[Frank Colver]

This blog's purpose and my ground rules:

To explore and develop a hang glider that makes beginning flight easy and rewarding. See my opening description of the project.

This blog is open to replies which must be "on subject" or they will be removed.

Positive or negative comments are welcome as long as they pertain to the design being discussed. I will attempt to reply to those comments as to the best of my ability.

General hang gliding subjects: only as they apply to the "training gliders / learning" subject matter.

I alone reserve the right to make the reply subject's application evaluation.

No personal attacks will be tolerated.

This blog starts with my Basic Trainer thread copied from "hang gliding.org" web forum. It will be updated here from the end of those current postings.

Frank Colver (USHPA7)

 

Moderators Note:

    This topic has been "bootstrapped" with Frank's previous
    historical posts from other locations. Contextual posts by
    other people have been added as quotes to avoid any false
    impression that they have posted directly in this topic.

  

[Frank Colver]

A BASIC TRAINER DESIGN FOR TEACHING HANG GLIDING
Originally posted Dec 04, 2018 11:43 pm

THE HANG GLIDER BASIC TRAINER DESIGN PROJECT:
This open source project was run on another hang gliding forum and is now in its final stages of preparing to build a full scale prototype. I thought it was time to present it on this forum for an additional audience.

THE HISTORY:
Thousands of hang glider pilots taught themselves to fly on what has become known as the “standard Rogallo”. They just ran down a hill and flew. The glider was easy to ground handle, and the control was pretty much intuitive. It was light weight (about 30 lbs) so carrying back up the hill was not very difficult.

However, this glider design had some shortcomings. In launching there was a narrow window of angle of attack to successfully launch and when in turns it tended to lose a lot of altitude. The glide angle was poor ( about 3:1 or 4:1) so a steep training hill was required just to get airborne. If flown at higher altitudes it could be put into a non-recoverable dive, when the sail went into full luff condition. But, all things considered, this simple glider was responsible for many people entering this new sport even with the lack of flight schools at that time.

Beginning hang glider students at present are taught on general purpose hang gliders capable of long distance flights. These gliders are designed for performance rather than ease of use for someone who has never flown one before. The only hang glider, that I know of, that was designed specifically for beginning instruction, is the Wills Wing Condor 330, which is no longer in production. It was still based on the common plan form of the single surface gliders flying today but had a very large area (330 sq ft) and a high lift, soft stalling, high camber airfoil. This was a good trainer but was still a long span, hard to ground handle, glider. The structural tubing was reduced and the sail thickness was reduced in order to reduce the weight of this monster hang glider but it still weighs in at 55 lbs. The glider is not certified for anything and WW says not to fly it in any heavy conditions (or higher than you care to fall). Unless short packed, it would be a problem to car top on many vehicles. However, a lot of pilots began their learning on this glider and I love flying mine at the beach.

THE GOAL:
To design a basic trainer hang glider specifically for that use, disregarding any other performance goals. A glider that is under 40 lbs, has a high lift (high camber) airfoil, has a large sail area, is slow flying with a gentle stall, has a glide angle much better than the Rogallo, easy to launch and land, and easy to ground handle. A glider that avoids the aerodynamic problems of the “standard Rogallo”.

After a student gets confident with the launching, flying, and landing of this trainer they then “graduate” to a utility glider which they ultimately will fly from higher launches and in rougher conditions. THIS GLIDER IS THE “TRAINING WHEELS” EQUIVALENT OF LEARNING TO RIDE A BICYCLE. Most people riding a bicycle today are riding something that is much different than what they learned on. Such will be the case of the Basic Trainer hang glider in relation to what they will fly beyond the beginning training.

THE HG BASIC TRAINER DESIGN:
As I said, this project was started as an open source project last May (2018) on another forum. There were inputs from other people along the way, as I also developed my own design ideas. It culminated in the building and test flying of a free flight model scaled at 1/5 of the full scale design. The model’s battens are scaled from Condor 330 battens. 

