30 years ago when i did my first twin r/c design after numerous twin controline models in the late sixties was a twin had 3 times the power of a single engine not double because of the propeller area of the 2 engines so back then if you had a plane that used a 40 size engine instead of 2 .20's you used 2 .15's .example would be the C.G skylark of the period for both single engine and twin engine specs.