- What length of propeller should you use?
- What does the pitch mean?
- What’s up with the three and four bladed propellers?
- What is a bullnose propeller?
We want to make it all a bit easier to understand.
What length of propeller should you use?
Once you know what size propellers you frame allows, you may have a few options depending on the motors you have or plan to use.
The length of the prop determines the speed it needs to rotate in-order to generate thrust. Larger propellers can be more efficient but may require different motors.
Many motor manufacturers provide thrust charts for their motors and these can be used to find an ideal motor and propeller for your system and style.
Actual thrust numbers will vary as there are many variables in play when testing thrust.
These charts will give you a rough idea to the type of props your motor can handle.
– If you like to be agile and have a lot of punch you will want the most thrust without damaging your motor, this means that the motor temp runs only warm.
For the example above this would be the HQ 5x4x3 Nylon propeller.
– If you like to fly for long periods of time then you will want the prop with the highest grams/watt ratio.
For the example above, this would be the HQ 5×4.5 Nylon-Glass Fiber propeller.
For a mini-multirotor, a general size to kv recommendation would be:
3″ : ~3000kv+
4″ : ~2500-2700kv
5″ : ~2300kv
6″ : ~2000kv
Just be sure that your motor is never more than warm to the touch after a flight. If your motors are hot, the propellers are likely too aggressive or you’ve got oscillations in your tuning. This is why we recommend using the thrust charts to get a general idea of what your motor can handle.
What does the pitch mean?
The pitch of a propeller is the number of inches the propeller will travel per full rotation.
When you’re talking about multi-rotor propellers these numbers are not accurate and should be used as a guideline only.
A higher pitch propeller will generally make more thrust but also draw more current.
A lower pitch propeller will generally make less thrust, and use less current, thus flying longer.
What’s up with the three and four bladed propellers?
These propellers are designed with one thing in mind, more thrust!
Most are less efficient than a two-bladed propeller however, some can be as efficient and arguably more efficient than their two bladed counterparts.
I’ve found that three-bladed propellers produce more thrust at lower throttle ranges and you can fly longer, sometimes 5-6 minutes longer than the two-blade version of this prop.
I’ve had the longest flights on HQ 6×4.5×3, up to 14 minutes on a 1800mAh 4s.
On the other hand, you can also use extremely aggressive propellers like the GemFan 5x5x3 and drain that same battery in under 3 minutes (this kills the battery).
The more blades you add the less efficient the propellers become and the thrust does not always improve as we’ve seen with the latest HQ 5x4x6 thrust test video.
What is a bullnose propeller?
Bullnose propellers were originally a propeller that had been cut down to a smaller length to get more thrust out of a smaller propeller. Manufacturers are now making them this way instead.
These are generally less efficient than a standard propeller but provide more thrust.
Some low pitch bullnose propellers have been found to have very nice efficiency but this is not common.
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