X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 10 [X] Return-Path: Sender: To: lml Date: Mon, 05 Feb 2007 21:22:49 -0500 Message-ID: X-Original-Return-Path: Received: from wind.imbris.com ([216.18.130.7] verified) by logan.com (CommuniGate Pro SMTP 5.1.5) with ESMTPS id 1813882 for lml@lancaironline.net; Mon, 05 Feb 2007 20:14:38 -0500 Received-SPF: none receiver=logan.com; client-ip=216.18.130.7; envelope-from=brent@regandesigns.com Received: from [192.168.1.138] (cbl-238-80.conceptcable.com [207.170.238.80] (may be forged)) (authenticated bits=0) by wind.imbris.com (8.12.11/8.12.11.S) with ESMTP id l161DhFB018692; Mon, 5 Feb 2007 17:13:44 -0800 (PST) (envelope-from brent@regandesigns.com) X-Original-Message-ID: <45C7D646.2080405@regandesigns.com> X-Original-Date: Mon, 05 Feb 2007 17:13:42 -0800 From: Brent Regan User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Mailing List X-Original-CC: bob@bmackey.com Subject: Re: Wing pressure References: <28461.12.146.139.19.1170715730.squirrel@www.bmackey.com> In-Reply-To: <28461.12.146.139.19.1170715730.squirrel@www.bmackey.com> Content-Type: multipart/alternative; boundary="------------090303060507020406070009" This is a multi-part message in MIME format. --------------090303060507020406070009 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit bob mackey wrote: >has anyone experienced a downward blast from a landing aircraft? > > Yes, I have. As you can readily convince yourself, the vertical component of the airflow diminishes to zero at the ground surface. I did a series of experiments years ago with hang gliders that showed the vertical motion of the air behind the glider. It is substantial, and just exactly what you'd expect from F=ma, Bernoulli, Coanda, Langmuir, and Stokes... They are all in agreement, and all follow the same rules. BTW... Bob, There is a beach on San Maarten that is under the flight path of landing jets. Cool video of same can be seen here: http://www.youtube.com/watch?v=PvNONncieu0 If the entire mass of the 747 was being supported exclusively by accelerating air downward then then everything under the flight path would be scoured by hurricane force winds. Try putting your beach chair under a Delta rocket and light the fuse. You can see be the video there is only a slight disturbance. Where did all that energy go! It is true that the vertical component of an air blast diminishes to zero as it approaches the ground, because it turns into a horizontal component and diffuses radially. Point a leaf blower straight down and note that the air flow hits the ground and then travels in a thin layer radially. The layer "sticks" to the ground because it has a higher velocity (lower pressure) than the surrounding air. This is part of the mechanism behind "wind shear". As for your hang glider, it is a lot closer to a kite or a parachute than a laminar airfoil wing. There is an air disturbance in the aircraft's wake, some is vertical, some is horizontal, some is turbulence and some is heat. The total energy of the disturbance equals the energy released in burring the fuel, but not more (level flight). Here is another way to look at it. For the hose theory to be right then the airplane must be able to release enough energy to throw air downward fast enough to lift the mass of the airplane against the acceleration of gravity. If this were true, then the most efficient way to accelerate air and throw it downward would be to stand the airplane on it's tail and let the propeller do the job directly, without minimum aerodynamic drag from the body of the airplane. There are only a small handful of fixed wing aircraft that can accelerate straight up so there must be something else keeping the airplane in the sky. That something is the difference between the air pressure on the outside of the bottom of the wing and the air pressure on outside of the top of the wing. Paul's hose theory for aerodynamic lift is all wet. If anyone out there that doesn't get this then I would recommend you seriously reconsider the whole "I want to be a pilot" thing. Paul, please tell us you pulled a "Pariah Kerry" and just let a bad joke go too far. You don't actually believe this, right??? April first is still some time away. Regards Brent Regan bob mackey wrote: >>has anyone experienced a downward blast from a landing aircraft? >> >> > >Yes, I have. As you can readily convince yourself, the vertical >component of the airflow diminishes to zero at the ground surface. > >I did a series of experiments years ago with hang gliders >that showed the vertical motion of the air behind the glider. >It is substantial, and just exactly what you'd expect from >F=ma, Bernoulli, Coanda, Langmuir, and Stokes... >They are all in agreement, and all follow the same rules. > >BTW... > > > >>If you were flying at 70 Kts (118 Ft/sec) stall at an AOA of >>45 degrees (extreme example) and a projected wing / fuselage >>area of 100 square feet the you would be "intersecting" 11,800 >>cubic feet per (896 lbs) second. >> >> > >A better approximation of the "area" of disturbed air is pi*span^2/4, >or the area of a circle circumscribed around the wingtips. > > > > --------------090303060507020406070009 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit bob mackey wrote:
has anyone experienced a downward blast from a landing aircraft?
  

