Ground Resonance

[Vinger]

Still waiting to get my kit, but I see a lot more owners getting ground resonance on spool down. Is this common, what do you guys think is the cause and how to prevent it?

Don't want to spoil mine when I eventually get it!!

[Mercuriell]

Not sure of the exact physics but it seems to be a phenomenon of the combination of rigid head, high angle of attack and low HS on hard ground. Avoided by landing under power keeping HS up and pitch down, so best to avoid hot arrivals or autos, I think my Youtube vid from yesterday illustrates this nicely.

[helicraze]

And windy days dont help, only when it was windy did i feel uncomfortable

[Stolla]

Normally auto from meter high the best solution never a problem so far, however today unseen hole in long grass, tailfin bent break both tailblades against fin, luckily almost no headspeed left, just hope tail shaft still good, it certainly seems once something goes wrong it doesnt like the disturbance but its no worse than my tdr with carbon aftermarket skids, just be aware you need good grass surface and although i did spool downs under power think its better to ar, but really no problem. I think the main problem is you may have the shakes from the speed then screw up! This thing still scares me blikseeem!

[Vinger]

So the skids is then the problem, as Stolla and others have had the same on aftermarket TDR skids of similar design? Maybe fit original TDR type skids? We fly off rough grass and never had any problem with any of my helis, but HeliG had two violent tipovers with his Banshee! Scared to fly mine, if or when it shows up this week!!!

[Stolla]

No i dont think its a problem vinger, at least not on on grass, my heli fell in a 8 inch grass covered crevass, no skid would have helped, the rear fin actually prevented it from tipping over, in the process it bent in the way of the tailblades which cut them in half, strangely from what looked like a non violent impact, the fin is still in one piece it looks like tshaft is bent as rotating it quickly seems its not running in track, also seems bearings took a knock now crunchy. This was at almost no headspeed. But ive landed it many times no problems, this would have happened to any other machine, first dont let this get to your head, then set up a normal or hold curve with only about 6 degrees negative and land gently in that mode, ive never seen any spontaneous oscillation once its on terra firma, must have been something with heli g machine or fless unit, keep in mind its different to land a 3 kg machine with 710 blades and 14.5degree pitch, espescially in wind so dont be scared to set up a landing bank in normal, low agility, no paddle sim etc, this will make it easier for you.

[marcosp]

I agree, it is not a problem on grass and careful landing.

[Vinger]

Why do we have to land carefully? Plus the tipovers happens AFTER landing on spooldown!! ALL other helis go through their resonance rpm on spool up/down with no problem, why would the Banshee have to be different?

[Dr. M]

I don't have a Banshee (I wish), but my P6 also has a nasty resonance range at pretty high RPM during spool-up/down, which can literally shake the canopy off the frame. It only happens on hard surfaces (black top) and not on grass or bare earth. I've had limited success with adjusting blade tightness (i.e. tighter) and stiffening the frame.

The only thing that actually helps is to keep a good amount of negative pitch on the blades during spool-up/down. I usually set my collective stick to around inverted-hover pitch (5-6°) and click off TH to spool up. I have the ESC soft start set up for the fastest spool-up possible before blades start folding. For stopping, I either auto and bleed off as much HS as possible before touch-down, or click on TH after landing and immediately, but smoothly start applying negative pitch, going all the way down on the collective stick as the rotor slows down.

Hope this helps.

[Mercuriell]

Its not just associated with the Banshee, my Compass Odin was terrible on concrete and my MA Stratus had a few wobblies too. Problem seems to occur at the moment of touchdown when the HS is low and the disc is loaded. We had a play the other day and powered up landings on the Banshee, in level flight, with the collective around zero had no probs at all.

It is one of the prices paid for having a rigid rotor head that wont flutter in FFFF, which is after all is what the Banshee is designed for

[Vinger]

Sure, other helis have it, but they are a third of the price to buy and fix, never expected this from a limited edition, well designed and extensively test flown heli.

Other 700's have just as rigid heads, Compass Warp has zero damping, they don't do the chicken dance even on concrete. Well enough of comparing, WHAT can we do to stop the tipovers?

BTW Banshee team recommends zero pitch on spool down. I'll just have to wait until mine has arrived, but don't want $300-$400 tipovers!!

[CACN]

Originally Posted by Mercuriell

Its not just associated with the Banshee, my Compass Odin was terrible on concrete and my MA Stratus had a few wobblies too. Problem seems to occur at the moment of touchdown when the HS is low and the disc is loaded. We had a play the other day and powered up landings on the Banshee, in level flight, with the collective around zero had no probs at all.

