Why are prop blades not shaped like household fan blades?Why don't helicopter blades look like other...
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Why are prop blades not shaped like household fan blades?
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Why are prop blades not shaped like household fan blades?
Why don't helicopter blades look like other propellers?Why are aircraft external lights round, not tear-drop shaped?Why don't aeroplanes use propellers with more blades like the intake on a fanjet?Why do propeller blades not have winglets?What would happen if the blades of a variable pitch prop did not all have the same pitch?Why do turbofan blade tips exceed the speed of sound while prop tips should not?Why are RC rotor blades different from helicopter blades?Which are some planes shaped like an inverted wing?How are the Tupolev Tu-95's blades shaped?What would happen if blades are not pitched correctly on a propeller blades?
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My two projects right now are learning to fly and 3D modeling a replacement blade for antique fan, and a question occurred to me:
Why are airplane propeller blades not shaped like household fan blades?
They're both designed to push the same fluid with some degree of efficiency, but household fan blades look a lot more like ship screws/boat propeller blades. Is it a weight issue? A visibility issue? A drag issue, and if so, how?
aerodynamics propeller
asked 8 hours ago
schadjoschadjo
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add a comment |
$begingroup$
My two projects right now are learning to fly and 3D modeling a replacement blade for antique fan, and a question occurred to me:
Why are airplane propeller blades not shaped like household fan blades?
They're both designed to push the same fluid with some degree of efficiency, but household fan blades look a lot more like ship screws/boat propeller blades. Is it a weight issue? A visibility issue? A drag issue, and if so, how?
aerodynamics propeller
asked 8 hours ago
schadjoschadjo
1113 bronze badges
New contributor
schadjo is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
My two projects right now are learning to fly and 3D modeling a replacement blade for antique fan, and a question occurred to me:
Why are airplane propeller blades not shaped like household fan blades?
They're both designed to push the same fluid with some degree of efficiency, but household fan blades look a lot more like ship screws/boat propeller blades. Is it a weight issue? A visibility issue? A drag issue, and if so, how?
aerodynamics propeller
asked 8 hours ago
schadjoschadjo
1113 bronze badges
New contributor
schadjo is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
My two projects right now are learning to fly and 3D modeling a replacement blade for antique fan, and a question occurred to me:
Why are airplane propeller blades not shaped like household fan blades?
They're both designed to push the same fluid with some degree of efficiency, but household fan blades look a lot more like ship screws/boat propeller blades. Is it a weight issue? A visibility issue? A drag issue, and if so, how?
aerodynamics propeller
aerodynamics propeller
asked 8 hours ago
schadjoschadjo
1113 bronze badges
New contributor
schadjo is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
schadjoschadjo
1113 bronze badges
New contributor
schadjo is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
schadjoschadjo
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schadjo is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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asked 8 hours ago
schadjoschadjo
1113 bronze badges
asked 8 hours ago
schadjoschadjo
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4 Answers
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$begingroup$
1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with.
Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props has diminishing returns, because aircraft themselves move forward through the air, so a propeller adds drag to the aircraft however slow it is.
In household fans, size is critical, they have to be small in diameter. A high-span, low-chord (narrow) blade would be more efficient in a household fan as well - indeed, you can find household fans with such blades. But they have to either spin faster for the same amount of airflow, which adds noise, or be larger in diameter.
Ship propellers move in an extremely dense medium, which changes things even more. The drag of moving through water is extremely high and proportional to V^3 power-wise (while thrust force produced is only proportional to V). So their velocity has to be kept as small as possible. The drag cost of adding more chord is also relatively small in water.
On large ships, propellers are already as large as they can be made without sticking out of the water at low draft (on merchant vessels) or reducing the number of shafts that can fit (on combatants). This allows them to spin slower and lose less power to drag.
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
$endgroup$
add a comment |
$begingroup$
Some household fans are shaped like airplane propellers, the ones that need to move a lot of air at the highest speed. For a given motor. They have the highest efficiency, but the tip effect makes them noisy. Best suited for industrial applications.
For inside the family home there are other considerations:
- Silence. Best if we don”t hear the fan run at all.
- Low air speed. We only want to feel the cooling effect of moving air, not have our hair blown out of shape.
