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  #21  
Old December 1st 03, 07:06 AM
Hennie
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The centrifugal force generated by a rotor blade
is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from
the hub center to the CG of the blade
  #22  
Old December 1st 03, 11:27 PM
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Thanks for posting the formula. Let me see if I understand it
correctly. For the hypothetical small helicopter:

Blades are 10' long and the cg is half the length (no tip weights). R
would be 5' plus the distance from the center of the shaft to the
blade mounts. I'll call R as being 5.5' in this example.

I'll say the blades are 25 lbs each and the RPM is 600 (450 MPH tip
speed).

FORCE = (W * R * RPM^2) / 2900 = (25 * 5.5 * 600^2) / 2900
= 17069 lbs.

This is assuming that the units are supposed to be lbs and feet.

The result is less than I thought, but still pretty impressive.

By adding 2 lb tip weights, the CG force increases to about 23,500
lbs. That's a pretty big jump, but the biggest jumps obviously come
with the RPM.

Did I do it right?

Dennis.


(Hennie) wrote:

The centrifugal force generated by a rotor blade
is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from
the hub center to the CG of the blade


Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm

  #23  
Old December 2nd 03, 11:55 AM
Cam
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Hi, I was wondering if there was a simplified formula for working out
centrifugal force with a constant mass rotor.
Unfortunately I can't make sence of it, what is the constant 2900 derived
from?
When using, F= MV^2/r
F= force
M= mass
V= velocity
r= radius
By summing each calculation -- say at r=1m, 'X'm/s,M=1Kg
r=2m
'X'm/s,M=2Kg
and so on .(the smaller the increments the better)
The end result is not even close to the formentioned formula.
Where have I gone wrong?

Cheers Cam
(excuse the metric system)

"Hennie" wrote in message
om...
The centrifugal force generated by a rotor blade
is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from
the hub center to the CG of the blade



  #24  
Old December 2nd 03, 01:27 PM
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Default


Just guessing, but your formula uses Velocity and his uses RPM. The
2900 is probably due to the conversion of RPM to velocity in Miles Per
Hour.

V = (2*R*RPM)/28 (where units are V=Miles Per Hour, R=Feet)

Also, your formula is apparently using Kg's and M's instead of Feet
and pounds. Then again, I may be totally wrong as CAC is from South
Africa and they use the metric system too. (I know this because I did
a search for apartments in South Africa and all the square 'footage's
were in square meters.)

It would help if somebody would say for sure what the units are.

Dennis.

"Cam" wrote:

Hi, I was wondering if there was a simplified formula for working out
centrifugal force with a constant mass rotor.
Unfortunately I can't make sence of it, what is the constant 2900 derived
from?
When using, F= MV^2/r
F= force
M= mass
V= velocity
r= radius
By summing each calculation -- say at r=1m, 'X'm/s,M=1Kg
r=2m
'X'm/s,M=2Kg
and so on .(the smaller the increments the better)
The end result is not even close to the formentioned formula.
Where have I gone wrong?

Cheers Cam
(excuse the metric system)

"Hennie" wrote in message
om...
The centrifugal force generated by a rotor blade
is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from
the hub center to the CG of the blade




Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm

  #25  
Old December 3rd 03, 06:45 AM
Bob
external usenet poster
 
Posts: n/a
Default

IN CLARIFICATION TO THE ABOVE:

THAT WAS NOT "DONALD TRUMP'S AGUSTA THAT WAS LOST IN THE ACCIDENT UP IN NEW
JERSEY. THAT AIRCRAFT WAS LEASED THAT DAY FROM PARAMOUNT AVIATION. TRUMP
HAD FIVE (5) OF HIS L A R G E HELICOPTERS SITTING IN THE HANGAR ON THE DAY
THAT THE LEASED AIRCRAFT WAS LOST.

I WAS THE CHIEF INSPECTOR FOR TRUMPS HELICOPTER OPERATIONS AT THE TIME SO
YOU CAN TAKE THIS INFO TO THE BANK. HIS AGUSTA 109 WAS IN MAINTENANCE THAT
DAY AND WAS UNAVAILABLE. THE BLADE THAT FAILED HAD A "FORGING LAP": LEFT IN
THE M/R/B SPAR SINCE MANUFACTURE WHICH CREATED A "STRESS RAISER", EVENTUALLY
A CRACK, AND THE REST IS HISTORY. For the rest of the commenters, now with
many composite blades out there a better record can probably be expected
although no great inspection methods have yet been developed for composites.
Metal blades departed aircraft many many times, hence Sikorsky's "BIM"
indicators on the blade roots. Hundreds of thousands od pounds of
centrifugal force and cracked blades will always present a problem, huh?




  #26  
Old December 3rd 03, 06:51 AM
Hennie
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Default

I got the formula in the rotorcraft forum. If i remember correctly
it was written by Chuck Beaty
The units is in pounds and feet, thus imperial.
Yes we use the metric system but I was still brought up with the
imperial system so I still think that way.

