davidank

Is this correct thinking??

I didn't have much time with the holidays to mess with my 1st heli a honeybee cp2, but after I get the heli in the air, if the throttle/pitch is positive the heli will continue to rise in the air?

When I take the throttle/pitch back to zero pitch the heli should hover there with the same altitude and I just need to adjust the right stick-main blades to keep it stable?

Thanks!

-David

Jellyson

You wish.

Just kidding--think of it this way. The helicopter is like a marble on a sheet of glass. Pretend that you are holding a can of your favorite beverage in your right hand. Now put that sheet of glass on top of the circle formed by your thumb and forefinger. Put a marble on the sheet of glass. Now, walk around the room, keeping the marble exactly centered on the sheet of glass.

Now, think of doing that while alternately rubbing your belly and patting your head with your left hand, and that's pretty much what you have to do to keep a helicopter hovering in one place.

The left stick (throttle/collective) is like a thrust generator. When you have generated just enough thrust to offset the weight of the heli, it rises. A tiny bit more thrust and the heli climbs, quickly. A tiny bit less thrust, and the heli drops. Quickly.

And all radio manufacturers have conspired to make the correct throttle setting for hover occur at a point exactly between two of the throttle detents.

If this is really your first heli you will benefit greatly from RADD's (no joke this time.)
http://www.dream-models.com/eco/flying-index.html

Bing117

Hello,

Congratulations with your new gift. Helicopter models are tricky, difficult, prone to crashes, beset with all sorts of trimming problems which can be hard to figure out. If you're not prepared to put quite some time and a fair amount of money into it - forget about about and do something else. The money is needed for spare parts, upgrades and the helicopter number two which you will soon decide you need badly...Money is also required for auxiliary equipment (extra battery packs, a better charger, training gear, tools, special tools like e.g. a pitch gauge etc.)

RADD's school of rotary flight is great - consult that. I can also recommend Electric helicopters beginners guide (should be easy to google).

By their very nature helicopters are dynamically unstable, i.e. they will not stay a course not to mention staying in hover, they can move in all directions and require CONSTANT use of the controls. While a RC plane might be said to require effort to crash a helicopters requires a lot of effort not to crash.

Good luck,
Bing117 (a Danish heli newbie still trying to hit his first decent hover - pictures of my second heli attached)

Jellyson

To answer the question about pitch in hover, lift of an airfoil, like the main blades, is related to airspeed and angle of attack. When we say "pitch angle" we are roughly referring to the angle of attack of the blades. If you have zero angle of attack, you will have zero lift, no matter the airspeed (rpm). This should be pretty obvious to any kid who has ever held his or her hand out the window of a moving car.
So if you set zero pitch, you will drop out of the sky because you are generating no lift.

And technically speaking I think most of the helicopters we will encounter are actually not dynamically unstable, but rather "neutrally stable" or astable. This is the idea that I was trying to convey with the sheet-of-glass analogy. A dynamically unstable analogy would be like balancing a marble on top of a bowling ball. Dynamically unstable aircraft need computer assistance to be flown by human beings.
Most fixed-wing aircraft are positively stable, they return to a trimmed attitude and require force on the controls to deviate from that attitude. Acrobatic airplanes, and helicopters, are designed to be neutrally stable, hence they keep doing whatever they are doing until something changes it, like a control input or a gust of turbulence. They require very little force on the controls to change attitude, and will not spontaneously return to a trimmed attitude, but will not "diverge" like a truly unstable aircraft will.

Jellyson

Hey Bing, what kind of heli is that? Looks pretty cool, with that canopy it must be pretty easy to see at a distance (always a big problem for me!)

davidank

I will have keep adjusting from positive to negative pitch (keep going up and down on the throttle) to keep the relatively same altitude?

If I keep the pitch positive to keep it from crashing back down to the ground the heli will keep rising so I will have to then give some negative pitch to keep the heli going too high, then positive, etc, to keep it generally the same altitude?

Thanks for the info-I am just anticipating what to expect.

-Dave

HeliTB

davidank...If you set your pitch and thtrottle curve just right you maybe able to achieve the affect your looking for. Keep in mind the slightless wind can cause the Heli to rise or fall, so we have to constantly input for thrust.

