Olha só o que o Yuriy Yatsenko fala sobre as hélices.. 50% do modelo!! Eu não acho que chega a tanto.. mas fica acima dos 40% com certeza!!
Propeller is the main part of the model. It transfers the engine power to the model moving. It is in Team Racing and Speed, Combat models. The efficiency is the main characteristic for it. In aerobatic it creates not only the thrust. It must keep the model speed constant, in any weather conditions. That is why the aerobatic propeller is more complex. It has extra properties, like creating the back thrust when the model speed accelerates.
There is need to endow the efficiency to have some of these extra properties. The balance between the maximum possible efficiency together with another required capacities creates the perfect prop. The material of the prop, the diameter for this kind of the engine, pitch (constant or progressive), weight, rigidity, moment, thickness of the blade, airfoil, configuration. Changing just one parameter from this showed line, you can change totally the feeling of the model flight. So, successful prop it is 50 % of model success. Propeller is impossible to calculate. It is just the experience and the experiments.
My experience tells me that the best prop material is the wood of average hardness. It creates required rigidity, weight and moment. It was my experience to create the carbon props. It was the copy of the wooden prop, but it lost its advantages. Stability geometry from the mould was the single plus of this prop. More weight of the prop increases its moment, during the model turning it creates gyroscopic moment, that tries to turn the model around the fuselage axis, wing axis, vertical axis together. It explains, why symmetrically made model doesn’t fly symmetrically. We feel this on normal and inverted figures. Loosing the lines tension on some points of figures, especially on sharp corners, it is usually the gyroscopic moment action. You can do the experiment that will give you the possibility to feel the action of the prop moment to the model. For this you must get the bicycle wheel by the axis by 2 hands (both sides), ask somebody to rotate it to enough high RPM, then try to turn it to 90 deg. for example, even not very fast for the first time. I am sure, you will be very impressed. Try to turn the wheel to both sides. You will understand, why on normal and inverted figures the moment action to the model varies. More RPM with more prop weight, more sharp turning - more action.
The only way, that was found by myself to have stable result of the quality props production, is to create the wooden prop on CNC milling machine, with the following hand finishing and painting. It gives stable result, if you change one prop to another. To have this stability if you have hand made props is very difficult, just not visible geometry distinctions give various feeling of the model flight. And if you fly one prop for a long time, after this prop changing (for example, if it was broken), you will lose the advantage of a lot of training, because the model changes its reaction. At the competition it is a tragedy, you lose the result, because you have no time for the new model reaction studying.
I produce CNC made props, it gives me the possibility to change the prop capacities very easily, just to correct 3D model (pitch, its progress, airfoil, etc). That is why it is very easy to create the modifications of one prop. Thanks to many experiments the most perfect combination of capacities was found. Constant pitch has the best efficiency. But to fly constant speed with this prop, you must have a perfect engine, that “feels” the speed change and changes its RPM according to acceleration accordingly. That is why more often used props are props with the progressive pitch (less to the tip), that together with the engine and trimmed fueling system create constant speed flight. Better to have a universal prop, when you change the regulation for various weather conditions by the needle regulation only. Because if you change the prop for another wind, you change the model reaction to your handle moving. It is like another model, difficult to fly rapidly and correctly on another model.
2-blade prop is more universal and it is more easy to repeat it. Some sportsmen use 3- blade, not often, 4- blade props. Increasing the quantity of blades improve the possibility of the prop to struggle with the model acceleration. But it is need to reduce the prop diameter for the same engine. However, the prop of smaller diameter does the model more soft in control. Plus it increases the gyroscopic moment of the prop. Because it is heavier. Also, many blade props need to very thin engine RPM diapason of regulation. The small mistake of it to both sides does the correct model flight impossible.
2- blade prop forgives more wide diapason mistake.