Optimum nose shape
 

I may facelift my Porsche 944 Turbo, which to my eye has less than optimum aesthetics and aerodynamics.

Suppose we start with a clean sheet of paper and re-do the nose forward of the hood. This would mean a new single-piece bumper cover, fixed and covered headlights instead of pop-up headlights, and perhaps a splitter or spoiler.

Question: Can anybody here post pics or graphic from tested designs of optimum car nose shapes?

In other words, just are diffusers at the rear have been studied, surely nose shapes, radiuses, contours, cooling inlet and light placements, etc.must have been optimized, so any suggestions or insights would be much appreciated.

optimum nose
 

Hucho has a chapter section devoted to the 'ideal' nose.
It's basically what R.G.S.White displayed in his 'Method of Estimating Drag Coefficients,' 1968,which is just like Walter Korff's ideal nose of 1963,which is much like Paul Jaray's nose of 1922,which goes back to the half-teardrop form Hucho uses as his benchmark.
For what it's worth,and I've mentioned this elsewhere,the 'ideal' nose on my CRX meant virtually nothing at 100-mph,which meant it's contribution to drag reduction was very little and so it's value for mpg,also very little,whereas most of the speed record and 60+ mpg came from the boat tail.
The 944 has a pretty nice nose.And Porsche has probably already optimized it for the unibody chassis underneath.To significantly modify it would require structural modifications which could jeopardize other aspects of the cars makeup,especially progressive deformation and crumpling during impact should that ever happen.
If she were mine,I'd be looking at that Lange-type roofline and a way to push it out like the Porsche 917 Lange Hecht.

Thanks Aerohead.

I'd use all the same attach points, but where the 944 Turbo nose now breaks the natural sloping line of the hood and upper section of the panel between headlights, I'd just continue that line on down to the stagnation point. No more pop-up headlights, which are uber-draggy. Instead of long rectilinear slots for the cooling air intake, I'd consolidate that draggy design into on probably elliptical inlet at the stagnation point. Instead of a bumper cover, 2 headlight covers, and a panel between headlights, make all that one piece.

The front bumper is secured by shock absorbers, and that part would stay intact for safety reasons, as would all attach points.

Instead of separate light fixtures on each side for a headlight, 2 turn signal lights, a fog light, and a driving light down where they get sandblasted and rock chipped/broken, I'd consolidate all that into one covered fixture with the headlight, up out of the rock chip zone. Sorta a combination of Jag XKE and latest version Corvette.

This would weigh considerably less than what's on there now.

I'll check Hucho. Thanks for the suggestion.

Got any other sources of nose optimization ideas?

Way back when (30 years ago), my aerodynamics instructor in college gave the brick analogy. I probably don't remember the exact numbers correctly, but I am certain of the overall outcome.

Put the brick in the school wind tunnel, longways. Round the nose, drag drops by 8% (or something like that). Take a new brick and simply taper the tail (boat tail design) and drag drops by something like 70%. Combine the two and overall drag is greatly reduced.

Fast forward many years. The nose of piston powered Cessna/Piper single engine aircraft are often really ugly looking. Yet, they fly without excessive drag. Cowling mods produce nothing. However, reducing the cooling air inlet size does result in substantial drag reduction.

You might think about the drag increasing aspects of the hood to windshield angle and the cooling drag issues first.

...there's an old SAE article about the "design & testing" of the MoPar Daytona NASCAR vehicle that had some decent 'summary' information about the "optimization" of size, shape, and spoiler shape and position.

....see SAE paper #700036: "The Aerodynamic Development of the Charger Daytona for Stock Car Competition," by R. P. Marcell and G. F. Romberg, both of Chrysler Corp.

944s are beautiful! Don't geek it out! :eek:

Not gonna geek it out. Clipped a guard rail, dinged rt front fender, header panel between pop up headlights, headlight cover, and bumper cover. No frame damage. Got eBay replacement parts, ready to paint and bolt on. No frame damage.

I may make duplicate parts of fiberglass or high impact plastic, and with those do a pop-up delete and nose job, which would give it a face more like a Carrera GT, latest Corvette, Ferrari Maranello, etc.. This one-piece fascia would use the same attach points, but better internal cooling ducting and include a Calibra-like splitter. It would include proper exit vent for the intercooler, which stock just feeds into the engine bay to find its way out somehow. Porsche did a good job with cooling inlets, but sorta forgot about efficient cooling outlets.

Undertray would be pretty easy on this car, as well as rear diffuser by simply unbolting the rear valence and using its attach points.

Wheel fairings oriented to the relative wind would streamline the wide tires, and if done right feet the brake cooling inlets.

