From: reich@nosc.mil (Ronald S. Reich)
Subject: Re: Unstable big delta
Date: Tue, 19 Apr 1994 13:21:40 GMT

>From: alfa@werple.apana.org.au (Glenn Durden)
>Last  year  I had a big delta that I used to take  photos  from.   
>:-)  ( a message thread all in itself.  )

>This year I built a bigger one.  - about 8 foot across the base.

>However... its a bit unstable.

>During  flight,  it may tilt a bit to the left or  right...  and 
>keep  on  going  over, to thumpo head  first  into  the  ground, 
>sometimes  from  a great height. I have found I can  adjust  the 
>position  of the cross spar a bit to correct in  one  direction, 
>but a few moments of flying later, it may tip over and head into 
>the dirt in the other direction.  What can I do to make it  self 
>correcting and stable?
>-  I've added a high-drag tail (a small parachute from  a  model 
>rocket) - I've added a fuzzy trailing edge (lots of little tails 
>about  6  inches long at the rear) - I've added a keel  (on  the 
>bridle).

>Whats  next?    I dont care what it looks like - I just  want  a 
>stable platform.

     It  sounds  to  me  like  the  Dihedral  surfaces  are   not 
performing  efficiently.  Or, that their forces are not  able  to 
overcome  the displaced balance one the kite starts to lean.   If 
the  kite  is too flat, then as the kite leans to one  side,  the 
wind just slides along the entire kite instead of pushing the low 
side  back  up  where it belongs.  Try  increasing  the  Dihedral 
Angle.

               \                        /
                  \                  /
                     \            /    Dihedral Angle
                        \      /
                           \/


Note:  This is an intuitive theoretical analysis of the  symptoms 
you have described.

                 Just trying to help,  Ron Reich