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Old May 06, 2005, 07:50 PM
Registered User
Clintwood, Virginia
Joined Jul 2003
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Working on a new AP Wing..whadda ya think?

Modifying the zagnutz plans here, I' thickened the airfoil, and increased the sweep (hoping to help with CG range). 20" center chord to 10" tips. I plan on using 3/4" bluecore for the formers and 3F for the airfoil shapers (using a heatgun to form the bend). I'm thinking of adding a flap to the bottom, having my elevons go up slightly when the flap goes down to even out the pitch. 60" span, and I'll add a bluecore pod rubberbanded to the bottom.
Here's what I've got so far. Recommendations appreciated!
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Old May 06, 2005, 09:40 PM
I crash, therefore I FLY!
mad mike's Avatar
Spring Hill, FL
Joined Feb 2003
1,489 Posts
Why not ask the designer of the original to chime in? Gene has done the flaps thing and built them smaller and larger. Send a PM or email to CenTexFlyer, with a link to this thread.

His old web site is back up, you know. ZagNutz!

Mike S.
Spring Hill, FL
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Old May 06, 2005, 11:17 PM
It's been a while.
Daniel G's Avatar
Irvine, CA
Joined Jan 2005
2,690 Posts
I'm doing something similar, except it is solid core EPS and hotwire cut.
64 inch span with 16 inch root chord and 8 inch tip.
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Old May 07, 2005, 05:17 AM
Registered User
Clintwood, Virginia
Joined Jul 2003
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Quote:
Originally Posted by mad mike
Why not ask the designer of the original to chime in? Gene has done the flaps thing and built them smaller and larger. Send a PM or email to CenTexFlyer, with a link to this thread.

His old web site is back up, you know. ZagNutz!

Mike S.
Spring Hill, FL
Yeah, hopefully Gene will chime in here...
D Zipper, have you flown a wing for AP yet? I have one currently (72" WS), just wanted a slightly smaller one, possibly with flaps for tighter landings.
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Old May 07, 2005, 08:38 AM
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Near Austin
Joined Dec 2001
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Hey Newb!

Heckuva deal! I can tell you what we are discovering with the Shaker and the Slipstream. The optimum airfoil thickness for anything up to about 70" span is 2-/12" or so. And coincidently, that happens to be about the optimum wingspan too. If you want to go shorter on the span, come down on the thickness proportionally. Make it too fat and you end up with a real slow, floaty wing that won't penetrate the wind very well. On to sweep...... we've found that the standard of 35 degrees measured from the trailing edge works well on a wing that uses buried components in a center section that maintains the lines of the leading/trailing edge. If you intend to hang something underneath and stick past the leading edge, then you must REDUCE the sweep angle (thus moving the center of pressure) to easily get the CG in, otherwise you'll end up woefully nose heavy and if it does fly it ends up staying up by the good graces of speed and your elevons! Not a good thing.

We've done the flaps and they work great! But then there's that extra level of complexity. I would suggest you set your Nutz up without them to begin with and try to get the hang of flying in "high delta" mode. If you have everthing set up right, you can slowly start easing the stick back until you have full up elevator. The nose will start bobbing a bit and she'll almost come to a complete halt in the air - especially if there is any breeze at all. The descent is gentle and very controllable all the way to the ground. It's imperative that you use the "drooped" winglets and put 2 degrees of washout in the wing to perform this manuver. This manuver is also very handy for AP shooting since you can get a pretty good "station holding" attitude when at altitude. If there is any thermal activity at all, it almost appears to be frozen. I used to shoot my Nikon in "burst" mode but have turned it off since I end up getting 3-6-9-a dozen pictures of the same exact thing flying this way. This is kind of my little myth buster about flying wings - most people think they are too fast for AP - and the Slingers/Zagis/Wing Warriors may be..... the Nutz was designed as a training/thermal wing which quite happily is just the ticket for carrying AP gear! Just ask a few of the "converts" here on the Zone

Gene
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Old May 07, 2005, 10:35 AM
It's been a while.
Daniel G's Avatar
Irvine, CA
Joined Jan 2005
2,690 Posts
Quote:
Originally Posted by Newberry
Yeah, hopefully Gene will chime in here...
D Zipper, have you flown a wing for AP yet? I have one currently (72" WS), just wanted a slightly smaller one, possibly with flaps for tighter landings.
Not yet it is waiting for a motor(the shaft snapped off my Eflight 400 when I was taking off the gearbox ) And needs a couple spars to stiffen it up. But otherwise it is ready.

Thanks for the info CTF. That is very useful.
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Old May 07, 2005, 11:22 AM
Metallica
robe_uk's Avatar
Londonderry UK
Joined Nov 2004
414 Posts
looks great
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Old May 07, 2005, 02:21 PM
Registered User
Clintwood, Virginia
Joined Jul 2003
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Thanks for the replies all! CTF, are you saying that a wing with a 12" chord should have a 2" thickness? If so, I'm really close on the center, but a bit thin on the tips.

I do plan on hanging my camera off the bottom, similar to my current wing (this will be my third Zagnutz, thanks!) and I must be thinking backwards, but I thought more sweep would effectively lenghten the "plane" and increase the CG sweet spot.

Trying to calculate the CG, I get 12.75" back from the tip, using an 18% MAC. This is with the calculator here: http://www.geistware.com/rcmodeling/cg_calc.htm#cg
Not sure about that at all, but trying to get an idea!

