I'm not an engineer, or propeller designer, just an airplane pilot and owner. It's been said that propeller design is part science and part black art, but here's a few rules and thoughts:
Think of prop pitch like transmission gears. A flatter pitch is like low gear, faster to accelerate and quicker to respond, but with lower top speed and less efficient in cruise. Conversely, a coarser pitch will be less responsive to power input changes and will have a higher top speed. My airplane gets around this problem by having a variable pitch prop, analogous to the transmission in a car. For take off, a flatter pitch is used for faster acceleration, and for cruise,, a coarser pitch for higher top speed and efficiency. Another rule of thumb is that a longer, slower turning prop is more efficient than a shorter, faster turning prop. Higher prop tips speeds generate more noise. As prop tips approach the speed of sound, noise increases dramatically and efficiency drops.
Your drone has limited room and clearance for a longer prop, the tips need to clear the drones structure. The props are designed with flexible blades, to a degree this allows the prop to behave like my airplane's variable pitch prop, but it also means they prop needs more clearance to avoid striking the structure.
Prop pitch and length will also needs to match available motor power. Too much prop (pitch and length) will bog down a lower power motor, yet an undersized prop, or one with too flat a pitch, won't be able to harness and use more power from the motor.
Prop tip vortices detract from efficiency, the swept, thinner tips are designed to help improve efficiency, reduce tip vortices and reduce noise.
For the larger DJI drones, like my M2P, "Master Air Screw (MAS) makes slightly larger props that eek out a small increase in efficiency - they don't yet make them for the Mini.
Im a new drone pilot. Ive had my MM for a couple weeks now, and am having a blast. I have noticed that the MM struggles in any kind of wind, and has caused a few fly away situations that ive read about.
My experience with the Mini is that whilst it doesn't cope particularly well with strong winds, it does a good job in moderate winds as long as you're sensible about what you do with it. For example, avoid flying a long way downwind from the home point (ideally, position yourself so you fly upwind for most of your flight), generally fly as low as you can to achieve what you want and set the RTH height so that it's the minimum required to safely clear local obstacles. Most flyaways aren't really flyaways, they're blowaways - the Mini doesn't actually fly away, it just can't fly back against a strong wind. The Mini has a maximum flight speed of 29 mph in level flight so you can work out how fast (or not) the drone will be able to return to you if it's coming from a downwind position - if the wind is 30 mph, if you maintain height it will only ever get further away no matter how much you try to bring it back!
The only thing that helps is more attitude or weight.
Attitude (for a drone), yes. Weight - why?
Just think about it, the forward driving force can be written (a little bit simplified, not include wind drag increases with attitude):
F=m*sin(attitude)
Wouldn't that just apply to an aircraft in the glide? If you have 2 identical aircraft with the same power units and you increase the mass of one of them, there's no reason why it would penetrate the air any better in level flight - you'd just need more power to maintain the height at a fixed airspeed. There is no "wind drag" as such - aerodynamically, the aircraft doesn't know if it's windy or not. As far as it's concerned, it's just moving at a particular airspeed through an airmass. The fact that the airmass is moving (what we refer to as wind) doesn't change the amount of air moving past the aircraft at a particular
airspeed, it just changes the
groundspeed. Increasing the mass would just make it more stable in turbulence because it would have more inertia.
Attitude (for a drone), yes. Weight - why?
Wouldn't that just apply to an aircraft in the glide? If you have 2 identical aircraft with the same power units and you increase the mass of one of them, there's no reason why it would penetrate the air any better in level flight - you'd just need more power to maintain the height at a fixed airspeed. There is no "wind drag" as such - aerodynamically, the aircraft doesn't know if it's windy or not. As far as it's concerned, it's just moving at a particular airspeed through an airmass. The fact that the airmass is moving (what we refer to as wind) doesn't change the amount of air moving past the aircraft at a particular airspeed, it just changes the groundspeed. Increasing the mass would just make it more stable in turbulence because it would have more inertia.
The reason is that all mavics are attitude limted to about 30 degrees. It refuses to go more than that unless you hack some parameters. It also is ground speed limited (not so much in sport mode), which ever come first.
So for an aircraft that weight 500g you get a forward force like
F=0.5*sin 30 => 0.25N
For a 1kg you get
F=1*sin 30 => 0.5N
So you will have a stronger force to driving it forward.
Why you not see any speed increase in no wind is that the speed limit in firmware kicks in and lower the the attitude.
You get drag from the TAS, otherwise it would accelerate to infinity speed, which don't happen.
If you don't believe me, try it for yourself. You need an app that can show the attitude though, or use atti-mode
I think you mix up things since the mavic are booth attitude limited and speed limited which ever come first. Took me a while before I realized this myself. So you can't just calculate:
ground_speed = wind_speed - max_speed
its more like:
ground_speed > wind_speed - max_speed
since the firmware adds attitude to 30 degrees when going against the wind.
Edited:
Think of a weightless drone, will it get any forward speed when you tilt it
I always compares 0 and infinty to understand things.
I will try to do an video about it where I show the difference.
