Why does my helicopter lean in the hover?

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helicharter
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Why does my helicopter lean in the hover?

by helicharter » Mon May 07, 2007 7:43 pm

Why does my helicopter lean in the hover?


Why does my helicopter lean in the hover?
Ah well if you own a helicopter with a tail rotor system then you may have noticed that when it’s hovering that one skid sits lower than the other.
Now there’s a reason for this and no it’s not because you looking at it sideways :wink: . It is caused by the tail rotor and is because of a thing called tail rotor drift.
Here is an old picture of my T-rex 450 were you can see it leaning to the right in the hover:
Image
What is tail rotor drift?
Ok tail rotor is drift is caused from the reaction of the tail rotor thrust. Think about it like this because of (good old Newton strikes again) Newton’s 3rd law: For ever action there is an equal and opposite reaction.

To make the main rotor spin the motor has to produce power this is normally referred to as torque now on the ground this is fine. But the moment you leave the ground the helicopter would spin at the same speed as the head only in the opposite direction.

So you have to fit a tail rotor the tail generates thrust 90 degrees to the main rotor to stop the helicopter from spinning. The thrust needed is dependent on the torque being generated from the main rotor. So the helicopter is sitting in the hover all nice and stable (easier said than done :roll: ) if you applied Newton’s 3rd law to it the thrust stopping the helicopter spinning, is also thrusting the helicopter sideways because there has to be a reaction so says Newton!

So on a helicopter with a clockwise turning head (looking from the top) which most RC helicopters are. Without the tail rotor the helicopter would spin anticlockwise so the tail rotor thrust is pushed out to the right to stop it spinning this means from that the reaction is for the helicopter to want move to the left so you can’t call it a hover if the helicopter keeps moving to the left. So you tilt the head to the right then the drift stops but this means the helicopter is tilting with the right skid low there is nothing you can do to stop this real helicopter suffers from the problem too. There are ways they used to reduce this the most common why is to left the tail rotor up to the same height as the main rotor, because if you think about it having the tail below the main rotor disc means it’s not directly in line with the torque point so it’s having to twist or tilt the helicopter to stop the spinning. It’s not hurting the helicopter putting the tail rotor lower and the problems with weight and complex gearbox’s makes it not worth bringing the tail up on an RC helicopter and some real helicopters as well!
In the pictures below you'll see some real helicopters one with the tail rotor at the same height has the main and one with it lower than the main rotor.
This is a S76 as you can see it has the tail rotor at the same height as the main rotor.
Image
This is a A109 as you can see it has the tail rotor below the height of the main rotor.
Image

Why does my helicopter tilt more with training gear on?
Well that is simple when you think about it training skids upset the lift from the main rotor so you need more power to lift the helicopter more power = more torque. So the tail rotor has to produce more thrust, means more thrust, means more drift = more tilt.
Peter
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Technex
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by Technex » Sun Aug 19, 2007 10:50 am

Okay this is getting crazy! Every time I try to lift my Falcon 3D off the ground all that happens is that it goes flying off to the left. If I add right roll then it just seems to stay put and keep tipping (rolling) until the blade would hit the ground.

I can go to the left fine, well it does it's self but when I need to move to the right (roll) it just tips and won't move.

I'm about 5cm off the ground though and I don't really want to go much higher really... Gets expensive then...

Any tips guys? I've took of my training gear as recommended, no help really...

Please help, thanks!
[align=center]Image[/align][align=center]
Falcon 3D| DX7, AR7000, Hitec HS-50 Tail[/align][align=center]Robins 22| Xtreme blades[/align][align=center]2x Syma Fairies| 2x LW frame, 1x Picoo Z main rotor mod + extn tailboom[/align]

QuaCKeReD
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by QuaCKeReD » Sun Aug 19, 2007 11:44 am

First time i tried to lift off i had this too...almost crawls along the floor to the left! :shock: but, i want it to go UP...not across :(

This left drift is normal and is to do with rotation direction of main blades, lift caused, etc

How do you fix it? You need to get higher...expensive or not :P

At a hieight of a few cms you are in what is called the down wash. This is VERY turbulent air flow caused by the main rotors pushing air down which is then 'rolled' back up by the ground...and back down by the rotors...etc, etc.

Get a couple of feet of the ground and you will see a BIG difference - different lift, handling and stability. Just dont forget about the down wash effect when you are landing!!! :D

Good Luck!

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Technex
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by Technex » Sun Aug 19, 2007 12:08 pm

Awww your making me want to go higher off the ground... Can I have some tips for first time a few feet in the air?

