is there any equation/method that can calculate the amount of load/weight given the parameters of a motor?

thanks!

I'm not sure I have the right answer because I didn't follow up on it. There used to be a CAD program on disc that did exactly what you are searching for. I don't know who sold it or where it came from but I'm sure that the answer men from Quiet Flyer of Backyard Flyer will know about it. Suggest you contact the tech editor of those magazines.

I assume you mean max weight the aircraft can be based on engine displacement... NO. there is no calculation for that, because the design of the airframe has a lot more to do with it than the engine displacement does.

A Piper Cub (J-3) can fly on 40 hp, carrying 2 people and some luggage. (not much) The basic same airframe, as the PA-18 Super Cub has over double the horsepower, and very little added load capacity. It can fly faster, and can be more aerobatic... but its still a Cub.

I dont konw of an equation. If your thinking about scratch building something yourself then I might be able to help you. Give us a rough sketch of the design of the plane, or build the airframe and take a picture of it. Then give us the weight (with radio gear, etc.) and from that it should be fairly simple to determine the size of the engine just b/c a lot of us here have done this before.

Sorry Fred I have to disagree with your J3 analogy. My first flight was in a J-2 with a 37 HP Kitten engine. Takeoff
climb and cruise were all the same airspeed. I worked for Piper for a few years and can tell you that the PA-18A would carry up to 700 pounds behind the pilot in the dust or liquid hopper. More horsepower in the same basic design will make a whole bunch of difference in performance as well as weight carrying ability. The glide angle and distance was also greater with the PA-18, however you would hit harder because of the increase in airspeed. It was a ball to fly and to this day I have never flown anything that I enjoyed more. My days as a pilot of anything more than RC passed a few years ago and I still miss punching holes in the blue. I wish I could say the same about my models but I never scratched a 1' = 1' scale aircraft.
Best regards - - ballgunner