- Purchase cost. This is the one we directly see, the usage costs are hidden in the monthly electricity bill.
So for that purpose, a slow moving tip with many broad blades is best.
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
$endgroup$
$begingroup$
Let's try helicopter vs ceiling fan: helicopter - symmetrical airfoil. Ceiling fan - flat. Note long thin fan blades will help reduce interblade turbulence issues for a high speed industrial fan, but optimal airmoving shape that produces the LOWEST "lift" and LEAST DRAG would likely be a thin plate.
$endgroup$
– Robert DiGiovanni
5 hours ago
1
$begingroup$
@RobertDiGiovanni ceiling fans tend towards flat blades because of their lower production cost and because they are often intended to operate in reverse with some efficiency, not because an airfoil would be bad. I have owned several standing fans with airfoil shaped blades, as well.
$endgroup$
– AEhere
4 hours ago
add a comment |
$begingroup$
Learning to flying and modelling a fan blade, both spin in the air but the propeller tries to move the plane, and the fan tries to move the air.
How does this factor into design? Propellers stand above and apart from fans in that they generate lift not only by deflecting air (bottom lift), but also from their motion through the air (top lift). This is best explained by viewing the lift curve vs AOA of an airfoil from 0 to 45 degrees. Lift will increase up to stall, then decrease, then increase again up to 45 degrees. This means you have to move LESS air to get the same lift with an airfoil up to stall.
The fan really is opposite, unless you want it to pull it self around the room. The fan blade is designed to move air, period. Sensible design would make it compact, and thin flat blades with a wider chord would be fine, as one just looking for a cooling breeze from their product. Keeping the original style of fan on the "antique" may make it more valuable.
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
4,4121 gold badge4 silver badges22 bronze badges
$endgroup$
$begingroup$
You have a good point, but it doesn't need to involve the dubious concepts of 'top' and 'bottom' lift. Simply put, propellers are optimised to create lift (thrust) while disturbing the air as little as possible. This favours a large diameter in the first place, to move more air with the lowest possible speed. A fan is almost the opposite: it needs a certain diameter and move the air at a decent speed. (A cooling fan, that is; requirements may be different for a ventilation fan).
$endgroup$
– Zeus
1 hour ago
add a comment |
$begingroup$
Price is the main reason. Ceiling fans just stir the air around and flat paddles are the cheapest way to go.
More expensive fan blades can have some aerofoil shape and even winglets at the tips but this is mainly for show since these blades don't have twist.
answered 8 mins ago
Dermot McDermotDermot McDermot
1
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4 Answers
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active
oldest
votes
4 Answers
4
active
oldest
votes
active
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active
oldest
votes
$begingroup$
1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with.
Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props has diminishing returns, because aircraft themselves move forward through the air, so a propeller adds drag to the aircraft however slow it is.
In household fans, size is critical, they have to be small in diameter. A high-span, low-chord (narrow) blade would be more efficient in a household fan as well - indeed, you can find household fans with such blades. But they have to either spin faster for the same amount of airflow, which adds noise, or be larger in diameter.
Ship propellers move in an extremely dense medium, which changes things even more. The drag of moving through water is extremely high and proportional to V^3 power-wise (while thrust force produced is only proportional to V). So their velocity has to be kept as small as possible. The drag cost of adding more chord is also relatively small in water.
On large ships, propellers are already as large as they can be made without sticking out of the water at low draft (on merchant vessels) or reducing the number of shafts that can fit (on combatants). This allows them to spin slower and lose less power to drag.
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
$endgroup$
add a comment |
$begingroup$
1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with.
Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props has diminishing returns, because aircraft themselves move forward through the air, so a propeller adds drag to the aircraft however slow it is.
In household fans, size is critical, they have to be small in diameter. A high-span, low-chord (narrow) blade would be more efficient in a household fan as well - indeed, you can find household fans with such blades. But they have to either spin faster for the same amount of airflow, which adds noise, or be larger in diameter.
Ship propellers move in an extremely dense medium, which changes things even more. The drag of moving through water is extremely high and proportional to V^3 power-wise (while thrust force produced is only proportional to V). So their velocity has to be kept as small as possible. The drag cost of adding more chord is also relatively small in water.
On large ships, propellers are already as large as they can be made without sticking out of the water at low draft (on merchant vessels) or reducing the number of shafts that can fit (on combatants). This allows them to spin slower and lose less power to drag.
