ORIGINAL: neilga
When you have a max weight including the fuel, the guy whose plane is on the heavy side will be forced to fly with a small amount of fuel, possibly causing a flame-out. So in that way it is easier for the weight rule to specify empty tanks.
When I last flew with a glo motor I used the OS140. It could do a pattern on only 10 ounces of fuel. This is 300ml, and weighs about 260grams. Does a YS170 use much more than that? So 5500g total allows glo planes to increase their weight by maybe 200g, and electric planes by 500g. I think this would be a big relief to everyone. There would be less need for using tiny receiver batteries, or ultra light carbon props, etc
Neil
My Valiants running YS175cdi's, are using around 210ml per flight.