well, I think I figured it out.  The Transmitter manual says you should be able to set the flap channel (ch6) end point from +150% to -150%, but my transmitter doesn't allow - settings on this channel.  So I swapped servo connections between ch2 and 6 and reversed the ail throw,  now the flaps go down.  It would be a lot easier if the manual had been correct about setting -EPAs.

John