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HomeAircraftHelicopterHelicopter Main Discussion › Need advice on weird tail behaviour
04-20-2009 10:00 PM  9 years agoPost 1
pvande

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FL - USA

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I run a GY401 on Swift mechs in a FunKey Augusta fuselage and have a tail behaviour that is making me scratch my head.

After I spool up (running at 1700RPM head speed) as soon as my wheels lift off the heli's tail moves to the right about 10-15 degrees. After that my tail is stable. If I land, spool down and spool up again I get the same behaviour.

If I sit down without spooling the main rotor down I still get a tail movement but not nearly as pronounced.

Have double checked to ensure that I initialize the gyro in HH.

Gyro gain is at 80% and at max - if i up it any further I get a nervous tail...

Any suggestions for areas to investigate would be much appreciated.

Paul

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04-20-2009 10:14 PM  9 years agoPost 2
Furious Predator

rrProfessor

Kitchener, Ontario, Canada

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i have a feeling (my theory) the wheels themselves are gripping the ground compensating for the torque on the main rotor. therefore the tail is not working that hard. but once the wheels lift off, that compenstating force is gone and the tail suddenly has to work harder.

are you in heading hold or normal mode?

Shawn
Team Leisure-Tech
Team HelixRC

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04-20-2009 10:20 PM  9 years agoPost 3
VooDooX

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San Francisco Bay Area CA, US (San Mateo)

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this should work no matter what tho since skids do the same thing... and sero for gyro SHOULD be lightning fast what tail servo are you using? if nto it could be a binding issue where it has to push the gyro to a certain limit (10-15 degrees of turn) to overcome the binding i would

1.check for binding and make sure everything in tail is TIGHT and SMOOTH MOVING these are very important

2.Check your endpoints on the gyro maybe it thinks its moving the tail when its actually not

3.Check for slop in the tail linkage system from the servo all the way to the tail

Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001

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04-20-2009 10:27 PM  9 years agoPost 4
Furious Predator

rrProfessor

Kitchener, Ontario, Canada

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yeah, but the wheels on a heavy scale heli get a surprising death grip on the ground. my 30 size bell 222 can be a hand full on grass.

but i agree, the response should be pretty quick, but if your in normal mode, you could expect that type of response. i think a lot of scale heli guys fly normal mode.

Shawn
Team Leisure-Tech
Team HelixRC

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04-20-2009 10:48 PM  9 years agoPost 5
imnxtc

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BC.Canada

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I would bet that the head speed does not come up to the 1700 until you have lifted off, so it is lower (and the tail rotor will have less power) on the ground at the lower RPM.

As electric motors are not like nitro or gas motors, and develop torque instantly, as soon as you up the collective/throttle stick, you get instant power change if your ESC is not set for the same numbers on the ground as in the hover (which will result in the same rotor speeds - main and tail)then it will take a fraction of a second for all to catch up after lift off. That is also why there is not as much difference if you leave it spooled up.

So if you hover at half stick and use a radio with just 5 points andan ESC setting for exampe of 0/55/80/80/80 then you will have a problem as you go from the 55 point to the hover at half stick point of 80.

What I suggest is that if you wabt to hover at half stick, then use an 80/80/80/80/80 across the top in an idle-up and once you get about 3/8 stick then flick into idle-up. You will still not come up into the hover, as you dhould not have adequate collective pitch if your pitch curve is set properly. You will hear the rotor now come up to speed and you then can lift off and find no such change in Yaw.

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04-20-2009 10:56 PM  9 years agoPost 6
rotormonkey

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Ottawa, ON - Canada

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If I'm understanding the question properly, this is normal. Scale or not. My helis do it one way or the other.

As you're taking off your skids/wheels/whatever have a grip on the ground. While you're spooling up the tail rotor doesn't have a lot of authority to keep the heli in one spot. here's what happens:

You initialize the gyro in HH (this will be MORE pronounced with HH gyros). When you initialized it it was with a heading of let's say 250 degrees. Now you bring your heli out to the flight line, and it's pointed at say 270 degrees.

The gyro wants to correct it back to 250, but since the tail isn't spinning it can't. As you spool up it continues to try to correct, but the skids are on the ground, maybe you have a little negative or whatever, but once the tail rotor gains authority from speed and the heli gets lighter, the gyro will want to move the tail to wherever it thinks it should be.

