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Other › My T-rex some times makes a 180 degree turn while on fast descend....
03-12-2006 05:22 PM  11 years agoPost 1
lele

rrVeteran

italy

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did any of you experience a similar behave?
Any idea what this could cause this?
The 180 turn is in clockwise direction...could it be something related to the oneway bearing?
Thanks for any suggestions.
Lele

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03-12-2006 05:26 PM  11 years agoPost 2
ShellDude

rrElite Veteran

East Coventry, PA

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One possible reason would be that your tail rotor rpm is changing. Check to make sure your belt and/or rotor shaft isn't slipping.

This happened to me yesterday and I almost lost my heli because of it.

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03-12-2006 05:30 PM  11 years agoPost 3
Pistol Pete

rrProfessor

Seffner, FL

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concur with above specially if you have upgraded to a cnc tail where a new shaft was used and had no ridges for gear to grip.
OR
stop applying rigth rudder

Was gyro HH on/enabled/engaged?

~~Enjoying the hobby one flight at a time~~

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03-12-2006 05:56 PM  11 years agoPost 4
lele

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italy

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Pete & Shell

thanks for advice, but the tail gear is not loose. If I hold main rotor and try tu turn by hand the tail rotor I can't turn it more than what the flexibility of the belt could permit, not more than that even if I apply a good force. The gear is firmly connected to the shaft.
But any way I think that if this was due to a loose tail pulley it would have caused a left rudder turn and not right as it is...
The gyro is a 401 in HH. And in each flight, when I come down in fast descend it could happen once or twice that the heli make the 180 piro.
???could that be a glitch caused by carbon boom?? but I have the R149Dp on it....
I can't find explanations to that..

Lele

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03-12-2006 07:38 PM  11 years agoPost 5
Hellijunky

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Chicago

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are you running in non gov. mode ?

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03-12-2006 08:03 PM  11 years agoPost 6
lele

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italy

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hi Helli

yes I run no gov. moreover I fly in normal (no idle up), could this be the cause?

thanks
lele

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03-12-2006 08:16 PM  11 years agoPost 7
zrdcorp

rrApprentice

Caguas, PR

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The rotation is probaly the tail rotor pitch not being enough to counteract the torque from the main rotor.

Check that you get full travel of the bell crank on the tail shaft.

Roger's Law: If it is worth doing it, it is worth exceeding it.

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03-12-2006 09:24 PM  11 years agoPost 8
TRex888

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Monmouth, UK

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Hmmm... I'm not an expert but here are my thoughts.

Normally the tail wants to turn anti-clockwise due to clockwise rotation of main rotor. When you make a fast descent the rpm and pitch of the main rotor is reduced therefore less tail force is required to hold the tail still. If the tail/gyro did not change accordingly then the tail force would be excessive and pushes the tail clockwise.

If your HH is working correctly then maybe you have some bind in the tail control rod or a sticking servo that is slow to react to the sudden reductin in torque from the main rotor.

My thoughts only :0)

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03-12-2006 09:25 PM  11 years agoPost 9
sincity

rrVeteran

Pasco, WA

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Could also be since you're decending fast that your rotor rpm isn't high enough for the tail to compensate for the torque. Your blade speed may just be too low. Try turning up your 2nd and 3rd throttle curves a bit to see if it solves the problem.

Shawn

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03-12-2006 09:32 PM  11 years agoPost 10
lele

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italy

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thankyou alla Guys

I will try to make some fast descend with some idle up and see what happens.
But I am not still convinced that the head speed could be relevant to those piros since the HH should have taken care of that as it does in fast ascends...
What gain are you guys running on the 401?

Thanks
Lele

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03-12-2006 10:18 PM  11 years agoPost 11
djMidnight

rrApprentice

Petaluma, California

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Because you run the motor in governor mode, fast descent can actually completely stop power to the motor, since the blades don't require any power at all to keep spinning (it's an auto-rotation).

When this happens, there's a big reduction in torque, which should cause the tail to respond appropriately.

When you get to the bottom and stop descending, motor power is applied again and the tail needs to compensate for the hard torque, but it takes time for the motor to rev back up. Since you say the spin is clockwise, my guess is that this is where the spin happens.

If your motor controller has a "speed setting" ( on Castle Creations they call it "soft start" ) set it to the fastest setting available. This will cause the motor to respond faster when required to spin back up, which will keep your headspeed higher and improve tail hold.

Jason

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03-12-2006 10:39 PM  11 years agoPost 12
lele

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italy

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hi Dj

I have been thinking the same thing you say. That could be the real reason for this happens. What do you think about coming down in fast descend in idle up? let's say I would set the idle at some 40% motor in negative pitch...could this resolve? I am going to test that, but if you or any of you other guys have any additional suggestions about this...
thanks
lele

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03-12-2006 11:19 PM  11 years agoPost 13
djMidnight

rrApprentice

Petaluma, California

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If you're descending quickly in "normal" mode, IE don't have power applied to the lower 1/2 of the throttle curve, then your motor will probably turn off almost completely when you descend fast, and that will almost definitely be your problem.

If you are flying in one of your stunt modes (IE power available in neg / pos pitch) then the problem is more likely just from using governor mode on the speed controller, and it's much worse if the speed controller reacts slowly to the sudden power requirement at the bottom of the descent.

Mine "kicks" a bit when I descend quickly and stop hard, but it's nowhere near the 180 degrees you mention, and I have my speed controller set to respond as fast as possible, and I basically never fly in "normal" mode - I just use it to spin the blades up.

Jason

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