Idea fer an inflatable boat tail made from mylar space blankets... - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

thatguitarguy · 11-23-2009, 08:45 PM

The upsidedown hood scoop is kind of what I'm thinking, and with the ping-pong-ball check-valve that stevet47 is talking about, you probably wouldn't need a fan.

thatguitarguy · 11-23-2009, 08:50 PM

If you're going to leave it outside, you might as well make a perma-tail. I think the idea of an inflatable is to bring it inside. A genius with a boxcutter could ruin your day otherwise.

stevet47 · 11-23-2009, 09:00 PM

Quote:

Originally Posted by thatguitarguy

If you're going to leave it outside, you might as well make a perma-tail. I think the idea of an inflatable is to bring it inside. A genius with a boxcutter could ruin your day otherwise.

I was thinking you would just roll it up for around town use, then unstrap it and let it inflate for highway use.
Good point about the boxcutter though.
I suppose an inflatable boattail definitely has its issues. Still shouldn't be hard to do though.

And you guys dont think a hoodscoop for filling the boattail is essentially making a parachute? Unless you could block it once full.

thatguitarguy · 11-23-2009, 09:19 PM

Seems like it shouldn't be too hard, but none of us has done it yet...

I think a scoop doesn't have to be that big, and you can make an exhaust valve so once it's inflated it exhausts excess air like these inflatable funhouses or tennis courts. The thing about a parachute is its huge opening. Maybe as the bag inflates it also has a mechanism inside that pushes a flap into the intake scoop to close it off??

I'm just the idea man, not the engineer...

BamZipPow · 11-23-2009, 11:30 PM

Quote:

Originally Posted by thatguitarguy

I have been thinking about this also. Concerns of mine were more of safety and of the legality of mounting a highly reflective contraption on the rear of your vehicle. In many instances, if you are reflecting the road from the bottom and sky from the top as well as trees and passing cars, you could become virtually invisible. Some aero-modders like the extra attention they get, others would like less, but going full stealth in the middle of a busy highway would not be a good idea. And mounting a bunch of lights to be seen would require some kind of sub structure, nullifying the handiness of something small and inflatable.

Keep in mind that this is just fer a cheap test bed fer the right shape/development. Would you rather put a ton of money and effort in building a rigid structure and find out it doesn't quite cut the mustard? A quick inexpensive fab design fer testing can be the key to designing the right setup fer yer vehicle. One could also cover the mylar shape with an identical nylon ripstop (parachute material) shaped cover if you really wanted to cut down on the reflective properties of the mylar. Heck...if you really wanted to...you could even have the mylar sprayed with some Line-X bedliner material so it retains a rigid shape so that you can transition from flexible to a more permanent setup.

I'm all fer cardboard, coroplast, fiberglass, carbon fiber, FRP, etc...but I was looking fer an easier fab/test bed. I looked at custom rubber sheeting and that was ridiculous in fabrication. Even checked out rubber coating fabric...it would be rather heavy.

MadisonMPG · 11-24-2009, 01:16 AM

At speed, you are pushing in air into the bag of air behind you. Once it maxes out (the PSI in the bag vs the PSI of air being pushed into it by wind speed) it should just go around and make a high pressure bubble, much like the grill of a car.

Now, I haven't really researched Mylar yet, so bare with me. Do you all know that stuff those "bounce" things are made out of? You know, those little things kids jump in that have a fan inflating them? That stuff is incredibly hard once inflated and seems to be rigid enough not to flop in the wind. You couldn't get it hard lol enough to lift it off the ground with your speed alone. ( I don't think ) So you would have to inflate it before you left, or with a small 12 volt powered fan. It could be sewn together and rolled up like a truck bed cover.

This thread has REALLY got my brain working and i'm really interested in making one.

Bicycle Bob · 11-24-2009, 01:42 AM

Hot air balloons and modern Christmas yard decorations are a good place to look for an idea of what can and can't be done with inflatables. There are details of shapes that may be important for streamlining that just don't work, or flutter excessively. One refinement is to make a frame or surface by inflating tubes to fairly high pressure.

MadisonMPG · 11-24-2009, 01:58 AM

Bob, I don't see anything that you couldn't sew with a fabric with a boat tail, but I do know what you are saying.

Bicycle Bob · 11-24-2009, 02:14 AM

On a boat tail, it is hard to maintain a flattish top surface. It takes a lot of very precise tailoring to get close. The preferred concave rear panel might be done as a rigid panel including a small top lip to give the cleanest separation, and provide mountings for the license and lights in one tidy assembly.

hypermiler01 · 11-24-2009, 03:53 AM

Several problems with this idea:

Mylar is a thin, fragile material with very little tensile strength. As mentioned, the slightest rip and it completely shreds.

Thin, light materials flap in the wind. Plastic will fatigue at any connection joint where there is vibration. Then it will rip and turn into shreds.

Inflatible objects tend to adopt a spherical shape unless fitted with internal gussets like an air mattress. Not what you are going for here.

Air mattresses, designed for being durable with loads on them, are made out of heavy, fabric reinforced vinyl, not mylar.

I think a better idea would be a tent-like structure made out of convertible top fabric.