Rubber for Coupe?

[Sundance12]

What is the typical number and strands for a Coupe motor. My airplane is a "Les Tremaux"?

[dputt7]

  A Coupe can have a maximum motor weight of 10grams including lube. The plan should give an idea of the Hook to Peg distance so a good start would be as many loops you can get from a 10gram motor.

[Sundance12]

Ok, it's about 11 inch motor length.  I will try 1/8th first. whatever length gets me 10 grams.

[billdennis747]

It always used to be '6 strands of 1/4". Now it's 12 x 1/8". If the motor is a little short - stretch it! I've got two Trumeaux, a super model that glides forever.

[lincoln]

I'm sure it depends a lot on the propeller. I suspect that even two different builder's Trumeaux props might be best with different numbers of strands.

[billdennis747]

For fine tuning you need to go to 1/16" sq but it's a pain. I doubt it matters much, compared to finding good air.

[Jmk89]

I have sometimes made up a motor with an odd number of strands which, if you use 1/8"is the same as moving to 1/16" and using an even number of strands and is much easier to handle.

It really doesn't make anything harder, especially since the motor will be tight between the hooks and so you don't need to braid the motor

[calgoddard]

Optimum rubber motor sizing for rubber powered free flight models is a science unto itself. Consistent max flight times come from matching the rubber size to the prop for a given airframe.

In many classes there is a maximum weight limit for the rubber motor so this simplifies the process as one ordinarily uses the maximum rubber motor weight allowed in such classes.

For indoor stick duration classes such as Limited Penny Plane (LPP) there are no limits on the weight of the rubber motor but there is a sweet spot for the weight found through experimentation. Then for a given prop with a certain blade plan form and helical pitch distribution one strips rubber and relies upon grams per inch to determine the rubber motor that consistently produces the longest flight times. Since the thickness and width of the rubber cannot be controlled beyond a certain level of precision the rubber motor is measured is terms of weight, length and grams per inch.

Outdoors, the process is much simpler for Coupe with its ten gram maximum rubber motor weight. For large outdoor sport models, rubber is usually not stripped but various commercial widths can be mixed if necessary to achieve the optimum overall rubber motor thickness. For a Coupe, depending on its weight and design, and more importantly, the diameter, pitch, and blade form of the prop, one could learn through many test flights under calm conditions that a 10 x 1/8-inch 10 gram rubber motor might be optimum. In my experience, the most common make-up of a Coupe rubber motor seems to be 12 x 1/8-inch - 10 grams max.