[tomsines27]

Hi Bill, I see you have a sport2. Any chance you can tell me the approximate balance point on it?
Tom

[Bill Cummings]

Hi Bill, I see you have a sport2. Any chance you can tell me the approximate balance point on it?
Tom

Tom,
I don’t have an easy answer for you. If I assume that you mean when I get under the glider and pick it up from the ground I would have to say for left and right balance right near the keel tube is the balance point.

For nose to tail balance it would depend how much my cross bar was pulled back by my Sport 2’s VG cord, but approximately at the hang strap or somewhere near that general vasectomy.

If I assume you mean in flight I would say that my glider’s balance is exactly at the hang strap as I received it from the WW test pilot.

If I pushed the control bar ahead about two to three inches (moving my body (CG) back behind the CP (the gliders Center of Pressure or the lifting force of the glider) I would be at about minimum sink speed.

If I pushed the control bar almost as far ahead as I could reach (slowly) the glider would start to wallow as the root section of the sail would be stalling first and progressing toward the wingtips.

Having the hang strap in the right place would have me flying at trim speed between minimum sink speed and best glide speed with both hands off of the control bar. I would be closer to minimum sink speed than best glide speed at trim speed.

I would have to pull in on the control bar past trim by about four to five inches to achieve best glide speed.

These are approximate guesses that would change if I pulled out more VG, Variable Geometry Cord which pulls back the cross bars and spreads the wing tubes. Just like opening an umbrella further.

A light weight glider could still employ a VG system but it starts the slippery slope.

This 35 year plus text book stuff is all fuzzy to me now and I may have some or most of it wrong but I can still auger up through the riff-raff and smoke half the gaggle of pilots.

I once plugged on some floats to Gene Stone’s Firefly 2B. The tail tube was quite long and there were two floats on it. Gene was complaining about the glider always stalling in flight. I went up the bank of the railroad grade along the Mississippi River and found a tie plate and vice gripped it to his nose plate to shut him up.
Finally his glider was “Balanced!” (Trimmed.)

[Rick Masters]

Tom,

Hang gliding is serious business. Nobody ever got it right the first time. There were a lot of designers who were their own test pilots. They're dead. Hundreds of people died to get hang gliders to the point where they flew well and lost their killer tendencies. Your only realistic option is to take apart the sail from an old glider and make a new one from it, fit it to the frame and have an experienced pilot test it from a training hill. I suggest this because I don't get the impression that you know anything about building hang gliders. Today you have to be a genius to improve performance.

I don't like standard trikes like your Evette. They're death traps, in my opinion. The front wheel loses traction in cornering and they crash or roll over. Unlike most hang glider pilots, I own a Wildfire trike and a Tri-Magnum reverse trike. The Wildfire is clearly a death trap but the Tri-Magnum is awesome. It will skidpad with a Corvette. No standard trike could possibly do that. Yeah, you can build one and drive it around. But IMO reverse trikes are the only way to go and I always expect to see people who don't realize this to show up in the hospital, sooner or later.

So the feeling I get from a standard trike guy who wants to build a hang glider without any flying experience is a recipe for disaster. I see any encouragement in this direction as severely ill-advised. I do suggest you learn to fly hang gliders. It's the most fun I've ever had.

[tomsines27]

Hi Bill, Sometimes I don't make myself clear, I mean't the balance point along the cord.
Tom

[tomsines27]

Hi Rick, You make a common mistake. The EVette is not what you think. The front wheel is not a major load bearing wheel, nor does it steer the car. The car steers electronically from the back wheels.(drive by wire) As far as reverse trikes are concerned , they fishtail, not enough rubber on the ground. Not safe. I once gave a Palm Beach Post reporter a ride, he wrote, gut wrenching turns. Look it up.
Tom

[Bill Cummings]

Hi Bill, Sometimes I don't make myself clear, I mean't the balance point along the cord.
Tom

Tom,
I’m hitting 100% here. Meaning another question that I don’t have a specific answer for.

The question would best be answered by Bob. K.

