I Smashed My 'Nutz - RC Groups
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May 30, 2006, 12:18 AM
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I Smashed My 'Nutz

Alright Guys,

I had the first flight of my modified 'Nutz yesterday. I modified the design to carry the light weight Lipo battery that I am using. Took some inspiration from TaSaJaRa's splat. The root cord excluding elevons is 14.5" and the tip cord excluding elevons is 6" (per the original Zagnutz plans). The elevons I used were 1.5" constant cord.

The Zagnutz plans can be found here:Zagnutz Plans and TaSaJaRa's splat plans can be found here: TaSaJaRa's Splat

I made the elevons by doubling up the fan fold and sandwiching carbon fiber tape using epoxy. I used Tyvek for hinges. I thought that using carbon fiber in the elevons would stiffen it up a bit, but not so true... definitely nothing like balsa elevons. I was a bit skeptical about the elevons but it took me a while to build this thing, so I had to give it a try..... so off to the field i went.... I found a spot with over grown weeds and gave it a toss, the CG was right on. The plane did a smooth glide, so on the second toss I went WOT and it started climbing and banking to the right a bit, I gave it a little left stick and it banked abruptly to the right and took a full power dive into about 2 feet tall weeds. I was shocked... I recovered the plane, gave it another toss, plane banked right and I gave a little left stick and it again did the right hand bank and kissed the weeds. Recovered the plane and decided to go over the radio setup... to my surprise I found that I had hooked up the servos reversed... the servo that should have been in the elevator slot was in aileron slot and vice versa... I corrected and taped a couple of cracks that had been caused by the last 2 crashes.... third time is a charm... so off it went climbing out nicely but I noticed it was very pitch sensitive... I should have landed the plane and dialed in some expo in the elevator but the adrenaline rush was so immense that I kept flying but that flight was short lived I did another full throttle dive into the weeds. 4th flight ended the same way, I guess I needed someone by me to keep me insane and tell me to tame down the elevator... 4th flight was the was that caused most of the damage...

I think following are the reasons for over responsiveness:

1- Not too stiff control surfaces.
2- Dumb pilot with almost no experience with flying wings
3- Deviation in design from the standard plans

I figured that the hollow bluecor structure is light but can't take a lot of beating, so probably EPP would be the way to go. And now that I have got the planform right, I would like to have this built out of EPP so that it can take a bit more beating and stay alive through the learning curve...

Do you guys know of someone who can make EPP wings for me if I sent them the plans?

Also, what airfoil is recommended for the following characteristics?

1- Low flying speed
2- High lift
3- Low stall speed
4- Probably basic aerobatics

Basically I want a wing that I can fly slow and grow with on my flying wing experience. I am definitely a beginner in the flying wing category...

Here are a couple of lessons learned:

1- Dial in some expo on the elevator
2- Use balsa elevons, they'll save you time and headache at the expense of a few bucks

And finally some pictures:
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May 30, 2006, 03:55 AM
Registered User
Cool looking plane! I have a set of wing core templates for the Tzagi wing. Where are you in AZ? I'm in Tempe if you want to borrow them and hot wire your own. I built mine with EPP leading edges, but it would be even easier to do it all EPP ( but much more expensive).

May 30, 2006, 04:18 AM
Hermitt's Avatar
Sorry to see that you cracked your 'Nutz.
The nice thing about Zagnutz is that you can build a new one for just a few bucks.
Here's a good source for 100% EPP cores for a reasonable price.

Last edited by Hermitt; May 30, 2006 at 04:26 AM.
May 30, 2006, 10:25 AM
Registered User
Scott, I highly appreciate your offer but unfortunately I dont live in AZ anymore. I moved to Iowa about 6 months ago...

Hermitt, thanks for the link but seems like they dont have an option where you can send them your own desing and they'll make the cores for you.

Any recommendations for the type of airfoil I should be using for the flight characteristics that I mentioned in my 1st post??
May 30, 2006, 10:49 AM
Robots... robots everywhere
minifly's Avatar
You'll want a relatively thick wing...

You sure you got the CG spot on? it shouldn't be that pitchy....
May 30, 2006, 12:55 PM
Registered User
Minifly, I am pretty sure I had the CG right. I calculated the CG using some of the formulas posted in an earlier post, but then with this kinda plane you really dont have much control over the airfoil shape and the CG could have been off. But, since it did the glide test pretty well, I am assuming that the CG was right on. I think this is one other reason that I wanna make my next wing out of foam cores. At least that way you have more control of the airfoil shape and the formulas can get you a pretty good estimate of your CG. Also, I am thinking that building it with EPP (or at least just the first couple inches of LE) would make it a bit more crash/shock resistant.

