Why would a propeller have blades of different lengths?Why don't helicopter blades look like other propellers?Why don't aeroplanes use propellers with more blades like the intake on a fanjet?How do the propeller blades accelerate air resulting in thrust to push an aircraft forward?Can noise from contra-rotating propellers be reduced by having a different number of blades on each propeller?Why are there different number of propeller blades on the inboard and outboard engines?In what way are the airfoils used for a propeller different from the ones used in turbofan engine?Why divide the blades of a 9 blade propeller into 3 groups?Propeller Characteristics at Different AltitudesWhy does a hovercraft lift blade look one way, but a propeller another?Would a ringed propeller have any advantage over a standard propeller?
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Why would a propeller have blades of different lengths?
Why don't helicopter blades look like other propellers?Why don't aeroplanes use propellers with more blades like the intake on a fanjet?How do the propeller blades accelerate air resulting in thrust to push an aircraft forward?Can noise from contra-rotating propellers be reduced by having a different number of blades on each propeller?Why are there different number of propeller blades on the inboard and outboard engines?In what way are the airfoils used for a propeller different from the ones used in turbofan engine?Why divide the blades of a 9 blade propeller into 3 groups?Propeller Characteristics at Different AltitudesWhy does a hovercraft lift blade look one way, but a propeller another?Would a ringed propeller have any advantage over a standard propeller?
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$begingroup$
The Schempp-Hirth Duo Discus T powered glider has a five-bladed propeller, with blades of different lengths.
What is the purpose of such an arrangement?
propeller
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
$endgroup$
add a comment |
$begingroup$
The Schempp-Hirth Duo Discus T powered glider has a five-bladed propeller, with blades of different lengths.
What is the purpose of such an arrangement?
propeller
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
$endgroup$
$begingroup$
They look to me of the same length (google.com/…)
$endgroup$
– Trebia Project.
2 days ago
$begingroup$
I tried to find a conclusive source for the differing length, and funnily enough, only ran across it in this accident report: assets.publishing.service.gov.uk/media/5714f22aed915d1601000000/… It seems the propeller hub had some fatigue issues which were not detectable with the suggested inspection procedures. The manufacturer does not state anything about different lengths on the open portion of their website.
$endgroup$
– AEhere
yesterday
$begingroup$
Asymmetrical fan blades are nothing new. Automakers have used them for decades to reduce noise from radiator fans. They, however, are the same diameter because they are ducted.
$endgroup$
– Harper
4 hours ago
add a comment |
$begingroup$
The Schempp-Hirth Duo Discus T powered glider has a five-bladed propeller, with blades of different lengths.
What is the purpose of such an arrangement?
propeller
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
$endgroup$
The Schempp-Hirth Duo Discus T powered glider has a five-bladed propeller, with blades of different lengths.
What is the purpose of such an arrangement?
propeller
propeller
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
edited 40 mins ago
Adam
2781 silver badge8 bronze badges
2781 silver badge8 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
asked 2 days ago
Daniele ProcidaDaniele Procida
8,4161 gold badge40 silver badges75 bronze badges
8,4161 gold badge40 silver badges75 bronze badges
$begingroup$
They look to me of the same length (google.com/…)
$endgroup$
– Trebia Project.
2 days ago
$begingroup$
I tried to find a conclusive source for the differing length, and funnily enough, only ran across it in this accident report: assets.publishing.service.gov.uk/media/5714f22aed915d1601000000/… It seems the propeller hub had some fatigue issues which were not detectable with the suggested inspection procedures. The manufacturer does not state anything about different lengths on the open portion of their website.
$endgroup$
– AEhere
yesterday
$begingroup$
Asymmetrical fan blades are nothing new. Automakers have used them for decades to reduce noise from radiator fans. They, however, are the same diameter because they are ducted.
$endgroup$
– Harper
4 hours ago
add a comment |
$begingroup$
They look to me of the same length (google.com/…)
$endgroup$
– Trebia Project.
