Autorotation with shuttle zxx

Hey,

I was wondering, when I have both my rotors running on the ground (main and tail) and I move throttle to idle, the tail rotor stops spinning quite fast. does that mean I will never be able to do auto rotation with that machine? I have a belt drive that powers the tail rotor, but the main rotor does not seem to be connected with it.

You can still do autos even if your tail doesn't follow. It just won't allow you do to any pirouets during an autorotation.

The tail driven autos is something of the last 5-10 years invention I belive. Back in the late 80's aerly 90's most helis came without a tail driven auto rotaion unit.

Just make sure you learn nose in flying and hovering before you start practicing!

[darren_uk]

Hi tbone,

You might have missed another article I did about autorotations (I think it was in response to someone asking about "Collective or non-Collective").

In response to your query:

Again we see real similarities in the way the model helicopter flies and the way real helicopters fly,

First to clarify something: An autorotation in a real helicopter is a perfectly normal maneuver. Whenever I take a passenger out to experience helicopter flights, one of the things I will do is demonstrate how the helicopter can fly in the event of an engine failure.

However, one or two more nervous people explain they don't want to see! So I do the following:

(You'll see where this is going in a second tbone!)

Obviously they've already experienced climbing (we took off from the airport). And now they're in level flight. So far so good, then I want to decend so I start a gentle decent.

However what I do is gradually increase my decent rate (keep lowering the collective, whilst keeping the airspeed constant using cyclic (you need back cyclic as the collective is lowered because the nose tends to pitch down as collective is lowered).

I continue to lower the collective until it's fully lowered.

Hey guess what? Looking at the instruments we can now see the engine is no longer driving the rotors! (there are two needles on a helicopter amongst many others: one for engine speed, one for rotor speed: normally the two are together, but in an autorotation the "Needles are split" showing the engine is no longer driving the main rotors).

So I say to the passenger, "Look, we're still flying, I can still turn, but the engine is no longer flying the aircraft! This is what would happen in the event of an engine failure, and I can even land it like this".


BACK TO YOUR ANSWER: When climbing away, there's a lot of lift, so a lot of torque (the blades spin one way, the body of the aircraft wants to spin the other because to every action is an equal and opposite reaction). So to prevent to helicopter from yawing the other way the tail rotor is used to "blow" the tail back in line.

In a decent, less lift is required (because we're coming down) hence the torque reaction is less: the body wants to yaw less, so less rudder is used.

IN AN AUTOROTATION: there is *no* torque reaction (because the engine is no longer driving the engine, so there's nothing to react against) hence the ruddle pedal is not needed at all. So I need to give *full* right pedal (for an anticlockwise rotating main rotor - common on full-size helicopters) to flatten the tail rotor because I don't need the anti-torque at all.

(in a full-size helicopter, the tail rotor is connected to the main rotor via a gear box: the main rotor is what's driving the tail rotor in an autorotation. Different from a model heli where the tail rotor is almost always driven from the engine - hence when the engine stops, the tail rotor stops - you don't need it anymore)


So what keeps the helicopter going in a straight line when the engine stops? The natural weather-**** effect of the helicopter's shape.


Get a book on autorotations, but effectively the reaction is:
*immediately down collective* - if you don't, the rotor speed will decay in a matter of seconds and the heli will fall. In a real sized helicopter, the pilot has about 2-7 seconds to do this (depending on how heavy the main rotors are - the heavier, the more time)
* Maintain the speed and direction of the heli with cyclic: you will need back cyclic to prevent the nose from pitching down (and a little left or right cyclic - another aerodynamic phenomenon with helis)
* near the ground, ideally flare the heli. This reduces the rate of decent and also (curiously) increases rotor speed so you get more energy to play with.
* LEVEL the heli just before the ground to prevent a tail hit and a boom strike (if the tail hits, the heli will level suddenly, the main rotor won't be able to keep up, and the two will meet spectacularly - I've seen it on my model)
* use the remaining energy in the main rotor to cushion the landing: raise the collective.


The flare isn't necessary, but it helps a lot. If it's not used, the timing of the raising of the collective is more critical. If you find you're flying in the early stages of your training (and therefore cannot do normal approaches) and you get a dead donkey, just lower the collective and do your best to raise it at the right moment near the bottom. For goodness sake, just make sure you get that collective down as soon as you hear the buzzing stop: react, and think about it later. If you think about it first it's too late, just relax and watch your bird fall to the ground and break.

However, later in your flying, you'll learn how to do approaches (decent ending in a flare (which is the term given to raising the nose and arresting the decent and forward speed) back into a hover, and then land. This will help when landing after an autorotation.

thank you darren_uk. This has made clear a lot of stuff at once