I haven't gotten any suggestions on the airfoil yet, so I am still looking. Also whats a good source to by EPP sheets?

May 30, 2006, 03:31 PM
Robots... robots everywhere
minifly's Avatar
Theory can only get you so far, after that you need to test it. The designers have already tested, and recommend their cg, which they put on the plan. You should take this position over any position a theory gives you.

Slowfly.com has epp sheets, but I suggest you give one more try with your 'nutz with the CG forward before scrapping it. If nothing else, you should do this to stop your new plane from getting wrinkled.
May 30, 2006, 05:46 PM
Registered User
Well...I am not saying that I am abandoning the Zagnutz. I am just saying that I wana build Zagnutz using EPP with a known airfoil. I gotta rebuild one anyways coz this one is all busted up, so might as well build it with EPP...
May 30, 2006, 07:29 PM
Registered User
so where are you in iowa, I live in ames, and would love to get togeather and fly sometime if you want.
May 30, 2006, 11:24 PM
Registered User
Volts's Avatar
Sorry to hear about your Nutz.

I maidened a WildWing the other day and it was reallly pitch sensetive, more tha my old Zagi or Mini Speedwing. I tip stalled and did a kind of controlled crash. Second toss I could only control at about 1/2 throttle anything above that was crazy! I landed reduced elevator throw and dialed in -65 expo. Also moved battery ahead so CG is about 1/8" ahead of the mfg. recomendation. Sweet almost hands off. I do notice on my wings CG is criticle and motor thrust angle.
Your wing looked great, nice build wish I could do that kind of work.
Jun 01, 2006, 12:17 PM
Registered User
usmcculp: I am in Cedar Rapids... If you happen to swing by this side of the state, let me know...

Volts: yeah, you are right on about the CG... I will dial in about 50% expo for my next nutz... I spent quite a bit of time making sure i build it right and then spent some more painting it... But Oh well, it didnt cost me an arm and a leg.... I hope I have better luck next time!
Jun 01, 2006, 07:02 PM
FPV for Me
TaSaJaRa's Avatar
AirBorne_AZ You look like you got the shape right and CG not to bad.
But to make it slower just make it thicker. From the pictures it looks to be way to thin. Also I used coro on my first ZagNuts but a inverted loop low found that they are no where stiff enough for fast loops low. They flexed and let the plane hit nose first WOT... Darn thing bounced 3 feet high above the weeds then came to rest all busted up. That was when I quit using anything execpt balsa for my elevons. No more unwanted control problems.

Hope this helps..

Jun 01, 2006, 10:06 PM
Registered User
Tas, thanks for the advice, man. I am using the stock spar as per zagnutz original palns (24" long, 1.25" at the root and 0.5" at the tip). Do you think I should make it longer(may be 26 or 27") and taller? What do you recommend?

Also, I just want to explore the idea of making similar kind of wing out of foam cores (keeping the planform the same) but no one has suggested any particular type of airfoil and thats one of the areas where I lack the most. Any suggestions?
Jun 01, 2006, 11:06 PM
Registered User
Originally Posted by AirBorne_AZ
Also, I just want to explore the idea of making similar kind of wing out of foam cores (keeping the planform the same) but no one has suggested any particular type of airfoil and thats one of the areas where I lack the most. Any suggestions?
A simple clark Y makes a good, solid, stable flyer. We have also used an Acquila airfoil with great success. The near flat bottom makes alignment and build out very easy. Add about 2 degrees of washout near the tip and you'll make tip stalls go away and slow speed handling improve drastically! EPS foam works great, and when covered is strong and bounce-able. Ends up being much lighter than EPP if you are looking for a thermal ship.

Jun 02, 2006, 12:42 AM
Registered User
If you want a foil specifically developed for flying wings.....search for, download, and install the free foil plotting program called profili... the last two foils at the bottom of the list are zagi type wing foils. The program will print them any size you want. Cut out of thin brass shim stock with scissors for quick templates.. or shape out of aircraft ply, formica, or aluminum for longer lasting templates. Don't forget to raise the TE of the tip template 3/16 to 1/4 in. for washout.


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