Rear fairing on Prius

Discussion in 'Gen 3 Prius Main Forum' started by energyideas, Jul 29, 2018.

  1. energyideas

    energyideas Junior Member

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    Posting on gen 3 because that is what I currently have, after owning two gen 2s and owning a previous gen 3 so four Prius thus far. A few years ago I posted this blog on how to make a coroplast based fairing for a recumbent trike: Renewable Energy: Inexpensive, Lightweight Recumbent Fairing .

    More recently I drove from Colorado to California and back in my current gen 3 getting 47.4 mpg for 2,700 miles on the gen 3 just turning the 100,000 mile mark. I've been thinking of a lightweight rear fairing that juts out behind the car, mounted on the hatch so it can still go up and down. My curiosity is, has anyone done this before? Can't find any examples.

    I'm thinking 5 mpg more? Transparent plastic at the taillights. Possibly 4 feet in length, the shorter the better. Would be applicable to any gen Prius.

    Thanks in advance for any discussion.

    energyi
     
  2. Vman455

    Vman455 Active Member

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    To my knowledge, no one else has done this besides myself. I built a composite foam/fiberglass box for this year's Green Grand Prix:

    [​IMG]

    It worked well; mileage in the high 50's to low 60's on the interstate drive out to Watkins Glen, 62.8 mpg in the competition. I'm currently working on lightweight designs for next year--with the tail, cargo rack, and hitch receiver this was nearly 100 lbs hanging off the back of the car.

    if you do something, I'd love to see what you come up with.
     
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  3. Johnny Cakes

    Johnny Cakes Active Member

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    Seems like this could be marketable -- not for the gas mileage alone, but as a storage container that actually improves gas mileage.
     
  4. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    I don't know... o_O
     
  5. energyideas

    energyideas Junior Member

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    Thanks so much for the reply Vman455! Exactly what I was fishing for. Any use of a skirt to continue the line of the car to the composite foam/fiberglass box? You obviously have the gap for access to the hatch. That gap causes more wind resistance. Again, excellent reply. Thanks so much for this and any additional discussions.

    energyi
     
  6. bobzchemist

    bobzchemist Active Member

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    I'd buy one. On the other hand, I'm the guy who already wants to get a trailer hitch just so I can hang a tool chest on it.

    For me, the deciding question would be how much the improved wind resistance improved the mileage versus just a chest on a trailer hitch, and does that justify the (presumed) extra cost of buying the aerodynamic version.
     
  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    You might do well to check local and federal laws on externally carried cargo. I seem to recall that we get an allowance for 36" past the rearmost native part of the car in Pennsylvania, and I know there is a long list of specific Federal regulations if the vehicle has commercial plates.

    You might also need a high-vis ribbon or similar marking.

    Cool idea!
     
  8. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    I'm thinking about parallel parking, fitting into a garage. Looks, too.

    And blocking the lower-rear window: not a great loss, but hey.
     
  9. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    As far as parking and fit, there's a fair argument for making it collapsible, inflatable or easily removable.

    As far as looks go... you know it's a Prius, right? ;)
     
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  10. Vman455

    Vman455 Active Member

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    Had I kept it on, I was thinking about gap fillers--but kept running into the issue of hatch access. I sleep in back on road trips (including this Watkins Glen trip), so hatch access was a design goal for me. Next year's version, I think, will be attached to the hatch itself so it moves with the door.

    Illinois is 48" before the extension has to be marked with a red flag. I put tail/brake/turn lights on this and reflectors on the sides just to be safe. Some of the other competitors at the GGP complained that the brake lights were too bright.

    In case anyone on this thread can't tell already, I don't care if the car is conventionally attractive. Low drag is what looks good to me!
     
  11. Vman455

    Vman455 Active Member

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    Ah yes, that person started several threads on Prius boat tailing and then disappeared. I'm curious if they ever built anything.

    Speaking of Ecomodder, this thread contains everything I did up until this spring to further streamline the car. This thread has everything I'm doing to it now for next year's competition, starting with considerable weight reduction.
     
  12. Vman455

    Vman455 Active Member

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    Oh, you may also be interested in this earlier version of a tail, built out of corrugated plastic for a two-week trip to Connecticut last fall:

    [​IMG]
     
  13. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Have you ever looked into modeling this in a virtual wind tunnel? I did something like it once with the custom plane maker in x-plane.
     
  14. Johnny Cakes

    Johnny Cakes Active Member

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    Even if the extension has brake lights? That seems odd.

    I am going to be adding brake/turn lights to my bike rack since the bikes kinda block the OEM lights. Do you have a part number for the lights you used? I'd like to get something pretty bright. Also, I've been told that the harness hookup is extremely easy, but any pro tips to avoid problems?

    Cool, but Version 2.0 = major upgrade! :)
     
  15. energyideas

    energyideas Junior Member

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    Thanks for the excellent 27-page thread on your original modding and for the new catch-all thread. Toyota engineers are most likely lurking on your posts, you are doing their job for them.

    I liked your sculpting of the tail shown in this thread:
    3rd gen Prius aeromod thread - Page 24 - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

    energyi
     
  16. energyideas

    energyideas Junior Member

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    Vman455, PM in your mailbox.

    energyi
     
  17. Vman455

    Vman455 Active Member

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    I've actually gone back to school to get an engineering degree, starting this summer, so that's on the horizon! First computer science course this fall.
     
  18. energyideas

    energyideas Junior Member

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    I just started a Solidworks class, am trying to get my group project to be the fairing. Will keep you posted.
     
  19. energyideas

    energyideas Junior Member

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    Saw a trailer hitch box with this website: stowaway2.com. I think an aerodynamic lightweigh box could hang off the hatch without the need for hitch metal and expense. Again, this is the design I'm pitching to my group project.
     
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