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
$endgroup$
add a comment |
$begingroup$
1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with.
Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props has diminishing returns, because aircraft themselves move forward through the air, so a propeller adds drag to the aircraft however slow it is.
In household fans, size is critical, they have to be small in diameter. A high-span, low-chord (narrow) blade would be more efficient in a household fan as well - indeed, you can find household fans with such blades. But they have to either spin faster for the same amount of airflow, which adds noise, or be larger in diameter.
Ship propellers move in an extremely dense medium, which changes things even more. The drag of moving through water is extremely high and proportional to V^3 power-wise (while thrust force produced is only proportional to V). So their velocity has to be kept as small as possible. The drag cost of adding more chord is also relatively small in water.
On large ships, propellers are already as large as they can be made without sticking out of the water at low draft (on merchant vessels) or reducing the number of shafts that can fit (on combatants). This allows them to spin slower and lose less power to drag.
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
$endgroup$
1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with.
Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props has diminishing returns, because aircraft themselves move forward through the air, so a propeller adds drag to the aircraft however slow it is.
In household fans, size is critical, they have to be small in diameter. A high-span, low-chord (narrow) blade would be more efficient in a household fan as well - indeed, you can find household fans with such blades. But they have to either spin faster for the same amount of airflow, which adds noise, or be larger in diameter.
Ship propellers move in an extremely dense medium, which changes things even more. The drag of moving through water is extremely high and proportional to V^3 power-wise (while thrust force produced is only proportional to V). So their velocity has to be kept as small as possible. The drag cost of adding more chord is also relatively small in water.
On large ships, propellers are already as large as they can be made without sticking out of the water at low draft (on merchant vessels) or reducing the number of shafts that can fit (on combatants). This allows them to spin slower and lose less power to drag.
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
edited 8 hours ago
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
answered 8 hours ago
TheracTherac
8,90723 silver badges38 bronze badges
8,90723 silver badges38 bronze badges
add a comment |
add a comment |
$begingroup$
Some household fans are shaped like airplane propellers, the ones that need to move a lot of air at the highest speed. For a given motor. They have the highest efficiency, but the tip effect makes them noisy. Best suited for industrial applications.
For inside the family home there are other considerations:
- Silence. Best if we don”t hear the fan run at all.
- Low air speed. We only want to feel the cooling effect of moving air, not have our hair blown out of shape.
- Purchase cost. This is the one we directly see, the usage costs are hidden in the monthly electricity bill.
So for that purpose, a slow moving tip with many broad blades is best.
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
$endgroup$
$begingroup$
Let's try helicopter vs ceiling fan: helicopter - symmetrical airfoil. Ceiling fan - flat. Note long thin fan blades will help reduce interblade turbulence issues for a high speed industrial fan, but optimal airmoving shape that produces the LOWEST "lift" and LEAST DRAG would likely be a thin plate.
$endgroup$
– Robert DiGiovanni
5 hours ago
1
$begingroup$
@RobertDiGiovanni ceiling fans tend towards flat blades because of their lower production cost and because they are often intended to operate in reverse with some efficiency, not because an airfoil would be bad. I have owned several standing fans with airfoil shaped blades, as well.
$endgroup$
– AEhere
4 hours ago
add a comment |
$begingroup$
Some household fans are shaped like airplane propellers, the ones that need to move a lot of air at the highest speed. For a given motor. They have the highest efficiency, but the tip effect makes them noisy. Best suited for industrial applications.
For inside the family home there are other considerations:
- Silence. Best if we don”t hear the fan run at all.
- Low air speed. We only want to feel the cooling effect of moving air, not have our hair blown out of shape.
- Purchase cost. This is the one we directly see, the usage costs are hidden in the monthly electricity bill.
So for that purpose, a slow moving tip with many broad blades is best.
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
$endgroup$
$begingroup$
Let's try helicopter vs ceiling fan: helicopter - symmetrical airfoil. Ceiling fan - flat. Note long thin fan blades will help reduce interblade turbulence issues for a high speed industrial fan, but optimal airmoving shape that produces the LOWEST "lift" and LEAST DRAG would likely be a thin plate.