2 days ago
$begingroup$
I tried to find a conclusive source for the differing length, and funnily enough, only ran across it in this accident report: assets.publishing.service.gov.uk/media/5714f22aed915d1601000000/… It seems the propeller hub had some fatigue issues which were not detectable with the suggested inspection procedures. The manufacturer does not state anything about different lengths on the open portion of their website.
$endgroup$
– AEhere
yesterday
$begingroup$
Asymmetrical fan blades are nothing new. Automakers have used them for decades to reduce noise from radiator fans. They, however, are the same diameter because they are ducted.
$endgroup$
– Harper
4 hours ago
$begingroup$
They look to me of the same length (google.com/…)
$endgroup$
– Trebia Project.
2 days ago
$begingroup$
They look to me of the same length (google.com/…)
$endgroup$
– Trebia Project.
2 days ago
$begingroup$
I tried to find a conclusive source for the differing length, and funnily enough, only ran across it in this accident report: assets.publishing.service.gov.uk/media/5714f22aed915d1601000000/… It seems the propeller hub had some fatigue issues which were not detectable with the suggested inspection procedures. The manufacturer does not state anything about different lengths on the open portion of their website.
$endgroup$
– AEhere
yesterday
$begingroup$
I tried to find a conclusive source for the differing length, and funnily enough, only ran across it in this accident report: assets.publishing.service.gov.uk/media/5714f22aed915d1601000000/… It seems the propeller hub had some fatigue issues which were not detectable with the suggested inspection procedures. The manufacturer does not state anything about different lengths on the open portion of their website.
$endgroup$
– AEhere
yesterday
$begingroup$
Asymmetrical fan blades are nothing new. Automakers have used them for decades to reduce noise from radiator fans. They, however, are the same diameter because they are ducted.
$endgroup$
– Harper
4 hours ago
$begingroup$
Asymmetrical fan blades are nothing new. Automakers have used them for decades to reduce noise from radiator fans. They, however, are the same diameter because they are ducted.
$endgroup$
– Harper
4 hours ago
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
You are right. They are unequal length blades. Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub. And obviously, the blades will be mass balanced to place the center of gravity at the hub axis.
I'll go out on a limb here and say that some genius figured out a way to reduce the horrific noise level caused by such a small propeller by having the blade tips each run in a slightly different path of rotation. Brilliant.
And here it is in action where the eccentric blade disc can be clearly seen.
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
$endgroup$
5
$begingroup$
They look like they are also unevenly spaced around the hub, which is a known technique to reduce noise. escholarship.org/content/qt9q75v9t9/qt9q75v9t9.pdf
$endgroup$
– MikeY
yesterday
8
$begingroup$
Excerpt from the conclusions of that paper: "The results showed significant increases in total acoustic intensity for propellers with uneven blade spacing, with very high concentrations of energy in the 0.5BPF tone. [...] This is beneficial for noise metrics such as flyover noise, as noise at low polar angles are “weighted” less than noise near the plane of the propeller." So it is more noisy, but in a lower frequency which is less annoying to humans.
$endgroup$
– AEhere
yesterday
3
$begingroup$
Noise is wasted energy, so my guess is yes, it is less efficient. Regarding safety, only as much as other unusual designs, by merit of being unusual. The early model prop hubs developed fatigue cracks that went undetected, but this seems to have been fixed.
$endgroup$
– AEhere
yesterday
1
$begingroup$
@AEhere: It's not that the noise is at lower frequencies, it's that the noise is "thrown" forward (along the axis) more than it would be with a symmetric design, and correspondingly "thrown" less in directions perpendicular to the propellor axis, including down towards the ground.
$endgroup$
– Michael Seifert
yesterday
3
$begingroup$
@MichaelSeifert that too. I realize that the part I quoted is not the best as it touches on both topics, so reference page 39 of the report: "The shift of acoustic intensity into the low frequency 0.5BPF tone is beneficial because the human ear is much less sensitive to low frequency sounds." and the accompanying graphs; you can clearly see additional peaks in the 1-5 kHz range.
$endgroup$
– AEhere
yesterday
|
show 8 more comments
$begingroup$
Just a guess, but it might be an attempt to reduce the chance of resonance at the blade frequency.
The tail will receive pressure pulses from each blade, but they won't be evenly spaced.
