Gen 3 Prius See Through Boat tail Idea
 

I used the template, both vertically and horizontally to draw an aerodynamic boat tail.

The floor, end piece, and front is plywood, and the sides and top are clear plexiglas pulled into curves that match the template.

The floor is bolted to a trailer hitch ball mount, and the plexiglas is built on the plywood pieces.

I also plan a plexiglas piece that would stretch from the top of the rear hatch window to lay on the flip up part of the spoiler, thus allowing the air to flow without the flip at the rear. I doubt I will be driving at a speed where I might need a spoiler.

The boat tail will reduce the vertical area to about 144 square inches, 6" high X 24" long.

Well, I have drawings, but I seem to have misplaced the attachments button.

OK, here are the drawings:

http://ecomodder.com/forum/attachmen...3&d=1517906764

http://ecomodder.com/forum/attachmen...4&d=1517906779

http://ecomodder.com/forum/attachmen...5&d=1517906795

http://ecomodder.com/forum/attachmen...6&d=1517906813

http://ecomodder.com/forum/attachmen...7&d=1517906835

http://ecomodder.com/forum/attachmen...8&d=1517906857

I worry a bit about the necessarily high angle of the plywood floor, that it may produce such a reverse lift that the front of the car becomes lighter.

I hate to use anything to direct the air toward the floor that would increase drag. Maybe a second floor skin hinged at the front of the tail that could be drawn downward by the lower pressure?

http://ecomodder.com/forum/attachmen...9&d=1517925907

Or, maybe just a spring loaded second floor, without the end or side pieces. At slow speeds, where you would be enter driveways, the second floor would be held up against the real floor by the spring loaded hinges, but at higher speed, where reverse lift would be produced under the boat tail, the second floor is drawn down by the lower pressure, and keeps the lower pressure off the real floor.

Would this work?

http://ecomodder.com/forum/attachmen...1&d=1517938802

Or, maybe I should leave the sides on the second door to keep down spill over?

http://ecomodder.com/forum/attachmen...2&d=1517939704

http://ecomodder.com/forum/attachmen...p;d=1517906779

I'm no fan of The Template, but get some other opinion on whether you have applied it correctly. The top view Template[s] are complete, but the side view is butchered. The ground plane and departure angle have been deleted. What you have is suitable for off-road rock crawling. IMHO it should also slide forward to match the contour at the roof.

I know you're fixated on reducing down to the height, if not width of a license plate. You're compromising a lot to get there.

Beard, I used the portion of the profile from the highest point (widest point when laid horizontally) because I didn't want to cut off part of the rear fenders to match the profile. Nor did I want to add width to reach the profile. Yes, that would be more tear drop, but I'm giving up the profile forward of the rear corners of the car, and using it from that point back.I can post the unbutchered profile on the top view: (You know, I think you may be right!) Thanks!

http://ecomodder.com/forum/attachmen...8&d=1517944910

Just trying to help. People apply the template to everything. The thing is the back 70% depends on the airflow set up by the forward 30%. You can't just tack it onto the back of some arbitrary form. Mair starts with an extended body (fineness ratio is your friend) with a circular cross-section. There is (somewhere) some middle ground, hence the wind tunnel rules over theory.

http://ecomodder.com/forum/member-fr...perellipse.jpg

I like the Tropfenwagen, it's shaped like a submarine conning tower. I tried combining several aero-forms into one:

http://ecomodder.com/forum/member-fr...15-4-45-47.png

This would need serious filleting and tweaking, but could accommodate specific internal space requirements.