The car could be restored to stock easily.

any other
 

Everything I have basically says ignore the nose,work on the rear of the car.
Hucho refers to 'saturation',which infers that beyond a certain degree of leading edge radius,increasing the radius will return basically zero benefit.
It's my opinion that a nose should be 'idealized' as White showed in his Cd 0.24 recipe car.A full semi-circular nose ( in plan view ) with Morelli's dropped fenders,highly rounded,everything faired in under Lexan.
This would give the best sectional density,most gentle pressure gradients,average flow accelerations,minimum pressure spikes,and best quality flow aft,to allow best performance of aft-body streamlining which is TOTALLY DEPENDENT on fore-body flow.But that's just MHO.
Much of what is printed is within the context of maintaining the 'flavor' of a stylist's 'design'.
The Record Vehicles use the good stuff.
You might re-visit Solaraycer,MG EX 181,Mickey Thompson's "Pumkinseed," the Viking series of vehicles from Western Washington State Univ.
basjoos AERO CIVIC' nose wouldn't hurt.
The 'experts' will whine.Follow your inner voice.

That depends on your definition of "excessive". Ever try to glide one, and compare the performance to even an old Schweitzer trainer?

Seriously, though, do you suppose the lack of effect of nose aerodynamics on single-engine performance might have something to do with the propellor hanging out in front, and shielding the nose from the actual airflow?

The Porsche Carrerra GT, the Boxster, and the Cayman S all have virtually semi-circular nose planforms.

In profile, the Carrera GT and Boxster noses both have upper edges with a ~4-6" radius curve, the Cayman somewhat less.

Such shapes should not be too difficult to duplicate. Well-rounded and with gentle curvature, presumably they are efficient aerodynamic shapes.

up/down
 

Otto,if you could do a movable front airdam like Volvo had for awhile and Ford did with Probe-IV you'd have best of both worlds.
She wouldn't get knocked off in town( Corvette,New Beetle,Camaro/Firebird,Chevy HHR,etc.. ) and then, when safely out of town,she drops to give lower drag where it really matters.
The T-100 is getting one of these.It's never had a proper nose either.And it's got to move,as with the racing tires and lowered ground clearance now,she has some real clearance issues!

Got pics of the Volvo or Probe IV airdam? I'm not familiar, so will Google for those. Thanks.

For around town driveability and speed bump/curb issues, I've wondered about inflatable or ramair actuated devices, including splitter or air dam, side skirts, etc.. That way, no deployment until highway speed. A simple electromagnetic deployment would work, if you do not forget to retract.

pics
 

Otto,I think I've got images of both,but it may be Saturday before I can get Al to post them.I'm months behind on images.
On the deployment issue,seems like any cruise-control logic/sensor technology would dovetail right in.
A 'speed' preset enables or disables a solenoid,air ram,hydraulic ram,servo motor cable winch,ad infinitum,to lower and raise the unit.
Also,electronic ranging,as on any digital camera system could be hijacked to provide a 'forward-looking' hazard avoidance provision,should you drive up onto road debris,road-kill,etc.,especially after dark,when the event-horizon is really brief before 'contact.'
Something else to consider,and I think we kicked this one around before,is that whatever you construct,make it really low mass so if it has to 'move in a hurry' it won't get bogged down with inertial forces.This is where carbon composite would shine.Model airplane technology would give the low mass,but stone-toss from a car ahead could spell doom for the light skin.
An inflated structure might have to have vacuum available for quick-collapsing.

carlos made a deployable air dam but i haven't heard anything about how it's working out lately.

http://blog.modernmechanix.com/mags/...1/med_nose.jpg

And then again, maybe not. :o

Well, to tell the complete truth, I've given thought to putting Great Stuff expanding insulation foam on the nose, then sculpting it to shape, and/or using smooth plexiglass as a curved form to hold the foam in place until it sets up, just like using plywood forms to pour a concrete building foundation.

Best method is probably to glue foam blocks onto the naked (stock nose cover off) front of the car, and sculpt that to shape as a male master for a female mold. On homebuilt airplanes, most guys use this foam glued to engine method to make engine cowlings. Gasoline fumes will destroy the foam, leaving little powdery residue.

pics Volvo VCC 1980
 

Otto,I found a better photo of the Volvo than mine.I GOOGLED :Volvo Concept Car 1980 and got:
http://www.swedespeed.com/news/uploads/features/vcc.jpg

photo: Probe IV
 

GOOGLE has a bunch of pics of the Probe IV.And cgg83 has a thread for the controls at: cfg83-albums-car-styling

I'll bet that spoiler would work even better if instead of a bulldozer blade shape, it were semi-circular or elliptical in planform, shedding air laterally out and past the front tires.

ya ya
 

Yeah,that would be my take on it.I suspect that they made the best of a bad situation without altering the Volvo's front end.Cheap and quick!
Volvo's more modern designs are getting the organic shapes and Cds will reflect that.
The semicircular airdam might require more of a vertical,guillotine type motion rather than a simple hinged/swinging motion in order not to bind during articulation unless the hinge is way rearward,close to the tire face.

