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Old Apr 15, 2012, 11:39 PM
A witty saying proves nothing.
kcaldwel's Avatar
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Has anyone built a model of an ATOS hang glider?

It seems like a very good Nurflugel candidate. The later ones have sprouted a small horizontal to add some pitch damping to stop tumbling with the low CG. If the CG was up higher and without a big mass hanging from a string, that wouldn't be needed.

It has an elliptical lift distribution, no fins, and no adverse yaw issues because it uses spoilers for roll control. Use the flap for pitch trim, maybe coupled with a CG shift?

This paper has an analysis of the aerodynamics, and does a comparison with a Horten:

http://ozreport.com/data/AIAA-2006-446-418.pdf

More photos here:

http://www.a-i-r-usa.com/content.asp?ID=4259

Kevin
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Old Apr 16, 2012, 12:30 AM
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Kevin,

I hadn't seen that paper before but it really got my blood boiling! Most people on this forum won't care about my rant on this, but having been involved in hang glider design and manufacture for over 20 years, I feel entitled to rant a little.

The Atos is not a Class 2 hang glider, it's a Class 5 glider. Class 5 was created by the FAI because the Atos-style gliders couldn't match the Swift's performance, so they made them a class of their own. This was a big political battle at the FAI that lasted several years. The Swift, Millennium, and Archeopteryx are the only Class 2 hang gliders of relevance that I'm aware of. The paper claims the Swift has a 20:1 L/D when we measured 24:1 in repeated tests. Others have measured higher numbers on the Aeriane version of the Swift. I have flown against both gliders in competition and can guarantee that the Swift has at least 5 points glide advantage over the best outfitted Atos at all speeds above 35 MPH. The Swift has 30% laminar flow wing and significantly lower pilot drag than the Atos, hence the higher L/D. The paper also claims the hook in weight of the Atos is 150kg = 331 lbs! I think they mean the maximum rated payload weight, not hook in weight.

The aerodynamic analysis they did is probably valid, but the comparison to my favorite hang glider left me a bit irritated.

The Atos is still an amazing glider, primarily for it's extremely low sink rate, a consequence of this design's enormous wingspan (the Atos VR has a 45 ft span!) It outperforms all conventional flex-wing hang gliders but it still falls short of the raw X-C soaring capability of the Swift.

Steve
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Old Apr 16, 2012, 01:12 AM
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Hello,

Interesting wing ... is that little stub of a tail really needed? seems almost there as an afterthought but I know about as much about aerodynamics as the average cow does about riding a bicycle sooo ... I wonder if you could build this thing as an RC model with a pilot doll hanging underneath (could be used to stash the Rc gear like the battery and Rx). The technical paper is largely over my head but ... interesting all the same.

Jens
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Old Apr 16, 2012, 09:15 AM
A witty saying proves nothing.
kcaldwel's Avatar
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Steve,

I remember the hang glider class battle well, and thought it ridiculous the Atos had it's own class without the Swift and Millennium too. Having flown with both I know the Swift far outperforms the Atos. But the Atos is still a very nice hang glider and flying wing design. The simple control system using a HG like control frame was a brilliant idea to simplify the transition for HG pilots, despite the higher drag of the exposed pilot.

Jens,

As I said in my first post, the little tail is a later add-on to add pitch damping. It isn't required if the CG is higher and/or the main mass isn't allowed to shift to unstable CG positions. The early ones flew for many years without the little tail even with the low and shifting CG.

Kevin
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Old Apr 16, 2012, 09:58 AM
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Steve: Feel free to rant... That's what we're here for. I did not know about the class battle.

The "little stub of the tail" is really needed if you are unlucky enough to get into a tumble or what's called a "tuck". I remember years ago seeing a photo of a prototype wide nose angle hang glider, new at that time, with the same same tail. Hand written on the white tail, in bold felt marker was "F*** the Tuck". That photo told the whole story.

Kent
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Old Apr 16, 2012, 10:28 AM
A witty saying proves nothing.
kcaldwel's Avatar
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Kent,

The hang glider tuck phenomena is largely due to the low CG with 2/3 of the mass way below the wing, and the loose attachment of the mass. With the low CG and the pilot aft in slow flight, and sudden lowering of the AoA from a gust will move the CG to an unstable position.

The attached drawing shows the CG shift with AoA from a low CG. If the CG starts near the aircraft neutral point, it is easy to have it shift behind the neutral point causing pitch divergence. On a hang glider with 2/3 of the mass below the wing, the CG shift with AoA changes can be dramatic.

The little tail just adds some damping to slow the tuck, and allow the pilot to shift forward to a stable CG position. The low sweep angle of the Atos and other rigid wing hang gliders meant they had very low pitch damping, and the tuck could happen very quickly. Conventional hang gliders have other techniques that increase the wing reflex when the sail is loaded negatively.

On an RC version of the Atos, if you keep the CG higher and firmly located, it wouldn't need the little tail. Or if you want to be able to perform tucks on command, leave the CG low. I think Eric Raymond used to do that on the Sunseed?

Kevin
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Old Apr 16, 2012, 11:03 AM
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Here's how you can rig the controls for true hang glider flight:

http://airplanesandrockets.com/airpl...r-1974-AAM.htm

I built one of these in 1974 and it worked!

Steve
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Old Apr 16, 2012, 11:10 AM
A witty saying proves nothing.
kcaldwel's Avatar
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Quote:
Originally Posted by mlbco View Post
Here's how you can rig the controls for true hang glider flight:

http://airplanesandrockets.com/airpl...r-1974-AAM.htm

I built one of these in 1974 and it worked!

Steve
Steve,

I remember that article!

I was busy throwing myself off hills (into hills?!) on a very similar full size contraption by then, so I never built one.

Remember the radical high aspect ratio Cronkite V with the spoilers for roll from that era? I still have the plans for that one...

Kevin

Edit: I love his control mixer! Hold the Tx at 45 degrees!
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