The Double Whammy was designed by Chuck Markos, who published plans in AMA's Model Aviation magazine in November 1999.  It is so-called because it may be converted to a more competitive plane with simple modifications. 

The original version has a flat plate wing, and was used in the Bong Eagles in a best of three rounds contest called the "Cash Bash". I've made it out of the first round a few times with flights of over a minute, reaching the 40 foot ceiling, but I've never won. Winners get flight times of nearly 2 minutes with this simple plane. They would get longer flights with a better propeller. For the contest, the one that comes with the AMA Cub, a 5 3/8 inch diameter plastic one, is required.   Wingspan is 17 inches and wing area is 64 square inches.  

The rubber for the motor at the contests is handed out at registration, so test flying is required to feel it out.  My best flight came with a  freshly built Double Whammy and rubber about 0.080 inches wide, weighing 1.7 grams for a 14 inch loop.    When I wound it to nearly 1500 turns, the flight lasted 77 seconds.  Wing loading for the Double Whammy is quite low, at 0.7 ounces per square foot, and cube loading is just above 1 ounce per cubic foot.  This is lower than for No-Cal Scale planes, but about the same as for the plane I built to 2015 Science Olympiad "Wright Stuff" rules.