Civic VX Boattail
 

I may take the plunge... I drive 150 miles a day...

How does this blueprint look? I assume good. Before I begin thinking about fabrication (I teach auto shop, so this will be a fun class project) I just want to make sure that my theory is good.

Woohoo! Boat tails are so awesome. What an excellent idea to involve the class.

First: The top looks great.

On the bottom, I wouldn't go so "fast". The reason: you're not dealing with clean flow on the bottom of the car as you are on the top, so the angle can't be as extreme. Bottom flow is already turbulent, so more prone to complete separation if you arc away from horizontal too aggressively.

I've tuft tested the bottom surfaces of both my Insight & Metro/Firefly tails, and observed attached flow on both by not exceeding ~13 degrees on the Honda and respecting a much more conservative 6.5 degrees on the Metro/Firefly. (Arguably the Honda has a much cleaner underbody design, which is why I went steeper with it.)

• http://ecomodder.com/forum/showthrea...mpg-10691.html

• http://ecomodder.com/forum/showthrea...uft-25223.html

Another critical consideration to keep in mind: the "transitions" from the side to top/bottom surfaces. Use generous radii there, not hard corners, to minimize the chance of "tripping" the flow into vortices.

lean burn loves boat tails
 

Postscript: adding a tail to the VX is extra-brilliant because it effectively expands the "lean burn window" inside which that magical Honda engine gives you astounding cruising fuel economy. You'll be able to hold lean burn at higher speeds, or under other higher load situations like accelerating or climbing.

The gains from a boat tail are greater on a lean-burn equipped car than a conventional one.

Well if its all for the children's benefit, you should also have them design and build a full belly pan and rear wheel skirts :)

Hi gijoe985,
I say its just fine as its damn near a copy of Basjoos's car.
And heres the proof your overlay on Basjoos.;)

Well, we just did an ( overly aggressive) air dam today. As well as a simple warm air intake.

if we came up with a very efficient air dam and side skirt setup, how beneficial would the belly pan be?

Also, what do you guys favor for fabrication material? Abs seems popular. We have thin sheets of stainless. We could possibly fiberglass.

With respect to the AeroCivic, I'm not convinced the bottom of that tail is optimal. And Mike will tell you he has never tuft tested it. :P

Obviously the tail is "good", but maybe it could be "better".

Ha. Yes! Think of the children!

I'll add, discussing the bottom of the boat tail, if we do aggressively block off air from going under the car, how will that affect the bottom of thr boat tail design? Though real world testing will be the final say, I'd like to get as good of a design on paper as ai can before we start building...

then there is the whole practicality factor. I hope to make it so that space is usable. We'll see...

Re: air dams....

You never see a super high-efficiency aerodynamic concept that has a giant air dam. (EV1? Nope. VW 1L cars? Nope. Etc..)

Air dams are band-aids to fix dirty underbodies. Why not smooth out the underbody instead, like AeroCivic, and then you know you're "feeding" relatively clean flow to the bottom of your tail?

I'm not sure what would happen if you put a giant air dam on a boat-tailed car. I never thought to test it out the combination.

Looking forward to seeing how this develops also! Will be heading up to east Washington state in April, so would enjoy seeing the project first hand if you're in that area.

Live in Ellensburg, teach in Grandview.... about 75 miles away...

Boat tail and rear wheel skirts and you can do that on one gallon of fuel ;). Good luck, you definitely have one of the best cars to start with.

Thanks!!! We'll see about 75-80mpg on my work run. I have three mountain passes that always hurt my numbers. Though I get over 6-7 miles of engine off coasting a day... ;)

Got 50mpg today on the way to work. That's closer to what I get in the Spring, so I think the HAI is helping.

I redid my boattail design. Look better?

how does
 

Here is 'Kamm's boat tail.You'll need to weigh out your departure angle so's not to rip her off on a driveway ramp.Just a comparison.:)
http://i1271.photobucket.com/albums/...85x11Scan2.jpg

Although the best gains are from the rear, I believe in starting from the front to back. The better the front is, the better the gains at the rear.

As Metro said, increasing frontal area is better than a dirty belly- but a clean belly is better than that bigger front end.

I just had a brain tsunami, and have to cut this post short- only posting a halfee because I want to subscribe and am interested in following your journey :thumbup:

front
 

Here are some canopy images to look at.If you compare line 2 with line 3 you see no change in drag in spite of the 'more aerodynamic' nose of the line-3 canopy.Just something to think about.
As to line-1,construct it on paper or computer and see if you could live with it.
PS,it's a 'laminar' shape.something we don't get on real roads.
http://i1271.photobucket.com/albums/...2/Scan2-14.jpg

Right now I am trying ti determine what materials to use for the mock up. I dont have any large cardboard on hand. I could use 1/4 plywood. I could also buy foam. I thought fiberglass in the end would be pretty cool. We've got some lexan on hand for a rear window.

http://ecomodder.com/forum/showthrea...yle-26022.html

:)


>

I would say so! Phil's illustrations confirm it, but departure angle is a real world consideration, as he points out.

GIJOE985 - If you're still searching for large pieces of cardboard for your Cardboard Aided Design, stop by a furniture store. Lots of stuff gets shipped in large boxes with big flat pieces; they'll probably part with some for you.

