Tail stop bounces: 2nd try

[Block137]

Many things I tried, that somewhat worked, look more like a mess up.

This is my second try to fix this "correctly"

Originally Posted by georgi UK

=] Block, set your travels to 100% on each side and lower the control rates, then please post a log outside of this thread, we can check the state of the tail gyro for you. I imagine that is your real issue?...

From: https://www.helifreak.com/showthread...=731893&page=7

Here it is:
Notes: 100%/100% travels
Default Sport Setup
Control Rates lowered to 300
You can see bounces more clearly as I reduce tail gain later in this log (40>>30>>24)

Thanks for helping (2nd time)

PS: Feel free to fix my poor English

[georgi UK]

=] Block thanks. Your log / gyro will get a deep scan, the things I notice on initial impressions, the tail servo is pulling a fair bit of voltage, it would have been an advantage for you to have switched to Tail 1 in the flight also to monitor this drop further.

I can't see a stable accelerometer flat-line and wonder if the unit has seen some impacts? The playback doesn't work for me, is the SD card saturated?

I will check in with you later with more info, I'm sure we can determine the issues you are having, cheers.

[Block137]

Do you have any recommended values for tail 1?

Accelerometer flat-line? What is it?
Can't remember whether I've dropped this unit, atleast not from height.
And no hard crash.
Can this be related to high temp?
It's just below 40°C in the afternoon and with some current flowing this thing could have been at 50°C.

I can watch the playback just fine.
Less that 100logs+vibe on the SD.

PS: it still say tail servo is reversed when using wizard.

[GaryDT]

Originally Posted by Block137

It's just below 40°C in the afternoon and with some current flowing this thing could have been at 50°C.

That's hot. I'm smiling

[georgi UK]

=] You have 900 deg/s on Tail 1 at full stick. I would like to see the voltage for that. Your accelerometers are showing a 'ripple' when at idle on either side of the actual flight, so unless you are flying off a boat or such?.....

Please await the scan results, this will show temp. drift also....

[georgi UK]

=] Block, your tail gyro appears to be ok, so we need to be looking more at the heli side of things. Make no mistake here as this can be so subtle and easily missed.

1, remove mains (tails on) and disconnect the control linkage at the tail servo end.

2, power the headspeeds up and using hand felt movement work the control linkage on either side of zero blade pitch looking for resistance,

3, exercise extreme caution when doing this, fix the heli down if needs be.

4, depending on what you find doing this, next logical step is to inspect the thrusts, for correct assembly/damage and greased.

5, if you have a new spare tail hub with grips, please fit it, or get one.

6, if you run grommets on the servo, please remove these. (applies to cyclics also)

7, I still would like to monitor your tail servo voltage on Tail 1.

I will add as we go here..... good luck!

[Block137]

That's a relief! Mailing back to SK is not a good experience at all.
Thank you for the scan (no idea how)

Didn't have a chance to go to the field and no way I'm gonna do 900degs/sec in my garage.

But I believe this [attached log] should help you look for volt drop.
FYI:
-Heli locked to the ground using a milling vice
-Main blades off
-Cyclic servos active

*************************
For hand felt mode: at 50% THR
I can't feel any resistance other than re-centering force (wow, tail servo is working that hard!)
I myself don't think the cause is here.

BUT while testing, I heard belt skipping during extreme pitch (along with noticeable RPM drop).
I might test again with new belt because its brown outer layer has gone completely and it's been 2 years.

*************************
lastly, here is "Slop-ness vid"
https://www.dropbox.com/s/pw5an7v46m...84438.mp4?dl=0

[georgi UK]

=] No log? You need to eliminate that slop. Yes, the tail servo is working for it's money!

[Block137]

Originally Posted by georgi UK

=] No log? You need to eliminate that slop. Yes, the tail servo is working for it's money!

Wha..?
Nevermind re-uploaded

Every joint has a slop and they add up to that much.
I will need a new tail to eliminate that....and a belt.
The reason why 1 heli is not enough

[georgi UK]

=] You just need to build a spare tail assembly, slop being a primary reason for tail bounce, = more slop = more bounce.

It's like go metal if there are upgrades available. Will go thro' your log tomorrow, thanks. It's getting there!

[Xrayted]

Hey Block, Gerogi is spot on and I think you have shown the mechanical reason for your tail bounce.

Contrary to popular belief, all that slop isnt doing much to harm you in stable hover or even FF sport flight, however rudder jabs and solid stops are another thing.

That spring like restoring force you felt on the tail rod when doing the spun up rudder test is the same force that removes all the slop from our rotor or tail linkages when the model is stable and the rotor seeks center.

