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Old Dec 21, 2009, 02:59 PM
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Stork 1 - a swept flying wing DLG

I finished my first attempt at a flying wing DLG (I called this one the Stork), and this Sunday I took it for a spin. I had help from Craig and Oleg with tossing and filming - the first 2-3 pizza tosses showed that the 22% MAC CG was a bit too much too handle, so I added a 1/4oz (7g) on the nose to quiet it down. After that it flew much better. On the fifth pizza toss (the second one in the video below) without any good reason the right fin just broke off - Oleg confirmed that the ZAP foam safe CA is crap. Oh, well, I really wanted to see what it does on a DLG launch, so I taped it a bit and gave it a spin. Actually about five - shown in the video is the first and the one before last (which was also the highest). It launched pretty good - due to the broken fin I went quite conservatively on power - maybe 30% of a normal launch the first spin and 60-70% of a normal launch on the last one. To my surprise the taped fin did OK. At the last launch the fin broke completely and I retired the ship for the day awaiting fin repair.

All in all, I'm pretty happy with how it turned out - it launched pretty well for the power I put in it - I expect it to go better as I increase the power. It seemed to float quite well - it's about 11.5 oz at a pretty big wing area (quite a bit more than a conventional DLG). I'm not convinced about the penetration - on the other hand, it was a pretty windy day and my conventional wide wing Taboo was not penetrating either without ballast.

Speaking of ballast, that will be a problem: it turns out that the CG of this beast is right at the hinge of the flaps - the foam there is about 3mm thick - no place to put a ballast tube there - any suggestions for a ballast tube are welcome!

I can't wait to fix the winglets and take it for another spin - I didn't get to trim it right with all that turbulence in the air - I'd like to have a late afternoon session in calm air to figure it out - it seemed to float especially nice with a touch of flaps. The last landing (hovering above the ground) is with full flaps down (not visible in the video).

If I like the way it behaves, I'll probably go for a pair of foiled winglets - the current ones are from foam paper plates (in case you wonder about the shape ). If I don't like it, I'll make it a sloper :-).

Stork 1 - maiden flight (2 min 1 sec)
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Old Dec 21, 2009, 04:26 PM
Oleg Golovidov
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Mihai, that is one cool flying wing you made! It definitely has potential. Takes a lot of experimentation (building time, materials, etc.) to figure out the correct configuration - twists, CG, airfoils, tailfins... Make stronger tails next time!!!
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Old Dec 21, 2009, 04:43 PM
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Oleg, coming from you this means a lot! The tails didn't fail - it was the darn CA that held them to the rods that let go! It's very unlikely that it will perform very well, but I think that it can be a good data-point toward a better one. So far, from the little I saw, it looks like it needs a bit more sweep (only a bit more) and a bit less chord - I'll know more after I fly it for a while.

Best,
M.
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Old Dec 22, 2009, 12:44 AM
Wood Chucker
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The A/R looks pretty high already but I'm hardly an expert. Sweep will help your CG placement I'm sure. I'll be following this without a doubt since I've been thinking about this very thing recently!
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Old Dec 22, 2009, 01:08 AM
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Dude.. that looks like it has a little potential!! Very nicely done.. Keep the updates coming!

Jim
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Old Dec 22, 2009, 04:57 AM
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I'm quite impressed at how straight it launches, to be honest!

One thing maybe that might help launch it even better? A long and bigger central vertical - not unlike that of the Alula, except expanded a bit on the vertical scale to get you more straightening on launch.

What airfoil series are you using? Or is that a trademark secret?
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Old Dec 22, 2009, 08:40 AM
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The big central fin would require a sort of a fuselage, which I'm trying to stay away from.

One thing that would help with the launch it to get a real airfoil for the winglets - right now they are flat (a bit sanded at the TE) - I don't want to go bigger if I can help it - it both increases the tail weight (which I don't want - I already have 3/4 oz of lead in the nose in addition to a hefty 400mAh battery and fairly heavy 9g flap servos). Also bigger would likely increase drag - a proper airfoil should be much more efficient - I only tried to figure out if the size is enough - seems to be enough.

