Tip over on spool down

Posting on behalf of a friend, Banshee, 1960rpm HS, Radix 710 FBL main blades and Radix 105mm tail. The heli has now tipped over twice in four landings without any warning, it happens on spool down after landing. Blades are tightened according to specifications (really tight) and spooldown is done with zero collective pitch as per instructions.

We were told that the VBar might be the culprit by the manufacturer, so it would be appreciated if you look for anything wrong with the setup. Ignore the last part of the log, the tipovers happened where the ELEV and AIL sensor out of range is logged.

Thanks

VControl, VBar on all.
TDR, TDR2, TDF, TDS and TDSF
Peter

Hi.

The issue is usually caused by vibration rising over a certain level, the sensors going blind in the 'noise' for a short time.
The 'sensor out of range' values happen when the sensor gets a hard hit, aka in a crash or the tip over.

It's been reported that this can happen (on different helis) while spooling up, but afaik it's not been reported to happen on spooling down, yet.

Where and how's the Mini V mounted (please provide pics)?

Did you do vibration analysis (without blades)?

Kind regards

Eddi

Born to fly ...
forced to work.

Mounted in stock position on Banshee with a single layer of Mikado foam. Vibration analysis shows overall vibration to be less than 300, but this is under power.

The log shows the vibration from landing, then throttle was cut and on spool down the heli violently tips over and self destructs. I know that sensor out of range is the resulting crash indication, so you will see two of the innstances in the log, both similar. The first tip over was landing with a headspeed of 1600, throttle cut and spool down resulting in the mangled mess!!

The other vibrations in flight is normal for 3D flying.

Hi.

The overall vibration gauge does only give a ballpark figure on what really happened. The spektrum analyzer would be the way to check it.

On what surface were you landing when this happened? With it's rigid carbon/alum frame and head, and the carbon skids there's hardly any part that can absorb vibration or so it seems.

Did it start spooling down, did you see something like a ground resonance in this situation, or did it just yank over like you hit full aileron when you flipped the switch?

What type of radio are you using? Can you check by the servo monitor or the transmitter analyzer tool (see here) if there's an erratic output from time to time, especially if you hit the throttle cut?

Anyway, if it really was a sensor problem, we can only check for this at the service shop.
But even then, it could be coincidence and a replacement could show the same effect.
Since the sensor doesn't show erratic behavior in flight and no particular warnings either, I'm not yet convinced

Therefore, it's important to us to get the picture, since every try eventually costs you money.

Kind regards

Eddi

Born to fly ...
forced to work.

Hi Eddie

Using a Futaba 10 radio with a normal RX. The same radio is used for other helicopters including a TDR, all fitted with VBar minis. The tip over starts with a wobble and then suddenly it violently rols over as if one has given full aileron input. The second tip over was violent enough to break the carbon tail boom in pieces and lift the heli off the ground with it landing on ot's nose and right hand side.

He did a vibration analyzing with the blades off and this showed no significant peaks at all. The tip over starts after throttle cut and after the head has spooled down a significant amount, we estimate it to below 1000 rpm.

We both only use the VBar and are OK with the installation and setup of it, so I think we rule out user error in setup or installation. The Banshee team wants him to fit another make of FBL unit to eliminate the VBar as a source for the trouble, but as you have said we are not convinced as the two proper flights he had out of four, showed NO problem in flight, both 3D and high speed flight. Not a murmur from the head to show that gain was to high as well.

Stumped on this one, maybe he can try another mini VBar, as all our others are the older sensor ones, where this is one of the new ones with the newer sensors.

Regards

TX analysis

Ail - 1610 and 1601 en -6
Elev - 1597 and 1599 en -6
Rud - 1603 and 1594 en -6
Col - 1603 and 1607 en -6

Vib analysis

284 Hz - 243
280 Hz - 308
351 Hz - 309

Total vibe 177

Hi.

I would always go for the standard VBar on any bird bigger than a 450, but that's my personal opinion.
The Mini is nice and tiny, but with all the wires going into the box it's not the optimum under all circumstances ... the separate sensor imo is the better and more versatile design.

Imo you're having a ground resonance issue here, the heli starting to shake, then VBar loses it for a short time, in the shake/vibration.
I had that once with a semi scale Hughes 500 D ... when she started to shake while spooling down (usually on concrete, not on grass) I had to lift her slightly to get through the resonance faster. Pushing her down only made it worse.

Do you see that wobble too when spooling up?

To remedy the symptoms, you could weigh the VBar with a metal plate like people do on nitros, test other pads, only land on soft surfaces or cut throttle while still in the air and let the headspeed bleed until you touch down.
Since you have other Mini VBars at hand, you could try an other device to rule the one in question out or not.
But all that bears the risk of another disaster ...

Kind regards

Eddi

Born to fly ...
forced to work.

Another hint: A bend spindle shaft can cause such things too - i had this on my BO 105 scale ship ...

regards (EN) / Gruss (DE)

Rainer Vetter

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Thanks guys, we are using the mini VBar on all our heli, from 500 upwards, both the TDR and Banshee has VERY limited space and they just work, only this one that has us stumped. Jan Henseleit even recommends the mini for the TDR and it works perfectly.

We have dismantled the Banshee, very unique style of head construction, has no spindle shaft, but we have DOUBLE checked everything on the helicopter, alll is straight and true, running with very little vibration. It is completely belt driven and all the componenets are earthed properly.

Will do further investigation and see what we can come up with as the Banshee flies in other parts of the world perfectly with the same setup as what he has.

If you have a setup file for a test ... i can modify ist (disabling the swash control loop) and it is " flybarless by hand".

So .. you can possibly use this file for a spoolup/Spooldown test (don'tfly if you are not used to fly w/o a system) just to figure out it is something with the Vbar or not ;-)

regards (EN) / Gruss (DE)

Rainer Vetter

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Posting and answering - please use a PC and a standard keyboard. Answer all questions fully, take the needed time, don't forget probably requested attachments.

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The .vbr file is in the first post, thanks we might just try that.

Please double check stick moves - and don't do a bank switch to another setup during test

regards (EN) / Gruss (DE)

Rainer Vetter

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Posting and answering - please use a PC and a standard keyboard. Answer all questions fully, take the needed time, don't forget probably requested attachments.

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Thanks Rainer will try.