Writer seeking examples of tested DIY aero mods for book

[gumby79]

(But I am still struggling to understand how that helps on engine modifications, as you suggested.)

An engine that is more effectively extracting energy from the fuel being inserted will go faster by translating more power off the same fuel at the same throttle setting. EG :this would allow modifications targeting a specific throttle% setting.

If all the parasitic losses are isolated meaning not changed,then a positive or negative result in speed is to the engine modification.

especially if it is repeatable with Aba.

In my opinion motor modification testing in this manner would have to occur with absolutely no crosswind. Julian has kindly demonstrated and charted how much of a skew this is had on the Windows Up Down Baseline test

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Julian may I suggest an amendment to your test procedure.

Windows up > down as Baseline skue/ calibration run at the beginning of a test session to establish the current environmental conditions versus Baseline so that multiple iterations of a modification can be compared through time

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But a fixed amount of fuel does not equal a fixed power! It closer approximates a fixed torque. But given the influence of that on the drag calculation (^2 rather than ^3), the basic approach should still be valid (on diesels anyway)

No.
Only for naturally aspirated diesel ( ancient dinosaurs not applicable to this discussion)
Diesel is a fixed amount of fuel not a fixed amount of power measured in Horsepower or Torque ,Diesel is a variable ratio engine. Therefore can make a variable amount of power on the same amount of fuel based on how hard the turbocharger is spooling changing the fuel ratio and power output.


With a fixed fuel rate if you increase the load on the engine it lights the turbo better resulting in a higher pressure ratio going into the intake leaning out the engine changing the power output continue loading the engine and continue building boost at the same fuel position. Observation of this fact, is the dividing line between Gas and Diesel Chassie Dyno operators; gas guys go to the floor and read the graph industry-standard that works, is accurate, and is backed up at the track. Diesel Dyno operator is going is going to throttle up to the window hit the brakes and throttle up to load the turbo once the turbo is loaded the brakes are released now you have a loaded dyno test for accuracy of your all out effort, that you can back up at the track. EG a diesel tuned on a chassis dyno using Gas techniques for 9.8sec in the 9.9 bracket class( bracket race speeds/times are dictated by safety equipment limitations) will brake out (produce more power than expected and exceed the safty limmits of of class required equipment, resulting in a banned from competition until New safety requirements of the next higher class are met ).

[JulianEdgar]

Originally Posted by gumby79

Julian may I suggest an amendment to your test procedure.

Windows up > down as Baseline skue/ calibration run at the beginning of a test session to establish the current environmental conditions versus Baseline so that multiple iterations of a modification can be compared through time

Yes that could be done. However, at this stage I use throttle stop testing only for changes that are made on the spot.

[gumby79]

Originally Posted by JulianEdgar

Yes that could be done. However, at this stage I use throttle stop testing only for changes that are made on the spot.

I guess I was thinking too far ahead. Any future changes to the barge boards / Edgarwit external air curtains to correct the lack of attached flow past 1/3-1/4 cord at "any angle of attack/yaw angle " a direct result of using the wrong airfoil profile as we both agree the only way we can find out if a modification is done right is to test. This modification was done well not right, the only way to do it wrong is to get a net negative result, do not let this statement detract from the Brilliance of your device I have a similar design drawn years ago. Inspired by the Dodge racing team that attempted reverse flow Cooling, in high-pressure with a base of the windshield out through the front. They were successful in their designing and function testing up to 205 miles an hour where the belt would start slipping next iteration was going to be a COG belt, the team member that return my email said NASCAR stepped in and they're not even allowed to talk about outside of what was published in the article. for every team member would be banned from Nascar for life.

"Further testing and versions will be required to get it right." you're advice to us, our advice to you

Future Generations will need calibration runs . I still need to post my retractionon on that thread. I was completely wrong about my analysis of the flow with the eroding clay. I assumed a single yaw angle. A very nice presentation would be a series of eroding clay different yaw angles, to see the impact this has, at least two with the same yacht angle but from opposite sides.

...
(But I am still struggling to understand how that helps on engine modifications, as you suggested.)

This would be the perfect use case of Windows Up Down pretest calibration step to cancel out inherent environmental changes over time. Let's face it back-to-back tests among many other RPM targeting things, changing a turbo from a cast wheel stocker to a forged Billet wheel(effect of swap: less inertia lighter material faster spin capability less lag lower spool more power and Tq on the same fuel) is going going to take too long to have an accurate run because a few millibars of pressure priming the new turbo is going to have a direct effect on the result and this does not matter where you live in the world weather happens. helped to pick out the small gains and losses.
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I plan to apply /mix your goodness and this,accurate temperature measurement to help with with accuracy of assment of modifications.


another conundrum in your presented understanding of diesel is that changing speed due to a change in drag will change the RPM/speed but the torque will stay steady, yet more RPM at the same torque value equals more horsepower regardless of fuel type.

