Understanding Throttle and Pitch Curves 101

[phil_br]

I am a little confused about the flight modes for a CP helicopter. My current understanding is as follows

Normal mode. CP and throttle are controlled by the throttle stick. with throttle and cp a zero when the stick is fully down.

Idle up. throttle is no longer controlled by the throttle stick but stays at a constant rate (with a fine tune on a dial or slider). The Throttle stick controls CP only with negative pitch at full down, zero pitch in the middle and positive pitch at the top

Throttle hold. Throttle is switched of for auto rotations and as a safety switch.

My futaba set has the ability for three different idle up modes but I am not to worried about that yet.
Have I got this right. Especially normal mode or in normal mode is the CP at zero at 50% stick and below?

[ArchmageAU]

Originally Posted by phil_br

I am a little confused about the flight modes for a CP helicopter. My current understanding is as follows

Normal mode. CP and throttle are controlled by the throttle stick. with throttle and cp a zero when the stick is fully down.

Idle up. throttle is no longer controlled by the throttle stick but stays at a constant rate (with a fine tune on a dial or slider). The Throttle stick controls CP only with negative pitch at full down, zero pitch in the middle and positive pitch at the top

Throttle hold. Throttle is switched of for auto rotations and as a safety switch.

My futaba set has the ability for three different idle up modes but I am not to worried about that yet.
Have I got this right. Especially normal mode or in normal mode is the CP at zero at 50% stick and below?

Close, but not quite.

For a collective pitch RC helicopter, in all modes (normal and idle up), both throttle and collective pitch are controlled by the throttle stick. The control the throttle stick sends has on throttle and collective is controlled by curves you program into the transmitter.

Lets ignore collective for the moment.

For a normal mode, the throttle curve usually starts quite aggressive. Zero to half throttle for the first quarter of the throttle stick movement, then to three quarter throttle for the next quarter, but then stays at that speed for the test of the movement of the throttle stick from half to full.

For Idle up modes, even at low stick the throttle is near full. If using a flat idle up throttle curve, the throttle is the same speed for all positions of the throttle stick. For a V idle up curve, the throttle is highest when the throttle stick is at the low and the high extremes, but less in the middle.

I will not go into governors.

Lets now ignore the throttle curve and look at the collective/pitch curve.

For normal mode, the pitch curve usually starts with a little negative collective, and increases to 0 collective when throttle stick at mid position. The pitch curve then applies increasing positive collective through to full positive collective at full throttle stick. Certain scale setups move 0 collective further towards low stick throttle stick, but usually the advice is to hover above mid stick, not at mid stick or below.

For Idle up modes, the pitch curve usually starts with at full negative collective, and increases to 0 collective when throttle stick at mid position. The pitch curve then applies increasing positive collective through to full positive collective at full throttle stick. The usual idle up curve most use is linear (straight) from full negative to full positive.

Now lets combine the two.

These curves operate in pairs throttle and pitch curves work at the same time (but work on the different aspects). If in Normal mode, the helicopter uses simultaneously a normal pitch curve and a normal throttle curve.

Thing to remember is that at greater pitches (angles fro 0), the blades experience greater resistance. This is often why throttle curves increase (like a V curve) as the pitch incerases.

Hold is primarily a way to idle the motor (so it n longer sends power to the blades). On an electric RC helicopter this is engine off, for a combustible fuel (nitro/gasoline) RC helicopter, this means engine idle (not off). A lot of transmitters allow you to set a separate pitch curve for the hold throttle curve (or value). Also for RC helicopters powered by combustible fuel (nitro/gasoline), there is often a separate switch/button to stop the engine entirely (instead of just idle).

In a full scale helicopter, pitch and throttle are handled by separate controls (often lever for pitch and twist handle on pitch lever for throttle). As it is impractical for RC helicopters to control by this method, the hobby had adopted the RC plane controls and adapted pre-set curves to control two channels from the one stick.

