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Bell 407


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According to technical bulletin 407-03-51 the operator can remove the aerodynamic cover with the frahm damper underneath. The advantage is that you have circa 25 kilogramms more payload, but you then have more vibrations especially in the rear-cabin.

 

I photographed this 407 in Canmore in 2005 - it had the cover removed:

 

bell407ofalpine1ib.th.jpg

 

 

Merry Christmas,

 

Jan

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Ok guys, I'll be the one to reveal my ignorance. I take it the FRAHM is a vibration absorbing device or damper, but could you enlighten me at to what the acronym actually means, and what method it uses to do it's job?

 

thanks, and Merry Christmas

 

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The FRAHM damper is named after Herman Frahm who invented tuned mass dampers. Basically you take a specific mass and tune it to vibrate in opposition to the natural frequency of a vibrating object. In addition to helicopter applications, the tuned vibration mass is used in high rise buildings to minimize the effects of vibration due to wind currents. Many of the world's high rise buildings incorporate this technology.

 

In the case of the 407 the FRAHM is used to minimize the effect of the natural 4/rev vibration from the main rotor. That being said, each helicopter is sufficiently different that the FRAHM is not really a requirement for most. You can remove the FRAHM and if the 4/rev vibration levels are acceptable to the pilot and passengers, then it need not be installed. As mentioned it saves about 50 pounds of empty weight, not to mention removing the operating cost of the FRAHM itself.

 

Merry Christmas to all!!

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The FRAHM damper is named after Herman Frahm who invented tuned mass dampers. Basically you take a specific mass and tune it to vibrate in opposition to the natural frequency of a vibrating object. In addition to helicopter applications, the tuned vibration mass is used in high rise buildings to minimize the effects of vibration due to wind currents. Many of the world's high rise buildings incorporate this technology.

 

In the case of the 407 the FRAHM is used to minimize the effect of the natural 4/rev vibration from the main rotor. That being said, each helicopter is sufficiently different that the FRAHM is not really a requirement for most. You can remove the FRAHM and if the 4/rev vibration levels are acceptable to the pilot and passengers, then it need not be installed. As mentioned it saves about 50 pounds of empty weight, not to mention removing the operating cost of the FRAHM itself.

 

Merry Christmas to all!!

 

Many thanks 47G, I learned something new today.

(Never too old !)

Merry Christmas

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