The model, without any external control, flew in stable flight above the low bluff at Dockweiler beach CA. The wind that day was a little gusty, especially for a beach site. Pitch recovery was good with the CG at 30.5% of MAC (mean aerodynamic chord). Directional stability was good and the model climbed in slope lift and one time it even soared the low bluff for a distance of several hundred feet on its own. When the model would turn off the wind it didn’t have any tendency to tighten the turn but made fairly flat stable turns. Because of the encouraging test results on the scale model, I’ve decided to go ahead with the full scale glider construction.

I present this design as “open source” and I have no commercial interest or claim on any products built from these ideas. All I ask is that I be given credit for any of these design ideas if utilized by other persons.

The design is a low aspect ratio, short span, high lift (high camber), large area glider. There is tip twist for pitch stability reflexing and to stall the tips last and a "swallow tail" center that is also reflexed. It should be slow flying, with soft stall, stable but very responsive to weight shift control of pitch and roll. Some people have expressed concern about tip weight slowing roll response, because of the 6 feet long truncated tips. I point out that the 13.5 feet moment is shorter than other gliders of similar area, which will help. The complete glider weight goal is to be under 40 lbs.

The final design comes out at 27 feet span and approximately 280 sq ft. The weight will have to wait to be seen. I’ll use the lighter sail cloth also used on the Condor 330 and tubing sizes will be less than what would be used on a general purpose glider. The airfoil is the Condor 330 airfoil, and I will be using some of the actual 330 curved battens.

One area this glider might find its use beyond basic training is in soaring low beach front dunes “dune grooming”. Its short span, large area could make for good close in ridge soaring, keeping more of the glider in the better lift zone and the turns would be tighter.

All of my drawings are in AutoCAD, so I can’t attach them but I have attached a jpeg image of one drawing. I’ve also attached a photo of the model glider rising in slope lift above a hand launch.

I’m also looking for a wrecked salvage glider, preferably a WW Falcon or Alpha that I could cannibalize for fittings. Since I will not be selling this prototype glider I don’t need new fittings. I’ll be using all new tubing so I don’t care what condition the tubes are in or the sail. Please let me know if you know of one that’s available.

Frank Colver

Basic Trainer, sail & battens design.jpg (324.29 KiB) Viewed 5505 times

Soaring the bluff.jpg (248.34 KiB) Viewed 5505 times

[Frank Colver]

Originally posted May 13, 2018 12:39 pm

My intent is to build a glider so easy to ground handle with good roll control response in flight and good pitch damping + slow flight and landing, that we almost return to the days of the rogallo but without the bad characteristics of that flat flex wing design. Many people taught themselves or took lessons with gliders that were easy to ground handle and fly but lacked the good parts of the fixed camber airfoil (battens) and reflex of today's flex wings. This is strictly a "training hill" or "dune grooming soaring" glider.

Shooting for a all up weight of less than 40 lbs using 1-1/2" cable braced tubing (similar to the WW SST) and thin light sail material.

I'm assuming a low sink rate with a glide ratio somewhere between that of the old standard rogallo and today's single surface flex wings. Maybe the L/D will be in the neighborhood of a large paraglider.

My first thoughts on this design is shown below. Please carefully read all of the text on the drawing before commenting.

Frank Colver

file-22.jpg (196.12 KiB) Viewed 5505 times

[Frank Colver]

I like your thinking.

Shortening the wing span should make roll control much easier when standing on launch.
In my experience, that's what people struggle the most with at Dockweiler.

Yeah, that's the general idea, Bob. That's why the old standard rogallo was so much easier to ground handle. But without a permanent defined airfoil it was harder to launch. You had to be more careful of angle of attack as you started running.

Higher aspect ratio & span is needed when we want a good L/D but not necessary for a low sink rate. That's where large area and high camber airfoil can get you. I plan to copy the Condor 330 airfoil in the front.

Note the return to the WW "swallow tail" for reflexing the center batton of the sail and a generous amount of movement of the keel pocket in roll control.

If I decide to go further along these lines I'll build a 1/5 scale free flight model to test, like I did with my Skysail in '71.

If I were to build the full scale HG I could probably purchase a lot of the hardware from Wills Wing. Like for the three corners that are 120 deg I could use WW Falcon or Alpha nose plates, etc.

