tail rotor pitch control

[astro_peter]

Hi Guys,


Being a new boy I am having some problems getting my MiniTitan E325 stable enough to fly properly and one thing I notice that could be a cause is the following:


The tail rotor pitch control on my machine is very asymmetrical. Looking from the rear of the helicopter, full right on the pitch control slider gives 15 degree pitch angle in the correct direction to counter the main blade torque reaction i.e. to rotate the helicopter clockwise. Full left on the pitch control slider gives 45 degree pitch in the direction to reinforce the main blade reaction. Centre (rest) position therefore gives 15 degree pitch in the wrong direction to counter the torque reaction and, without a large control input, to spin violently anticlockwise. To get zero pitch requires the slider to be at 75% of full right leaving only 25% of further movement right. I do not know how much pitch angle is required to just counter the torque reaction and hold the heading steady but say it is 10 degrees, this leaves only 5 degrees further movement for control in this direction but 95% in the other direction! This seems wrong to me and I suspect could be the reason why HH mode does not function properly on my model. I would have thought that, at least, the centre position should give zero pitch and preferably 5 – 10 degrees in the direction to counter the torque reaction and not to aid it! The only way I can see to achieve this is to reverse the direction of rotation of the tail rotor opposite to what the manual shows. Has anyone else found this or have I got something else set up incorrectly? Any advice would be gratefully appreciated.

[coptermanic]

That setup is wrong.

Quite correctly, you stated the requirements for with torque pitch [not much] and counter torque pitch [more].

Your slider should actually be about 1/3 way along the tail drive shaft towards the boom, if you are initialising in RATE mode to give you some tail blade pitch at start up.

For initializing in HH, which is far easier to set up as the gyro takes the guess work out of just how much pitch to start up with, make sure the slider is mid shaft, with zero blade pitch. Then after power ON, when you power up the main rotors, the gyro will apply blade angle to counter the torque for you.

[coptermanic]

......Can I also add, that when I used to initialise the gyro in RATE, I used the recommended technique of finding the "ideal" spot for the tail servo on the boom so that at start up, the tail was steady. With the servo in neutral and horn and link at 90 degrees [-ish], I moved the servo along the boom to find this "ideal" spot using trial and error. Eventually you will just "know" what pitch angle is needed.

Hope this helps.

[waveydavey]

With the above mechanical setup something sounds wrong. Are you sure you have built the tail assembly correctly Have you perhaps got the tail blade holders leading or lagging or vice versa. Most blade holders have their control balls off centre. If you have these turned round you can connect them up 180 degrees out which would give you very unequal pitch one side.

Just had a look at the manual and the control balls look as if they are on centre. Something very wrong if your off to one side to get 0 degrees

[astro_peter]

Hi – thanks for replies guys – I agree with all you say and have set up the tail rotor to sit at 0 degrees with power off. It just seems strange that it is then the “wrong” side of centre. I agree that I could have assembled it incorrectly but have looked at it long and hard and cannot see any other way that would make a difference as none of the critical parts are offset. What happens now is that on power up in HH mode it flips left about 120 degrees but does then stabilize. I wonder if the tail servo I am using is not fast enough – it is a HS-65HB with speed of 0.14 secs/60 degrees. I originally had an ACER RC C0915 with a speed of 0.095 secs/60 degrees but two of these burnt out just setting up on the bench!

[coptermanic]

Might be a tad slow. How about posting a few pics of your tail rotor setup - might help the diagnosis!!

[astro_peter]

Further to my previous post you may be interested in the way I am testing at the moment. I have borrowed the wife’s cake icing turntable and fixed the heli to that with the pitch curve set to apply no positive values so that it does not try to take off.

[waveydavey]

Hi – thanks for replies guys – I agree with all you say and have set up the tail rotor to sit at 0 degrees with power off. It just seems strange that it is then the “wrong” side of centre. I agree that I could have assembled it incorrectly but have looked at it long and hard and cannot see any other way that would make a difference as none of the critical parts are offset. What happens now is that on power up in HH mode it flips left about 120 degrees but does then stabilize. I wonder if the tail servo I am using is not fast enough – it is a HS-65HB with speed of 0.14 secs/60 degrees. I originally had an ACER RC C0915 with a speed of 0.095 secs/60 degrees but two of these burnt out just setting up on the bench!

As I said above there are no built in blade grip offsets so again there is something very wrong if mechanically you have to be way off to one side to get 0 degrees. Regardless of gyro/servo problems, speeds etc it's not right. Post some pics and let us have a look.

[astro_peter]

Thanks to you guys I have found and corrected the problem. You are quite right - it is possible to assemble the tail pitch mechanism 180 degrees out and it is a pity that the manual does not warn you of this. I disconnected the links between the pitch control slider and the blade holder, turned the rotor through 180 degrees and reconnected the links and bingo it now works the right way round with the largest pitch angle with the slider left against the boom now countering the torque reaction. It is just all down to me now to learn to fly it as it behaves just like the simulator! I must admit when I set out to make the change I quite expected it to make no difference as it is not at all obvious (to me at least) that it matters. Anyhow thanks again for your replies which have got me flying at last!