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Old 10-28-2021, 11:35 PM   #631 (permalink)
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As highlighted by Aerohead, the tail light areas was known to be "tricky" to blend nice with those aspects
You might take a sheet of clear acrylic, cut a slit in it and create an overlap seam. This would make a shallow cone and if the apex is off-centered appropriately it would approximate a blown bubble.

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Old 10-28-2021, 11:42 PM   #632 (permalink)
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If you don't need optical clarity, acrylic and many other plastics are very easy to heat form. For something that size, I'd think of a cardboard box oven with a heat gun, and a crude form covered with a few layers of soft cloth. Also, oven mitts.
However, to keep the lights visible from both sides, it might be easier and neater to just extend the electrics to another set on the back of the box, selected for the shape wanted.
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Old 10-29-2021, 11:56 AM   #633 (permalink)
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fins

Quote:
Originally Posted by tomi_k View Post
Latest box with vertical fins... and changed top surface... this is the one which I used on my latest record (11.20 liters / 100km)...

Fins will be moved few inches "out" (closer to the tail lights) as I have room for it... and side fairing might show up ...

In a 90-degree, sidewind gust, the fin would be in the range of Cd 1.15, same as a sheet of plywood. That far back, behind the rear axle, she could present quite a yaw-moment, good, safety weather-vaning, flat-out at Bonneville, but maybe freaky out on the open road.
I've driven Spirit in pre- lethal, supercell cyclonic inflow, out in the Texas Panhandle, at 75-mph, and had no handling issues.
If you have a chance to safely test for stability, it would be very valuable data.
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Old 10-29-2021, 12:08 PM   #634 (permalink)
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tail light fairings

On SPIRIT, the boat-tail outer edges wrap around the radii of the bed box, just above and below the lenses, providing attachment points for the Plexiglass fairings.
You can kind of make it out in the latter part of the video.
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Old 10-29-2021, 07:16 PM   #635 (permalink)
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BicycleBoB : The fins were a quick trial to reduce airflow wrapping around the box corner (towards the tail light "cavity / recess") based on tuft tests I did. I haven't found a good article what would give guidance what aspects of fins / end plates need to be factored in (other than the vertical angle) so I gave it a shot and made them to that size and shape... Fortunately, it gave me fairly significant improvement on gas mileage but before saying that for certainty, I need to run more tests... but looks promising... As part of that, I realized the fins / end plates can be further out to "scoop" more air from the blended side and top surface between them so that's next what I do. At the same time moving the fins / end plates more "out" (towards the side wall of the bed), it also reduces the size of the cavity / recess shape around the tail lights... which I assume just helps...

Aerohead: totally agree with you about the side winds and yaw -moment. Though, putting it in perspective by looking size of overall side surface of the truck, those fins are fairly small... but they are there, true. Plan was to try to find more info about what factors of fins / end plates are important but haven't found good articles yet. And I don't, back to tuft testing I go....

Looking side surface difference between the cap + the tailbox vs. with the cap + the tailbox + fins - yes, fins/end plates do increase the surface area but doesn't look that big increase. And like said, those were initial prototypes just to see impact and now those can be optimized more as they seems to help... In overall, that whole tail light corner area needs some thinking how to factor all aspects in (thanks for ideas, suggestions, comments, and feedback) and see how to incorporate them into design ....
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Old 11-03-2021, 11:28 AM   #636 (permalink)
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fins / endplates

* At 'normal' driving speeds, designers like to build understeer into the vehicle.
If a side wind pushes the nose leeward, the driver simply turns the wheel 'upwind'. It's intuitive for the average driver, driving on, with the steering wheel 'crabbing,' as with the rudder on an aircraft in a crosswind.
* In a high-performance sports cars, or race car, if understeer was built in, at high speed, a side gust would push the nose leeward, increasing the relative wind from the side, increasing the yaw-moment, requiring even more steering correction. In extreme crosswind gust, the yaw moment might overwhelm the reaction time and steering effort, ending in a crash.
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* The addition of rear fin / capping plates, creates 'arrow feathers' / 'weather-vane' into the vehicle.
* If you're hit by a strong crosswind gust at high speed, the car will automatically steer the nose into the crosswind, canceling out the yaw moment.
* This high speed oversteer can be a lifesaver.
* At the Bonneville Salt Flats, the added rear tray and capping plates help provide a cleaner flow region for the pilot-chute to 'grab some air' in which to deploy the drogue parachutes. ( last September, our Gumby79 volunteered at World of Speed, and had to respond to one race car that had a #1 parachute deployment failure at the finish line ). It can take eleven miles for some of these cars to coast down to a speed at which the brakes can be applied.
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Old 01-09-2022, 07:21 PM   #637 (permalink)
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I owned a Bret Herndon Aerolid from November of 2014 until August of 2015 for my 2014 Ford F-150 XLT with a 6.5 foot bed. I sold it in exchange for a G-4 Bed Cover because we had bought a 5th Wheel trailer and this gave us much better access to the bed of the truck. I have been keeping fuel data on the truck since 2014 in its various permutations. I got curious and started wondering what the fuel log data could tell me about the performance of the Aerolid versus the G-4 Bed Cover. I had to try to extract data by looking for comparable log entries. At first I settled on all numbers above 18 mpg to get highway miles .

The numbers were real close with the Aerolid averaging 18.05 mpg over the Bed Cover 17.79 mpg for a 0.08% difference.

However including my data for fuel runs down to 17 mpg reversed the slight advantage that the Aerolid had. Aerolid over 6,469 miles used 361.7 gals of fuel for a 17.88 mpg composite average. The G-4 Bed Cover over 5,076 miles used 281.1 gals of fuel for a 18.05 mpg average.

Post Script: There is no mass advantage to either configuration. The Aerolid mass was about 200 LBS and the G-4 Bed Cover while lighter covers a 5th wheel hitch assembly that weighs about 200 pounds.

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