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Old Feb 26, 2013, 05:05 PM
Director of Entropy
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Fast Slope Soarer - Questions, then Build Log!

I have a few questions about scratch building my first plane. I've flown 2M balsa ships and a Zagi THL for a while, but now I have the itch to build a faster slope soarer for 15 to 25 mph winds. I know comparatively little about nurflügels but have started piecing a design together from info here and airfoil databases. I'm thinking:

1. Swept wing
2. PW51 foil with PW51-10.5% tips, unless convinced otherwise (see thread here: http://www.rcgroups.com/forums/showt...=589179&page=3)
3. Span of 2 meters or a little less
4. Foam core wing with carbon spars, maybe some glass or carbon covering if needed
5. wing loading: ??
6. Sweep angle: ??
7. Chord width: ??

I was originally thinking of something like a CO5, but they seem more complicated to build and I haven't heard anyone comment if they make better slope soarers than chevron (zagi like) wings.

Any comments or suggestions on the items above??

Also - when cutting templates for a foam wing, should the airfoil cross section be kept perpendicular to the leading edge along the length of the wing or parallel to the long axis of the plane? It's kind of hard to explain, I can draw a picture if need be.

Please let me know what you think, I'm really itching to start building this thing!
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Old Feb 27, 2013, 10:36 AM
Director of Entropy
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So after more reading and research (I've built up a four page sheet of links and notes), I'm leaning towards a CO5 type wing with MH45 foil. I was hoping to find something 2 m or under for small slopes and ease of transport (I intend to make it a one piece wing to keep things simple), but 2.5 m is how the plans are listed.

About the airfoil sections and their orientation - I've reverted from my previous statement; after even more reading I think the "correct" way to do it is to keep the desired airfoil section parallel to the airflow. This has been a contentious topic...

I'm thinking foam core with carbon or glass sheeting. Thoughts anyone?

EDIT: Link to discussion on swept wing airfoil sections: http://www.rcgroups.com/forums/showthread.php?t=806512
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Last edited by EarthMagnet; Feb 28, 2013 at 09:48 AM. Reason: Correction again to airfoil profile
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Old Feb 27, 2013, 11:08 AM
I don't like your altitude
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You may find this interesting
http://www.rcgroups.com/forums/showthread.php?t=1587639
I've just built a balsa sheeted foam wing using Verns tow spar technique and it's very rigid.
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Old Feb 27, 2013, 11:56 AM
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C05 type will fly well and is easy to build. Would be a good first build if you have never done this type before. You can cut it down to 2m if you want, you'll need to recalculate the cg.

As for structure, sheeted or glassed foam is good, as is built up and glassed.

If you cut the cores with the section perpendicular to the LE you will no longer have the section you think. Instead it will be longer and thinner with lower camber. Might not cause problems.
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Old Feb 27, 2013, 04:10 PM
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wing loading

If you're shooting for 15 - 25mph winds, I'd start with a wing loading around 15 oz/s.f. My Plank 101 can thermal at 17 oz/s.f. The heavier planes require a stiff and strong wing for flying and landing loads. Don't forget torsional strength if you have lots of wing sweep.

Kent
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Old Feb 28, 2013, 10:13 AM
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Thanks for all the tips guys. I believe what I'll make is a scaled down version of Miniphase's 3.0 meter wing (http://www.rcgroups.com/forums/showthread.php?t=1577195). I like the idea of starting with something well designed and working from there. At least then I'll stand a chance of making something flyable despite my lack of building experience. I'm working up the 3D model now, will post when that's roughed out.

Stupot - thanks for the tip on the carbon spars, that's an excellent idea. One of the many things I haven't decided on yet is how I want to cover it. A 2 meter wing with MH45 airfoil... should I: Option 1. Use the carbon spar technique and balsa cover or Option 2. Cover the wing in thin carbon or glass and vacuum bag it, creating a stressed skin with minimal or no spars? Would Option 2 end up being too heavy or twisty for a 2 meter slope ship?

To compound the problem... I forgot I never finished building the workbench in my garage. I designed a nice mortise and tenon framed bench, but got sidetracked with other things. I foresee taking tomorrow off from work to finish the workbench and start a hot wire cutter this weekend.
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Old Feb 28, 2013, 11:07 AM
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Option 2. Cover the wing in thin carbon or glass and vacuum bag it, creating a stressed skin with minimal or no spars? Would Option 2 end up being too heavy or twisty for a 2 meter slope ship?
Oh this is an easy one......
If you can afford to cover the wing top and bottom with carbon fabric and vac. bag then that would be best. Strong, smooth, shiny....nice. You can lay up more fabric at the high stress areas. Composites are ideal. The stressed skin approach engages all of the foam for use as a shear web, where as the carbon spar is more of a concentrated shear load on a small strip of foam. (not as good)

At 2m span, the stressed skin should look and perform well for every thing except dynamic soaring.

