Good comments guys. Thanks. I need the inspiration.
I'll try again out on the sand next weekend.

In the mean time, I can still bungee launch. Today into near calm conditions. Was surprised to see a flutter at rather low speed..... this is my first "light" plane and I already miss my dual spar.

Kent

SW 2 1ST BUNGEE (0 min 50 sec)

SW 2 FLOAT BUNGEE (1 min 39 sec)

SW 2 toying with flaps (0 min 57 sec)

SW 2 toying with flaps2 (1 min 15 sec)

Here's the flutter. Looks like those big dangling rearward winglets have added some interest for this plane. Wing skin is 1 1/2 oz glass.

SW 2 Flutter (2 min 3 sec)

Some hikers got a good shot of the flutter......I'll live with it. 9 paces gives a good launch. Just need some thermals now.

SW 2 Flutter 2 (0 min 47 sec)

The camera battery was exhausted after an hour so this is as close as I got on getting the flaps set up on film. Got them nearly dialed in but need to do some mechanical work. I'll finish tweaking next week. Got some nice slope flying in too when the winds picked up in the afternoon.

SW 2 tweaking flaps (0 min 49 sec)

Looks like it flies quite nicely.
As far as the flutter, I have been told, with thin swept wings you need a "bullet Proof" shear web at the back of the "D" tube.

From the video, it's clearly a torsional weakness. I'm half thinking of attempting a torsional fix by adding a disser pattern of 3K carbon tow OR I might just replace those big winglets with lighter winglets mounted on the wing OR do nothing and limit the launch force, which is my current favorite. I'm sure that a real shear web would help a lot too, but a little late for that now.

BTW, the new orange paint GOT REALLY HOT in the Big Sur sun today. I thought that it was light colored enough to protect the epoxy but there is nothing like white.

Kent

Seems pretty likely that the mass of those fins is contributing to the oscillations that you are experiencing. I suspected that might happen even while you were building them.

Since it appears that it's not going to be a good DLG model, and that it does fly very nicely, I think you could easily get rid of about half of that fin area and still have an excellent flyer. Sometimes just changing the weight a small amount can move the dynamics out of the resonance range.

But the bottom line is that while you can delay flutter on a swept flying wing, if you go fast enough you can be pretty sure to get it. And the higher the speed at which it occurs, the more destructive it will be.

Ken two small tips,

1° keep the turn smooooooooth dont try to launch hard at the end, just let the plane go

2nd release it earlier you are hanging to long on the wing that is why it is trying to yaw to the left

EZ

All planes have a VNE, if it is performing as you anticipated otherwise don't worry about it, unless you are looking for higher speed flight. Right now you have a nice flying plane that is light on the wing and capable of slow speed flight, if it meets all of your goals just fly it.

Well Kent, I took two models out to do some DLG video for you. First is the little experiment I did some time ago - the Wedge! It launched pretty well - despite the fact that it is so light that it is like trying to toss a potato chip.

Then I got out the javelin launch wing - the one in my avatar. I tried an easy toss, and it did just exactly what your model did. Then I tried a harder toss and it did it even worse. That model is pretty light also, so weight isn't a factor. After the second toss a fin was loose and the model had been impacting nose down on hard playground turf, so I quit at that point. The video of those launches is not instructive so I didn't bother to upload it. If you want to see what happened - just look at yours - except the launcher guy is way older.

It's interesting in a way that the Wedge has no twist -- zero. And it has full span elevons. So no twist but with the elevons a bit of reflex. There may be a hint from that. The javelin launch model has eight degrees of twist - soooooo. I don't know - maybe that means something.

DLG the Wedge (4 min 16 sec)

THAT'S THE VIDEO that I wanted to post !

Nice job. No problems with the Wedge DLG. I can't tell you how happy I am that you had the problems with your avatar glider.....misery DOES love company.

So the plank style ship (Wedge DLG) was discus launchable but the swept wing with twist was a problem for us but Jürgen was able to launch his.

Working from memory:
Jürgen has 30 degree nose and 6 degrees of twist
Mine has a 25 degree nose and 4 degrees of twist
and yours has about 25 degree nose and 8 degrees of twist.
Launch technique is apparently more critical with the swept wing.

I'll try again (if my back ever recovers) and really work on technique and trim pre-sets. The launch has been far more challenging than I had previously thought. My original thought was that if I could discus launch this glider, that would save me from carrying the bungee up to the top of the mountain when I fly in Big Sur. Just hike and toss into a thermal. But after yesterday, it's clear to me that at 60 years old, doing several all out discus launches after hiking to the top of the mountain is just too difficult. I can barely stand up by the time I get to the top and the bungee launch is a lot less stressful than the discuss launch. This sort of thing was not a problem 20 years ago.

BTW, some of the fiberglass has delaminated from the foam (no surprise after so many crashes) so I'll peel those skins off and add a stronger version at a bias. The heaviest DLG on the planet is about to get heavier. The flutter was largely the result of those loose skins. Also, those dangling winglets are history sooner rather than later. Some thing lighter at the end of the wing should allow me to remove that ounce of lead I put in yesterday. If I do figure out the discus launch, I think that the least of my worries will be a little energy loss due to extra yawing.

Thanks for the video.

Kent

Kent - I spent some quality time studying the launch that Hans-Jürgen Parchem uploaded. Particularly the slow motion version of it was pretty revealing. I also threw some small stuff around in the back yard. I think you've seen this one too

Christian Behrens' Nurflügel DLG (1 min 15 sec)

pretty huge yaw right after release for his as well.

All of that has led to a temporary conclusion that the combination of high sweep and large fins is what is making it work. His launch technique looks pretty much like the norm for a good DLG flyer. The model does go up very steeply, and the yaw oscillations are pretty dramatic IMHO. But they do damp out, and the strength of his launch allows it to get high enough that they have damped pretty well before he pushes over.

Anyway the high sweep gets the fins further back and may have some other more subtle effects, but that seems to me to be about it.

So a plank with no sweep launches fine and a swept wing with significant sweep launches fine, but not an intermediately swept wing.........certainly is unsatisfying data.

I would be delighted if a little yaw wiggle-waggle during the initial phase of launch was my only problem. My best guess is that my typical launch went immediately into some sort of a high speed tip stall. For a variety of reasons, my second attempt at discus launch may be seriously delayed. Of course, I would like to figure this out.

Kent

Bit of a long shot,but could a little bit of flex/flutter be developing in the outer wing as you 'wind up' to throw?

I re-skinned the outer panels with 4oz. glass on the bias and the wing is quite strong now. With the new smaller winglets AUW is 20 oz.....still quite light. Turns fine with the smaller fins. Probably could go smaller still.

Kent


http://www.youtube.com/watch?v=qQMIwWUBOG4

Sounds cool.
Video comes up as "private".

Thanks for the heads up. It's working now. Let me know if it still comes up as private. I'm also baffled by the way the vids get posted. Sometimes the video viewer is embedded and others there is just a link, as in this one.

Just a quick vid of the new fins.


Kent

Kent,

nice video!

I'm also baffled by the way the vids get posted. Sometimes the video viewer is embedded and others there is just a link, as in this one.

The software that recognizes the videos is somewhat restricted. Try changing in the above link youtube.be into youtube.com. If still not working, try putting www. before youtube.

Cheers,
Andrés