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JulianEdgar · 09-29-2020, 02:50 AM

A collection of SAE aero papers arrived today (SAE SP-1600) and it contains a very interesting paper on rear spoilers. The paper is 2001-01-1267, written by Hyundai engineers in 2001.

A few things make it interesting.

First, it covers squarebacks, notchbacks and fastbacks.

Second, it was written when Hyundai had only just got their full-size wind tunnel. You can see the engineers struggling a bit with the relationship between wake size, attached flow giving downwash (that they call the coanda effect), rear lift and drag.

Because I think it was all new to them, they did some really interesting 'basics' test. One good example is plotting pressures around a notchback (and one with a 'modern' rear window angle, too) with and without a front undertray and rear spoiler. (I tried to scan these diagrams to post here but the reproduction quality is pretty bad.) But as one example, a rear spoiler on the trunk / boot clearly improves flow past the front undertray.

They also have very clear measurements of reduction in rear suction peaks at the end of the trunk / boot lid giving reduced drag and rear lift, and a very interesting section where on a squareback, they trial a gap between a rear roof extension / spoiler and try different spoiler angles, all correlated against drag coefficient.

They also go out on what today would be regarded as 'on a limb', drawing a very tight mathematical correlation between rear coefficient of lift (note: not overall CL, but CLr) and increases in drag. But - and again this is very interesting - they then give no less than 61 examples of measured data in the wind tunnel to show real world examples of their mathematical relationship. There's plenty of scatter in the graphs but you can see what they're getting at. (Their relationship? CD = CD value (no rear lift) + 0.8996 *(CLr)^2)

A bit like with wings on cars, when you go looking for SAE papers on spoilers there aren't a lot around - and I wasn't aware of this one until today. For people measuring pressures, it's an especially interesting paper.

09-29-2020, 02:50 AM	#1 (permalink)
JulianEdgar Banned Join Date: Nov 2017 Location: Australia Posts: 2,060 Thanks: 107 Thanked 1,605 Times in 1,136 Posts	Excellent paper on rear spoilers A collection of SAE aero papers arrived today (SAE SP-1600) and it contains a very interesting paper on rear spoilers. The paper is 2001-01-1267, written by Hyundai engineers in 2001. A few things make it interesting. First, it covers squarebacks, notchbacks and fastbacks. Second, it was written when Hyundai had only just got their full-size wind tunnel. You can see the engineers struggling a bit with the relationship between wake size, attached flow giving downwash (that they call the coanda effect), rear lift and drag. Because I think it was all new to them, they did some really interesting 'basics' test. One good example is plotting pressures around a notchback (and one with a 'modern' rear window angle, too) with and without a front undertray and rear spoiler. (I tried to scan these diagrams to post here but the reproduction quality is pretty bad.) But as one example, a rear spoiler on the trunk / boot clearly improves flow past the front undertray. They also have very clear measurements of reduction in rear suction peaks at the end of the trunk / boot lid giving reduced drag and rear lift, and a very interesting section where on a squareback, they trial a gap between a rear roof extension / spoiler and try different spoiler angles, all correlated against drag coefficient. They also go out on what today would be regarded as 'on a limb', drawing a very tight mathematical correlation between rear coefficient of lift (note: not overall CL, but CLr) and increases in drag. But - and again this is very interesting - they then give no less than 61 examples of measured data in the wind tunnel to show real world examples of their mathematical relationship. There's plenty of scatter in the graphs but you can see what they're getting at. (Their relationship? CD = CD value (no rear lift) + 0.8996 *(CLr)^2) A bit like with wings on cars, when you go looking for SAE papers on spoilers there aren't a lot around - and I wasn't aware of this one until today. For people measuring pressures, it's an especially interesting paper.