Tail Still Whipping

I'm a left-piro guy. I'm still experiencing whipping, and my goal is to eliminate all whipping in my tail during holding large collective with simultaneous left rudder input. However, it also has whipped harshly during an aerobatic auto (without power) during left rudder input, so it may not necessarily be associated to torque or load, perhaps.

My hypothesis on what might be happening:
Maybe the vbar is releasing the right-thrust hold a little too fast in combination with the large torque from the electric motor, and the vbar doesn’t catch it until the tail has whipped almost 180 degrees left. I expect it to have a totally consistent pirouette rate no matter what, and especially no whipping with wind, collective, etc. Is my hypothesis incorrect?

I’m mostly confident my hardware setup is correct (see setup below). I figure I would have sufficient tail performance, and certainly enough authority. It certainly was sufficient with this same tail gear ratio on a 700N while using a Spartan tail gyro (flybared) several years ago, and there's nothing I could do to yield a whip or otherwise inconsistent left pirouette with ridiculous amounts of collective & cyclic inputs while pirouetting. So I believe I have a realistic expectation that it is possible to have the perfect tail.

I'll add here that the problem did improve a little when:
• decreased the tail pitch for right thrust at servo center, from ~3 degrees down to ~1 degree.
• When I increased the travel limits to 120,120

I’m trying very much to isolate the issue. Assuming the tail servo is ok, what is a comprehensive list of factors to consider when troubleshooting such a chronic issue?

Setup:
• Trex 700E
• 17mm tail servo horn linkage ball from center. (4th hold on a star horn)
• servo 90, rear arm 90, and ~2 degrees right thrust.
• 4.272:1 tail gear ratio (new 22T faster speed than stock Trex700e).
• 105mm Align tail blades.
• Leading edge tail grip links.
• Balanced counter weights on the tail grips (easy to move by hand when full head speed on the work bench).
• No binding at all, and frequently lubricated.
• Tail thrust bearings smooth, and smaller diameter on the outside.
• Very small amount of slop.
• Carbon push rod, with one support guide on the boom.
• Very rigid servo horn (round wheel)
• Well balanced tail rotor by evidence of holding the boom with my hand while at full head speed with the tail blades installed (no main blades).
___o There only a minute amount of “buzz” felt while holding the boom primarily coming from the motor.
___o The comparison is the “buzz” felt with the tail blades installed and not installed, and feels the same amount of “buzz.”
•
• 1900RPM, 9.583:1 gear ratio
• Motor ~3500 watt, 450KV, NEU 1915 1Y
• BLS251 on 5v (assumed to be functioning ok)
• Silverline vbar sensor, black vbar unit.
• 40 Collective Add, 30 Cyclic Add
• 0 Collective Dynamic
• 80 P gain
• 90 I gain
• Collective Pre-Comp 10
• Cyclic Pre-Comp 3
• 120 left/right travel (same values)
• 60 Gov gain (vbar gov)
• Optimizer 53, 23
• ESC Turnigy HV120 Opto ESC

The only alternative I can think of is to reverse the main rotor direction and tail rotor direction, flip blades, flip the one-way bearing, and tell the vbar the direction, so the torque is clockwise, and left rudder is going against the torque vs with the torque. But I wouldn't prefer doing that until I have tried absolutely everything.

Thanks for your input and feedback while trying to help me think through this.

Here's a video of the offending maneuver I do that causes my tail to whip. Advance the video at 0:33-35. He gives full collective with left-rudder input. It's at that moment my tail get angry and whip; it pirouettes and holds relatively well, but whips.
http://www.youtube.com/watch?v=YadawDFu1VI

_Sam B_



Edited 3 time(s). Last edit at 12/18/2013 02:45AM by sam2b.

With some experimentation, I've helped the whipping. However, during some traveling high speed with heavy collective the tail still likes to whip with the following characteristics all within about 1.5 seconds.

* When giving left rudder, the tail hesitates for a moment (almost sticky).
* then it lets go (the whip).

My Questions:
* Is the hesitation (sticky) a bad sign? That concerns me most. I have 19 degrees of left pitch.
* What is an indication of? Not enough left pitch?
* Is torque compensation a contributing factor?

--> If this is because of not enough left pitch, I fear that would invite the whipping again since I had good results decreasing it.

