Although I do not yet own one, in due time I will. I will either break down and buy one or I will scrape together some parts and build one. Either way, I hope to have one by Christmas. Welcome all fans of Multirotors!!!!!!
Although I do not yet own one, in due time I will. I will either break down and buy one or I will scrape together some parts and build one. Either way, I hope to have one by Christmas. Welcome all fans of Multirotors!!!!!!
:cool: Just saw one of those brushless/propless fans, to use in an office. It would be cool :cool: if that could work on the quadcopter!
Speaking of propellers and fans. I'm curious about that too. A 3 inch brushless tubaxial fan for cooling works on say 7 volts at maybe 0.4 amp. On the other hand, the brushless motor for elev-8 propeller may work on 7 volts at upward of 20 amps. The elevate has a 30 amp ESC and it says the operating time on a 3.3 amp-hour LiPo is about 10 minutes, which works out to 3.3 * 60/10 = 20 amps average current. Not a fair comparison. The elev-8 has a 10 inch propeller. A 10" brushless fan may draw 5 amps.
A brushless fan may be available with a tach and PWM speed control build into the fan hub, its own ESC.
The propeller is typically two relatively narrow blades, whereas the fan has several vanes with a steeper pitch. The air volume moved by a fan greater when the fan is thicker. A 3" (60mm) fan may rotate at speeds from 2000 to 5000 RPM and move 40 CFM whereas a 10 inch fan will be slower, and move 800 CFM.
How fast do Elev-8 propellers spin? What is the salient difference aerodynamically between a fan and a propeller? Weight is one.
Another question. Elev-8 motor is rated 1050 Kv. What does Kv mean?
Speaking of propellers and fans. I'm curious about that too. A 3 inch brushless tubaxial fan for cooling works on say 7 volts at maybe 0.4 amp. On the other hand, the brushless motor for elev-8 propeller may work on 7 volts at upward of 20 amps. The elevate has a 30 amp ESC and it says the operating time on a 3.3 amp-hour LiPo is about 10 minutes, which works out to 3.3 * 60/10 = 20 amps average current. Not a fair comparison. The elev-8 has a 10 inch propeller. A 10" brushless fan may draw 5 amps.
A brushless fan may be available with a tach and PWM speed control build into the fan hub, its own ESC.
The propeller is typically two relatively narrow blades, whereas the fan has several vanes with a steeper pitch. The air volume moved by a fan greater when the fan is thicker. A 3" (60mm) fan may rotate at speeds from 2000 to 5000 RPM and move 40 CFM whereas a 10 inch fan will be slower, and move 800 CFM.
How fast do Elev-8 propellers spin? What is the salient difference aerodynamically between a fan and a propeller? Weight is one.
Another question. Elev-8 motor is rated 1050 Kv. What does Kv mean?
Kv is RPM per Volt. 1 Volt equal 1000 RPM. Typical RPM on the Elev-8 is around 7000 RPM.
I have been playing with ducted fans, as they are more efficient than props, as my many years of hovercraft builds have proven. As I just got my Elev-8 built, I would like to spen some time flying it before I put ducted fans on it.
Kv is RPM per Volt. 1 Volt equal 1000 RPM. Typical RPM on the Elev-8 is around 7000 RPM.
I have been playing with ducted fans, as they are more efficient than props
It depends on the application. For building pressure, as required to float a hovercraft, a ducted fan, especially with a good solidity ratio, is going to be far superior to an open propeller. However, for producing static thrust, which is just moving the largest mass of air at the fastest speed possible, an open propeller will win. The exception is if you have a very precisely made duct where the tip clearance is measure in the thousandths of inches. That would gain some additional thrust efficiency but is not practical to construct. I suppose the other exception would be when you have a severe constraint on the diameter of your propeller - such as in ducted fan RC. An open propeller inside one of those would be just silly.
The propeller is typically two relatively narrow blades, whereas the fan has several vanes with a steeper pitch. The air volume moved by a fan greater when the fan is thicker. A 3" (60mm) fan may rotate at speeds from 2000 to 5000 RPM and move 40 CFM whereas a 10 inch fan will be slower, and move 800 CFM.
How fast do Elev-8 propellers spin? What is the salient difference aerodynamically between a fan and a propeller? Weight is one.
Another question. Elev-8 motor is rated 1050 Kv. What does Kv mean?
These questions fall into mass transfer problems. There is a way to establish the volume of air to watt and other ratios may be beneficial to your inquiry. Charts can be made to
establish and track whatever unit you want to. There may be simulators, spreadsheets, or math models already avaliable..
:cool: The right question is half of the solution; The other half is the answer.:cool:
Okay, I found lots to read online about kV and the tradeoffs inherent in low values vs high values. I guess 1000 kV must be some sort of sweet spot for the elev-8?