I flew my MM last week near my house in moderate winds that some may consider questionable. I received wind warnings suggesting it wouldn't be able to RTH, even though I was flying away from home into the wind, not going full forward stick, and still able to go at least 3mph. I was flying 90 to 120ft, enough to clear all trees.
Mass won't help thrust, but it will dampen it appearing to struggle as it compensates for constant wind changes.
The MM may sound horrible hovering in moderate and shifting winds, but it handles well for me. Just take it easy and gradually learn what it can and cannot handle.
The only no win situation I can think of is when you lose signal and RTH altitude and wind can't get it home. If you still have signal and you're drifting, lower altitude or just land. Point gimbal down while you land so you can see by landmarks where you're landing.
Hi, when flying smaller (5" to 10") copters in fast forward flight, three-blade propellers are almost standard, because they produce less vibration. The most commonly accepted reason seems to be that with three blades, the oscillation of angle of attack of the blades in forward flight is more balanced than with two blades (where always one blade has a high angle of attack, and the other has a small angle of attack, producing vibration).
If you are looking for more details, kindly visit Rayi.
But on larger copters, I still mainly see two-bladed props.
I recently built a custom 3-blade propeller hub for the T-motor MF propellers that we are using on our 5 kg, 18" quadrotor. I noticed some vibrations while flying at higher speeds in a large wind tunnel (video), and I thought that the 2-bladed props might be the reason.
And today I tested the new 3-blade setup, and I like it much better. I was flying the same auto mission with both setups. The mission is to oscillate several times between two waypoints at 30 meters distance with 5 m/s and with 7 m/s.
Vibrations decrease by a factor of 3, the power consumption is almost identical, the mean throttle drops. What is the reason that 2-blade props are so popular on larger drones…?
Edit: I accidentally flipped the labelling in the vibration table… Now it is correct. 3-blade has of course a much lower vibration level in forward flight.
You have raised an interesting topic because our props on multi rotors are operating as props were never intended to operate.
From a fixed wing perspective it is well tested that more blades is less efficient, where the prop directly faces the oncoming air flow.
The most efficient in this case is actually a single blade prop, and yes, they were a thing, although you don’t see them much anymore.
But considering the direction of airflow on multi rotors its a whole different story.
It would be interesting to hear if people have actually tested the characteristics of props in horizontal for ward flight.
Im just going down the same path. My copter has max power and hover time with 11"-2.
But i noticed with 10"-2 it flies much more sporty and can do a flip with half the height loss (in spite of the lower max power).
Now if a 10"-3 gives me the max power of the 11"-2 and the handling of 10"-2 that would be great.
The company is the world’s best large drone propeller supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
For efficiency ecalc predicts a loss of 3 minutes out of my 34 minutes hower time, which is not too bad if the performance gains are what i expect.
It seems the bigger the prop, the smaller the efficiency losses because the blades are further apart and the lower rpms mean more time until one blade reaches the turbulence of the previous one. Also the hover RPM of 3 blades is lower helping here.
So it is clear that efficiency suffers more on small, high kv builds, but even there the handling gains seem worth it. So why dont we see 3-blades on larger general purpose copters? While hover time may decrease a bit, in dynamic flight the drag decreases and max flight distance improves again. I’m excited to try soon, I could be wrong.
If anybody has experience with 3-blade influence on filter parameters and thrust expo i would be very interested.
I think the “efficiency benefit” of 1- or 2-blade props vs. 3-blade is a misunderstanding. I had the same opinion for a long time, but now I think differently.
2 or 3-blade props with the same diameter do not have a noticeable difference in efficiency. But, if your aim is to generate a specified maximum static thrust, then you will use a smaller 3-blade prop and a larger 2-blade prop (as these will generate the same amount of static thrust at a certain input power).
Naturally, the larger 2-blade prop will have a higher efficiency (due to the decreased disc loading related to Froude efficiency).
To conclude:
At same diameters, there is hardly a difference in efficiency, but using 2-blade props instead of 3-blade allows to use larger diameters (at the same power input), and that gives you more efficiency.
Dr. Martin Hepperle, a pretty renowned aerodynamicist states the following:
[…] The Number of Blades has a small effect on the efficiency only. Usually a propeller with more blades will perform slightly better, as it distributes its power and thrust more evenly in its wake. But for a given power or thrust, more blades also mean more narrow blades with reduced chord length, so practical limits have to be considered here. The chord length can be increased while decreasing the diameter to keep the power consumption constant, but a diameter reduction is usually a bad idea in terms of efficiency, as long as the tip mach number or tip cavitation is not an issue. […]
from: JavaProp
Keep in mind that the propellers need to be as light as possible for motors with a small diameter, otherwise the motors will not have enough torque to accelerate them. Some propellers from MasterAirscrew are awfully heavy. I had the best experience with very cheap 3-blade props from ABS, but they are not available anymore. And you can convert every folding prop to 3-blade when you mill your own hub from carbon.
You’ll also need to increase the D-term quite a lot On my .
Here are more props:
Are you interested in learning more about Foldable drone propellers? Contact us today to secure an expert consultation!
Comments
Please Join Us to post.
0