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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Force Calculation.
04-05-2010 03:46 AM  10 years ago
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jake21

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ontario canada

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Force Calculation.
Can someone calculate what the load is on the blade grips when using 680 mm blades at 1800 rpm vs the load on 620 blades at 2100 rpm on a raptor 50 Titan. I would also like to know the formula. I know the weight of the blades makes a difference so let me know if possible what blades you are using in your calculation.
Thanks Kindly.
Jake.
The only way to not crash is up
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04-05-2010 03:52 AM  10 years ago
george0079

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USA

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http://www.grc.nasa.gov/WWW/K-12/airplane/wteq.html

Best I can do on short notice
Hell... I can fix that.
Uh oh..
Nope.
It's ***ked!!!
RE-KIT!!!!!
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04-05-2010 06:16 AM  10 years ago
QuantumPSI

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Atlanta, GA

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F = m * r * omega^2

F = force (Newtons)
m = mass (kilograms)
r = radius (meters)
omega = angular velocity (radians per second)

For the radius, measure from the center of the rotor head to the CENTER OF THE BLADE (or wherever the spanwise CG is, but if you don't know where that is exactly, half is not a bad estimate). This formula assumes the blades are point masses (which there clearly not). However, if the blades have uniform weight distribution (and they do for the most part), this approximation will get you pretty close.

You should be able to calculate what you want from this (too sleepy to do the calculations myself, sorry)
...now where was I, dh/dt = BS-dx/dt
I will fly you forever... till earth do us part
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04-05-2010 09:50 AM  10 years ago
tripergreenfeet

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SA

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http://www.archeli.com.au/forums/sh...+thought&page=9

This is a link to a blade force calculator made up by an Archeli member, go to post #43. Gives blade tip speed and blade bolt loading.
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04-05-2010 04:24 PM  10 years ago
heliguy

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Boulder, CO

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Here is an online calculator.

http://www.calctool.org/CALC/phys/newtonian/centrifugal

Remember the radius is not the tip of the blade, see QuantumPSIs post above.

Edit: Well, you got me interested...

So using the above calculator and my Align 600mm blades weighing 125 grams and CGing at 14" from the main shaft (I think it's):

1800 rpm = 355 lbf
1900 rpm = 395 lbf
2000 rpm = 438 lbf
2100 rpm = 483 lbf

My SAB 710s on my Fury at 175 gram and 18.25" comes out:

1800 rpm = 647 lbf
1900 rpm = 721 lbf
2000 rpm = 799 lbf
2100 rpm = 881 lbf

Al
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