when inverted flight is there changement of helicopter behaviour? character

[trexamanic]

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...?

doesnt the heli then suffer from the air being drawn down past the body causing turbulent air?

[450man]

You are right abut symetrical sections producing no lift at zero degs AofA. That is the same for symetrical wing sections on fixed-wing planes as well as heli blades. My point was that the bulk of lift is generated by pressure differential and not air deflection.

As for your second point... you are not thinking in terms of couples. When you have two forces that are not aligned exactly opposite they create a turning moment called a couple. Follow my example through with the string and you will see exactly what I mean. The pendulum effect is a direct result of this couple and nothing else so yes it will pendulum... when either way up... but it will always pendulum to being non-inverted and that is the problem.

[FuturaSE]

TX for info and answers did read whole topic however im still digging a hole through all this

[450man]

Yes, we have got rather theoretical haven't we - sorry.

All this theorectical talk is interesting and fun but it doesn't actually answer the OP query... specifically, is inverted flight easier or more difficult that upright flight? Perhaps we should pull the discussion back to the practicalilties and help to answer the OP question... how does inverted feel to you when compared to normal flight? I can't answer that because I only fly inverted on the sim at the moment.

[FuturaSE]

I only fly inverted on the sim at the moment.

me too it even is not flying im still struggling for an inverted hover

[unwind-protect]

This amount of downward deflection is insufficient to account for the amount of lift generated.

[...]

I am not discounting air deflection and Newton completely but that tends to only be significant at very high AofA and/or slow airspeeds.

Unless you're claiming that Newtonian physics at non-relativistic speeds is wrong, I'm pretty sure that conservation of momentum ensures that the air deflected downwards is sufficient to account for the lift generated :-)

Unless I misunderstand it, the Bernoulli principle does not itself account for attachment of the flow to the upper surface of the aerofoil via boundary effect or laminar flow; and once you required these, the deflection of air (from both the top and bottom surfaces) is sufficient to account for the lift generated via conservation of momentum (as well as wingtip vortices/ downwash). It's also the flow attachment that accounts for stalls as the flow separates from the surface, rather than Bernoulli.

[milly0812]

when inverted flight is there changement of helicopter behaviour? character

Oops .......have I stumbled upon geekthread.com ?? Lol

[450man]

Clearly you do understand the principles involves but I am not convinced by your argument that air deflection alone can account for lift generated. 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? If so then that flies in the face of accepted teaching at even commercial pilot level.

[450man]

Oops .......have I stumbled upon geekthread.com ?? Lol

LOL!

Yup! Call me a geek if that means that 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! Sorry if we are boring you.

I have asked others to chip in with some practical comments on the OP but until there are we are dicussing how the theory might affect a heli in inverted flight... it is related to the OP in that if the primary principle involved in a heli flying is air deflection and not Bernoulli then the heli body might have more of an effect on flight characteristics, particularly when inverted.

Do you have a view?

[tomatwalden]

Clearly you do understand the principles involves but I am not convinced by your argument that air deflection alone can account for lift generated. 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? If so then that flies in the face of accepted teaching at even commercial pilot level.

If that were the case, then a stall would have no effect (assuming enough force was applied to counteract accellerated levels of drag), and direct reaction lift would keep the aircraft aloft. This clearly isn't the case ...

[tomatwalden]

Oops .......have I stumbled upon geekthread.com ?? Lol

Ah - you may jest, but learning the physics of flight may help you out someday! For example, do you understand the principle of "settling with power" ?

If yes - Cool!
If no - understanding it, and understanding how to get out of it may save your expensive heli one day!

As Capt Tesco says ... Every little (bit of understanding) helps!

[milly0812]

when inverted flight is there changement of helicopter behaviour? character

LOL!



Do you have a view?

No I was just trying some humour on a very heavy thread

[450man]

Ah - you may jest, but learning the physics of flight may help you out someday! For example, do you understand the principle of "settling with power" ?

Is that where you descend into your own downwash? Sure do... although I am not 100% sure of the best way out of it but that is perhaps for another thread!!! I know you can prevent it by not descending too fast in a hover.

No I was just trying some humour on a very heavy thread

Thanks for lightening the mood. Personally I don't find these in-depth and often rather theoretical discussions heavy but I can certainly see that to most people all this stuff can seem rather unimportant when they just want to fly. Point taken.

[tomatwalden]

Is that where you descend into your own downwash? Sure do... although I am not 100% sure of the best way out of it but that is perhaps for another thread!!!

Yup - aka vortex ring state.

Thanks for lightening the mood. Personally I don't find these in-depth and often rather theoretical discussions heavy but I can certainly see that to most people all this stuff can seem rather unimportant when they just want to fly. Point taken.

Yeah - I am a total geek I suppose. I find all this stuff fascinating.

Don't see any problem in discussing helicopter aerodynamics on a heli forum! It is part of the hobby after all! I think helifreak has an aerodynamics sub-forum. Can't recall if RCHA does too ?

[sp4rky-m4rky]

You are right abut symetrical sections producing no lift at zero degs AofA. That is the same for symetrical wing sections on fixed-wing planes as well as heli blades. My point was that the bulk of lift is generated by pressure differential and not air deflection.

As for your second point... you are not thinking in terms of couples. When you have two forces that are not aligned exactly opposite they create a turning moment called a couple. Follow my example through with the string and you will see exactly what I mean. The pendulum effect is a direct result of this couple and nothing else so yes it will pendulum... when either way up... but it will always pendulum to being non-inverted and that is the problem.

Yes but this doesn't quantify the effect, the effect perhaps not being at all significant. If the distance between the lift and the center of mass is small (which it is compared to the width of the blades) the pendulum effect will be very small also. I have to admit that couplings although I understand where they may be associated, I have yet to have it explained how they work.

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.

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