A furniture shop up the street from me has several large boxes, unbroken, just waiting on the sidewalk about twice a week for pickup. They don't even think about recycling. A few times I've gathered enough cardboard to shove into the wood stove for a quick burn, about an hour's worth.

A cardboard fire will tell you if your stove is sealed. Mine isn't. Dang it gets hot. Gotta fix that.

The underside of the Aerocivic's boattail is steeper than the calculated optimum, but I had a steep angled driveway and also didn't want to be limited where I could drive by worries of a low hanging tail dragging on the ground. The alternative would have been to put rollers on the underside of the tail and make it strong enough to support the weight of the car if it got low centered.

http://ecomodder.com/forum/attachmen...3&d=1394041846

I tried to stay away from the site for a week so that I would take care of more important things. Good idea. Xist-standard implementation.

This coming with the guy whose profile tagline says "Should be playing WoW"...

:p

I really thought that I changed that to "Should be studying!"

I've started my prototype... at least the shape. No idea of how I will attach it yet. Ive got 3, 1/4" plywood pieces and 3 of thick cardboard. I aligned them and then drilled 3/8 holes through and now I am putting dowels through the holes... it should at least hold the shape. I'll try to snap a picture tomorrow.

Here is my mock up. Just to get the basic shape down. Did a lot of scale measuring with the shape of my car. Tried to keep it as "scientific" as possible.

Very nice!

Deja vu!

http://ecomodder.com/forum/attachmen...1&d=1258682908

Yeah, because of the wood, it is stronger, but heavy. I don't string would cut it. IN fact, my dowels have a hard time supporting the wight. I may just need to get some more cardboard and redo those panes...

Cut out the middel of the plywood pieces. They dont add anything but weigth for the construction.
Cutting out the middles will reduce weight with 2/3 or more.

Here is some progress. I DID cut out the middle sections. It reduced the weight a ton. I am now just fabbing up the shape. We're trying to decide of we want to piece together sheets of abs or FRB OR if we want to create a fiberglass shell. I think a two piece shell would be cool. We'll see.

Craftsmanship looks great. Can't wait to see the final product.

Well... This project was not abandoned. Just moving slow.

how does this approach sound: shape the foam as close as possible, fill with what, plaster? Car filler? Once filled and smooth I could cover with fiberglass or I could make a female mold and then make a super nice mold... If I make a fiberglass mold, I assume I'll need to reinforce the inside. And then comes the fun of figuring out how to attach it. I was waiting to cross that bridge when I got there.

Thoughts? I'd like it to look nice. I'd also like to figure out a way to have a hatch that opens still too...

http://i698.photobucket.com/albums/v...ps1nq8zpb7.jpg

approach
 

Since you're working in foam,check out 'Honda Insight Tail Extension Project',by 3-Wheeler.
He used micro-baloons (CABOSIL,fumed silica) and epoxy as a ultra light weight filler.You might want one coat of resin on the foam first.WEST SYSTEM sells this.I get mine at a local marina which does Chris Craft restorations.With a single layer of glass it would be strong enough to remain on the car.Or you could make a female mold from it and layup your finished part.

http://ecomodder.com/forum/showthrea...ect-13533.html by 3-Wheeler

Honestly, I think that anyone planning on building a boat tail or anything out of foam and fiberglass should start with this thread. He has some of the most beautiful craftsmanship that I have seen on this site!

My introduction to the thread was that last picture, then I went back and read the whole thing. My thought is that everything up to the penultimate picture sounds reasonable, but that last picture is scary!

If you want to know why read CarBEN EV5 Full Sized Prototype Construction - 5 Seat Electric Car ..., around page 31 where he starts confronting the problems of fiberglassing over glued-up foam strips.

Were it I, I'd strip off all the foam and figure out how to attach it to the car. Wrap it with plastic cling film until it holds it's shape. Then use a thin material that has a finish surface that can be rolled into simple curves (to save hours of tedious finish work). Or dampen, slump-form, and dry cardboard.

Here's an example of a form made from gored flat strips.
http://ecomodder.com/forum/member-fr...llmystery2.jpghttp://ecomodder.com/forum/member-fr...llmystery1.jpg

See also
http://ecomodder.com/forum/member-fr...ticuda-tb5.jpghttp://ecomodder.com/forum/member-fr...lboxlayout.jpg

Freebeard- I'll look into it.

That aside, for the fiberglass. If eventually it was only fiberglass, how many layers of oven cloth should I go?


These guys seemed to have decent success.

http://www.rqriley.com/frp-foam.htm

The guy in that article states this-

I have a lot of cloth, the woven kind. Not a lot of mat. Think I should buy some mat? I thought cloth would work better...

You can purchase fan-fold foam board from Hope Depot, Lowes, and Menard's, although I needed to special-order mine. It is about a quarter of an inch thick, so it should be really easy to handle, but I would recommend just purchasing thin sheets or use a wire cutter on heavier ones, this comes with a thin layer of plastic with many perforations. When I tried to peel off the plastic, it hit the holes and just shredded, it would be way too much work.

I mention this because it seems like two layers of fiberglass with foam in between is the best solution and I wondered how much foam you really needed.