A motor like this is designed to be started and stopped during flight, and will this accelerate and decelerate through a range of speeds. Somewhere in the range between 0 and full power may be the resonant frequency of some part of the tail. When the motor hits that frequency, the tail could shake violently.
By spacing out the pressure pulses from the prop, there won't be any speed where they all resonate with the tail.
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
$endgroup$
$begingroup$
Cars (and laptops, apparently) reduce objectionable noise similarly: mechanics.stackexchange.com/questions/24327/…
$endgroup$
– Camille Goudeseune
7 hours ago
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
You are right. They are unequal length blades. Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub. And obviously, the blades will be mass balanced to place the center of gravity at the hub axis.
I'll go out on a limb here and say that some genius figured out a way to reduce the horrific noise level caused by such a small propeller by having the blade tips each run in a slightly different path of rotation. Brilliant.
And here it is in action where the eccentric blade disc can be clearly seen.
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
$endgroup$
5
$begingroup$
They look like they are also unevenly spaced around the hub, which is a known technique to reduce noise. escholarship.org/content/qt9q75v9t9/qt9q75v9t9.pdf
$endgroup$
– MikeY
yesterday
8
$begingroup$
Excerpt from the conclusions of that paper: "The results showed significant increases in total acoustic intensity for propellers with uneven blade spacing, with very high concentrations of energy in the 0.5BPF tone. [...] This is beneficial for noise metrics such as flyover noise, as noise at low polar angles are “weighted” less than noise near the plane of the propeller." So it is more noisy, but in a lower frequency which is less annoying to humans.
$endgroup$
– AEhere
yesterday
3
$begingroup$
Noise is wasted energy, so my guess is yes, it is less efficient. Regarding safety, only as much as other unusual designs, by merit of being unusual. The early model prop hubs developed fatigue cracks that went undetected, but this seems to have been fixed.
$endgroup$
– AEhere
yesterday
1
$begingroup$
@AEhere: It's not that the noise is at lower frequencies, it's that the noise is "thrown" forward (along the axis) more than it would be with a symmetric design, and correspondingly "thrown" less in directions perpendicular to the propellor axis, including down towards the ground.
$endgroup$
– Michael Seifert
yesterday
3
$begingroup$
@MichaelSeifert that too. I realize that the part I quoted is not the best as it touches on both topics, so reference page 39 of the report: "The shift of acoustic intensity into the low frequency 0.5BPF tone is beneficial because the human ear is much less sensitive to low frequency sounds." and the accompanying graphs; you can clearly see additional peaks in the 1-5 kHz range.
$endgroup$
– AEhere
yesterday
|
show 8 more comments
$begingroup$
You are right. They are unequal length blades. Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub. And obviously, the blades will be mass balanced to place the center of gravity at the hub axis.
I'll go out on a limb here and say that some genius figured out a way to reduce the horrific noise level caused by such a small propeller by having the blade tips each run in a slightly different path of rotation. Brilliant.
And here it is in action where the eccentric blade disc can be clearly seen.
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
$endgroup$
5
$begingroup$
They look like they are also unevenly spaced around the hub, which is a known technique to reduce noise. escholarship.org/content/qt9q75v9t9/qt9q75v9t9.pdf
$endgroup$
– MikeY
yesterday
8
$begingroup$
Excerpt from the conclusions of that paper: "The results showed significant increases in total acoustic intensity for propellers with uneven blade spacing, with very high concentrations of energy in the 0.5BPF tone. [...] This is beneficial for noise metrics such as flyover noise, as noise at low polar angles are “weighted” less than noise near the plane of the propeller." So it is more noisy, but in a lower frequency which is less annoying to humans.
$endgroup$
– AEhere
yesterday
3
$begingroup$
Noise is wasted energy, so my guess is yes, it is less efficient. Regarding safety, only as much as other unusual designs, by merit of being unusual. The early model prop hubs developed fatigue cracks that went undetected, but this seems to have been fixed.
