Air Pressure at the rear of the car - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 05-12-2007, 02:53 PM   #1
Registered Member
 
Join Date: Mar 2007
Posts: 191
Country: United States
Air Pressure at the rear of the car

I observed something puzzling this morning.

I have the hatchback opened, but sealed with a loose piece of plastic.... loose enough so that it snaps outward when the pressure is higher in the cab and snaps inward when the pressure from the rear is higher.

I noticed the following, regardless of speed:

Turn the vent fan on high, the plastic gently pushes outward, indicating a slightly higher cabin pressure than in the rear of the car (again at any speed).

Open a window ever so slightly and the plastic snaps forward into the cab, indicating a higher pressure outside the back.

Nothing open, the plastic is loose, lufting, indicating zero pressure differential between the inside and outside (center of the hatchback). Even at 60+ mph.

This latter result surprises me. I would expect some amount of vacuum near the outside back at speed, with respect to the inside of the car, but it does not seem to be the case.

Any insight?
__________________

lca13 is offline   Reply With Quote
Old 05-13-2007, 07:18 PM   #2
Registered Member
 
Join Date: Oct 2005
Posts: 1,978
Country: United States
Air Flow

Even in the "Fan-Off" position, nearly all vehicles have fresh-air flow, mostly based on speed. The one-way flap in near the rear bumper allows the air-flow to exit.

Has this been accounted in the equation? It could mimic a zero-pressure situation...

RH77
__________________

__________________
rh77 is offline   Reply With Quote
Old 05-13-2007, 09:05 PM   #3
Registered Member
 
Join Date: Mar 2007
Posts: 191
Country: United States
Yeah,m my other cars have had good fan off air flow, but the VX is pretty bad in this respect (I think because the space between the hood and the cowling is extra tight and the air inlet is fully underneath the hood.

I think the explanation is relative "lack" of airflow... in that the inside pressure simply equalibrates with the outside rear, in absence of any strong pressure or vacuum introduction. The window open and the fan on high does the latter. It makes sense but indeed seem counterintuitive. Looking at some of the CFD simulations out there shows that the area immediately behind the hatch often has neutral air pressure with respect to the overall outside pressure. A foot or two back shows significant changes though.
lca13 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fuelly Android App - eehokie Fuelly Web Support and Community News 2 07-14-2010 09:59 PM
Incorrect Milage Calcuatlion PatM Fuelly Web Support and Community News 4 07-17-2009 08:21 PM
Gallons per Mile? nerb Fuelly Web Support and Community News 1 11-12-2008 04:33 AM
DIY: Wire Tuck!!! SVOboy Experiments, Modifications and DIY 11 09-21-2006 05:17 AM
Condensator orevgym General Fuel Topics 0 07-23-2006 11:25 AM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 12:47 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.