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Originally Posted by Vman455
Are you satisfied with sub-optimal? Why? If it's easy enough--quite easy, in fact--to do a little testing and find out what the actual optimal angle and actual optimal shape for your car are, why on earth wouldn't you do that instead of just guessing?
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The phrase: "there comes a point of diminishing returns." comes to mind. The question I'd have is how much would I benefit from the work involved. To get everything "optimal" in my mind requires not only redesigning the rear window and trunk area, but also making my own windshield and hood. At what point does optimal become OCD?
Quote:
Originally Posted by JulianEdgar
1. By simple testing of mock-ups.
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If all it takes is a "little testing" "simple testing" that makes sense. However, in my mind it sounds like a lot of work. I'd be tempted to see if I get good mileage with the first mockup and then leave it on permanately if it does.
I've tried testing fuel/air ratios and degrees of advancement. And even though with those it's just a small twist of an ajustment screw or a distributor it's still a lot of work. Now building not just a 3 dimentional mock up but several of them sounds a bit harder than just twisting a screw, at least for me. Or maybe I just don't understand the concept of "simple testing of mockups."
However, I'm still interested in trying a boat tail at some point as it seems to be the best way of getting better fuel mileage. So thank you, I'll keep these points in mind.
Quote:
Originally Posted by JulianEdgar
2. Yes it would, but why would you want to do that? Gains are hard enough to get without even following a completely wrong approach (copying a shape).
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Why? Because it's easier to just go with something predesigned. And if it produces possitive results, it stays on the car. If it doesn't it gets taken off.
But you make it sound like the level of effort isn't much different either way, template or mock-ups.
Quote:
Originally Posted by JulianEdgar
I can endlessly describe why a template-based approach is rubbish in car aero modifications - and I have done so previously - but here's one straightforward example.
1. You want flow to stay attached to the sides/top/bottom of a boat-tail extension.
2. Flow attachment is heavily dependent on boundary layer thickness - the thicker it is, the more easily separation will occur.
3. Boundary layer thickness varies, depending on the car and the surface roughness / change of shape / length of body ahead of the boat-tail.
4. So when shaping a boat-tail, how can a predetermined shape (a template) take into account the variation in boundary layer thicknesses between different cars?
Answer: it can't.
A simple low drag shape (incidentally, one of many that have been produced) has been extrapolated into purported car modification uses which are quite absurd.
Unfortunately, believing that a template can be used for all sorts of car modifications like....
Guide the shape of extensions to cars, to guide the heights of spoilers, to assess the 'aerodynamic purity' of shapes, to determine where there will be attached and separated flow etc, etc
... then has flow-on impacts on a whole range of aero understandings. That is, get the basics wrong and then so much that follows is also wrong.
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Fair enough.
Quote:
Originally Posted by freebeard
I was thinking you were saying the best shape is no shape and the best angle is no angle, but now I can't explain the gap between a mock-up and a template.
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May I point out:
Quote:
Originally Posted by JulianEdgar
BBut determining its optimal angles from a template is absolute rubbish.
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Quote:
Originally Posted by JulianEdgar
Quote:
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Originally Posted by Isaac Zachary
Wouldn't a suboptimal shape, template or not, still have the possibility of providing some improvement?
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2. Yes it would, but... |
It's not that Julian disagrees with the concept. He disagrees with a one-sized-fits-all approach as being optimal.
Sounds like he can't be happy with someone trying something that's not optimal, even if it ends up giving them a small benefit.
That's what makes it hard to follow his posts, for me anyhow. It's kind of like one guy saying he's going to lean out his carburetor and another ridiculing him for not installing fuel injection and tuning each cylinder's AFR.