Why does it rip??
04-12-2003, 09:15 PM
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Why does it rip??
Polle-DK:
If you are speaking of the noise, it is causedby the prop tips going supersonic. This is to be avoided - not because ofthe noise, but the reduced efficiency.
Bill.
If you are speaking of the noise, it is causedby the prop tips going supersonic. This is to be avoided - not because ofthe noise, but the reduced efficiency.
Bill.
04-12-2003, 09:29 PM
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Why does it rip??
Quist:
Actual tip speed at "Start of Rip" depends on the tip shape. The APC's are noisy at a lower speed than the Master Air Screw props, for example.
Bill.
Actual tip speed at "Start of Rip" depends on the tip shape. The APC's are noisy at a lower speed than the Master Air Screw props, for example.
Bill.
04-12-2003, 09:30 PM
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Why does it rip??
I don´t believe it goes supersonic either.
Then my 3W150 should go 8000rpm with a 32x10, and my 3W75 should go 9800rpm with a 26x8 Menz.
Then my 3W150 should go 8000rpm with a 32x10, and my 3W75 should go 9800rpm with a 26x8 Menz.
04-12-2003, 09:52 PM
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Why does it rip??
Polle-DK:
Do the math.
Your 26 inch prop has a tip speed of 600 mph at 7757 RPM, the 32 inch is 600 mph tip speed at 6303 rpm.
At 8000 rpm the 32" prop has a tip speed of 761.6 mph, the 22" at 9800 rpm is going 758.03 mph.
A lot of people used to believe you'd fall off the edge if you went too far out to sea. They were wrong too.
Welcome to the 21st century, Charlie.
Bill.
Do the math.
Your 26 inch prop has a tip speed of 600 mph at 7757 RPM, the 32 inch is 600 mph tip speed at 6303 rpm.
At 8000 rpm the 32" prop has a tip speed of 761.6 mph, the 22" at 9800 rpm is going 758.03 mph.
A lot of people used to believe you'd fall off the edge if you went too far out to sea. They were wrong too.
Welcome to the 21st century, Charlie.
Bill.
04-12-2003, 10:05 PM
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Why does it rip??
26x2,5x22x7757x60 = 950km/t = 527mph
7x100000
Then you can add the factor off the airspeed, lets say its 50mph:
V (527x527)+(50x50)=529mph........NEVER MACH 1
7x100000
Then you can add the factor off the airspeed, lets say its 50mph:
V (527x527)+(50x50)=529mph........NEVER MACH 1
04-12-2003, 10:36 PM
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Why does it rip??
thought the mph was 1,8km/t.....its not........its 1,6....sorry
26x2,5x22x7757x60 = 950km/t = 593mph
7x100000
I said that my 26 inch should go 9800rpm to reach Mach 1:
26x2,5x22x9800x60 = 1201km/t = 746mph
7x100000
Fact: at 9800rpm you will get the speed of sound with a 26 inch prop
Wasn´t that what I said???????????
26x2,5x22x7757x60 = 950km/t = 593mph
7x100000
I said that my 26 inch should go 9800rpm to reach Mach 1:
26x2,5x22x9800x60 = 1201km/t = 746mph
7x100000
Fact: at 9800rpm you will get the speed of sound with a 26 inch prop
Wasn´t that what I said???????????
04-12-2003, 10:58 PM
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Why does it rip??
And my 75ccm runs 5800rpm on the ground.........it rips at level flight.........should it take 4000rpm more in the air?
Should it run 9800 at level flight with the biggest prop 3W recoment?
When it may not get over 8500rpm
Should it run 9800 at level flight with the biggest prop 3W recoment?
When it may not get over 8500rpm
04-12-2003, 11:23 PM
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Why does it rip??
Polle-DK:
Apologies for living in the 19th century, but a lot of us are still not using the metric system as an everyday thing.
You have rounded too many numbers. To start with, you have used an inch equivalent of 2.5 instead of 2.54, introducing your very first error, caused by casual metric conversion.
Since we are talking minutes, hours, and miles we'll avoid any metric conversions, but we'll stay with the 26" (not 66.04mm) prop.