The tail blades do not go tracking all around randomly out of plane with each other causing massive vibes as some think, as that is not how a balanced spinning mass behaves even if each side is articulated and able to move individually, but instead the restoring forces causes each blade to seek center in the same path plane and will actually run quite smoothly. This is exactly how the individually articulated main rotors of real helis work.

The problem occurs as soon as you jab the rudder quickly and release, and then that restoring force has all that mechanical slop in the slider to bounce back and forth quickly a time or two as it seeks its restoring center point, especially if there is another force pressing back against it.

You say this only happens on a CW yaw release which makes sense since you are moving the tail against the main rotors natural torque which is always pressing back against its movement. CCW yaw movement is much easier for it since it follows the natural direction it wants to move in the first place with no resistance.

I think you should see a big improvement with a more slop free tail setup.

[Block137]

I can see the point now.
What you said are so true!
I've always been told that "fixing slop is a waste of money + it does not hurt stability".
Never liked those ideas

Now it's shopping time!

[georgi UK]

=] Log is good thanks, Given a choice between binding and slop, it's better to have 'some' play in the linkage to avoid tail wagging, is perhaps what you were told?

I think we are on the right road now, so get a precise upgrade on her!

[Luvmyhelis]

Originally Posted by Xrayted

Contrary to popular belief, all that slop isnt doing much to harm you in stable hover or even FF sport flight, however rudder jabs and solid stops are another thing.

That spring like restoring force you felt on the tail rod when doing the spun up rudder test is the same force that removes all the slop from our rotor or tail linkages when the model is stable and the rotor seeks center.

The tail blades do not go tracking all around randomly out of plane with each other causing massive vibes as some think, as that is not how a balanced spinning mass behaves even if each side is articulated and able to move individually, but instead the restoring forces causes each blade to seek center in the same path plane and will actually run quite smoothly. This is exactly how the individually articulated main rotors of real helis work..

Hopefully this was aimed at trying to rebuff guys such as myself. So I will joyfully jump in here and disagree. Should I post a four page paragraph educating the masses here on how tail rotors work in real life? I think I will!

Originally Posted by Xrayted

I think you should see a big improvement with a more slop free tail setup.

Now we agree!

Tail rotors act exactly like your main rotor in many ways. We just don't want to see any actual rotor lean induced by a swash here. Where we have more thrust being produced on one side of the disc than the other. What we ultimately want to see is exactly the same thrust being produced by each tail blade. Never one more than the other. Or off balance. Tight is right in the tail just as it is critical in the main head system!

Here is why. Lets ignore the balance issue and just go after slop.
First off, the static rotating mass of the tail does try to retain its rotating center. However, we have blades inducing massive thrust against the 'neutral' that are never neutral. Why? Most tail setups on RC helis have the tail rotor about a third of the way introduced into the massive rotating thrust of air coming off the main rotor. So the forward part of the tail disc is already being forced off at an angle, even in a hover! Give us some grip slop or any other slop here, and the forward blade tries to lean out farther in its pitch angle than the retreating blade does. The tail is never static, always always is under a thrust condition that is always changing dramatically from one second to the other. Even in a hover! Air is moving around in dozens of directions.

Understand the tail grips have two pivot points. One, the tail shaft hub, and the other is the pitch control arm. So if the tail grip is sloppy, it will lean out farther under that severe blade induced thrust than the other side will. Even though centrifical force wants the blade to return to center, it simply can't. The much greater pitch induced thrust causes it to lean as far out as it can against the restraints of the bearings controlling it. This case sloppy right? So, it leans farther than the other side which has tighter control does. Yet the angular control pivot hasn't changed! So the lean either induces greater pitch, depending on whether or not you have a leading control arm or following, or it creates less pitch than the other side does. It really doesn't matter. The result is the same. More thrust with one tail blade than the other!
So the entire tail shaft tries to lean accordingly as you instantly have more thrust on one side of the disc than the other. Almost always the leading forward disc that is dealing with the accelerated main blade rotating mass of air. It never blows straight down, or up when inverted, but always creates more force on one side of the leading tail disc enveloped in the faster air flow than the other retreating edge. Basically causing it to want to lean off angle even in a hover! Remember the main rotor wash is always rotating. Creating more force on one side of the tail disc than the other. Even if the argument the blades are neutral, we now have a higher pressure side on one side of the disc than the other.

So neutral is never neutral.

Now, lets add in slider slop. Or even the slider support bearings being sloppy around the slider! This is the bane of single sided sliders btw. You push your tail to turn left lets say. And the servo pushes the tail rod, which in turn pushes the lower tail bell crank out farther on the tail shaft. The force it takes to do this to move the disc is enormous. If you think this is wrong remove your tail servo and try and move the tail control rod by yourself with the tail blades at full steam with your heli anchored down. It will scare the pants off you, and is like trying to move iron.

