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

[Otto]

Originally Posted by Recumpence

No worries. I am fine with people posting whatever they want.

Oh, I have to address the comment made on the last page about fog light position and air acceleration at that point. That was my assumption too. That was one point of my questions earlier in this thread that the fog lights and lower grille are in that area and both are there contributing to the turbulence of each other.

Matt

Bingo.

Bugger the accelerating airflow and you have half angles of turbulence of about 15 degrees all the way back from there, like a boat wake. You want a nice smooth and orderly acceleration of the airlow. In a sailplane, you may get laminar flow most of the way back on the canopy, then turbulent but still attached flow well aft of that. On a road vehicle, pretty much forget laminar flow, but keeping the turbulence as low and attached as possible would be most helpful, so a smooth and well faired nose is key. OTOH, if your nose is shaped like a bulldozer, it might not make much difference how good the shape is further downstream.

Down low where the foglights go is naturally draggy, since much of the stagnant nose air can't flow downward due to the ground, it has to mostly go laterally around the sides or up and over the hood. Then, there's gross buggery due to the effective yaw angle of the spinning wheels/tires, which really screw things up. So, the foglight region gets more air, accelerating even faster due to the concentration, and irregularities or bumps there are even draggier than they otherwise might be. Also, lots of crud accumulates, as well as rock chip damage.

You've done well go fair the foglights, and please report results as able.

[radioranger]

I think your theory about the turbulence is correct, at some point perhaps the stock foglight opening is breaking up the smooth air flow, the idea of a open cavity filling in is great if all forward facing, but on the side like yours are could be a factor,

[Recumpence]

I can tell you all of these changes really add up. I did some 50mph cruise testing by running north, then south repeatedly on the same road with cruise set at 50mph. I eliminated the variable of acceleration and reset my mpg on my scanguage as soon as I hit 50mph on each return trip. This was done on a 2.4 mile road with 12 total trips (6 round trips) and saw an average cruising mpg of 52.25mpg. This was done at a frigid 21 degrees-f. Before all mods, the best I would have seen would have been around 44 to maybe 45 at best. Last winter I saw a couple trips that were 47 in similar areas, but those were rare. I struggled to top 44mpg without mods.

I love this hobby!

Matt

[Susanne]

Did not mean to sound rude. Meant to express frustration that some old chatter effects discourse and your posting behavior. Thank you for your participation on all levels.

[Recumpence]

I just don't want that argument brought into this thread.

Matt

[radioranger]

If this holds true that smoothing the foglight opening on the corner is a greater thinng than expected, it could change a lot of designs out there as today almost every newer car had similar openings, what a waste if they dont take advantage of it, on the same vein, I'm thinking of stretching out the outside edges of the front bumper cover on my escort to better fair in teh oversize wheels I have on th ecar now, maybe I can just put a bracket under there to hold it out a bit more,

[Recumpence]

So, what are your thoughts on sealing up all the gaps around the headlights and hood as well as smoothing out edges as much as possible? I plan on doing it because it is really easy to do. I think any gains would be painfully small. But, since it is so easy, I may as well do it.

Matt

[aerohead]

Originally Posted by Recumpence

So, what are your thoughts on sealing up all the gaps around the headlights and hood as well as smoothing out edges as much as possible? I plan on doing it because it is really easy to do. I think any gains would be painfully small. But, since it is so easy, I may as well do it.

Matt

Dr.Wolf Heinrich Hucho measured the drag of an 'ideal' aerodynamic nose,compared to that of the production 1974 VW Golf/Rabbit and saw virtually no difference between the two.

[Recumpence]

Well, after sealing up the gaps in the nose of my car, I noticed my intake temperature went up 35 degrees.

So, if nothing else, sealing everything up will help keep heat in the engine. That will help my FE a touch as well as making my heat work better.

Matt

[Otto]

Originally Posted by aerohead

Dr.Wolf Heinrich Hucho measured the drag of an 'ideal' aerodynamic nose,compared to that of the production 1974 VW Golf/Rabbit and saw virtually no difference between the two.

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?