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

I've wanted to post some case-studies of some "aero-modded" vehicles for the benefit of members and lurkers whom don't have access to some of the technical press.

The M-B 111/III knocked my socks off when I read about it, and I was still very impressed with the car when I got to see it first-hand at the Mercedes-Benz museum in 1997.

http://www.autoblog.com.es/fotos/mercedes/c1113.jpg

I can't format the material with tabs,'n such,so please forgive me for the "randomness" of the material.---------------------------------

The car	Mercedes-Benz 111/III
Height	1,029mm(41.16 inches)
Width	1,688mm(67.5 inches)
Length(competition)	4,784mm(191.36 inches)
Curb Weight	1,347 kg(2,965 pounds)
Power	171.58 kW(230-hp)
Final Drive	1.65:1
Engine	5-cyl TD with intercooler
Chassis	all-composite,fiberglass and carbon-fiber
Cd(competition)	0.195
Roof slope @ tail	11.5-degrees(my measurement)
Maximum cross-sectional area location	2,589mm(103.56 inches from nose)
Fineness-Ratio	4.64:1
Truncated Boat-Tail Length	700mm(28 inches)
.	.
PERFORMANCE	.
Top Speed @ Nardo Test-Track,Italy	315.157 km/h(195.398MPH)-continuous 24-hour driving.
Fuel Economy	6.26 km/l(14.7mpg) @ 195.398 mph

Development of the car included an investigation of a full boat-tail,which added 1500mm length to car and dropped drag to Cd0.178.

A compromise was set at 700mm,which reduced the cars "base-drag" of Cd0.2378 down to Cd0.195 (a 18% drag reduction)

The full boat-tail reduced drag of the base car by 25%.

In full-tail form,the C-111 has a fineness ratio of 6.106:1,which in free-stream,above ground-effect would equate to 3:1,near the ideal teardrop.

Reference: CAR and DRIVER,September,1978,also Dr.Hans Liebold,Research Engineer,M-B,Report,as cited in Hucho,page 142,2nd edition.

whoops!!!!!!
 

Sorry,the Cd in the thread header should read Cd0.178,not 0.173(senior moments!)

Playing around with the newly introduced tables in the bb.

The car	Mercedes-Benz 111/III
Height	1,029mm(41.16 inches)
Width	1,688mm(67.5 inches)
Length(competition)	4,784mm(191.36 inches)
Curb Weight	1,347 kg(2,965 pounds)
Power	171.58 kW(230-hp)
Final Drive	1.65:1
Engine	5-cyl TD with intercooler
Chassis	all-composite,fiberglass and carbon-fiber
Cd(competition)	0.195
Roof slope @ tail	11.5-degrees(my measurement)
Maximum cross-sectional area location	2,589mm(103.56 inches from nose)
Fineness-Ratio	4.64:1
Truncated Boat-Tail Length	700mm(28 inches)
.	.
PERFORMANCE	.
Top Speed @ Nardo Test-Track,Italy	315.157 km/h(195.398MPH)-continuous 24-hour driving.
Fuel Economy	6.26 km/l(14.7mpg) @ 195.398 mph

I love that car

http://www.autoblog.com.es/fotos/mercedes/c1113.jpg

The first "green" super car?! :turtle:

Dorsal ridge - Stability at speed?

or possibley veintilation - rear visibility?

Not louver... dorsal "fin".

It's not a fin, scientifically... fins are independently mobile. It's a dorsal "ridge". Unless it's mobile.

If it has any function at all, I'd assume stability, since that's what just about anything that still has a dorsal ridge uses it for.

Anyone else notice the close appearance likeness to most european exotics?

Put a boattail on a Lambo Diablo and you've got that car, basically. At least it seems that way to me. PhotoChop, anyone?

Thanks for posting the picture. :D

14.7mpg @ 195mph?! :eek:

DO WANT! :D

If it can do that at 195, I can only imagine what it gets at more sane speeds. :thumbup:

Reminded me of the Bugatti Veyron top speed fuel economy stat...

3 miles per US gallon (1.3 km/l/3.6 mpg-imp) 1.39 gallons per minute @ 408.47 km/h (253.81 mph)

Bugatti Veyron - Wikipedia, the free encyclopedia

stability
 

Yes,the fin keeps the center-of-pressure behind the center-of-gravity.

Darin,thanks much for the formatting!

tasdrouille,thanks for the pic!

So the fin is for crosswind stability?

Thank TestDrive for the formatting - I just pasted his work into your post. :)

I think so.Morelli licked the stability issue,but it came a little later,and the sharp-edged front fenders on the M-B lend themselves to cross-wind issues.Morrelli rounded everything dramatically to let pressures bleed away.The tapering tail doesn't have much of a "moment" in gusts,and the vertical stabilizer adds some area aft,to help maintain the CP behind the CG,to provide for "oversteer",which is preferred at high speed.If the car should "weather-vane",it will turn itself into the wind,canceling the yawing moment.Should the car have more area in the front,if it yaws away from the gust it will "catch" more air,turning a larger "face" at the gust,and the yawing moment can increase to a level such that the driver's steering inputs cannot compensate.Don Schroeder,the fella that tested my CRX at Chrysler was killed in the wreck of a RennSport V-12 Mercedes at Ft.Stockton(where A.J.Foyt fought hellacious crosswinds in the OLDS Aerotech).The investigation was unresolved last time I looked. It looks like the engine blew,and if he was in a controlled power-slide at the time,he would not have had power to control the rearend.If the winds were strong that day,as they often are,he may have had too much to compensate for without the power.------- These speeds are obviously potentially lethal,and I suspect Mercedes wanted to stack the deck,best they could in the event of bad air with the C-111.