I'm wishing for good tutorial links to the physics of lift, thrust, air-mass acceleration, all that with propellers. Good animations?
Okay, I found lots to read online about kV and the tradeoffs inherent in low values vs high values. I guess 1000 kV must be some sort of sweet spot for the elev-8?
I'm wishing for good tutorial links to the physics of lift, thrust, air-mass acceleration, all that with propellers. Good animations?
I am thinking that I saw this type information on the Mathematica website. The animations...well......have seem some on Wikipedia; but would not trust them exclusively.
To be sure about the solving of the problem; acquire all the information that you have, Vs. the information you want. The data that you have on both sides could fit into a
model that someone has already made. If not, (I hate it when that happens), The problems have to be broken down into sub- parts. If you could post the data, I would not mind
helping you, form the data into a solution. Once a viable solution is calculated, the next step is the real-world test.
If there is a pattern, then there is a sequence; If there is a sequence, then there is a function; If there is a function, then there is a family of functions; If there is
a family of functions, then there exists a solution for every variable in the problem, from begining to end. (You know it!)
It depends on the application. For building pressure, as required to float a hovercraft, a ducted fan, especially with a good solidity ratio, is going to be far superior to an open propeller. However, for producing static thrust, which is just moving the largest mass of air at the fastest speed possible, an open propeller will win. The exception is if you have a very precisely made duct where the tip clearance is measure in the thousandths of inches. That would gain some additional thrust efficiency but is not practical to construct. I suppose the other exception would be when you have a severe constraint on the diameter of your propeller - such as in ducted fan RC. An open propeller inside one of those would be just silly.
{Hovercraft Mode On}
Rich, we tend to use only ducked for lift, (1/8"-1/4" clearance on tip). On thrust we use 1/4" clearance a 28" duct. It's hard to keep a 28" fiberglass duct round.
We use 6-9 blade fans, not props. So we may be talking different specs.
{Hovercraft Mode Off}
On a 8,9, or 10" molded duct, with the correct fan, built at the correct specs, might be efficient.
Speaking of propellers and fans. I'm curious about that too. A 3 inch brushless tubaxial fan for cooling works on say 7 volts at maybe 0.4 amp. On the other hand, the brushless motor for elev-8 propeller may work on 7 volts at upward of 20 amps. The elevate has a 30 amp ESC and it says the operating time on a 3.3 amp-hour LiPo is about 10 minutes, which works out to 3.3 * 60/10 = 20 amps average current. Not a fair comparison. The elev-8 has a 10 inch propeller. A 10" brushless fan may draw 5 amps.
The ELEV-8 uses a three cell Li-Po battery for about 11.1V. Due to voltage depression under load, the voltage the motor sees may be something like 10V. You never use the full capacity of a Li-Po battery, that would destroy it. At most, plan on using 80%.
3,300 mAh *.8 = 2,640 mAh. 2,640 * 60/10 = 15.84 Amps average current. Or about 4 Amps per motor average current.
What is the salient difference aerodynamically between a fan and a propeller?
Propellers are wings, fan blades are like paddles. A fan makes pressure, a propeller makes thrust (lift). Using the example of a ducted fan RC airplane, the ducted fan inside the aircraft is followed by a restriction - the fan builds pressure forcing the air into somewhere that it does't want to go, the restriction increases the velocity of the exiting air and that produces thrust. For a fixed amount of available power an open propeller will produce more thrust than a ducted fan.
Nearly all high speed aircraft use turbofan engines, as opposed to the turbojet engines of the past. The majority of thrust is provided by a ducted bypass fan, it's called a bypass because the air does not go through the turbine (power producing) portion. They use a ducted fan in this case because a propeller would not work at the high speeds that they need. The propeller would have to turn so fast that the tips would be supersonic. They have tested scimitar shaped propellers on jet engines in the hopes of gaining the efficiencies that open propellers offer. I guess it didn't work out...
You can also look at it another way. When you want to produce thrust you use the largest diameter propeller you can. When you run out of room you then add blades to your propeller. A ducted fan is the result when you have lots of power but a very small space to work with. At some point as you keep adding blades you will find that the air isn't getting out of the way fast enough so you need to contain it with a duct and force it through with more and wider blades that overlap each other.
Rich, we tend to use only ducked for lift, (1/8"-1/4" clearance on tip). On thrust we use 1/4" clearance a 28" duct. It's hard to keep a 28" fiberglass duct round.
We use 6-9 blade fans, not props. So we may be talking different specs.
For the amount of power you are putting into that 28" duct you have no choice but to add blades. Now if you were to apply the same amount of power to a 72" propeller I guarantee you would get more thrust.