Training gear on or off?

I can't today, maybe tomorrow or Monday. Some of my tailboom screws have sheared in half -_-.
[align=center]Image[/align][align=center]

Falcon 3D| DX7, AR7000, Hitec HS-50 Tail[/align][align=center]Robins 22| Xtreme blades[/align][align=center]2x Syma Fairies| 2x LW frame, 1x Picoo Z main rotor mod + extn tailboom[/align]

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by Vertigo_Edge » Sun Aug 19, 2007 5:12 pm

Technex wrote:Awww your making me want to go higher off the ground... Can I have some tips for first time a few feet in the air?

Training gear on or off?

I can't today, maybe tomorrow or Monday. Some of my tailboom screws have sheared in half -_-.


Don't take the gear off until you can un-grasshopper forward flight it. And until you can do nose-in.

Put the paddles even.

Learn to hover it before you try to do anything else. Then try moving in triangles with the nose pointed straight ahead and then learn nose-in. BEFORE you do forward flight.

If it really is groundwash and shiat then you could try flying it on one of those tables with holes in them. I don't have much problem on my Raptor but concrete does make it worse and you could try on grass. With the gear ON. Don't take it off.

Also unblock me biatch.

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by helicharter » Sun Aug 19, 2007 6:42 pm

Hello all,
The bottom line is they will always want to drift that is the nature of having a tail rotor going higher won't make it stop wanting to go to the left it will take it out of ground effect but thats it you just need to learn to live with it you will find that 1 day you won't even notice your doing it you can use a bit of trim to help reduce it but it won't get rid of it.
regards
Peter

Cp BELT Carbon: Mental Head speed makes for a cool helicopter :lol:

Raptor 50v2 big nitro big noise big laugh :lol:

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Technex
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by Technex » Sun Aug 19, 2007 7:15 pm

helicharter wrote:Hello all,
The bottom line is they will always want to drift that is the nature of having a tail rotor going higher won't make it stop wanting to go to the left it will take it out of ground effect but thats it you just need to learn to live with it you will find that 1 day you won't even notice your doing it you can use a bit of trim to help reduce it but it won't get rid of it.
regards


I've tried and tried, 8 batteries now, just can't do it it either tips to much if I add right cyclic to stop the drifting left...

Any more help please?

Training gear back on tomorrow or soon anyway.
[align=center]Image[/align][align=center]

Falcon 3D| DX7, AR7000, Hitec HS-50 Tail[/align][align=center]Robins 22| Xtreme blades[/align][align=center]2x Syma Fairies| 2x LW frame, 1x Picoo Z main rotor mod + extn tailboom[/align]

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unwind-protect
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by unwind-protect » Sun Aug 19, 2007 9:18 pm

You can't apply right cyclic to counterract the left drifting tendancy until you're in the air (even a cm or two will do. Accept that it's going to drift left as you lift off, then give a small short prod of right cyclic to get a 5-10 degree lean. If the helicopter is trimmed out properly, it'll keep that lean when you centre the cyclic. Trying to establish this lean on the ground is probably a recipe for disaster (look up dynamic rollover).
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by Technex » Mon Aug 20, 2007 5:59 am

I suppose that might have been my problem, although I do try to get the skids of the ground but sometimes it just tips to much or it rolls to far over to the left.

So it's not wise to trim this left hover or only slightly? (because trim will even do it on the ground correct)
[align=center]Image[/align][align=center]

Falcon 3D| DX7, AR7000, Hitec HS-50 Tail[/align][align=center]Robins 22| Xtreme blades[/align][align=center]2x Syma Fairies| 2x LW frame, 1x Picoo Z main rotor mod + extn tailboom[/align]

QuaCKeReD
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by QuaCKeReD » Mon Aug 20, 2007 6:55 am

Any trim you set is equivalent to applying a constant stick movement. Your heli will always drift left at lift-off - you do need to understand this, accept it (took me a while too) and not look to trim to correct this.

Once you are up, in clean air, with no ground effect and comfortable in hovering and basic controls then you can start looking at trimming it. You want to be comfortable enough with basic control as trimming it requires letting go of the sticks, watching for movement (and knowing it isnt from wind etc) and adjusting the trim levers - if you arent comfortable with the heli in a hover then dont start trying to trim, yet. You will only end up snatching at the sticks to correct that slightly faster then expected movement and crashing.

Take it easy, take it slow. Only do what YOU are comfortable in doing. Most importantly...do it often - the more you do it, the better you get. Its all about practise.

