Sorry nubian,
All I know about a Rotorway can be written on a postage stamp no bigger than the space needed to write 'Rotorway'.

nubian,

According to the AAIB report http://www.aaib.gov.uk/cms_resources...US%2009-09.pdf the aircraft in the video is a Rotorway Executive 162F

Please explain to me with my postage stamp knowledge, why in the CAA Check Flight Schedule for the Rotorway Exec, Exec 90 and 162F helicopters, does it say;

http://www.caa.co.uk/docs/1455/SRG_F...2_16102006.pdf


Just need to know if I should pop down to the post office for a bigger stamp.

"Ground resonance" is an undamped vibration of increasing amplitude. I was of the understanding that a semi-rigid rotor system (or any other) was not immune, but perhaps less prone.

I hope I can still take to the skies at 74 years young..... I'll remember to take my shoe horn with me..... Pardon??? :{

SilsoeSid,

As to your question about why the UK CAA have the sentence written in their check-forms, I must answer with a question; What is "lateral padding"?? This is a term I have never come across before.
It is followed up with "the landing gear functions satisfactorily". I would assume that the function should be: "keeping the helicopter fuselage a foot or 2 safely off the ground". After all this is a small helicopter with skids, not with hyd. operated retractable gear.
I have been asked once by a CAA-representative on an audit, how we would go by to change the tyres of our helicopter (when the gentleman did not see a jack in our hangar) when I replied friendly that I would take the ground-handling wheels to a tyreshop and have it done there, as we were operating 206B's and L's....

So, the note on the checkform, could maybe be along those lines..

I'm not sure if it fits your stamp, but I went back to my old Helicopter-books to confirm that I had forgot my aerodynamic knowledge.

The vibration you get in GR, is when you get an offset center of mass in the main-rotor. This has a few causes, but mainly due to lead-lag dampers in the head being weak in combinations with shocks from the landing gear (skids or wheels). usually due to; main-gear dampers being faulty, incorrect tyrepressure, hard landings, slope-landings (partial landing, loading pax from steep slope etc.)

From "Basic Helicopter Handbook": In general, if groung resonace occurs, it will occur only in helicopters possesing three-bladed, fully articulated rotor systems and landing wheels. (however, the term here should be undercarrige, as it also involves skidded helicopters)

From "Principles of Helicopter flight": Rotors that have substantial in-plane stiffness and that are not fitted with lead-lag (drag) hinges, or their equivalents, are not susceptible to ground resonance and so require less damping in the rotor head or undercarrige"

Have had a few onset encounters over the years in diffrent machines, all being 3 bladed rotorsystems, skidded gear. In which MR or landing-gear dampers have been replaced shortly after.

Nubian,

Lateral padding, as I understand it would be the aircraft rocking lightly from skid to skid. Incipient GR?

Demonstrated classically in a Gazelle with the nose up slope, light on the skids and just about on the stops.

Mmm, I believe the first BO105 was destroyed on the ground due to Ground resonance, mind you it was with a Scout MR head. Last time I was in one they had 4 blades.

Nubian
UK Military Aircraft Losses

Quote:
Let uss know when you manage to get ground-ressonance with a semi-rigid rotorsystem


Although the AS350 is three bladed system and has a little lead and lag, through the elastomeric bearings, ( or as my engineer calls them Lamanated thrust bearings) it is offially classed as a semi-rigid system, and you can definately get ground resonance in it

Suprising what you look up while sitting in an exploration camp waiting for freezing fog to lift, ha ha.:ugh:

http://www.ntsb.gov/ntsb/GenPDF.asp?...06LA057&rpt=fi

Three blades only? No. The number of blades has little to do with it. I know of at least two (four bladed) Wessex that ended up on their sides. The word on the block was two seconds from beginning to helicopter on it's side.

If any rotor system goes out of balance for any reason, and lateral padding begins, the undercarriage, by design, wheels or skids, should damp it out. If it doesn't, and the amplitude increases, it's possible for the aircraft to rock very violently until something major happens.

True ground resonance occurs when the frequency of a vibration within the main rotor system is the same as the resonant frequency of the landing gear. The rotor feeds energy into the resonating system and produces a very large amplitude vibration. It is usually suppressed by dampers within the landing gear which lower the resonant frequency to prevent resonance at frequencies which would be damaging. I cant recall if lead-lag dampers help suppress ground resonance - edit - They do by helping suppress lateral out of balance vibration which could set up resonance if there is a problem with the landing gear damping. 2 bladers are not prone hence no skid dampers.

Lateral padding occurs due to tracking errors in the main rotor system which result in vertical bounce. There is also - usually - a horizontal component to the tracking error which when very light on the skids, or just about hovering, will cause the skids to alternately lift and lower, hammering the ground. It only happens at flying rpm with significant pitch applied. Number of blades irrelevant. Not the same as rocking caused by simple imbalance in the main rotor.

Ground resonance can occur at any RPM with or without pitch applied.

Neither feel nice.

SilsoeSid,

As for my previous post focusing on 3 blades, it should have been multibladed.
Sorry for misleading focus.

No question about you get it in the Gazelle, similar type rotor.

With regards to the Bo-105, with the Scout head, well what can I say other than, similar type rotor. Allthough 4 bladed, it has dampers, which is the clue here. Haven't heard of incidents in the 105 with the current Rigid head.... (no dampers)

With dampers in the head, you will have the posibility for the Center of mass to be displaced and causing the imbalance that will ultimately destroy the helicopter if not corrected for.

Newfiboy,

Yes, the 350 can get it as well, as it has a type of Lead-lag damper. As long as you can get more/less degrees between the diffrent rotorblades than what it should have, you will displace the Center of Mass from what should be centered equally around the mast.
Therefore you'll need more than 2 blades that are not rigidly connected, to do so.

For those who haven't seen it:



...and from the side:

Could this have been saved?
 

Was this operator error,lack of skill or ???

Well the skills of the pilot, don't impress me. It also seems he's setting it down by reducing power and accordingly rotor rpm. Obviously the place he tried to set it down wasn't the right one and there was movement in all directions, what caused the dynamic roll-over was the sideways movement.

Here is another pilot I guess that is showing off.Looks like he even has passengers.I would guess that he bent the skids or did some kind of damage to it.

A rotorway accident not caused by a mechanical defect. Must be a first!

The Rotorway accident was already discussed please refere to: http://www.pprune.org/rotorheads/402...-rotorway.html
And to put it into layman's terms 'yes' all he had to do was drop the collective.

I would expect the fuselage skin to be wrinkled just behind the honeycomb roof panel - if not the tailboom as well.

That pilot should be quietly led away and re-trained as a bulldozer driver.

several hundred thousand euros worth of damage on the 206 in that video. The pilot became known as "touch-and-go-joe" - as far as I know, he is still flying.