Since I have good results of whipping has improved with these gradual changes:
* reduced the left pitch slider to 100 (from 120) moving 19 degrees left and installed 115mm blades.
* I've also reduced the servo horn to 15mm (from 17mm).
* 100 common gain tail
* 80 i gain tail.

The maneuver where the left tail sticks (or hesitates) is this:
1) Clockwise backwards inverted fast speed.
2) Sudden left rudder input (rotating counter clockwise)

I believe I should have an absolutely flawless functioning tail, and should never ever whip under any circumstance. I don't even do as aggressive maneuvers as the Pro pilots, and they do similar maneuvers (see video above) without the tail hesitating or whipping. Who can give me a comprehensive list of troubleshooting steps, and what to look for? I'm very meticulous on the workbench, and I'm sensitive with intuition while flying. In my strong opinion this issue should be able to be solved, please. I'm asking for specialized help, please.

The pictures below show the pitch slider:
* At neutral with the servo 90 degrees while in the software setup menu. 3 degrees right thrust with evidence of a calibrated digital pitch gauge.
* showing full right pitch.
* Showing full left pitch. (19 degrees)
* Showing zero degrees pitch (very close) while in the swash trim software setup menu.

_Sam B_



Edited 5 time(s). Last edit at 09/21/2014 11:32PM by sam2b.

OK, this might be not a esasy task here - and we also might to get close to physical limits.

Some experiences out of my mind:

In last IRCHA i did a setup session with Jakob and Mark Gitin and we tried several tail thorws on our Logo 700 together with full collective and against / witch the torque maneuvers. Doing it with the torque (like you) wasn't a big problem, but against the torque we needed every kind of throw.

So ... having a look at your deflection with the torque here - it shouldn't be a problem of the throw.


But - as it gets clear in your second post with the "delay" - it would be either a mechanical problem (check bearings etc.), a physical problem (i see the long screws there - the resulting centrifugal forces could be a reason) or a setup thing.

- Can you please test with stock tail blade screws?
- Can you please upload the current setup file?

regards (EN) / Gruss (DE)

Rainer Vetter

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Thanks. Here is my config file from my last flight. I have sent you a special private video to watch also, so check your PM.

Notes:
1) I set zero for the gov Dynamic Collective while trying to help the whip problem because I noticed throttle is added when I give left/right rudder on the workbench. Let me know if I should set this back to default, or other value.
2) I set my cyclic ring to 70 because it seems to be a better feel to me.
3) I set the tail i gain to 80 while troubleshooting this whip issue as per MrMel's video on tweaking the tail.
4) I'm not so sure this problem is related to pre-comp, but I will let you decide. :-)

Remember:
* I have 115mm tail blades.
* I have a tail ratio of 4.727:1
* I am running 1900 RPM head speed (vbar gov)
* The reason I have the long screws is they act as counter weights to help the wind forces to the servo. I've tested the control rod with my hand on the workbench, full throttle with the tail blades installed, and the control rod is very easy to move with just 2 fingers lightly. I figured this would be helpful for the tail servo, but I can test with the original bolts on my next few flights.

Thank you again,
Sam

_Sam B_



Edited 3 time(s). Last edit at 01/01/2014 01:33PM by sam2b.

A few hours before Rainer's post above, I made this video to demonstrate my actual issue. Then, please read my next post below with results after Rainer's suggestions, as well as two additional changes.

Demonstration of the whipping problem:
http://www.youtube.com/watch?v=7DOPENZAbzw

Disregard when I say "it seems normal to me." No, it's whipping all over. Almost every time you hear a large sudden bog in the motor, it is because of a whip as the gyro is trying to catch it with a sudden full right thrust.

Remember: this video had the following configuration:
•1900 head speed
•22T tail gear, 4.727:1 ratio
•115mm tail blades
•zero Collective Dynamic on the gov
•100 left limit, 120 right limit
•3 degrees of right thrust at servo center
•100 common gain tail
•75 i gain
•Precomp collective/cyclic 22/9, then 11/4, then 0/0.
•CG not correct, tail heavy

_Sam B_



Edited 6 time(s). Last edit at 01/02/2014 05:26AM by sam2b.

Today (after the video above) I had one more test flight with Rainer's two suggested changes:
1) Max physical limits for left/right pitch slider. (Bank#2)
2) Removed the long bolts (counter weights), and replaced with the stock short bolts on the tail grips.
3) Fixed the CG from being tail heavy

Still whipping, and I am still making videos when I get the chance.

