Lillienthal

[asra]

Dave, consider it this way, we have a carefully made observation by one of the towering pioneers of flight, we can explain the phenomenon by Bernoulli. Our next step should be to show whether or not Lillienthal's observations are repeatable. If no one else will I'll put it on my list of things to do. Unfortunately it's a pretty long list.Until that is done there's not much point debating it in purely theoretical terms, we might as well debate how many angels can dance on the head of a pin.I can understand your scepticism, but that approximately 8 degree difference in the vertical componments of upwind and downwind air can easily account for your obsevations. While Jim Byrd has very nicely demonstrated the gradient in wind velocity as height is gained, and the effect it has on rate of climb, it does not explain what is happening on T/O or LDG when a constant height is maintained.Some of your questions in the last post can be answered if you accept that air is an elastic medium and so can expand and contract.John EvansThink logically and do things well, think laterally and do things better.

[Tim]

This was discussed exactly 12 months ago (9/1/2005) - interesting stuff. Viewable under:- Piloting Techniques > Pilot Techniques and Suggestions > Lilenthal.Tim McClure

[asra]

Bear in mind, the database has been archived of anything older that 12 months so if you cannot find information and it may be more than 12months old, click on the archive icon to the right of the screen.Barry Ferguson,ASRA WebmasterPh (07)5464-4993Int +61 7 5464-4993logic will get you from A to B - imagination will take you anywhere

[birdy]

If wot your testing is to be at all relivent to fly'n Doc, there's one thing you have to have in mind. We don't fly stationery. We move about a bit, so wot ever method your going to test it with, needs to follow the parth of a gyro, or the test ain't worth jacks.Personaly, i think you'll be wasting your valuable time, coz its logical, ALL SURFACE WIND CAN'T BE GOING UP."This was discussed exactly 12 months ago (9/1/2005) - interesting stuff."The Lilenthal thing mita been Tim, but not wot i'm on about. Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[Brian]

I have been wondering about that first 500 feet of air ever since 81 when I got my pilots licence [FW] and then when I learnt to fly gyros,it was plain obvious that the first 200 feet were really intersting !! I have no idea why most of the stuff happens and it defies most logic as conditions can change so much from one minute to another let alone the diference that 24 hours can bring or how even another season can change flying conditions.What I do know is that nearly every day I fly, I encounter one new thing I havent expereinced before, some are very minute changes, other's arent so subtle !!Brian

[asra]

Currie, the German sailing expert who wrote the book crediting Lillienthal with this discovery, was intrigued by his observations of the soaring flight of the albatros. Apparently it can soar for long periods over the ocean without moving its wings as long as it's flying upwind, it's a different story downwind.That rise in the angle of the wind would seem to be the only rational explanation for this.If no one else does it I will try to repeat Lillienthal's work one day.John EvansThink logically and do things well, think laterally and do things better.

[Brian]

John, now you raise an interesting point with the Albatross and the ocean. Has anyone onthe forum flown over the ocean and expereinced the flying conditions ?Brian

[birdy]

Not that i'm any sorta expert on anythn to do with them big puddles, but back when i was a tacker, i remember watch'n a Richard Attinbourough show bout how these Alby's can fly for so long, just off the water without flap'n. And his conclusion was logical, after watch'n them for a while, he realised they were 'ridge sore'n' off the waves.[ smart critters them birds]Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[asra]

Far be it from me to challenge the eminent Sir Richard Attenborough Dave, but for me his theory has more problems than you have with Benoulli!They would have to be monsterous waves to get much in the way of a ridge effect, and whether you accept it or not Bernoulli's law would also apply, just as it does in everything to do with flying.John EvansThink logically and do things well, think laterally and do things better.

[birdy]

I don't think so John. Ever held your machine a couple o feet off a tree in a strong wind?. Theres enough ' ridge effect' from a tree to be felt by a human in a gyro, so theres plenty of effect off a wave for a bird, which is much more efficiant than our gyros.I'v also watched crows, galahs n hawks ridge sore off trees, in no more than a gentle wind.Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[asra]

Believe it or not we are now probably entering "common ground"!I would contend that rather than giving rise to a ridge soaring effect the tree ( or the wave) is locally slowing the wind and so converting its energy into pressure in accordance with Bernoulli, this energy released as pressure pushes the following air up, giving rise to the effect we are haggling about.I would understand ridge effect as being due to the wind going over a ridge being forced up and over, resulting in a standing wave which can be used for soaring, but only in that immediate locality. On the other hand "Lillianthal's effect" happens contiuously as the wind loses its energy to surface friction, this effect would be locally enhanced by a tree as explained above.John EvansThink logically and do things well, think laterally and do things better.

[Greg Mitchell]

Gents,Whilst watching (recorded) Pelicans Of The Ghost Lake, chronicled the teaming pelican colony at South Australia's Lake Eyre.There were several good shots of Pelicans gliding mere centermetres off the surface of the lake. As they would lose forward airspeed and apparently, lift, as they began to 'sink' ever so close to the water, they would change the angle of attack of their wings, climb slightly to a couple to three feet, then beat their wings 4 to 6 times before settling in to a short glide again.I believe they said a pelican with a wing span of 2.3 metres, weighs about 7 kilos and when entering a thermal can climb to 3000 mtrs with out flapping its wings.Whilst gliding over Lake Eyre there were no waves to speak of, which may account for short glides and continual wing flapping to sustain same.Further, even whilst flying/gliding apparently upwind the glide runs were still relatively short. So having watched carefully several times, I'm still trying to think it through.What say you John? Pelican is one of the famous gliders of all time with a 100 million year history and yet sustained glides over the lake surface were not forthcomming. Help!Mitch.www.thebutterflyllc.comA thinker sees his own actions as experiments and questions--as attempts to find out something. Success and failure are for him answers above all. - Friedrich Nietzsche

[asra]

With no wave motion on the lake Greg, how could you pick the birds are flying upwind?Pete

[NiqueNaque]

Hm,Does anyone here surf? Or go fishing and watch the mutton birds. There is no doubt in my mind that the mutton birds surf on the air that is moving up on the face of a swell, if you watch them they fly near parallel to the wave front so their relatively fast forward speed ties in with the forward motion of the swell and they are more or less about a foot in front of the crest at all times, they are really great to watch on a big swell day, effortless and totally graceful flight. Believe me, they're plenty busy flapping on a still day with little wind or swell. What is a surprise is how late they stay up, I've been off Cabbage Tree island and Broughton Island north of Port Stevens while fishing and seen them out at midnight.As to the surf, if you're trying to crack a wave and it is blowing a stiff westerly [tubes man] the wind can be that strong that it stops you from getting on, the wind accelerates up the face of the wave quite remarkably.Hope this helps,Nick.

[Greg Mitchell]

Peter,The tightly packed colony have feathers reacting to the wind (first give away) and second whilst there may not be waves, there is enough wind to see movement on the water surface (ripples) indicating direction of wind. The water at the waters edge with the onshore breeze is roughed up. When the wind comes from the other direction the water is still near the edge.These observations factored in to determining wind direction.The slow mo replay is a big help. Mitch.www.thebutterflyllc.comA thinker sees his own actions as experiments and questions--as attempts to find out something. Success and failure are for him answers above all. - Friedrich Nietzsche