Inflatable boattail

[dremd]

First off I need to apologize for my attitude, I was been dealing with a family member with mental illness all day yesterday, That family member didn't drive me nuts, but others did, by constantly defending their (patient) actions. I got to a point where where I was forced to disagre with everything, and that has carried over to this thread.

My position on bleeding off turbo air does still stand, however I still don't know about gasoline cars. I did a quick quasi experiment in the 89 last night (driving the car was like therapy for me) by blipping the throttle at 75 the manifold pressure will jump up to about 2 psi, this will obviously vary from vehicle to vehicle, but there is some pressure available. I almost wish I had FE instrumentation (and a map based ecu) to see what affect bleeding that air off would have.

As far as the venting of gasses out of the tail goes, that is definitely a proven method at high speeds, I'd be interested to see some results at highway speeds.

And another idea for a blower; A/C blower from junk yard.

[dremd]

Originally Posted by donee

Maybe the VGT control is just shooting for as high an ouput pressure it can achieve, all the time in the TDI ? As the fuel is going to detonate anyway...

That is a good question, I think we would have to discuss that with one of the chip tuners. One of their claims is quicker spool, weather that is due to more fuel (and thus more flow), or some N75 programing, I don't know.

Another bit of data may be the fact that when the N75 goes bad the ecu will throw a code before you reach peak boost (around 5 psi) Ask me how I know.

[tputus]

It's a common misconseption that there's detonation in a properly tuned diesel engine. Actually the fuel burns as it is injected into the cylinders. There is a small delay after the injection first starts and this is what makes the typical "diesel knock" you hear. The better your cetane number the less knock. The
low and varying cetane numbers and generally low quality of US diesel fuel is a big reason why it is difficult for manufacturers to introduce modern diesels to the USA.

[dremd]

Originally Posted by tputus

It's a common misconseption that there's detonation in a properly tuned diesel engine. Actually the fuel burns as it is injected into the cylinders. There is a small delay after the injection first starts and this is what makes the typical "diesel knock" you hear. The better your cetane number the less knock. The
low and varying cetane numbers and generally low quality of US diesel fuel is a big reason why it is difficult for manufacturers to introduce modern diesels to the USA.

No Joke on the variable quality.
I put some D2 in at a wallmart a while back, Car sounded like a 12 valve cummins, just smaller, added a double dose of Powerservice and a few gallons of bio then it was back to normal. I wish that the Cetane ratine was easier to access at the pump.

[aerohead]

Originally Posted by buckyball

You don't have any pictures or diagrams perchance?

I think I did post a pic of it over at maxmpg,in the misc.photos.It will be a week before I can check.Also,If you go to maxmpg,and go to "links" I left a link to NASA's research on boattails.The shape is what works,although its not inflated.Crude patterns can be used to tailor the envelope,and I have purchased rip-stop nylon for my next go-around with inflatables.I invented a mechanical 3-way reversing valve which allows the fan to empty and evacuate the envelope for non-highway driving.Simple cruise-control logic can make the whole thing automatic.

[diesel_john]

the diesel knock could be caused by high cylinder pressure before TDC. the actual impact generating the knock, could be the piston swinging over center from rubbing the compression side skirt to the thrust side skirt.

i have measured about 750 psi right before TDC.

[metroschultz]

Thats what I've been told.
Knocking noise in a diesel is created when the piston skirt hits the inside wall of the sleeve on the down stroke.
And I've been working on them since 1982.
You want a quiet diesel, make it a Gas Turbine.
in a gasoline motor the pistons are installed so the skirt lays flat on the upstroke.
diesel pistons are 180* out so they lay flat on the down stroke.
so you are not really hearing detonation, only the slap of piston against cylinder.
BTW the Cetane #s are supposed to be clearly visible from the pump nozzle.

[aerohead]

Originally Posted by dremd

I've been thinking about this a lot lately.

My biggest question at the moment is how many/ much internal braces would be required so it did not turn in to a bubble, but stayed shaped more how I'd like it to look. Do you guys think it woud be posable to have all of the braces run paralel to airflow? (reduced drag)

I am considering using pictures of Basjos's car from side, top and using that as a pattern for the top/ sides (scaled to golf size) (and ofcouse if he would give permission).

Considering convertible plastic rear window material for the upper portion to retain visibility(in a final version) Maybe visquine to start.

As far as stiffness goes, I'm not sure where/ how, but I believe that the structure could be greatly enhanced with plywood panels and / or tent poles glued/ sewn in.

And a final thought, wouldn't it be great if it could be collapsed entirely just by sucking the air out? How about using the tension from the top to hold the boat tail from hitting the ground, then having tent poles (or plywood)hinged in 2 (folding so the "V" is inverted) collapse in such a manner that the entire assembly sits between the bumper and the back window?

Goodyear Aerospace (the blimp people in Dayton,Ohio) came up with an inflatable airplane for the air force.It never saw service,however,there may be de-classified patent images that would illustrate the internal construction used to prevent shedding eddies from setting up wild cyclic deformations.I think inflatables would be a multi-billion dollar/euro/yen/piaster/peso/etc.,idea for the ground vehicle industry.I'm prior-art,so I don't worry about patents,and any one of you entrepreneurial-spirited modders,with access to venture capital could be drowning in cash if your first to market.You can get the patent later.

[Otto]

You guys are all making this way too complicated: Just look to those self-inflating parasails or parachutes for the answer, where the leading edge rams air into the internal channels to inflate and stiffen the sail. Made of inexpensive Dacron, one could taylor a very aerodynamic bed cap for a pickup truck, a boat tail for a car, truck, or motorcycle, or whatever.

Deflates when you slow down and falls back into the bed of the truck.

[tasdrouille]

Originally Posted by Otto

[...]the leading edge rams air into the internal channels[...]

That would be a major source of drag.