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Old 03-18-2009, 11:22 AM   #1 (permalink)
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Inflatable boat-tail - concept stage...

I recently went through Indian Motor Vehicle Rules 1989 - the statute that governs road-legal status of vehicles in India. The rules state that modifying a vehicle substantially (an aerocivic-style mod is extreme, so would fall under this category), would result in voiding the road-legal status of the vehicle.

Rules enforcement in India is chaotic at its best, and left to individual enforcer's whims at worst. That means any cop can quote this rule, and take any step he thinks fit, including upto impounding the vehicle calling it a danger to traffic.

A boat tail reduces turbulence related drag very effectively, and can help FE substantially, if implemented. But it is in conflict with the rules as explained above. So what do we do?

I am thinking of an inflatable boat tail, which will be built using a tarpaulin so that it is a water and air tight balloon of conical shape, its base corresponding roughly with the rear surface of the vehicle. The base could be rigid, secured to the rear surface at a few easy-snap-fit points. it could have an inlet for inflation that could be done from an exhaust bleed. The cone can have a small opening at the tip to bleed excess exhaust gas.

Please keep in mind I am thinking of this for a sedan, where the balloon is only for the last part of the boat-tail, starting at the end surface of the boot. If this is not sufficient, a clear - aerocivic style tapering panel will be required to keep view through rear windshield. Or else, a rear view camera with a monitor could be used. (Yeah I know, but thinking don't cost a thing!)

The stock lights can be maintained, with tapering plastic covers on them that would meet with the inflated profile of the balloon. Similar cover can be put over the number plate. In the absence of the balloon, the only evidence of mod would be those tapering covers over the lights and number plate.

Will this work? I am too delusional? What could go wrong here? Any better suggestions?

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Old 03-18-2009, 11:37 AM   #2 (permalink)
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If your reasoning for wanting to make it inflatable is for legality, what's to stop the police officer from stopping your car while it's inflated? Wouldn't it then still be considered a 'danger to traffic', especially if the officer can pretty much determine what he deems fit?

Either way, have you looked at this thread - http://ecomodder.com/forum/showthrea...ttail-896.html?
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Old 03-18-2009, 11:39 AM   #3 (permalink)
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I think an inflatable boat tail is a good idea. I would be concerned about inflating it with poisonous gas from the exhaust.

If you look at how parafoil parachutes are inflated by a wind intake, you might find a way to inflate the tail using an opening under the vehicle. If the tail were short enough, it could deflate into a net or holder and hang behind the vehicle when the vehicle is not moving, or moving slow. When vehicle speed picks up, the tail could inflate and form a stable shape. There might be driver or automatic control of when the tail inflates so that it only inflates when the vehicle is moving fast enough to keep adequate pressure to hold the shape of the tail. So the shape should be designed to be realatively stiff when inflated. A pyramid shape comes to mind.

I would assume that a moving inflatable tail would cause turbulence and would not be as effective as a tail that is properly inflated and relatively stable.

I think this is a great idea and worth trying. A prototype could be made out of a simple fabric such as canvas.
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Old 03-18-2009, 12:41 PM   #4 (permalink)
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Inflating it with parafoil-like openings would create drag, negating any benefit of the boat-tail. Using engine exhaust makes sense from the standpoint that it's already being produced, no extra power required to run a blower fan. But, please make sure none of it gets into the passenger compartment!
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Old 03-18-2009, 01:17 PM   #5 (permalink)
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Sheesh! I was so taken by the idea, that it did not occur to me to search before posting. :P Well, a lesson learnt!

If we can remove something easily when objected to, probably we can save ourselves a ticket / further hassles - that was the inspiration behind thinking this up.

Inflating from the passing air will lead to drag, so no use doing it. Bleeding exhaust would also lead to a rise in back-pressure, so maybe like a balloon it should be inflated and held in place, disconnecting further exhaust flow through it.

A better idea could be having a tent-like structure with the number plate and light assembly on it (a la AndrewJ's boattail), with a clear pyramid/tent shaped cover for the number plate itself. the number plate (bearing plank) would be pushed out through an electrically operated jack like structure - it would require no inflating, and will remain tout against the buffeting caused by the turbulence...