Me too. I'm old enough to remember being blown away by the C-111. The picture above is mostly aero add-ons to the normal C-111 body. Someone at M-B clearly had a nice aero research budget that year.

Here it is in its normal clothes and in racing trim. Note the front wheel skirts.

Nice hats! :p

Also remarkable for being a performance supercar powered by a diesel engine, for the purpose of improved fuel economy.

Hmmm 195mph and 14mpg... now that is BAD-A!

Think people stare at basjoos civic? Imagine this!

People would think its an airplane about to take off or landing from the rear fin!

Some additional pictures:

http://www.emercedesbenz.com/Images/...11_3Frontp.jpg
http://www.emercedesbenz.com/Images/...11_3_Heckp.jpg
http://www.emercedesbenz.com/Images/...11_3_Seite.jpg
http://www.emercedesbenz.com/Images/...C111_3_Top.jpg

There was talk of making a road going version using the 5 cylinder diesel to replace the 4 rotor rotary of the experimental cars and Mercedes did extensive research and published quite a few papers on the idea.

Other demands meant the project was halted but the 5 cylinder moved to the production line and was used in the W123 series cars initially (1976 to 1985) and other variants later.

There were also scale models made in die cast in 1:18 th scale of the road going prototypes and some were available from MB dealers at the time.

Pete.

Is that a pointy nose I see?


Why does it have louvres instead of a smooth rear window though?

My guess its to cool the engine that is probably located behind the cockpit?

You can see through the louvers (probably) very well. It sure looks like the cooling is in the front.

At the speeds that cars run at, a pointy nose is not required. Look at the Schlörwagen and the Boxfish...

Phil, bit hard to tell. Was the radiator intake below the stagnation point on the front. I see that the engine compartment was vented to the windwhield "pocket." Looks like a superb setup to minimize radiator drag and windshield stagnation.

looks like
 

I'm away from home so I don't have my own photos to look at,and I can't remember ( hey at my age I'm authorized now ) but it looks like the area below the lowest slat is open right at the stagnation point,and then they've opened up the area,snagging more air with the additional slats/louvers.
Remember,this was a 'track' car,and operated at W.O.T. for hours/days at the Nardo,Italy track.
Daimler would have been very concerned with engine cooling,operating at the ragged edge for so long.
In day to day operation,the car would never require this amount of cooling air.
At Bonneville,My CRX ran with the temp gauge nearly pegged,so I know this is an issue.
As to the cooling system itself,it is exactly what Walter Korff was pushing in 1963,and it also happens to be what put Wunibald Kamm on the map.The energized flow going over the windshield helped to keep the air from stalling which allowed his roofline to work.
And a safety note: Should a radiator or AC condenser explode ( I've experienced this 3-times ) the hot gases from the cooling system will hit dew-point on your windshield,condense,blind you,and you will in all likelihood crash.The gases from the ruptured AC unit will outright blind you.
It's my opinion that the safety risk of this type of mod overshadows any aero benefit.
Maybe better to move the heat-exchangers rearward as in the Ford concept cars.

I found another great thread on this car, including press release data directly from Mercedes.

C111-IId and C111-III details from Mercedes

http://www.superturbodiesel.com/std/...nt.php?aid=647

pointy
 

WOW! Sorry I missed this from so very long ago!
Yes,it is a 'pointy' nose.And after revisiting Fachsenfeld's book of 1951 I have a different take on it.
It is the only reference I've seen in which a 'teardrop' was tested 'backwards,' with the pointed end into the airstream.
It's drag is about 29% higher than when going the other direction,but when lowered into ground proximity,and after wheels are added,the drag is less than 15% higher.
The other thing to consider,is that Mercedes-Benz was approaching transonic flow,whereas some parts of the car would be experiencing compressabilty effects and the nose would play a greater role.
What's curious,is that the next year,in 1979,for the C-111 IV,Mercedes shortened and flattened the nose (more like Porsche's 'Flachbau-Schnoz)and then extended the boat-tail almost all the way to 1,500 mm.
Even festooned with all the extra down-force winglets,the C 111 IV measured no higher drag than the III with no wings,but shorter tail,and with extra power pushed above 250 mph for the 1st time.
'Pointy' is okay aerodynamically,but from an automotive standpoint it may not share the architectural caveats allowed the traditional 'teardrop 'forebody,and the necessary windshield angles might render forward vision an optical impossibility.Hucho touches on this aspect of vehicular design.

boat-tail and C-111 III drag pictorial
 

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.
http://i1271.photobucket.com/albums/.../drawings1.jpg

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.

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.

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

C-111
 

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).

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
http://i2.photobucket.com/albums/y10...s/P1110920.jpg
http://i2.photobucket.com/albums/y10...s/P1110915.jpg
http://i2.photobucket.com/albums/y10...s/P1110913.jpg
http://i2.photobucket.com/albums/y10...s/P1110926.jpg

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

917 air slot
 

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.