The reason it's less pronounced after you've already landed it once is because the tail is already in the "right" spot. The gyro has the correct heading. But once again as the heli's tail gains authority the gyro is trying to move the tail to wherever it needs to be to keep the heading. That point changes as the tail spins quicker, so you still see a little shake.

Make sense? That's my take on it anyway.

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04-20-2009 10:58 PM  9 years agoPost 7
rotormonkey

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Ottawa, ON - Canada

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Oh.. The point of all that was it's normal. I just live with it, it's not that big a deal. I do however move the rudder so the tail blades have about 8 degrees (just eyeballing it) while on the ground. Seems to mitigate the effect a little.

If you want to test it, move the rudder all the way one direction while you're on the ground, then re-center, and take off. I'll bet it'll swing a bit more when you take off.

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04-20-2009 11:09 PM  9 years agoPost 8
Blade_Master1

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Canada

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OR try moving your rudder back and forth (3 times on a 401) to re-center the gyro just as the blades spool up.

never fails

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04-20-2009 11:09 PM  9 years agoPost 9
VooDooX

rrElite Veteran

San Francisco Bay Area CA, US (San Mateo)

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ok TRY THIS set your throttle curve to like 0-45-50-75-100 in normal and see if its still messed up well not that thats for electric but equivalent like set your second spot about 5% less then ur mid point on throttle and see if it works this way rpm should be nominal at takeoff

Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001

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04-21-2009 01:49 AM  9 years agoPost 10
pvande

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FL - USA

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Wow - lot of responses with many questions - appreciate it... below answer to the questions

Furious Predator - I fly in HH only.

imnxtc - Head speed is at 1700. I fly with my ESC in gov mode - so I spool up at mid stick (zero pitch) and move to hover at 2/3 sticks. Rotor RPM is constant from half stick to 2/3 stick when it lifts off to hover.

rotormonkey - I test fly the heli in my yard - so it doesn't move after I power it up, i.e. the nose remains pointing in the same direction while the gyro initializes until I take off. Also the tail ALWAYS moves to the rigth (so I assume it has to do with the torque from the motor) and always about the same distance (10-15 degress).

blade_master1 - This is what confuses me - I've recentered the gyro using that method when at first I thought I wasn't initializing the gyro correctly - but it made no difference.

VooDooX - I have a JR DS8900G on my tail. As certain (as you can be without doublechecking) that there is not binding or tightness and I have a lot of tail authority in flight - but I will double check.

I tested it again this afternoon and it isn't so pronounced if I hover, land, spool down and then spool up again - but very much in evidence on my first liftoff.

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04-21-2009 02:26 AM  9 years agoPost 11
rotormonkey

rrKey Veteran

Ottawa, ON - Canada

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If you haven't set it up to hover in rate mode, my theory still works. You initialize the gyro, and it "centers" the tail servo. If that center isn't where it needs to be to hover right from the get-go it still has to correct once you're in the air.

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04-22-2009 06:58 PM  9 years agoPost 12
pvande

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FL - USA

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rotormonkey I have to disagree with you. I used to set up my heli's mechanically so that it would hover in normal mode but learned through much reading that it is not required with the 401.

All my other helis's are setup so that the tail servo is centered at neutral stick and the heading hold takes care of the rest.

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04-22-2009 07:03 PM  9 years agoPost 13
VooDooX

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San Francisco Bay Area CA, US (San Mateo)

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rotormonkey I have to disagree with you. I used to set up my heli's mechanically so that it would hover in normal mode but learned through much reading that it is not required with the 401.

All my other helis's are setup so that the tail servo is centered at neutral stick and the heading hold takes care of the rest.
+1

i have had a 401 and i never set it up in rate mode and it held like a champ even at liftoff

Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001

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04-22-2009 07:17 PM  9 years agoPost 14
rotormonkey

rrKey Veteran

Ottawa, ON - Canada

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Maybe we aren't talking about the same thing. I understand the heli will still hold fine if you haven't set up for rate mode. Just saying it could be a contributing factor to the kick on takeoff.

Remember his headspeed is quite low at 1700 rpms, so his tail probably doesn't have as much authority as yours when he starts to lift off.

Mind you these are just theories as to why it happens. The disclaimer: I don't really know what I'm talking about - so don't take my word for it. These things just make sense to me.

Regardless of the cause, my helis have always kicked around a little bit before takeoff. I say it's normal.

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