[N_Lander]

Well you guys are a great resource, so i will lean on you once again! Was looking around for some recent books/DVDs on hang gliding flight theory and basic principles. All i could come up with were a set of videos made in the 90s that seem outdated. A wing is a wing is a wing but i was hoping for something more resent. Thanks for the help

[PilotGuy]

I haven't seen much in the way of HG physics, but you're right when you say a wing is a wing. What kind of questions do you have in mind? I'm sure we can tackle a few of them right here.

[tizeagle]

1st have you taken any flight training yet?

If you have you should have received a manual called Hang Gliding Training Manual, at least this is the most common used book, by Dennis Pagen.

It covers a great deal on the science behind it. I have never looked at where to get the book because I received it from my instructor. It is a very in-depth book and I continue to study it, I plan to reach Beginner Instructor Status by spring.

Tiz

[PilotGuy]

N_Lander, you asked about the relationship between the size of a wing and the amount of lift that it produces. I can try to answer that one.

There are a couple of things that determine how much lift an airfoil will produce. These things are airspeed, air density, angle of attack, size of the airfoil, and the "liftyness" of the airfoil.

Let's take an average afternoon on the California coast. The density of the air isn't going to change much if we keep about the same altitude and temperature, so let's forget about density for a bit. The "liftyness" that I mentioned is something inherent to the particular airfoil shape used to make your wing. As you can probably guess, an airfoil that is very flat will apply a different force on the air, and hence feel a different force from the air, than a very curved airfoil under the same condtions. Some airfoils are shaped to work well at high speeds, and others are shaped to work well at low speeds. Two different airfoil shapes will produce different amounts of lift at the same angle of attack, i.e. some shapes are more "lifty" than others. The number that quantifies this liftyness is called the lift coefficient. The lift coefficient is a number, with no units or anything, that tells the engineers how much lift an airfoil section will produce at a certain angle of attack.

I have included the formula for calculating lift below. In this equation L is the amount of lift force generated (in pounds), C subscript L is the lift coefficient, rho (the lowercase italic P) is air density in slugs per cubic foot, V is airspeed in feet per second, and A is wing area in square feet.



The lift coefficient for a standard airfoil that you might find on a Cessna or a hangglider will have a lift coefficient in the range between 0 and 1.5, for instance. The lift coefficient changes depending on the angle of attack of the airfoil. As you pitch up (raise the nose) you increase the angle of attack and the lift coefficient increases. With everything else like airspeed, air density, and wing size staying the same, when your lift coefficient increases the lift produced by the wing will increase, and you will climb.

Here is a graph that shows the variation of lift coefficient with angle of attack.


If you look at that graph you'll see that the lift coefficient (y-axis) keeps increasing up until the angle of attack (x-axis) reaches about 16 degrees. At 16 degrees AOA you'll see that the lift coefficient starts to dramatically decrease, at which point your lift decreases dramatically and you stop flying and start falling. This is the stall that you've heard about and will keep hearing about.

So that's the engineering explanation of how it works, there's a lot more to it, both mathematically and physically. I've got to run for now, if anyone has any questions or anything to add speak up.

[N_Lander]

Don't want to sound stupid, but i guess i can always change my name- How do Pilots achieve lift and not just control their decent? How is speed achieved with out loosing altitude? How can you tell your in a thermal? Is it possible to "float" in one place like the birds or are you always traveling forward? O.k. Yeah i guess i will probably change my name after a few more questions like this. Will be picking up that book and thanks for all your time guys.

[fifelo]

[tizeagle]

There is never a bad question. The book will tell you a great deal. Also there are a bunch of articals on USHGA web site that will also answer allot of the questions you probably have.

The only bad question is the one asked to late.