r22butters Posted November 15, 2017 Report Share Posted November 15, 2017 Seems the first argument I hear when it comes to training in a Cabri (Schweizer in the old days) vs. a Robby, is the teetering rotor system. So which situation are students more likely to get into? Quote Link to comment Share on other sites More sharing options...
takefootoff Posted November 15, 2017 Report Share Posted November 15, 2017 in my limited experience with the 300s, I only got into ground resonance like 4 times over the course of approx 700hrs. and it was always in one particular ship out of three available Quote Link to comment Share on other sites More sharing options...
r22butters Posted November 15, 2017 Author Report Share Posted November 15, 2017 in my limited experience with the 300s, I only got into ground resonance like 4 times over the course of approx 700hrs. and it was always in one particular ship out of three availableAround 700 hours between 35 different R22's,...zero low-G and/or mast bumping! Looks like you got me beat! Quote Link to comment Share on other sites More sharing options...
DizzyD Posted November 15, 2017 Report Share Posted November 15, 2017 (edited) Only one of these threats was deemed hazardous enough to require its own Special FAR. Also, one of the local G2 operators has experienced no issues with ground resonance and I hear that having the skids connected to the fuselage by elastomeric mounts instead of being bolted directly on has reduced ground resonance occurrence. The 300 has some form of skid damping as well correct? Edited November 15, 2017 by DizzyD Quote Link to comment Share on other sites More sharing options...
Eric Hunt Posted November 15, 2017 Report Share Posted November 15, 2017 Ground resonance will only come if something is wrong with the aircraft - drag damper, oleo, tire pressure. Zero G will only come if something is wrong with the pilot - didn't listen to thousands of people telling him DO NOT PUSH OVER! 1 Quote Link to comment Share on other sites More sharing options...
Hand_Grenade_Pilot Posted November 16, 2017 Report Share Posted November 16, 2017 Seems the first argument I hear when it comes to training in a Cabri (Schweizer in the old days) vs. a Robby, is the teetering rotor system. So which situation are students more likely to get into? Its's pretty easy to get ground resonance in the S300. Experienced it dozens of times over the course of two years and about 1100 hours while instructing. Usually from a sloppy setdown on rough/uneven pavement and on a few occasions while doing run-on landings to a runway. Definetly a topic I stressed w/ my students (recognition and recovery). No expereince w/ the Cabri so can't comment on that. Experienced it only once in an MD500. Never in the AS350 or 407, although it is possible. Only encountered low-g roll once, while flying an R44 in Hawaii. A massive updraft caused the rotor to become unloaded resulting in a rapid, uncommanded right bank. Instinctively moved the cyclic back which immediately leveled the helicopter. Was a fascinating expereince to say the least; until that point I had thought it could only occur as a result of doing a hard pushover with the cyclic. So I'd say ground resonance is a much more common experience. Also worth noting that any helicopter can experience a low-g induced roll (but only teetering rotor systems are subject to mast bumping). Quote Link to comment Share on other sites More sharing options...
Wally Posted November 17, 2017 Report Share Posted November 17, 2017 Ground resonance will only come if something is wrong with the aircraft - drag damper, oleo, tire pressure. Zero G will only come if something is wrong with the pilot - didn't listen to thousands of people telling him DO NOT PUSH OVER!I can't argue with your theory on ground resonance, except that it can be induced in an aicraft that has no apparent mechanical issue, and I think- in a sound aircraft if you work really hard at it. Seems to me that I encountered ground resonance on run-ups and then it doesn't just happen, it sort of indicates that something is wrong, rocking and rolling unusally before the full ground resonance thing starts happening.Or it can happen as you land in an otherwise serviceable aircraft if you isolate part of the damping mechanism, the running landing with one skid down first and a jar to the system to upset the rotor. Soft/hard oleos on the 300 skids, hanging an Astar skid heel off the deck or the skid tub on a rock- and a jar to the airframe can set it off. Again, you just stop what you're doing and change things when you land again. None of this is uncommon in the real world, but it probably won't kill you. Aerospatiale says 'dynamic divergent excitation' (ground resonance) can happen in flight... Teetering rotors and low G can be over much quicker- unloading the main rotor and not controlling the aircraft appropriately ended some Huey pilot's Vietnam tour early. Didn't this very problem underly the Robinson's SFAR? Don't be stupid with either rotor and you'll be fine. Quote Link to comment Share on other sites More sharing options...
RockinRob Posted November 17, 2017 Report Share Posted November 17, 2017 I flew the 300 for about 100 hours of my initial training. Experienced ground resonance once on a running landing, recovered to a hover and set back down. Had one stick a valve in a hover and settle, ground contact lead to gr, recovered to a hover and set back down. (this one happened after a fuel stop on solo x/c) I have 2k or so hours in 22s, 44s, and 66s at this point; including some more "aggressive" turning maneuvers in aerial application environments, and a fair amount of mountain flying. Never experience low g in years in Robbies. I think proper pilot education and training on avoidance, recognition, and recovery of these dangerous scenarios does wonders to aid in the overall safety and longevity of our rotorcraft brethren. Quote Link to comment Share on other sites More sharing options...
Boatpix Posted December 13, 2017 Report Share Posted December 13, 2017 The R22 is simpler and cheaper to fly. Quote Link to comment Share on other sites More sharing options...
johnnyb Posted January 7, 2018 Report Share Posted January 7, 2018 Ground resonance will only come if something is wrong with the aircraft - drag damper, oleo, tire pressure. Nope. I've experienced GR multiple times in different aircraft including the 300 and the Astar, instances where there was nothing wrong with the aircraft.Direct results of the surface of a specific uneven helipad, or a skid touching down just a little too hard. 1 Quote Link to comment Share on other sites More sharing options...
helicodger pilot Posted January 29, 2018 Report Share Posted January 29, 2018 Yes, but...Ground resonance is seldom fatal but mast bumping usually is. True or not? Quote Link to comment Share on other sites More sharing options...
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