You could lose all the [upper] taper and optimize the sides. Here's a study of putting a back window like the 1948 Studebaker Starlight coupe on a Beetle:

https://i.imgur.com/YHtUq.png

When I was building my diffuser fer the first iteration, I had single bungee cords holding it up. At speed, I got banging from the diffuser gitting sucked down, the air stalling, and then from the lack of suction/negative air pressure, the diffuser would retract back. This would repeat until I slowed down where the bungee cords were able to keep the diffuser in place. I would expect yer design to be similar and would probably function in the same way. ;)

If you do go in the direction of a retractable floor, look at the rear door of the P-51 Mustang. ;)
http://www.ipmsstockholm.org/magazin..._p51_f_004.jpg

As far as yer choice in materials, you might want to look at Coroplast and aluminum angle to build out the floor pan with instead of plywood. Waterproof and there isn't a propensity to degrade with inclement weather. It will be lighter and more durable than plywood. It will last longer and be easier to work with and install. ;)

I'm not sure you would want the upper part to be plexiglass as the suggested angle you have would make it rather difficult to see out of especially as the thickness increases. ;)

After studying the design a bit more, I'm thinking the second floor idea is more trouble than it's worth. I may just have to employ a gear driven lower-able wing to combat rear suck down at speed, and dropping from near the bumper into the airstream. Unlike the usual wing on cars, which applies a down force at speed to combat lift, this one would apply lift at speed to combat down force created under the boat tail. Perhaps the wing could be operated mechanically by the change in the distance between the rear axle beam, and the car under body.

You know, I'm just brainstorming, don't you?

Thanks for the Coroplast suggestion.

One you prove out the design in Coroplast you can rebuild it in Polymetal.

I'm going to stop you right there: if you put tufts on the rear window and go for a drive, you'll see that there is attached airflow already over the back of the Prius. There's no need to build it up to meet a theoretical template; rather, you should change the angle of the spoiler, which currently sticks out nearly parallel to the ground (to combat rear lift). The tail extension you'll have to test to see if it can continue the same angle as the window (somewhere around 17 degrees from horizontal) or if it needs to relax that to avoid flow separation, like the EV1 LSR tail cone. The cargo carrier I'm building right now relaxes that angle, because I didn't want to mess with the spoiler for now and I want to ensure flow attachment of the air coming off of it. In a future iteration I might try something more aggressive.

Maybe I'm looking at it wrongly. Instead of trying to holds the rear up, maybe I should put a wing in front of the grill to push the front down.

True, but below and aft of the spoiler, there is a large draft area that I'm trying to fill in with a template shaped boat tail. I want a draft area slightly larger than a license plate. The clear cover over the hatch is in place of removing the rear wiper and spoiler, and to more closely follow the template.

http://ecomodder.com/forum/showthrea...tml#post466139

aerohead's verdict. Note the max camber is centered on the driver's door and the nose is at the front wheel.

attached airflow
 

I agree.If it's not to the 'template',it does satisfy Rolf Buchheim's 23-degree maximum angle,which Hucho shared.On the 1981 VW 'flow' body,Buchheim et al. measured Cd 0.14,so it can't be bad.
Also,I don't think the photo of the Prius is true-length,as in a blueprint.The camera appears to be looking from a forward-biased location,which would throw off any template alignment.

wing
 

The wing will ruin the flow.Hucho would consider the factory nose already 'ideal.'
I would recommend that you put your effort into cleaning up the belly and rear wheel openings to guarantee quality flow to the boat tail.Then see if you can figure out how to get the 'final' diffuser angle as close to 2.8-degrees as you can.
If the bottom of the tail is steep,it will create high-drag,attached,counter-rotating longitudinal vortices below the tail; and probably enough turbulence to cause flutter.

