For some reason Wombat’s message never got to my computer so I am replying
through a reply!
The usual (and I think sensible) argument is that junctions between surfaces
constrict the airflow and cause drag. A fin that only exists above the tip
of the tailplane only has one right angled junction whereas a circular fin,
extending above and below, has two. Therefore there is only half the
interference drag on the ‘Little Square’ layout! I know, I know, the
interference drag is probably very tiny but you did ask.
I also wonder about the tip vortex which will be there if the CG is well
back and the tailplane is lifting. I don’t like the idea of messing with
the vortex in two places, as would happen with the circular fins. I know
some of the early proposals for tip fins did have small extensions below the
wing but I think most of the airliners now confine their fins to the upper
surface.
John Barker - England
[Non-text portions of this message have been removed]
Received on Thu Nov 16 2006 - 10:45:47 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:44 CET