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Ground Resonance and Langing Gear

Ground Resonance and Langing Gear

Ground Resonance and Langing Gear

I've read and heard a lot about how Ground Resonance sets up and can quickly progress into an oscillation that upsets a helicopter.  I've got references from Ray Prouty that lead me to believe that all helicopters, regardless of the configuration, are vulnerable to this.  

A co-worker says that he's been to a conference where an expert stated that 2-bladed helicopters aren't susceptible to ground resonance.  

Who's right?

In this vein, why did Bell change the landing gear configuration between the 206L and the 206L-4?

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

RE: Ground Resonance and Langing Gear

He's some additional information on Ground Resonance, which might be if value. http://www.unicopter.com/1246.html

To my limited knowledge, all teetering rotors are without lead-lag hinges, with the exception of the Kaman intermeshing helicopter. The Kaman heads appears to provide for lead-lag between the two rotors and, ALSO, between the two blades on the same rotor.

Dave J

RE: Ground Resonance and Langing Gear

Two bladed rotors are typically stiff-lag rotors (the lag frequency is greater than 1). When the lag frequency is greater than one, the system is always stable -- in other words, free of ground resonance.

Heidi M.

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