I was thinking a semicircular air dam hinged at the back corners near the tires would work pretty good, and fair the tires, too, a kind of Coroplast bandana under the chin of the car.

Speaking of Coroplast, since it's hollow, you could use thin strips of wood, dowel rods, or carbon fiber fishing pole segments and slip them into the hollow flutes as stiffeners.

My bro has a Volvo wagon, great highway mileage even loaded with heavy stuff, but looks like an animal cracker box with wheels. Some sculpted foam at the nose could easily fix that, maybe a Coroplast undertray too.

What was Volvo thinking when they made so many boxy cars? If they just took one out on a windless, snowy day, and turned it nose-up vertical, the snow would accumulate in a shape much more aerodynamic.

if you were to take a car into a wind tunnel, then spray sicky foam pellets at it, what shape would you get? the pellets would presumably stick to places air gets trapped in.

I had a lesson on aerodynamics last time there was a blowing snowstorm here. strange how much like a boattail the rear looked......

bandana
 

Back corners is basically my plan too.I'll do glass,I enjoy working with it and complex shapes are easy.
Neil Blanchard helped somebody,maybe today,recommending a certain dimension of wire inserted within the' plast as a stiffener also.
As to Volvo's styling,perhaps they are also waiting on consumer acceptance,not daring to venture too far with design.

bandana
 

I said an elliptical or circular planform bandana, hinged or pivoted at the back corners.

Perhaps a better analogue would be the hinged/pivoted visor on a motorcycle helmet. In this case, maybe 4-6" high, so that it could easily be raised and locked in up position just aft of the front bumper. This for around town driving, where those pesky parking lot railroad ties and curbs eat low hanging fruit.

As for nose shapes, few advanced cars now have anything but a circular or elliptical planform, i.e, as seen from above. Google images of Porsche, Ferrari, etc. In profile, these typically have gently radiused leading edges, often with ~3-6" radius. Lower lip (ie.e, splitter) is often smaller radius, though, maybe ~1/2 the upper.

BTW, thanks for the pics, esp. Ford Probe IV. My plan for headlight covers and front wheel fairings for my Porsche 944 Turbo bears some resemblance.

Perhaps it was your pics of a winter snow that I had in mind. It would be fun next time it snows with fairly steady and strong surface wind, to park the car straight into the wind, then photograph and/or measure the snow deposition on the car, as the buildup of snowflakes would be at stagnation points, as the wind would sculpt more efficient contours. Then, re-create those shapes at headlights, bumper, base of windshield, etc. with foam, then test in wind tunnel or coast-down. I'll bet Mother Nature is a pretty good fluid mechanic.

Yes, I own a 177RG. With the prop spinning (engine dead), the drag is incredible. The big windmill out there creates, in essence, a solid disk. With the prop spinning, but with it nearly feathered, the drag is greatly reduced. With the prop stopped (very difficult to achieve, btw) the glide is nearly double.

No, the airflow is more rapid over the nose, with the engine producing power. Still, the drag is quite minimal. Testing shows that no performance or speed improvement is practically possible with simple nose mods on my aircraft. HOWEVER, reduction in cooling drag results in a 6 knot increase in speed. This has everything to do with engine baffles, cowl exit and inlet size and incredibly little to do with shape. Take a look at the FLAT "cup" area under the prop. Conventional wisdom would say "that is horrible". However, a comprehensive re-work of that area gains NOTHING. Even at it's 163MPH cruise speed.

http://www.cujet.com/assets/images/DSCN3091_resize.jpg

We operate some really high performance gliders. A DG1000 and a DG808b. Both have tiny frontal areas, high aspect ratio wings and are optimized for 65Kts and less. To compare lift over drag of the 2 aircraft is absurd. Put 100 foot of wingspan on the cardinal, remove the prop and it would do the same thing. It might even achieve a L/D of 50 to 1 just like the best gliders, regardless of nose shape.

The nose and pod shape in a modern sailplane is essentially a body revolution, and you are, in effect, saying that nose shape makes little or no difference.