$endgroup$
– Robert DiGiovanni
5 hours ago
1
$begingroup$
@RobertDiGiovanni ceiling fans tend towards flat blades because of their lower production cost and because they are often intended to operate in reverse with some efficiency, not because an airfoil would be bad. I have owned several standing fans with airfoil shaped blades, as well.
$endgroup$
– AEhere
4 hours ago
add a comment |
$begingroup$
Some household fans are shaped like airplane propellers, the ones that need to move a lot of air at the highest speed. For a given motor. They have the highest efficiency, but the tip effect makes them noisy. Best suited for industrial applications.
For inside the family home there are other considerations:
- Silence. Best if we don”t hear the fan run at all.
- Low air speed. We only want to feel the cooling effect of moving air, not have our hair blown out of shape.
- Purchase cost. This is the one we directly see, the usage costs are hidden in the monthly electricity bill.
So for that purpose, a slow moving tip with many broad blades is best.
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
$endgroup$
Some household fans are shaped like airplane propellers, the ones that need to move a lot of air at the highest speed. For a given motor. They have the highest efficiency, but the tip effect makes them noisy. Best suited for industrial applications.
For inside the family home there are other considerations:
- Silence. Best if we don”t hear the fan run at all.
- Low air speed. We only want to feel the cooling effect of moving air, not have our hair blown out of shape.
- Purchase cost. This is the one we directly see, the usage costs are hidden in the monthly electricity bill.
So for that purpose, a slow moving tip with many broad blades is best.
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
answered 5 hours ago
KoyovisKoyovis
34k8 gold badges90 silver badges177 bronze badges
34k8 gold badges90 silver badges177 bronze badges
$begingroup$
Let's try helicopter vs ceiling fan: helicopter - symmetrical airfoil. Ceiling fan - flat. Note long thin fan blades will help reduce interblade turbulence issues for a high speed industrial fan, but optimal airmoving shape that produces the LOWEST "lift" and LEAST DRAG would likely be a thin plate.
$endgroup$
– Robert DiGiovanni
5 hours ago
1
$begingroup$
@RobertDiGiovanni ceiling fans tend towards flat blades because of their lower production cost and because they are often intended to operate in reverse with some efficiency, not because an airfoil would be bad. I have owned several standing fans with airfoil shaped blades, as well.
$endgroup$
– AEhere
4 hours ago
add a comment |
$begingroup$
Let's try helicopter vs ceiling fan: helicopter - symmetrical airfoil. Ceiling fan - flat. Note long thin fan blades will help reduce interblade turbulence issues for a high speed industrial fan, but optimal airmoving shape that produces the LOWEST "lift" and LEAST DRAG would likely be a thin plate.
$endgroup$
– Robert DiGiovanni
5 hours ago
1
$begingroup$
@RobertDiGiovanni ceiling fans tend towards flat blades because of their lower production cost and because they are often intended to operate in reverse with some efficiency, not because an airfoil would be bad. I have owned several standing fans with airfoil shaped blades, as well.
$endgroup$
– AEhere
4 hours ago
$begingroup$
Let's try helicopter vs ceiling fan: helicopter - symmetrical airfoil. Ceiling fan - flat. Note long thin fan blades will help reduce interblade turbulence issues for a high speed industrial fan, but optimal airmoving shape that produces the LOWEST "lift" and LEAST DRAG would likely be a thin plate.
$endgroup$
– Robert DiGiovanni
5 hours ago
$begingroup$
Let's try helicopter vs ceiling fan: helicopter - symmetrical airfoil. Ceiling fan - flat. Note long thin fan blades will help reduce interblade turbulence issues for a high speed industrial fan, but optimal airmoving shape that produces the LOWEST "lift" and LEAST DRAG would likely be a thin plate.
$endgroup$
– Robert DiGiovanni
5 hours ago
1
1
$begingroup$
@RobertDiGiovanni ceiling fans tend towards flat blades because of their lower production cost and because they are often intended to operate in reverse with some efficiency, not because an airfoil would be bad. I have owned several standing fans with airfoil shaped blades, as well.
$endgroup$
– AEhere
4 hours ago
$begingroup$
@RobertDiGiovanni ceiling fans tend towards flat blades because of their lower production cost and because they are often intended to operate in reverse with some efficiency, not because an airfoil would be bad. I have owned several standing fans with airfoil shaped blades, as well.
