Optimum nose shape

[Otto]

Originally Posted by aerohead

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.

[ShadeTreeMech]

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......

[aerohead]

Originally Posted by Otto

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.

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.

[Otto]

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.

[Otto]

Originally Posted by ShadeTreeMech

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......

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.

[cujet]

Originally Posted by jamesqf

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?

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.

[cujet]

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.

[Otto]

Originally Posted by cujet

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.

[cujet]

Originally Posted by Otto

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.

[Otto]

Originally Posted by cujet

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.