Coordinated Helicopter Flight?

[HeliSmelly]

Ok, so here's a stupid question:

First, I'm brand new just flying a Blade CX2 and a Realflight Sim.

With the Sim I've noticed something that I never knew (or thought about) before. Here's the question:
When an airplane banks, the slight slip induced causes a small side-load on the vertical stabilizer and if the pilot doesn't do anything else, the airplane will yaw in the direction of the turn. In other words, the nose always points towards the direction of travel. (I realize this may be an oversimplification but it is how I learned it in Navy flight school's aerodynamics class).

So, as I've been scootin' around in my Real Flight Sim, I noticed very quickly that a helicopter's bank and where the nose is pointing is not connected. When it banks, it just moves in that direction and in order to affect a turn, I have to keep putting yaw input all the way around the corner. Is this correct? If it is, is this how ALL helicopters fly? This Heli stuff is very strange stuff to a fixed winger.
Tim

[Daz(DJLFlapper)]

Hi,

What you have is a heli that is flying in heading hold mode, You need to use the normal rate mode setting and then it will also weather vain pointing in the direction of flight unless being affected by wind. In which case it will vain into wind.

So find the gyro gain switch and try changing it. you heli's nose should then point into wind signalling that you are in the rate/normal mode in the gyro. If when you try and bank the heli points in the same direction this would indicate you flying in the heading hold mode.

[HeliSmelly]

Ok, that makes since. Now, does the gyro somehow work to achieve this? Or exactly what is that gyro for anyway?
Tim

[chaos]

Hello HeliSmelly.

The "gyros" in use today aren't really gyros. You're probably familiar with the aircraft 'rate of turn' indicator, and full size heliclopters have them also. Those devices use a gyro. But in our RC helis this thing called a gyro is really an accelerometer, it measures the rate of heading change but not by using a gyro. It's a solid state device. There is a mass stuck to a piece of piezoelectric material, and if the heading changes this small mass is pressed against the material producing a voltage. That voltage is proportional to the rate of change in the sensitive axis. The basic gyro is therefore a rate of turn detector but without using a gyro, and it drives the tail servo in such a way as to establish zero rate of turn. But it can't make any correction unless there is an error, and there can't be any error unless the heading is changing by some amount. The basic gyro is therefore unable to hold a heading... it can only reduce the rate of change of heading. And short of any input by you, that's what it attempts to do.

The "heading hold gyro" has an additional device, an integrator, which keeps a running count of how much error there is and for how long, and that running count provides heading deviation information. The gyro is therefore able to "unwind" this accumulation of error and bring the heading back to where it was.

Either kind of gyro will fight a turn. The heading hold gyro will be more successful at it. Full size helis don't have this kind of gyro hookup and so no rudder pedal is used in turns during normal flight. In airplanes the rudder is used only to the extent necessary to overcome the "adverse yaw" caused by the differential drag caused by aileron deflection. Once a bank is established the ailerons are neutralized and so the rudder is then no longer needed. But the RC heli, if it has a gyro at all, is going to need some rudder input to cancel the efforts of the gyro in order to make a coordinated turn. In the case of a heading hold gyro you can't make a turn at all without using some rudder. But even a plain standard non-heading-hold gyro will cause the heading to lag behind where it should be, resulting in a less than coordinated ("slipping") turn. So the bottom line is, you always need some amount of rudder in a turn when using a gyro, to make a coordinated turn, and in the case of a heading hold or heading lock gyro you must use some rudder to get the turn to happen at all. And if you don't use a gyro at all you can do some mixing in the TX to reduce the workload on the rudder to some extent, but you will still end up being bothered with the rudder and it will be near impossible to fly backwards at much of any speed.

[uneverno]

Damn,
that was worth the price of admission

Thanks chaos

[nellster]

Chaos,
If you write a book, I'll buy it!

Nellster

[VermillionX]

That was a really good article. I ahve been wondering what they do and how they work. Thanks Chaos.

[HeliSmelly]

Thanks, Chaos!
When's the movie coming out?