$endgroup$
– AEhere
4 hours ago
add a comment |
$begingroup$
Learning to flying and modelling a fan blade, both spin in the air but the propeller tries to move the plane, and the fan tries to move the air.
How does this factor into design? Propellers stand above and apart from fans in that they generate lift not only by deflecting air (bottom lift), but also from their motion through the air (top lift). This is best explained by viewing the lift curve vs AOA of an airfoil from 0 to 45 degrees. Lift will increase up to stall, then decrease, then increase again up to 45 degrees. This means you have to move LESS air to get the same lift with an airfoil up to stall.
The fan really is opposite, unless you want it to pull it self around the room. The fan blade is designed to move air, period. Sensible design would make it compact, and thin flat blades with a wider chord would be fine, as one just looking for a cooling breeze from their product. Keeping the original style of fan on the "antique" may make it more valuable.
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
4,4121 gold badge4 silver badges22 bronze badges
$endgroup$
$begingroup$
You have a good point, but it doesn't need to involve the dubious concepts of 'top' and 'bottom' lift. Simply put, propellers are optimised to create lift (thrust) while disturbing the air as little as possible. This favours a large diameter in the first place, to move more air with the lowest possible speed. A fan is almost the opposite: it needs a certain diameter and move the air at a decent speed. (A cooling fan, that is; requirements may be different for a ventilation fan).
$endgroup$
– Zeus
1 hour ago
add a comment |
$begingroup$
Learning to flying and modelling a fan blade, both spin in the air but the propeller tries to move the plane, and the fan tries to move the air.
How does this factor into design? Propellers stand above and apart from fans in that they generate lift not only by deflecting air (bottom lift), but also from their motion through the air (top lift). This is best explained by viewing the lift curve vs AOA of an airfoil from 0 to 45 degrees. Lift will increase up to stall, then decrease, then increase again up to 45 degrees. This means you have to move LESS air to get the same lift with an airfoil up to stall.
The fan really is opposite, unless you want it to pull it self around the room. The fan blade is designed to move air, period. Sensible design would make it compact, and thin flat blades with a wider chord would be fine, as one just looking for a cooling breeze from their product. Keeping the original style of fan on the "antique" may make it more valuable.
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
4,4121 gold badge4 silver badges22 bronze badges
$endgroup$
$begingroup$
You have a good point, but it doesn't need to involve the dubious concepts of 'top' and 'bottom' lift. Simply put, propellers are optimised to create lift (thrust) while disturbing the air as little as possible. This favours a large diameter in the first place, to move more air with the lowest possible speed. A fan is almost the opposite: it needs a certain diameter and move the air at a decent speed. (A cooling fan, that is; requirements may be different for a ventilation fan).
$endgroup$
– Zeus
1 hour ago
add a comment |
$begingroup$
Learning to flying and modelling a fan blade, both spin in the air but the propeller tries to move the plane, and the fan tries to move the air.
How does this factor into design? Propellers stand above and apart from fans in that they generate lift not only by deflecting air (bottom lift), but also from their motion through the air (top lift). This is best explained by viewing the lift curve vs AOA of an airfoil from 0 to 45 degrees. Lift will increase up to stall, then decrease, then increase again up to 45 degrees. This means you have to move LESS air to get the same lift with an airfoil up to stall.
The fan really is opposite, unless you want it to pull it self around the room. The fan blade is designed to move air, period. Sensible design would make it compact, and thin flat blades with a wider chord would be fine, as one just looking for a cooling breeze from their product. Keeping the original style of fan on the "antique" may make it more valuable.
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
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$endgroup$
Learning to flying and modelling a fan blade, both spin in the air but the propeller tries to move the plane, and the fan tries to move the air.
How does this factor into design? Propellers stand above and apart from fans in that they generate lift not only by deflecting air (bottom lift), but also from their motion through the air (top lift). This is best explained by viewing the lift curve vs AOA of an airfoil from 0 to 45 degrees. Lift will increase up to stall, then decrease, then increase again up to 45 degrees. This means you have to move LESS air to get the same lift with an airfoil up to stall.
