when inverted flight is there changement of helicopter behaviour? character

[FuturaSE]

does the helicopter has another 'character' when flying inverted?

seems logical after all now all parts (weight) are at the upside or am i wrong is there really no difference?
does it react faster maybe?

i have no clue never done inverted

[tourerjim]

Not sure if its just me but inverted feels more stable

[milly0812]

when inverted flight is there changement of helicopter behaviour? character

No it's not just you, I can hold a more stable inverted hover than upright too ;-)

[450man]

OK... this is comments from a newbie so feel free to shoot me down in flames...

I would guess that it might be more stable. When it is upright the downward thrust from the blades has the body to go around creating a lot of turbulence underneath. When it is inverted there is nothing int he way of the down draft meaning the heli has a smoother column of air to "sit" on.

But then again...?

[NoFixedAbode]

Re: when inverted flight is there changement of helicopter behaviour? character

OK... this is comments from a newbie so feel free to shoot me down in flames...

I would guess that it might be more stable. When it is upright the downward thrust from the blades has the body to go around creating a lot of turbulence underneath. When it is inverted there is nothing int he way of the down draft meaning the heli has a smoother column of air to "sit" on.

But then again...?

Sounds right plus you don't have a pendulum effect. I mean if you balance a broom on your palm it is more stable with the head on top.

[Baldie]

when inverted flight is there changement of helicopter behaviour? character

OK... this is comments from a newbie so feel free to shoot me down in flames...

I would guess that it might be more stable. When it is upright the downward thrust from the blades has the body to go around creating a lot of turbulence underneath. When it is inverted there is nothing int he way of the down draft meaning the heli has a smoother column of air to "sit" on.

But then again...?

Except........ Thrust is not what keeps the heli in the air but lift generated by the blades.......

[trillian]

I have never had the sensation of a heli feeling more stable inverted but that could be because I am not nearly as relaxed as I am having to think more and my flying inverted is not nearly as precise as upright.

As a side-note, the Futura was the first heli I ever did an inverted hover with, way before I would do it on the 450 even.

[KevDavies]

I too find inverted easier than rwu. I must just be wierd

[NoFixedAbode]

Re: when inverted flight is there changement of helicopter behaviour? character

Except........ Thrust is not what keeps the heli in the air but lift generated by the blades.......

Semantics. In this case thrust is correct as the OP said flying not hovering.

[Baldie]

when inverted flight is there changement of helicopter behaviour? character

Semantics. In this case thrust is correct as the OP said flying not hovering.

Not really....
The air flowing over the blades has lower pressure on the upper surface causing lift. This is true in a hover or in ff . In ff some of the lift is lost as the angle of attack of the blades is lost by the forward pitching of the heli, which is why as you go faster and faster forward you need more an more pitch to maintain the same hight.

[tomatwalden]

when inverted flight is there changement of helicopter behaviour? character

OK... this is comments from a newbie so feel free to shoot me down in flames...

I would guess that it might be more stable. When it is upright the downward thrust from the blades has the body to go around creating a lot of turbulence underneath. When it is inverted there is nothing int he way of the down draft meaning the heli has a smoother column of air to "sit" on.

But then again...?

Don't know about shooting down in flames but as somebody else mentioned, it's the lift generated by the blades due to the Bernoulli effect the hovers the heli, not thrust. On top of that, when the right way up, the weight of the body sits naturally underneath the heli (like a pendulum). Whereas inverted, the weight of the body is balanced on the disc. So logically, the most stable orientation is right way up. (At least, in my opinion!)

[miniman]

Not really....
The air flowing over the blades has lower pressure on the upper surface causing lift. This is true in a hover or in ff . In ff some of the lift is lost as the angle of attack of the blades is lost by the forward pitching of the heli, which is why as you go faster and faster forward you need more an more pitch to maintain the same hight.

Agree 100% it is the lower air pressure that "sucks" the heli into the air, not thrust "blowing" the model around.

Peter

[450man]

Except........ Thrust is not what keeps the heli in the air but lift generated by the blades.......

You are correct in part. Lift from the blades is in part what keeps a heli in the air but there is also a significant contribution from the air displacement. We know that because if we hover low down we can see the air being forced downwards and onto the grass. So there must be a significant contribution from the air displacement which you call thrust and so my argument stands.

[450man]

Don't know about shooting down in flames but as somebody else mentioned, it's the lift generated by the blades due to the Bernoulli effect the hovers the heli, not thrust. On top of that, when the right way up, the weight of the body sits naturally underneath the heli (like a pendulum). Whereas inverted, the weight of the body is balanced on the disc. So logically, the most stable orientation is right way up. (At least, in my opinion!)

I think there is a confusion over the term "thrust" in this thread. Can I clarify my understanding...

I am a fixed-wing commercial pilot and instructor and with a fixed-wing the total aerodynamic force generated by the engines is considered as "thrust". Some of that force is created through air displacement (by Newton's third law of motion) and some generated through "lift" generated by the aerofoil section of the propeller. The ratio of these two changes depending on the speed of the aeroplane, the power of the engine, the pitch setting etc. With a jet all of the thrust is air displacement. However, my point is that in this context thrust is the total aerodynamic force generated by the engine and not just the air displacement component.

Putting that into our model heli context, the blades of the heli creates a downward "thrust" keeping it in the air. Just as with a propeller on a fixed-wing some comes from air displacement and some from lift.

Now consider what happens when the heli is moving forward... the same situation exists and the same rules apply... some "thrust" comes from air displacement and some from lift but in this case there is an extra bit of lift generated because the heli is now moving through the air, the rotor disc is moving into air that has not been affected by the heli already and so is more efficient and so more lift is generated. This is translational lift. We still have the air displacement component though. Now, because the heli is tilted forward slightly the thrust vector is no longer equal and opposite to the weight vector and there is now a component of it forward and it is that component that moves the heli forward. So we need to increase the vertical component of thrust to equal the weght of else the heli will descent. The way we do generally that is by adding a bit of power/pitch but once the heli is moving it is very likely that the translational lift will be sufficient to give us that extra thrust and so once moving we might have to reduce power again to prevent a climb.

The way I see it... there are two aspects to flying inverted which are significant... the fact that the downward column of air is undisturbed in inverted flight and also the pendulumn effect mentioned already. They are opposite in effect in that the first will make inverted flight more stable and the second will make it less so. I do not know enough about model heli dynamics to make any kind of call as to which has the most effect but from the evidence of people saying inverted flight is a bit easier and more stable I would suggest that it is the air displacement that is the most significant aspect.

It is difficult to properly explain all this in words alone and a diagram would help here... sorry.

[tomatwalden]

So here's a thought ... The blades generate most of their lift/thrust (not going to argue on that one anymore ) towards the outside of the disc - since that's where the blades have the highest speed.

Near the root, the lift generated is much smaller ... and it's this airflow that would be near the body of the helicopter. so perhaps the body of the heli is only affecting this part - where the effect is potentially smaller?