$endgroup$
– AEhere
yesterday
1
$begingroup$
@AEhere: It's not that the noise is at lower frequencies, it's that the noise is "thrown" forward (along the axis) more than it would be with a symmetric design, and correspondingly "thrown" less in directions perpendicular to the propellor axis, including down towards the ground.
$endgroup$
– Michael Seifert
yesterday
3
$begingroup$
@MichaelSeifert that too. I realize that the part I quoted is not the best as it touches on both topics, so reference page 39 of the report: "The shift of acoustic intensity into the low frequency 0.5BPF tone is beneficial because the human ear is much less sensitive to low frequency sounds." and the accompanying graphs; you can clearly see additional peaks in the 1-5 kHz range.
$endgroup$
– AEhere
yesterday
|
show 8 more comments
$begingroup$
You are right. They are unequal length blades. Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub. And obviously, the blades will be mass balanced to place the center of gravity at the hub axis.
I'll go out on a limb here and say that some genius figured out a way to reduce the horrific noise level caused by such a small propeller by having the blade tips each run in a slightly different path of rotation. Brilliant.
And here it is in action where the eccentric blade disc can be clearly seen.
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
$endgroup$
You are right. They are unequal length blades. Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub. And obviously, the blades will be mass balanced to place the center of gravity at the hub axis.
I'll go out on a limb here and say that some genius figured out a way to reduce the horrific noise level caused by such a small propeller by having the blade tips each run in a slightly different path of rotation. Brilliant.
And here it is in action where the eccentric blade disc can be clearly seen.
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
edited yesterday
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
answered yesterday
John KJohn K
33.9k1 gold badge60 silver badges112 bronze badges
33.9k1 gold badge60 silver badges112 bronze badges
5
$begingroup$
They look like they are also unevenly spaced around the hub, which is a known technique to reduce noise. escholarship.org/content/qt9q75v9t9/qt9q75v9t9.pdf
$endgroup$
– MikeY
yesterday
8
$begingroup$
Excerpt from the conclusions of that paper: "The results showed significant increases in total acoustic intensity for propellers with uneven blade spacing, with very high concentrations of energy in the 0.5BPF tone. [...] This is beneficial for noise metrics such as flyover noise, as noise at low polar angles are “weighted” less than noise near the plane of the propeller." So it is more noisy, but in a lower frequency which is less annoying to humans.
$endgroup$
– AEhere
yesterday
3
$begingroup$
Noise is wasted energy, so my guess is yes, it is less efficient. Regarding safety, only as much as other unusual designs, by merit of being unusual. The early model prop hubs developed fatigue cracks that went undetected, but this seems to have been fixed.
$endgroup$
– AEhere
yesterday
1
$begingroup$
@AEhere: It's not that the noise is at lower frequencies, it's that the noise is "thrown" forward (along the axis) more than it would be with a symmetric design, and correspondingly "thrown" less in directions perpendicular to the propellor axis, including down towards the ground.
$endgroup$
– Michael Seifert
yesterday
3
$begingroup$
@MichaelSeifert that too. I realize that the part I quoted is not the best as it touches on both topics, so reference page 39 of the report: "The shift of acoustic intensity into the low frequency 0.5BPF tone is beneficial because the human ear is much less sensitive to low frequency sounds." and the accompanying graphs; you can clearly see additional peaks in the 1-5 kHz range.
$endgroup$
– AEhere
yesterday
|
show 8 more comments
5
$begingroup$
They look like they are also unevenly spaced around the hub, which is a known technique to reduce noise. escholarship.org/content/qt9q75v9t9/qt9q75v9t9.pdf
$endgroup$
– MikeY
yesterday
8
$begingroup$
Excerpt from the conclusions of that paper: "The results showed significant increases in total acoustic intensity for propellers with uneven blade spacing, with very high concentrations of energy in the 0.5BPF tone. [...] This is beneficial for noise metrics such as flyover noise, as noise at low polar angles are “weighted” less than noise near the plane of the propeller." So it is more noisy, but in a lower frequency which is less annoying to humans.
$endgroup$
– AEhere
yesterday
3
$begingroup$
Noise is wasted energy, so my guess is yes, it is less efficient. Regarding safety, only as much as other unusual designs, by merit of being unusual. The early model prop hubs developed fatigue cracks that went undetected, but this seems to have been fixed.