Yes, I have. As you can readily convince yourself, the vertical
component of the airflow diminishes to zero at the ground surface.

I did a series of experiments years ago with hang gliders
that showed the vertical motion of the air behind the glider.
It is substantial, and just exactly what you'd expect from
F=ma, Bernoulli, Coanda, Langmuir, and Stokes...
They are all in agreement, and all follow the same rules.

BTW...

Bob,

There is a beach on San Maarten that is under the flight path of landing jets. Cool video of same can be seen here:

http://www.youtube.com/watch?v=PvNONncieu0

If the entire mass of the 747  was being supported exclusively by accelerating air downward then then everything under the flight path would be scoured by hurricane force winds. Try putting your beach chair under a Delta rocket and light the fuse. You can see be the video there is only a slight disturbance. Where did all that energy go!

It is true that the vertical component of an air blast diminishes to zero as it approaches the ground, because it turns into a horizontal component and diffuses radially.  Point a leaf blower straight down and note that  the air flow hits the ground and then travels in a thin layer radially. The layer "sticks" to the ground because it has a higher velocity (lower pressure) than the surrounding air.  This is part of the mechanism behind "wind shear".

As for your hang glider, it is a lot closer to a kite or a parachute than a laminar airfoil wing.

There is an air disturbance in the aircraft's wake, some is vertical, some is horizontal, some is turbulence and some is heat. The total energy of the disturbance equals the energy released in burring the fuel, but not more (level flight).

Here is another way to look at it. For the hose theory to be right then the airplane must be able to release enough energy to throw air downward fast enough to lift the mass of the airplane against the acceleration of gravity. If this were true, then the most efficient way to accelerate air and throw it downward would be to stand the airplane on it's tail and let the propeller do the job directly, without minimum aerodynamic drag from the body of the airplane. There are only a small handful of fixed wing aircraft that can accelerate straight up so there must be something else keeping the airplane in the sky. That something is the difference between the air pressure on the outside of the bottom of the wing and the air pressure on outside of  the top of the wing.

Paul's hose theory for aerodynamic lift is all wet. 

If anyone out there that doesn't get this then I would recommend you seriously reconsider the whole "I want to be a pilot" thing.

Paul, please tell us you pulled a "Pariah Kerry" and just let a bad joke go too far. You don't actually believe this, right??? April first is still some time away.

Regards
Brent Regan

bob mackey wrote:
has anyone experienced a downward blast from a landing aircraft?
    

Yes, I have. As you can readily convince yourself, the vertical
component of the airflow diminishes to zero at the ground surface.

I did a series of experiments years ago with hang gliders
that showed the vertical motion of the air behind the glider.
It is substantial, and just exactly what you'd expect from
F=ma, Bernoulli, Coanda, Langmuir, and Stokes...
They are all in agreement, and all follow the same rules.

BTW...

  
If you were flying at 70 Kts (118 Ft/sec) stall at an AOA of
45 degrees (extreme example) and a projected wing / fuselage
area of 100 square feet the you would be "intersecting" 11,800
cubic feet per (896 lbs) second.
    

A better approximation of the "area" of disturbed air is pi*span^2/4,
or the area of a circle circumscribed around the wingtips.
--------------090303060507020406070009--