From WW archives I have the "wingpost" LE cable bracing drawings which I could duplicate if they turn out to be what I need there. As it is presently shown, I would need to brace the LE's on the inside, under the sail instead of out in front because the cross spar goes all the way out to the LE tip corner. The pull on the sail would be trying to bend the LE inward in the center instead of tip flexing.

A lot of mechanical and structural design yet to be done before a simple outline becomes a buildable (& foldable) glider.

Thanks for your comments, Bob.

Frank

[Frank Colver]

Regardless of design, after a few flights students will want to fly the one that goes the farthest.
It's human nature.

Right Rick that's the idea! Get them used to an easy handling glider that flies like a rigid PG and then move them on to one of the utility gliders for mountain flying.

Are you saying you are not for this approach to learning? The status quo is good enough?

But for beach dune soaring the basic trainer is the best. Being able to work in closer to the dune and fly slow is a big advantage there. So, even advanced pilots would still be using the trainer for that type of flying, like Dockweiler soaring.

Frank

[Frank Colver]

Are you saying you are not for this approach to learning? The status quo is good enough?

Frank, while I do believe the status quo as defined by a novice learning to fly on any old, bagged out single surface wing IS sufficient and proven over generations, I am open to new ideas.
But I'm afraid the idea of winning soaring parachutists over to hang gliding by designing even more responsive trainers doesn't explain why we once had tens of thousands of hang glider pilots without them.

Hang gliding is inherently harder to learn than paragliding.
That isn't going to change.
Greater effort yeilds a greater reward.
I'm fine with that.
I don't care if pilots struggle with wide wings at take off.
That's a skill you learn.
Struggling at takeoff is how you learn it.
Greater effort and learning produce better pilots.
The problem with dwindling hang glider pilot numbers has to do with the absence of a real national hang gliding association.
Too high a bar for training, absence of honesty and a shameful level of advocacy.
The potpouri we have now doesn't work for hang gliding.
Until that changes, I doubt any innovations will matter much.
But I encourage you to prove me wrong.

Rick, Jim's suprone harness and flybar will prove you wrong.

Frank

[Frank Colver]

The problem with dwindling hang glider pilot numbers has to do with the absence of a real national hang gliding association.
Too high a bar for training, absence of honesty and a shameful level of advocacy.
The potpouri we have now doesn't work for hang gliding.
Until that changes, I doubt any innovations will matter much.
But I encourage you to prove me wrong.

I think everything we can do can help some. Those who want to design new gliders can help. Those who want to design new harnesses can help. Those who want to build new associations can help. Without the benefit of omniscience it's hard to know which little part will help the most. But every little part helps some.

The key is to find a part - any part at all - that inspires you and do it. Whether it's publishing great historical accounts (thanks Rick) or designing new gliders (thanks Frank) or holding meets (thanks Sam) or finding new training hills (thanks Scott) or posting to hanggliding.org (thanks Mike) or attending Supervisors meetings (thanks Joe) or quitting USHPA (thanks Bill) or posting regular club events (thanks Robin) or testifying in court (thanks Ernie), or doing any of the hundreds of other things our members have done ... they're all a part of saving the sport that we all love.



The key is to go out there and DO SOMETHING!!!

Jim's suprone harness and flybar will prove you wrong.

I hope you are right.
He showed it to me the other day.
It looked really comfortable.
And there's not much question in my mind that suprone is probably much safer than flying prone,
and I like what Jim has done to ensure roll authority on par or perhaps greater than prone.
That should be a big deal.
It may attract parachutists and older folks to hang gliding.
As for performance-oriented pilots, I doubt they'll show much interest.
Two horizontal bars present too much drag.
Hold a base tube out a car window at 50 mph to see what I'm talking about.
The fact that only one horizontal control frame member is needed is key to a new suprone hang glider design.
The trick would be to make a control bar shaped like a capital "A".
The horizontal section would be bowed forward for comfort and a cable runing through it for safety.
The side wire attachment points could be engineered to be higher on the frame, closer to the horizontal member.
Overall, of course, this produces more stress on the horizontal bar.
The flybar and the lower legs to the side wire attachment points would probably have to be stainless steel to withstand tension at 4 gs from the side wires without yielding or work-hardening.
If you didn't want to go to that much trouble, then simply replacing the base tube with a cable would help.
It's not that I don't like the new harness. I do.
What bothers me is that I think the new harness requires a new design of control frame to be complete.
That lower crossmember is completely unnecessary.
If it was gone, the drag presented by the suprone harness and the control frame would approach that of a prone pilot on a conventional frame.
It would do away with the interference of the lower bar in launching and landing.
It would also look extremely cool.

