Eric's Beijing Diary

In the previous lesson, we introduced the glider as an aircraft that flies without an engine. We also talked about the difference between a conventional glider (or perhaps I should say “pre-Treaty of Versailles” glider) and what we have come to call a “sailplane.” As mentioned in the previous lesson, the Treaty of Versailles is important, because it is the historical event that motivated the Germans to focus on developing super efficient gliders.

In this lesson, we want to focus on how sailplanes work. To begin, then, we want to be sure we understand how a sailplane differs from a regular glider. Both sailplanes and regular gliders need to be towed aloft, usually by a powered airplane. The difference between them is that once they are released, the regular glider will simply glide back to earth, while the sailplane will search for rising air currents and try to use these rising air currents to stay aloft or even to gain altitude. The process of floating back to earth is called “gliding.” The process of using rising air currents to stay aloft is called “soaring.”

The video above explains how sailplanes use air currents to stay aloft. There is one error I should point out do you. He says, “gliders, also known as sailplanes.” That’s not correct. That implies that “sailplane” is just another term for glider. No. A sailplane is a specific type of glider. All sailplanes are gliders, of course. But all gliders are not sailplanes. But aside from the fact that he keeps saying “glider” when he should be saying “sailplane,” this video is the best technical description of how sailplanes work that you will ever see. It is excellent.

After you have watched the video above, take a look at the one below. The video below is interesting, because it shows a modern version of the gliders from 1930 that we introduced at the beginning of the previous lesson. Very similar. Essentially the same design. So why would anyone want to have such an old fashioned glider like the one below (that is no good for soaring) in the modern age when high performance sailplanes are available? The reason is that these old style gliders are very good as trainers, because they are so easy to fly. A kid could fly one. Mind you, you still need training, and you should limit your flying to days with almost perfect weather, but training gliders like this are very good for learning. So science takes a giant step backward. This is why there will always be a difference between gliders like the trainer below (which is also built by a German company) and high performance German sailplanes like the one we introduced in the video at the end of the previous lesson. So the need for conventional gliders is not going to go away, but It is probably also true that future innovations in powerless flight, especially the ultra light variety, will focus on taking advantage of rising air currents to extend flight.

Comments       Science Night Home

Labels: Aerospace, Glider, Sailplane

What is a glider? Why would you want to fly an airplane that had no engine? First of all, engines are heavy. They add a lot of weight and make the plane harder to fly (although the power provided by the engine compensates for this). Gliders don't need fuel. Of course, because there is no engine, you will have a towing fee. But I think a towing fee would be quite a bit less than fuel. Basically, it's a good way to develop flying skill by flying a vehicle that is very easy to maneuver.

So how did gliders develop into the sophisticated aircraft we see today? To answer that question, we need to go back to the Treaty of Versailles, which the Allied Powerthe s forced on Germany after World War I.

This treaty restricted Germany from developing powered aircraft. But gliders were not prohibited. The Germans took advantage of this loophole to develop very efficient gliders. That's why most of the high performance gliders that you see today are from Germany. They were developing them while everyone else basically saw gliders as a thing of the past. The common thinking was, "Now that we have airplanes with engines, why do we need gliders?"

The effect of this focus the Germans placed on the development of gliders between World War I and World War II is that we now have gliders that are so efficient that, not only do they come down much more slowly that previous heavier and less efficient gliders, but they are so light and so effiecient that they can actually fly even higher than they were when they were released from the two line, by searching for rising air currents. These new, highly efficient gliders that can rise higher by finding air currents are called "sailplanes."

There are two main types of rising air currents. Thermals are rising columns of air that are caused by different rates at which heat from the sun is absorbed by the land. Sailplane pilots can find these by looking for cumulus clouds. The "thermal," or rising air column is actually what produces the cumulus cloud.

The other type of rising air current is caused by wind blowing across the land, which hits a mountain ridge and is forced upward. The video below shows a pilot using this current of air along a mountain ridge to stay aloft for a long period of time. The goal of sailplane pilots is not to see how high they can go. It is to see how long they can stay aloft even though they do not have an engine. Because sometimes a sailplane pilot will get stuck a long distance from the airport and suddenly not be able to find a rising air current, some sailplanes have a small, battery powered engine with a collapsible propeller that pops out and helps the pilot gain some altitude so he has time to find another rising air current.

Comments       Science Night Home

Labels: Aerospace, Glider