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HelicopterRadio - Servo - Gyro - Gov - Batt › Very violent tail wag - GY401/S9254 fitted - Any ideas?
11-08-2005 02:38 AM  12 years agoPost 1
Skeeter Pilot

rrApprentice

England

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I am running a Futaba GY401giro with an S9254 digital servo on the tail of my Century Hawk Pro (Electric Conversion). Everything is New and five 20min hovering sessions have been completed without a problem. Today on the sixth hovering session just before lift the tail started to oscillate (wag) very violently, the wag was so violent that had it happened in flight I think something critical would have failed.

It did not wag every time and I could induce it by a small sharp tail input. I initialised with Heading Hold on but the wag was still there even with H/Hold switch off.

The 401 'delay' is set to 'Zero' and the 'Limit' set to prevent any binding. The 'rudder' endpoints are set to 100% and the switch on the 401 is set to 'digital servo'.

Has anyone got any ideas what the cause of this might be?

Many thanks,

SP
---------------------------------------------------

If there is soil going over the canopy, you're too low!

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11-08-2005 03:47 AM  12 years agoPost 2
mbkite

rrVeteran

usa

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One thing haptened to me its a long shot thoue
Check the tail pitch slider mine cracked and i had a lot of play and the tail shook back n fourth . this small plastic part dose come in a crash kit . Now i know why it dose.

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11-08-2005 04:49 AM  12 years agoPost 3
JKos

rrProfessor

Redondo Beach, CA

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Check the gyro mounting tape. When (not if, but when) it starts to separate, the gyro will start acting funny. That's your first sign. If you ignore it, it gets much worse when the gyro comes all the way loose. Not saying this is definitely the problem, just an idea.

- John

RR rules!

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11-09-2005 11:38 PM  12 years agoPost 4
Skeeter Pilot

rrApprentice

England

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Thanks everybody for your replies to my post, sorry I have not got back sooner.

pth3k you were absolutely right. I have a new radio and do not know my way around it. It did not occur to me that it was giro as I had flow it previously with exactly the same settings with not a sign of wag. Now I understand the radio a little better, I left my ch5 end points at 100% but have now activated the 'Giro Sens' function in the advanced menu at 80% and then increased my rudder end points to 110% to make the tail a little more responsive. Now the tail is gorgeous but I notice, when on the ground if I spool up quickly the tail does do a little shimmy but this is gentle and short lived and as soon as the revs. get to flight rpm the tail shimmy stops.
I am on 80% at the moment but have tried setting giro down to 50% but still get the small shimmy......... is this expected?
SP
.......................................................

If there is soil going over the canopy, you're too low!

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11-10-2005 12:23 AM  12 years agoPost 5
PaulJC

rrElite Veteran

Hertfordshire UK

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is this expected?
Yes the gyro is trying to counteract the torque of the main rotor but cant move the heli because its still on the ground.

A few people i know turn on in HH, switch to rate mode, spool up and then just before take off turn back into HH, it stops the shimmy or any rotation on take off

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11-10-2005 12:29 AM  12 years agoPost 6
Skeeter Pilot

rrApprentice

England

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Thanks for that PaulJC,

When you say 'rate mode', I take it you mean 'normal' as in non-heading hold.

Mine still shimmy's on the ground as described when in non-heading hold.
SP
----------------

If there is soil going over the canopy, you're too low!

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11-16-2005 12:23 AM  12 years agoPost 7
Skeeter Pilot

rrApprentice

England

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Thought I'd let you know that I have sorted the problem.

Reducing my giro gain did help a little but it was still there at 30% gain which is ridiculously low, plus it wasn't there on previous flights with my old giro settings. As soon as the heli left the ground everything was ok so there was obviously a resonance there when the skids were in contact with the ground. It was incredible, apart from the tail wag, the whole frame oscillated side-to-side. This resembled the 'full size' phenomenon called 'ground resonance' which only happens when the main rotor is being driven by the engine (not at the end of an auto) and the main gear is lightly in contact with the ground. A lateral pad will commence and if not checked by either lifting clear of the ground of landing and applying the rotor brake, the helicopter will disintegrate into its component parts within seconds ........... two Skeeter Test Pilots were killed due to this in the 60's. I would imagine the model may never suffer as dramatically from 'ground resonance' as the full size due to its relative strength and low inertia.

Anyway, the problem was, one main blade at slightly lesser tension than the other.
SP
.........................

If there is soil going over the canopy, you're too low!

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HelicopterRadio - Servo - Gyro - Gov - Batt › Very violent tail wag - GY401/S9254 fitted - Any ideas?
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