questioning DJI propeller design

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I have seen several threads in these forums that go something like this:

OP: Should I use third-party propellers on my Phantom for better <X>?

Overwhelming Response: No, the DJI engineers know best and already gave you the best possible propeller design!
I am writing this post to dispell a myth that bothers me, as an engineer. The DJI engineers are amazing, I do not question that. The myth here is that there is such thing as a "best design" for anything other than a stated set of requirements, or, more precisely, that the engineers magically optimized their design for the OP's specific set of requirements. That is simply not possible. The conventional wisdom is dead wrong.

The DJI engineers who designed the OEM props were given a set of requirements around performance, durability, noise, manufacturability, variability, and most importantly (my guess), safety and cost. When it comes to performance, the engineers were also told (likely by the product lead) to optimize for a specific flight mode, i.e. ONE of the following: climb, hover, cruise, or max forward speed. Production cost at scale was likely a top requirement. And the most impactful decision, which throws some requirements under the bus in favor of others, was likely the choice of propeller pitch.

So, it's entirely possible that someone else could design propellers that optimize one requirement over the other. Examples:
- Use a more expensive material to make harder or thinner blades, throwing cost and safety out the window in favor of general performance.
- Steepen the propeller pitch, increasing maximum speeds but requiring more power to hover.
- Flatten the propeller pitch, making lower noise and lower power requirements at hover but killing maximum speed.
- Use an exotic material, harder to mass-produce but OK for a kickstarter person to make each one by hand.
- Adding a third-blade in combination with any of the above, also produces similar trade-offs.

So there it is. When another OP reports good results with third-party props, don't be so skeptical.
 
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I agree with barefoot that the major concern for most is the build quality, I have never seen a photo of a dji P4 prop that has snapped in flight or read any threads that the bird flew squirly but I have of third-party props. I am sure that some after market props have some benefits in one area at the cost of loosing another. DJI made a prop that is dependable and serves most requirements well. I am not willing to take a chance with my craft to try to minimally gain one at the cost of a potential crash.
 
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I like this viewpoint. I'm not at all an engineer (I'm really bad at math) but fixed-pitch propeller driven planes can have different props installed to enhance performance in certain aspects of flight at the expense of performance in other areas, say better climb performance but a lower cruise speed and vice versa. So why wouldn't this apply to multi rotor aircraft?
 
I have seen several threads in these forums that go something like this:

OP: Should I use third-party propellers on my Phantom for better <X>?

Overwhelming Response: No, the DJI engineers know best and already gave you the best possible propeller design!
I am writing this post to dispell a myth that bothers me, as an engineer. The DJI engineers are amazing, I do not question that. The myth here is that there is such thing as a "best design" for anything other than a stated set of requirements, or, more precisely, that the engineers magically optimized their design for the OP's specific set of requirements. That is simply not possible. The conventional wisdom is dead wrong.

The DJI engineers who designed the OEM props were given a set of requirements around performance, durability, noise, manufacturability, variability, and most importantly (my guess), safety and cost. When it comes to performance, the engineers were also told (likely by the product lead) to optimize for a specific flight mode, i.e. ONE of the following: climb, hover, cruise, or max forward speed. Production cost at scale was likely a top requirement. And the most impactful decision, which throws some requirements under the bus in favor of others, was likely the choice of propeller pitch.

So, it's entirely possible that someone else could design propellers that optimize one requirement over the other. Examples:
- Use a more expensive material to make harder or thinner blades, throwing cost and safety out the window in favor of general performance.
- Steepen the propeller pitch, increasing maximum speeds but requiring more power to hover.
- Flatten the propeller pitch, making lower noise and lower power requirements at hover but killing maximum speed.
- Use an exotic material, harder to mass-produce but OK for a kickstarter person to make each one by hand.
- Adding a third-blade in combination with any of the above, also produces similar trade-offs.

So there it is. When another OP reports good results with third-party props, don't be so skeptical.


All engineering is a trade-off.
Cost, weight, strength, durability, environment, manufacture-ability, reliability, etc.

Skepticism is healthy and especially warranted with no data and when the comparison is described as 'feels' or 'seems'.

DJI's propulsion systems are tuned for the application.
 
