Gound resonance
Joined: Nov 2010
Posts: 880
Likes: 225
From: Australia
ATSB report of a ground resonance accident on an A109E conducting pilot transfer from a ship in Australia in February this year:
https://www.atsb.gov.au/publications...rt/ao-2025-009
Unrelated, but I witnessed ground resonance on an AS350B years back. It developed rapidly after the helicopter touched down. But the pilot reacted swiftly and took off again. He would have been on guard during his next landing attempt which went without incident.
https://www.atsb.gov.au/publications...rt/ao-2025-009
Unrelated, but I witnessed ground resonance on an AS350B years back. It developed rapidly after the helicopter touched down. But the pilot reacted swiftly and took off again. He would have been on guard during his next landing attempt which went without incident.
Joined: Dec 2005
Posts: 1,581
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From: England
It's less of a problem with teetering heads because they don't have drag dampers - they are actually the most suceptible to GR, but articulated heads have dampers. And contrary to popular belief, you can get it in an AS 350 - a friend of mine got into it on the factory course in the USA of all places. And, as crab says, skids are better than wheels....
The first was a Lama in Scotland which had landed for a hot refuel. As I stepped over the skids with the refueling hose and was removing the fuel cap the pilot took off.
I threw the hose clear and walked out round the back of the skids. I stopped to give the pilot a hard stare. On shut down he explained that ground resonance had set in. Probable cause was the
landing site which was a loose gravel track. That could have been worse if the hose had get caught up.
The second was a skidded 365C. Pilot had three goes before getting it safely on the ground. Much work was done but the aircraft continued to want to go into resonance.
Among the work was new set of undercarriage dampers. Eventually a third set of dampers fixed the problem. Apparently the overhaul shop were setting them up incorrectly.
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
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From: Wandering the FIR and cyberspace often at highly unsociable times
I instructed on the RAF Puma HC1 OCU for a couple of tours. We used to get a fair number of ex Wessex pilots coming through. The first start up they experienced, the standard “Puma lateral dance” always caused them great concern. The Puma’s forward slanting main rotor mast, and very basic oil filled main rotor dampers allowed the main blades to swivel forwards, so they were no longer at 90° to each other. The mass imbalance caused the whole aircraft to rock left/right until the spin drier effect sorted it all out. Very worrying for pilots with time on the ground resonance prone Wessex.
A certain 72 sqn pilot at Odiham decided to authorised a Wessex sortie with a recently arrived, fresh out of the OCU young pilot. During start up they ended up with the aircraft lying on its side in dispersal after ground resonance set in. During the unit inquiry it was discovered that the flight had been authorised as “Pre Northern Ireland Shake Down” training. A legend was born, plus a new song written for the SH Song Book!
”There’s a Wessex on the ground (on the ground)
With it’s rotors going round (going round)
And it jumps up and down and shakes itself to bits
And gives its passengers the $hits, $hits, $hits!”
A certain 72 sqn pilot at Odiham decided to authorised a Wessex sortie with a recently arrived, fresh out of the OCU young pilot. During start up they ended up with the aircraft lying on its side in dispersal after ground resonance set in. During the unit inquiry it was discovered that the flight had been authorised as “Pre Northern Ireland Shake Down” training. A legend was born, plus a new song written for the SH Song Book!
”There’s a Wessex on the ground (on the ground)
With it’s rotors going round (going round)
And it jumps up and down and shakes itself to bits
And gives its passengers the $hits, $hits, $hits!”
