# HSA conference in Tehachapi (Sept 3-6)

Discussion in 'Soaring' started by Rienk, Aug 25, 2010.

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1. Aug 25, 2010

### Rienk

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OH MY GOSH !

I went to the ESA (experimental soaring association) website to look up some info from last year - and I see that I'm a speaker at this years Western Workshop...

I HAD NO IDEA !
(you'd think they'd confirm with me).

ANYWAY, I've been playing around with this design since last year, but I haven't gotten the support that I was expecting, so I have nothing ready!

I've posted some threads in the Design section, which I can use some feedback on, but more importantly, those of you who are into soaring and can offer some feedback on this design concept...

I CAN REALLY USE SOME HELP !

(the workshop is in two weeks)

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2. Aug 25, 2010

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*The airfoil is rather horrible. Nasty stall (the Astir can be flown close to stall with a huge rate of descent) and horrible performance. The Astir is nicknamed "concrete swan" and that's not because of it's grace. Try the airfoil Wortmann FX 81-K-130/17 for very good performance and very friendly stall behavior.
*I really don't like those dragbrakes, since they give rather big performance losses. I think my comments are in one of your other threads already.

And some minor points, but first a couple of questions for you. *What's the goal, performance, fun, easy trainer?
*Did you do a market survey (or do you have an idea) about that market?

I believe there's no market for "affordable gliders with decent performance". Not because people don't want them, but because gliders are there forever and thus many 2nd hand gliders are affordable. I've flown many hours on a Ka-6, manufactured before my grandfather got married. I've even flown a Grunau Baby, manufacturer before Hitler reigned, both in perfect condition and both easy and cheap to maintain, with similar performance (the 2500US$Ka-6) as a current day ultralight glider (the 40000 US$ Sparrowhawk).
Looking into seriously performing gliders it's even worse, a 40 year old Nimbus II can be had for US$20000, a new ship of equal performance (though a bit more compact and light) is way over a 100,000. This might be an interesting read too: http://www.foamworks.co.nz/ Last edited: Aug 25, 2010 3. Aug 25, 2010 ### Rienk ### Rienk #### Well-Known Member Joined: Oct 11, 2008 Messages: 1,364 Likes Received: 190 Location: Santa Maria, CA (SMX) Thanks for the reply. The goal of this craft is to have a rolling-launch or winch tow aircraft, that can fly with hang gliders. The price goal is for someone to be able to build it in 100-200 hours, for a cost of less than$9k. Simple enough for highschool students to build, and easily transported/stored in a small trailer (20').

I am curious about the airfoil recommendation.
The airfoil current shown was recommended by Dan Armstrong, an aero engineer and avid glider pilot (helps run the ESA). He recommended the Eippler for this design, as it is VERY low wing/span loading, and meant to perform between the airchairs and light gliders.

I would appreciate more feedback on the airfoil - as I'm getting ready to redraw the wing - and the airfoil shape is where I need to start.

Thanks!

4. Aug 25, 2010

### Autodidact

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Rienk, howdy. Does the airfoil matter a great deal for this application? For the wing loading and speed, it seems like and old fashion (simple) airfoil, like the clark Y or an old Goettingen (better for the pizzaz factor) might work fine.

Nice design, and I think you could sell some if it was cheap enough, despite the fact that there is no market, since people are sometimes swayed by the newness of things. Especially here in America; Europe seems to be lousy with classic gliders!

Also, a thick section would help with the strength.

5. Aug 25, 2010

### Topaz

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Hi Rienk,

Glad to see you spending a little time on this one, even if it's just for a conference presentation.

This aircraft is basically one step up from an air-chair, correct? Basically a micro-lift 'floater' for light thermal and weak ridge days, yes? Other than the one brief mention, I haven't seen your other "Design" section posts on this one, so excuse me if I go over something you've already stated elsewhere.

Overall? Nice. The airchair segment has been getting some small attention, but it'd be nice to see something a little upscale from that as you have here. That segment has been largely abandoned since the Carbon Dragon vanished from the scene. AFAIK, the ULF-1 is the only thing in that market with any sense of reality.

