when inverted flight is there changement of helicopter behaviour? character

[tomatwalden]

....

I think it is clear to say that physically, inverted flight is less stable than normal flight. However certainly with flybarless systems where the gyros are incredibly effective at stablising the model, inverted flight is incredibly stable. With a model set with the center of mass higher up, closer to the plane of the blades, inverted flight is not noticeably different to normal flight.

Exactly my thoughts from earlier. I think flybarred models will be harder inverted than FBL as FBL models have the gyros automatically compensating for the pendulum effect.

Isnt all the physics of flight what underlying makes flight so fascinating? Great discussion in my opinion.

I agree, but you should see the look the faces of the guys at my club if I mention gyroscopic precession. I think it's clear we're in the minority!

[450man]

... I think it's clear we're in the minority!

true

[unwind-protect]

It seems to me, and correct me if I have this wrong, that you are saying the Bernoulli and pressure differential plays no, or very little part, in how a wing generates lift?

My understanding is that the Bernoulli method and the conservation of momentum method are different ways of modelling the same phenomena.

I could point you to the Wikipedia Airfoil page where it says "When oriented at a suitable angle, the airfoil deflects the oncoming air, resulting in a force on the airfoil in the direction opposite to the deflection."... and you'd point out later where it says "The pressure gradient between these two surfaces contributes to the lift force generated for a given airfoil." :-)

The difference - for me at least - is that I have an intuitive understanding of conservation of momentum, whereas my understanding of Bernoulli is purely textbook.

[450man]

Wiki is the scurge of all things technical I am afraid. Anyone can edit anything or put up anything without any experience or true understanding of the subject. I don't treat anyting on Wiki as anything other than suspect...

That aside... I think to a large extent we are in agreement but I just have a stronger recognition as to the contribution that the pressure gradient makes towards total lift. I think that recognition comes from practical experience flying real aeroplanes where it quickly becomes clear that there is something more than just air movement involved not least of which has been pointed out by Tom regarding laminar flow and the stall. If it were air deflection generating the bulk of the lift then the break up of the laminar flow at the stall would not result in such a huge loss of lift.

Another indication of this is the fact that it is not at all uncommon for top sections of a wing to be dislodged by the pressure gradient. I owned a Grumman AA5B "Tiger" and as it's wings were glued and not rivetted, we did regular inspections to the wings, especially the top surface, to ensure that it was not de-laminating and coming apart! The pressure gradient is quite significant and exerts a significant upwards force.

[dillwhacker]

PM sent

My understanding is that the Bernoulli method and the conservation of momentum method are different ways of modelling the same phenomena.

I could point you to the Wikipedia Airfoil page where it says "When oriented at a suitable angle, the airfoil deflects the oncoming air, resulting in a force on the airfoil in the direction opposite to the deflection."... and you'd point out later where it says "The pressure gradient between these two surfaces contributes to the lift force generated for a given airfoil." :-)

The difference - for me at least - is that I have an intuitive understanding of conservation of momentum, whereas my understanding of Bernoulli is purely textbook.

[Rotorhead]

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.

Nope, that is an oft repeated myth, a lack of pressure will not produce a force, lift actually comes from the DIFFERENCE in pressure between the two sides, so it is the side that is of higher pressure that is doing the work, but it can't do that work until there is a pressure difference, if you dropped the pressure on the bottom of a wing as much as on the top you've not produced any lift, it's a mistake to only consider what's going on on top of the wing, you have to consider both sides, and it is entirely possible to produce lift by increasing the pressure under the wing as much as it is by decreasing it over the wing.

When you generate lift you don't tend to only reduce pressure on the top of the wing, you at the same time increase pressure on the bottom of the wing, it's not one, it's both working together.

[Rotorhead]

Wiki is the scurge of all things technical I am afraid. Anyone can edit anything or put up anything without any experience or true understanding of the subject. I don't treat anyting on Wiki as anything other than suspect...

That aside... I think to a large extent we are in agreement but I just have a stronger recognition as to the contribution that the pressure gradient makes towards total lift. I think that recognition comes from practical experience flying real aeroplanes where it quickly becomes clear that there is something more than just air movement involved not least of which has been pointed out by Tom regarding laminar flow and the stall. If it were air deflection generating the bulk of the lift then the break up of the laminar flow at the stall would not result in such a huge loss of lift.

Another indication of this is the fact that it is not at all uncommon for top sections of a wing to be dislodged by the pressure gradient. I owned a Grumman AA5B "Tiger" and as it's wings were glued and not rivetted, we did regular inspections to the wings, especially the top surface, to ensure that it was not de-laminating and coming apart! The pressure gradient is quite significant and exerts a significant upwards force.

But in this case it is correct, the resultant lift force is the consequence of moving a lump of air downwards, which is where the downwash of the airflow comes into it.

[Rotorhead]

There are several ways of modelling what is going on on a wing, circulation, newton, and Bernoulli, although Bernoulli is actually not a particularly good way to model it, especially at any speed over about M0.3 as it starts to lose accuracy due to air compressibility becoming a bigger and bigger factor at those speeds, you need to start to add correction factors in from M0.3 onwards until 0.8, and after that it gets even worse since you're in the transonic region.

[tomatwalden]

when inverted flight is there changement of helicopter behaviour? character

With regards to the original question however, modelling of wing aerodynamics is a red herring surely? A wing works the same inverted or otherwise - it has no notion of up or down. The difference, as mentioned earlier, is gravity - not aerodynamics. Inverted, a heli is inherently more unstable due to the mass of the heli pushing down on the rotor disc, rather than pulling it from underneath?

[ModelGuard.Com]

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

I and anyone I've ever asked finds inverted hovering more stable than upright. Just to add to the thread.

[Snaaakeey]

when inverted flight is there changement of helicopter behaviour? character

We spend a fraction of our flight time inverted compared to upright. I think this perceived higher stability while inverted is due to our higher state of concentration whiles at the edges of our comfort zone. Fbl doesn't really care if we are upside down or not. It will hold the last command for as long as the hillier decay algorithm in its setup tells it to. I feel I'm just on it more when inverted.

[pgkevet]

I find inverted blance quite difficult. Has anyone tried ankle straps?

[Snaaakeey]

when inverted flight is there changement of helicopter behaviour? character

I find inverted blance quite difficult. Has anyone tried ankle straps?

You doing it all wrong! You should be balancing on your head.

[pgkevet]

You doing it all wrong! You should be balancing on your head.

Is that thumbs/pinch or toes?

[Mike Sanders]

I can stand on my head but I need a cushion on the floor nowadays. It is definitely harder than standing upright. I can't do any forward motion on my head. I can't do any fast forward motion at all. I am too old.

I am someone who is interested in the physics behind how a thing can fly, particularly helis! It is my opinion that they shouldn't but that fact this forum exists suggests they do!

I once read a quotation " It is a well known fact that helicopters can't fly. They are just so ugly that the earth repels them".
Mine must be quite beautiful!