Triple XXX

My Feedback: (1)

While hovering my Christmas bird (Hawk Sport) at about eye level, an instant pirouette happened. I landed and realized the set screws for the drive wire must have come loose. After inspection this was confirmed.
Completed the repair, confirmed gears in tail rotor looks great, drive wire looked great, entire assembly put back together no problem.
However, upon spin up just before lift off, the tail rotor started acting funny, sudden snap pirouettes to the right, full left correction only slowed the rotation down until about 3 rotations completed and then she started the left pirouette from the left rudder input. Checked trimmed, confirmed gyro was working correctly and made a dozen more attempts with the same result. It always happens just before lift off.
Run up engine, stick just at mid throttle, 5 degrees positive pitch, just as she is lifting off I get a sudden snap pirouette to the right.

What’s happening? Feels like the tail rotor is having issues but everything checks out. Consistent rotation of the tail feathers so it does not look like it slipping but it sure is acting like it. Gyro appears to be working correctly.


Any suggestions would be very helpful.

Thanks
jack

bdphil

My Feedback: (26)

Jack,

I'm not familiar with that heli, which way does the main rotor turn? I ask because if the piro problem you're having is opposite of the rotation of the main rotor you may still have an issue with the tail drive slipping.

I don't suppose you could see what the tail servo was doing at the time of the piro's? If the piro direction is the same as the main rotor direction, you may have a gyro/servo problem or radio glitch.

I don't suppose there is any way that the tail isn't turning the correct direction or the tail blades (and/or grips) aren't assembled correctly? I was helping a guy who had a piro problem and it was that he had the tail turning the wrong way (long story, but didn't take long to solve that one).

Are you sure the tail drive wire is inserted into the drive fitting correctly at both ends? You may not have them engaged completely and the set screws don't have good contact. Is the gear mesh correct on the main gear/tail drive gear correct? What about the gear mesh in the tail gear box? Do you have all the gears properly fastened to their shafts (tail output shaft, front tail gear transmission shaft)? Are you using Loctite on all of the set screws? Are there flat spots machined on the tail drive wire, tail output shaft, etc? If so, are you sure the set screws are engaging them properly?

These are just some of probably a thousand things you should ask yourself. It's usually pretty easy to find mechanical problems, hopefully it's not an electrical problem.

Ben

Triple XXX

My Feedback: (1)

The heli is a simple 30 size with a wire drive system to the tail rotor. The rotation of the main rotor is Clockwise, the unscheduled piro is Clockwise. We can see the rudder servo in action as the canopy is clear, it moves when the heading of the heli is shifted and then quickly returns to zero. The radio is a Futaba 9zwc, my guess is that the transmitter is working correctly as it is used on multiple models without issue. Confirmed battery on TX and RX are fully charged, LCD readout on TX and 100mAh load check on RX.
I have checked the rear gear mesh, looks good. Locktite is used on all Metal to Metal screws, rechecked on the rotor. The rotation of the rotor must be correct as this has about 30 mins (2 tanks) of hover time when things were trimmed and almost a hands off stable hover. All the gears on nylon and have pins through the shafts, all set screws have been double checked. Drive wire engagement at the rotor is set screwed. Drive wire engagement at the main body is square drive and fully engaged.

So I think we are on the same train of thought,
1. Rotor is inducing a clockwise pirouette
2. Could be a radio glitch, very un likely but possible
3. Could be part of the rotor drive system ( pulling apart again tonight to ensure everything is correct)
4. The only thing that changed from a good hover to pirouette queen is the darn rotor drive wire set screws; otherwise I have made no changes.
5. I agree completely mechanical issues are predictably easy to reproduce and find, electrical glitches are not as easy.
6. The pirouette happened at 2 different locations so RF interference is taken out of the equation.
7. All the teeth in all the gears driving the tail rotor look brand new.
8. I did notice the mechanics that move the rotor pitch is a bushed system, verses a ball bearing system so some drag could exist.