However I should probably not talk out of my hat and let it get a bit more detailed before barking out. And also should read the other thread before posting further
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Old 03-18-2009, 03:09 PM   #6 (permalink)
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Consider having a small air compressor and air tank in the trunk with a lever or other mechanism to inflate/deflate. It'd be great to figure out a suction mechanism with spring loaded door/flap so that it can used and put away automatically.

Some of the best ideas are jotted down on bar napkins, so don't worry about talking out of your hat. Unless, of course, your hat really does talk and that would just be creepy... ;-P
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Old 03-18-2009, 10:21 PM   #7 (permalink)
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Unless the fabric is quite taut, it will flap in the breeze. I don't think that will be good for aerodynamics.

Exhaust air is hot. Hot enough to melt plastic tarps, right by the tailpipe. It also has a lot of water in it. An aquaintance of mine once used his car's exhaust to inflate an enclosed balloon, trying to get it to float because of the "hot air" going in. It actually sat up a ways, and then the car's engine died. The water in the exhaust had condensed in the balloon, and come back to the tailpipe of the car, choking the engine and killing it.

(I hope he wasn't just pulling my leg with that story, but someone else backed him up on it...)

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Old 03-19-2009, 12:56 PM   #8 (permalink)
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Regardless of heat or poisons, I would think the restriction placed on the exhaust would more than kill any effeciency gained by the kammback. The bleed off would have to be a pressure higher than required to keep the kammback stiffly inflated.

But they make 12v high volume inflators for air mattresses and things like that. Just fill it when you need it before driving, maybe even incorporate a pressure switch that kicks the inflator on and off if needed.

Back when I was a kid, I remember this "as seen on tv" product that was for jacking up your car in a pinch. It was a big balloon that attached to your exhaust pipe. Didn't see it advertised for too long and never heard about it again, probably for obvious safety reasons.

If vehicle mods are basically banned, my first thought is to make it something that you could consider a piece of cargo, rather than something attached to the vehicle. Maybe make something that fits securely in your trunk/hatch with the lid bungeed down to an appropriate angle, that sticks out and forms an envelope that happens to be shaped like an appropriate boattail. If you could make it foldable or inflatable it would be even better since if you are deemed a safety hazard by some bad officer, you could just collapse it and take it with you.
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Old 03-19-2009, 02:01 PM   #9 (permalink)
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Yeah, I realize the permanent bleeding of exhaust for inflation and a relief hole at the tail apex is a bad idea. However, the exhaust bleed is only used for inflation (of a conical tail without a hole at the apex), and then the bleed is shut off, it might not affect the the engine at all during (rest of) the run.

In any case the jack-operated retractable version with no inflation (mechanically held in place) gets rid of all issues pertaining to inflation.

Seeing inflation is such an easy answer to the problem of putting together a collapsible structure, having those options go out the window on points sucks
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Old 03-19-2009, 11:33 PM   #10 (permalink)
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What model vehicle do you have, and have you done anything to it already? I'd love to see some pictures...

Exactly how strict are these laws of yours? Do they cover, say, solid wheel covers? Turning a paddle-mirror into a tapered one via Coroplast or Fiberglass? Taking an exterior radio antenna and moving it inside the car? These minor mods can benefit Cd more than you think-I went from roughly 43 MPG to an average of 46 just by duct-taping my wheels, deleting my antenna (and radio since I never listened to it) and placing some flexible tape between my body and door jamb as a seal. All for $10. If you wanted to do say, a partial Grill block for faster warm-ups, I doubt most cops would even notice!

Note that NONE of the above mods are considered 'substantial' by most people.

What do your laws say about interior mods? You may be more mechanically inclined than I am (it would in fact be impossible to be less so, heh) or you may have access to mechanics willing to tinker a bit. If so, you could play with the gearing, add weight to your flywheel, and a dozen other engine mods that other Members have already Posted here-plenty of options, and a Cop can't ticket what he can't see...under the hood.

I guess what i'm saying is-there are plenty of options to boost FE. If a massive bodymod is going to get your car impounded-just don't do it, at all. Failing that, perhaps you could fashion a Coroplast fairing, easy to add or delete in minutes with some Duct tape-then go to your local official body, show them what you want and get permission for it. If they say no, you've only wasted a little time, and if they agree then you now have an official permit to show any Cops who might try to ticket you. Even with a permit though, you'll still likely be pulled over a lot...

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