Too Close for Comfort?

The DJI Phantom Quadcopter is a real screamer. It’s loud, uncomfortably loud, sometimes even confused for a massive bee swarm. Don’t blame the motors, with the propellers removed, the phantom sounds just like any other quadcopter with inexpensive motors. So for a long time now, I have been looking for the ultimate propeller for the DJI Phantom.

Blade pitch or simply pitch refers to turning the angle of attack of the blades of a propeller or helicopter rotor into or out of the wind to control the production or absorption of power.

The size of a propeller is usually defined by its diameter and pitch. Originally, the DJI Phantom shipped with 8 inch propeller, with a 4.5 pitch, which would be called a 8.0×4.5 or 8045 propeller. While both, diameter and pitch influence the produced thrust, the diameter is mostly responsible for the thrust and the pitch controls the speed of the air leaving the back of the propeller.

DJI Phantom with the original 8045 propellers

The motor output power shows this as well, which is calculated like so:

power = k * rpm3 * diameter4 * pitch

k is the propeller material constant.

This may not tell us all that much, but the next generation of propellers that DJI shipped with the Phantom, were larger: 9.4×4.3, i.e. 9.4 inches long, with a 4.3 pitch. The flight time increased significantly with the larger propeller, but the craft also got a lot louder and I found the sound to be a little pitchier and more uncomfortable. Most importantly however, descending got a lot harder, because the propeller downwash got worse, which may easily result in a crash if descending fast or not in a corkscrew-like movement.

The vortex ring state is a dangerous condition that may arise in helicopter flight, when a vortex ring system engulfs the rotor causing severe loss of lift. Essentially, the helicopter descends into its own downwash. When the condition arises, increasing the rotor power merely feeds the vortex motion without generating additional lift.

Cheaper knockoff propeller from Chinese retailers like Banggood or GoodLuckyBuy have the same size, but are lighter and less stiff, which makes them sound even pitchier, but their flight behavior is just as good, if not better.
The same retailers also offer Carbon Fiber propeller, which have the exact same form and 9.4×4.3 specification. The carbon fiber propeller are hardly heavier, but extremely stiff. They are loud and while landing seems more difficult with all the 9443 propellers, I found it to be even more difficult with the carbon fiber propellers.

HobbyKing, sells 9.4×4.3 Wood Propeller, which are super stiff, but also very heavy and decrease the flight time down to where the original 8 inch props were. Handling also did not improve at all, in fact, it was never worse, making HobbyKing’s MultiStar White Edition 9.4×4.3 Multi-Rotor Wood Props, the worst propeller I have ever mounted on the Phantom.

Phantom with 9443 Propeller attached

More recently, DJI introduced a new 9,4×5,0 propeller, which provides extra thrust and better power efficiency than the 9443. I didn’t experience a noticeable increase in flight time, but strangely the sound seemed to suggest that sometimes motors would briefly stall, which of course is not really happening.

Propeller: DJI 8045, DJI 9443, 3DR 9545

The 3DR-IRIS  has about the same size as the Phantom and overall is very much comparable in just about everything. Fortunately, with just a little bit of work, we can mount the IRIS’ 9.5×4.5 propeller on the DJI Phantom. Just like the Phantom’s propeller, these are self-tightening propellers (the color-coding is different though, counterclockwise propellers have a silver nut and clockwise propellers have a black nut.)

After removing the key-ed nut, the whole in the propeller hub needs to be widened with a 5/16 or 21/64 drill bit. Moreover, a thin light (preferably fiber) washer, again with an inner diameter of 5/16 or 21/64, needs to be placed on the motor-shaft. With all that done, the nut can be reattached to the propeller and the propeller mounted on a DJI Phantom. With 9.5 inches the IRIS’s propeller are a little bit larger, which puts them even closer together, maybe a little too close for comfort.

3DR IRIS Propeller with Nut removed and widened whole
3DR IRIS 9545 propeller mounted on the DJI Phantom

More Propeller

Hobby King Wood Props 9443, Carbon Fiber 9443, Carbon Fiber 8045, Carbon Fiber 9050 Aeronaut Cam Carbon Light (Top to Bottom)

Conclusion

The made in Germany 9.0×5.0 Aeronaut Cam Carbon Light Electric Propeller is probably the propeller that lets the DJI Phantom fly the most stable and predictable. However, it hardly improves the flight time, when compared to the original 8045 DJI propeller. If flight time is important, then the 3DR IRIS 9.5×4.5 propeller shows the best behavior, with or without payload (like a camera) on board.

Gains

Upgrading from the original 8″ propeller also requires adjusting the gain-settings in the copter’s firmware. (Gain adjustments are probably not necessary, for the Aeronaut Cam Carbon propeller)

Default Gains for the DJI Phantom 1.1.1

  • Pitch 125
  • Roll 125
  • Yaw 100
  • Vertical 100
  • Atti Pitch 125
  • Atto Roll 125

Default Gains for the DJI Phantom 2

  • Pitch 125
  • Roll 125
  • Yaw 125
  • Vertical 140
  • Atti Pitch 260
  • Atto Roll 260

My Settings for the DJI Phantom 1, w/ Propeller larger than 9 inch

  • Pitch 180
  • Roll 180
  • Yaw 140
  • Vertical 150
  • Atti Pitch 120
  • Atto Roll 120

DJI Phantom 1.1.1 with 3DR IRIS+ Propellers