many questions :)

Hello,

This afternoon I was hovering on my backyard, but there was moderate wind. Sometimes the gusts became stronger and I had the impression this had an impact on the engine, like it started running at much higher RPM?
Another question, how do you know that your rotor headspead is good?
When in hover and I give a bit more collective, the tail tends to swing to the left while ascending, although when I do a gyro test with engine off, I can see the gyro counter my movements, all be it that the servo horn never moves more then half a millimeter at the end of the horn. How much movement should one have here? I have put my gyro at max gain on the gyro using the screw, and on the tx I have it at 90%. I have a hitec gy-130 gyro

Cheers

[darren_uk]

Hi tbone,

Thanks for your recommendation over on the simulator forum - I'm having a look now.

Back to your questions: I'm answering from the point of view of a real helicopter pilot (and the same goes for models):

(I've just read this post - it's quite heavy, I'm trying to give a complete answer and probably getting everyone confused - sorry if it does. Just trying to share my knowledge)

Engine running at higher RPM when gusting:

Gusts are terrible things to glider, plane and helicopter pilots. A gust can change the angle of attack of an aerofoil.

So it could be that the drag on your disc (common name for the blades as they spin around, because it looks like a disc on the top of your helicopter) is suddenly being reduced, so the engine is momentarily not having as much resistance, and is speeding up.

Tail swing when altering collective:

Perfectly normal phenomenon. As you alter the collective, the reaction against the air is being altered, hence the body of the aircraft twists in the opposite direction with different torque, hence the anti-torque rotor (the tail rotor) has to be altered.

In a real helicopter where the blades, for example, turn right to left as you see then from the cockpit (anticlockwise as seen from above) and I raise the collective, I have to apply more left pedal. As I lower the collective I have to reduce the left pedal.

Left pedal is applied in the hover, and when I move forward into normal flight, because of translational lift and the natural weather-**** effect of the tail, I find the pedals enter their "middle" position.

Similarly when I'm in a decent, I have to apply right pedal (when I'm in an autorotation, it's full right pedal as there is no torque reaction at all, full right pedal effectively "flattens" the tail rotor - it's not needed).

Anyway, back to the model: this counteracting of the tail rotor is sometimes "mixed" in the radio: as I raise the collective, I can not only see my engine throttle increasing too (extra power required) but also my tail rotor is also applied.

Perhaps this mixing is absent on your set-up? In which case you have the hard task of altering the tail yourself depending on how much collective is applied.

Well that all makes sense to me, but I still wonder : dont we have gyros on RC helis to take care of the pedaling part ? increased torque on the disk will induce swinging tail, wich should be countered by the gyro, or am I wrong ?
I do have tail/pitch mixing on my radio, al be it that I was advised not to configure it cause I allready had a gyro.

[colin]

Hi TBone,

First thing I need to ask you is whether your rotor is rotating clockwise or counter-clockwise (seen from top).

If it's clockwise like most RC heli's, then the tail tendency is to swing towards the RIGHT when throttle/collective is increase.

--> More collective, more torque, tail swings opposite to rotor direction.

Anyway, this tendency can be corrected by manually keeping the rudder from moving by YOU. Yes.... by controlling the rudder stick as you increase power or decrease it.

Alternatively, use your radio's Rudder/Collective Mix to do it.
On my radio, the Mix is roughly as follows:


Collective LOW : Rudder Mix : -10%
Collective LOW 1/4 : Rudder Mix : -5%
Collective Center: Rudder Mix : 0%
Collective High 1/4 : Rudder Mix +5%
Collective High : Rudder Mix +10%

This simply means that at Hover (Center Stick), there is no compensation done to the rudder.
If I move the Collective Up, the rudder Pitch will automatically incease up to 10% of normal pitch at full collective. And as I reduce collective, the rudder pitch will accordlingly reduce pitch as well ....

On my futaba 8UHP, this is known as Revo Mixing.

Cheers

[colin]

Originally posted by tbone
Well that all makes sense to me, but I still wonder : dont we have gyros on RC helis to take care of the pedaling part ? increased torque on the disk will induce swinging tail, wich should be countered by the gyro, or am I wrong ?
I do have tail/pitch mixing on my radio, al be it that I was advised not to configure it cause I allready had a gyro.

Do you have a heading lock gyro?

If not, setup your revo mix. This is tricky, as you need to adjust it by flying and then adjusting accordingly.

Do this on a calm day if possible.

First, hover, ensure that your gyro keeps it straight. If the tail is swinging in one direction, use your rudder trim on the radio to keep it straight.

Do a Power Climb by smoothly increasing power firmly. Observe the direction of tail swing. It should swing right (for clockwise rotating blades).

Land, and cut power. Adjust your Tail Mixing accordingly for center to high stick.

To adjust for Center to low stick. You need to hover at a higher altitude, and then reduce your stick to low (make sure you got a good idling engine or you'll be doing autorotations).

Land and adjust again.

You may need to do this several times as it a matter on trial and error. Also, different days may see this going off, but you can attribute it to change of air density etc....

ok, thanks; I will try to kick in some revo mixing tonite
whats is actually the difference between a normal (I guess mine is ) and a heading hold gyro? wich is better to have ?
I saw a movie from Jason Kraus, and the way that guy rockets his heli in the air I find it hard to believe that he does tail compensation manually

[colin]

Hi TBone,

A heading Lock gyro is exactly what the name says. It locks your heli in one direction, and you can even fly backwards and still keep
the heli pointing in the same direction.

I've not really used one before, so can't really comment too much on it.

I dont really understand what a normal gyro does then? shouldn't it counter all unwanted movements too? resulting in some kind of heading lock ? Moreover, how can I check that my normal gyro does what it is supposed to do ?