I respectfully disagree. So do aerodynamicists such as Hucho, Hoerner, Carmichael, Lopresti, all the Germans who design modern sailplanes, NASA guys I talked with years ago, and mathematical modelers such as Zedan. Their research and published results show significant improvement of nose shapes over the years. That is why your DG1000 or an ASW22 noses look like they do and not like your Cardinal.

But, to prove your point, I double dog dare you to saw off the DG1000 nose and bolt on a Cardinal nose sans propeller, and see how she flies.

Well, in aerodynamics 101, we learned that nose shape is not as critical, in subsonic flow, as, say, the shape of the tail. The classic rain drop comes to mind. Please don't get me wrong. I know it makes a difference. In the case of the cardinal and many other aircraft, Lopresti (who is right up the road, BTW) reduces cooling drag and increases manifold pressure to get the speed. The shape plays a very, very small role on such a slow aircraft as the cardinal. The manufacturers got it fairly close to begin with.

The drag curve on the gliders is beyond belief at design speeds. They truly are works of art. However, when speeds increase, just like any vehicle, the drag increases to the point where terminal velocity is reached.

My point remains, cooling drag is important. Nose shape is less important and tail shape is very important. I don't, for instance, believe that drag can be cut by as much as 30% with a casual re-shape of the 944's nose. More like a couple of percent or less. But, I could be proven wrong, and have been before.

Well, if I do the daunting task of a reshape of the nose on my Porsche 944 Turbo, I'd like to get aerodynamic improvement, and the drag of the nose itself may improve substantially, but improvement to the whole car probably won't be anything like 30% unless by blind dumb luck.

The whole car, btw, had a published cd somewhere around .35, not as good as the .31 of Porsche 356B of 20 years prior.

That said, looking at the 944 Turbo vs. the Opel Calibra, or moreso the Ford Probe IV, I think there is considerable room for improvement.

And, the 944 Turbo cooling flow ain't so great: It does have a batwing and engine underpanel, better than the average bear, but certainly not what it could and should be. No good exit path for the intercooler air, although they did a good job ducting air to the intercooler. I may add a cowl flap on little hinges, that would vent the intercooler air out into the slipstream at the leading edge of the hood. May make side vents just behind the front wheels, and duct air from around the turbocharger and exhaust manifold out that way, keeping the engine bay cooler.

Combustion air intake is a spaghetti warehouse abortion: Rather than a ram-air straight shot to the air filter and then on to the turbo, it is routed all over hell's half acre through tubes of various diameters and cross sections (one bottleneck a narrow triangle), with multiple sharp changes in direction, heat soaked by engine bay hotness all the way. A clever guy in NZ chucked all that and the pop-up headlights, and used the space for straight or gently radiused plumbing of 2.5" circular diameter and about 1/4 the length, gaining hp and losing unwanted heat and weight in the process.

Looking at the nose of the Carrera GT, one sees a much more rounded (semi-circular in planform) shape, gentle radius curves, no sharp corners, efficient intakes for cooling of brakes, etc., smooth flat bottom and undertray straight back to the tail diffuser, and side vents taking advantage of low pressure behind the front wheels. Cayman has some similarities, as does Boxster.

We are in complete agreement about cooling air issues, and I envy you for your proximity to Lopresti. Also, a copy of Kent Paser's Speed with Economy is worth having, or Peter Garrison's cowling work, etc.. What I have in mind for my Porsche is essentially a synthesis of ideas from guys like them. This car should be getting much more than 25 mpg cruising at 75-80.

Back to nose shapes: What did the bullet makers and sailplane guys learn and do?

On the spectrum of nose shapes with Caterpillar D8 at one end and ASW 22 sailplane at the other, I prefer the latter. Mo better, and looks it, too.

Another thought on the nose-isn't-very-important theory
 

Remember about 10 years ago when that Navy P3 Orion was hit by the hotrodding Chinese fighter plane off the China coast?

If nose shape is insignificant and the afterbody is what really defines drag, then the P3 should have flown just as fast and well after its nose cone was knocked off as it did before. After all, the fuselage and afterbody was not changed in any way, but the radome/nose cone was knocked off the P3.

Well, that thing was an absolute ***** to keep airborne due to buggered flow and uber-high drag. Speed dropped radically, as did control and stability. I'm sure fuel consumption spiked, even at much lower speed.

Maybe it's time to dispense with the old wives' tale that nose shape is relatively unimportant. Otherwise, we're saying Porsche, Ferrari, Nascar, and Mother Nature are all flat wrong. If nose shape were relatively insignificant, largemouth bass could swim as fast as tuna. Can they?

