Heli aerodynamics question for you experts.

[Chumpy]

I've relatively new to heli's and am trying to learn why they react the way they do to wind and control input.

When the heli is way up high and I need to bring it back down why does it seem to be extremely unstable when you come down with the collective trying to descend straight down?

What is the best way to descend? I am not comfortable hovering nose in down low yet so I keep the tail towards me close to to ground.

When in forward flight and you want to stop forward motion and hover, what are the control inputs to do this without a lot of bobbing about before settling down? In other word, how do you manage your collective properly during the transition from forward flight to hover?

If you haven't guessed I don't have any experienced help. I fly right outside my shop as there are no clubs or heli pilots that I know of near by.

Any help is greatly appreciated.

All the best,
Chumpy

[Deftone45075]

Forward flight gives you quite a bit of lift. When you want to stop and pull back on the cyclic the heli will climb if you don't reduce the collective at the same time. However, after reducing the collective while stopping forward flight, you will need to add some more collective to stay in a level hover since you have now lost the additional lift of FF.

[MarkWebber]

And the reason for your problem when decending in a hover is you are decending in your own rotorwash. This effect is reducing your blade effeciency and will make your control inputs sluggish. Drop fast enough and you'll find out how bad it can get. If you don't add collective early enough, you'll end up smacking the ground.

To avoid this scenerio, decend in slow circles, race track pattern or any maneuver that maintains some forward flight.

[woodturner]

Colin Mill has a great sequence of slides that discuss multiple aspects of heli theroies..

http://www.w3mh.co.uk/articles/html/csm1_2.htm

[Chumpy]

Great link woodturner! I'm a woodturner also. Are you a member of AAW?

All the best,
Chumpy

[freightrain33]

I am new to this page and I know I am a few days late to this discussion But I just can’t resist putting in my 2 cents.
Everything the other guys said is right but if you want to see what it looks like “on paper” check out this link.

http://www.copters.com/aero/settling.html

Keep in mind they are talking about full scale but in this case size does NOT mater :wink:

[Rickenbacker]

Re: loss of controll in steep descents, are you using a governor? Are you in idle up? If you lose headspeed in the descent, you have less control of your helicopter.

And yes, settling with power is an issue, but you have to descent suicidally fast before it happens, in my experience. I have experienced dynamic rollover, though, cost me a set of nice carbons :(.

[MarkD]

Colin Mill has a great sequence of slides that discuss multiple aspects of heli theroies..

http://www.w3mh.co.uk/articles/html/csm1_2.htm

Fantastic page

It will also explain to peeps why heli's tilt - which has nothing to do with the tail thrust which seems to be the be all answer to .....

"Why is my heli at an Angle" :arggg:

[Rickenbacker]

Well, it does, indirectly. Tail thrust causes a sideways drift, which is counteracted by tilting the heli in the opposite direction. Look at his diagram again :).