My new way of measuring on-road drag

[JulianEdgar]

A good example of aerodynamic modification testing.

Modification:

Diffuser wing



Intent:

Working with full undertray, change wake pattern to reduce drag

Mock-up:

GOE222 wing extrusion with plywood endplates, attached to rear diffuser with aluminum angle.

Test:

Throttle stop testing, 30 per cent throttle, top speed in km/h, Breadalbane straight, New South Wales, Australia. Weather: 13 degrees C, light head wind, 26/5/20, 8.30am

Results:

No wing - 100
1 finger upper gap - 100
2 finger upper gap - 100.5
3 finger upper gap - 99.5
4 finger upper gap - 100.5

Conclusion:

Makes no difference to drag

Outcome:

Remove mock-up.

[California98Civic]

I am trying to create a throttle stop block that will safely and reliably hold my car somewhere between 60 and 70 MPH on flat highway. In testing, I have figured that about 17.5% throttle position in fifth gear should do it. But I cannot seem to create a stopper that reliably yields the same TPS reading each time. Compressibility of carpet and materials under the carpet seems to be the culprit. Maybe it is just my Civic.

Two questions for any of you who have tried this method: (1) did you use your TPS readings to confirm that the stopper is reliably stopping the throttle in the same position each time and (2) if you did how did you make your throttle stopper?

Thx!

[Snax]

Originally Posted by California98Civic

I am trying to create a throttle stop block that will safely and reliably hold my car somewhere between 60 and 70 MPH on flat highway. In testing, I have figured that about 17.5% throttle position in fifth gear should do it. But I cannot seem to create a stopper that reliably yields the same TPS reading each time. Compressibility of carpet and materials under the carpet seems to be the culprit. Maybe it is just my Civic.

Two questions for any of you who have tried this method: (1) did you use your TPS readings to confirm that the stopper is reliably stopping the throttle in the same position each time and (2) if you did how did you make your throttle stopper?

Thx!

1) No reason to for me with the energy display.
2) I use a series of large washers stacked under my pedal taped against a solid part of the pedal box underneath.

But what I think you may be able to do is to mount a bolt or something that contacts the metal below your carpet to provide a solid stop. Possibly something like a button head bolt drilled through the throttle pedal. Not sure how practical that would be, but throwing ideas out there . .

[MeteorGray]

I made a throttle stop for my Mazda3 in less than 30 minutes with materials I had hanging around in the garage.

I made it after Julian's brilliant posts on the throttle stop topic. I've noticed he's not posted here for a while. I hope he's not given up on us. I'm afraid his aggressive approach when he's trying to correct others' mistakes he identifies has caused some friction here. But we should recognize his ideas are profoundly important. IMHO, he's provided more information here on practical information and testing for aerodynamics in a few weeks than I've seen since joining the group several years ago. And, dare I say, in doing so, he's corrected some misinformation too.

Anyway, the materials I cobbled together in a few minutes: a piece of 3/8in thick plywood board with rectangular dimensions of about 3 inches by 10 inches; a threaded bolt that is six inches long; two nuts and two washers to fit the bolt.

I dilled a hole in the top part of the board to fit the bolt so that the board fits over the accelerator with the bolt reaching the floorboard from the top. I put the bolt through the hole with two nuts and washers on either side of the board. This allows infinite adjustment for what speed is desired. It works very well.

In my '15 Mazda3, the floorboard has a hard plastic portion where the bolt reaches it. If there wasn't that hard portion already on the floorboard but instead it were carpet, I'd fit a piece of plywood there so that there is no "mush" where the bolt makes contact.

I adjusted the bolt with the two nuts so that it was three inches long from throttle-to-floorboard. With that three-inch gap, I found that a speed of about 70mph was achieved at WOT, which varies with highway grade and the direction-and-speed of the wind. If I want more or less WOT speed, I'd simply use the nuts to change the throttle-to-floorboard gap.

Regarding the throttle percentage factor, on average mine shows about 27% when at a steady-state 70mph speed with no wind on a level highway. However, percentage varies by a point or three with variations of the road and wind. I quit looking at this value. I think it is more important to test and compare aerodynamic ideas on a flat section of road and under wind conditions (hopefully zero) and that allow valid A-B-A tests.

[California98Civic]

Thanks for your notes on making your stops, guys. I imagine I need not worry about any remaining small changes in the throttle position reading, once I find a way to secrute the stopper on a hard surface that does not flex. At that point, any changes in the TPS reading might just be an artifact of the sensor, gauge, and maybe minor voltage fluctuations.

