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09-08-2006 09:38 PM  14 years ago
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MattJen

rrElite Veteran

UK

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ROBBE HEAD ADVICE NEEDED -
Hi all

I have a hotcat turbine, and the head on it is the S2992 3D strenghtend head.

I want to know (from people who knowor fly with this head) what is the maximum head speed using 850 mm blades with a 70mm blade cord.

SAB blades say 1200 for the blades, but i want to know what the head max is

Many thanks for any help, i have sent an email at the beginning of the week to Robbe and asked the same question, but no one has got back to me.

Matt
All The Best
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09-09-2006 06:51 AM  14 years ago
dela

rrApprentice

Stillwater Oklahoma

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I don't have any experience with larger blades, but it seems to me that you are safe if you limit the centrifugal force on the grips to no more the force that is safely carried by standard configurations with smaller blades.

The centrifugal force is mass * radius * (blade rotational speed)^2

Pick a system that you know is commonly viewed as safe with this head (how about 680 mm VBlades, running at a head speed of 1800 rpm)

Force is proportional to: (weight of 680 vblades) times (radius from center of head to CG of the vblades) times (headspeed) squared.
Call that number the "head constant"

Now, for the set of 850 mm blades, choose a headspeed so that:

(weight of 850 mm blades) times (radius from center of head to CG of 850 mm blades) times (headspeed for 850 mm blades) squared
equals the "head constant" calculated from the Vblades ( or some other "safe" blade set.

This calculation only considers the centrifugal force in the grips, and ignores the lift load and bending load on the grips, but the centrifugal load should be the dominant load on the grips.

This should give you a headspeed that is safe, but it won't tell you the maximum headspeed that the head can withstand.

Ron
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