[Bob Kuczewski]

Robert, you're getting lots of good help from some very very experienced pilots!!

A wind speed of 2 mph going to 4 mph the lifting force isn't just doubled the force jumps to 16.

That's exactly right. All aerodynamic forces depend on the velocity squared. Twice the speed ... four times the forces. Three times the speed ... nine times the forces. Four times the speed ... sixteen times the forces. That's true for lift and drag, and it's what limits the upper speed of your car. Eventually the drag gets so great that it equals 100% of your engine's power.

I worked in a wind tunnel for a couple years in college. The primary results we produced were lift and drag coefficients. What are they? I'm glad you asked.

A lift coefficient (CL) is just a number that describes the amount of lift for a given wing of a given size at a given speed in a given air density:

  Lift = CL x 1/2 x density x velocity x velocity x wingarea

You'll note that I included velocity twice because the lift force goes up with velocity squared.

The cool thing about that equation is that you can ask questions like:

How much larger does a wing have to be to carry twice the weight at the same speed in the same air density?

Well, if you're requiring twice the lift and keeping everything else the same, then you're going to need twice the wing area.

How much would your speed go up to carry twice the load at the same conditions?

Since the lift depends on the velocity squared, you'd need to double your squared velocity. That means your velocity would have to up by the square root of 2 ... which is about 1.4.

If you understand that equation it can help answer a lot of questions. But it does leave out an important point. Does CL depend on anything else? The answer is a big YES!! CL depends very directly (and nearly linearly) on alpha - the angle of attack. And that's what we control directly with pitch. But as we increase alpha, we also increase drag ... which reduces velocity.

[Robert Hutchinson]

Aaaak! MATH! lol

wow...ok, firstly, THANKS guys! For taking the time to explain all of this to me; I really appreciate it!

Secondly, while I've shallowly read of some of these concepts, I didn't understand how critically necessary it was for them to come together in the right ratio to achieve flight...I kind of thought that the limiting factor of my weight was due to the weaknesses of the materials that made up the kite; it now seems that such heavier loads require external power sources just to remain airborne! (perhaps explaining why there are no 747-sized soaring gliders...or 300 lb. hang glider pilots!)

It seems that, no matter how I slice things, I would always kind of be pushing the envelope in the best of circumstances, and crashing in the rest of 'em. Neither of which sounds like a lot of fun!

I think I'm beginning to glimpse the wisdom of Rick's earliest posts!

So, with all this said, how difficult is it to add an engine to a hang glider to get that external source of power, and would the falcon still be the best choice? Or, should I simply start saving my beans until I can afford a proper aircraft?

p.s. Sorry for keeping you up past your bedtime, bill!

[Rick Masters]

Jeez, we go through all this work to determine your satisfactory wing loading and now you want to hang an anvil on it.
I've lost count of my hang gliding friends who've been killed in the early days by hanging engines on their hang gliders.
At least they've worked out most of the bugs, now.
Except the big one.
Weight shift is a poor choice for power.
The thrust vector is all over the place. Better to go with 3-axis, IMHO.
http://www.northwing.com/
I like the NS hang gliders, though.
In Big Air, you don't need to come down to refuel.
(I've had several hang gliding flights of around 10 hours.)
Engines vs gliding are entirely different things.
I can't really help you with the engine stuff.
Too boring. Too much can go wrong. I like it simple.
I say "simple" - but staying up on a hang glider is one of the most challenging and complex games in human experience.
I liken it to playing 3D chess with God.
I do like the idea of electric assist to get you up to the thermals, though.
http://www.icaro2000.com/Products/Swift/Swift.htm
Of course, we're ranging far afield and getting into big money.
You still need to learn to hang glide first.
Our biggest thrill, regardless of what we accomplish later, is the first time you get lifted off the ground.
You never forget that.
Find a school with a big hang glider and take a lesson.
Maybe even a lesson in a tandem sailplane.
You'll know what to do after that.
Personally, I would stay away from paragliders and engines.
They'll bite you.

[Frank Colver]

Robert,

I weigh 230 now (naked), at age 82, and only fly at the beach now. I either use my WW Alpha 210 or the WW Condor 330 depending on the wind conditions.

However, during my younger hang gliding years from 1971 to 1979 I was lighter (probably 190 - 200) and flew smaller gliders but the control in turbulence is always an issue with me. I used to tell my friends, some of whom were flying the Owens Valley in the late 70's, that I would not do distance cross country flights because I was unwilling to fly in the conditions that would enable those flights. I made the conscious decision to only fly in the fall, winter, and early spring months. During the hotter, more turbulent, months I did whitewater river boating and mountain biking which would fill out my outdoor recreation year.

This is not to say I never encountered turbulence, even in those mellow months. I was flying from high mountains and on a SoCal "Santa Ana wind" warm winter day there can be some hefty thermals or cross-ridge wind induced turbulence. However, the percentage of fairly mellow flights, even while soaring in lift, was higher in those months.

So, there are a lot of choices of when and where you fly that can determine what glider you choose. For some HG pilots, never having made a long cross country flight would be a real downer, I'm sure Rick would feel that way. For me, I have some fantastic memories of great flying days while never having left the launch point very far behind. It's all up to you.

Frank Colver

BTW - I saved my cross country flying for a foot launch hot air balloon. Those flights are almost always cross country but not as much fun (for me) as hang gliding.