Re: [ATM] Venting Holes in a solid OTA

[Mark Holm <mdholm@telerama.com>]

Jack Swaton @ Starry Host wrote:
> > In a solid OTA, would you recommend putting ventilation holes in the
OTA to
> > combat tube currents?

You really should read the relevant literature.  In this case:

Alder, Alan, Thermal Management in Newtonian Reflectors, Sky &
Telescope, Vol. 103, No. 1, January 2002, pages 132 - 136

Greer, Bryan, Understanding Thermal Behavior in Newtonian Reflectors,
Sky & Telescope, Vol. 100, No. 3, September 2000, Pages 125 - 133

Greer, Bryan, Improving the Thermal Properties of Newtonian Reflectors -
Part 1, Sky & Telescope, Vol. 107, No. 5, May 2004, Pages 128 - 132

Greer, Bryan, Improving the Thermal Properties of Newtonian Reflectors -
Part 2, Sky & Telescope, Vol. 107, No. 6, June 2004, Pages 122 - 126

Video examples from Bryan Greer's article are available at
http://skyandtelescope.com/howto/scopes/article_1182_1.asp
or at
http://www.fpi-protostar.com/bgreer/may2004s%26t.htm This second link
has more content than the one at S & T.

These articles push strongly for front blowing fans.  Some of the list
members argue that back blowing fans are nearly as effective and easier
to mount.  If the back of the tube is closed off except for the fan
inlet, then the tube will be pressurized forcing a gentle flow up and
out.  This will help keep tube currents down.  I have my soubts about a
back blowing fan clearing off the boundary layer on the front of the
mirror though.

Most any public library can get you the S&T articles, or you can buy
copies on-line from S&T
http://pqasb.pqarchiver.com/skyandtelescope/advancedsearch.html

-- Mark Holm mdholm@telerama.com

_______________________________________________
ATM mailing list http://www.atmlist.net/