Hello,
I have a KingTech KT800-H turbine heli. She is about 13 lbs. I have been chasing an uncommanded yaw event when going from 1550 rpm to 1750 rpm head speed. It occurs precisely as the head speed increases and I switch from Flight Mode 2 to Flight Mode 3, as evident from the logs. I tried adjusting the gain both up and down, with the canopy off, and checked to ensure that all wiring and FBL were isolated from vibration. As you can see, I experience a rapid oscillation on the tail, and it occasionally displays an error code 106. The tail usually rotates clockwise into the rotor torque. Flies great at 1550 rpm even with the tail gain down, but the tail is a little soft. Any help or ideas are appreciated, as I have been scratching my head on this one for about 5 weeks. It's not fun when it decides to go for a spin. I really appreciate any help you can provide.
Regards,
Dana
In Events, we frequently see the event 106 ‘The required Rudder speed is higher than the model can achieve,’ which indicates that the MAXIMUM THRUST of the tail rotor is not sufficient to reach the required rotation speed or to maintain the position when the torque generated by the main rotor increases, which the tail must be able to counteract.
In the Recorded Logs, we see that shortly after the throttle signal increases above 50% (speed 2 set in the governor), the tail command reaches its maximum, beyond which it is obviously impossible to go.
This could be the reason for the loss of tail position.
This indicates that the thrust of the tail rotor should be greater, either by increasing the aerodynamic efficiency of the tail blades (greater length, greater width, better aerodynamic profile) or by increasing the rotation speed of the tail rotor.
From the vibration graphs, we can see that the maximum rotation speed of the tail rotor does not even reach 7500rpm, which is an unusually low value for a tail rotor.
Therefore, if possible, the rotation speed of the tail rotor should be increased or longer blades should be used to achieve the greater thrust required.
One thing we notice in the Recorded Logs graphs is that when selecting the part of the graph relating to flight, the average value (Avg) of the tail output signal is not around zero but is always around 12.5%, which reduces the maximum excursion (100%-12.5%) to 87.5%. It would be better to adjust the tilt of the tail blades so that with the central output signal of the tail control, the blades have a tilt that counteracts the torque generated by the main rotor. This is achieved not by changing the 90° position of the tail servo horn zero control but by changing the length of the tail control link.
Furthermore, we see conflicting information in the configuration files received.
We see that the tail gains of the flight controller are set to very low values, and despite this, the tail signal curves still show oscillations typical of when the gain is excessive.
Such low values (19%, 20%) are usually only used on micro-models where the rotor spins at 4,000/5,500 RPM and are so light that there is no inertia or delay in moving such a small mass.
Therefore, this would indicate that the mechanical tail gain is excessive and the uniball mounted on the tail servo horn be moved towards the centre of rotation to reduce the mechanical excursion because it is excessive.
However, this conflicts with the high values set in panel 9 of the Wizard for maximum positive and negative excursions which, if the mechanical excursion (mechanical gain) were high, would be very low and would need to be increased after moving the uniball. Instead, they are already set to very high values for a servo with a centre pulse of 760us.
The two things are in total contrast to each other.
Unless the maximum tail blade angles are enormous, which would cause the blades to “cavitate” in the air because, once a certain maximum angle is exceeded, they would begin to lose thrust in the air. This would be a further explanation for the tail loss.
We hope this information will help you solve your tail problems.
Hi BrainDev,
Thank you for the insight. So I have installed larger tail blades 130mm vs 115mm that were on it. Adjusted the tail rod length (now a little too short), verified all ball positions (10mm from servo center). I am still having the issue, but I did find one common denominator. It flies perfect with the canopy off. Install the canopy and instantly I have issues at the higher head speed. The FLB unit is isolated under 3m VHB foam tape and .04" 40duro urethan sandwich and has been since the original build. I have attached the logs from both flights. When it loses the tail, it jerks clockwise very rapidly, and you can see the isolation in the log file (toward the end of the flight is where it happened 324s-328s) the period is about .06-.08s. The early 100 rudder out events were me playing around with it on the ground as it spooled up. I don't believe it is a lack of tail authority as it is rotating against the rotor torque not with it. The canopy is just fiberglass and attached at 4 points. It doesn't touch anything or the wiring. Thanks, in advance please let me know if need an more information from me.
Regards,
Dana
The new files clearly show the effect of your problem on the tail output signal towards the end of the flight.
There do not appear to be any significant problems in the configuration and signal curves before and after the event.
The fact that you report that the problem only occurs when the canopy is mounted may be significant because it reminded us that an accessory manufacturer supplied, upon request and if necessary, a cover for the control units made of spongy material so that the ultrasonic vibrations sometimes generated by some turbines would be shielded and would not reach the gyroscopic sensors.
Although it is a remote possibility, it could be that when you mount the canopy, these ultrasonic frequencies generated by your turbine are “reflected” by the canopy towards the flight control unit sensors.
Although we have not seen this “accessory” on model shop websites for a long time, it is still worth trying as there do not seem to be any other issues to fix that could solve the problem:
If you have a sheet of spongy material and, using scissors and rubber glue, you can make a kind of cover/cap to mount and fit “over” the control unit, it may be worth checking whether ultrasonic frequencies are really the cause of your problem.
Otherwise, the problem could be with your tail servo.
Although the behavior of the tail servo should not change with or without the canopy mounted, unless the tail servo remains “inside” the canopy or the canopy can mechanically interfere with the cable and tail servo.
Do you have another tail servo that you can mount in place of the current one?
So I think I have solved the issue. It had to do with the sound/noise of the turbine reflecting inside of the canopy. I added some automotive sound reducion foam to the inside of the canopy and made a shell for the FBL. The intake of the turbine was “inside” of the canopy which I believe exacerbated the issue.
Thanks for the assistance this was interesting one.
Regards,
Dana