I will keep looking
Thanks for reading this
jax

rwainw

Jack,

In reading your second post here, you say that the rotor direction is clockwise AND the piro is clockwise. Unless I'm completely mistaken (always a possiblity ), if the t/r was failing/slipping then the piro would be counter-clockwise. That would lead me to believe either a gyro issue or something reversed in the radio set-up. Food for thought anyway. Good Luck.

bdphil

My Feedback: (26)

Barring any discoveries of mechanical problems, it's beginning to look like the gyro/tail servo is causing your problem. Losing rpm's in the tail rotor (slipping, etc) would cause the heli to piro opposite the main rotor direction. BTW, is the tail completely letting loose, or is it like the tail kicks out then recovers? Does the engine sound smooth or are you hearing a different note when the tail kicks? Sometimes a rich engine can cause a tail twitch (generally not a severe twitch though).

Did you have any crashes or have the tail hit the ground before this problem? Not likely, but check the gears in the tail servo just to make sure they're not stripped or missing teeth. Check you're servo/gyro wire routing, maybe passing too close to the engine and picking something up. Make sure none of the wires have been abraded by rubbing the frames, etc.

Possibly try a different gyro/servo if you have access to one.

You may not have inteference from the location you're flying at, but could be getting a signal generated by the heli itself. Bearings that are wore out can cause RF noise. Gyro's are so sensetive that you often see it there first.

Ben

siclick33

Just to confirm, you say that the rotor spins clockwise and heli spins clockwise. If that is 'rotor spins clockwise when viewed from above' and 'tail pirouettes left' (i.e. nose to the right) then you do not have a slipping tail drive. Friction caused by bushes in the main rotor drive system should only show up during autos (if at all).

If this is correct then you have too much tail rotor power.

This can be caused by

a) gyro reverse set back to front (check that when you do your tail rotor servo check that the servo opposes the rotation. It is not enough just to check that is is moving). This is unlikely if you have flown the model ok before but is not unheard of.

b) Might be worth checking that the tail rotor neutral point is correct. Check the manual to see where the tail rotor linkage should be when the controls are in the centre.

c) Check that the tail rotor reverse on the radio is in the correct direction. (again not likely if you have flown this model OK before (with this transmitter) If you have to change this, recheck item (a))


Still a little unclear on the symptoms.

If you let us know more, such as

a) does it rotate as soon as you lift to the hover?
b) do you get it into the hover and then it pirouette?
c) does it happen all the time, is it a smooth rotation or an aggressive kick?
d) what gyro are you using (is it in Heading Hold mode or rate mode)?

we'll see if we can help

Triple XXX

My Feedback: (1)

OK stayed up till midnight and rebuilt the entire boom and rotor section in hopes that during the inspection I would find something. I found a couple little things, 1. the pushrod for the tail rotor pitch was not as smooth as I would have liked but not bad and 2 the bushing that slides on the tail rotor main shaft did not move as smooth as I would like.
Changes made:
new tail rotor pitch servo (S9001)
polished the tail rotor main shaft in the drill press with 2000 grit and WD40

To confirm some of the questions
the pirouette is clockwise, it is sudden and only happens on lift off. It is consistent as it has been duplicated a dozen time playing with rotor pitch and trims without improvement.
Helicopter is only a couple weeks old, no crashes or strikes of any kind ( I can hover base on prior heli experience but thats about the limit right now)
All the gears and bearing for the drive system to the tail rotor and all the tail rotor bearings have been confirmed perfect condition
No missing teeth on any of the gears
Noticed the TX antenna was a little close to the remote nicad wire but not super close, (relocated to ensure I was not getting any hits off that)
I did change the tail rotor servo with brand new
I am not sure that changing the gyro after the bird was flying perfectly is in the equasion right now, I guess if the problem persists, I will need to try another gyro or playing with the settings. (Gyro is the century pg2000 in stock settings)
Reverified the neutral point in my reassembly last night
Reduced the overall throws of the tail rotor (in hope that I could walk up to the pirouette if it still persists)
Radio and rotor reverse direction I dont think is an issue as the heli was hovering

It does piro just as I am lifting off the ground
the engine is very smooth
the tail rotor rotation is consistent from a view perspective
gyro is the $80 jobby not the head lock one

Today I will see if the changes and clean up worked and post the results

bdphil

My Feedback: (26)

What gyro brand/model are you using? If it's not heading hold, are you using revolution mixing? Are you setup to hover at half stick (most rev. mixing sttings are initially set to operate from a half-stick hover).

