Study: Optimal Design of an Ecofriendly Pickup Truck Overhang and Roof to Reduce the Drag Coefficient

[vteco]

Great thread, looking forward to reading it through.

Interesting word "garnish", I think of these simple trailing surfaces as trim tabs. I build and fly models of several sorts, R/C and F/F -- the most critical designs are the rubber powered indoor models, and temporary trim tabs are sometimes used when trying out a new one which is out of trim.

So it sounds like you got and liked a fair amount of negative lift as a benefit towards traction.

[kach22i]

Originally Posted by vteco

So it sounds like you got and liked a fair amount of negative lift as a benefit towards traction.

Yes, but I cannot overemphasize that 10% downward slope roof wing per PDF on post #5 results in positive lift, whereas my experiment with straight horizontal wing used in conjunction with bed cover and rear spoiler is net reduction in lift (via seat of the pants opinion and visual confirmation of bed cover deflection/depression.

As I recall the CFD study on my pickup truck done by an aerodynamicist confirmed some theories but also downplayed other theories of mine.

One item was the air slot gap between trailing edge of cab and leading edge of wing. The CFD study confirmed it was at work, but at such a small scale as it may be considered unnecessary or insignificant.

However when looking at a Honda Civic 2021 hatchback in the parking lot at work where the taillights blend into a rear wing in lieu of rear deck or rear spoiler one may conclude more advanced studies have given merit to the air slot approach.

Similar to below, air slots top and bottom:
https://www.reddit.com/r/Honda/comme...ort/?rdt=54602


Another similar photo:
https://www.directautopartsonline.co...ear-bumper-oem

[vteco]

It's very complicated. Deflecting air downward at a tab will create an upward force on the attachment there, but if the flow then impinges on the tonneau, there will be a local downward force at that point

The net result (in a simplified world) would be a tendency to change attitude or squat. There may not be much "lift" ie. a sum upward force on the truck. Actual lift overall is different than a rotational trim change force.

Deflecting air upwards with a tab would create the complementary situation. The tab attachment has a downward force. Below and behind it is decreased pressure tending to pull upward on the tonneau and the pair would tend to rotate the truck toward a negative attitude.

HOWEVER, it seems like there's so much else going on with eddies and turbulence in the pickup box and vortices off the back, I feel like the above is just one trivial and incomplete mental picture of my own. I think it does happen, but how much, when and where.... nope. Just have to try things and see.

[aerohead]

Originally Posted by freebeard

I'm perplexed. Can anyone explain their use of words like 'overhang length'? Figure 16 seems to be concerned with the 'windscreen' angle.

HotVWs magazine used to run an ad on the inside cover that showed Beetles racing in the rain and they all had rooster tails of water coming off the windshield. But the flat, upright windshield has a radiused header, especially the pre-1960s models, that compensated. Air has less mass.

The authors of the research aren't 'automotive' people, so they don't 'know' that they're using improper nomenclature. I see it a lot!
In automotive parlance, 'overhang' is describing and degree of body extension 'forwards' of the front wheel forward tire face, or 'rearwards' of the rear wheel tire's rear face.
Following Dr. Wolf-Heinrich Hucho's language, what the authors are referring to, would be 'Forebody.'