CASE-STUDY: Mercedes-Benz C-111 / III (Cd 0.178)

[Grant-53]

There were 3 versions of the C-111 body for the rotary engined car. All had front radiators. The one shown above as the IId was the third also known as the Geneva show car and had the four rotor engine. A 1/24 scale paper model form was published in Motor Trend magazine. I always thought the C-111 would be a better shape for the Ridley Tri-Magnum.

[aerohead]

Originally Posted by Grant-53

There were 3 versions of the C-111 body for the rotary engined car. All had front radiators. The one shown above as the IId was the third also known as the Geneva show car and had the four rotor engine. A 1/24 scale paper model form was published in Motor Trend magazine. I always thought the C-111 would be a better shape for the Ridley Tri-Magnum.

I think it was Patrick who sent me a package on the Tri-Magnum.It seems like the design evaded the compound curves which are so difficult to fabricate,allowing a builder a shot at actually completing the 'car.'
The T-M probably has an advantage over the C-111 in plan-view,but the sides were compromised as well as the rear underside.I've never seen a Cd posted for one of them.It would be interesting to know.

[kach22i]

Originally Posted by aerohead

I have taken a table from Hucho and created three images of the C-111 III with :zero,partial,and full boat tail,and their corresponding drag coefficients.

Thank you aerohead, you know I saved this one for future reference.

[aerohead]

Originally Posted by kach22i

Thank you aerohead, you know I saved this one for future reference.

There are not many photos of this car,but if you'll do a search for the 1979 C-111 IV you'll notice that Dr.Liebold blunted the nose ('flachbau-schnoz' I think Porsche calls it) and then extended the boat tail out nearly all the way.
After festooning the car with induced-drag splitters and wings the car's drag remained at Cd 0.195.
At Fiat's Nardo,Italy test track,and with more power,the C-111 IV pushed over 250 mph.This is the record that GM's OLD's long-tail AEROTECH would beat in 1987,out at Ft. Stockton,Texas.
And we notice,that for the long courses,and highest speed,Ed Welborn also chooses the full boat tail.(A.J.Foyt saw 281-mph on one lap and this was not the top speed of that car).

[kach22i]

While we are mentioning other cars, these scale model Porsche 917's are pretty telling of top speed when side by side.

AutoArt 1971 Porsche 917K #3 Martini & Rossi
DiecastSociety.com • View topic - AutoArt 1971 Porsche 917K #3 Martini & Rossi





I'm still trying to figure out how the air slot before the rear wheel of the long-tail "K" is supposed to work.

[aerohead]

I will have to guess.It's a faster car,designed for faster tracks,and it's lower drag body won't decelerate at closed-throttle like the short-tail.Since it's still a track car it see's nothing but transient loading,with a lot of kinetic energy that must be dissipated by the brakes since it lacks the higher drag,and the air slot may join a duct which channels the air directly at the caliper/rotor to forestall brake fade.