So your Futaba has three non-hold throttle/pitch modes (known as idle up modes). How you use them is up to you (you can have three normal node combinations if you really want).

Hope this clarifies things.

[phil_br]

ArchmageAU Many thanks. That is a great expiation and has helped me out a lot.

[kriswithak]

If pictures tell a thousand words then Words and pictures together tell the whole story.
Thanks very very much for this resource. Kris

[#1Nubie]

First Post... Wahoo!!

[airgoon]

Great thread, guys, thanks!

I just did my first re-assemble of my v911 (replacing some worn parts) and wondered what to do with the swash plate. The model came with the swash plate skewed to one side but it was easy to fly overall. After re-assembling the whole thing I decided to adjust the swash plate to be properly level, because one would think that's how it has to be. But now it's harder to fly. Why? this post beautifully explained the sideways push of the tail rotor and suggests that some actually skew the swash plate to one side to compensate for that - there's the explanation right there and I didn't have to post my question about this problem.
Thanks guys for looking after us newbies with informative posts like this

My two cents worth...

[mazar83]

Awesome video! Thanks so much!

[XY-FELLY]

Originally Posted by DebianDog

Bob uses a few radios and paper to make this an easy concept

Thank You man. great stuff. now I am good to go

[htse]

Well i followed everything, although i use a different transmitter everything was able to be followed easily. THANK YOU for doing this. now i need to figure out what are gains. and learn more about the rudder more. just built my first heli - 450L, looking into flying it this weekend!

[ChopperFreak]

Hi! I started watching Curves 101 and it references another video. Is this part of a series? Can I start at the first video?

What's a "servo?" (this last question defines my whole post)

[ArchmageAU]

Originally Posted by ChopperFreak

....
What's a "servo?" (this last question defines my whole post)

Servos (also RC servos) are small, cheap, mass-produced servomotors or other actuators used for radio control and small-scale robotics.

https://en.wikipedia.org/wiki/Servo_%28radio_control%29

Servos control movement of the swash plate an the tail slider on a CP heli. They control the movement of control surfaces on planes and gliders. They control searing on RC cars.

Each is drive by a continuous signal telling the servo how far to move the actuator. This signal is repeated many times a second (50 or more) and the servo tries to keep the actuator as close to the signal's request as possible.

Inside a servo there is a method for identifying the position of the actuator. this way the servo knows if it needs to move the actuator forward of backward to obtain the desired position.

The servo signal often lines up to "channels" in the transmitter. Before FBL and flight control units, they always lines up with channels.

Hope this helps.

[woodchip25]

The video was very helpful. I thank you very much on behalf of the newbie crowd,

[Bigsby]

Just Brilliant

Thank you SO MUCH Bob

[rossmoney]

Hey y'all! new here...

just got a hobbyking assault 450 RTF.

flew great out of the box until I laid it down (blades stopped dead in the grass)
Had to replace a DFC arm and the whole swashplate (it became unbalanced from the impact)
Now when i'm flying it, It spins so much that even with sub trim at 100% right and main trim all the way right it still spins a little bit (and now obviously i have a lot of push to the left from all the rudder trim.)

Wondering if I put something together wrong, or if i can adjust some ratios to compensate for the rotation. Thanks so much for your time!

[soulman994]

Originally Posted by rossmoney

Hey y'all! new here...

just got a hobbyking assault 450 RTF.

flew great out of the box until I laid it down (blades stopped dead in the grass)
Had to replace a DFC arm and the whole swashplate (it became unbalanced from the impact)
Now when i'm flying it, It spins so much that even with sub trim at 100% right and main trim all the way right it still spins a little bit (and now obviously i have a lot of push to the left from all the rudder trim.)

Wondering if I put something together wrong, or if i can adjust some ratios to compensate for the rotation. Thanks so much for your time!

Your DFC arm is not correctly installed. You'll have to check to make sure that at Mid-stick that your blades are at 0 degree of pitch. I did the same thing recently on my 500.