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Other › strange cyclic behaviour
10-03-2005 11:13 PM  12 years agoPost 1
ndibiase

rrNovice

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after building my first model helicopter (TREX 450 x V2) i noticed a very strange behaviour:

with cyclic forward the rotor disk (viewing from tail) in inclined forward and left

with cyclic backward the rotor disk (viewing from tail) in inclined backword and right

and so on..... it seems that there are a 45 degree shifing on the correct inclination (pardon me i am an absolute begineer and for me with cyclic foward the rotor must be going straight forward.

i had put maximun attention to construction detail (linkage , flybar , cross check with internet photos etc)


if someone had information on that item i will very appreciate

thanks in advance


nicola di biase

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10-04-2005 12:26 AM  12 years agoPost 2
Gary Hoorn

rrKey Veteran

Annapolis Maryland​USA

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What Tx are you using? Do you have any mixing turned on in the Tx? Correct swashplate method selected on the Tx? This should be easy to figure out on a V2 as each servo has only one job to do. Post your Tx and I am sure one of us can assist.
Gary

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10-04-2005 12:40 AM  12 years agoPost 3
dkshema

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Cedar Rapids, IA

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With a stock V2 when you push the cyclic stick forward, or pull it back towards you, only one servo should move.

When you move the stick side to side, only one servo should move. If two or more move with just pure fore/aft or left/right cyclic, then you have somehow enabled a mix function in your transmitter.

Also make sure you have the three main servos -- elevator, aileron, and pitch plugged into the correct sockets of your receiver.

Per Gary's request -- we need more info as to transmitter type, if you have any swash mixing enabled (for a stock V2, NO swash mix as in CCPM should be selected).

Dave

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10-04-2005 10:15 AM  12 years agoPost 4
ndibiase

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t rex strange cyclic behaviour

thanks for your help

my helicopter,as your replay states, uses no CCPM

my radio is graupner mx-12 - r700 receiver .

there are no mixing funtion enabled and swashplate method is normal - one servo (no CCPM).

when acting on cyclic, per example elevator forward, only one (and the correct servo) acts. The moviment are correct the effect no.

i've also tried to change blades - no difference

even when rotor is rotating (cyclic forward - main rotor disc left 45 degress) the swash plate is tilted only forward. Can be to be something with flybar

there must be somewhat subtle (for a beginner like me) and in my opinion concerning mechanichal assembly/linkage

if you can give me an email i can post you photo of rotor assembly

thanks for helping a beginner

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10-04-2005 12:00 PM  12 years agoPost 5
rotarypower3

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Melbourne, AUSTRALIA

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If the swash plate moves in all the correct directions you should be fine. If you're talking about holding the heli while the blades are spinning, then I think you'll find that this is normal. There's some scientific reason it does this, some rubbish like gyroscopic something...... it's the whole swash moving the flybar paddles before the main rotor thing....

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10-04-2005 01:11 PM  12 years agoPost 6
dkshema

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Cedar Rapids, IA

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Any chance you can post a picture of the rotor head and swashplate, showing the linkages and levers? Maybe your washout base is upside down on the MR shaft.

Dave

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10-04-2005 01:30 PM  12 years agoPost 7
Kaos2800

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Cary, NC

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This is normal. It's called Gyroscopic Precession. Go back and make sure everything is setup correctly to verify you didn't change something you shouldn't have in trying to figure this out. Here's a little info on what you ran into. I hope it helps.

"A very peculiar feature of the cyclic is that the lift is made to occur 90 degrees of rotation before the direction of tilt. This is because when one tries to tilt a spinning object (like a rotor), it moves at right angles to the direction of the force. This is called "gyroscopic precession." So control forces on the rotor are rotated 90 degrees before the desired motion. For example, forward motion requires less lift at the front of the disk and more lift at the rear of the disk, so the pilot pushes the cyclic forward. The helicopter's control linkages rotate the pitching forces 90 degrees backwards against the rotor spin, to push on the sides of the rotor rather than its front and back."

http://www.mywiseowl.com/index.php?...creativecommons

http://www.helicopterflight.net/gyroscopic P.htm

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10-04-2005 01:33 PM  12 years agoPost 8
Pitounet

rrApprentice

France

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The reason is probably when you make your tests the blades aren't running fast enough. You need enough speed to have a good cyclic control. The reason is when you push the cyclic forward, the direct effect is a force that is directed sideways (i don't remember if it's left or right but we don't really care). The rotor moves forward as a result of the gyroscopic effect that makes, the rotor reacts to this force by a greater force due to it's rotation. If it doesn't rotate fast enough, the gyroscopic effect won't be strong enough and the effect of the sideways input will be visible thus, the 45deg inclination that you can see.

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10-05-2005 06:10 PM  12 years agoPost 9
Rickenbacker

rrApprentice

Örebro, Närke -​Sweden

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Has anyone actually looked at their swashplate? It tilts the most intuitive way, i.e. directly forward for forward rotor tilt and so on. The reason it can do this in spite of gyroscopic precession (which does indeed delay all control inputs by 90 degrees) is that the paddles (which change the rotor cyclic pitch) are 90 degrees from the blades. Thus swashplate forward makes the paddles tilt to the side, which makes the rotor tilt forward.

I'd check that mechanical setup and any mixes again.

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10-09-2005 11:02 AM  12 years agoPost 10
ndibiase

rrNovice

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reference found for this

thanks for your answers. i'd like to share with you additional info on that subject i'd found googling around.

ref. http://www.w3mh.co.uk/articles/html/csm9-11.htm

so it seems that rotor head geometry and damper stiffness are involved in this at this point normal behaviour.

even the other "practical teories" articles on that site seem interesting .

Nicola di Biase

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