ilasa

I have an Hirobbo Shuttle Scadeau 30 and have started with forward flight recently. Last weekend my engine stopped when I was high in the air and my heli went into autorotation and landed safely. I was surprised everything went so well because I had never tried autorotation, I just kept the machine leveled and the throttle-pitch stick in the middle position. Was I just lucky or is it the way to go?

wisdom-seeker

You were lucky. Correct autorotation requires that your blades go to negative pitch in order to "glide" and to put energy into the rotor. Just before touchdown, you go back to positive pitch to trade rotor energy for lift to cancel your fall and touch down gently.

Furyflyer2

My Feedback: (117)

You were lucky, auto's are not hard to do and are very fun. But like everything else you must practice it.

hroachen

Autorotations do not require negative pitch, but having negative pitch available definitely increases your options.

wisdom-seeker

Yeah? Without negative pitch, how do you keep your head speed up? While it does not completely support my statement, here's an authoratative reference:

http://www.dynamicflight.com/aerodynamics/autos/

siclick33

That's a good description in your link.

As you say, it does not completely support your statement. You will notice that all of the diagrams show the blades at positive pitch during auto. This is quite normal for full size helis.

I don't know how much pitch is required on a model. I guess the only way to really find out would be to increase pitch until the model doesn't auto any more. I am not volunteering to try this out though!

FBaity

My Feedback: (2)

I don't see how you can maintain head speed with out neg. pitch. Please explain how that works, thanks.

Prophex

same here

siclick33

This could get complicated if we aren't careful. It's all about vectors!

Click on the link and try and follow that.

Basically when you are in auto you have a rate of descent. This creates a 'rate of descent flow' which is the air coming up through the rotor disk. The rotor is also spinning so you have a rotational flow too (like across a wing on a fixed wing aircraft). The two vectors combine to produce a single vector that approaches the blade from below (as in the diagram).

Lift is always perpendicular to the air approaching the aerofoil (irrespective of the blade angle). At certain points along the blade where the correct conditions exist between the 'rate of descent flow' and the 'rotational airflow' the resulting lift vector is angled slightly forwards. This now has a horizontal component of lift pulling the blade round. This is the autorotative section of the blade and what stops the blade slowing down.

As can be seen from the diagram you do not need negative pitch for this to occur.

I hope someone else can make sense of my ramblings!

echobot

I have another question. When you flare just before touchdown, do you land as you are flaring or do you flare to slow down and then level off before touchdown?

Thanks

ilasa

I guess after reading all the replies to my message that I was just lucky not crashing my heli. It stopped and I just kept the pitch stick in the middle position until it landed safely. Didn't increase the pitch in any moment.
If it happens again should I do the same?

FBaity

My Feedback: (2)

The flair does two things, slows forward speed and builds rotor RPM. On my heli I am just below 0 degrees pitch in the flair and most always tuck down with no forward speed, I do slide on some times if I am stretcking for the spot.

hroachen

Flare, level off, then land. In some cases you may need to land with some forward motion and slide, but you'll still want to level off before setting down. If the machine is nose high when the skids contact the ground they will quickly force the nose down and the likelihood of a main blade striking the boom is greatly increased, since the main rotor blades can "float" somewhat in the dampeners they won't go nose down as quickly as the rest of the heli in that situation, and the rising boom can and often does meet the rotating blades.