Resonance in the Cabri happens when the engine is at 2000 RPM, which is unfortunately where the ignition and carb heat checks are done. The usual issue is because the landing gear foam pads are either worn/loose or there isn't enough clearance between the fuselage and the landing gear bows. A good way to check for proper clearance of the bows is to rock the fuselage laterally and listen/feel for it impacting the bows. A light touch is okay, but if it's clearly making hard contact, the position of the gear bows needs to be adjusted. The clearance of the fuselage to the gear bows is more important than the gear being centered. It's okay if the fuselage is lightly resting on the left rear gear bow when the aircraft is mostly/fully fueled and unoccupied, but rocking the aircraft should still give good clearance with minimal impact. The second, rarer cause of resonance is a bad lead/lag damper. If the aircraft is smooth in hover and steady flight but develops a vibration in autorotation, that's a good indication that one of the lead/lag dampers is bad.
I thought i had ground resonance in a cabri once before but i realized the cyclic was slightly to far back and the aircraft started to rock as in your video but a slight adjustment of cyclic forward and it completely disappeared. The rocking is worst around 2000rpm as that's were it was in your video. Good call to lower rpm.
Good information for future flights. The G2 is a lot of fun to fly. In this particular case the rotor head was inspected by engineers and a track and balance was done. I flew this aircraft a couple of weeks later with no issues.
I had an rc heli and i can tell you if you have the slightest bend in any shaft youll get that very vibration and if your rotors are not weighted and balanced correctly same deal and i used to make sure they weighed to the 100th of a gram apart at most. And if everything was right it was as smooth as glass
I notice there seems to be a strong cross wind.. would that contribute ? Also could you have moved the cyclic around to maybe find a more neutral spot perhaps?
Was anything significant found in the track and balance check? Because if not, I think you inadvertently connected and induced an oscillation through your input. And once you were getting jiggled side-to-side, all you could do is reinforce it. I am NOT an expert, but other than shutting down at that point, perhaps loosening your grip on the cyclic or grabbing lower on the shaft and bracing against your thigh might've gotten you out of that, or might prevent it in the future? Because you have to do *something* to change the natural frequency of that system. Part of what makes me think along this line is that your habit is to not guard the collective and are using your left hand to operate switches. There's really nothing you need to do with the cyclic while full down, so why palm it?
Hi Ben, all I know is the engineer’s did. Track and balance and no other issues were found. I did later find out later that the previous pilot left the cycle trim all the way back which may of contributed to it. Also if the helicopter is on u even ground can also contribute to ground resonance.The collective friction is left on during run up checks. The best way to stop the resonance while on the ground with less than full power is to shut down and apply the rotor break to slow the rotor down. If you have full power when ground resonance occurs then you quickly get the helicopter into the air to stop the interaction with the ground that induces the resonance.
What you suggest is the correct recovery technique when the rotor is at flight rpm. But I was below flight rpm as I was still doing the run up checks. In that case the recovery technique is to roll the throttle off and shut the engine down followed by applying the rotor break to slow and stop the rotors as quickly as possible, which is what I did. You notice that when I rolled the throttle off the resonance slowed down very quickly.
@@Tom-zs6bb Don't believe in every internet expert's comment on CZcams! It's a good advice, trust me! This was the last thing Abe Lincoln told me before his assassination.
@@Tom-zs6bb If you detect ground resonance, you don't power down, you take off ASAP. Powering down doesn't stop the oscillation and in fact can increase its amplitude. You learn it in basic flight training.
@@oliverreno4734 Son, I'm a CFI in airplanes and helicopters and in fact, in 2001, experienced ground resonance in a S300CB at Spacecoast Regional Airport so your preaching to the choir. My question was directed at someone who made an unfair comment about the pilot in question.
