Quote:
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.
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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.