Cere Giuseppe,
If you achieve a weight of 42 ounces ready-to-fly, then you will consume approximately 1.8 or
1.9 Amp-hours of battery capacity from a 4S battery, in order to fly the schedule.
The Battery capscity should be approximately 2500 mAH, which offers several options from 2200 ~ 2600.
The 2200 mAH battery will be lighter and will be adequate if the overall package weighs less than under 40 ounces.
The average in-flight power will be between 200 and 250 Watts, and the momentary peak powers maybe 30% higher.
The motor will be similar to the E-Flite Power-10, weighing approximately 4-1/2 ounces with a Kv between 900 and 1200.
The Power-10 has a Kv of 1100.
The motor weight between 10% and 12% of the all-up weight assures the ability to handle the necessary power.
This combination will turn a propeller between 11-1/2 and 12 inches in diameter ...
probably an 11.5 X 4.5 or 12 X 6 electric pusher for the benefits of the reverse rotation.
Have you read enough on the forum to see the larger picture yet?
The preferred setup uses constatnt RPM governed operation, with the constant operation being provided by either the
ESC or a special timer-controller.
Please check the "List Your Setup" sticky thread above, with an eye toward airplanes that also weigh approximately 40 ounces.
There is much reading there, but I think you will find it helpful.
Regards,
Dean Pappas