The name means 'bird wing' The broadest interpretation of the word refers to a flying machine that gets its thrust from flapping wings. The narrower but usual interpretation is a machine that gets its lift as well from its wings. The narrowest meaning will appear later in the guide.
Why anyone would want to do this is actually the most interesting thing about it. We get around fine in the air now; so why would anyone want to go to a more difficult and inefficient way?
The first ornithopter of record was invented by the person who thought up the Daedalus myth. It must be called a myth because, although he described it as being a real machine made of feathers and wax, it couldn't possibly have flown. The choice of feathers is a romantic one. It shows magical thinking. The other reason for calling it a myth is the fate of Daedalus' son, Icarus, who, drunken with unfamiliar power and ignoring his fathers warning, flew too close to the sun. The wax melted and he plunged into the sea. In reality, the higher you fly, the colder it gets. Also, the sun is 150 million km from here, a substantial portion of which distance has no air and which would invlove much tiresome flapping against nothing and with no way to catch your breath and no lay-bys and no lunch.
The history of flight began much earlier than with Leonardo Da Vinci in the 15th century. It is very likely that the first flyer was a Muslim in the 9th century. Abbas Bin Firnas presented himself to the crowds on a hill near Cordoba, Spain in the year 880 where, as the chronicles recount, he covered his body in a bird costume, guided himself into the harness and told the crowd: “By guiding these wings up and down, I should ascend like the birds."
Like certain British sheep, he did not so much fly as plummet. For his pains, which were substantial, he got a broken back and the derision of the crowd.
Leonardo DaVinci made the first drawing (that we know of) of an ornithopter. It's very important because he gave serious thought to the engineering and so was the first to part from magical thinking. He didn't part by much. His understanding of physics was a little weak. He didn't realize that the human body can't make even nearly enough power to get his version into the air. There is a story that he built one and persuaded someone to leap from a tower in it. It's possible, but it could only have glided Bognor Birdman style; the flapping wouldn't have done anything except give the terrified pilot something to do in his panic.
The most important person in aviation history has to be Sir George Cayley. He was the first to entirely abandon magical thinking. A child of the Enlightenment, he knew that something real was holding the birds up.(Hint: it involves the air.) He described the first aeroplane (not the machine but the principle) then went on to invent the aeroplane (not the principle but the machine) He invented the control surfaces and described streamlining and why it was important. To top it off on the bottom he invented the tension spoke wheel to save weight. If your bicycle weighs less than a ton, thank Sir George.
Unfortunately, he did it all way too soon. The technology of the times (Napoleon was still rampaging around Europe) couldn't give him a powerful enough engine.
Nineteenth Century. The glorious reign of Victoria where anything is technically possible (self confidence ain't hubris 'til until all the scores are in) and many wonders are produced. They tried to overcome Leonardo's problem by using steam power. This made sense to a Victorian who knew that steam can power anything. They didn't get that it's a power-to-weight thing. The steam engines were much more powerful than Leo's victim, but rather heavier.
Twentieth Century. Wright Brothers. No magical thinking here. They didn't even try to make an ornithopter. Their success might be thought to discourage others but, fortunately, no. The reader may have seen a film, maybe a century old, of something that Mary Poppins might have seen in a nightmare. A great canvas bumbershoot is made to furiously bob up and down by what is obviously tonnes of smoking machinery. Magical thinking back again and someone invested in it. One can only offer conjecture as to what the inventor imagined would happen, but the film is likely much funnier.
[There's a whole block of stuff to go here that the researcher hasn't put together yet and will be included later]
In the second half of the twentieth century , someone finally figured it out.
Try this at home, kids! Take a longish piece of card and tape a stick lengthways down the centre with a bit sticking out to hold on to. Flap it up and down. It moves the air about but, otherwise , just flaps up and down. Now, get a scissor and cut some off the edge to one side of the stick. Flap again. This time, it will twist in your hand so that the side that you cut leads the twist. If you have very sensitive fingers, you will also notice that the card wants to move in that direction. That's where the ornithopters thrust comes from.
You can buy toys that do it[Google it] There is at least one version big enough to carry a person.
