How to Get 80 -100 MPG From The CMAX HYBRID

[ptjones]

 

Here are front and rear air dams that I installed on my 2013 CMAX which come standard on newer ones. I installed the front ones the way I thought they should be installed, not like factory.

Here are my LEXAN wheel covers.

:)

Paul

Edited June 18, 2016 by ptjones

[MaxHeadroom]

Here are front and rear air dams .....

ptjones,  OK now I see what the tire air deflector plastic parts are that they added.

 

 

Have you tried to order the rear side-spoilers?  Those are the ones Ford might have given 2013 C-Max buyers, although throwing $$ rebates at the EPA MPG problems also did the trick with many.

 

Liking your Lexan wheel skirt idea.  Some might say full skirts ruin "styling", but used to be they were all the rage:

[ptjones]

Tried a couple of years ago, but couldn't find a part #.   I guess we weren't convinced they did much. ;)

 

Paul

[MaxHeadroom]

Tried a couple of years ago, but couldn't find a part #.   I guess we weren't convinced they did much. ;)

I don't think anybody makes specific CMax skirts.

About how much they might help, its hard to say.  I took aerodynamics classes years ago, yet my specialty has always been NVH, controls, software, so I'm just skilled enough in aero to understand it's tricky.

For example, most excess drag is caused by creating too many low pressure areas to the rear of the car, which is why those blunt rear ends benefit from vortex generators and spoilers to direct airflow to the liftgate glass.

Also, the more turns and swirlies the flow makes as it hits the car, the worse drag is.

 

In the end, there's no substitute for a wind tunnel, or even a very fine mesh computational fluid dynamic (CFD) model to play with.

[ptjones]

fbov did some yarn aero testing a few years ago. I even cut up some yarn to do some testing , but my wife wasn't interested in helping me out. Oh well, LOL. ;)

Curious to see how much the GasPods were helping.

 

Paul

[SnowStorm]

In the end, there's no substitute for a wind tunnel, or even a very fine mesh computational fluid dynamic (CFD) model to play with.

Sure wish we could get hold of a model!

[fbov]

Use yours...

http://fordcmaxhybridforum.com/topic/3129-tuft-testing-a-c-max/

 

My conclusion was the C-pillar fins are useless, but Paul's wheel well flairs should be great!

 

Have fun,

Fran

[MaxHeadroom]

fbov, Nice yarn tuft experiments.  Makes me wonder if I can just get my hands on a pressure sensor, place it in the middle of the back window (outside), and see if the GasPods or Mitsubishi Evo-style vortex generators would cause an increase in pressure felt back there (higher the pressure on the back the window, lower the car's drag).

 

About those rear side C-pillar plastic pieces, I guess Ford's wind tunnel concluded they introduced a nice cylindrical vortex to the back window, thereby reducing drag.

I noticed today that they put those on the rear hatch glass of Ford Escapes too!

Still I wish Ford would have blessed (tested/validated) the use of GasPod-like or Mitsubishi Evo rear roof strakes (vortex generators).  I'd bet they do something to push the air down toward the rear liftgate glass OK, reducing drag.  Might have to get some for that.

 

Anyway, EcoModder.com seems to be the center of the universe for this subject.

 

Mitsu Evo drivers get all the cool factory rear roof vortex generators (aka, strakes, etc.):

 

 

I'm thinking about ordering VMS Racing's Universal kit and copying Mitsu Evo's positioning as best as possible (slant angle, how close to hatch, etc.).

Closer shape to the Evo's than the GasPods are.  Hence may generator vortices better.

 

 

I remember there was a roof-wing designed for the top of aircraft (737) fuselages which directed flow a bit, should work for us, but too elaborate:

 

Edited June 20, 2016 by MaxHeadroom

[MaxHeadroom]

Looks like our CMax's rear spoiler lip may not work well with the vortex generator fins.

The lip back there causes a horizontal lateral swirlie, while the vortex gen fins cause longitudinal swirlies.

