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Apr 16, 2015, 12:42 AM
B for Bruce
BMatthews's Avatar
Oddly enough the larger fancy "glass slipper" sailplanes that are up around 100 to 120 inch span tend to be in the same wing loading these days. For a 2 meter it would be considered somewhat heavy though.

At your size the wider chord aids the whole Reynolds number scale thing. So likely as not your 12.8 loading isn't as harmful as it might be. I know that I've got a lower aspect ratio model that is a trifle lighter a loading than yours but at around the same wing span it easily flies from my hand with a slight push. The key difference is that I provided for a good grip with a recess to stick two fingers into so I can give it a little bit of an extra shove to send it arrowing on its way.

What provisions did you make for holding the model for launching? And if there's no hand grip possible on the lower side how did you launch it during your fateful first flight?

I'm not doubting that you could have an actual CG issue. But it's likely equally possible that you simply could not give it the launch speed it needs if you have no good way to hold and guide it during the javelin launch style needed to send it on its way correctly. And in looking over the pictures I see no way to hold this thing for a proper launch unless you added something after the pictures.
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Apr 16, 2015, 01:08 AM
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There are currently no hand/finger grips, though it won't be too hard to add in.

I did add a hook in order to bungee launch and have made some flight attempts with that launch method. But due to pitch instability... failed. After I've made my 2nd prototype and corrected the CG, I bet hand launching will be feasible. Will keep you posted.

From Chilliwack eh? In Victoria here. Cheers.
Apr 17, 2015, 12:14 PM
B for Bruce
BMatthews's Avatar
Yep, it's not all that far for the electrons to fly is it?

To keep a clean belly on some of my own flights of fancy I've often thought that sprung fold in doors would work just fine. There would be a longer one on the one side to accept the four fingers and a smaller one on the other for the thumb. To avoid the problem of the doors biting down on the fingers as they are withdrawn the doors would be hinged along the inside edge and pressure from the fingers taken by the door and hinges against something more structural inside the wing. Likely some grip tape on the outside of the doors to give a good gripping surface would not be amiss for this either. With this setup the doors would never be at any risk of pinching the fingers as they are withdrawn. And a really stable and positive grip on the model for a hearty javelin like launch would ensure you can get the model up to proper speed before it leaves your hand. With a proper and good launch into any wind I think you'd be surprised at how easy it is to hand launch a model even if its stall speed is a trifle higher than what you can produce from a throw.

In your model's case it should NOT be an issue at all. Your wing loading might be well over a glider like wing loading due to the size. But it isn't any higher than a lot of sport models that can be successfully hand launched. Just don't let it go any higher on the new model. In fact work at lowering it a little if you can. For a model of this sort I like the idea of linking all the sheeting on the belly with a skin of resin and glass. But this means that the skin is the stressed part of the structure. So use only lighter grade balsa for the base sheeting and only a single layer of light glass cloth and minimal resin to bond it. On smaller models such as this grams count for either good or bad. And the more you take off the model and leave on the bench or shop floor the better.
Apr 18, 2015, 06:33 PM
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bcredneck's Avatar
as far as finger grips a simple dowel bonded to the spar at the tip is the best thing for gliders i even tossed 60'' gliders that way for slope soaring. I found that if i didnt have the updraft i needed from the cliff i had enough alltitude to get my glider back. It was a 2hr hike to get my glider if i didnt make it.

One thing to remember as you shave weight from your glider is that you need to be heavy enough to over come your drag i had to add weight to mine i needed 25oz to 820''sq or i would loss all my airspeed into the wind and drop fast on my launch or in turns trying to ride the face of the cliff
Apr 18, 2015, 10:41 PM
B for Bruce
BMatthews's Avatar
Since he's got a motor there won't be the same need as your slope glider for weight. Yes, on a glider SOME excess weight gives a higher speed range. But that's only so the weight in conjunction with gravity raises the power of "the motor" in a glider that uses gravity for it's power. On circuitgrove's wing the motor takes the place of that and generally in that case lighter is righter. In fact once you add a motor or engine a lighter model is actually potentially faster than a heavier model for a given power output from the motor or engine.
Apr 19, 2015, 01:19 PM
Registered User
It should be noted that the intention of this design is not to be a glider, but an efficient payload carrying airframe (robotics). I only incorrectly commented that it had glider-like wing loading. Thanks for helping me understand.

Regarding weight of the frame itself (no electronics), I found that I over design this airframe. I could easily cut down on total mass by reducing the thickness of the fuselage parts. I bet I could get it down to 600g.

The next design I generate will be lighter (but less resistant to crash). Learned a bunch with this 1st 3D printed one.
Last edited by circuitgrove; Apr 19, 2015 at 01:33 PM.
Apr 22, 2015, 03:45 PM
B for Bruce
BMatthews's Avatar
Just keep in mind that with a higher wing loading with the addition of the payload that the ability to hand launch quickly goes down the toilet. At that point you won't have any option but to either include landing gear or use a launch rail or possibly a take off dolly. Of the two options I'd suggest that a wire takeoff dolly is easier to transport and use. But obviously it does limit you to the smoother surfaces.
Jun 15, 2015, 07:17 PM
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Back on the job assembling the second prototype of the OpenRC Swift.
Jun 15, 2015, 07:24 PM
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BMatthews, those are good points and they got me thinking a bit.

For me, this is a proof-of-concept model. The design won't get much more development from me past the maiden flight of the completed design. It'll serve as an RC model, elastic launched and belly landed.

I want to start designing another mostly 3D printed model after this one. I'm already daydreaming.
Jan 03, 2016, 09:01 AM
Registered User
Hey, sorry if i missed the boat a little but i was looking to create something similar but a lot more lightweight. how did you apply monokote without warping the printed parts??
Jan 05, 2016, 01:20 PM
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I skinned the whole thing with 1/16" balsa sheets.
Jan 06, 2016, 10:29 AM
Registered User
Quote:
Originally Posted by circuitgrove
Back on the job assembling the second prototype of the OpenRC Swift.
It looks very nice

I would have made the main spar from two small and flat carbon beams and make a nice sherweb between them with a vertical and 45* pattern, it would look spectacular
Jan 09, 2016, 09:07 PM
Registered User
Interesting idea about the carbon fibre beams. I'll look into that for the next design. What is sherweb?
Jan 10, 2016, 02:10 AM
Registered User
Quote:
Originally Posted by circuitgrove
Interesting idea about the carbon fibre beams. I'll look into that for the next design. What is sherweb?
I'm sorry I think its called "shearweb", just like your ribs but seen from the front of the wing.
Mar 23, 2017, 09:30 AM
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omgsparks's Avatar
Just found this thread when surfing around. The concept greatly interest me.

I've used my 3d-printer to create a fuselage for a high performance wing but it was only possible basically because I had no weight constraints affecting me. The wings were already balsa, from a crashed ARF-model. https://www.rcgroups.com/forums/show...Lightning-Dart

Your hybrid approach opens up interesting possibilities. Would love to know about any progress on the project.


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