A more economical compromise might be to use Sig Manuf. Rhino hide for skin covering.

If you go with the carbon / vac. bag please post a build log so we (me) can learn from your efforts. It's what we do here on the Nurflügel forum !

Still itchng to build? ... Go for it !

Kent
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Old Feb 28, 2013, 02:35 PM
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Hmm, maybe I should keep my first one simple and inexpensive. I haven't seen the Rhino hide before, I'll have to consider that. My carbon/fiberglass skills are modest at best. I worked in aerospace composites for a few years, making and doing destructive tests on carbon/epoxy laminates, but that doesn't make me an expert in plane building by any stretch.

Here's something I knew was going to happen: I've scaled miniphase's 3.05m nurflugel down to 2.0 meters, but of course, the wing area does not scale linearly. At about 2/3 the size, the wing area of the 2.0m is less that half (0.45 or so) of the 3.0m. I'm thinking I need to increase the chord of the 2.0m model, but to what size I'm not sure as I don't feel comfortable guess the all up weight. Right now it's 6.48in chord in the model. Maybe till I stick my thumb in the air, guess an AUM and use a 10oz/sqft loading just to be safe?

3.05M ship on the bottom, 2.0M in black on the top




Thoughts on the chord size?
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Last edited by EarthMagnet; Feb 28, 2013 at 03:20 PM. Reason: forgot to include chord size
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Old Feb 28, 2013, 03:11 PM
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Many will argue that the 2m version needs a bigger chord, but I'm not one of them.

If you plan on flying slope, the added wing loading of the smaller chord will allow normal building methods to yield a high enough wing loading to be fun without adding ballast. I add 16oz. to my Plank 101 for sloping and that wing loading, 17 oz/s.f., 50 gr/sq dm, is barely enough. Of course the thinner wing will require a solid structure (carbon cloth). Mini servos should fit. If there is a slight bump at the servo, it's not the end of the world.

Of course the DS guys specialize in these smaller chords. Take a look at "flo" comments on this page.

Rhino hide link

Kent
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Old Mar 01, 2013, 02:04 AM
I don't like your altitude
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Originally Posted by mhodgson View Post
C05 type will fly well and is easy to build. Would be a good first build if you have never done this type before. You can cut it down to 2m if you want, you'll need to recalculate the cg.

As for structure, sheeted or glassed foam is good, as is built up and glassed.

If you cut the cores with the section perpendicular to the LE you will no longer have the section you think. Instead it will be longer and thinner with lower camber. Might not cause problems.
Mh,do you have a link to that thread where the perpendicular to the l/e/ airflow was discussed?
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Old Mar 01, 2013, 09:40 AM
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Mh,do you have a link to that thread where the perpendicular to the l/e/ airflow was discussed?
Here is one of them: http://www.rcgroups.com/forums/showthread.php?t=806512

There are others though. I'm not sure if it's this one, but somewhere I read that airfoils on full scale swept wings used to be designed with the airfoil perpendicular to the leading edge solely for ease of manufacturing.

I have a question out to an aerospace eng. friend about this. He also specialized in flutter analysis, one of the few in that field. I'll let you know what he says.
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Old Mar 01, 2013, 09:45 AM
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Oh, and here's the design as it stands for now:



Specs:
2.0 meter span, MH45 airfoil, 25 deg sweep, 3mm washout, chord size about 7.6in

Estimated AUW: between 3.0 to 4.0 lbs, which would give me wing loading of 10.5 to 14 oz/sqft. I'd like to have a higher wing loading as suggested earlier, but I've never flown anything with much more than 9oz/sqft and I'm worried about guessing the AUW on my first build.
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Old Mar 01, 2013, 09:49 AM
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I have a question out to an aerospace eng. friend about this. He also specialized in flutter analysis, one of the few in that field. I'll let you know what he says.
This article on Flutter Suppression suggests that a rear spar is key to controlling flutter.

Kent
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Old Mar 01, 2013, 11:38 AM
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I too would like to build a winglet as you have shown, but finding adequate structure for this configuration is a tough task.

I'd be interested in see how you plan on building this.

Kent
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Old Mar 01, 2013, 05:13 PM
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I too would like to build a winglet as you have shown, but finding adequate structure for this configuration is a tough task.

I'd be interested in see how you plan on building this.

Kent

Yeah, that's going to be tricky. I thought about doing a radius transition to the winglets, but I need to keep this simple. I'm thinking of extending the TE carbon spar out the tip of the wing when I lay it in, then anchoring the winglet onto that somehow. Downside to that would be the spar might get damaged if (when) I catch a wingtip. Not sure about this yet.
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