Head Speed

[Smarty]

I hear alot of talk about Headspeed in posts i read, and just wondered if someone could explain a few things about it, Like.

How diff speeds affect flight?

How you measure it?

How would a complete beginner who has just built a 450 heli know if it is correct?

How to change it ie. Throttle curve, motor, Pinion?

I have not got my heli airbourne yet but im just trying to get head around it all.

Many thanks in advance.

Martin.

[davemh]

Generally the faster the head speed the more stable the helicopter will become but also the more responsive it will become. Too low and the heli will wobble, too high and you risk parts failing. Head speed also varies with type of flying, extreme 3D requires a high head speed, hoevering and basic circuits you would generally use a lower head speed. Also worth remembering the higher the head speed the more damage you are likely to cause if the blades touch the ground or strike the boom.

I used to measure it with a tacho fixed to a solid base which I placed under the rotor blades before spinning up. Ultimately you tend to get a feel for head speed. The actual speed is not that critical, its far more about setting up to suit the heli and your flying style.

Head speed is dictated by the throttle and pitch curves. Difficult to put this simply as they interact.
The amount of lift the rotor produces will depend on the speed and the amount of pitch (ignoring blade sections for now).
For a given pitch setting the faster the head rotates the more lift will be produced. For a given head speed (not throttle setting) the more pitch the greater the lift.
All sounds simple so far. Now the tricky bit. The load from the rotor head has to be matched to the power available from the motor.
The greater the blade pitch angle the greater the drag and thus more power is required to maintain the same head speed.
When setting up the throttle and pitch curves for learning you want to aim for the heli hovering with throttle stick in the centre (huge debate on this one) and a soft response either side of that. If you find the head speed is OK but heli is hovering with stick above centre then you would need to increase both throttle and pitch at the hover point of the curve. If you just increased pitch the head speed would drop, just increasing throttle will increase head speed.
If heli is hovering with stick below mid point then both pitch and throttle will need to be decreased at mid point.

If heli is howvering at mid stick but head speed is too low then you will need to increase throttle and decrease pitch at centre point. If too high then the reverse applies. Its all a balancing act really.

What I do is get the heli hovering ath the desired stick position and then gradually adjust the mid point curves to get the head speed correct. Once thats ok I then set point 2 and 4 (assumes 5 point curves) to give me a consistent head speed with the desired pitch response then finally points 1 and 5.

Setting up pitch/throttle curves is as much an art as a science and I would strongly recommend you find an experienced heli pilot to help with the initial set up. As I was explaining to my lad last night, heli's are a catch 22. To learn to fly one you really need it set up correctly. To set it up correctly you really need to be able to fly it.

[scallybert]

I use a governor, so I can just dial in the desired headspeed. IMO, this makes things much easier. Opinions are split on this, but you do need a good ESC.

I seem to like quite high head speeds, even for basic flying. My T-Rex 450 Pro is 3050 RPM. (Roughly corresponds to full throttle, 3S 3500Kv 13T)

[Smarty]

So what is the benifit from a linear throttle curve?

As a beginner i am prob going to be a little more than hovering so would i be best with a flat throttle curve say "0-80-80-80-80" ?

This may be a stupid question but just to help me understand!!

Martin.

[johnsandywhite]

Hi Martin. The following link may give you ALL the information you may require:-

Setting up & flying your T-Rex

[scallybert]

Hi Martin. The following link may give you ALL the information you may require:-

Setting up & flying your T-Rex

"Well, in an ideal situation, during flight our helicopter will have a constant head speed."

"Finally, I need to say a word about governors. If you have a brushless motor the ESC may have a neat feature called 'governor mode' or something similar. This allows you to determine what your head speed is going to be electronically rather than by using the throttle curve. It's a bit like the cruise control on a car. Refer to your ESC's instructions on how to set up the governor mode. Once done you don't have to worry about accurately setting up the throttle curve to achieve the correct speed over a variety of different pitch settings. Instead, and depending on your ESC, you will probably just use the throttle curve to determine the head speed and it will look something like this..."

[AcidDrink]

There are 2 schools. First is that setting throttle and pitch curves is a science, second is that you set throttle curve to 80-100% linear (maybe a governor), pitch curve default linear from 0 to 100 and go fly. I went to second school
Check this link to prevent your heli from overgearing and annihilation.

http://www.readyheli.com/headspeed-calculator.html

I certainly never touched pitch curves on my tx.