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#21
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FES climb rate question.
The CalAir A-9b, for instance...
On 10/16/2020 8:50 PM, 2G wrote: On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote: On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote: Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move. My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can. Tom -- Dan, 5J |
#22
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FES climb rate question.
To follow up, if my simple arithmetic is correct, a 94 inch propeller
spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.Â* According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a typical summer density altitude of, say, 8,800' MSL, the CalAir's prop tips are supersonic. But I may have screwed up the math... On 10/17/2020 10:09 AM, Dan Marotta wrote: The CalAir A-9b, for instance... On 10/16/2020 8:50 PM, 2G wrote: On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote: On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote: Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier.Â*Â* That won't change between an electric vs petrol engine.Â* The longer the propeller, the faster the tips move. My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can. Tom -- Dan, 5J |
#23
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FES climb rate question.
Your math seems correct, but the speed of sound varies with temperature, and not pressure, so if your density altitude is 8800' because it is 90º F, then the speed of sound is 1252 fps and the tips are subsonic.
Mike |
#24
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FES climb rate question.
Thanks for that!Â* But come to Moriarty and listen to the unholy racket
that the CalAir makes. On 10/17/2020 2:21 PM, Mike Reid wrote: Your math seems correct, but the speed of sound varies with temperature, and not pressure, so if your density altitude is 8800' because it is 90º F, then the speed of sound is 1252 fps and the tips are subsonic. Mike -- Dan, 5J |
#25
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FES climb rate question.
On Sat, 17 Oct 2020 16:38:14 -0600, Dan Marotta wrote:
Thanks for that!Â* But come to Moriarty and listen to the unholy racket that the CalAir makes. Louder than these? https://www.youtube.com/watch?v=XSGYL3j5EXo (105.5 dB at 50m 400hp piston) https://www.youtube.com/watch?v=YOTwJ1ASz1c (750hp turboprop) -- Martin | martin at Gregorie | gregorie dot org |
#26
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FES climb rate question.
On Saturday, October 17, 2020 at 9:16:27 AM UTC-7, Dan Marotta wrote:
To follow up, if my simple arithmetic is correct, a 94 inch propeller spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.Â* According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a typical summer density altitude of, say, 8,800' MSL, the CalAir's prop tips are supersonic. But I may have screwed up the math... On 10/17/2020 10:09 AM, Dan Marotta wrote: The CalAir A-9b, for instance... On 10/16/2020 8:50 PM, 2G wrote: On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote: On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote: Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier.Â*Â* That won't change between an electric vs petrol engine.Â* The longer the propeller, the faster the tips move. My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can. Tom -- Dan, 5J What MG has such a prop? That is about 2.4m, 0.85m larger than the ASH26/31.. Tom |
#27
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FES climb rate question.
Not a motor glider.Â* The Callair A-9
https://www.google.com/search?q=callair+a9&safe=active&rlz=1C1CHBD_enUS89 2US893&sxsrf=ALeKk01KWvhDfRd1SaXXBOzZmMichhcvyA:16 03235108039&source=lnms&tbm=isch&sa=X&ved=2ahUKEwi TmOyYpMTsAhUFQ80KHQUmC9IQ_AUoAXoECAcQAw&biw=1536&b ih=722&dpr=2.5#imgrc=L7sDan_WSLAatM is an ag-plane.Â* I did some research and it seems the prop diameter is 84 inches instead of 94 inches.Â* I thought I measured it, but that was a long time ago... On 10/19/2020 6:53 PM, 2G wrote: On Saturday, October 17, 2020 at 9:16:27 AM UTC-7, Dan Marotta wrote: To follow up, if my simple arithmetic is correct, a 94 inch propeller spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second. According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a typical summer density altitude of, say, 8,800' MSL, the CalAir's prop tips are supersonic. But I may have screwed up the math... On 10/17/2020 10:09 AM, Dan Marotta wrote: The CalAir A-9b, for instance... On 10/16/2020 8:50 PM, 2G wrote: On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote: On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote: Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier.Â*Â* That won't change between an electric vs petrol engine.Â* The longer the propeller, the faster the tips move. My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can. Tom -- Dan, 5J What MG has such a prop? That is about 2.4m, 0.85m larger than the ASH26/31. Tom -- Dan, 5J |
#28
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FES climb rate question.
On Tuesday, October 20, 2020 at 4:45:35 PM UTC-7, Dan Marotta wrote:
Not a motor glider.Â* The Callair A-9 is an ag-plane.Â* I did some research and it seems the prop diameter is 84 inches instead of 94 inches.Â* I thought I measured it, but that was a long time ago... On 10/19/2020 6:53 PM, 2G wrote: On Saturday, October 17, 2020 at 9:16:27 AM UTC-7, Dan Marotta wrote: To follow up, if my simple arithmetic is correct, a 94 inch propeller spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.Â* According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a typical summer density altitude of, say, 8,800' MSL, the CalAir's prop tips are supersonic. But I may have screwed up the math... On 10/17/2020 10:09 AM, Dan Marotta wrote: The CalAir A-9b, for instance... On 10/16/2020 8:50 PM, 2G wrote: On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote: On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote: Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier.Â*Â* That won't change between an electric vs petrol engine.Â* The longer the propeller, the faster the tips move. My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can. Tom -- Dan, 5J What MG has such a prop? That is about 2.4m, 0.85m larger than the ASH26/31. Tom -- Dan, 5J That is a big difference and means that the tip speed is 675mph, well below the speed of sound. Tom |
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