450 Trex 450L Pitch Curve

[Harford]

I would appreciate some advice relating to pitch & throttle curves on my Trex 450L Dominator (standard Align build). I am a gentle hovering & subdued forward/backward flier (ie no 3D). This heli flies beautifully although I find a sharp reaction when applying throttle, ie hovering, a little more throttle and heli climbs very rapidly. I would like to slow this down. Current throttle curve is 0 40 65 80 100. Pitch curve is 40 45 50 75 100. I have also have a trex 450 Pro (Flybarred) with the same throttle & pitch curves but it more docile in this respect (which I like). I appreciate the 450L has a more powerful motor and no doubt different gearing.

Many thanks

Michael

 

[Tony]

Before we dive into pitch and throttle curves, what is your overall collective pitch set at right now?

 

[Harford]

-/+ 11 degrees

 

[Tony]

Try lowering that down to 9 to 10 which will soften up what you are having an issue with. also, your pitch curve is fine, but adjust your throttle curve to 0 75 75 75 75. Part of the issue is not only are you adding collective pitch, but you are also adding power from the motor at the same time.

 

[Harford]

Great Tony, I will do this and report back. To digress, if you have a flat throttle curve, is there a point at which the power available (75% in this case) is inadequate for the pitch you want eg if you were wanting 11 degrees pitch would 75% power be enough ? I am sure this is a naive question (and I would never use 11 degrees of pitch anyway)

 

[Tony]

There could be a situation like that. In that case, I would just raise it up to 85% and try that. another option and a better option is to run a governor which will regulate your head speed.

 

[Harford]

I was wrong with the information I gave you about the current pitch range. It is actually +/- 9.5 degrees. I could take it down to +/- 9 degrees but not sure if this will make a material difference. Should I go lower ?
Many thanks
Michael

 

[Tony]

No, it will not make any noticeable difference. this might just be a case of learning collective management. It was quite hard for me, I know that. But it will come after a while.

 

[Harford]

Yes, I understand. Thank you again.

 

[Jimbo]

I noticed that in your pitch curve 50 is zero pitch, then it jumps to 70, 100, which could be causing the abrupt movement you are talking about. I run a seven point curve, with smaller steps and find it is much smoother. Just a thought.

Jim

 

[holtneil]

Hi mate I was like you to start off had the same sort of problems I went to a fixed head speed with a governor and this made flying so much nicer ,the only thing i found a bit scary was using throttle hold to stop and start the motor but you soon get over this

 

[Harford]

Thanks Jim - good suggestion. I have a DX9 so can do this. Could you possibly let me know the values for the 7 point curve you use please ?

Thanks also for the advice about the fixed head speed. I will need to do some research here as I have no experience with the governor function.

 

[Jimbo]

Some folks say that you have to have some negative pitch in the curve to fight wind, but I find this not to be true. The old Huey had 12 degrees positive pitch at bottom collective and it came down. Size and weight ratio are the same, so flatten the pitch and the wind has nothing to work with, so the helicopter will come down. I use to have six degrees negative at the bottom, until I got messed up one day, lowered the collective all the way and the negative pitch slammed me into the ground. So, with that said, I use 50, 60, 65, 70, 75, 80, 85.

I an still learning about head speed and governors, so I can't help ya there.

Jim

 

[Tony]

The negative pitch is for when it is sitting on the ground and the blades are spinning. If a gust of wind comes up and there is 0º of pitch on the blades, it can pick up the helicopter and tip it over. Happened to me more than once unfortunately.

 

[Jimbo]

Tony, I am afraid we will have to agree to disagree on this one my friend.

Jim

 

[Harford]

In any event, a value of less than 50 at low point with a progressive curve using 7 points overall up to 85 would be an improvement on my current position ?

 

[Smoggie]

IMHO your pitch curve looks fine for gentle flight. I think your problem is your throttle curve. The idea with a CP heli is that the rotor RPM should remain constant and 'up and down' is controlled with collective pitch change only. If you have a steep slope throttle curve the RPM will change as you move the collective stick and as those RPM changes lag behind stick movement (because the rotor takes a few moments to speed up or slow down) the heli ends up yo-yo'ing with you constantly 'chasing' it.

The best way to maintain a constant headspeed is with a governor, and that's what I'd recommend, however if for some reason you arent comfortable with a governor then use a almost flat throttle curve. If you want to maintain normal mode the curve would look something like: 0, 75, 75, 80, 85 which would match your pitch curve quite well... But like I said and Neil mentioned previously, governor is better.

 

[Harford]

I will flatten out the throttle curve, just as you and Tony suggest. The governor function is a new area for me so presently I am poorly equipped to apply this option.

Thank you for you advice.

Michael

 

[Harford]

In relation to the 7 point pitch curve, I am still trying to reconcile the established wisdom of 0 pitch at mid stick (ie 50 at mid stick) and the fact that the heli is mechanically set up to achieve this, with where the pitch curve setting at mid stick should be using a 7 point curve. Appreciate this is my comprehension problem but advice would be much appreciated.

Many Tks
Michael

 

[Jimbo]

You put zero at mid stick to do the initial setup of the head. Then you can put zero at the bottom of the curve in the TX and everything will be fine.

Jim