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Delta & Flying Wings Discuss electric powered delta (flying wing) style aircraft here.

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Old 07-22-2014, 11:48 PM   #1
mclarkson
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Default Wing dives for no reason

I recently built a prototype flying wing with a 24" wingspan. I went out today to maiden it and ... wow. It acts a bit tail-heavy but nothing I can't handle. However, it keeps suddenly, violently tucking its nose down. Very suddenly. For no discernible (to me) reason.

Here's a short video of two short flights so you can see what I'm talking about. The second, longer, flight is most remarkable.

YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


Any idea what the heck is causing this?

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Old 07-23-2014, 12:34 AM   #2
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It would be a lot easier if you changed the privacy settings of the video. Can't view it...

AMA #959089
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Old 07-23-2014, 12:56 AM   #3
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Yep... video set private.

Wings can be VERY sensitive to CG and aft just a bit too much acn make them tuck and dive at speed. So first thing fix the CG.

Any flexibility in the construction material can also cause the wingtips to flex down at the TE as speed increases this will tuck it (sometimes very suddenly) You may simply be exceeding "VNE" for the airplane.
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Old 07-23-2014, 01:35 AM   #4
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Oops. Permission should be fixed now.

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Old 07-23-2014, 02:27 AM   #5
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CG is really bad.
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Old 07-23-2014, 03:09 AM   #6
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Thanks, guys. I knew the CG was back but I've flown planes with bad CGs before and I've never seen that particular behavior. That snap-tuck maneuver is a new one to me.

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Old 07-23-2014, 04:05 AM   #7
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Too fat a leading edge can also lead to that behavior. Had the same problem with a scratch built wing a couple of years ago. After spending too much time messing with it trying the get the cg right. Nothing worked till I rebuilt it with a thinner leading edge.
I'm still not 100% sure as to why it behaves that way but it is most pronounced with abrupt and aggressive pitch changes. The leading edge stops cutting through the air and acts like a wind break. The prop keeps wanting to push through and swings around the nose of the wing.
Try the wing again but with much much smaller throws. You should find that the instant tumble will be less pronounced.

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Old 07-23-2014, 04:07 AM   #8
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I also get a delta wing to dive when flying wot and the wing changes shape by flexing to much. the design of the delta is for slower aerobatics. I put a carbon fiber rod across the with of the center approx 8" long and it helps a lot.

I did over power the delta for fast vertical climbing and love to fly it acrobatically both fast and slow also.

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 07-23-2014, 04:30 AM   #9
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I'm gonna push the CG forward and see if that helps.

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Old 07-23-2014, 05:39 AM   #10
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Yep, CG too far back. Also possibly lack of directional stability due to having no vertical stabilisers. Moving the CG forward will help with directional stability too but if problems remain try adding verticals near the trailing edge of the wing tips.
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Old 07-23-2014, 09:37 AM   #11
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I've been reluctant to add even more weight (in the form of winglets) to the rear.

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Old 07-23-2014, 11:46 AM   #12
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Looks Like your battery keeps getting ejected you need a better way of holding down the battery your control surfaces are to wide too, thats why it flies so Squirrelly, make your control surfaces out of balsa. thats what i do with my wings, foam control surfaces on a wing IMHO are a bad Idea. they bend and twist to much.

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 07-23-2014, 11:55 AM   #13
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Originally Posted by mclarkson View Post
I've been reluctant to add even more weight (in the form of winglets) to the rear.
all in all, I Think the Main Problem is the Big Loose Nut behind the Transmitter LOL, OK, Just Kidding

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 07-23-2014, 03:41 PM   #14
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whaaaaaat isssss thaaaat he said in a hushed tone. I laughed listening to that. Not at you, just at the situation. It's maddening when something keeps happening and you can't figure it out. Been there, done that. Looks like all good advice has been given.
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Old 07-23-2014, 09:17 PM   #15
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I chopped a big chunk outa the middle and moved the motor forward by nearly 3 inches, which in turn moved the CG forward by about 3/4". It is much more stable now, but also much louder.


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Old 07-23-2014, 09:56 PM   #16
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V out the slot the prop is in a bit more... and cut it even more forward. noise is generated by the prop being too close to the "sharp" edge.

Unless you like the noise... It doesn't hurt anything except for annoying the neighbors
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Old 07-24-2014, 12:44 AM   #17
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Also looks like the inboard part of the Control surface is to close to the prop, the prop wash could be causing turbulance with the inboard part of the control surface, cut the control surface the same angle as the outboard control surface instead of having it in the prop wash. also to get a better CG, lay the battery from wing tip to wing tip rather from front to back, more towards the front
that will move the cg forwards more,


I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 07-24-2014, 03:59 AM   #18
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Man, everybody's a critic!

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Old 07-24-2014, 06:17 AM   #19
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Here it is, guys: the (less than) epic journey from utter failure to full flyability:

YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


Thanks to everyone for their help.

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Old 07-24-2014, 06:47 AM   #20
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Good job Yea, the fins added top and bottom of the wing helps to make a wing fly like if its on rails You stuck with it and got it to fly Great





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I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 07-24-2014, 01:53 PM   #21
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What motor, esc, battery, and prop size's did you use? (I'm asking because i just built my first wing, it's a 30" have servo's on next installing the power system)
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Old 07-24-2014, 07:07 PM   #22
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It's built from stuff I had lying around, to wit:

I've flown a lot of poorly built and badly balanced planes in my short career but I have never seen anything quite like that bizarre 'tuck-and-dive' move this one was doing. I thought it had to be something other than CG cuz I've never seen a tail-heavy plane act that way before but, sure enough, fixing the CG totally cured it of that.

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