"Discovery Universal" - Light wooden aircraft wind propellers (props)
and half-finished props, for control line F2B aerobatic models planes.
Developed by Yuriy Yatsenko, made with CNC machine using.
| Propeller model||Wooden half-finished propellers ||Light wooden propellers|
for control line F2B aerobatic models
Propeller is the main part of the model. It transfers the engine power to the model moving. The efficiency of the prop is the main characteristic for Team Racing and Speed, Combat models. Aerobatic propeller creates not just the thrust. It must keep the model speed constant in any weather conditions. That is why the aerobatic prop is more complex. It has extra properties, like creating inverted thrust when the model speed accelerates.
This needs 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 propeller. 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 act to the propeller capacity. Changing just one parameter from this showed line changes totally the feeling of the model flight. So, successful prop it is 50 % of model success. Aerobatic propeller is impossible to calculate total. It is just the experience and the experimental trimming.
My experience tells me that the best prop material is the wood of average hardness. It creates required rigidity, weight and moment. One time It was made carbon propellers for test. It was the copy of the wooden prop, but it lost some of its advantages. Stability geometry from the mould was the single plus of this propeller. More weight of the prop increases its moment, during the model turning it creates higher gyroscopic moment, that turn the model around the fuselage axis, wing axis, vertical axis together. This 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 various. More RPM with more propeller weight, more sharp turning - more action.
The only way, that was found by myself for stable result of the quality props production, was a creating the wooden propeller on CNC milling machine, with the following manual finishing and painting. It gives stable result, if you change one prop to another. With hand made propellers even not visible geometry distinctions give various feeling of the model flight. Also if you fly one prop for a long time, then this propeller changes (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 loose the result, because you have no time for the new model reaction studying. Just CNC production gave me enough stable geometry.
I produce CNC made wooden props, it gives me the possibility to change the propeller capacities very easily, just to correct 3D model (pitch, its progress, airfoil, etc). That is why it is very easy to create some modifications of one diameter of prop. Thanks to many experiments the most perfect combination of capacities was found. Constant pitch has the best efficiency. But for flying with f constant speed it needs to have a perfect engine, that “feels” the speed change and RPM change according to acceleration accordingly. That is why often uses props with the progressive pitch (less to the tip), that together with the engine and trimmed fueling system create the change the thrust according to the model speed change. This helps to keep the constant speed. Better to have a universal propeller, when you change the regulation for various weather conditions by the needle regulation only. Because if you change the prop pitch, you change the model reaction to your handle moving. It is like another model, difficult to fly rapidly correct on like another model.
2-blade wooden prop is more universal and it is more easy to repeat it. Some sportsmen use 3- blade, not often, 4- blade propellers. Increasing the quantity of blades improve the possibility of the prop to reduce the model acceleration. But it is need to reduce the prop diameter for the same engine. However, the propeller of smaller diameter does the model softy in control. Plus it increases the gyroscopic moment of the prop. Because it is heavier. Also, many blade props need very thin engine RPM diapason of regulation. The small mistake of it does the correct model flight impossible.
2- blade propeller forgives wider diapason of mistakes.
My wooden propellers are trimmed to keep the constant speed of flight, that is why it was call as “Discovery Universal”.
With constant and progressive pitches.
Clockwise and counter-clockwise rotation direction.