Regards

Hennie


wrote in message ...
Just guessing, but your formula uses Velocity and his uses RPM. The
2900 is probably due to the conversion of RPM to velocity in Miles Per
Hour.

V = (2*R*RPM)/28 (where units are V=Miles Per Hour, R=Feet)

Also, your formula is apparently using Kg's and M's instead of Feet
and pounds. Then again, I may be totally wrong as CAC is from South
Africa and they use the metric system too. (I know this because I did
a search for apartments in South Africa and all the square 'footage's
were in square meters.)

It would help if somebody would say for sure what the units are.

Dennis.

"Cam" wrote:

Hi, I was wondering if there was a simplified formula for working out
centrifugal force with a constant mass rotor.
Unfortunately I can't make sence of it, what is the constant 2900 derived
from?
When using, F= MV^2/r
F= force
M= mass
V= velocity
r= radius
By summing each calculation -- say at r=1m, 'X'm/s,M=1Kg
r=2m
'X'm/s,M=2Kg
and so on .(the smaller the increments the better)
The end result is not even close to the formentioned formula.
Where have I gone wrong?

Cheers Cam
(excuse the metric system)

"Hennie" wrote in message
om...
The centrifugal force generated by a rotor blade
is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from
the hub center to the CG of the blade




Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm
  #27  
Old December 3rd 03, 10:04 AM
Cam
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Posts: n/a
Default

Whooops, I used the radius instead of the CoG of one blade (approx 1/2
radius).
Now it works, far easier than my approach.
Thanks.

ps/ I like to use both metric and imperial as well, it comes in handy when
building international space stations (I'm sure)

Cheers Cam


  #28  
Old December 3rd 03, 12:31 PM
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Its probably the same formula used to calculate how fast the space
station must rotate in order to create artificial gravity. Now if the
space station actually did that, it would be really cool.

Dennis.

"Cam" wrote:

ps/ I like to use both metric and imperial as well, it comes in handy when
building international space stations (I'm sure)

Cheers Cam



Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm

  #29  
Old December 3rd 03, 12:36 PM
external usenet poster
 
Posts: n/a
Default


Forgive my ignorance, but I need some clarification on your
clarification. Describe exactly what a 'forging lap' is. What do I
look for when inspecting a blade? Can it be seen outright, or is an
X-ray necessary?

Also, I thought that composite blades still used a metal spar. Is
this not correct. If not, please describe their construction.

Dennis.

"Bob" wrote:

I WAS THE CHIEF INSPECTOR FOR TRUMPS HELICOPTER OPERATIONS AT THE TIME SO
YOU CAN TAKE THIS INFO TO THE BANK. HIS AGUSTA 109 WAS IN MAINTENANCE THAT
DAY AND WAS UNAVAILABLE. THE BLADE THAT FAILED HAD A "FORGING LAP": LEFT IN
THE M/R/B SPAR SINCE MANUFACTURE WHICH CREATED A "STRESS RAISER", EVENTUALLY
A CRACK, AND THE REST IS HISTORY. For the rest of the commenters, now with
many composite blades out there a better record can probably be expected
although no great inspection methods have yet been developed for composites.
Metal blades departed aircraft many many times, hence Sikorsky's "BIM"
indicators on the blade roots. Hundreds of thousands od pounds of
centrifugal force and cracked blades will always present a problem, huh?





Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

"A RECESSION is when you know somebody who is out of work.
A DEPRESSION is when YOU are out of work.
A RECOVERY is when all the H-1B's are out of work."
To find out what an H-1B is and how they are putting
Americans out of work, visit the following web site
and click on the "Exporting America" CNN news video:
http://zazona.com/ShameH1B/MediaClips.htm

  #30  
Old December 3rd 03, 06:29 PM
Bob
external usenet poster
 
Posts: n/a
Default

Unfortunately, my clarification, specifically as to the cause of the
Agusta109 main rotor blade separation is in error. In that particular case,
I was informed that at manufacture too much bonding material was applied to
a weight that is bonded inside of the spar to achieve balance to
manufacturing tolerances. That excess bonding material was "scraped" out
leaving a tooling mark that eventually led to the crack.

Now to briefly answer your questions:
A "Forging Lap" is a flap of metal that should not be present after a
forging or hammering type of process. Those spars are not forged, they are
extruded (pushed or pulled through a die). Typically, manufacturing defects
are not as blatent as to be seen by the naked eye, and many times are inside
of the spar requiring x-ray, eddy current, or some other form of
non-destructive detection.

Composite (meaning totally composite) main rotor blades do not have a metal
spar. Some newer composite main rotor blades incorporate a carbon fibre
reinforced plastic spar and are filled with a Nomex honeycomb material. The
blades are corrosion and damage resistant. Sorry for my error.


 




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