There is no secret and no series . I used Peter Wick's plank airfoil for SALs - PW1211 with a touch of washout at the tip (1 degree) for tip stalling resistance - we'll see if that's enough when I get to thermal it. There is a single panel with a 50% taper - I didn't want to complicate this first one - of course a two panel (or 3) would perform better.

M.
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Old Dec 22, 2009, 10:23 AM
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I'm not sure it would require a fuse - but the tail weight addition is a good point.

Now I'm wondering how a forward swept wing would do... Since that would be ideal for the central fin, as it might require tail weight... Oh, ideas ideas, if only we had enough time to pursue them all!
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Old Dec 22, 2009, 02:07 PM
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Mihai, Im really happy to see your wing working as well as it is. I built a similar wing which has been moved to the "back burner" for now. Seeing this makes me want to continue experimenting.

It is interesting to note that you are using the PW series. I am using AG's transitioned to a symmetrical foil at the tip. My wing has much more of an issue with pitching up on launch than yours appears to have. It could very easily be the choice of foils (or any 1 of the other different variables).

Goeland: I have been thinking about forwards swept wings as well. As you mentioned, the positioning of the central fin does make it seem like a better planform (in theory) than a rewards swept wing. The main thing I have been wondering is whether a swept forwards wing needs either washout or wing twist. It seems to me like it wouldn't as the lift of the wing tips would counter act the negative pitching moment of the root. That being said, it also seems like swept forwards wings would self dis-correct in the pitching axis rather than self correct as a normal swept wing does. Ideas, Ideas, Ideas! : )


Michael
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Old Dec 22, 2009, 02:21 PM
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Quote: " The last landing (hovering above the ground) is with full flaps down (not visible in the video). "

I would be interested to know IF you remember what you were doing with Elev at the time, that is while Flaps were down? I suspect you were holding UP Elev or in effect Crow.

What is supposed to happen, any surface behind CG should just act as Elev. not Camber. This was learned years ago building CO7 HLG ( prior DLG ) and it works quite well. But, you mentioned CG is on the Hinge Line. Or , as Herk mentioned, as Twist control.
http://www.glide.net.au/flyingwing/co7hlg.htm IF you look at the 3D, CG is well ahead of the flaps and a fuse, well at least 90% of them. Also the CG is further back than the plans. mmm Actually I didn't build per actual plan, it was a Foamie not composite and had major Pitch issues. I can't fault the model as not building per plan and I refused to run -4 degs of washout, -2. I have threatened to revisit this model many times but I would rethink the airfoil as well as building as a composite. I did have a lot of fun with it before scraping it.

I didn't run the wing loading but a desirable weight would be around 25% less than a modern conventional DLG to have a chance at being competitive IF that is what you want. Lots of fun no matter what, I hope you post some more as you gain more experience with it.

OH,, Launch Preset: I was impressed how quickly it recovered in Yaw but on the final harder launch, she went up rather straight then up some more heading for a loop. Did you preset the +.5 deg as Peter suggested for that airfoil?

I will be also interesting to see how well she launches once you come up with a Preset Plan. I was thinking you could have the momentary on +.5 degs and hold right after she goes vertical but that might mess you up for conventional launching. Might be better to go as normal with a 3w Switch at +.5 , momentary to add UP elev until she is pointed up.

Ballast idea #1 : Say you decide you want another 1 oz. Pour 1 oz of lead and beat that into the shape of airfoil around the CG Hinge area, you will have work out how long and wide you can live with. Join the center section ( cut the flaps ) enough to build in a box to hold the now shaped Lead on the bottom or top. You will have to work out the placement of the lead as it's tapered so you can't center on CG. Build a box to hold the ballast and another piece of the same shape ( maybe foam ) to take the ballast's place when not being used, an insert if you will. I would through bolt it from the top and not trust just taping it in. Just an idea.

Amazed and impressed that these wings showing up can be DLG'd.