Ornithopters are not just a curiosity, a gimmick or a romantic idea, though. Well, maybe so far they are, but that doesn't stop us visionaries.The way we fly now is too costly in terms of noise, danger, pollution, etc. In the future, you will be able to step outside your door and get into a machine that takes off vertically and takes you where you want to go without roads and without waking your neighbours when you leave.
A researcher in Canada is working on a version that gets its power from a Stirling cycle muscle that works silently and burns any kind of fuel, even firewood; in Canada that's a big deal.
The narrowest sense of the word ornithopter--A machine that flies like a bird. It gets lift, thrust and control from the ability to move the airfoils. A pedant would offer that this meaning could also include machines that fly like bats or pterosaurs. Only one pedant is allowed in the room at one time, otherwise, any Guide Entry becomes interminable.
Try This at Home.
The reader is strongly encouraged to perform certain excercises in order to gain an intuitive sense of bird flight. This makes technical descriptions easier to understand.
Obtain four pieces of cardboard as from the faces of a large box. Cut each card the same size and shape. Tape them in pairs face to face with tape only on three sides. The fourth, open side is for your hand.
Go outside on a breezy day. It's probably a good idea to wear some yellow boots and a funny hat since your neighbours will think you're daft anyway.
Hold your wings outward and flat to the horizon. By the time you get them there you will have discovered that most attitudes present much more drag in the wind. The wind now has the least force (drag) while the wing is edge on to the wind. What drag there is is parasite drag. Air sticks to the wing surface. Air has to move to get around the wng. All that takes energy.
Tilt the wings forward edge up. Right away your arms are drawn up and back. The up part is lift, the back part is induced drag. Any time you use the attitude of the wings to do the work of lift, the energy has to come from somewhere. Ultimately, you need an engine for this. You can, it's true, get energy from gravity as in a glider, but that usually runs out in useful form quite close to the ground.
If you've chosen a park or some such public place you may by now have attracted the beginning of a crowd. Tell them you're doing High Chi. Here are some maneuvers you can demonstrate.
PITCH Points up, points down.
Move your arms so that the wings are forward of your body and into the wind. Tilt them up. Since the lift is now forward of your centre of gravity, you feel a pitch up. Tilt down, pitch down. Move your arms behind you. The whole thing is reversed.
ROLL Banks left and right.
Tilt your right wing up more than your left. That side lifts more so you lean to the left. Left tip up, you lean to the right. If you were actually flying, you wouldn't just lean that way, you would go that way. It's how regular aeroplanes turn too. If you're particularly sensitive you may notice that, even though you're leaning one way, your nose wants to point the other way. This is because the increased lift drags that side more. If you weren't a bird you could correct that with a rudder. You are, however, so now you have to find another way to control...
YAW Points left, points right.
Right now, since we haven't discussed thrust yet, there's probably no way with your cardboard wings that you can increase the drag on the inside wing without also increasing the lift. So, smile, take a bow for the spectators and go home.
Difficulties in Ornithopter design.
The wings go down, something has to go up to compensate. It can’t be the pilot or passengers or warm cans of Coke
The trick is to get the largest possible mass centred between the wings and make it go -up and -down in time with the wings.
The easiest way is to use the engine and all its supporting systems including as much as you can. Fuel systems cooling systems air systems etc.
The fuel system can’t include the actual fuel since that's consumed during the flight and the changing mass of it would screw up the motion.
The moving masses rotate around the centres of mass at the ‘shoulders’
Since the landing gear has to act through those points it can’t be included in the moving mass.
Centre of Lift
Hearby renamed ‘Vector’ since it includes more information
Since your moving the wings up and down, you might as well let them move forward and back and be able to play with the yaw.
Since you’re sending the control surfaces in every direction, it’s easier and intuitivly simpler to use the vector. It’s the centre and direction of the force on the foil. It’s easy to diagram. Easy to visualize.
In toys, usually a twisted rubber band. Larger toys use electric motors or small internal combustion engines. In all cases the fast rotary motion of the engine is translated into slow reciprical motion for the wings by means of some gearbox/crank combination. The weight and complexity of this is one of the main blocks to practical ornithopter design.
to be continued...