[MeteorGray]

As an addendum to my post above, I will say that I use my throttle stop not to test aerodynamic ideas at the moment, but to use on long highway trips as a CRUISE CONTROL.

You see, my Mazda3 did not come with an OEM cruise control. So, I have been using my foot instead. But on hours-long trips, I find that my competitive foot wants to match the speed of passing cars and so, in a sneaky move imperceptible to me until I look at the speedometer, it tends to advance the throttle without permission to those higher speeds.

May I say the throttle stop has proven to be an effective watchdog and enforcer to my wayward foot. It also may save me from a speeding ticket some day as well.

As an aside, I'll also say that surely the throttle stop is more fuel-conservative than a factory cruise control, which wants to add fuel every time a hill is encountered in order to maintain speed. My throttle stop won't do this unless, of course, I temporarily remove it and let my foot loose again. I usually choose to lose a few MPHs when traversing upward on undulating roads. However, for any occasions that I actually might want to add speed, I have installed a string that is held down by a third nut that I have installed on the bolt of the throttle stop. This string reaches to the console, and it allows me to very quickly remove the throttle stop from the accelerator if-and-when I want more throttle. I have found that the throttle stop can be easily placed back on the accelerator while underway without undue effort on my part. The long six-inch bolt helps with this.

[California98Civic]

Originally Posted by MeteorGray

... I use my throttle stop not to test aerodynamic ideas at the moment, but to use on long highway trips as a CRUISE CONTROL. ...

Dig it!

[aerohead]

Originally Posted by JulianEdgar

It is still raining, so no testing for the moment - the tape won't stick.

But I was thinking about the above situation, where wing angle seems to increase drag to a greater extent than would be expected. I think perhaps it's because the nose of the car is being lifted.

The wing is positioned behind the rear axle line, and we know it develops measurable downforce. The air suspension control system is not set to rapidly correct at speeds over 80 km/h (50 mph) and so it is likely that when the wing angle is set to provide lots of downforce, the rear suspension is being compressed and the front slightly lifted.

Of course, the beauty of on-road testing is that all factors are taken into account - the outcome is what it is.

This was found to be the case when the 1st-gen Chevy Camaro was tested at 115-mph.
Adding an airdam helped the matter.
Removing the spoiler, while maintaining the airdam was deemed the most satisfactory configuration.
The Camaro had quite a bit of rear overhang, so the downforce, acting over that moment arm was responsible for lifting the nose, exactly as you describe.

[aerohead]

Originally Posted by JulianEdgar

Rather than my having to wade through lots of anecdote-style evidence about The Template and box cavities, can you just direct me to some current peer reviewed tech papers (or published textbook material) on them? And what on earth does “capturing vortices better” mean?

(And I have had a look on here for the source material that supports The Template and box cavities but cannot find it. I don't remember either a 'perfect shape style template' or 'box cavities' being mentioned in any of my car aero textbooks - but I am very happy to follow up if someone can nominate some references.)

1) Hucho specifically addresses the box cavity. He himself conducted studies on this technology, and claimed that, with the exception of body elongation/ boat-tailing, that the box cavity was the only other device which actually demonstrated a drag reduction in his ten years running Volkswagen's climatic wind tunnel. ( he shows a graphic of a VW Transporter with the cavity, along with a drag curve as a function of cavity length.
2) The 'template' is a derivative of around ten talking points on the ground rules of fluid mechanics, listed throughout the 2nd-Edition. I've described the evolution in the threads dedicated to it. Hucho told you to study these on the first page of his 2nd-Edition book.
3) I provided 4-'templates' in all. They will provide fully-attached flow, their full length, the only way to really low drag according to Hucho.
Hucho doesn't use 'perfect', just optimum.

[aerohead]

Originally Posted by freebeard

From first principles: The Holy Template, based on a half-circular cross section, is commonly applied to vehicles with a rectangular cross section. Mair is more useful.

Reattachment.

Careful! The Mair boat-tail is also based upon a streamlined body of revolution with ogival nose.
Jaray actually blended his body from circular section, to 'square', then back to round for the tail. Just as an HVAC contractor might do with ductwork ( Dallas Museum of Art has this hidden in the walls ).
Walter Lay, at the University of Michigan, used exclusively 'square' bodies. Seventeen degrees downslope on top, eleven-degrees on his boat-tailing. Cd 0.12 was his drag minimum. The FKFS reproduced his research and didn't dispute his numbers.