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e-Align T-REX 250-450-500-600 > T-REX 450 When I flip my 450 and go to inverted hoover tail out, it drifts to the left really bad.
 
 
kingofcrash
Heliman
Location: Battle Creek, MI usa

why does my heli drift to the left inverted it also shakes a little when spooling up. I ballanced my blades.whats the best bat motor combo for 3d 4cell or three cell
02-12-2008 01:08 AM
 
 
2atlo8
Senior Heliman
Location: Cedar Park, TX -- USA

I think the left drift is normal. When you are in an upright hover and trimmed out, there will be some right aileron trim required to conteract the thrust of the tail rotor, which tries to pushe the heli to the left. When you invert nose in, the tail rotor still pushes the heli toward the left, but the aileron trim is reversed (left is rigth and right is left when inverted nose in) and is adding to the tail rotor drift rather than counteracting it.

The same kind of thing happens if you are a little tail heavy and counteract that with forward elevator trim. When you invert the elevator trim works WITH the tail heavyness instead of against it, and you wind up having to apply some back elevator to hold a hover.

2atlo8
3D+1 is my age....in hexadecimal.
02-12-2008 02:32 AM
 
 
T-Rex-Flyer
Key Veteran
Location: Panama City, Fl

Hi 2atlo8 - The second paragraph is 100% correct, the first paragraph I'm still trying to rap my head around, but sounds reasonable.

If the wings are traveling faster than the fuselage, it's probably a helicopter.
02-12-2008 02:35 PM
 
 
The_Widowmaker
Key Veteran
Location: Huntington Beach, CA

Quote 
When you invert nose in, the tail rotor still pushes the heli toward the left, but the aileron trim is reversed (left is rigth and right is left when inverted nose in) and is adding to the tail rotor drift rather than counteracting it.

Nothing reverses. Everything is still left, right, up down in relation to the heli itself. The tail still pushes the heli in the same direction and the aileron still operates in the same direction. So it will not add to the drift effect.


EDIT: See my last post. It does add to the drift because your inverted but not because your nose in.

"I'm a Virgin.. I'm just not very good at it. "
02-12-2008 03:01 PM
HOMEPAGE  
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

I think 2atlo8 is right. If you visualize the situation. upright you are hovering but some right roll trim is required for a stationary hover. If you flip inverted, same roll trim will be aggrevating the translational thrust from the T/R instead of counter-acting it.

I drew out a quick drawing to help me sort it out.

If you avoid failure, you also avoid success.
02-12-2008 03:14 PM
 
 
The_Widowmaker
Key Veteran
Location: Huntington Beach, CA

Post a sketch because now Im confused

"I'm a Virgin.. I'm just not very good at it. "
02-12-2008 03:19 PM
HOMEPAGE  
 
 
The_Widowmaker
Key Veteran
Location: Huntington Beach, CA

Ok I got it now Left and Right are still left and right. The thrust has changed.

This is what threw me..
Quote 
(left is rigth and right is left when inverted nose in) and is adding to the tail rotor drift rather than counteracting it.

It sounds like hes saying right aileron will add to the drift because your nose in, which is partially right. The right aileron is going to add to the drift regardless of being nose in or not , as long as your inverted.


Personally I do not trim for this. I run a level swash and a balanced heli and just fly it straight.

"I'm a Virgin.. I'm just not very good at it. "
02-12-2008 03:21 PM
HOMEPAGE  
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

I visualized it tail in upright and tail in inverted. The direction of the T/R thrust changes (with respect to the pilot but not the helicopter) but the roll control remains the same, ie, right movement of the stick is right roll and left movement of the stick is left roll. Since the tail rotor thrust changes direction, when keeping the tail in both upright and inverted, and the roll trim remains unchanged, the upright trim to counteract the lateral thrust of the T/R now adds to the T/R thrust instead of counter-acting it.

That help?

If you avoid failure, you also avoid success.
02-12-2008 04:04 PM
 
 
The_Widowmaker
Key Veteran
Location: Huntington Beach, CA

Heheh... no that made it worse The only thing changing is the thrust of the main blades. The tail does not switch directions, the aileron does not switch. As if sitting in the heli... disc still tilts right, the tail still pushes the the left, regardless of upright, upside down, nose in, tail in...

Excuse the sketch. Black arrows show direction the disc will travel and red is the thrust.



"I'm a Virgin.. I'm just not very good at it. "
02-12-2008 04:18 PM
HOMEPAGE  
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

the T/R thrust changes with respect to the pilot. It does not change with respect to the helicopter.

If you avoid failure, you also avoid success.
02-12-2008 04:25 PM
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

That's the exact sketch I had. Are you spying on me?

If you avoid failure, you also avoid success.
02-12-2008 04:26 PM
 
 
The_Widowmaker
Key Veteran
Location: Huntington Beach, CA

Heheh.. I did that earlier and lost it and just did it again. Bad thing is even after drawing it the first time I was confused until I added the arrows.


Quote 
the T/R thrust changes with respect to the pilot. It does not change with respect to the helicopter

I must have been editing while you were posting

"I'm a Virgin.. I'm just not very good at it. "
02-12-2008 04:28 PM
HOMEPAGE  
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

yup, mine had arrows too. The only good way to visualize it and not confuse yourself.