Resonance in the Cabri happens when the engine is at 2000 RPM, which is unfortunately where the ignition and carb heat checks are done. The usual issue is because the landing gear foam pads are either worn/loose or there isn't enough clearance between the fuselage and the landing gear bows. A good way to check for proper clearance of the bows is to rock the fuselage laterally and listen/feel for it impacting the bows. A light touch is okay, but if it's clearly making hard contact, the position of the gear bows needs to be adjusted. The clearance of the fuselage to the gear bows is more important than the gear being centered. It's okay if the fuselage is lightly resting on the left rear gear bow when the aircraft is mostly/fully fueled and unoccupied, but rocking the aircraft should still give good clearance with minimal impact.
The second, rarer cause of resonance is a bad lead/lag damper. If the aircraft is smooth in hover and steady flight but develops a vibration in autorotation, that's a good indication that one of the lead/lag dampers is bad.
Good call mate, shut it down as soon as you recognise it. nicely done!
I thought i had ground resonance in a cabri once before but i realized the cyclic was slightly to far back and the aircraft started to rock as in your video but a slight adjustment of cyclic forward and it completely disappeared. The rocking is worst around 2000rpm as that's were it was in your video. Good call to lower rpm.
Good information for future flights. The G2 is a lot of fun to fly. In this particular case the rotor head was inspected by engineers and a track and balance was done. I flew this aircraft a couple of weeks later with no issues.
I had exactly the same issue, 2000 rpm, right where you do your mag checks!
I had an rc heli and i can tell you if you have the slightest bend in any shaft youll get that very vibration and if your rotors are not weighted and balanced correctly same deal and i used to make sure they weighed to the 100th of a gram apart at most. And if everything was right it was as smooth as glass
I notice there seems to be a strong cross wind.. would that contribute ? Also could you have moved the cyclic around to maybe find a more neutral spot perhaps?
Was anything significant found in the track and balance check?
Because if not, I think you inadvertently connected and induced an oscillation through your input. And once you were getting jiggled side-to-side, all you could do is reinforce it.
I am NOT an expert, but other than shutting down at that point, perhaps loosening your grip on the cyclic or grabbing lower on the shaft and bracing against your thigh might've gotten you out of that, or might prevent it in the future? Because you have to do *something* to change the natural frequency of that system.
Part of what makes me think along this line is that your habit is to not guard the collective and are using your left hand to operate switches. There's really nothing you need to do with the cyclic while full down, so why palm it?
Hi Ben, all I know is the engineer’s did. Track and balance and no other issues were found. I did later find out later that the previous pilot left the cycle trim all the way back which may of contributed to it. Also if the helicopter is on u even ground can also contribute to ground resonance.The collective friction is left on during run up checks. The best way to stop the resonance while on the ground with less than full power is to shut down and apply the rotor break to slow the rotor down. If you have full power when ground resonance occurs then you quickly get the helicopter into the air to stop the interaction with the ground that induces the resonance.
1:43 Both ball earthers and flat earthers are wrong. Earth is not ball or flat, it is wobbly.
😂😂😂
You also can opt to go directly to hover, no ? this will fix the feedback loop too
What you suggest is the correct recovery technique when the rotor is at flight rpm. But I was below flight rpm as I was still doing the run up checks. In that case the recovery technique is to roll the throttle off and shut the engine down followed by applying the rotor break to slow and stop the rotors as quickly as possible, which is what I did. You notice that when I rolled the throttle off the resonance slowed down very quickly.
This guy is SUPER lucky. By all rights, he did 100% the wrong things and by some miracle, the helo didn't self-destruct. Horrible pilot.
What should the pilot have done?
@@Tom-zs6bb Don't believe in every internet expert's comment on CZcams! It's a good advice, trust me! This was the last thing Abe Lincoln told me before his assassination.
@@Tom-zs6bb If you detect ground resonance, you don't power down, you take off ASAP. Powering down doesn't stop the oscillation and in fact can increase its amplitude. You learn it in basic flight training.
@@oliverreno4734 Son, I'm a CFI in airplanes and helicopters and in fact, in 2001, experienced ground resonance in a S300CB at Spacecoast Regional Airport so your preaching to the choir. My question was directed at someone who made an unfair comment about the pilot in question.
@@oliverreno4734 Why do you insist on arguing with a course of action that resulted in a positive outcome?