Dan
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Old Dec 22, 2009, 02:37 PM
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[QUOTE=FairlyFaded;13881689]Mihai,

I
Quote:
t is interesting to note that you are using the PW series. I am using AG's transitioned to a symmetrical foil at the tip. My wing has much more of an issue with pitching up on launch than yours appears to have. It could very easily be the choice of foils (or any 1 of the other different variables).
What are you doing for a Launch Preset? You should be finding Zero Lift taking out any reflex so she just goes straight, it's a speed issue in combination with CG and airfoil. Same thing happens with DS'ing a plank, you can have enough reflex to fly level front side for the avail lift and when picking up speed have to trim some down and then some up coming back to the front.... or you have to correct with your thumb but being a correctional flyer relying on a neutral trim, I can' t do it.

Quote:
dis-correct in the pitching axis rather than self correct as a normal swept wing does. Ideas, Ideas, Ideas! : )
Keep in mind, building stiff in Twist is going to be even more important than it already is.

Dan
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Old Dec 22, 2009, 03:20 PM
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Quote:
Originally Posted by FairlyFaded View Post
Goeland: I have been thinking about forwards swept wings as well. As you mentioned, the positioning of the central fin does make it seem like a better planform (in theory) than a rewards swept wing. The main thing I have been wondering is whether a swept forwards wing needs either washout or wing twist. It seems to me like it wouldn't as the lift of the wing tips would counter act the negative pitching moment of the root. That being said, it also seems like swept forwards wings would self dis-correct in the pitching axis rather than self correct as a normal swept wing does. Ideas, Ideas, Ideas! : )


Michael
Michael, actually a forward swept wing probably wouldn't have too much dis-correct pitching momentum, so long as the forward sweep isn't severe. Also using a curved trailing edge (so you have more chord at the root) would probably tend to attenuate any pitch disturbances you might find.

Now the next grand idea is going to be a Canard DLG... Which should launch quite well, seeing as a forward sweep wing would put the peg just where you'd need it compared to the CG.

And yes, it would look like you're thermaling backwards if you're too far up!
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Old Dec 22, 2009, 06:13 PM
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ah, Forward swept like this :-) I was quite surprised to find a current build thread going on when I searched for it. Oldie but a goodie. I have only seen one fly that was DS'ing,quite the site.

http://www.rcgroups.com/forums/showt...php?p=13832685
Dan
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Old Dec 22, 2009, 06:15 PM
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I confirm that when I was landing it with flaps down the elevator was a bit up. I didn't hold it up myself, but I did program elevator compensation on the flap stick (which was the throttle). It didn't need much - for 70% down flap about 7-10% elevator if I recall exactly - that is indeed like crow.

For launch preset the first launch didn't have any, but the elevator had a bit of up-trim anyway - I could not trim it properly on pizza toss. After that, I had another launch (not shown when it was clear that it had up trim, and I down trimmed it to fly nice and level). The third launch (also not shown) was then very flat (scary so), perhaps only 5-6 yards up at 20 yards in front, so for the fourth launch (the one shown) I added a bit of up preset (5% if I recall exactly) and it looked like it worked well.

I know what Peter said - that it will require zero trim at release time, that it will go up all by itself, then it will require some down-trim for the up portion, but this is not what I experienced - it behaved like a conventional DLG in this respect that needs a bit of up-elevator preset at release, then no elevator trim for the climbing part.

Regarding the swept forward wing that will require a fuselage to balance as the CG will have to be close to the LE at the root of the wing, practically impossible to achieve without a significant fuselage.
I'm sure it will launch well and fly well (the Alula does), but the fuse will require (much) more work (at least for me wings are easy, fuses are hard - for now).

I'm still gluing winglets, if I'm lucky, maybe I'll trim it tomorrow.

M.
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Old Dec 22, 2009, 09:27 PM
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Mihai, I was just throwing the idea for a forward sweep wing out there - I'm quite impressed with the fact that you have a rearward sweep wing throwing like a DLG at all!

As for making a forward pod to counteract the CG - the simplest way is to take 4 pieces of balsa, cut them in a triangle-ish shape, put a light balsa block in the nose, round it with sanding, then lay .75 oz glass over it, with a length or two of 6k carbon tow along the sides to withstand the side stresses on launch.

Please post a video of how it flies without wind! I really like the idea, it's pretty fantastic, because it's so easy to transport!

EDIT: heck you could make a mount on the back of the car's trunk and use it as a spoiler when you're not flying
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