It has a circumference of 81.68" (Pi*D), multiply that by 7757 (rpm) to get 633600 inches per minute, divide by 12 to get 52800 feet per minute. Now divide by 5280 and you have 10 miles per minute. We are almost there, be patient. Now, 10 miles per minute. If we multiply that by 60 we should have miles per hour, right? guess what. 600 miles per hour tip speed at 7757 rpm with a 26" prop diameter. And that's without considering forward speed. Using your number of 50 mph the resultant tip speed is 602.09 mph. I will not hold your hand for that bit of math, since your calculation was very close for that part.
But do recheck the other math, sir, you have a monstrous error in yours. And the tips DO go supersonic.
Even with 19th century measures of length I am living in the 21st century.
Bill.
PS: Sorry it took so long to get back to you. wr.
Apologies for living in the 19th century, but a lot of us are still not using the metric system as an everyday thing.
You have rounded too many numbers. To start with, you have used an inch equivalent of 2.5 instead of 2.54, introducing your very first error, caused by casual metric conversion.
Since we are talking minutes, hours, and miles we'll avoid any metric conversions, but we'll stay with the 26" (not 66.04mm) prop.
It has a circumference of 81.68" (Pi*D), multiply that by 7757 (rpm) to get 633600 inches per minute, divide by 12 to get 52800 feet per minute. Now divide by 5280 and you have 10 miles per minute. We are almost there, be patient. Now, 10 miles per minute. If we multiply that by 60 we should have miles per hour, right? guess what. 600 miles per hour tip speed at 7757 rpm with a 26" prop diameter. And that's without considering forward speed. Using your number of 50 mph the resultant tip speed is 602.09 mph. I will not hold your hand for that bit of math, since your calculation was very close for that part.
But do recheck the other math, sir, you have a monstrous error in yours. And the tips DO go supersonic.
Even with 19th century measures of length I am living in the 21st century.
Bill.
PS: Sorry it took so long to get back to you. wr.
04-12-2003, 11:32 PM
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Why does it rip??
Polle-DK:
You are a lot closer, but this still gives you a round off error. It's really easier to stay with "English" measurements doing this. If you want to end metric, then make the conversions on raw data at the start or the result at the finish, not in the middle of the calculation.
I had started my response when you posted number 8, got called out, and did not see your later posts until I put my last in. Sorry.
Bill.
...thought the mph was 1,8km/t.....its not........its 1,6....sorry.
I had started my response when you posted number 8, got called out, and did not see your later posts until I put my last in. Sorry.
Bill.
04-12-2003, 11:35 PM
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Why does it rip??
Polle-DK:
If you are 5800 rpm on the ground (26" prop) it takes less than 2000 rpm more to exceed Mach at the tips.
Bill.
Originally posted by Polle-DK
And my 75ccm runs 5800rpm on the ground.........it rips at level flight.........should it take 4000rpm more in the air?
And my 75ccm runs 5800rpm on the ground.........it rips at level flight.........should it take 4000rpm more in the air?
Bill.
04-13-2003, 12:08 AM
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Why does it rip??
What speed is Mach 1? I think it is around 700mph, but I dont know the exact speed.
I have a DA 100 that turns a 27 10 menz at 6200 rpms and it is ripping. With our math 26.5*3.1417=83.25*6200=516181.31*60=30970878 this is inches per hour /12=2580906.5 feet per hour/5280=488.80 miles per hour. If you use 700 mph as Mach 1, I am running .698 mach
btw a 27 inch menz measures 26.5 inches.
I have a DA 100 that turns a 27 10 menz at 6200 rpms and it is ripping. With our math 26.5*3.1417=83.25*6200=516181.31*60=30970878 this is inches per hour /12=2580906.5 feet per hour/5280=488.80 miles per hour. If you use 700 mph as Mach 1, I am running .698 mach
btw a 27 inch menz measures 26.5 inches.
04-13-2003, 12:20 AM
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Mach speed
Q:
That is exactly what I'm working on right now. A temperature to Mach module to plug into my spreadsheets.
All of my (computer) models use 600 mph as Mach, but they are also intended to be working with aircraft at 30 to 40 thousand feet, and sea level Mach is approx 750 mph at standard temperature and pressure. Actually temperature is the determinant, wont go into it but pressure being directly related to temperature can be ignored.
Back soon.
Bill.
Originally posted by quist
What speed is Mach 1? I think it is around 700mph, but I dont know the exact speed.
