Originally Posted by
Steve Hamblin
FAR 1.1 defines a light sport aircraft as having a gross weight of 1320 on wheels, 1430 on floats.
FAR 1.1 defines nothing for empty weight or useful load, etc. This is where the ASTM rules come into play.
An S-LSA is required to have a minimum useful load-this equation is found in ASTM F2245. This equation takes into account how many people and how thirsty the engine is.
This formula is:
Useful Load = # of seats x 190 lbs plus 1/2 the max continuous horsepower.
Example: Carbon Cub=(2 x 190) + (1/2 x 80). The minimum useful load for the Carbon Cub is 420 pounds.
Using the FAA's definition of an LSA of 1320 gross, subtract 420 from 1320 and you get 900. 900 lbs is the maximum empty weight of the aircraft.
However, an S-LSA aircraft (already found to be in compliance with the S-LSA rules to get certified) can then be converted to E-LSA. Now, some of the limitations that come with the S-LSA rules (such as minimum useful load and the trickle down calculation of empty weight) no longer apply, you are now only bound by FAR 1.1 that defines gross weight maximums (and other things as well, but the topic is weight).
I hope this helps-Do let me know if I can help clarify at all.
Steve