Aero cap VS cross winds

[freebeard]

So essentially a welded wire mesh w/ 8x8" holes? I'd hardly call that a 'sheet' material. What would you skin it with? Stretch some fabric or film across one of your tomato cages and see if it gets you a smooth surface.

Pull the bed completely and make a flatbed with curved sides. That what a friend of mine did in the 80s. Reinstall the original bed for resale.

[Grant-53]

The use of hardware cloth or 1/8" plastic to make the conic sections for the sides of the aero cap is not hard. The front air dam will help keep the front lift to a minimum and make for a stable drive.

[NewMPGfrontier]

The 8X8 mesh is providing the structure, on top of that I have 4ftX8ft sheets of 18ga sheet metal to provide for a smooth continuous surface. Removing the bed offers a few challenges for the items that are mounted to the cross members under the bed. Unless I can find a bed in a JY to cut up. Thinking I may just stick to making the aero cap and revisit the aero bed idea later after working on a better front air damn and other areas that need improvement. Got my eye on the exhaust system that's rusting apart at the seams (that maybe better suited for another thread).

[freebeard]

Well that explains that.

How much does a square foot of your welded wire mesh weigh? How much does a square foot of the sheet metal (steel or aluminum?) weigh? Which will conform to the other?

[NewMPGfrontier]

I wasn't sure how much the materials weigh so I did some searching online for very similar materials. The sheet metal is 18ga and according to discountsteel 1sqft weights 2lbs. The panel is 50in X 16ft and weighs 32lbs for round numbers I'm calling it 4ft X16ft for 64sqft that would equal roughly .5lb per sqft. The stats for the panel came from RedBrand that is very likely the brand that Tractor Supply sells. put them together for 2.5lbs per sqft humm that might be a bit heavy...
For the sake of estimating the bed is 4ft X 7ft (not really but for estimation) 28sqft over the top. From the bed to the 3rd brake light is 18in so 1.5ft X 7ft for 10.5sqft for the triangles on the sides (again simplification and estimate purposes) for a total of 38.5 sqft 38.5sqft X 2.5lbs comes out to 96.25lbs est for the cap. That doesn't sound too bad at least not on top of a pickup.

[freebeard]

I wasn't sure how much the materials weigh so I did some searching online for very similar materials... comes out to 96.25lbs est for the cap. That doesn't sound too bad at least not on top of a pickup.

It's good you're doing some estimating. Add maybe 10% for stiffening ribs, flanging, brackets, hinges, etc.

The reason I compared the [unknown] weights was to suggest not to expect a rigid sheet that weighs 2 pounds to conform to an open net that weighs 1/2 pound. The mesh is redundant. It becomes a question of how to shape the sheet material.

When Art Arfons was making his jet-powered car for Bonneville in the 60s, he famously rolled the sheet metal around the trunk of a tree.

What is the cost of the 18ga sheet steel? Look at PolyMetal™

Product Description
PolyMetal sign panels are comprised of a recycled thermoplastic core sandwiched between two sheets of finished aluminum on one or two sides. The recycled thermoplastic core lends itself to resisting moisture. PolyMetal panels also feature the ability to digitally print direct to the panel, thereby allowing for complete design flexibility.

I weighd a piece 15x7.5" and it weighs 10 ounces. It's available locally at three price levels. Right-off-the-street is about $150 for a 4x8 sheet. It also comes in 4x10 and 5x10 sheets.

Prefinished. You'd have to paint the steel.

[aerohead]

I'm just coming off a 4,800-mile trip through the remnants of three hurricanes.Through Texas,New Mexico,Colorado,Utah,Nevada,California,and Arizona I experienced nothing funny as far as directional stability.
I sense a bit of understeer,since I can't lower the diffuser as low as I'd like,which means my center of pressure is a bit forwards.
In strong crosswind there is just a push.You just give the steering some constant nudge.In gusts,you nudge it a bit harder,but nothing unruly.
Goro Tamai,of MIT reported on the inherent stability of the fastback,with zero lift easy to achieve in crosswind and gust.
The 3,800-lb T-100,at 130-mph,generates -30-lbs at the front,+22-lbs at the rear,essentially 'zero' lift for 3,800-lbs.
I wouldn't be concerned about it.

[NewMPGfrontier]

I'm still on this haven't built it yet, but took some more exact measurements to draw it out and check angles. The bed is 79.5 inches long on the outside and its 2.25 inches higher in the back, and the bottom of the third break light is 18 inches from the top of the front of the bed. Drawing all this out on paper and measuring the angle from the bottom of the third break light to the tail gate it looks like I'm at the ideal 12 degrees. I also found a sheet of .45mil EPDM roofing rubber that should be a better covering than the heavy sheet metal. The rubber might also be nice for other aero mods if I can glue it to sheet metal it would help make a durable full front air damn and side skirts maybe even wheel well covers too.

[NewMPGfrontier]

I got the wire frame welded together. It's pieced together from odds and ends. The frame will be covered by roofing rubber (45mil EDPM) so the frames doesn't have to be pretty. I have a little clean up to do on it to smooth out of of the rough edges that might tear at the rubber. I'm hoping I can find time this weekend to cut and attach the rubber. I'll post pics of the final results with closeups of how its attached. My plan is to use an arrangement of clamps to hold the rubber down with out having to use adhesives.