I agree but what Jim is starting out with I think is the right approach. Start first with a system that existing HG pilots can go with on their current gliders and then evolve into new glider designs specifically for suprone.

Meanwhile, I'm going back to seated with an option to use a Flybar or legs below the bar as in the days of yesteryear. Remember, not everyone wants to fly cross country.

That said, this thread should return to discussions about basic trainer design ideas. I make the case that more people will take up hang gliding and become enthusiasts and then advance into more sophisticated better performance hang gliders if their first flights off a training hill are easy and fun without a lot of struggle. It took me a lot of time to learn to fly because I was learning on a high performance glider, my Skysail. If I hadn't designed and built it myself I might have given up.

Once the Skysail got beat up to the point I was concerned about its airworthiness I bought an Eipper Flexi Floater (standard rogallo) and discovered why so many people had taught themselves so quickly. It was a "piece of cake".

I'm for returning to that easy beginning to the pilot learning curve for hang gliding but with a better design than the "standard" Rogallo. Get people "hooked" first, then advance them.

Frank

[Frank Colver]

Using a geometric approach shown to me by Mike Meier at WW I have approximated the CG of my basic trainer glider design. There will be more error in my calculations because my sail is not cut in the straight line at the TE. To be more accurate I would have to come up with the straight line equivalent of the area back there.Mike showed me how to find the Mean Aerodynamic Chord and then set the CG at 25% of that chord line. This should get me into the "ballpark" for the initial tests so that the CG is not way off to begin with.

I'm getting close to building the 1/5 scale flying model.

Frank

Basic trainer approx CG .JPG (235.96 KiB) Viewed 5497 times

[Frank Colver]

I see you have increased the truncated portion compared to the initial drawing sent to me via email Frank. As a matter of observation, I also see the truncated portion, the leading edge, and the crossbar all share a common junction point. Also, the crossbar is drawn straight across.
I have two questions so far.
1. Is the crossbar going to be divided and floating like current hang gliders?....and
2. How are you planning to join the crossbar, leading edge, and truncated portion? I can imagine a regular type junction for the L.E. and crossbar but with the junction plate extended on the truncation side to provide a "pivoting point" for the truncation....so all three tubes are actually joined by a single plate?
3. If the crossbar is going to be floating, and the truncated portion is also going to be foldable, I see a fairly short package if this is the case. If the truncations could fold to lie parallel with the L.E. the disassembled glider will not be much longer than the keel itself....and only 40 pounds?
Yes please!
The shape is almost identical to one of my favorite paper airplane designs.
BTW....to everyone else...
I had the privilege of being at Wills Wing as Frank was sharing his ideas with Mike Mier...Kinda like a fly on the wall....
I was actually pretty surprised as Frank suggested smaller diameter tubes like we used to use cable braced via deflexors and Mike didn't flinch an inch....Mike said, "sure, why not"?
I remember the tests done on the wills wing SST....they hung six pilots from that cable braced glider made from 1 1/2" by .049 tubing and the glider never broke even though the leading edges were horribly deformed....that old glider was super light and strong as a bull.
I love it Frank.
Although no design of any aircraft can be totally idiot proof.....this design is going to come awfully close.

I am sure you have your own plan for holding the truncations in the "flying" configuration....to hold tension in the trailing edge and to determine washout, etc. etc......
Since all three tubes are coming together at one point (the L.E., the truncation, and the crossbar)....I can see multiple possibilities....
Any of the ends of those three tubes.....the rear of the L.E., the front of the Truncation tube, or the outside ends of the Crossbar, can be extended beyond the junction of all three to provide a point of attachment

Thanks for your comments, Jim.

