Article: “Aerodynamic Drag” (1966)
– Posted on July 31, 2021
Interesting detail on the R8. I had always wondered about that up-facing cooling vent; it seemed intuitively that it should be an air-blocker like a tailgate. I figured it was needed to force air backwards into the radiator. Turns out it’s a ‘trap-diffuser” that helps streamlining!
One thing not mentioned here is the effect of crosswinds, on drag not just stability. Significant portions of highway in the US get significant crosswinds, and with fairly low-speed and large side area vehicles like semi trucks, the effective yaw angle generated by a 10-15 mph wind on a vehicle going 60 mph, can impact both Cd and true frontal area. Features like aftermarket side skirts on box trailers can significantly help, as well as cab design. I believe this is taken into account in the design of modern “streamlined” conventional tractors which are so popular in the US, as well as some cabovers.
Have a good look at any modern cabover there are front quarter vents to channel air down the sides of the cab to aid fuel economy and help it push thru the air, conventionals are easier to create that effect and usually feature adjustable aero kits.
Speaking of crosswinds, my ’05 Taurus was noticeably affected by them when they came on abruptly. I noticed it when I first got it. I’ve never had another vehicle in which it was so noticeable. Not scientific of course, but my opinion is that the coke bottle shape of the sides aided lowering straight-on drag, but the sidewinds got “caught” in this inner-curved area shaped like a boat sail. I wonder if anyone else noticed this on the “jellybean” Tauri.
I don’t know your actual answer, and have never driven one of those Tauri, but I do remember that the highly aerodynamic C3 Audi 100 (5000) was often noticed to be affected by sidewinds back in the day. I don’t hear of the complaint these days when all cars are as aerodynamic, so I presume some trick has been discovered to counteract the issue. I wonder if at least part of that is modern tyres, which are so large and (comparatively) low in profile that it’s just hard to budge them off line?
Its a compliment to the jellybean Taurus to be compared to an Audi 5000 in any way.
Probably doesn’t get that a lot.
I’ve driven the same highway since in an ’03 Chrysler T&C, a 2003 Avalon, 2000 Concorde and 2011 Escape and none were affected in that way. It didnt move the car, but you could feel the “push” in the steering wheel.
Thanks for the reply, Justy.
Aero tuning regular cars for racing back in the 60s showed excellent improvements over factory designs one obvious one was fitting ‘fastback’ rear body work on 105E Ford Anglias eliminating the reverse slant back window those very light easily hotted up little sedans made great circuit cars but the drag from the back glass worked against them so the breadvan style back end was developed and worked well.
Aerodynamics. The art of making the unseen, seen.
It’s interesting that after many decades of making airplanes someone only recently thought of the little winglets at the ends of the wings to fix some turbulence there.
Those projecting hoods over the rear window of every SUV today are I assume a way of cutting turbulence/making the exiting airflow smoother, kinda like the Kamm thing. On the other hand, the hoods over windshields seen on early 50’s cars must have been the opposite. It’s a wonder they didn’t tear themselves off at 60 mph.
The Forward Look Chrysler cars had more slanted windshields and fast rooflines plus those aero fins. Very aero, well except for maybe the cut off forward slanted front ends.
Forces of wind are pretty amazing. Well, it’s how sail boats work. I was once getting sheets of plywood from outside racks with a coworker who was demonstrating just how strong he was by moving a sheet himself. Then a slight breeze came up.
Racing Fiats with rear hoods propped up.
Reading this in little bits between other things broke it down enough that I understood most of it. It’s fascinating. In parts, the fluid dynamics stuff is quite counter-intuitive.
I really enjoyed this. It’s well worth a go, CCers.
Excellent as always….
Thanks!
The 55 mph. speed limit was an attempt to optimize the real world fuel economy of a national fleet of not too aerodynamic vehicles. It worked somewhat, we all have experienced lower fuel economy at higher operating speeds. My F150 gets substantially better fuel economy at 60-65 mph, ( 20-21 mpg. ) as opposed to constant driving at 85 mph. ( 16 mpg.) With modern designed cars the drop off is much smaller and there is less penalty in driving so fast.
This is an excellent article, Hot Rod magazine has a very good series in the 1970s and a later one entitled, “Aero tricks that you can use”. It is interesting to note how big rigs have adopted more aerodynamic features and add ons; roof mounted panels to integrate into the top of the trailer, side skirts, trailer tails, even enclosing the area between the cab and the front trailer. It has a real pay off for them, lower fuel use affects their bottom line.
I remember how my ’77 Cdv, and other GM B bodies, had a small black plastic panel that was attached under the radiator that hung down below the bumper that functioned as a front spoiler, every little bit was an improvement with that brick like shape, which I really loved! No jelly beans yet!
Excellent post. I vaguely remember reading this article in the early-70s when I was in junior high school. All of my drawings back then of the “ideal car” were tear dropped shaped (viewed from the top) until high school.
As I grew up, I learned that drag in the form of side winds is important for driveability too. My second gen Sienna has an excellent CD forward but not so good with heavy side winds, common in the Midwestern US. High lateral loading makes an easy drive tiresome.