Ground Resonance and Langing Gear

[Sparweb]

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

 

[Intermesher]

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

 

[hovergirl]

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.