sound barrier
Submitted: Saturday, Jan 15, 2011 at 22:11
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Member - MUZBRY(Vic)
Good evening
I was just wondering how many RPM your fan would have to do to break the sound barrier and what is the equation ?
Murray
Reply By: Member - Craig F (WA) - Saturday, Jan 15, 2011 at 22:23
Saturday, Jan 15, 2011 at 22:23
As a rough guess I think my fan would need to do 9000 rpm. I dare say my motor would be everywhere before that happened!
AnswerID:
441985
Reply By: dereki - Saturday, Jan 15, 2011 at 22:53
Saturday, Jan 15, 2011 at 22:53
I just tried a rough calculation and got about 15000rpm based on a 44cm diameter fan which is about what my car has.
But I have probably buggered my calcs up somewhere.
Speed of sound at ground level at 20degC is 343 meters/sec (Wikipedia)
Thats 20580 meters per minute.
Pi x Diameter of fan = circumference of the fan. ie distance travelled per revolution.
RPM revs per minute x 3.14 x Fan diameter = meters/minute
RPM x 3.14 x Fan Diameter = 20580m/min
RPM = 6554 / Fan diameter in meters
RPM = 6554 / 0.44
RPM = 14895
That would give a speed at the tip of the blade at the sound barrier.
Please correct me if I have made a mistake.
D
AnswerID:
441989
Follow Up By: Member - MUZBRY(Vic) - Saturday, Jan 15, 2011 at 22:59
Saturday, Jan 15, 2011 at 22:59
Gday Mr D
Thanks , i will do the math when I am at work next. Imagine the racket at 14000 + rpm down the main street at mid night . It would be like a screaming banshee.
Murray
FollowupID:
714073
Reply By: Dave B ( BHQ NSW) - Saturday, Jan 15, 2011 at 23:03
Saturday, Jan 15, 2011 at 23:03
G'day Muzbury, there is a bloke here with me who says "The Washerwoman" would know.
Dave
AnswerID:
441991
Follow Up By: Member - MUZBRY(Vic) - Saturday, Jan 15, 2011 at 23:19
Saturday, Jan 15, 2011 at 23:19
Gday Dave
She is in bed asleep.
Muz
FollowupID:
714076
Reply By: Roughasguts - Saturday, Jan 15, 2011 at 23:55
Saturday, Jan 15, 2011 at 23:55
Heres a link to a Cessna 210 at take off I use to fly these things from time to time there 3 blade prop hits the speed of sound at around 2700 RPM on take off.
Turn the sound up and enjoy, But the prop won't last long at that rate let
alone a fan
C 210 prop hitting the speed of sound.
Cheers
AnswerID:
441992
Reply By: Member - John - Saturday, Jan 15, 2011 at 23:55
Saturday, Jan 15, 2011 at 23:55
Heater fan, air con fan or radiator fan? Just wondering..................
AnswerID:
441993
Follow Up By: Member - MUZBRY(Vic) - Sunday, Jan 16, 2011 at 08:27
Sunday, Jan 16, 2011 at 08:27
Gday John
Imagine the noise in the car
FollowupID:
714096
Follow Up By: Member - Doug T (NT) - Sunday, Jan 16, 2011 at 20:29
Sunday, Jan 16, 2011 at 20:29
Muzbry
You want to hear a car, listen to this , turn your volume UP
AWESOME
.
FollowupID:
714153
Reply By: Mick O - Saturday, Jan 15, 2011 at 23:57
Saturday, Jan 15, 2011 at 23:57
WHY?
| ''We knew from the experience of well-known travelers that the
trip would doubtless be attended with much hardship.''
Richard Maurice - 1903Lifetime Member
My Profile My Blog Send Message |
AnswerID:
441994
Follow Up By: Member - MUZBRY(Vic) - Sunday, Jan 16, 2011 at 08:19
Sunday, Jan 16, 2011 at 08:19
Gday Mick o
Its the ramblings of an old man. I have a new lawn mower and was wondering as I walked around the yard. I thought i would be moderated if i said lawn mower . So far so good.
Murray
FollowupID:
714094
Follow Up By: Hairs & Fysh - Monday, Jan 17, 2011 at 11:02
Monday, Jan 17, 2011 at 11:02
I reckon you woke up yesterday morning and doubled up on the blue pills.
Murray, you need one of them see through lidded boxes that let you know what day your up too.
FollowupID:
714187
Follow Up By: Member - Mark G Gulmarrad - Monday, Jan 17, 2011 at 11:03
Monday, Jan 17, 2011 at 11:03
Jon
i do believe that Cruiser would be able to help him out with that.
FollowupID:
714188
Follow Up By: Member - MUZBRY(Vic) - Monday, Jan 17, 2011 at 11:17
Monday, Jan 17, 2011 at 11:17
Thanks Jon
Thats all I need, pill packets like old grandma.
FollowupID:
714189
Reply By: mikehzz - Sunday, Jan 16, 2011 at 00:14
Sunday, Jan 16, 2011 at 00:14
The velocity= radius X revs. Only catch is you have to make sure all the units are the same. So if the revs are rev per minute and radius is in cm then the velocity will be cm per minute. The radius never changes and velocity of sound is fixed so the revs required will be speed of sound in cm per minute divided by the radius of the fan in cm.....I think....it's been 40 years since I used that equation. My head is now spinning as well...
AnswerID:
441996
Reply By: Cruiser .- Sunday, Jan 16, 2011 at 10:48
Sunday, Jan 16, 2011 at 10:48
Muzbry
At what altitude, as the speed of sounds varies with altitude.
Cruiser
AnswerID:
442012
Follow Up By: Member - MUZBRY(Vic) - Sunday, Jan 16, 2011 at 12:52
Sunday, Jan 16, 2011 at 12:52
Gday Cruiser
The highest
hill or mound around here is on the freeway, so i have to get the revs right at 100 kph or they will book me.
FollowupID:
714112
Reply By: Member - Graham H (QLD) - Sunday, Jan 16, 2011 at 12:24
Sunday, Jan 16, 2011 at 12:24
Presumably a lawnmower wont get to any significant altitude.
Except of course if he lives in the Snowy area
LOL
AnswerID:
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