If you avoid failure, you also avoid success.
02-12-2008 04:29 PM
 
 
alwallash
Senior Heliman
Location: Morgan Hill, CA (near San Jose)

king of crash,
It is normal for a heli, trimmed for upright hover, to be out of trim (a little) in inverted hover.

Just us two 5 point programmable mixes (pmix). Use PITCH as the master channnel, and elevator or aileron as the slave channel.
then adjust the values of elevator and aileron when the pitch is NEGATIVE, ie inverted, to trim for inverted hover. On my JR radio, I usually need up to +/-6 in mixing.

This works really well, and your machine will fly inverted much better.
Al
02-12-2008 05:34 PM
HOMEPAGE  
 
 
T-Rex-Flyer
Key Veteran
Location: Panama City, Fl

So... Bottom line is Trim makes it worse? and I should zero out the corrective trim before I go inverted.

Edit:
alwallash - I like you're technique.

If the wings are traveling faster than the fuselage, it's probably a helicopter.
02-12-2008 05:35 PM
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

yeah, I like the programming idea too. I'm too lazy and not serious enough to implement it.

I'll let my brain and thumbs do the mixing for now

If you avoid failure, you also avoid success.
02-12-2008 06:06 PM
 
 
dpcarey
Senior Heliman
Location: Ontario, Canada

Hey guys,

Is it possible we have gotten too technical on this question? Perhaps this fella just hasn`t balanced his heli well enough. We all know that a weight distribution problem tends to be magnified while inverted. If he has a little more weight to one side, he is going to drift towards the heavy side pretty quickly while inverted.

...just a thought.

Dave
02-12-2008 08:13 PM
 
 
SSN Pru
Elite Veteran
Location: Massachusetts

dpcarey,

Possibly.

Lets back up.

Quote 
why does my heli drift to the left inverted it also shakes a little when spooling up. I ballanced my blades.whats the best bat motor combo for 3d 4cell or three cell

1. Why does my heli drift to the left inverted...

An explanation has been given based upon your trim status when upright.

the use of "inverted" implies that there is no drifting tendency when upright which would lead us back to the trim status explanation.

The probability of putting so much weight off to one side of the heli to cause it to be out of balance laterally is highly unlikely unless you are strapping a batter to the side frame on only one side.

These model helis are, for the most part, designed to be extremely symmetrical with respect to weight from side to side.

the largest weight discrepancies are going to be found from nose to tail. This is the most common problem when it comes to drift problems upright to inverted.

2. ...it also shakes a little on spool up.

Does it shake on every spool up or only on the first spool up.

If it only shakes on the first spool up then that is normal due to the fact that you can not perfectly align the blades along the feathering axis when you unfold them. On spool up, centripetal forces will straighten them out perfectly for you, assuming everything is balanced correctly.

If it shakes on every spool up you have to determine if everything is balanced in the rotating rotor head. This is to include the flybar, main blades, and rotor head too, preferably balanced all put together.

Another possibility to the shaking on every spool up routine is that you are experiencing some magnitude of ground resonance. Does the shake occur at a certain RPM and disappear if you decrease or increase the RPM? If this is true then you are experiencing some ground resonance which again is find if you don't stay at that RPM for too long.

3. whats the best bat motor combo for 3d 4cell or three cell?

This is largely up to the individual. You could get 1000 different batt/motor combo's from different people here.

4s vs 3s is a bit more black and white though. 4s will allow you to pull the same amount of overall power or wattage as a 3s system while keeping your components cooler and not shortening their lifespan. You can also increase your overall power but sacrifice your components due to increased heat. I'd hazard a guess that the typical 3s Trex 450 power combo can put out around 400 watts. The typical 4s Trex 450 power combo is likely capable of 500watts.

a 4s system will weigh more which will increase the disk loading but at the same time it will increase your power to weight ratio. Both are important to increase though if you are searching for higher performance.

phew! all done!

If you avoid failure, you also avoid success.
02-12-2008 09:13 PM
 
 
Shawn Pierce
Veteran
Location: Galliano, La.

Just a test but have someone watch your fingers. you could be mindlessly moving your sticks.

"Synergy" Cajun helicopters
"Hyperformance Rc Equipment"
Insane Canopy
02-12-2008 09:23 PM
HOMEPAGE  
 
 
dpcarey
Senior Heliman
Location: Ontario, Canada

Quote 
The probability of putting so much weight off to one side of the heli to cause it to be out of balance laterally is highly unlikely unless you are strapping a batter to the side frame on only one side.

Huh ...The various positionings of the ESC and tail servo do not always result in a "symmetrical"/balanced distribution of weight.

My suggestion is from first-hand experience. If he has his ESC and his tail servo both mounted on the same side of his heli, I can assure you it may cause his heli to drift quite a bit while inverted.

My moto is: check the simple stuff first - make sure the heli is balanced.

Dave
02-12-2008 09:28 PM
 
 
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e-Align T-REX 250-450-500-600 > T-REX 450 When I flip my 450 and go to inverted hoover tail out, it drifts to the left really bad.
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