Maybe, like Heinrich Hertel, it's a good idea to look to Mother Nature and see her empirical handiwork of the past 200 million years. I bet Mom could give us a few pointers on cooling drag, re-introduction of spent cooling air back into the slipstream, nose and afterbody shape, etc..

Interesting point about the P3. I'll have to look into that.

I'll have to counter that with banner towing aircraft that remove the entire front cowl for engine cooling. And, they fly just fine, and often just as fast. I was involved with this in a past life and almost forgot about it.

From Wiki: ""On the third pass, it collided with the surveillance aircraft. The J-8 broke into two pieces, while the EP-3's radome detached completely and its No. 1 (outer left) propeller was severely damaged. Airspeed and altitude data were lost, the aircraft depressurized, and an antenna became wrapped around the tailplane. The J-8's tail fin struck the EP-3's left aileron forcing it fully upright, and causing the U.S. plane to roll to the left at 3-4 times its normal maximum rate.[6]

Area of the collision in the South China Sea

The impact sent the EP-3 into a 30° dive at a bank angle of 130°, almost inverted. It dropped 8,000 feet (2,400 m) in 30 seconds, and fell another 6,000 feet (1,800 m) before the pilot, Lt. Shane Osborn, got the EP-3's wings level and the nose up.""

nose
 

In automotive applications,the aft-body performance is governed by quality flow arriving from the fore-body.
The FLUIDs professor/textbook writers say that below 250 mph,a semispherical nose is plenty good and to concentrate on the aft-body for drag reduction.
The add-on nose to the CRX,which is in the direction of where you're going with the Porsche,made no measurable difference at 100 mph.
I don't think it is physically possible for any nose mod,regardless of how 'slick' it is,to make a significant showing at the pump,driving at posted speed limits.I do think that if you are going to modify the back of the car,then a really clean nose will help in that context.
With respect to the Orion,I don't know if that's germane to what we do.
When at DaNang,an Airman -of-the-Month won a back-seat ride in an F-4 Phantom.An avionics guy had not properly fastened the nose radome and they lost the whole thing in flight,causing the radar antennae to be shredded away by the airstream.The pilot had no problem with flight stability,however a hydraulic line had been severed,with time the plane would become un-fliable,and with the fluid all over the windscreen he had no forward vision.
They talked them down okay.The pilot was unshaken,the 'Airman' had to change his clothes.
And the thing about fish,they're governed more by skin friction,with the 833 times more dense water,than they are with profile drag,of which neither of the fish possess.
The Bluefin has the ' lowest' Frontal Cd of fish but is not the fastest fish.That title goes to the sailfish,clocked at over 60-mph.And for 'sustained' velocity,the bottlenose dolphin is given the credit,at around 30-mph and bursts to 45.
If memory serves me,Hertel gives the lowest frontal Cd of any measured 'structure' to the gentoo penguin.

nose drag example
 

Here's a graphic for the drag breakdown measured for the Ahmed body model,researched, probably by half a dozen investigators now.
For the zero slant back configuration you can see that the entire nose drag constitutes less than 6% of overall drag,while the base drag,due to the turbulent wake is over 70% of the overall drag.This is why Hucho repeatedly emphasizes the importance of a vehicles aft-body.
We can't do anything about skin friction,so we basically ignore it.If it were an airplane we'd obsess over it.
http://i1271.photobucket.com/albums/...itled15_19.jpg

I agree.

Just put some conveyor belt material attached to the lower valance and make a zero clearance chin spoiler like the track guys do.

Drive around with the windows rolled up if you want maximum aerodynamics.

Similar:
Yellow Bird Chin Spoiler - Pelican Parts Technical BBS
http://forums.pelicanparts.com/uploa...1152378932.jpg
http://forums.pelicanparts.com/uploa...1152378984.jpg
http://forums.pelicanparts.com/uploa...1152379026.jpg

More similar images:
http://forums.pelicanparts.com/911-9...t-spoiler.html
http://forums.pelicanparts.com/uploa...1395466577.jpg

Better than this:
http://speedconceptsonline.com/buysp...ler-lower.html
http://speedconceptsonline.com/buysp...iler-lower.jpg

EDIT: perhaps a polycarbonate rear glass to save weight?

http://forums.pelicanparts.com/porsc...ml#post8976924

^^^^??????

That picture raises a lot of questions. Not least is the scale, I'd guess 1/10th. What's the cable connector hanging under the left front? What's the translucent overlay over the flip-flop paint?

The Porsche air-dam is nicely done. The fasteners are in the middle of the strip instead of the top, so it holds it's shape better?