RE: Double Hammer Head?
As with any maneuver timing is key to get this done. You cannot be stopped completely at the top unless you have gobs and I mean gobs of extra power as well as loads of rudder throw and extra servo power. Soft rudder power will allow the rudder to be blown back as the tail comes around under power and you can see this happen as the rudder goes around, you'll see the tail straighten out a bit. I'd agree long tail moments have a much harder time doing this but the UCD has the same tail moment as the 33% Edge in the video and the Edge brings the tail around and it's not that overpowered. It hovers close to 3/4th throttle but has dbl the servo power required for "normal" 3D
As described, you need to come over the top in the hammer and then add power just as the nose is pointing straight down, be ready for the torque to pull it out hard to the left as well as roll it to the left. Now if you took the time to properly trim your plane, torque will have little effect, but if you have not trimmed your plane (thrust angles and such) then be ready to counter with a little right aileron but leave the rudder alone and you want to do them to the left since the torque will help a lot. You may also have to work the elevator depending on your up/down thrust and if you wings were perfectly vertical in the hammer. It's also best to do the into the wind, it helps keep the wings vertical.
If you watch the video I posted earlier on the Edge, look very closely at the surfaces and what they are doing.
Like learning any other 3D maneuver, burn lots of fuel.