I would guess since I have never devoted any time on this question until today that Bob’s answer might go like this:

The balance point along the cord length (between the leading edge and the trailing edge) would be more of a shifting area than a definitive point for a “Flex Wing,” as apposed to a ridged wing.

I could be wrong here but I’m thinking that if I pulled my VG on my Sport 2 tighter which will flatten out some of the camber in my wing, more so at the root than closer to the wing tip, that my effective cord length would be increased. (Mostly near the root. It seems to me that this would change the balance point or area.

The balance point or area (if I’m right about that.) moves as I bank the glider.
In a turn my balance area moves rearward so I have to move my body rearward to stay under my shifting CP (lifting force/ balance area also described as Center of pressure) so that I don’t speed up too much in the turn.

Putting thoughts to print has always been difficult for me and I find that I’m a lot less sure now of what I was thinking than when I first got here.

[Bob Kuczewski]

Hi Tom,

I would endorse the comments made by Bill and Rick. In particular, I think Rick's warnings come from a lifetime of experience with things that fly.

I don't think there's a simple answer to your question about the balance point along the chord unless you're talking about static balance. Static balance is simply the point where the glider will be balanced with no wind. That's certainly important in glider design because you want the carrying location of the glider to be near that static balance point so you don't have to constantly fight to keep it level while moving the glider on the ground.

But there's also a dynamic balance point that has to do with the airflow over the wing. That's much more complicated. In fact, it's so complicated, that it generally takes either a supercomputer or a wind tunnel to figure it out ... and even with the supercomputer it's good to use a wind tunnel as confirmation. In fact, it was the Wright brother's extensive use of wind tunnel testing that eventually led to their successful flights.

In addition to being complicated, dynamic balance is highly influenced by speed. The basic aerodynamic forces go up as a square of velocity. So if a glider is balanced at one particular velocity, that's no guarantee that it will be balanced at another velocity. These relationships can be highly non-linear and a glider that handles nicely at one speed may become completely uncontrollable (or even unstable) at another speed.

I have a Bachelor of Science degree in Aeronautical and Astronautical Engineering, and I worked for two years at a commercial grade wind tunnel. But even with that experience, I would be quite timid about experimenting with anything that's going to fly a living person. I'm not saying that to discourage you, because I don't know your background (maybe you were one of my professors!!). But I do want to emphasise Rick's warnings about how dangerous and unforgiving it can be to experiment in aviation.

I don't know if that's an answer to your question yet, so please feel free to elaborate and maybe we can converge on a better answer for you.

Thanks again for your participation in the forum, and thanks very much to Bill and Rick for sharing your decades of experience here as well.

P.S. This discussion also reminds me to be thankful for all the people who've done the hard work to make this sport as safe as it is today. Many people died to bring us the generally safe and stable hang gliders we have today. Whenever I fly my Falcon I try to remember to give thanks to all those who made it possible.

[tomsines27]

Hi Bob, I do appreciate the warnings. When I learned to fly, I had enough close calls to know flying is dangerous! I have no intention of building some strange device, and jump off a cliff to see if it works. I'm a very slow methodical inventor, I calculate every risk carefully. Also, I have been following the progress of hanggliders for years. I know they are dangerous. One of the things I hope to do is make them less dangerous. So, let me ask you again, for a slow flying fixed wing hangglider, what is the approximate balance point along the cord of the wing? Remember the horse and buggy days, they thought they had the ultimate form of transportation, then along came Henry Ford.
Tom

[tomsines27]

Hi Bob,Sorry, I meant the static balance point
Tom

[Bob Kuczewski]

Hi Bob,
    :
So, let me ask you again, for a slow flying fixed wing hangglider, what is the approximate balance point along the cord of the wing?

Hi Bob,Sorry, I meant the static balance point

It depends too much on the shape and mass distribution of the wing for me to give you an answer. If by "static balance point" you mean the balance point with no wind, then it would be the point where the integral of the mass times the moment arm sums to zero.

By the way, this question seems very odd to be asking since it depends so heavily on what you're actually building.