Here's an on-topic picture that shows the distortion you want to avoid (when you're measuring for a bellypan).
http://mannphoto.com/prius/bottom/smbottomcenter.jpg
http://ecomodder.com/forum/showthread.php/question-about-prius-boattail-implementation-28930.html#post424002

And here's a thread from 2011 that has some relevant pictures posted by aerohead (perhaps he forgot? :))
http://ecomodder.com/forum/showthrea...tml#post238321

At that time he was using a higher loft line, compared to the 2014 thread. I show this for the wheel spats.
http://ecomodder.com/forum/attachmen...p;d=1305404486

Somewhere on Ecomodder there's a picture of a blue Insight with a matching teardrop trailer that might be relevant. I did find this thread: http://ecomodder.com/forum/showthrea...d-gen-978.html

http://ecomodder.com/forum/attachmen...p;d=1202612003
http://www.mooncraft.jp/yuratakuya/g...prius02-01.jpg

https://images.duckduckgo.com/iu/?u=...AAtUY2.jpg&f=1https://duckduckgo.com/?q=prius+rock...ages&ia=images

Hope This Helps

When you address the underbody everything will be dependent on the size and offset of the four tires protruding into the air flow.

http://www.tacomaworld.com/forum/tir...155x70xR19.pnghttp://www.tacomaworld.com/forum/tir...155x70xR19.pnghttp://ecomodder.com/forum/showthrea...res-25208.html

I'd consider fitting BMW i3 tires (w/ appropriate wheels) with an offset such that they flush to the standard body panels. aerohead appreciates a round air intake at the stagnation point.

http://ecomodder.com/forum/member-fr...7-12-29-57.png

That Photochop was intended for a VW flat fourin front. With the stock Prius drivetrain it needn't be any bigger than this:

http://ecomodder.com/forum/member-fr...1-100-1194.jpg

Are you saying that I should pull the template rearward to the point that the highest point on the template is at the spoiler tip?

I don't see that bias. I can't see the grill openings, not the license plate. There may be some perspective creeping due to closeness of the camera. I guess I could take a telephoto picture of my Prius to minimize that.

My problem is that a 2.8 degree angle on an extended tail piece will drag on driveway ramps. Maybe doing the 2.8 degree thing, and hinging the tail at the spoiler, and raising it for those abrupt grade changes?

template/photo aligment
 

The template is always positioned from the point of maximum roof height.From other images of the Prius,it seems to be okay,falling at around 23-degrees,the most aggressive angle allowable.
Really accurate photos are shot with a telephoto lens from at least 200-meters away from the vehicle and produce an image close to what you'd see with a technical image (blueprint).I think your photo was shot much closer to the car,was elevated,and was towards the front of the car,rather than from its geometric center.This will throw things off when attempting to use the template tool.

OK, I'll shoot my own.

The passenger door window should be perfectly centered in the driver's door window, if you do.

But if you have an adequate computer to run 3D modeling software you could use one of these free models and add your designs to it.

https://www.stlfinder.com/3dmodels/p...del-comparison

https://www.3dcadbrowser.com/th/1/15/15310.jpg
https://www.cgstudio.com/imgd/l/541d...a016b/1379.jpg

My system needs upgrading, I'm struggling to bring a new machine up under the threat of Spectre, Meltdown and BadUSB. I think I need a hardware firewall.

When I did have it together I couldn't merge my modelling with the download, but it was adequate for pulling dimensions. It looked like this:

http://ecomodder.com/forum/member-fr...four-tails.jpg

Attachment 23475OK, I think I've figured out how to do the 2.8 degree, and still get clearance for driveways:

I'm primitive. I use Paint XP

Oh, in answer to someone telling me Plexiglas wouldn't be good for looking through when curved, I'll build the tail opaque, and mount rear view cameras in it.

I use a variety of methods. I assembled this to show these steps:

http://ecomodder.com/forum/member-fr...how-sketch.jpg

The original picture was cut up in Photoshop for step 2. Step three was putting tracing paper over the screen and doing a pencil sketch, which was scanned back in. The final step was done back in Photoshop.

In practice the bubble windshield would be three flat facets.

More skills than I have. I'm impressed

It's a poor workman that blames his tools, but the 3D software is borked and the scanner is long gone. :( I'm coasting on fumes.

I bought Photoshop Elements at a Goodwill for IIRC $8.00.