Google for 'RADD Flight School' and read - annoying teaching habit, but if you think about it, it will work.

Good luck :)

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by ddracer » Mon Oct 22, 2007 9:59 am

Hi guys new to posting here but thought I would add my 2p worth. If you are listing left that bad have you checked that you heli is set up ok swash is level etc. I'm new to flying first on a Esky cp2 now on a Belt-cp and building my Hurricane 550.

Mine to list on take off but i add a small ammount of oppersite cyl and once out of the ground effect its fine, (more so on the belt than the cp2). I know it seem like the higher you are the more expensive it gets but remember trying to fly in the ground effect is like trying to balence the heli on a bubble and you are more lightly to fall off it and do damage.

I know nothing and cant do circuts yet just hover around the yard scaring the birds and always fly over concrete, so just tell me to shut up if you dont agree.

Adam

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by Guest » Mon Oct 22, 2007 10:06 am

HI Adam,

No I wont tell you to shut up as I totally agree :)
You'll soon be scaring the low flying planes.
Thanks for your contribution!

Joe

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by evergreen » Tue Dec 25, 2007 2:33 am

Hi there
I am also new to helicopters and just doing my hovering in. Anyway, I had the same problem when I started and basically, my heli had become a punching bag....crushed due to the same problem over :( and over :( and over :x again,,for some reason, it just liked the left side.
Got upset :evil: , had the connecting rods measured out perfect and flew a little higher(Above knee level) to avoid down wash..that helped a lot. Flying too high can be scary. would not recommend that.
I only know this little, I hope I am right and hope it can help.
All the best.

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by gtokarsk » Fri Jan 11, 2008 5:54 pm

I have quite a few videos at http://youtube.com/profile_videos?user=gtokarsk and you can see how I have been progressing (slowly as I am on the cautious side). Anyhow, I agree with the post above as to the altitude being a fix.. You can actually learn to hover right above the ground, almost touching but that means you gonna have to alternate cyclic from right to center more or less, then you got to compensate tail direction with rudder and altitude with throttle and some more forward/back cyclic and it's an endless vicious circle that never ends.. Now.. Imagine flying real heli with real people that are killable onboard! Yes, that's is what real heli pilots go through ;)
I now moved onto Falcon 3d and have to rework many of these skills as compared to my honeybee the falcon responds quite differently.
Fear and not being relax is quite a obstacle to overcome, but keep in mind that lack of caution and being over relaxed is a problem too, so as to everything there's balance.
When you see me "hover" somewhat all over the place in my basement - that's really the worry of hitting something kicking in, increasing the stress level and making my control responses more jerky and overcompensating because "I loose my cool"...
I think especially on something as powerful as the falcon putting on the training gear till the hovering is acceptable is the way to go.
Above all have fun ;)

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by Guest » Fri Jan 11, 2008 6:05 pm

Hi There,

Thanks very much - you have more than a few! :)

Joe

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by gtokarsk » Sat Jan 12, 2008 2:13 am

Yes Joe, I have a bit much there.. :) It's fun to show what's going on, even for someone like me who's not very good. It's fun to see how things have progressed.. than sort of stalled as the larning curve flattened off....

I hope that at least some of these will help some beginner to get more comfortable in the garage air, or a small basement!

I remember being very frighten of altitude.. still am, but on the esky I have found many times that when things get weird, adding some trottle, just to get up motion, gets me stable, then I can decrease to stop going up. I am finding the same on the falcon, accept the fear factor kicks in and I lower ;)

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by jimbyjoe » Wed Jan 16, 2008 3:59 am

Hi guys

This is kind of related - I have a Co-Comanche which doesn't have ana active tail rotor- it does everything from the main blades. So does that mean when I upgrade my heli to a "normal" one, that it's going to totally throw me? or is it like going from roller skates to roller blades, ie. you still retain the basics?
k
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by PsiLo » Wed Apr 16, 2008 6:44 am

Jimbyjoe, having moved from a Lama V4 to a Belt CP I can tell you that all you retain from the coaxial is the basic stick control. Everything else is different and harder! When I fly my Lama now it is like a little toy. The thing which kept getting me when I first moved up was the need to cancel your movements. So, with the Lama I give right cyclic it banks right when I return cyclic to center the heli levels out. With the belt CP I give right cyclic it banks right, I return to center it keeps banking right until I give left cyclic to level the swash out or hit the ground! When you first move up you tend to go back and forth and side to side all the time as you are constantly overcorrecting the cyclic inputs.
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