$endgroup$
– AEhere
yesterday
1
$begingroup$
@AEhere: It's not that the noise is at lower frequencies, it's that the noise is "thrown" forward (along the axis) more than it would be with a symmetric design, and correspondingly "thrown" less in directions perpendicular to the propellor axis, including down towards the ground.
$endgroup$
– Michael Seifert
yesterday
3
$begingroup$
@MichaelSeifert that too. I realize that the part I quoted is not the best as it touches on both topics, so reference page 39 of the report: "The shift of acoustic intensity into the low frequency 0.5BPF tone is beneficial because the human ear is much less sensitive to low frequency sounds." and the accompanying graphs; you can clearly see additional peaks in the 1-5 kHz range.
$endgroup$
– AEhere
yesterday
5
5
$begingroup$
They look like they are also unevenly spaced around the hub, which is a known technique to reduce noise. escholarship.org/content/qt9q75v9t9/qt9q75v9t9.pdf
$endgroup$
– MikeY
yesterday
$begingroup$
They look like they are also unevenly spaced around the hub, which is a known technique to reduce noise. escholarship.org/content/qt9q75v9t9/qt9q75v9t9.pdf
$endgroup$
– MikeY
yesterday
8
8
$begingroup$
Excerpt from the conclusions of that paper: "The results showed significant increases in total acoustic intensity for propellers with uneven blade spacing, with very high concentrations of energy in the 0.5BPF tone. [...] This is beneficial for noise metrics such as flyover noise, as noise at low polar angles are “weighted” less than noise near the plane of the propeller." So it is more noisy, but in a lower frequency which is less annoying to humans.
$endgroup$
– AEhere
yesterday
$begingroup$
Excerpt from the conclusions of that paper: "The results showed significant increases in total acoustic intensity for propellers with uneven blade spacing, with very high concentrations of energy in the 0.5BPF tone. [...] This is beneficial for noise metrics such as flyover noise, as noise at low polar angles are “weighted” less than noise near the plane of the propeller." So it is more noisy, but in a lower frequency which is less annoying to humans.
$endgroup$
– AEhere
yesterday
3
3
$begingroup$
Noise is wasted energy, so my guess is yes, it is less efficient. Regarding safety, only as much as other unusual designs, by merit of being unusual. The early model prop hubs developed fatigue cracks that went undetected, but this seems to have been fixed.
$endgroup$
– AEhere
yesterday
$begingroup$
Noise is wasted energy, so my guess is yes, it is less efficient. Regarding safety, only as much as other unusual designs, by merit of being unusual. The early model prop hubs developed fatigue cracks that went undetected, but this seems to have been fixed.
$endgroup$
– AEhere
yesterday
1
1
$begingroup$
@AEhere: It's not that the noise is at lower frequencies, it's that the noise is "thrown" forward (along the axis) more than it would be with a symmetric design, and correspondingly "thrown" less in directions perpendicular to the propellor axis, including down towards the ground.
$endgroup$
– Michael Seifert
yesterday
$begingroup$
@AEhere: It's not that the noise is at lower frequencies, it's that the noise is "thrown" forward (along the axis) more than it would be with a symmetric design, and correspondingly "thrown" less in directions perpendicular to the propellor axis, including down towards the ground.
$endgroup$
– Michael Seifert
yesterday
3
3
$begingroup$
@MichaelSeifert that too. I realize that the part I quoted is not the best as it touches on both topics, so reference page 39 of the report: "The shift of acoustic intensity into the low frequency 0.5BPF tone is beneficial because the human ear is much less sensitive to low frequency sounds." and the accompanying graphs; you can clearly see additional peaks in the 1-5 kHz range.
$endgroup$
– AEhere
yesterday
$begingroup$
@MichaelSeifert that too. I realize that the part I quoted is not the best as it touches on both topics, so reference page 39 of the report: "The shift of acoustic intensity into the low frequency 0.5BPF tone is beneficial because the human ear is much less sensitive to low frequency sounds." and the accompanying graphs; you can clearly see additional peaks in the 1-5 kHz range.