I don't see any problem with your airfoil at all. Eppler 603? Okay. My sole point on airfoils is that this glider will be operating at relatively low airspeeds (and high CL) almost the entire flight. High-speed performance is more or less irrelevant, and cross-country performance isn't even on the radar. As such, wing loading, span, and trim drag will play a far larger part in performance than wing section drag. Stall behavior can be tailored by wing shape (you're already there - hershey bar) and twist, if necessary. So you'll be picking your airfoil for its low-Reynolds number characteristics primarily, then thickness (for a light wing), then for the fact that whatever low drag it has occurs at a relatively high Cl. Low-Re lift and drag values will completely dominate your selection, since this aircraft will be flying very slowly almost all the time. If this Eppler 'foil meets those requirements, use it.

I have to disagree with Autoreply on the drag brakes. These are simple, light, and cheap. If they cost you a couple of percent of performance, so what? This isn't a competition ship. It's a weekend floater. Go simple, go light, go easy. The only ones simpler than these are Schweizer brakes, but those are heavier.

The only thing I'd change outright on your design is to switch to a single mainwheel, and a pneumatic one. A glider like this is going to live its life on dirt strips. You want a main that has a little 'give' to get over the small rocks and bumps that inevitably find their way onto such strips, but you can't afford the weight of any kind of springing or suspension. An inexpensive airplane-style pneumatic tire/wheel will do the job nicely, but is heavier than the ultralight-style wheels you have drawn here - so use just one (which is conventional to sailplanes) and come out ahead. A Lamb tire and wheel from Aircraft Spruce is a good example, or the Azusa polymer wheels. The other worthy addition might be a nose skid. You can save the expense and complexity of wheel brakes by simple expediency of a skid. After the landing is stabilized, the pilot just pushes the nose over onto the skid. Very effective, very simple, nearly fool-proof, and probably not much, if any, heavier than the entire installation for wheel brakes. Check out the SGS 1-26 for a visual.

I do have a slight bit of pause about the height of the wingtips above the ground. The dirt strips of which I speak often aren't groomed well at the edges - there's weeds. Catching them with a wingtip can result in a ground-loop. It's one of the main reasons all the other aircraft that have been in this category (Marske Monarch, Carbon Dragon, ULF-1, etc.) are all high-wing aircraft. IF IT WERE ME, I'd lengthen the tail slightly to reduce trim and parasite drag from the horizontal tail, move the pilot slightly forward to counterbalance, then move the wing up until the upper surface of the root is flush with the canopy sill. Get every inch of ground clearance for the wingtips you can. SGS 1-26/2-33 style tip wheels complete the protection (the trailing spring tends to push weeds out of the way, rather than hooking them).

Picking tiny little nits:

• Check the vertical tail area. Gliders are notorious for needing lots of vertical tail power - that long wing.
• Fair the lower edge of the rudder into the bottom fuselage mold line. Gets it up out of the dirt a little, and it just looks better.
• Lower the aft fuselage upper mold line towards the tail slightly? Reduces wetted area a little, but mostly this is just my personal aesthetic.
• See if you can't adapt an existing glider canopy to your fuselage. Even though I love the shape and expanse of it, the single most expensive component on this design is going to be that custom canopy. If this really is intended for sale to high schools and such as a project aircraft, you can save them considerable money by going to a off-the-shelf canopy. If I were building this just for me, I'd absolutely keep the one you've drawn, though.
Overall, I like your design a lot. I'd fly one in a heartbeat.

Last edited: Aug 25, 2010
6. Aug 25, 2010

### Hot Wings

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I can't tell for sure from your drawings but if this is to be a fabric covered wing I'd not consider either airfoil.

Anything with an inflection point is going to deform between the ribs. D. Mitchell tried this with the U-2 and ended up with a plane that, in theory, should have been better than his B-10. It wasn't

For a roll launch glider intended for training I'd not get too carried away with airfoil selection. Pick something between 15% and 20% thick, with low pitching moment, a benign stall, and build it!

Off the top of my head I'd probably just use something like a 4415 or a 4418. If you need a nice thick wing so you can move the spar back like your drawing just make it 21% thick, or sweep the wing forward a bit and make the tip 21% thick?

If you plan to skin it with ply or glass then maybe it will be worth the time to try to find a better airfoil.

7. Aug 25, 2010

### Hot Wings

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2 Posts while I type. I have to get faster:emb:

I concur on the wheel. I happened to be at Harbor Freight last week and spotted some foam filled wheel barrow wheels that are surprisingly light and appear to be durable enough for this application.

