I built a larger version of the Aerodactyl, designed by Bill Warner, making a version with a Wing Span of 22 inches, instead of 15 inches.  I used a 7 inch Sig propeller mounted on a nose bearing like the one supplied with the Sig Thermal Dart. An article in Model Aviation from April 2016 describes this plane, revisiting the original article by Bill Warner in Model Aviation from January 1995. The Wing mount slides on the fuselage stick, to adjust center of gravity. Covering on the bottom of the wing is polyethylene from a light produce bag. I have gotten flight duration of 20 seconds outdoors.

Wing area is about 60 sq inches, and flying weight about 21 grams.  The wing loading is 1.77 oz /sq ft , and cube loading is  2.75 oz/cu ft.  Length from propeller hook to the hook for rubber at  the tail is 10.5 inches.  I used 5.1 g, 2 loops ( 4 strands) 14 inch long, of 1/8 rubber wound 600 turns to get a flight lasting 20 seconds with good climb.   Rubber weighed 24% of the total takeoff weight.