$endgroup$
– AEhere
yesterday
|
show 8 more comments
$begingroup$
Just a guess, but it might be an attempt to reduce the chance of resonance at the blade frequency.
The tail will receive pressure pulses from each blade, but they won't be evenly spaced.
A motor like this is designed to be started and stopped during flight, and will this accelerate and decelerate through a range of speeds. Somewhere in the range between 0 and full power may be the resonant frequency of some part of the tail. When the motor hits that frequency, the tail could shake violently.
By spacing out the pressure pulses from the prop, there won't be any speed where they all resonate with the tail.
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
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$begingroup$
Cars (and laptops, apparently) reduce objectionable noise similarly: mechanics.stackexchange.com/questions/24327/…
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– Camille Goudeseune
7 hours ago
add a comment |
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Just a guess, but it might be an attempt to reduce the chance of resonance at the blade frequency.
The tail will receive pressure pulses from each blade, but they won't be evenly spaced.
A motor like this is designed to be started and stopped during flight, and will this accelerate and decelerate through a range of speeds. Somewhere in the range between 0 and full power may be the resonant frequency of some part of the tail. When the motor hits that frequency, the tail could shake violently.
By spacing out the pressure pulses from the prop, there won't be any speed where they all resonate with the tail.
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
$endgroup$
$begingroup$
Cars (and laptops, apparently) reduce objectionable noise similarly: mechanics.stackexchange.com/questions/24327/…
$endgroup$
– Camille Goudeseune
7 hours ago
add a comment |
$begingroup$
Just a guess, but it might be an attempt to reduce the chance of resonance at the blade frequency.
The tail will receive pressure pulses from each blade, but they won't be evenly spaced.
A motor like this is designed to be started and stopped during flight, and will this accelerate and decelerate through a range of speeds. Somewhere in the range between 0 and full power may be the resonant frequency of some part of the tail. When the motor hits that frequency, the tail could shake violently.
By spacing out the pressure pulses from the prop, there won't be any speed where they all resonate with the tail.
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
$endgroup$
Just a guess, but it might be an attempt to reduce the chance of resonance at the blade frequency.
The tail will receive pressure pulses from each blade, but they won't be evenly spaced.
A motor like this is designed to be started and stopped during flight, and will this accelerate and decelerate through a range of speeds. Somewhere in the range between 0 and full power may be the resonant frequency of some part of the tail. When the motor hits that frequency, the tail could shake violently.
By spacing out the pressure pulses from the prop, there won't be any speed where they all resonate with the tail.
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
answered 10 hours ago
Robin BennettRobin Bennett
3935 bronze badges
3935 bronze badges
$begingroup$
Cars (and laptops, apparently) reduce objectionable noise similarly: mechanics.stackexchange.com/questions/24327/…
$endgroup$
– Camille Goudeseune
7 hours ago
add a comment |
$begingroup$
Cars (and laptops, apparently) reduce objectionable noise similarly: mechanics.stackexchange.com/questions/24327/…
$endgroup$
– Camille Goudeseune
7 hours ago
$begingroup$
Cars (and laptops, apparently) reduce objectionable noise similarly: mechanics.stackexchange.com/questions/24327/…
$endgroup$
– Camille Goudeseune
7 hours ago
$begingroup$
Cars (and laptops, apparently) reduce objectionable noise similarly: mechanics.stackexchange.com/questions/24327/…
$endgroup$
– Camille Goudeseune
7 hours ago
add a comment |
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They look to me of the same length (google.com/…)
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– Trebia Project.
2 days ago
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I tried to find a conclusive source for the differing length, and funnily enough, only ran across it in this accident report: assets.publishing.service.gov.uk/media/5714f22aed915d1601000000/… It seems the propeller hub had some fatigue issues which were not detectable with the suggested inspection procedures. The manufacturer does not state anything about different lengths on the open portion of their website.
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– AEhere
yesterday
$begingroup$
Asymmetrical fan blades are nothing new. Automakers have used them for decades to reduce noise from radiator fans. They, however, are the same diameter because they are ducted.
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– Harper
4 hours ago