What happens with a sloppy tail slider is the slider leans as you try and push it with a single control arm system. They actually chatter rocking as they are pushed or pulled along the tail shaft. Nice huh? Imagine what those stresses are doing at this point to your stuff?
That induced lean also leans the tail control Y arm, which now induces more tail pitch to one blade again than the other. Also resulting in trying to lean the tail shaft again. There are volumes of info just on tail slider chatter here at HF in the early 450 threads. And the reason they finally came out with dual tail slider control systems is a result of that foot work and research diagnosing those severe problems.

Now we are into tail shaft control. Trying to control it from leaning one side over the other. Any bearing slop here is going to allow that to happen, and the tail shaft will violently try and stir around leaning at 10k. The early version Sab's (and Aligns) had nasty issues here. They called it the Goblin tail howl. Guys thought it sounded cool. But what was actually happening was the tail was coming unglued with all the tail slop. Allowing the tail shaft to lean out off center. Tearing up the bearings, bearing races, and even causing crashes by tail vibes upsetting guys gyros. Additional slop just allows the tail shaft to wallow around, lean or stir violently. Much like a dremel caught in a small hole you are trying to file out. Ever had that happen? The entire dremel tries to rip out of your hand.


See where this is going? Tight is right.

Hmm, maybe the reason my own tail bearings are still tight and smooth after 600 flights has nothing to do with bearing quality? Or lube? None of that matters when they are getting hammered apart.

Now lets add in bell crank related slop. Here things get dicey right around both sides of neutral. And another quick paragraph explaining why this isn't good.

[Xrayted]

Randy, my post had nothing to do with you and I'm not wasting any time or effort rebutting the 90% so called nonsense "science" you make up as you go along on most subject matters, as you will never ever consider the possibility that you dont quite understand much of the things you claim to be an expert on.

How many topics do you have to be discredited in over and over by multiple people before you start actually listening and learning rather than working so hard to continuously try and convince everyone how important you are and that your opinion somehow rises above question simply because you say so? The internet is full of made up personas by those with otherwise boring lives and every forum has its "mall ninja"

It's a rhetorical question and I'm not asking for an answer here because its already known, and I gave up long ago.

[georgi UK]

=] The point being is for Block to grasp tail Bounce, main cause from when the tail gyro operation speed (fast) and the heli operation (response) speeds differ. Hard stops show us how well these two are matched.

Hence my Tail 1 (900deg/s) and voltage obsession! ie, we need to find Why these are not matched, and is exactly what we are doing here, tail slop Will unbalance the two......

[Xrayted]

Exactly Georgi, and if Randy had bothered to actually take the time to read and understand my post he would have seen that I clearly said the slop WAS contributing to the issue!

Instead his arrogance tells him that I somehow must be subliminally speaking to him for some reason, because after all he is the most important person here in his mind so it must be him, when the only point I was making that even a sloppy tail can run smooth with little vibes as the restoring force of the blades causes them to seek center when spun up and not some random out of track plane like many believe.

This can fool the pilot into thinking the ship is smooth, but then issues such as are being described here can arise when other forces are applied and start to come into play.

I'm sorry, but there are long established laws and facts that already govern these principles, and one doesnt get to dismiss them and create their own "facts" simply because they dont have any knowledge or understanding of them such as calling the force on the tail we are talking about centrifugal which is not a force at all and is just inertia, when the actual restoring force keeping the grips and blades in track is centripetal. Yet again a self proclaimed expert on another subject and here to "school" us all without even understanding the very basic forces and terminology at play to begin with himself.

The rambling nonsense explanation attempt that followed was never part of the discussion in the first place.........when did this discussion have anything to do with Goblin tail geometry issues???? Sorry but I'm just tired of the constant self promoting bullshit credential pushing in every post and calling it what for what it is finally

Sorry to ruin your thread with this Block and I'm out for good I promise. You're on the right track and will get it resolved.

[georgi UK]

This isn't right with 2 senior members at odds here. Block I will pick up if you want a fresh thread, this one has taken a dive, or continue up to you bud,,,,,,

[Block137]

Never mind, a new thread might dive even deeper

Talking about diving...my Warp took a dive while testing tail upgrades
Lost tail control 10secs after take off.

Broke:
1x Skid Plate
1x Delrin Canopy Bar
1x Carbon Canopy Bar
Bent a frame cross member
...That's all

Everyone at the field suggested that the heli would spin like crazy if something came loose/popped off.
0:22 in the log clearly shows that it didn't......after that I just panicked.

Opinions?Tail servo?

[georgi UK]

=] yes, a linkage fail would leave you literally not being able to know what commands to give!

It looks like we have been chasing a failing tail servo with centring issues, your stop settings would suggest this also.