fala..znal da ide dodas oduzmes no ipak pitati i uciti nije sramota
no i sam malo njuskah pa nadoh dva neovisna teksta o tome. evo u cijelosti, za stare i za mlade, nek se nade zrno znanja
Izracun za odabir i prelazak sa dvo-tro ili cetvero krakih propelera:
"always used this formula: 2/x to the .25 power. 2 = number of blades of two bladed prop. This is a constant. X = number of blades you want (usually 3 or 4) The answer you get is a decimal. Multiply it by the diameter of the two bladed prop and your answer is the new prop. Use the same pitch.
To simplify; for a three blade, 2/3 raised to the .25 power = .903602 This is the two to three blade factor.
To go from a two to four blade, 2/4 raised to the .25 power = .8408964 This is the four blade factor.
2/5 to the .25 power = .7952707 5 blade
2/6 to the .25 power = .7598357 6 blade
So, if you have a 10-7 two blade and want a three blade: 10 x .903602 = 9.036 diameter. Round it off to 9, use same pitch, 9-7 three blade.
If you start with three blades and want to go to two, divide the three blade diameter by the same .903 factor to get the two blade diameter.
The load factor of a prop can be roughly calculated with the formula DxDxDxP where D is the prop diameter in inches and P is the pitch.
The full formula would be DxDxDxPx Sq.Rt. (N-1) where N is the number of prop blades. For a 2-blade prop, the N-1 term becomes 1 and the square root of 1 is 1 so effectively, that whole term drops out of the equation. For a 3-blade prop, the N-1 term is the square root of 2, which is 1.414. For a 4-blade prop, the N-1 term becomes 3, and the square root of 3 is 1.732.
For example, if you have a 15x8 2-blade prop, the load factor that the prop places on the motor would be 15 x 15 x 15 x 8 or 27,000. A 15x8 3-blade prop would have a load factor of 27,000 x 1.414 or 38,178. A 4-blade prop would have a load factor 27,000 x 1.732 or 46,764.
You can work these formulas backwards to determine prop diameter needed from a given 2-blade prop. For example, if you want to know what diameter 3-blade prop would have the same load factor, and pull roughly the same current, as a 15x8 2-blade prop, you would use the following process.
We know the load factor of the 15x8 2-blade prop is 27,000 from the eariler example. Since a 3-blade prop has an additional load factor of 1.414, first we would divide the original load factor or 27,000 by 1.414 to get 19,094. If our 3-blade prop will also have 8 inches of pitch we would divide 19,094 by 8 to get
2387 and then to get the diameter you take the cube root of this number, which is easy to do with any scientific calculator. The cube root of 2387 is 13.36, and that would be the required diameter of the prop.
They do not make a 13.16" prop, but you can find a 13 inch or 14 inch. If you go with a 13 inch then the actual load factor would be 13 x 13 x 13 x 8 x 1.414 which is 24,852. This is about 8% less than the original 15x8 2-blade prop, so the current draw would be about 8% less as well. With a 14x8 3-blade prop the load factor would be 14 x 14 x 14 x 8 x 1.414, which is 31,040. This is about 15% more than the original 15x8 2-blade prop, so the current draw would be about 15% higher.
The process would be the same for a 4-blade prop, you just use the correction factor of 1.732 instead of 1.414 when you do the math."
fala jos jednom...bas me zanima ova pticica sa tri kraka..a mozda i cetiri
Hangar: Avanti V2 80mmEDF, Viper 90mmEDF, Stream Glider V2 EDF, Marlin 64mmEDF, UltraStick 35ccm, Carbon Cub Saito4T, EDGE 540 33ccm, Husky SE, Pichler ARROW, MPX Extra 330 SC, EFX Racer, Waco, Hurricane, FunCub, ZOHD Dart XL, Timber Evo, Fokker DR1, Futaba 7C/14SG & Spektrum NX8. Buggy 30.5ccm.
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