Ben

Triple XXX

My Feedback: (1)

The gyro is the Century PG2000, no heading lock, seemed to work fine before yesterdays event. Futaba 9zwc radio in heli mode,,, wish me luck, will try the new set up in the next few hours

siclick33

I'm determined to help you here!

Just checked out the century website and their instructions for setting the tail neutral are misleading.

I forgot to check if they do a quick build (ARTF?) kit and a full kit but they have two sets of instructions. The setup instructions are different for each, although the heli is the same. The full instructions also contradict themselves (The text is different from the diagram!).

What version do you have? What have you set the tail pushrod length at (measured from where?) and what angle is the tail rotor bellcrank at? (as per the diagram in the manual).

Obviously all measurements should be with the tail rotor at neutral (and leave the throttle in the centre position to negate the effect of any revo mixing set)

Triple XXX

My Feedback: (1)

Problem Solved !!!!

This is a true example of a Rookie Move. Remember back in the first description of the clockwise pirouette? The set screws came off the drive wire. Once the set screws were tightened back up the problem started. What I forgot to mention, because I had no idea it happened is this.

Radio, Futaba 1024ZAP, Toggle switch F (top of radio, back left, 2 position switch)

This switch when viewed from the servo menu on the radio monitor moves channel 6, “gyro setting” from 100% positive position to 100% negative position when the switch is moved from front to back.

It was an assumption of mine that when you moved the nose of the heli from side to side, a visible compensation to the tail rotor pitch would been seen on the servo. With the switch in the full negative position, this movement of the servo is visible. With the switch in the positive position, it does not look like it compensates, or at least if it is the correction is so small that you cant really see the servo move.

Upon first flight after I went through every piece of the tail rotor and linkage including changing to a new servo, I spun the heli up and it appeared to be working, however I put the collective pitch servo horn on wrong (or at least not in the same place I had it before) and I did not have enough positive pitch. While changing the servo horn placement and setting the pitch angle up, it dawned on me that switch F turned on or off the gyro. Or so I thought. At this point I may have moved the switch to the negative thinking I needed to see the rotor pitch compensation on the servo.

Second attempt, fired up, spun the main head up, everything looked great, started to lift the heli off the ground, beautiful snap triple pirouette in the clockwise direction, I was so pissed I thought turn the gyro off, so I flipped the F switch and she came off the ground, smooth as silk tail rotor response, a couple of clicks of trim and this bird is hands off hover with the throttle right at middle throw.

I am so tickled pink!! A Boat racing friend came by with my brother and watched us play with it for hours. Its amazing how easy helicopters are to fly when they are trimmed correctly. Now all I have got to do is figure out how to disable switch F.

Thanks a million to all the helpful folks and the constructive suggestions. A lesson learned and I think with all the rebuilding of the rotor pitch assembly and pushrod linkage I actually got a much smoother and predictable tail rotor response. I am so happy what a fun toy!!!!!!!!!!!!!!

I should probably ask now, what is switch F doing to the gyro setting in the positive and negitive position?


jax

bdphil

My Feedback: (26)

Aren't these thing so much more fun when they are working correctly

Glad you got it worked out! You should be able to disable that switch in your tx. Depending on your programming and where you have the remote gain plugged into the rx your switch might be changing the gain settings rather than turning the gyro off/on. I'm not familiar with that radio, but on my 8U I have the remote gain function set to the idle up switch so that when I switch between flight modes the gain settings are switched accordingly.

Ben

FLYBOY

My Feedback: (11)

Just found this thread and was going to ask about that. What I tend to do is set mine up so that all the switches start away from me, unless I want something on. When I pick up the radio, I push all the switches away, then turn on the things I want on. That way, no matter what plane I fly, I have to look at it and make sure it is set the way I want it.

The only problem there, is when you have 10 planes in memory, remembering what switch you want on.

Glad you got it fixed.

grittykitty

I hear ya, Flyboy. I have 5 models in my 9C (4 planes & 1 heli), and I have to do a COMPLETE pre-flight just so I remember where I have set what on my switches. Some things remain on a constant switch, no matter what the aircraft (throttle cut, triple rates), but something like my Razzle 3D, where I use flaperons, ailevators, elevator/flaperon mixing, etc, I have to remind myself where I put everything!!