Jellyson

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Dave I think you have the wrong idea about "negative pitch". As i said earlier, at zero pitch the blades don't produce any lift. As the pitch goes positive, the blades start pushing air down, more and more as the pitch increases positively. Until at some combination of positive pitch and throttle rpm, the lift equals the weight of the helicopter and it lifts off. A bit more throttle/positive pitch and it climbs, a bit less throttle/positive pitch, and it descends.
Negative pitch, on the other hand, actually makes the blades blow air _UP_. So if you add negative pitch while you are in the air (rightside up) you will _slam_ into the ground even faster than if you were simply falling.
Negative pitch is used for flying upside down, mostly.
So yes, you will constantly be adjusting the left stick (throttle/collective pitch) to keep the heli at one altitude during a hover, because the air is turbulent, the heli's power changes as the battery charge decreases, and various other factors.
But you will never need negative pitch while hovering normally. You will be adjusting the left stick around some positive pitch value. But you don't really have to think about this to fly, you just learn to move the left stick according to what you want the heli to do.

davidank

Makes sense, thanks for the thorough info!

Bing117

Hello Jellyson,

The point of the paint scheme is exactly to make it a bit more easy to see what direction the ship is heading: The right half is green while the left half is red. This is inspired by the lighting on ships where green = starboard = right and left the other side. On a Corona 120 this is very easy as the canopy is delivered in two halfes anyway so I just painted those two before assembling them.

Best regards,

Bing117, Copenhagen, Denmark

Bing117

Hello Jellyson,

Thank you for your thoughts on heli stability. You obviously know a lot more about the subject than me. But I honestly don'y feel taht dynamically unstable inevitably means out-of-bounds for human beings. I like the picture of balancing a tennis ball on top of a football - difficult but not impossible. Dynamically unstable refers to the fact that any given equilibrium will only be temporary - this corresponds very precisely with my experience with RC helicopters so far. It is difficult to hit the equilibrium in the first place - and it will not maintain itself.

Best regards,

Bing117 Copenhagen, Denmark

bilboa

David,

If you want a heli which behaves more like your original description, i.e. has positive stability, get a coaxial rotor heli like a Blade CX(2). These are very fun for flying inside your house or office, and will hover hands off once trimmed correctly. These are mainly for indoors since they can't tolerate much wind. They can't do a lot of the things that a conventional heli can do, but unless you're a really expert flier you'll actually be able to do more with a coaxial heli in a space as small as a living room. It's only when you go outside or into some gym-size indoor area that a coaxial heli starts to feel limiting.

As far as the neutrally stable vs unstable question: I'd say that in principle helicopters are neutrally stable, but in practice, micro helis behave as if they were unstable. Maybe in a perfectly calm environment, where somehow even the air coming from the rotors wasn't creating any turbulence around the heli, it would exhibit neutral stability. In practice though a micro heli is constantly being upset by air currents, not to mention the fact that most micro helis aren't made from extremely precision parts. So to go back to the "balancing a marble on a sheet of glass" analogy, for micro helis it's as if your kid brother were standing nearby randomly tapping on the sheet of glass from time to time while you're trying to keep the marble still.

Jellyson

Soo right. Darn that kid anyway.
and throw in those random fluctuations in gravity, and there you have it...

Did you see that photo of the guy riding a unicycle while flying a heli? I'll bet he was chewing gum, too.

davidank

Thanks everybody for the info! I don't want a heli like a coaxial, I was just looking for some opinions-info on what to expect when the heli is in the air, since I never got to that point yet. I only have messed with my honeybee cp2 on y kitchen floor and there isnt much room for my experience to get it into the air without risking hitting something. I mainly was trying to understand, the question of when the heli gets into the air, once the throttle is at a certain position adn the heli is 'hovering' is it simply a matter of keeping the throttle in that position and the blades i n that certai pitch and the hali is basically going to stay at that altitude and the ansers above seem to point to no.

Thanks for the info, once again everybody!

-Dave

Jellyson

Why don't you want a coaxial? I have 2, a stock Blade CX and another souped-up one with hotter motors and some other mods. They are great fun to fly around the apartment when the weather is too bad for outdoor flying. A lot of more experienced pilots keep one or two around just for practice and fun flying. The coaxials will fly when the bigger helis have to stay on the shelf collecting dust.

davidank

hmmm,,,jellyson that is a good idea, lol. I will get one wometime then, but after I practice on my CP2 some.