One of the most common questions I see on the RC Forums concerns propeller equivalents.
The most common question:
"I have a 10×8 prop – what others can I use?"
A starting point for any RC flyer is to estimate the power load on the motor of the prop currently on it. The load can be estimated by using the following formula:
Prop Load Factor (PLF) = diameter³ x pitch
Solving this formula yields a pure number (no dimensions) – for a 10×8 prop, it equals 8000 (10 x 10 x 10 x 8).
To find a prop that will load the motor the same as the 10×8, it must be the same prop type (eg, slow flyer). By substituting terms, you can then find a prop that is perhaps a larger diameter, different pitch, etc. The table shown below shows some examples:
Selected Propeller Load Factors
If you want to use a larger prop for more speed than what you are using currently, using the formula will give you an idea of how much more power the new prop will take. For example, substituting an 11×8 for a 10×8 will take 33% more power. Users must determine if the increased load due to a prop that demands more power is feasible with their current setup.
Propeller Equivalents For Propellers with More Than Two Blades
If your objective is to find a three or four blade prop to substitute for a two blade prop, the PLF formula to use:
Prop Load Factor (PLF) = diameter³ x pitch x square root (# of propeller blades -1)
With two blades, the square root is 1 (ie, 2-1), so it drops out. For a three blade prop, the square root term becomes the square root of 2, or 1.414:
Prop Load Factor (PLF) = diameter³ x pitch x 1.414
To use this formula, calculate the PLF for a two blade prop; then use this value as the PLF in the formula above, pick either a diameter or pitch, substitute terms and solve. The result will give you the three blade equivalent to the two blade prop you want to replace.
Many thanks to Lucien Miller of Scorpion Products for sharing this formula with the RC Community.
Propeller Equivalencies
One of the most common questions I see on the RC Forums concerns propeller equivalents.
The most common question:
A starting point for any RC flyer is to estimate the power load on the motor of the prop currently on it. The load can be estimated by using the following formula:
Solving this formula yields a pure number (no dimensions) – for a 10×8 prop, it equals 8000 (10 x 10 x 10 x 8).
To find a prop that will load the motor the same as the 10×8, it must be the same prop type (eg, slow flyer). By substituting terms, you can then find a prop that is perhaps a larger diameter, different pitch, etc. The table shown below shows some examples:
If you want to use a larger prop for more speed than what you are using currently, using the formula will give you an idea of how much more power the new prop will take. For example, substituting an 11×8 for a 10×8 will take 33% more power. Users must determine if the increased load due to a prop that demands more power is feasible with their current setup.
If your objective is to find a three or four blade prop to substitute for a two blade prop, the PLF formula to use:
With two blades, the square root is 1 (ie, 2-1), so it drops out. For a three blade prop, the square root term becomes the square root of 2, or 1.414:
To use this formula, calculate the PLF for a two blade prop; then use this value as the PLF in the formula above, pick either a diameter or pitch, substitute terms and solve. The result will give you the three blade equivalent to the two blade prop you want to replace.
Many thanks to Lucien Miller of Scorpion Products for sharing this formula with the RC Community.