Rolling During Inverted Climb...Swash Interaction or Heli Dynamics?

[KDE Direct]

Hey Guys -

I've noticed with the Trex 600 and Trex 500 that when I flip the helicopter to inverted (tail-out) and give it full negative to climb (-13 degrees pitch), it wants to always roll to the left in a big, long arc. Is this normal and caused by actual helicopter dynamics, or swash interaction? I read on Trextuning.com about the phase issue he believes exists on the current swashplate and the upgrade Align swashplate (which I'm currently using), so is this what I'm seeing? Anyone try the QuickUK swashplate to solve this issue?

Thanks for the help!

[ckoelliker]

Have you tried to add some mixes to straighten it out. I found that my 600n needed some, but my 500 was very close to perfect. To check for phasing issues it is similar to when you are checking the amount of cyclic pitch. But in stead of watching your blades look at the fly bar paddles. In a perfect world they will be completely still when you add full aileron or full elevator. In an imperfect world they will slightly tilt when the control is added. With a helicopter like the evo 50 this is adjusted by rotating the radius block until the paddles stay still. On the 500/600 you need to adjust it by using the mixing options in your radio. On my 600 I had anywhere from 5-8% of mixing. On my 500 it was maybe 2-3%. I could tell the difference. Even with the 500. I was chasing tic-toc and my flips were moving all over the place. After the adjustments it flew noticeably better. Of course all of this assumes that you have a nice and level swash plate throughout your collective range.

[dieselracer]

Look at your swash. Looks like one servo its traveling more or less then the others. Power up the servos and with the throttle hold on or motor disconnected look at your swash as you move you pitch up and down. If it only does it on negitive climb outs then look at the swash when you give it full negitive. If you see that its not level. then use your end point adjustment to level the swash when you give it full negitive. Do not use subtrims. Sub trims is for centering your servos at center stick. You dont need to mess with mix's. Just look at you end points. Once you level that out. The whole travel will be level. Theres a chance that it will be vary hard to see it with you bare eyes. You should look into getting a trueblood swash leveing tool. it rides on top of the swash. Lets you level the swash at center stick. low stick and high stick with out killing your eyes .

[nickos#37]

Hi Kegerator

did you manage to sort this problem after? If so what did you do?

I've got exactly the same problem...and it's definately not an interaction issue as i run a cyclock1 and have no control issue with the heli apart from this rolling out of inverted climbs!!
Hope you can help me!

[nickos#37]

Any of the rest of you 500 fliers with an idea?

Would appreciate it!!

[martiol]

This is normal. The torque from the tail rotor is not in the same plane as the main rotor blades. Normally the heli rolls right when not inverted. SK360 and Vbar both have settings for avoinding this. It's called "Tail drag compensation" in the sk360.

The tail is is pushing the heli left, when hovering it must compensate. When climbing this tourque push the heli's body to the left and crates the roll.

Edit: I don't know why you don't notice when climbing upright... Trim maybe?

[nickos#37]

Hi Martiol

thanks for the reply! I wonder if the reason the heli does not do it when right way is because the tail is below the rotor blades and the heli is being pulled up? When inverted the tail is above the rotor and the heli is being pushed up??

what do you reckon?? Bummer if I cannot get rid of it though.

Can't understand why other folk have not had the same problem?

[martiol]

I notice it on normal climb outs, it's not much. I guess people correct it without noticing, or don't do long enough climb outs?? Or have trimmed the heli for hover and the trim takes care of it?

[Mentalic]

Originally Posted by nickos#37

Hi Martiol

thanks for the reply! I wonder if the reason the heli does not do it when right way is because the tail is below the rotor blades and the heli is being pulled up? When inverted the tail is above the rotor and the heli is being pushed up??

what do you reckon?? Bummer if I cannot get rid of it though.

Can't understand why other folk have not had the same problem?

Just ran a search looking for posts on this very topic and dug up this thread. I'm seeing this effect on all my helis to some extent. Its way more noticeable on the heavy machines though. First off I don't have any ccpm mixing issues, its spot on, this is something else and I think I know what it is..

When I really began noticing the roll out tendency was when I started flying allot inverted backwards. The heli acted like it was just out of trim, a slow right roll would occur the more negitive pitch I used. After a while this started bugging me and I wanted to fix it..
My quick fix was to program a multi point mix to add some left roll from 30% collective stick to zero. The amount of mix needed depends on your cyclic throws but for example my 600n takes about 10%. My mix begins at 30% collective stick and increases to 10% max at 0% collective.

The mix works great but I really wanted to know why this is happening. In upright hover most folks are aware that most heli's leans right (depending or main rotor rotation direction) in normal hover. Well thats caused by the combination of tail rotor pushing left correcting for the torque of the main rotor + the right roll trim to stop the heli from being pushed sideways left by the tail correction.
The lower the tail is below the main rotor the more roll correction required. Also I think on heaver helis there weight hanging under the main rotor is like a big plumb bob, it wants to hang vertical, so more right roll would be needed on heaver machines.

Ok now you roll inverted. The rotor torqe is still there and the tail correction is still required. What is different is that now the mass of the heli is above the rotor disk! So the right roll correction required to overcome the "plum bob" effect of the heli's mass is not required and ends up creating a slow roll to the right, then as the mass leans it adds to the problem causing it to roll right even faster. Think that the tail correction aggravates the mass push over at high negative collective stick. Sorta all makes sense...

Machines with flybarless configurations would have this effect corrected automatically by the multi axis gyros they run.

Just think most folks are not noticing the effect and just fly through it.

[nickos#37]

Hi Mentalic

I've managed to get rid of most of mine.....though not all. In a very aggresive inverted climb out it's still noticeable but still easily manageable.

I found my main problem was my blades were far too tight. This inhibits the blades from the flapping action they need. Now I've loosened the blades off my heli is a completely different animal. It's still just as agile but has much more composure and also it's stopped it's annoying habit of going out of trim!

I still think I'm getting some noticeable frame twist....probably the main cause of the roll when inverted climbing, coupled with the effects you were talking about.

Unfortunately I have a DX7 so the advanced mixing required for me to get rid of the rest is not available!

Merry Christmas!!