Zagi-ish wing for thermal?

[PunkerTFC]

I was thinking about building a zagi-ish wing out of fanfold (i.e. zag-nuts), because I have two HS-55s, a GWS rx, and a nicad 150 reciever battery, some fanfold, and an upstart (shorty histart). Is this a stupid idea? will it work? Think I'll be able to catch any thermals? Any suggestions as far as aspect ratio and wing thickness go?

Alek

[Ollie]

Reflexed and zero pitching moment airfoils for flying wings have lower maximum lift coefficients than simply cambered airfoils. For similar sinking speeds the flying wing should have 25 to 50% lower wing loading. Swept back wings are subject to much higher twisting forces than non swept wings. The structure has to be much stiffer torsionally. When a sept back wing is towed strongly, any bending along the length of the wing results in increased washout and the pitch trim becomes more nose up. Therefore a histart or winch launched swept wing has to be very stiff spanwise or it will pop off. It is very, very difficult to design and build a swept back flying wing that thermals as well as an ordinary thermal model. The items mentioned above only scratch the surface of the problems that are peculiar to the configuration.

[Ken J]

I tried high-starting a zagi-thl.

very short flights

avg. 45 secs. ,longest was 2 1/2 minutes. It wouldn't penetrate the wind at all.

[John Gallagher]

What wingspan are you talking about. If you copy the 48" span of the zagi and keep the weight below 8 ounces, it will probably thermal pretty well. The zagi thl is around 11 ounces, which makes thermalling difficult.
You'd might also consider trying a fan fold red herring.

[PunkerTFC]

I really don't know about the wingspan, that's what I was asking about. I think I could make it within 8 ounces with the equipment I have.

[Ollie]

Because of lower maximum lift coefficient, flying wings have to be launched faster. This results in lower launches. The best I have seen only launch about 80% as high as conventional configurations.

[thepilotbruss]

I have thermaled out many times using a beat to he11 Zagi 3C without winglets. I used a very short bungee (all rubber no string) in a school field. It's not easy and usually I only get very short flights but there have been a few times where the conditions were so good that a brick would thermal.
If you really want a cheap thermal wing get a pink foam core wing. Use sub micro servos, ultra light covering, no spars, super thin elevons and winglets, and a very small battery. I got a pink foam core wing for 20 bucks a while ago but I can't remember where I got it...

[fprintf]

I built a 60" wingspan Meganutz hoping to achieve some kind of thermal performance. It didn't happen. My launches either caused popoffs, as Ollie suggested it would, or I would move the tow hook so far forward that I would only achieve 60-90 foot launch heights. More often than not it was so pitch sensitive that at maximum speed it would go into the ground rather than in the air.

I gave up on it. It was fun to build it and try something new but it wasn't a satisfying flier. I bet if I had some slopes nearby it would have been excellent.

Now I enjoy thermalling my slow stick parkflyer (when there is <10 mph wind) or back to my foam Highlander.

[MikeC]

http://members.ozemail.com.au/~flyingwing/herks.htm

[Peter K]

Whats about a little plank? Easy to build, lightweight, cheap, .... perhaps like this?

[PunkerTFC]

that would be VERY easy for me to build... perhaps I'll try it!

[patv]

What about a moth or m-60? Do they have any ability to thermal? Can they only be flown for slope/ds?

[Ollie]

Thermals come in all sizes, strengths and shapes. If you are willing to wait for one that is big and strong enough and have the skill to keep the model in the strongest part of the lift, almost anything (even leaves and plastic garbage bags) will thermal. One of my favorite stories is a case in point:


This reminds me of a story that a good friend in the SOAR club will tell
occasionally, to protect his name a little bit, let's just call him TK. 8-)

TK was dragged out to a power field on a Sunday morning to see an old
friends immaculate 1/3 scale Piper Cub, that he had just finished over the
winter, fly for the first time. Well, after they got the motor and
everything straightened out on the ground, he asks TK to take the first
flight, "just in case". He wasn't expecting to do the test flying as it
was a big power club and there were lots of "experts" in attendance, but he
didn't want to see his friend break his model either so he agreed to take
the first flight. So here is a senior guy, a brand new 1/3 scale Piper
Cub, a glider guy to do the test flying, and the club "experts" have now
broken away from running gas thru their engines on the ground to checking
this out like a bunch of vultures.

TK taxis the cub out, takes off, trims it out, starts backing off the
throttle a bit and the engine sputters and quits. Next thing he knows guys
are screaming up and down the flight line, "DEAD STICK - - DEAD
STICK" He's like thinking to himself, no big deal, got flying speed, got
altitude and over the field, why are these guys screaming... so he goes to
set up an approach and the wing gives a bobble. He sets the cub in a
thermal turn and spends the next 10 minutes specking it out. Brings it
back down, sets up a nice approach on their paved strip, and rolls it out
to his feet... and yells DEAD STICK.

[PunkerTFC]

HAHAHAHAHA, great story! If I'm dead sticking a plane, and my wing "bobbles" it usually means I'm about to stall and crash, the next thing I definitley WOULDN'T do is make a turn!