It is one of the prices paid for having a rigid rotor head that wont flutter in FFFF, which is after all is what the Banshee is designed for

Since you are using HC-3SX on the Banshee, have you tried 40% SL during landing? I use it to assist me to land during windy condition and it works great.

[Stolla]

Vinger i wasnt present with HG 's tipovers so cant comment on that, but on grass there is no difference between the bshee and my other machines, as with any other machine with flexible skids you have to be careful in that any forwards sideways or backwards movement on landing can get you into trouble as the skids will flex and react accordingly. I will take video as soon i have my tailbearings replaced to show you there is no resonance issues, maybe because i have a blade tightness setup procedure described by Curtiss Y, you tighten blades so when you hold heli horizontal the blades dont fall under their own weight but the slightest shake will make them drop SLOWLY, when you get your machine spool it up to midstick but before you take off spool down to zero again, you should have no issues whatsoever. I wont spool down zero pitch as in wind a sudden gust can lift the heli, as its very light for the size blades. Just below midstick will suffice. You really should get this out of your head or what you fear shall come over you!

[Vinger]

Thanks Stolla, in HeliG's case both tip overs happened after landing, heli completely stationary, on grass and just suddenly it started to wobble and tipped over. My estimate of the HS is about 1000rpm and spooling down. The second tip over was violent enough to crack to canopy and break the boom in three pieces!!

OK will just fly mine as soon as it gets here, just need DHL warehouse in JHB to release the parcel to local SAPO........ it has been stuck there for a week!

[Stolla]

Just saw your post on vstabi, the mention of oscillation then sudden like full aileron tipover points a direct finger to the fless unit, whether it gets upset by oscillation or something else like loose board cant say but i would have changed that unit immediately if it responded with uncommanded input like that, even with very bad vibrations like mid flight bent spindle in tdr it would become very difficult to fly as the swash jitters all over the place but never uncommanded to the extent itvwill flip, i didnt read thoroughly, is it blue or black mini?

[Vinger]

Blue mini, the log indicates nothing, no vibrations, only the aileron out of range, but that is the physical crash!!!

[Stolla]

Ok blue is good but i wont trust the log too much sometimes what we see as the crash may have been the reason for the crash, tbh in 4 years of lfying many dfferent units and dealing with many a different vibration issue i have not yet seen a full uncommanded input, yes i have read about it but will only believe it when i see it. Did you guys pull apart to see if board loose inside?

[Vinger]

Yes, did all those, the mini is one of the new ones with the new sensors fitted as per the original units as the single chip sensors are no longer made. Even the vibration log shows it to be lower than any helicopter we have seen. VStabi has sent us a firmware that removes the control loop so that it will not correct any disturbance, but the heli is a bit to exclusive to experiment with!!

Really stump on this, but my personal opinion is that the skids are to flexible, especially towards the front and when you land on uneven grass with more weight supported by front part of skids it just wobbles and dies???? Those aftermarket TDR skids with a similar design, does exactly that. Maybe change the skid design to a carbon piece with pipes as per TDR design will eliminate this.

[Mixmaster Pilot]

This ground resonance issue has reminded me of something Sebastian Zajonz cemmented on about why the 7HV was not designed like the 6HV.

Originally Posted by Sebastian Zajonz

Risk for ground resonance is far higher with a lower frame.

Perhaps this is the key, I'm not sure, but I think he means a lower frame creates a lower CofG. Looking at (and not owning ) a Banshee, the packs and motor are low set, maybe this is the issue

[Stolla]

Originally Posted by Vinger

Yes, did all those, the mini is one of the new ones with the new sensors fitted as per the original units as the single chip sensors are no longer made. Even the vibration log shows it to be lower than any helicopter we have seen. VStabi has sent us a firmware that removes the control loop so that it will not correct any disturbance, but the heli is a bit to exclusive to experiment with!!

Really stump on this, but my personal opinion is that the skids are to flexible, especially towards the front and when you land on uneven grass with more weight supported by front part of skids it just wobbles and dies???? Those aftermarket TDR skids with a similar design, does exactly that. Maybe change the skid design to a carbon piece with pipes as per TDR design will eliminate this.

I use the same aftermarket on my tdr no problem on grass either but on concrete had spoolup issue once due to loose blades,