Groups > sci.electronics.design > #489407

Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts.

Newsgroups	sci.electronics.design
Date	2017-12-27 09:01 -0800
References	(1 earlier) <8o454ddg48f1ho5lbj2e7omarr896dlfdl@4ax.com> <XnsA8586DD37A7Bidtokenpost@69.16.179.22> <61H0C.24094$uY5.14366@fx21.iad> <XnsA8581666945CAidtokenpost@69.16.179.22> <p20io8$bsp$1@dont-email.me>
Message-ID	<5fdda9b3-30ff-42e4-ab86-cd9f9bea8501@googlegroups.com> (permalink)
Subject	Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts.
From	tabbypurr@gmail.com

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On Wednesday, 27 December 2017 16:46:09 UTC, amdx  wrote:
> On 12/27/2017 1:12 AM, Steve Wilson wrote:
> > FMurtz <haggisz@hotmail.com> wrote:
> >> Steve Wilson wrote:
> >>> John Larkin <jjlarkin@highlandtechnology.com> wrote:
> >>>> On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
> >>>> <sylvia@not.at.this.address> wrote:
> >     
> >>>>> For reasons I need not go into, I wanted to make a cheap pedestal fan
> >>>>> blow backwards, by putting the fan on backwards, and running the
> >>>>> motor in reverse.
> >     
> >>>> Wouldn't those two things cancel?
> >     
> >>> Many turbine propeller aircraft can reduce their landing roll by
> >>> placing the propellers in reverse pitch. The blades are still turning
> >>> in the same direction, but the thrust vector is reversed. They are not
> >>> very efficient in this mode, but are still able to slow the aircraft.
> >   
> >>> To visualize what would happen in a pedestal fan, imagine turning it
> >>> around 180 degrees. The motor is still spinning the propeller in the
> >>> same direction, but the thrust vector is reversed in relation to the
> >>> floor.
> >   
> >>> In order to reverse the thrust vector, either the propeller pitch has
> >>> to be reversed, or the motor has to be reversed.
> >   
> >>> John is right. Doing both would cancel.
> >   
> >> Wrong,reversing motor would reverse air flow, reversing the propeller
> >> would be same air direction but would put the leading edge in the right
> >> position for efficiency.
> > 
> > Wrong. Think about it. Reversing the propeller pitch reverses the thrust
> > vector. This is how turbine aircraft shorten their landing roll.
> > 
> > 
>   OK I took the cover off a 3 blade fan that turns clockwise. I removed 
> the blade put it on backwards. The fan still blows air in the same 
> direction. It doesn't blow very much air though.
>   Certainly is some design consideration in the way the blade is curved.
>                                              Mikek

so if you then also change the motor direction, you get reverse flow with good efficiency. It's ain't rocket science, it's fan science.


NT

Thread

OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-26 17:54 +1100
  Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Rheilly Phoull <froggins@iinet.net.au> - 2017-12-26 19:29 +0800
  Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. mpm <mpmillard@aol.com> - 2017-12-26 04:49 -0800
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 09:52 +1100
  Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. tabbypurr@gmail.com - 2017-12-26 06:07 -0800
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 09:58 +1100
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. mpm <mpmillard@aol.com> - 2017-12-26 18:52 -0800
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 14:57 +1100
  Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-26 10:21 -0800
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-12-26 11:48 -0700
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. rickman <gnuarm@gmail.com> - 2017-12-26 14:03 -0500
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. John S <Sophi.2@invalid.org> - 2017-12-26 14:31 -0600
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-12-26 15:44 -0500
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. John S <Sophi.2@invalid.org> - 2017-12-26 15:06 -0600
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. John S <Sophi.2@invalid.org> - 2017-12-26 16:16 -0600
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-26 17:26 -0800
          Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 14:42 +1100
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. not@telling.you.invalid (Computer Nerd Kev) - 2017-12-26 21:00 +0000
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. rickman <gnuarm@gmail.com> - 2017-12-26 18:37 -0500
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. "David Eather" <eather@tpg.com.au> - 2017-12-27 09:48 +1000
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. FMurtz <haggisz@hotmail.com> - 2017-12-27 15:57 +1100
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 09:50 +1100
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. whit3rd <whit3rd@gmail.com> - 2017-12-26 18:55 -0800
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Steve Wilson <no@spam.com> - 2017-12-27 05:40 +0000
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. FMurtz <haggisz@hotmail.com> - 2017-12-27 17:24 +1100
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Steve Wilson <no@spam.com> - 2017-12-27 07:12 +0000
          Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. FMurtz <haggisz@hotmail.com> - 2017-12-27 18:40 +1100
            Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Steve Wilson <no@spam.com> - 2017-12-27 12:34 +0000
              Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. FMurtz <haggisz@hotmail.com> - 2017-12-28 00:36 +1100
              Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. rickman <gnuarm@gmail.com> - 2017-12-27 17:59 -0500
          Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. krw@notreal.com - 2017-12-27 09:39 -0500
          Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. amdx <nojunk@knology.net> - 2017-12-27 10:45 -0600
            Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. tabbypurr@gmail.com - 2017-12-27 09:01 -0800
              Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. amdx <nojunk@knology.net> - 2017-12-27 12:34 -0600
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. rickman <gnuarm@gmail.com> - 2017-12-27 18:03 -0500
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. tabbypurr@gmail.com - 2017-12-27 15:18 -0800
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. amdx <nojunk@knology.net> - 2017-12-28 09:18 -0600
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-28 12:38 +1100
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. M Philbrook <jamie_ka1lpa@charter.net> - 2017-12-30 09:41 -0500
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. makolber@yahoo.com - 2018-01-03 13:48 -0800
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. DemonicTubes <tlackie@gmail.com> - 2018-01-03 14:08 -0800
                Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-01-04 15:18 +0200
            Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-28 12:36 +1100
          Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Jasen Betts <jasen@xnet.co.nz> - 2017-12-28 06:36 +0000
            Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Phil Allison <pallison49@gmail.com> - 2017-12-28 00:16 -0800
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Phil Allison <pallison49@gmail.com> - 2017-12-26 22:38 -0800
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. krw@notreal.com - 2017-12-27 09:40 -0500
  Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 15:02 +1100
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 18:11 +1100
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. FMurtz <haggisz@hotmail.com> - 2017-12-27 18:42 +1100
      Re: Running a pedestal fan in reverse - failed - a rant of sorts. "P E Schoen" <paul@pstech-inc.com> - 2017-12-27 03:17 -0500
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. tabbypurr@gmail.com - 2017-12-27 01:59 -0800
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-27 21:29 +1100
          Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-12-27 14:24 +0200
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. krw@notreal.com - 2017-12-27 09:43 -0500
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-27 11:25 -0800
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. tabbypurr@gmail.com - 2017-12-27 11:32 -0800
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Jasen Betts <jasen@xnet.co.nz> - 2017-12-28 06:20 +0000
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. amdx <nojunk@knology.net> - 2017-12-27 10:50 -0600
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. FMurtz <haggisz@hotmail.com> - 2017-12-28 14:49 +1100
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. FMurtz <haggisz@hotmail.com> - 2017-12-29 11:34 +1100
    Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. bloggs.fredbloggs.fred@gmail.com - 2017-12-27 10:22 -0800
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. Sylvia Else <sylvia@not.at.this.address> - 2017-12-28 09:41 +1100
        Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. bloggs.fredbloggs.fred@gmail.com - 2017-12-27 15:29 -0800
      Re: OT: Running a pedestal fan in reverse - failed - a rant of sorts. rickman <gnuarm@gmail.com> - 2017-12-27 18:40 -0500

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