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450 Class Electric Helicopters 450 Class Electric Helicopters manufactured by Align, Tarot, SYMA, Airhog, Chaos, HK and similar.


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Old 09-07-2007, 06:19 PM   #1
ams11
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Default my trex keeps drifting left

Just wondering if anyone had this problem. Everytime I try to hover as soon as it starts coming off the ground it just drifts off to the left side. No matter where I set the trim it just keeps going to the left. I've changed the feathering shaft and dampers, main shaft and flybar, I'm pretty sure I've set the pitch correct with the pitch gage. It doesnt matter if I turn it into the wind or away from it,it just keeps drifting left. Its not turning like a gyro problem just drifting to the left. Does anyone have any suggestions?????
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Old 09-07-2007, 06:24 PM   #2
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gyroscopic effect.. you have a gyroscopic device being held stable by a TR... which pushes to the right.. Once you break free from the ground the heli has no left resistance and drifts just slightly to the left.. There is no part you can change to fix it on that airframe. If you notice your heli when hovering ever so slightly leans to the left as well.. Unelss you fly a vario which leans to the right.. If you ever get a chance to fly a Vario you will notice how weird it feels to have the heli lean right.. Should be no big deal but it is in feel.

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Old 09-07-2007, 07:18 PM   #3
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My TRex blades rotate clock-wise, so the heli wants to rotate anti-clockwise (because of motor) - each action produces reaction...

For that reason we have tail trust to stop the heli from rotating anti-clockwise, so the tail disk pushes the tail to the left (clockwise) to cancel the anti-clockwise push from the main motor.

So both rotating moments cancel out, but the forces do not - there's one force up from the main blades which is canceled by gravity, and there is a second force left from the tail which is not canceled.

So your heli starts drifting to the left.

The moment you start hovering, you tilt your heli to the right so that the main force is still up but also a bit to the right so that it cancels the left force from tail. So you hover a bit tilted to the right.

This question has been raised in many forms:
Why drifting to the left?
Why my right skid is lower?
Why my heli is not straight up?
...

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Old 09-07-2007, 07:42 PM   #4
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Rick actually its the opposite. Left hand rotating main rotors lean right, varios lean left.

BTW the phenomenon is called Translating Tendency, they all do it even the full scale helis.
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Old 09-07-2007, 08:10 PM   #5
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I had simular problems... my problem was more evident on turns and pop outs. I just fixed my problem this afternoon... it was a slipping tail shaft that slips when I apply more torque than norm. Read about it here.

http://www.helifreak.com/showthread.php?t=45060
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Old 09-07-2007, 08:38 PM   #6
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Default Translational tendancy

It is simple. Your heli slides to the left because the tail rotor is pushing the heli to the left. You cannot "fix" this tendency because this is just physics, and a natural tendency that happens to ALL helicopters in the world.

Yes, this tendency therefore requires your heli hover tilted to the right. It looks kinda weird, but there is no fix. And obviously when the heli hovers nose-in, the heli should be tilted to the left.

Actually this is why a slow, stationary pirouette maneuver is somewhat tricky, as you need to constantly "wobble" the heli to stay in a spot.
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Old 09-07-2007, 11:00 PM   #7
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It is a common design flaw. There should be a third rotor on the nose blowing the opposite direction of the tail so there's no net side thrust... my V2 is missing this too, perhaps the V3 will add it
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Old 09-08-2007, 04:18 AM   #8
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A HH gyro will hold the tail pretty solid. I think he is not talking about the physics of the heli. In my instance... my drift was caused by a slipping tail shaft (plastic gear on tail shaft slipping) and when this happens, gyro does not hold direction because there is not enough thrust (rpm) at tail to hold position.

He's got a HH gyro... so I'm betting his problem is somewhere in his drive train to the tail. Check all gears from the main shaft's one way to the tail gears (both sides). I bet something is slipping.
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Old 09-08-2007, 05:02 AM   #9
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As the op say : "Its not turning like a gyro problem just drifting to the left.". As some have allready said, this is a natural tendency in all helicopters. But the drifting is worse near the ground than higher up due to ground effect. So just 'hop' it into the air 2-3ft and the drifting should be less noticeable, but still there. Over time you will be more confident at holding it steady for slow take offs and landings.
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Old 09-08-2007, 12:33 PM   #10
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Altitude doesn't matter. Translating tendency is still there - it's just more apparent when you have the ground as a reference point. It's even present in forward flight. Just do what you have to do with the controls to get the heli to go/stay where you want it and don't worry about it.

If you thought about all the stuff that's going on while the heli is airborne (translating tendency, transverse flow, translational lift, ground effect, inflow, disymmetry of lift etc etc..) , you woulnd't have enough brain cycles left to control the thing.

Do like we do in full scale.. Just fly the aircraft.
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Old 09-08-2007, 05:10 PM   #11
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Quote:
Originally Posted by Skiddz View Post
Altitude doesn't matter. Translating tendency is still there - it's just more apparent when you have the ground as a reference point. It's even present in forward flight. Just do what you have to do with the controls to get the heli to go/stay where you want it and don't worry about it.

If you thought about all the stuff that's going on while the heli is airborne (translating tendency, transverse flow, translational lift, ground effect, inflow, disymmetry of lift etc etc..) , you woulnd't have enough brain cycles left to control the thing.

Do like we do in full scale.. Just fly the aircraft.
You forgot the important one. Settling with power
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Old 09-08-2007, 05:28 PM   #12
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Quote:
Originally Posted by Skiddz View Post
Altitude doesn't matter. Translating tendency is still there - it's just more apparent when you have the ground as a reference point. It's even present in forward flight. Just do what you have to do with the controls to get the heli to go/stay where you want it and don't worry about it.

If you thought about all the stuff that's going on while the heli is airborne (translating tendency, transverse flow, translational lift, ground effect, inflow, disymmetry of lift etc etc..) , you woulnd't have enough brain cycles left to control the thing.

Do like we do in full scale.. Just fly the aircraft.
Yep, newbies always notice this cause they expect the heli to just stay stationary once it has gotten of the ground. Think of holding peice of flat glass with a marble on top and trying to keep the marble in the center. Its more like that.

Rick
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Old 09-16-2007, 04:24 PM   #13
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BH thanks for the correction got my words twisted around.. At least its translated well and hopefully he understands what we are saying

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Old 09-16-2007, 04:34 PM   #14
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For everyone who thinks its a mech. problem, it's not! Like waykewl said, it's physics
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