# Tag Info

18

Thrust is proportional to the change in momentum of the air passing through the prop - i.e. how much the prop speeds it up. The power required to do this is proportional to the kinetic energy of the air, which is proportional to speed squared. That 'squared' is the problem. A smaller prop acts on less air, so it has to speed it up more to generate the ...

17

An explanation for why this is can be found in this Aviation.SE answer: Why aren't large, low-speed propellers widely used?, which I'll paraphrase here. The thrust a propeller generates is a function of its velocity and geometry. It makes sense that a propeller spinning faster will also generate more thrust. For a smaller propeller to generate the same ...

17

One practical advantage is increased ground clearance, reducing the likelihood of a prop strike on landing or take-off. Aerodynamically, a pusher1 design can be less efficient because the propeller is spinning through the wake of the fuselage - this results in 'lumpy' air, causing vibrations. I don't have exact figures, but I've heard anecdotally that this ...

14

Expanding on @Kralc's answer: Here's a study (unfortunately behind a paywall) that I'm going to copy key parts of below: The hexacopter was mounted on a load cell test stand, and data were collected in the University of Michigan’s 5 × 7 ft wind tunnel over different freestream flow speeds, motor thrust percentages, and hexacopter angles of attack. To ...

13

You know those rubber wristbands that are given out at lots of events? You can wrap one of those around the motor bell to get better purchase on it, and then torque down the prop nut. There are also specialised tools to hold motor bells, such as the one pictured below which can be found here, on Thingiverse.

12

Overview The most efficient propeller is single bladed, has infinitely narrow chord, has infinitely thin airfoil, has an infinitely long blade, spins infinitely slowly, and requires infinite torque. So at the risk of stating the obvious, propeller design is a study of the tradeoffs and compromises required to make something practical. Here's a list of some ...

9

In theory, you can't accelerate and decelerate the props as quickly. If the motor accelerates, the props lower angular velocity keeps it from accelerating too quickly. Same for deceleration: if the motor decelerates, the prop's momentum makes it want to stay fast. It is only when the prop's position exceeds the motor's position, that the centrifugal force ...

9

At least at the small/model scale, the answer is no. There is significant efficiency loss due to the stacked propellers not receiving the same clean air as they would if they were horizontally separated. This is demonstrated experimentally in a Youtube video by rctestflight which compares the efficiency/thrust production of three different propeller ...

7

Theoretically the pitch of a prop is supposed to be the distance it would move in a full rotation (in an ideal world). As most modern props vary pitch along their length, a single number is almost impossible to measure. Manufacturers tend to give a number which is an indication of how the user would expect the prop to perform. Most propellers will work on ...

7

The decision between CW (clockwise) and CCW (counterclockwise) propellers has to do with the direction your motor/engine will spin, not really in regard to where you're putting the engine on the plane. CW props will create thrust behind them when spun in a clockwise direction, and CCW props will create thrust behind them when spun in a counterclockwise ...

6

Comment number 7 at this link is an excellent source (and fairly trustworthy as it was written by Joshua Bardwell). The main reason specified for the efficiency is that for a given amount of thrust, a larger propeller (on a motor with an appropriate KV) will draw less current than a smaller propeller on a higher KV motor, so there is less sag. Another ...

6

Surprisingly, that flexible coupling is actually a good thing. If you look at helicopters, this is called a lead-lag hinge, and it allows the propeller to match flight loads when flying around. What happens is the blade advances in the hinge as it retreats in the airflow, and retreats in the hinge as it advances in the airflow. (Watch a fully-actuated ...

6

Rounded leading edges are better for subsonic aerofoils. Props and wings have to work at a range of angles of attack. The airflow has to split to pass either side of the aerofoil, and a rounded leading edge allows the separation point to move smoothly. Sharp leading edges cause a lot of drag at extreme angles of attack when air has to flow across the sharp ...

6

It looks like you are missing a piece of the prop adapter. There should be three pieces, the nut, the central shaft with a thread for the nut on one end and a taper on the other, and a collar that matches the taper. You're missing the collar. The nut forces the collar onto the taper, which squeezes the slots together, gripping the shaft. They're normally ...

6

You use one of the provided rubber rings to attach the propeller to the motor. The 2 protruding screws with their heads are the anchor points for the rubber before it is wrapped over the prop to the other screw. The propeller motor connection is not rigid but has a little give and comes loose on impact, hopefully saving the propeller and the motor that way.