As for the canopy suggestion, I like the flat wrap on my Duster. Cheap and easy to make. Looks just as good as the blown versions IMHO. Also consider an open cockpit as an option.

Last edited: Aug 25, 2010
8. Aug 25, 2010

### Topaz

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Well THAT's a darn good point!

If it's fabric-covered, go Clark Y or something similarly flat-bottomed and easy to build, as Hot Wings is saying. Section characteristics are going to be a minor factor for this aircraft anyway.

I was assuming ply covering, or glass, despite the portrayed wing structure. Which was a bad assumption.

How is this wing covered, Rienk?

9. Aug 25, 2010

### Topaz

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Hey! You've got a Duster? How is it? I've heard nothing but good about them. A fun, simple, inexpensive airplane.

10. Aug 25, 2010

### Hot Wings

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I've not yet flown it. There is the little problem of not having any way to get it off the ground and I don't have a glider rating - yet. The nearest glider operation is 213 miles from my door, so lessons are hard to schedule.

I had rounded up a tow plane + pilot, an instructor that is only 2 hours away that would travel on the weekends for teaching at a club setting, about a dozen others that were "very interested" in a glider club, and even started rounding up parts for a winch that I offered to build. But when it came time to actually part with some time or money the "very interested" parties turned ghost.

I sold the SGU's, but I will find a way to get my glider ticket. It wasn't the most rewarding thing I've ever attempted to do and one of the reasons I'm so pessimistic about any group projects getting things done.

11. Aug 25, 2010

### Topaz

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At the risk of drifting this thread, yeah. What you're describing is the bane of every club's existance, even after they get up on their feet.

If you have any interest and might find yourself in the SoCal area for any extended period, my club (Lake Elsinore Soaring Club) has temporary, three-month memberships available for those living out-of-state, and four flight instructors on-staff as well as aircraft in which to train. If you've got any flight experience at all, that's more than enough time to pick up a glider rating.

PM me if you are interested, and we can discuss it without drifting Rienk's thread any farther.

12. Aug 25, 2010

### Monty

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Personally I'd go with high wing, strut braced, mono wheel. You might be able to do a flat wrap canopy and make it still look OK. You need a nose skid or a wheel even if you have a hand brake in case somebody noses it over. If you want to eliminate the brake, the skid works just fine. So go with KISS just use the skid. Definitely go with outriggers. Wheels that close together are not going to keep you from dragging a wing tip and will probably be harder to deal with from a ground handling stand point. It's really not that hard to handle even without a wing runner once you get used to it.

13. Aug 25, 2010

### Monty

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It's just awfully hard to get a tow pilot, tow plane, a glider, me, and the weather all in the same place at the same time.

You might look into auto Tow. Find a cheap heavy $500 beater with a V8 and use that to get you in the air. Cut a hole in the roof or get one with a sun roof. Use one of those wide angle or road race mirrors so you can see the airplane behind you. Make sure to be in radio contact. Now we are down to 2 people and one doesn't even have to be a tow pilot....but I wouldn't let my mother in law drive the car. ;-) I bet you can find somebody who is either already glider rated or wants to get into it nearby. You will both need to go get certified for auto/winch launch. It is different from aero-tow. If I lived nearby I'd show up. There are places where this will work great, like a field near a ridge or on a ridge. It's more location specific and less versatile, but cheap. 14. Aug 25, 2010 ### autoreply ### autoreply #### Moderator Joined: Jul 8, 2009 Messages: 10,732 Likes Received: 2,542 Location: Rotterdam, Netherlands No, you don't :gig: If performance is less of a concern, you might trade in a couple percent performance. Make sure they're BIG since that's one of the major factors, determining how easy it is to land. As for the airfoils I do definitely disagree. The Eppler is a plastic airfoil with a 35 kg/m2 load, not one for fabric and 12 kg/m2 and I mentioned its sometimes nasty stall habits. Pick something proven in a glider. The Ka6 is about the best fabric glider ever, it uses the NACA 63-618. I would go for that one, not for something that "might be" good or is good "according to someone". Most airfoils aren't designed for such low wing loads and turbulence. There've been numerous airfoils that performed excellent in a wind tunnel and on powered aircraft and horribly in reality. Since gliders (and especially floaters) fly 80% of the time in turbulent thermals that makes sense. Please do this. I've seen so many people think "they knew better", ending up either ruining their aircraft, their whole company (LS) or crashing it. Most did all and many of them were advised by qualified aerospace engineers... Having said that, I don't think there's a market for such a plane. The glider population is small and won't grow fast and there's still a sufficient amount of affordable 2nd hand gliders you can never beat on price. If you overhaul them (less work than building one) you have a practical new glider, with a guaranteed resale value and easy insurance. Here's club class: View With radio, instruments, trailer, parachute and certified for 4000 US$. You can never beat that, even if you give them away for free