They might not play well together. :cry:

So I don't recommend Mitsu Evo vortex gen fins after all.  Need wind tunnel.

Definitive guide to Mitsu's fins:

http://bpi-us.com/papers/vortexgenerators.pdf

[plus 3 golfer]

Looks like our CMax's rear spoiler lip may not work well with the vortex generator fins.

The lip back there causes a horizontal lateral swirlie, while the vortex gen fins cause longitudinal swirlies.

They might not play well together. :cry:

So I don't recommend Mitsu Evo vortex gen fins after all.  Need wind tunnel.

Definitive guide to Mitsu's fins:

http://bpi-us.com/papers/vortexgenerators.pdf

A couple years ago I ran coast down tests with "gas pods" on my C-Max.  Bottom line: I wouldn't recommend spending $ on them for the C-Max as I saw worse coast down data with pods than without. 

[MaxHeadroom]

A couple years ago I ran coast down tests with "gas pods" on my C-Max.  Bottom line: I wouldn't recommend spending $ on them for the C-Max as I saw worse coast down data with pods than without. 

Me too thinks GasPods don't really work.  It would be rare if someone just happened to place them correctly, talking about cant angle, positioning, and aero interactions with what a car maker already did in lip spoilers etc.  

Even the experts at Mitsubishi could only get -0.006 worth of cD subtracted from their Evo with the vortex generators properly shaped and positioned!!!

 

So the "idea" of vortex generators is good, and used on airplanes & race cars, yet you can't just throw them on there anywhere, and shape/angles matter.

http://bpi-us.com/pa...xgenerators.pdf

Edited June 21, 2016 by MaxHeadroom

[obob]

Me too thinks GasPods don't really work.  It would be rare if someone just happened to place them correctly, talking about cant angle, positioning, and aero interactions with what a car maker already did in lip spoilers etc.  

Even the experts at Mitsubishi could only get -0.006 worth of cD subtracted from their Evo with the vortex generators properly shaped and positioned!!!

 

So the "idea" of vortex generators is good, and used on airplanes & race cars, yet you can't just throw them on there anywhere, and shape/angles matter.

http://bpi-us.com/pa...xgenerators.pdf

 

I was thinking that the effects of a lot of aero dynamic additions are conditional on speed.  So the sweet spot changes with speed.  And some of the best spots for a vortex may not even be on the body of the car but behind the car and also a function of speed.

[MaxHeadroom]

I was thinking that the effects of a lot of aero dynamic additions are conditional on speed.  So the sweet spot changes with speed.  And some of the best spots for a vortex may not even be on the body of the car but behind the car and also a function of speed.

It is true that speed here is the only thing changing the Reynolds Number for our highway speeds, say 55 mph to 85 mph.

Yet the approximately 2 to 8 million Re number our rear roof encounters over that range of highway speeds (55 to 89 mph) results in a very constant CD, as seen in the circled part of the CD vs. Re plot below:

from http://www.mne.psu.edu/cimbala/me325web_Spring_2012/Labs/Drag/intro.pdf

Conclusion: The sweet spots for placement of vortex generators on the rear roof or sides should be about the same for all common highway speeds encountered, since CD is truly a constant for those low mach number flows.

And since CD really is constant, the flow is behaving about the same for our typical range of speeds we care about.

Any lower speeds and drag becomes very small, so its just highway speeds where vortex generators do their magic.

 

The problem is finding where the sweet spots are, and knowing how to cant (angle) them to the air flow, without using a wind tunnel.

Likely we'd guess wrong.

Edited June 22, 2016 by MaxHeadroom

[fbov]

fbov, Nice yarn tuft experiments.  Makes me wonder if I can just get my hands on a pressure sensor, place it in the middle of the back window (outside), and see if the GasPods or Mitsubishi Evo-style vortex generators would cause an increase in pressure felt back there (higher the pressure on the back the window, lower the car's drag).

