ORIGINAL: HighPlains
I've read thousands of Dick's posts and if there is one underlining theme it is the significance of aircraft weight on performance. So often you read of accounts of someones efforts in stuffing twice a big a motor into an already overweigh bloated design and wondering why it don't fly well. While more motor may make an airplane fly faster or climb faster, being able to operate at a wider range of flight speeds with a lighter weight usually makes for a better flying model.
If you cut the weight of the structure of the Cub by half, the total flying weight is reduced by a third. It would take a third less wing area, and thus the drag would be reduced by maybe 10-15%. So less power would be required to maintain speed. Excellent examples of doing more with less would be Van's Aircraft RV-9 with a O-235 (30 mpg at 150 mph), and his new RV-12 which weighs about 80 lbs less than a quite simular Rans S-19. 80 lbs means a lot in an airplane limited to 1320 lbs, and represents an increase in useful load of 16%.
Another one would be the Vagabond basicly a cub less wing and weight, nice airplane.
And a way not to do it would be the Legend 850 lbs with 100hp.
And Dick as you pointed out is right, weight is one of the most limiting factors on how a plane flys.
Lighter is better, or more "air" in the airplane!
Edit to add:
If I recall the 65 hp engine weighd in at about 170 lbs in the 680 lb airframe. If you took that off of the all up dry weight that would leave you with a total of 510 lbs for the rest of the airframe. If it were possibe to cut that in half that would mean an all up weight of 425 lbs dry, I wonder what that would do as far as the power requirements and wing area. If you were to maintain the parameters of 80 knot cruise and 37 knot stall as being to design goals, to keep it well within the LSA limits.