15. Aug 25, 2010

### Topaz

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That's the route I'd go myself, in this class. Sort of a mini-SGS 2-33, built as lightly as possible to keep the wing loading down for the light lift conditions for which these aircraft are intended. And the high wing keeps the wings out of the weeds. The ULF-1 is right there, but is too complex a build for my tastes. Too many little parts.

ULF 1 - Description

What I like about Rienk's design is that it looks higher-performance, while staying with the airchair mentality. A fun deviation from the airchair norm.

All discussion of airfoils is completely moot until Rienk discloses the construction method for the wing, and how it's covered.

16. Aug 25, 2010

### Hot Wings

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Gliders must be cheaper in your part of the world. The asking prices on Wingsandwheels.com is almost double. :cry: I don't know how many actually sell for asking price.

But I do tend to agree that the market is limited and kind of saturated. The main factor in favor of having a kit available for such a low cost glider is that it is available NOW. You don't have to wait to hear about that good deal that has been setting in the back of the hangar for the last 10 years.

We also have to keep in mind that one of Rienk's goals is to change the demand side of this equation. We are never going to do that, at least here in the US, with 30 and 40 year old equipment no matter how competent it is for the task. The consuming public is image driven and there is nothing in the near term we are going to be able to do about it.

As for strut braced - I'd not go that route. A cantilever high wing will be heavier, but in my opinion it's easier and quicker to rig than a strut braced. That is worth the weight unless you are trying to make part 103 weight.

I'd also consider the long center section like my Duster. It's not normal and makes a trailer kind of odd, but it makes the outer panels just that much smaller and easier to lift. Moves the attach point out to a lower stress location too.

17. Aug 25, 2010

### Topaz

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Out on the playa here in the southwest this can be a great option, too. Used to be more of it than you see now. Auto tow up a few hundred feet, then catch the omnipresent thermals up as high as you want.

Doesn't take much performance. Sure looks like fun. :gig:

(See attached, from the BUG photo gallery: Picasa Web Albums - M-SANDLIN.info - Basic Ultrali...)

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18. Aug 25, 2010

### Rienk

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Wow! I have a lot of catching up to do on this thread. Sorry for the multiple posts coming, but i want to address many of the pointsi
The airfoil choice was given to me by an aero-engineer (and concurred by others at ESA), being the same airfoil that he is using on a VLG (very light glider).
I am open to suggestions.

The D tube will be plywood covered to the spar, and i am open to using very light wood for the rear as well. (I can get .020" and 040" material). I was intending the control surfaces tyo be ply covered - hopefully not needing fabric additionally wherever there is ply.

My understanding is that I should be able to get laminar flow with the ply, but that fabric should be okay on the back half. But since the craft will fly at such slow speeds, this may all be moot.
Still, with CNC cutting of parts, it's just as easy to do a 'nice' airfoil as opposed to a 'basic' one.

19. Aug 25, 2010

### Topaz

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The Duster and the kit-built versions of the SGS 1-26 brought a LOT of new people into soaring, at least here in the USA. It's a real shame there isn't something like that available now. I understand some of the Schweizer family have bought back the rights to the SGS 1-26 and are intending to reintroduce the aircraft as a kit, but we'll have to see if that really happens.

A new, more modern aircraft in this class could do more, IMHO, but of course it's a bigger business risk than most wish to undertake. If kit airplanes are a niche market, kit sailplanes are a niche inside that niche.

There will always be used airplanes lying around, some in very good condition. But there really is a pride of ownership in something new, and that's worth money to people. Why else would they buy new cars?

20. Aug 25, 2010

### WonderousMountain

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Can someone get me an invite?

I've biked 2,000 miles and will be in the area just in time. Coincidence?

I've never worked with ply that thin. Cool.

Wonderous Mountain