I got as far as a dual-manometer set-up, but needed help to run it. I planned a center-line sampling, moving one at a time using the other as a control. I think the tuft test predicts a low rear glass pressure, if only by the clean break at the sides (where Ford added things). I was very surprised by the low flow rate over the glass. 

 

I was thinking that the effects of a lot of aero dynamic additions are conditional on speed.  So the sweet spot changes with speed.  And some of the best spots for a vortex may not even be on the body of the car but behind the car and also a function of speed.

Drag is a function of speed squared. Force = Cd x cross-sectional area x v^2. Not a big deal at walking speeds, but no big deal at 4 mph is 100x greater at 40 mph. 

 

And yes, placement matters. Tiny things matter. It's the data that makes Hucho such an entertaining read. 

 

It is true that speed here is the only thing changing the Reynolds Number ...

Huhhh? You seem to have referenced data that says this doesn't matter. 

 

The Mitsubishi study doesn't really apply here. They weren't testing the drag reduction effects of vortex generators, they were optimizing a sedan with a wing. Cd and Cl (lift) are both important, and much of the result is from the wing as much as the rear glass.

 

This is the classical application for roof-line VG's, but a fair test would compare a wingless sedan, preferably with a rear window angle a little steeper than 18 degrees, separation angle for rear glass if I recall my Hucho correctly. VG's are very effective at preventing separation as the angle increases, thus the common use in airfoils, where stall latitude is critically important to safe flight. 

 

If you're interested in automotive aerodynamics, Hucho makes for a great read. 

https://www.amazon.com/Aerodynamics-Road-Vehicles-Mechanics-Engineering/dp/0768000297

 

Have fun,

Frank

[MaxHeadroom]

Huhhh? You seem to have referenced data that says this doesn't matter. 

 The Mitsubishi study doesn't really apply here. They weren't testing the drag reduction effects of vortex generators, they were optimizing a sedan with a wing. Cd and Cl (lift) are both important, and much of the result is from the wing as much as the rear glass.

fbov, I put up the graph to explain why the sweet spots (aka, optimal placement) likely do not change over our speed ranges.

obob made a great supposition that made me think how I could find out if CD really was constant over our speed range, and the graph shows it is, so the flow doesn't really keep dancing around as we change speeds, for our range of low Mach speeds anyway.

I was saying to obob,

that since CD was constant over our speed range (see graph above),

and Reynolds Number is proportional to speed in our low Mach number regime,

the conclusion is that the sweet spots are not shifting around as much as you might think at first.

The classic rough sphere (blunt object) graph, which flat-lines nicely at our Reynolds Numbers (proportional to speed in our case), like a baseball with seams, has a constant CD with speed as we go through highway speeds.

 

Understanding what the variable CD really is requires you to think how it captures the Drag Force using merely Dynamic Pressure x Area.

To get that simple, for a complex flow, requires CD to change over a wide range of Reynolds Numbers, but it happens to smooth out & flat-line vs. Reynolds Number which is proportional to speed in our case.

 

Sorry about the engineering techie stuff, just answering why a vortex generator fixed in place would probably be effective over a wide speed range, if placed correctly, and the problem is to find the sweet spots.   I can't.  Wind tunnel could.

 

Mitsubishi, in their Evo tech paper, wanted BOTH drag reduction and more wing down force.  They showed the pressures across the back glass to demo drag reduction.

 

Vortex generators do have the potential to reduce drag a little by increasing the static pressure on the back glass with or without a wing.

Mitsu got very little drag reduction though.

[Redshift]

I put on 215/55-17 snow tires, no problem, in fact I think they "fit" better than 225/50-17 OEMs.

Remember variable valve timing can kick our engine into and out of Atkinson (late intake valve closing) at will, although its true efficiency does elevate when Atkinson vs. the usual Otto cycle. Power is down when in Atkinson, but efficiency is higher.

The ICE in the C-Max does NOT switch from Otto to Atkinson. It is always in Atkinson mode.