Explanation of "rotor disk" = rotary wing = aerofoil

[quoj]

Hi,Can someone give me a good explanation of how a spinning rotor forms a virtual "wing" and thus usable just like a fixed wing (just as a gyrocopter does!)I was trying to explain this to a "I reckon I know what I"m talking about" w@nker (who had absolutely no flying experience, I might add!) who claimed "Nah! Nah! Nah! That"s a load of bullsh1t!" and that spinning rotors only work by pushing air down (like a hovering helicopter.)I was trying to explain how the spinning rotor forms a disc that is an aerodynamic surface (like a helicopter using translational lift) but couldn"t put it in words convincingly.Unfortunately, as conversations like this go, we were interrupted by some rude *******, right when I was struggling to get it through his thick head that his understanding of aerodynamics was flawed, and I ended up looking stupid in front of everyone.There seem to still many people out there who know what a gyrocopter is, but don"t realise that the rotor is unpowered.Can anyone put it succinctly?Thanks.

[bosca]

quoj,
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[Russell]

Quoj........hang in there ol mate..........kym, ol chum.........get back under your rock.In short....gyros........ the "relative wind " encountered in flite is up through the blades....exiting via the top. Helicopters are exactly the opposite .The "forces generated" by the gyro blades spinning at ??? revs, creates lift. ( underside of blade is flat, top side is curved ).....helo is curved both sides. Helo when executing "auto rotation" emergency landings, ( engine has shyte its self, it"s blades have lost their power source ) must reverse it"s "relative wind" from topside feed, to underside feed, to now perform as your gyro does. You reduce your "relative wind " in your gyro, you simply begin to sink, your blades need to generate enough energy/lift ( controlled by the amount of relative wind you supply them ) to maintain level flite. The more you feed those blades the more energy/lift they will give you.It"s a great topic blades etc. Could get more techo, but this is the short version. ( somewhere i have a real good ref book on helo/gyro stuff, will hunt it up and get back to you )russ

[chook]

Quoj sorry about the rebuke, every forum has one - ours is called bosca.When arguing at such a basic level some people respond better to practical examples. Aviation theory (and the purists) would have you believe that you can only get lift from an appropriately shaped aerofoil with a curve on top. The thinking that as the air goes past the wing it has to travel faster over the top (a longer distance) which produces a vacuum thus "lifting" that wing.The basics are if you place a piece of flat wood out the window of a car (say) travelling at 60km/h with the thin side pointing forward you will be able to hold it. Now try twisting the thing one way or the other and try holding it. It will dive or climb and that is purely the action of the air acting on it. In fact don"t bother with the wood - use your hand! I agree the efficiency is improved by using an aerodynamically shaped wing but a plank will still fly. (or produce lift)With the gyro if we turned both blades so that they faced forward and locked them to give us a very long but thin wing (the chord) and travelled down the runway VERY fast it would eventually produce enough lift to get us airborne. What the helicopter and us gyro types do is cheat and artificially produce that extra speed by spinning the rotor. The helicopter uses brute force to obtain that lift, we use the air to do the same thing but passing through the "disc". It"s more of a resistance that keeps us airborne as we claw our way upwards. And if all else fails to convince your "friend" just tell him that helicopters don"t fly - they are so ugly that the earth repels them. But we love em anyway now go and get me another beer.Regards........Chook.

[louww]

Hi Chooky, I love your explanation. Short, sassy, precise and accurate. We"ll definitely have beer this upcoming weekend. LouPS: I finally got my "crashed" laptop fixed

[quoj]

Thank you Russ & Chook for your explanations.Bosca - the reason I believed it to be this way is that this is how the idea of the "rotary wing" was explained to me by two aeronautical engineers and some bloke who owned a JetRanger. I figured that these were sufficiently expert sources such as not to question their wisdom!I guess it goes to show, however, that there is still some dispute over how aircraft actually fly!I am a fixed-wing pilot with a few hundred hours, but was surprised to read a section of Jim Davis" book that says that modern day ideas on aerodynamics dispute the "air moves faster over the top, curved section and slower on the underside" and combined with Venturi/Benouilli effect.Jim Davis claims that it"s a combination of the Coanda Effect (similar but different) and the fact that an aerofoil basically pushes air downwards!He provides a link to the NASA site that explains it. (I"ll post it later!)One of my points, however, was that we all come across "armchair experts" on various topics with little-to-no experience who"ll try to tell people with reasonable experience that they"ve got it wrong, simply because "I reckon I"m right, therefore I"m right!" and the good ol" classic line of "Well, think about it..." (...as if prefacing their arguement with this line will make you immediately see the righteousness of their position on the matter.)Russ - I look forward to you digging up that book and paraphrasing it here.Thanks.

[bosca]

quoj.
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[quoj]

Well, please accept my most sincere apologies for any offence caused, Kym.In all fairness, though, I"ve been around this forum long enough to know that I am neither first, last nor worst offender in using the odd "colourful metaphor"/ naughty word to describe nameless, faceless people that we have found to be frustrating or reprehensible.And the words I used were part of the common vernacular that I have no doubt most of us use daily, and indeed have been used countless times before in this forum.But if you found them to be upsetting, then please accept my most profuse apologies!

[asra]

Try this.
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[bosca]

Accepted quoj.

[GraemeMonro]

Hi,I was trying to explain how the spinning rotor forms a disc that is an aerodynamic surface (like a helicopter using translational lift) but couldn"t put it in words convincingly.Unfortunately, I ended up looking stupid in front of everyone.So when you finish explaining the rotor disc theory to your mate, see if you can convince him that gyro"s are weight shift also.Graeme.

[quoj]

So when you finish explaining the rotor disc theory to your mate, see if you can convince him that gyro"s are weight shift also.Hah!That"ll be a laugh!

[quoj]

Try this.Thanks, Murray.That"s a good picture and explains the phases well.

[GraemeMonro]

So when you finish explaining the rotor disc theory to your mate, see if you can convince him that gyro"s are weight shift also.Graeme.This was not meant to be funny. If you are going to teach "rotor disc theory", you may as well teach "weight shift theory".Both are wrong for gyro"s. Know what you are on about before you correct others.Graeme.

[tonydenton]

i usually just say , it"s like a 2 bladed windmill