Ps I'm not trying to fight with you I don't think anyone here is trying to fight with you please lose the aggression a community without aggression functions a lot better

[California98Civic]

Originally Posted by gumby79

... barge boards / Edgarwit external air curtains ...

Cheek spoiler? Dimple wings? Aerogils? Shoulder pads?

[JulianEdgar]

Latest videos:

Improving intercooler airflow. Not so relevant to ecomodders, but technique is based on measuring aero pressures.

https://www.youtube.com/watch?v=o60jC6EIgPU

Getting lowest drag - what you need to know about lift.

https://www.youtube.com/watch?v=SStOHM8kgIs

Making good aerodynamic belly pans (undertrays).

https://www.youtube.com/watch?v=L9WCVlWPcys

[JulianEdgar]

Latest videos.

Using a pitot tube under the car. Seeing what is happening when you can't use wool tufts.

https://www.youtube.com/watch?v=S2tHdldwao8

Using a pitot tube reference when measuring aero panel pressures, improving the accuracy of on-road surface panel measurements.

https://www.youtube.com/watch?v=WAg2lJvcw0k

Does a box cavity actually increase pressure in the wake and so reduce drag? I find out.

https://www.youtube.com/watch?v=J8j61XTBSVQ

[freebeard]

You keep busy. And that's not even counting the speaker enclosures.

I only found the time for the third one. There exists a picture that aerohead posts occasionally (that I can't find via Search). His friend in the 1980s had a VW camper that he drove to Mexico one a year that had a conduit and boat wrap open-ended boat tail — a bigger cavity than the one you tested. There was some claim associated with it.

[California98Civic]

Your box cavity pressure measurements are interesting and encouraging, but I think your specific build might be part of the reason you got quite different results than Ali. Ali observed in his article that the effect on drag was very sensitive to other mods. There was a lot of "interdependency" (his word) between the cavity, the difuser, and wheel well covers and such. You mention that in your video, too. But your tested design is radically different from Ali's in several ways that quite possibly matter a lot. Ali's final design was much smaller and was not an extension of the side, top or undercarriage body lines. Here is the final optimized box cavity from Ali's Audi A2 test subject:



Remember that he also claimed that the carefully optimized cavity was how he was able to get even more drag reduction through a 2° difuser.

Ali presented this research at Coventry University on October 19, 2011. I downloaded it on March 29, 2012 when it was still fully available on the conference website without a password. I don't see the 2.3% drag reduction claim in the slides detailing the box cavity. I am not saying he did not make the claim, but I don't see it. Which slide is it on?

[JulianEdgar]

Originally Posted by freebeard

You keep busy. And that's not even counting the speaker enclosures.

I only found the time for the third one. There exists a picture that aerohead posts occasionally (that I can't find via Search). His friend in the 1980s had a VW camper that he drove to Mexico one a year that had a conduit and boat wrap open-ended boat tail — a bigger cavity than the one you tested. There was some claim associated with it.

I was surprised by a couple of things with box cavities.

1. How low the gain was in the wind tunnel tech presentation that people quote - just 2.3 per cent on the Audi A2. I had assumed from people's comments that it would be higher.

2. That I could actually measure a change (improvement) in wake base pressure with the very large box cavity I trialled on the Insight. But that change, as I described in the video, is very small in terms of drag force - so the small reduction in Cd with the A2 (even with its much bigger wake area) makes sense.

But for vehicles with really large wakes, it could be beneficial. Otherwise, separation edges are easy and cheap to add.

[JulianEdgar]

Originally Posted by California98Civic

Your box cavity pressure measurements are interesting and encouraging, but I think your specific build might be part of the reason you got quite different results than Ali. Ali observed in his article that the effect on drag was very sensitive to other mods. There was a lot of "interdependency" (his word) between the cavity, the difuser, and wheel well covers and such. You mention that in your video, too. But your tested design is radically different from Ali's in several ways that quite possibly matter a lot. Ali's final design was much smaller and was not an extension of the side, top or undercarriage body lines. Here is the final optimized box cavity from Ali's Audi A2 test subject:



Remember that he also claimed that the carefully optimized cavity was how he was able to get even more drag reduction through a 2° difuser.

Ali presented this research at Coventry University on October 19, 2011. I downloaded it on March 29, 2012 when it was still fully available on the conference website without a password. I don't see the 2.3% drag reduction claim in the slides detailing the box cavity. I am not saying he did not make the claim, but I don't see it. Which slide is it on?

The percentage change can be worked out from the bar graph. Cd = 0.215 with mods up to box cavity, Cd = 0.210 after box cavity. A 2.3 per cent reduction.

It's a very small change in drag. What I measured was also a very small change in drag, so I can't see how you can say that I "got quite different results than Ali". Given the different size wakes, I'd say they're in the same ballpark.

Without further evidence, I'd say that box cavities - especially on cars without large wakes - probably aren't worth pursuing... certainly not as first steps in drag reduction, anyway.