I think I mentioned somewhere that the cross spar would be floating and foldable but maybe it was just in my head. I was thinking I could buy the ball and socket joint from WW and modify it if it didn't fit the tubing I use.

As far as folding goes I just have a general idea floating around in my head. The truncated tips would have the diagonal braces removed and then folded inward along the LE's. I'm hoping that with a "noseplate" type of junction at the place where the tips, cross spar, & LE come together I can get a configuration where all of those can fold together. This is something I can physically model to try different things if I can't work it out in AutoCAD. The "fly in the ointment" will be how much room the sail requires as it bunches up against the tubing as it is folded.

For holding the upward twist in the tips I'm counting on cable from the king post. The short span will give me a greater angle of the support cables which will help and I may also have to go with a fairly tall king post. I'll probably need cable to the tip ends from the base tube also. That diagonal brace from the tip centers to the LE's is going to be a very important component that the support cables work with.

There will be three main design stages:

1) Test the flight performance in a 1/5 scale model. Make any changes needed from results there.

2) Decide on tubing sizes and cable bracing methods, where used.
At this point I will need to evaluate the tubing size/weights for "complexity vs benefit". It may be that with the short span that 1-1/2" x .049 6061 cable braced may not be much of an advantage over 2" x .032 7075 not cable braced. BobK suggested this evaluation. Although I have an inclination to trust more the structural integrity of the cable braced approach.

3) Design detailed junctions of folding components and other hardware components. Probably going to be some physical full scale modeling done here.

Next will be the construction of the full scale airframe and getting battens made by WW. At this point it won't be complete with control bar or king post. Just a lay on the floor airframe. Now beg, conjol, plead, with Steve at WW to make me a sail for it. Actually before the battens ar made I hope to get some input from him on the exact cut of the trailing edge curves for distribution of loading and airflow without flapping edges.

I envision the sail tension along the LE's to be a grommet with a line extending out to the corners with the tips to pull tension outward. The ends of the tips could be done the way it is done on current glider wingtips.

Jim, I may follow your lead and offer to buy a block of time from Wills Wing for getting more input from Steve. If they would sell me several hours for an "advice and sail design details conversation" it would be money well spent. Remember at this point I have the basic airframe done and I will have my batten curves design approximated.

To be continued.............

Frank

[Frank Colver]

Amazing project Frank!

If I weren't closer to the Atlantic than to the Pacific then I might offer to help in the development.

Hey gang,

Not sure what the plan is, to attach the truncated tips to the main wing spars. In the true spirit of HG "R & D" (as in, Rip-off & Duplicate), I would suggest using bent joiner tubes (rather than any heavy bolted structure), similar to what was used on the ASG-21 Albatross.

Those joiner tubes were bolted to the leading edge, but I re-made mine with three equally spaced Stainless Steel 0.25" blind rivets (instead of bolts), to save weight. Together with other crafty hardware mods there, I removed (IIRC) about 60% of the tip assembly weight on the ASG-21, and I was able to demonstrate to Tom Price that my Albatross had about the same 45/45/45 roll rate as a WW Raven. He said if he had not seen it, he would not have believed that.

Now I recall that the ASG-21 joiner tubes were bent rather sharply, with some minor kinking in the middle of the bend. I believe we can make those bends better today, using a slightly larger radius, and bending the joiner tubes before applying the T-6 tempering process.

Hope that helps a bit.

Thanks for the suggestion Red.

I was also thinking of using the "joiner tube" method you suggest but since I will be fabricating this glider in my shop, using the machine tools I have, I was going with bolted plates because it would be easy for me to fab those fixtures. However, I definitely agree that bent tubes would be better from a weight standpoint and avoid sharp places where someone bumping into the tips would get cut.

However, the use of plates and bolts also facilitates my folding of the tip tubes in along the LE after removing the diag brace tubes. Additionally, if I want to adjust the horiz tip angle slightly greater or lesser than 120*, to change the tip sail tension, I can do that by changing the length of the diag braces when using plates instead of a fixed bent tube.

If someone were to put this "one off" experimental glider into production, then the joiner tubes could be the way to go, as you suggest.

Frank