Comments
A brushless fan may be available with a tach and PWM speed control build into the fan hub, its own ESC.
The propeller is typically two relatively narrow blades, whereas the fan has several vanes with a steeper pitch. The air volume moved by a fan greater when the fan is thicker. A 3" (60mm) fan may rotate at speeds from 2000 to 5000 RPM and move 40 CFM whereas a 10 inch fan will be slower, and move 800 CFM.
How fast do Elev-8 propellers spin? What is the salient difference aerodynamically between a fan and a propeller? Weight is one.
Another question. Elev-8 motor is rated 1050 Kv. What does Kv mean?
Kv is RPM per Volt. 1 Volt equal 1000 RPM. Typical RPM on the Elev-8 is around 7000 RPM.
I have been playing with ducted fans, as they are more efficient than props, as my many years of hovercraft builds have proven. As I just got my Elev-8 built, I would like to spen some time flying it before I put ducted fans on it.
It depends on the application. For building pressure, as required to float a hovercraft, a ducted fan, especially with a good solidity ratio, is going to be far superior to an open propeller. However, for producing static thrust, which is just moving the largest mass of air at the fastest speed possible, an open propeller will win. The exception is if you have a very precisely made duct where the tip clearance is measure in the thousandths of inches. That would gain some additional thrust efficiency but is not practical to construct. I suppose the other exception would be when you have a severe constraint on the diameter of your propeller - such as in ducted fan RC. An open propeller inside one of those would be just silly.
These questions fall into mass transfer problems. There is a way to establish the volume of air to watt and other ratios may be beneficial to your inquiry. Charts can be made to
establish and track whatever unit you want to. There may be simulators, spreadsheets, or math models already avaliable..
:cool: The right question is half of the solution; The other half is the answer.:cool:
I'm wishing for good tutorial links to the physics of lift, thrust, air-mass acceleration, all that with propellers. Good animations?
To be sure about the solving of the problem; acquire all the information that you have, Vs. the information you want. The data that you have on both sides could fit into a
model that someone has already made. If not, (I hate it when that happens), The problems have to be broken down into sub- parts. If you could post the data, I would not mind
helping you, form the data into a solution. Once a viable solution is calculated, the next step is the real-world test.
If there is a pattern, then there is a sequence; If there is a sequence, then there is a function; If there is a function, then there is a family of functions; If there is
a family of functions, then there exists a solution for every variable in the problem, from begining to end. (You know it!)
{Hovercraft Mode On}
Rich, we tend to use only ducked for lift, (1/8"-1/4" clearance on tip). On thrust we use 1/4" clearance a 28" duct. It's hard to keep a 28" fiberglass duct round.
We use 6-9 blade fans, not props. So we may be talking different specs.
{Hovercraft Mode Off}
On a 8,9, or 10" molded duct, with the correct fan, built at the correct specs, might be efficient.
The ELEV-8 uses a three cell Li-Po battery for about 11.1V. Due to voltage depression under load, the voltage the motor sees may be something like 10V. You never use the full capacity of a Li-Po battery, that would destroy it. At most, plan on using 80%.
3,300 mAh *.8 = 2,640 mAh. 2,640 * 60/10 = 15.84 Amps average current. Or about 4 Amps per motor average current.
Propellers are wings, fan blades are like paddles. A fan makes pressure, a propeller makes thrust (lift). Using the example of a ducted fan RC airplane, the ducted fan inside the aircraft is followed by a restriction - the fan builds pressure forcing the air into somewhere that it does't want to go, the restriction increases the velocity of the exiting air and that produces thrust. For a fixed amount of available power an open propeller will produce more thrust than a ducted fan.
Nearly all high speed aircraft use turbofan engines, as opposed to the turbojet engines of the past. The majority of thrust is provided by a ducted bypass fan, it's called a bypass because the air does not go through the turbine (power producing) portion. They use a ducted fan in this case because a propeller would not work at the high speeds that they need. The propeller would have to turn so fast that the tips would be supersonic. They have tested scimitar shaped propellers on jet engines in the hopes of gaining the efficiencies that open propellers offer. I guess it didn't work out...
You can also look at it another way. When you want to produce thrust you use the largest diameter propeller you can. When you run out of room you then add blades to your propeller. A ducted fan is the result when you have lots of power but a very small space to work with. At some point as you keep adding blades you will find that the air isn't getting out of the way fast enough so you need to contain it with a duct and force it through with more and wider blades that overlap each other.
For the amount of power you are putting into that 28" duct you have no choice but to add blades. Now if you were to apply the same amount of power to a 72" propeller I guarantee you would get more thrust.