The fan really is opposite, unless you want it to pull it self around the room. The fan blade is designed to move air, period. Sensible design would make it compact, and thin flat blades with a wider chord would be fine, as one just looking for a cooling breeze from their product. Keeping the original style of fan on the "antique" may make it more valuable.
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
4,4121 gold badge4 silver badges22 bronze badges
edited 7 hours ago
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
4,4121 gold badge4 silver badges22 bronze badges
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
4,4121 gold badge4 silver badges22 bronze badges
answered 7 hours ago
Robert DiGiovanniRobert DiGiovanni
4,4121 gold badge4 silver badges22 bronze badges
4,4121 gold badge4 silver badges22 bronze badges
$begingroup$
You have a good point, but it doesn't need to involve the dubious concepts of 'top' and 'bottom' lift. Simply put, propellers are optimised to create lift (thrust) while disturbing the air as little as possible. This favours a large diameter in the first place, to move more air with the lowest possible speed. A fan is almost the opposite: it needs a certain diameter and move the air at a decent speed. (A cooling fan, that is; requirements may be different for a ventilation fan).
$endgroup$
– Zeus
1 hour ago
add a comment |
$begingroup$
You have a good point, but it doesn't need to involve the dubious concepts of 'top' and 'bottom' lift. Simply put, propellers are optimised to create lift (thrust) while disturbing the air as little as possible. This favours a large diameter in the first place, to move more air with the lowest possible speed. A fan is almost the opposite: it needs a certain diameter and move the air at a decent speed. (A cooling fan, that is; requirements may be different for a ventilation fan).
$endgroup$
– Zeus
1 hour ago
$begingroup$
You have a good point, but it doesn't need to involve the dubious concepts of 'top' and 'bottom' lift. Simply put, propellers are optimised to create lift (thrust) while disturbing the air as little as possible. This favours a large diameter in the first place, to move more air with the lowest possible speed. A fan is almost the opposite: it needs a certain diameter and move the air at a decent speed. (A cooling fan, that is; requirements may be different for a ventilation fan).
$endgroup$
– Zeus
1 hour ago
$begingroup$
You have a good point, but it doesn't need to involve the dubious concepts of 'top' and 'bottom' lift. Simply put, propellers are optimised to create lift (thrust) while disturbing the air as little as possible. This favours a large diameter in the first place, to move more air with the lowest possible speed. A fan is almost the opposite: it needs a certain diameter and move the air at a decent speed. (A cooling fan, that is; requirements may be different for a ventilation fan).
$endgroup$
– Zeus
1 hour ago
add a comment |
$begingroup$
Price is the main reason. Ceiling fans just stir the air around and flat paddles are the cheapest way to go.
More expensive fan blades can have some aerofoil shape and even winglets at the tips but this is mainly for show since these blades don't have twist.
answered 8 mins ago
Dermot McDermotDermot McDermot
1
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$endgroup$
add a comment |
$begingroup$
Price is the main reason. Ceiling fans just stir the air around and flat paddles are the cheapest way to go.
More expensive fan blades can have some aerofoil shape and even winglets at the tips but this is mainly for show since these blades don't have twist.
answered 8 mins ago
Dermot McDermotDermot McDermot
1
New contributor
Dermot McDermot is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
Price is the main reason. Ceiling fans just stir the air around and flat paddles are the cheapest way to go.
More expensive fan blades can have some aerofoil shape and even winglets at the tips but this is mainly for show since these blades don't have twist.
answered 8 mins ago
Dermot McDermotDermot McDermot
1
New contributor
Dermot McDermot is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
Price is the main reason. Ceiling fans just stir the air around and flat paddles are the cheapest way to go.
More expensive fan blades can have some aerofoil shape and even winglets at the tips but this is mainly for show since these blades don't have twist.
answered 8 mins ago
Dermot McDermotDermot McDermot
1
New contributor
Dermot McDermot is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 8 mins ago
Dermot McDermotDermot McDermot
1
New contributor
Dermot McDermot is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 8 mins ago
Dermot McDermotDermot McDermot
1
answered 8 mins ago
Dermot McDermotDermot McDermot
1
1
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Dermot McDermot is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
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add a comment |
add a comment |
schadjo is a new contributor. Be nice, and check out our Code of Conduct.
schadjo is a new contributor. Be nice, and check out our Code of Conduct.
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