_Sam B_



Edited 3 time(s). Last edit at 01/03/2014 06:17AM by sam2b.

Hello Sam,

i had a look at the video together with Ulrich and we see a strange tail move there:

At approx. 5:13 the tail slider does a sudden kick. We would like to have a look at the event log of this flight.

regards (EN) / Gruss (DE)

Rainer Vetter

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Log attached. Thank you so much for you both studying the video! I'm honored to have your time.

Note: as I have stated above, in that flight video I admit my CG was tail heavy since I have attached the camera. I'm guessing that also is a significant factor.

In this whip, the maneuver first raises the tail upwards to 12 o'clock against the wind, fighting both tail heavy and against the wind, and other things. Then from 12 o'clock through 6 o'clock the tail whips tail heavy and with the wind.

_Sam B_



Edited 2 time(s). Last edit at 01/03/2014 06:18AM by sam2b.

Final Result and Conclusion
Since I've done the following, the tail has greatly improved performance and feels very good while flying. The clicking is a broken tooth on my main gear, but I didn't have a spare, so I flew anyway. The previous test flights' whipping actually broke it.

Video: http://www.youtube.com/watch?v=NaDpVhECBlw

Results: Now I have confidence my tail will be where I put it and where I expect it to be in many fast speed maneuvers. However, while greatly improved, the optimal choice is to not input full left-rudder while traveling fast speed. I found if less/slower left-rudder is input, the gyro can do a better job keeping the rate of pirouette. In my own words, in high speed maneuvers, giving left-rudder is a self-induced blow out. That said, don't stop pursuing an optimal hardware setup, and do so by experimenting. I know first-hand what works and what does not work for my issue, and in the process I found what hardware setup works best (at least for me, and good chance for other pilots too). The proof is test during demanding maneuvers in flight, and tweak until it performs that way you want it to perform and the way you expect it to perform. My experimentation these last 2 weeks have taught me it is possible with diligence and patience.
Here's the combination that works for my heli and my flight style:• moved the ball in 10mm on the tail lever (but left the servo horn 15mm)
• re-installed the counter weights on the grips (long 37mm bolts)
• Vbar pitch slider physical limits: 94/112
• Tail common gain 60, p gain 85, i gain 75
• 115mm tail blades, 22T tail gear 4.727:1 ratio
• 1900 RPM head speed 9.583:1 ratio (20% motor head room)
• Futaba BLS251 @ 5v regulated (very consistent voltage with zero dips as per the VoltMagic device at over 1,000 samples per second)
• CG adjusted from being tail heavy.

Note: yes, the 10mm adjustment is extreme, and may sound ridiculous. But it puts the vbar limit values within normal value range while enabling maximum physical limits for the pitch slider. The 10mm adjustment also has essentially sped up the servo in the process, but the mechanical disadvantage is not experienced because of the counter weights installed. I've also taken the time to balance parts to 0.01g of the tail grips, blades, bolts, nuts, and washers. The bolts also have the same length as well as the same weight.

This is a little more aggressive flight with the same configuration.
Video: http://www.youtube.com/watch?v=eTSQX3h3ExQ

Perhaps you have ideas or comments, all of which are welcome. For now I'm finally satisfied with the performance.

_Sam B_

Quote:

I found if less/slower left-rudder is input, the gyro can do a better job keeping the rate of pirouette. In my own words, in high speed maneuvers, giving left-rudder is a self-induced blow out.

I have a comment for this:

If you want to do this by the VBar - just lower the tail acceleration value ;-)

It describes how much the servo output can be changed in one calculation frame. So lowering it (45 down to 30) will give smoother inputs from stick.

regards (EN) / Gruss (DE)

Rainer Vetter

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Posting and answering - please use a PC and a standard keyboard. Answer all questions fully, take the needed time, don't forget probably requested attachments.

Für Posts und Antworten bitte einen PC und eine richtige Taststaur benutzen sowie alle Fragen vollständig abarbeiten. Nehmt Euch Zeit, beantwortet Rückfragen in Ruhe und vollständig.
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Hi, Rainer. Thanks for the advice! Do you have any more comments on my thoughts and results posted above? For example, what do you think about the 10mm adjustment to reach max limits at 90/112? Also, what are you comments on the videos?

_Sam B_

How does the optimizer work in this scenario? Why is it when I have manually decreased the left optimizer value to 15 that the whipping has improved?

_Sam B_