Jeff and SmallFly (Tom) are exactly right. If you look at the movies I have posted on my website of climbing flat spins, you'll see that the aircraft can not be perfectly flat to accomplish a climbing flat spin. Every aircraft wants and needs something different to get it into that perfectly flat - flat spin. I find that if you over cross the ailerons from the flat position, the aircraft will be more apt to climb. Coming out of the rudder will typically allow the tail to drop and perform a Tornado. Once again, you'll find a 'sweet' spot where the aircraft will maintain altitude and even climb, provided that there is enough power on the aircraft. The Sledge is perfectly capable of any of these manuvers. It just takes practice and patience, not necessarily a different aircraft.
Burn that glow fuel!
Kevin