EDIT: apparently the images either didn't work or I'm impatient. If the images do not show up heres the links to the pics of the wire frame on the bed.
https://www.dropbox.com/s/r7c8ng6j2y...o%202.JPG?dl=0
https://www.dropbox.com/s/ayphfl6p7f...o%201.JPG?dl=0

[slowmover]

" . . The majority of my driving is north south driving and living in the midwest with lots of farm fields I have a lot of cross winds. Does an aero cap help hurt with cross wind drag?"

Commercial electricity production with wind turbines depends on a high average wind speed. Where I live and drive is such a place. Spring time crosswinds travelling north-south remain constant in the 20's and higher. Some days the average stays up in the thirties with gusts into the 50's. So this is a topic of familiarity, not just of interest, to me. Driving in such a headwind beggars belief as to fuel consumption . . . one is effectively "doing 90" in such scenarios while dropping recorded speed to around 50. Watching high profile vehicles heel over like a sailboat is a common sight.

What I've found is this: the steps taken to maximize fuel economy, but not to lower the ability of a pickup truck to do work (otherwise there is no point to having one) shouldn't be sidetracked, much less de-railed over this concern. After all, one's goal is the percentage improvement to the annual average mpg. If that is on track then seasonal variations aren't much of a concern (I could see where winter driving could conceivably exact a greater penalty).

However, there is no doubt that increasing sail area can have a decided effect on handling (meaning steering and braking). I would say that going after steering slop and upgrading [preferably] to KONI or BILSTEIN shock absorbers is first on the list as are polyurethane anti-roll bar bushings. Bringing steering corrections per 100-miles to a minimum -- no matter the driving conditions -- is the immediate goal. As with braking, where duration and degree can be minimized in keeping upright and lane-centered, changng sidewinds (now present, now gone) and most especially from a 3/4 angle to direction of travel is the condition at which to take aim. This, not sidewinds, is the main FE degradaton culprit.

Towing opens another can of worms (greater vulnerabilities to wind, natural and/or man-made), but the above approach is the beginning of thinking, IMO. I would not assume that vehicle alignment is correct even if new, nor that brake drag is not occurring, beyond steering slop (see "tolerance stack" as a discussion). Have them verified. FE is just part of a larger puzzle of pieces whose shapes must be known.

A numerical baseline is what is called for on any vehicle, and more so on a pickup (the tendency to rollover, not spin out as with a low COG car; statistically this is not a skill question). To that end I would weigh all four corners of the truck as equipped for travel and adjust tire pressure on that basis alone. Chasing another tenth via too-much tire pressure is the wrong way where it contradicts safe operation. The vehicle manufacturer offers guidelines to this end (drivers door placard). Use that for a constant in gauging "lane-centeredness" .

To now take this discussion to a higher level -- the work capable by a pickup truck -- I would like to strongly suggest that testing be done with the truck at or near GVWR. This will highlight any flaws in the approach. As most of what goes on around here is just a game in what a solo driver in a somewhat modified car can do on the morning commute and does not take into account knowing fuel burn under under all condtions, one is well-advised -- as I see it -- to put that trucklet to the test. Otherwise, why a truck?

I've recently received a larger front anti-roll bar and a new rear anti-roll bar (where none previous existed) and will likely add a Panhard rod to the rear axle to minmize forces introduced by winds and in towing. Yes, increased sail area is noticeable at the wheel with my cab-height LEER cap. Movement of the body relative to the axle is noticeable. For a pickup, any change that increases the chance of oversteer is not to be undertaken without changes to driving style.

This is discipline moreso than skill acquisition. I drive solo as if my 9k trailer were always hooked up. Not perfectly so, but generally so. I believe my default habits should always reflect longer stopping distances, etc. This in no way contradicts driving best FE as I see it, even if some of the stupid practices (tailgating big trucks) are left out.

As my trucks adjusted "empty" weight is now 1,000-lbs higher than the as-delivered condition, suspension/steering changes are being made. FWIW I would much like to have an "Aerolid" with a bedslide. I can make the load fit, even if COG changes are likely. 66-mph is my top speed, and 58-mph is my preferred speed, even on 80-mph Texas Interstates, solo or towing. Pickups are handicapped. As yours will change, so will its' reactions.

Take a wide-angle snapshot. Acquire empirical numbers. Make changes on that basis. Be able to predict fuel burn under empty and loaded conditions. Account for weather whether temps or winds. How far can you reasonably travel given 80% useable fuel tank capacity? What is the cost to travel X-miles with Y-fuel at an average speed (another area of understanding crucial to a pickup truck as it is well under the stated travel speed.)

This is the goal of a pickup truck: Is it cheaper for me to make a round-trip or to pay shipping? What price convenience? An Aerolid is leverage to the weights of that question as pickups are cheap to buy, but highly expensive to operate. Fuel is not much more than a third of that question if understood correctly as the scope is greater than immediate costs. The dollars at stake are also future earnings capability, thus it is more than just "money".

Good luck, and look forward to more.

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