What speed is Mach 1? I think it is around 700mph, but I dont know the exact speed.
All of my (computer) models use 600 mph as Mach, but they are also intended to be working with aircraft at 30 to 40 thousand feet, and sea level Mach is approx 750 mph at standard temperature and pressure. Actually temperature is the determinant, wont go into it but pressure being directly related to temperature can be ignored.
Back soon.
Bill.
04-13-2003, 01:06 AM
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Why does it rip??
Quist:
Mach is 741.43 mph at 32F, and rises to 795.76 mph at 104F. This is the range from 0 Celsius to 40 C. In meters per second the range is 331.45 m/s to 355.74 m/s.
If we stick with 750 mph the error won't exceed 2% in the temperatures we normally fly.
I need to alter my spreadsheet models to reflect this.
Bill.
Mach is 741.43 mph at 32F, and rises to 795.76 mph at 104F. This is the range from 0 Celsius to 40 C. In meters per second the range is 331.45 m/s to 355.74 m/s.
If we stick with 750 mph the error won't exceed 2% in the temperatures we normally fly.
I need to alter my spreadsheet models to reflect this.
Bill.
04-13-2003, 07:47 AM
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Why does it rip??
Bill - I realy don´t get your point.
5800rpm on the ground - and you say I should need 2000 more to hit supersonic..............
That means that My tips should go supersonic at 7800rpm?
You say that 7800rpm gives a tipspeed 600mph....
I don´t know in what level you fly your models........I stay so close to the ground that I use the speed of sound at sea-level.
Denmark is a flat country.......
That means that it should go 9800rpm to get 750mph.
9800 - 5800= 4000..............
I said that it should go 4000 more in the air to hit Mach 1
I know that my numbers are not precisly, this is not a math test.
If it was, your way to find "circumference of 81.68" is wrong too.
Don´t know what Pi you use........many people use 3,41xxx.........Pi is 22/7 as a correct number...........26x22/7=81,71.........
Wellcome to the ground
5800rpm on the ground - and you say I should need 2000 more to hit supersonic..............
That means that My tips should go supersonic at 7800rpm?
You say that 7800rpm gives a tipspeed 600mph....
I don´t know in what level you fly your models........I stay so close to the ground that I use the speed of sound at sea-level.
Denmark is a flat country.......
That means that it should go 9800rpm to get 750mph.
9800 - 5800= 4000..............
I said that it should go 4000 more in the air to hit Mach 1
I know that my numbers are not precisly, this is not a math test.
If it was, your way to find "circumference of 81.68" is wrong too.
Don´t know what Pi you use........many people use 3,41xxx.........Pi is 22/7 as a correct number...........26x22/7=81,71.........
Wellcome to the ground
04-13-2003, 08:11 AM
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Why does it rip??
Polle-DK:
See my last post, number 17. I realized my error in Mach, my spreadsheet models were all set for 30K feet (Approx 10,000 meters) and not sea level.
And just for general information 22/7 is acceptable as an approximation of pi when no precision is desired, but 3.41 is never acceptable. 3.14, however, and 22/7 are equally accurrate, to two decimal places. I use 3.1415926536 normally, and go to 14 significant digits when I want to be precise. Sorry, it's a bit of engineering training coming out.
Also in that post, #17, I included metric numbers for you.
Can we call a truce?
Bill.
See my last post, number 17. I realized my error in Mach, my spreadsheet models were all set for 30K feet (Approx 10,000 meters) and not sea level.
And just for general information 22/7 is acceptable as an approximation of pi when no precision is desired, but 3.41 is never acceptable. 3.14, however, and 22/7 are equally accurrate, to two decimal places. I use 3.1415926536 normally, and go to 14 significant digits when I want to be precise. Sorry, it's a bit of engineering training coming out.
Also in that post, #17, I included metric numbers for you.
Can we call a truce?
Bill.
04-13-2003, 08:18 AM
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Why does it rip??
Ok - I have read that site Quist linked to.
Then I understand.
The Airspeed accelerates to Mach1 because of the preasure.
That gives sence.
The tips doesn´t turn with Mach1,,,,,,,,,,,,,,,,,,
Then I understand.
The Airspeed accelerates to Mach1 because of the preasure.
That gives sence.
The tips doesn´t turn with Mach1,,,,,,,,,,,,,,,,,,