Here's the plan above with the angles dimensioned. I'm seeing 37" on the LE, so it may be a tad too much.
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Old May 07, 2005, 03:03 PM
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Near Austin
Joined Dec 2001
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Quote:
Originally Posted by Newberry
Thanks for the replies all! CTF, are you saying that a wing with a 12" chord should have a 2" thickness? If so, I'm really close on the center, but a bit thin on the tips.
hehehehe. I think we both need to get back on track here. I should've noted that you are talking about 20" chord on your drawing - but then you've stated a 12" chord..... I'm so confusing! Our 12" chord Nutz are coming in right at 1-3/4" - our 70" span wings have a 13-1/2" chord and they are coming in at 1-7/8". This is the wing I flew the one pound lead weight in. If you are indeed building a 20" chord wing, then I would think something along the lines of a 2-1/2" foil would be optimum.

Quote:
Originally Posted by Newberry
I do plan on hanging my camera off the bottom, similar to my current wing (this will be my third Zagnutz, thanks!) and I must be thinking backwards, but I thought more sweep would effectively lenghten the "plane" and increase the CG sweet spot. Trying to calculate the CG, I get 12.75" back from the tip, using an 18% MAC. This is with the calculator here: http://www.geistware.com/rcmodeling/cg_calc.htm#cg
Not sure about that at all, but trying to get an idea!
OK - Wings 101..... With a swept wing, flying body, there are two forces you must contend with (and balance!) to get a wing that flys well. The center of gravity (CG) and the center of lift (CL). In just about all aircraft these are located in two different places, but especially so on a wing. It is most advantageous for these two points to be as close together as we can make them! When you add more sweep to a very lightly loaded wing, the CL shifts further back than the CG which lifts the aft end and makes it head for mother earth regardless of the elevons best efforts to oppose the lift. Does that make sense?

Quote:
Originally Posted by Newberry
Here's the plan above with the angles dimensioned. I'm seeing 37" on the LE, so it may be a tad too much.
I'm thinking so for a camera hauler

CTF
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Old May 07, 2005, 06:54 PM
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St. George UT
Joined Apr 2005
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shifting the CG

All excellent information CenTexFlyer! I have a specific question about the CG in relation to the CL. You mentioned the plane would head for mother earth if the CL is to far aft of the CG. If on the same airplane, the CL is proportionally to far forward of the CG , could you expect an indirectly proportional climbing tendency? The reason I ask is because I am planning to build a flying wing that will be controlled by shifting a weight that will alter the CG in relation to the CL. Have you ever tried this setup or do you know of any other shifting CG airplanes? Thanks for your help.
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Old May 07, 2005, 07:09 PM
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Clintwood, Virginia
Joined Jul 2003
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Thankc CTF, I'll do some tinkering with your recommendations in mind. VEEEEERY helpful, and your explanation about CG vs CL makes perfect sense. I'll be adding a touch of dihedral like my current wing (which has worked great).
I even considered making a polyhedral wing with the tips bent up slightly, but that may need to wait for the 5th wing....
Thanks again!
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Old May 07, 2005, 09:05 PM
It's been a while.
Daniel G's Avatar
Irvine, CA
Joined Jan 2005
2,690 Posts
I just measure my sweep and it is about 25/30 degrees.
Does this mean that my plane will have a tendancy to be less stable?
Also when you talk about the "center of lift" do you mean the thickest part of the airfoil?
Thanks again for all of the information.
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Old May 08, 2005, 12:14 AM
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Near Austin
Joined Dec 2001
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Quote:
Originally Posted by moonbase1
All excellent information CenTexFlyer! I have a specific question about the CG in relation to the CL. You mentioned the plane would head for mother earth if the CL is to far aft of the CG. If on the same airplane, the CL is proportionally to far forward of the CG , could you expect an indirectly proportional climbing tendency? The reason I ask is because I am planning to build a flying wing that will be controlled by shifting a weight that will alter the CG in relation to the CL. Have you ever tried this setup or do you know of any other shifting CG airplanes? Thanks for your help.
Probably the best known "weight shifter" wing is the Rogallo wing used by hang gliders. Granted, you do change the angle of attack of the foil, but it's the weight that does it, rather than a control surface. Yes, you can expect the pitch up tendency as well with everything reversed. I'm sure Jason could tell you some stories about the development of his BOP with its' forward swept wing and CG/CL problems!

I know in theory it's possible to control a rigid with with weight shifts, but it is a very slow response control - in other words, if you get pointed straight down, you better have alotta weight to shift to the rear, poste haste! You can ENHANCE the effectiveness of movable control surfaces by shifting the weight (CG) in flight, but that can be a double edged sword! Too far back and you get a nasty snap that may be difficult to recover from!

CTF
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Old May 08, 2005, 12:16 AM
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Near Austin
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Quote:
Originally Posted by Newberry
Thankc CTF, I'll do some tinkering with your recommendations in mind. VEEEEERY helpful, and your explanation about CG vs CL makes perfect sense. I'll be adding a touch of dihedral like my current wing (which has worked great).
I even considered making a polyhedral wing with the tips bent up slightly, but that may need to wait for the 5th wing....
Thanks again!
I've never tried dihedral on any of my wings - not to say it's bad - or even good! But the sweep in a wing has the same effect as dihedral in a straight wing. We fiddled a bit with polyhedral and found that it wasn't worth the effort. Just extend the wing and get more lift!
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Old May 08, 2005, 12:20 AM
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Near Austin
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Quote:
Originally Posted by D Zipper
I just measure my sweep and it is about 25/30 degrees.
Does this mean that my plane will have a tendancy to be less stable?
Also when you talk about the "center of lift" do you mean the thickest part of the airfoil?
Thanks again for all of the information.
No, I don't think so. I have reduced the sweep on several of our new designs and it is just as stable as the 35 degree wing when you hit that sweet spot between the CG and CL. As a matter of fact, my frontline AP wing is a reduced sweep design with a pod. Never thought I'd back off the original design or sweep but here I am....... Guess I'm not such an "old dawg" after all!

CTF
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