Aeromods must transfer force to be effective

[freebeard]

There is a history from before your join date. I wouldn't follow an aerohead post with a reference to the other party involved, out of respect.

Originally Posted by aerohead

A 'half-tonneau' works better due to reattachment, plus the low pressure of the vortex core telegraphing under the cover, to the forward face of the tailgate, increasing the pressure differential between the front and rear face.

I've never understood whether the front wall under the half-tonneau is necessary or not. Is the pressure at the floor of the bed and at the tailgate similar or different?

[Vwbeamer]

Originally Posted by aerohead

As far as automakers are concerned, pickup trucks are just large sedans, without a trunklid.
Flow separates off the rear of the roof, and there's nothing to reattach to.
There's no pressure recovery.
High drag and high lift.
A tonneau cover is essentially a 'trunklid.'
If it's sufficiently close enough, vertically, and sufficiently 'far' longitudinally, it provides a surface for reattachment.
A vortex is captured on top of it, and the outer free stream will skim over the 'locked-vortex' as if it were a solid structure, plus 'touch' the back of the cover before separating.
If 'smoked', you'd see streamline filaments diverging as they decelerated down the 'contour' of the vortex, picking up pressure as they lost velocity.
This is the drag reduction.The higher pressure is communicated to the base, behind the tailgate, raising the base pressure, which lowers the pressure drag, the largest component of aerodynamic drag; and why we streamline.
And since slower, higher pressure air impacts the rear of the tonneau, it also kills most of the rear lift.
A 'half-tonneau' works better due to reattachment, plus the low pressure of the vortex core telegraphing under the cover, to the forward face of the tailgate, increasing the pressure differential between the front and rear face.
GM has the US Patent on it.
If you watch a vinyl cover, you'll notice a dip at the rear where air is attacking it.
At the front, behind the cab, it will look like Yoda's under there trying to get out, creating an upwards bulge in the fabric. Highs and lows.

The patent
https://www.freepatentsonline.com/4573730.pdf

Results on my truck

https://ecomodder.com/forum/showthre...oma-39148.html

[aerohead]

Clarence 'Kelly' Johnson, of Lockheed's Skunkworks is remembered for 'just enough and no more' in design.
For every pound saved on the U-2 Dragon Lady, they could get one more foot of altitude ( important when you're in the other guy's airspace, and he's got surface-to-air missiles to go with his radar ).
'Kelly' would engineer no further than necessary than what was necessary to satisfy an aircraft's performance criteria.
'Aluminum foil'- thick fuselage skin, which could be dented just by looking at it.
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My first aeroshell 'exploded' under aerodynamic loading, on it's maiden voyage.
My second aeroshell was destroyed one night by young goats which thought my pickup was a great thing to climb and jump off of.
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So yeah, some strength, rigidity, and toughness are more than welcome.
And since drag is a function of frontal area and shape, the rigidity guarantees that your shape will hold.
Take care of the shape, and the shape will take care of the pressures.

[aerohead]

Originally Posted by freebeard

There is a history from before your join date. I wouldn't follow an aerohead post with a reference to the other party involved, out of respect.



I've never understood whether the front wall under the half-tonneau is necessary or not. Is the pressure at the floor of the bed and at the tailgate similar or different?

Both are exposed to the core's tornadic low pressure.
Low pressure exposed to the floor might imply 'lift', however, the slower, higher pressure air, decelerating down the rear of the locked-vortex, slams into the top rear of the tonneau, appreciably behind the rear axle, creating a positive aerodynamic moment arm ( torque ) as Wolf Heinrich Hucho discusses in his 2nd-Edition.
Rear lift is significantly reduced, along with drag.
The Cd 0.315, GMC S-15, 'Syclone on the Salt,' used the patented 1/2-tonneau as part of the aero kit which helped it secure a land speed record at Bonneville. 210+ mph.
And considering that they started @ Cd 0.475, that's a pretty good hat trick!
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The US Patent mentions the 'partition' which was tested underneath the tonneau. If it had any significance, it didn't stick in my shriveling mind.

[freebeard]

The strongest shell structure would be a geodesic spheroid.

[aerohead]

Originally Posted by freebeard

The strongest shell structure would be a geodesic spheroid.

We'd have to consider the panel strength of each individual facet, each with a center of percussion, resonant frequency, plus harmonics.
The irregular perimeters of the facets would also open the door to 'superposition' and rogue waves communicating across the asymmetrical spans.
Reflections. Amplifications. Standing waves.
The superstructure would survive anything you threw at it, but if any panel got to 'singing' it could suffer repetitive bending fatigue, rupture, and ultimately failure.
Finite element analysis, CFD, or wind tunnel could reveal suspect areas.
( Any university undergraduate seniors, graduate students, want to take on a fascinating project ? )

[Talos Woten]

Originally Posted by freebeard

The strongest shell structure would be a geodesic spheroid.

I've moved to geodesic-like design from the box-like thinking I used in earlier iterations. I had a great conversation with an actual aeronautical engineer, and he summed up how to build solid frameworks succinctly: "maximize interlocking triangles."

Apparently triangles are the simplest building block that keep their shape under a variety of loads from different angles. So if we can interlock them, it adds a lot of structural rigidity. I'm finding triangles overlapping rectangles are particularly effective. The only issue I'm having is creating "smooth planes", because the framework bars have to go "over and under" each other, so to speak.

[freebeard]

I'm finding triangles overlapping rectangles are particularly effective.

Not getting the over and under part.

If you look closely the design at #16 is based on an octahedron. There are four-way connections at the front, rear, top and sides. This is what allows the differential prolating.

Also, the triangles can be rendered as diamonds or hexagons. The triangulated shell over a diamond frame would [technically] be triangles over quadrilaterals.

edit: look what I found, A Wellington but instead of showing it's Lamella frame, it's under a canopy that is diamonds over squares.

http://www.airpowerworld.info/bomber...wellington.jpg

Embed is thwarted.

[Talos Woten]

Originally Posted by freebeard

Not getting the over and under part.

Sorry. I meant like basket weaving we get a tighter mesh by "sewing" struts over and under each other. It also keeps the face plane more flat, rather than having many levels at each junction we limit it to around two. The aluminum bars that I'm using are thick enough that it's difficult to even have a four-way interconnect, let alone attach a sheet on one side.

Hehe. In your picture I thought the airman was being impaled by the propeller!

[freebeard]

Okay. If the 'struts' are flat bars I can see it.