C-Max aero mod success questions.......

[aerohead]

Originally Posted by Otto

Well, page 158 (fig. 4.31) of Hucho's 4th ed. book says the optimum shape is 14% less drag than the base shape, does it not?

Perhaps I'm misreading pages 157 & 158. Upon reviewing them, what's your take?

I believe that in the bar graphs,you see that after the very small radii were introduced to the 'basic' profile,that VW essentially achieved (within spitting distance) the same drag reduction as with the 'ideal' nose.
This is the concept of detail optimization that Hucho has hammered away at for decades.And why he is so quick to encourage the aft-body streamlining.
The forebody is in the most favorable pressure gradient,with the flow held against the body as it accelerates along the increasing body section towards the minimum pressure line.
You can have a lot of sins up front and still maintain attachment.

[Recumpence]

Ahh, that clears it up.

I have noticed that sealing up the nose has, what I would call "Secondary" benefits. For one thing, there is less air whistling that is audible, and the under hood temp is far higher. My intake air temp went from 3 degrees above ambient to 30-40 degrees above ambient. So, I assume the gains are small, but there.

Now, to work on the air dam and kammback..........

Matt

[Otto]

Originally Posted by aerohead

I believe that in the bar graphs,you see that after the very small radii were introduced to the 'basic' profile,that VW essentially achieved (within spitting distance) the same drag reduction as with the 'ideal' nose.
This is the concept of detail optimization that Hucho has hammered away at for decades.And why he is so quick to encourage the aft-body streamlining.
The forebody is in the most favorable pressure gradient,with the flow held against the body as it accelerates along the increasing body section towards the minimum pressure line.
You can have a lot of sins up front and still maintain attachment.

Granted, the airflow may stay attached on the upslope even if the entry shape is not so smooth, but per Hucho's page 158 graphics, the "optimum" nose looks a lot like that of the early Porsches, i.e., smooth, well radiused curve, with stagnation point set at ~20% of vehicle height.

I doubt we get much attachment with cars, especially after the airflow turns the front corners. A sailpane, otoh, can stay attached all the way to and sometimes beyond the thickest point of the fuselage, assuming excellent contour and surface quality. Not gonna happen with road vehicles.

I'm also curious about optimum shape of the nose as seen in planform, i.e., from above. Seems to me the lateral airflow would be best with an elliptical planform, smooth surfaces, no irregularities, as with Porsche 718.

Google Image Result for http://www.finecars.cc/typo3temp/GB/5a538db5f8.jpg

[vskid3]

Originally Posted by Recumpence

I have noticed that sealing up the nose has, what I would call "Secondary" benefits. For one thing, there is less air whistling that is audible, and the under hood temp is far higher. My intake air temp went from 3 degrees above ambient to 30-40 degrees above ambient. So, I assume the gains are small, but there.

Intake temp increase is pretty good. Did you notice any difference in warm up time? Did you just tape the gaps or use a more permanent method? I may have to block my upper grille and seal the gaps if it helps that much.

[Recumpence]

I lowered the hood 1/4 inch to tighten up the gap. Then I added weather stripping around the hood to seal it. I added more weather strip in other areas and I blocked all 3 grille openings.

No tape was used.

Matt

[renault_megane_dci]

Well, to start with, why would it be an optimal shape if it wasn't better than any shape ?
Or else the front end of a Mk1 VW Golf would be The optimum shape ?
(Giugiaro's design by the way)

[Otto]

Originally Posted by renault_megane_dci

Well, to start with, why would it be an optimal shape if it wasn't better than any shape ?
Or else the front end of a Mk1 VW Golf would be The optimum shape ?
(Giugiaro's design by the way)

Good question.

And, if the original shape of the vehicle nose in this thread is good, and modification to it would not produce much benefit, then why do the OP's modifications make such great benefit? In other words, if it was good to begin with, modifications to the fog light geometry would not help, would they?

Reviewing the information on optimum mirror shapes, one finds that a smooth, rounded body which continues its lines past the plane of the mirror, makes the least drag. Why would the nose shape of the vehicle be any different?

When the OP finishes his modifications and smoothing of the nose of his car, he should do ABA tests to compare the original shape with the modified shape.

I suspect the factory designers either did not know what they are doing (very common) or simply ignored known science and published data and just used whatever the marketing department wanted (also very common).

[radioranger]

Has anybody done any testing as to the max temp you should run under the hood, I am tempted to seal up the gaps for the colder weather on the escort but have to climb several big hills and also only have an ultra gauge which i am not sure if it reads the intake temp, any help on this would be welcome

[Recumpence]

I do not know. That is a good question.

I know that older carburated cars had issues with high under hoods temps (vapor lock). But, I do not know about FI systems.

Matt

[aerohead]

Originally Posted by Otto

Granted, the airflow may stay attached on the upslope even if the entry shape is not so smooth, but per Hucho's page 158 graphics, the "optimum" nose looks a lot like that of the early Porsches, i.e., smooth, well radiused curve, with stagnation point set at ~20% of vehicle height.

I doubt we get much attachment with cars, especially after the airflow turns the front corners. A sailpane, otoh, can stay attached all the way to and sometimes beyond the thickest point of the fuselage, assuming excellent contour and surface quality. Not gonna happen with road vehicles.

I'm also curious about optimum shape of the nose as seen in planform, i.e., from above. Seems to me the lateral airflow would be best with an elliptical planform, smooth surfaces, no irregularities, as with Porsche 718.

Google Image Result for http://www.finecars.cc/typo3temp/GB/5a538db5f8.jpg

In Hucho's 2nd-edition,p.61 "On the drag problem of a body,it might be mentioned finally that the shape of a body in front of the largest cross-section has only minor influence on the total drag.The main contributions to the drag force originate from the rear part of the body.It is not important to find a proper shape to divide the oncoming flow but it is very important to design a rear body surface which brings the divided streamlines smooth;y together.Optimum shapes are 'streamlined' bodies having a very slender rear part."
Bear in ind that the 2013 C-MAX/Focus already has a nose which is far superior to anything manufactured when Hucho penned these words.