5

TLDR: The thrust would not double. You can get close but it won't be easy. There are a lot of factors affecting this but in my experience the distance between props dominates. I once built a push-pull RC airplane and got close to 180% the thrust of a single prop. The configuration is similar to the Dornier Do335: Dornier Do335 So you can get quite close ...

5

It's really a challenging question to answer because flexible and stiff propellers both have their advantages and disadvantages in terms of efficiency. Flexible propellers are typically lighter than stiff propellers, so they spin-up more efficiently than stiff propellers. On the other hand, when a propeller is spinning at higher speed, a flexible ...

5

As is explained briefly here on Aviation.SE and here on Physics.SE, the differences in chord length (and other properties of the propellers like diameter and pitch) are mostly derived from the fact that water is ~800x denser than air and results in different optimal properties for highly efficient propellers. Boat propellers generally are constrained in ...

5

The first step to getting the right propellers is to figure out what size propellers will fit your drone. What you can do is measure the distance from the center of the motor to the closest thing (probably the frame) that would block the propeller. Multiply that by two, and a few millimeters smaller than that is the maximum prop size/diameter. (smaller props ...

5

You don't need to hold it with a tool, it's enough to pinch it with your fingers. Using a tool to hold it increases the risk of damaging the threads if you are not careful. But I can understand if you want to use a tool to simplify things, and in that case the other answers are good. Just remember to be careful. Some examples of how I like to hold:

5

There are commercially-available tools that are designed to grab around the bell using a rubber band, like this one: However I felt that it's a fair bit too expensive for what it is. So I made my own, molded specifically for my motors' size: It grabs the motor well (especially thanks to the teeth), but it's quite bulky and motor-specific, so I'm still in ...

4

This table provides guidance to propellor size: ╔══════════════════╦═══════════════╦═════════════════╦══════════════════╗ ║ Frame size ║ Prop size ║ Motor size ║ KV ║ ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣ ║ 150mm or smaller ║ 3" or smaller ║ 1306 or smaller ║ 3000KV or higher ║ ╠═══════════════...

4

Aside from fancy material science which can result in propellers that interact with air more cleanly and is highly proprietary, the primary way a propeller could gain more "grip" on the air is by being more aggressively pitched or having more blades. In a propeller spec which can be displayed either as: [diameter in tenths of an inch][pitch in tenths of an ...

4

Since only you can be the judge of what you feel is too loud, and noise level from a drone is the result of many parts working together, this is a tough question to answer and I'm not sure you will succeed in finding "the" prop to suit your needs. That said, if reduced noise is what you are looking for, and we remove the other parts of the drone from the ...

4

This is an age old problem, there is no solution, only methodology. First, your budget is a HUGE constraint. To build a drivetrain, without years of experience, is very difficult, I doubt you will nail it. The approach you use to decide motor is critical, more on that as we progress. Some things to consider FIRST: what are your power train expectations? 10+...

4

I have a working theory for why this may be the case; some micro-quad designs support this theory more than others. Due to Newton's third law, the thrust force created by the propellers also has the effect of trying to lift the propeller up off of the motor in traditional multirotor designs where the propeller is on top of the motor. Aside from ensuring that ...

4

If a plane has a preference, it's probably for a clockwise prop. This dates back to before electric motors, when people hand-started glow motors. You'd kneel next to the plane, hold the fuselage with your left hand and flick the nearest blade of the prop down with your right hand (or a short piece of wood, if you valued your fingers!). That resulted in a ...

3

The easiest way to think about this is to remember that drag increases with the velocity squared. A smaller propeller will have to spin faster to achieve the same thrust as a larger propeller, and spinning faster creates more more drag.

3

No matter how quickly you slow down the propellers after an impact with the ground, much of the damage actually comes from the impact directly into the ground and the force from the mass of the quad, so the speed of the props shouldn’t make too much of a difference. If you mean the slowing down the props after it’s on the ground would save them, it may ...

3

The main differences are: Fiberglass-reinforced plastics: Very stiff for their weight which allows the propeller to keep the correct shape and be more efficient regardless of how fast it spins (less prop flattening), but when these props hit something hard, that stiffness means it will shatter and the drone won't be flyable. Fiberglass-reinforced props are ...

Only top voted, non community-wiki answers of a minimum length are eligible