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Designing parts that "will do the job for minimum cost" would be DJI's highest priority here, and they do. Prop noise seems to be the main concern and although not an Aeronautical Engineer, I do know that the critical portion is prop tip design (other complexities too), and could be improved, but at a cost. As drones of any sort become more prevalent, and noise affects sales and thus any companies "bottom line", then we'll see the standard prop design improved. I'd happily pay more for a set of third party props that met or exceeded DJI's material standards and reduced noise but so far aren't available. Till' then we wait and see...
 
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Please cite your reference for cost being the high priority.

If noise was another priority why not improve that too?

They have already revisited the design several times...
9443 to 9450 (pitch), metallic to non-metallic hubs, non-threaded mounts, folding types, and reinforced nylon.
 
Please cite your reference for cost being the high priority.

If noise was another priority why not improve that too?

They have already revisited the design several times...
9443 to 9450 (pitch), metallic to non-metallic hubs, non-threaded mounts, folding types, and reinforced nylon.
To clarify, "performance vs. cost" is the driver here. This is a consumer/prosumer product and priced and spec'd accordingly. If "money was no object" in the design philosophy, most of us wouldn't be able to afford one...
 
To OP:

No one is saying that DJI engineers have designed the best props and no one is saying that others can not design better props. Most of us are saying that DJI props are known to work and are also cheap thus there is absolutely no need to go for other third party props and take unwanted headache at back of mind.

Our main focus is on quality flying with lots of fun.
 
So, it's entirely possible that someone else could design propellers that optimize one requirement over the other. Examples:
- Steepen the propeller pitch, increasing maximum speeds but requiring more power to hover.
etc, etc
The people swapping propellers assuming that more blades or carbon fibre or more expensive props will make their Phantom do something better all miss the point that it's the flight controller parameters that determine speed etc.
Putting a set of hotshot props doesn't make the Phantom fly longer, faster etc.
That would require changes to things like tilt angle settings in the flight controller.
So there it is. When another OP reports good results with third-party props, don't be so skeptical.
So far all that's ever offered is vague assessments like ... the Phantom seems to .... it feels faster ...
When someone says their modification makes real changes in flight performance AND backs that up with recorded flight data to support their claim, I'll believe them.
Until then skeptical is the way to go.
 
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To clarify, "performance vs. cost" is the driver here. This is a consumer/prosumer product and priced and spec'd accordingly. If "money was no object" in the design philosophy, most of us wouldn't be able to afford one...

That's an Argument from or Appeal to (unsubstantiated) Authority.

What additional cost was waived?

How much would it cost to have supplied the 'better' prop?

Without that information it would be hard for me to agree.
 
Argument is not my intent here. My information is based on my own Engineering experience and some experience with product development. Any experienced Design Engineer will tell you more or less the same thing no matter what the product may be.
 
Argument is not my intent here. My information is based on my own Engineering experience and some experience with product development. Any experienced Design Engineer will tell you more or less the same thing no matter what the product may be.

Argument from Authority is a fallacy suggesting that the presenter has knowledge or experience (i.e. authority) that makes their statement fact.

Here's what we've seen here:
>No 3rd party props, including those from well known manufacturers, have proven to perform better than DJI's on their equipment... in any category. Many, many candidly report that they experienced problems or crashes with non-OEM offerings, even clones. All contrary reports are anecdotal and as such subject to Confirmation Bias.
>There are no reports of DJI prop failures not attributed to trauma, misuse, or improper mounting.
>DJI offers multiple models of props for some of their quads.
>DJI tunes their propulsion systems for matched/optimized performance.

Of course there's always opportunities for improvement but where has DJI specifically traded performance for cost?
 
Argument from Authority is a fallacy suggesting that the presenter has knowledge or experience (i.e. authority) that makes their statement fact.

Here's what we've seen here:
>No 3rd party props, including those from well known manufacturers, have proven to perform better than DJI's on their equipment... in any category. Many, many candidly report that they experienced problems or crashes with non-OEM offerings, even clones. All contrary reports are anecdotal and as such subject to Confirmation Bias.
>There are no reports of DJI prop failures not attributed to trauma, misuse, or improper mounting.
>DJI offers multiple models of props for some of their quads.
>DJI tunes their propulsion systems for matched/optimized performance.

Of course there's always opportunities for improvement but where has DJI specifically traded performance for cost?
...You're absolutely right, I was just trolling you to see if I could get an argument. I'm going back to Twitter now to further explore these examples of Argument from Authority;)
 

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