Why were gliders not invented WAY earlier?

You can get the basic idea of how a glider works, simply by observing birds. People have been observing birds for as long as people have existed.

I realize that there were early attempts at building powered aircraft by trying to duplicate the concept of flapping wings, which failed. But why did people not simply attempt to refine the design of unpowered gliders?

They did. Lots of early aviation pioneers worked on them. Including the Wright Brothers.
But, frankly to work as a modern glider, you need a strong machine to give it the energy it needs needs to glide for a distance and have the air speed to be controllable. That means either another powered vehicle, or a big ass catapult. Well, do that and you you have already done most of the work leading to powered flight.

What about hang gliders? Why did these not exist thousands of years ago in any region with high elevations that they could be launched from?

Thousands of years ago, people did not have the materials and manufacturing methods necessary to make a strong, lightweight glider capable of carrying a person and being controllable.

You beat me AK - I was about to offer https://en.wikipedia.org/wiki/Glider_(aircraft)#History_of_gliders

Looks like the concept is about a thousand years old. Practical examples getting on for two hundred.


Howstuffworks says the ancient Chinese invented them in the 6th century (AD). I can’t find much info on it though.

Gliding wasn’t good enough, people wanted to fly. And so they got sidetracked into attempting to build flapping wings, which given a human’s strength/weight ratio wasn’t going to happen before modern ultralight materials. Even Leonardo Davinci tried to do it that way.

Chinese kites were limited because they worked simply by air drag against the wind, and couldn’t glide if not on a rope.

And the Rogallo Wing a.k.a. hang glider took a surprising amount of modern aerodynamic theory to develop.

Many people, for a long time, looking at birds to figure out flight were looking at the wrong things, the wrong way. Like thinking the feathers were the key (the Icarus story) or the flapping (they were not looking at efficient gliding birds like eagles and storks.) What is needed to make a working glider is an air foil, a structure that generates net vertical force as it travels through the air. You can make a lot of gliders that look like birds, but if the wings do not act as airfoils it ain’t going to fly. A few people made gliders that sort of worked, because they stumbled onto a wing shape that provided a bit of lift, but their understanding of what their glider was doing and why was not correct, and they could not / did not learn the correct things from their experience to allow them to improve their glider.

When people started making props for steam powered boats and ships, they noticed some worked better then others. Trying to figure out why and what was the best shape for a prop led to the science of hydrodynamics. People took the discoveries in hydrodynamics and learned variations of the same concepts applied to air flow. One of these people, Otto Lilienthal, used the new aerodynamic principles (and his observations of birds and bats) to build working, reliable hang gliders. Through careful scientific methods he was able to improve the performance of each successive glider he built, and publish his finding so other could improve further.

You definitely do not need a powered vehicle or a catapult to fly a glider. You can launch off a hill - this is done routinely with hang gliders, and occasionally with 3-axis-control gliders.

You can also launch on level ground (with some help from your friends).

You don’t need modern materials - bamboo and silk would do. You don’t need manufacturing - just build one by hand.

What you do need is some non-trivial knowledge of aerodynamics. Gaining this took a good long while, and killed a fair number of experimenters along the way.

Man-powered flight has barely succeeded using sophisticated pedal-propeller arrangements. Flapping-wing flight still looks to be a long way off.

Well, not completely reliable.

I question this.

Lilienthal makes no mention (that I’ve been able to find) of hydrodynamics in his well-known book Birdflight as the Basis of Aviation - the source of his inspiration is given in the title. He definitely wasn’t interested in aircraft propellers - he though flapping flight was clearly the way to go.

The Wrights intended to use existing hydrodynamic theory in designing the propellers for their 1903 Flyer - but found there basically wasn’t any. At that time ships’ propellers were all designed by rule of thumb, and their best efficiency was around 75% of what the Wrights knew they’d need.

It was only just before the Wright brothers that people were able to make fairly safe dependable man-carrying kites.

People had been working on lifting people with kites for a very long time. They always started with kites that were far too small, and sometimes advanced to kites that were unstable and far to weak.

Following the development of capable kites, the Wright brothers had some idea about how much surface area they would need, how to make something structurally strong enough to handle the weight and power, and, from rope tension, how much power would be needed.

I’ll also note that landing and take-off are notoriously the most difficult part of any flight. Many early glider experimenters didn’t get much flight time up before they died. Part of the advance was just the accumulation of flight hours, and part of it was accumulated ‘simulator’ hours of various types.

Which leads back to another factor: gliders (and airplanes, and kites) don’t scale linearly. If you make a small model, and it flies well, it won’t work when scaled up. The Wright brothers had the advantage that full-size kites and flying machines preceeded theirs.

Finally, of course the great inovation of the Wright brothers was the new control surfaces. Before that, gliders always crashed.

OK does not look like I can edit my original post, but better wording would be:

“When people started making props for steam powered boats and ships, they noticed some worked better then others. Trying to figure out why and what was the best shape for a prop led to the science of hydrodynamics. People took the discoveries in hydrodynamics and learned variations of the same concepts applied to air flow. Several people sought to apply these new aerodynamic principles to the problem of manned flight. Otto Lilienthal was the most successful of these early pioneers, using the new science to analyze bird and bat wings to figure out how they provided lift, instead of just copying the shape. This allowed him to build hang gliders that were far more reliable and capable than any previous ones. Through careful scientific methods he was able to improve the performance of each successive glider he built, and published his finding so other could improve further.”

I may be miss remembering (doing that more and more lately) but I believe the progression was ships props, to electric fans, to Lilienthal’s air foil wings.

Here’s a lesson about not appreciating aerodynamics: for centuries people built windmills with simple angled slat arms, taking no advantage of airfoil techniques. This despite the fact that they could have looked at a maple seed, supposed that nature would have found a near-optimum air catching shape, and imitated it.

This was definitely a limitation in adapting one invention from another at that time, that knowledge was so empirical and specific, even though a lot of progress was made that way. IOW ship’s props ca. 1900 were way more advanced than 1840, but with a very limited way of explaining exactly why.

But the other issue with plane v ship props even to the extent some theoretical comparison was possible, which it was in rough terms, was the pretty different flow regimes of the two cases. Ship’s props are generally constrained to be much smaller area relative the thrust they have to produce, thus they speed up relatively little water by fairly a lot. Airplane props can generally speed up more air by less. That makes the ship prop inherently less efficient on basic momentum principal known at that time, even assuming a completely efficient black box mechanism for speeding up the fluid. It’s still true though that the particular shape of the props’ blades was not determined by theory, in either ship or airplane props. Not even 100% totally now, though more in the last few decades. But little changed from 1900 to well past mid century, exactly what shape of prop blade would work best for either ships or planes. It was based on empirical tests.

And I directly question this statement. Bamboo and silk are the lightest, strongest materials available, but they are in no way strong enough to support a human glide. The freshest bamboo is too weak, and dried even worse. Silk is light and strong, and absorbs less water than other natural fabrics but is too weak unless the wingspan is ridiculous and even absorbs some moisture adding to its waste weight.

PBS did a special where they tried to create Leonardo’s glider from his design. The woman who was going to risk her life inside of it wasn’t going to take it and the natural materials at face value.

Of course, another difference is that propellers turn in a circle, instead of moving straight through a fluid, and thus different parts of the blade are moving at different speeds. And in typical propeller designs, the width of each blade is a sizeable fraction of the radius, so there’s no portion of the blade for which this can be neglected.

Well, somehow these gliders made from wood and fabric worked: