Tail blowout

[curmudgeon]

I am experiencing tail blowout.  This is my equipment:

Rail 806/116 blades
14S
12T pinion
25T tail gear for 5.1:1 tail gear ratio
KDE 700XF-455kv-G3 motor
Kontronik 200HV, BEC set to 7.4v, using Kontronik governor
Spirit Pro

I am using a head speed of 1750rpm on 80% on the Kosmik (upper acceptable limit).  When I stress the heli by "punching" the collective or just trying to go inverted, the tail blows out between 90* and 180*, which is very scary.  The Spirit log shows lots of instances of "tail limit reached".  I know I still need to tweak the tail gains on the Spirit, but I want confirmation that my current 806/116 blade combination is sound, and the 1740rpm head speed with the 1:5.1 tail gear ratio is sufficient to avoid tail blowouts.  It concerns me that the Spirit log is telling me that the tail limit has been reached, and I still get tail blowouts.  Do I need higher head speed to make the tail blades spin faster (tail is currently spinning at 8,925rpm)?  Do I need longer tail blades?

[Chris Sexton]

Yeah you should be fine. I'm running the stock 27t spur on my 806/116 combo and not having any tail issues from 1660 up.  Hard punches as 1660 kick a touch, but not bad. Certainly not any blow outs.

Your tail should be locked in.  I know very little about the spirit pro, but I have had some issues with tail servos on other customer's birds.  Tune your gains, do all the normal mechanical gain checks/linkage smoothness checks, but don't rule out a tail servo either.

[curmudgeon]

OK.  That is reassuring to know that the mechanical setup is sound.   The tail servo is the BK BLS-8005HV.  I'm powering it with the Kontronik BEC at 7.5v.  I'm also using an R2 super capacitor buffer unit.   The tail servo looks to be working well on the bench, but I don't know of a good way to verify that it  is working properly doing flight.    I am going to spend my efforts now optimizing the tail tuning on the Spirit Pro.

Thank you

[Jason Cummings]

Simple things to check. Full deflection of tail blades. I've seen very experienced pilots with one or more tail blade on backwards. Servo arm too short. Too much main blade pitch. Let us know what you find if anything.

[Grimmy]

Just from my experiences, I thought my tail was all sound, and when I went up and switched into rate mode, I was far from mechanically sound.  Once I adjusted the tail control rod so I have very little drive, it was a whole new machine that I barely had any kick on punch outs.  I have a small amount, which I can tune out with pre comp......it's part of the last 10% of tuning.  I know it's there, but I choose to fly anyways and continue to grow my skills.  I tend to run a lot lower headspeeds as well.  1650 on my E7SE, and I think 1750 on my E5s with 626s.  I'm thinking about 1450 on my 806 once I get it built.

[alan]

Checking in rate mode may help sort it out but I don't typically have issues with Synergy's if the bell crank is set at 90 degrees with the tail servo at Zero.
I would suggest you rule out a tail servo issue.  First I would run your BK's at 8.2-8.4 for max efficiency.
Then I would also replace the tail servo with a good quality Futaba or MKS servo.  There have been some occasional issues with the BK tail servos.  I do speak from personal experience that...

Cheers
Alan

[Charles Carrington]

Make sure you ball on the tail servo is 16mm from center. Also how much cyclic an collective pitch

[Rchelipastor]

Hey my friend, i use the spirit FBL and ti can almost guarantee that the rudder common gain setting is set to 100 percent. for the 806 configuration, you need to set it to at least 130 percent and that will solve your problem....let me know if that does the trick...

[curmudgeon]

Hey my friend, i use the spirit FBL and ti can almost guarantee that the rudder common gain setting is set to 100 percent. for the 806 configuration, you need to set it to at least 130 percent and that will solve your problem....let me know if that does the trick...

I am first going to increase the Kontronik BEC voltage from 7.5v to 8.0v.  Based on the recommendation of a Synergy veteran, I will also swap out the current BK BLS-8005HV tail servo and install an MKS HBL-980 tail servo that had worked well on a Whiplash and an E7SE.  It certainly would be helpful to know what is the minimum tail servo torque specifications needed when spinning 806/116 blades at 1800rpm with the 5.1:1 tail gear ratio.

As far as the Spirit Pro, I would like to learn what you are using for these parameters (or recommend for me spinning 806/116 blades):

1) Rudder gain in the transmitter

2) Rudder Common Gain multiplier in the software (1.00x to 1.50x)

3) Rudder delay

4) Rudder dynamic

5) Rudder - Revomix

6) Pirouette consistency

Thank you in advance