We had a thought in my a&p class today
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Piotrsko
Legendary member
Depends on the airfoil. The flapjack was just a low aspect ratio wing with all those failings. A Frisbee is a symmetrical airfoil with spinning for stabilization. This you tube thing isn't technically a round airplane .
Wouldn't be hard to cut a 24" circle out of DTFB and fly it on a slow stick fuselage AET.
Wouldn't be hard to cut a 24" circle out of DTFB and fly it on a slow stick fuselage AET.
What makes a frisbee different from a plane is that the "wing" is rotating, that is the LE and TE are continualy changing. To make a plane fly like a frisbee, it would need to spin, not just be round. Another interesting problem is the Aerobie, pictured below. They have an airfoil completely different from a frisbee. Here is a description of the Aerobie airfoil http://www.aerobie.narod.ru/aerobie.htm
Vimana89
Legendary member
The FT Nutball has some dihedral but is otherwise a disk/saucer shape. A version could probably be made with elevons and no dihedral so a flat circle. This is definitely a good wing shape and the "filled in" full disk wing will have a more generous wing loading than a ring shape.
Piotrsko
Legendary member
I was using the frisbee as an example of airfoil. It is stable because it spins, and by definition has to be symmetrical. Toss either one without spinning it and see how that goes. I'll wait.
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Ok, back to the original question: what airfoil? @Vimana89 has an excellent series of desgns along this line and his nutball shows what the typical DTFB round wing might fly like. Could even use a series of steps like a symmetrical KFM wing. At 24" probably would even fly pretty decent
Hmm sounds like a @Vimana89 challenge. You up for it?
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Ok, back to the original question: what airfoil? @Vimana89 has an excellent series of desgns along this line and his nutball shows what the typical DTFB round wing might fly like. Could even use a series of steps like a symmetrical KFM wing. At 24" probably would even fly pretty decent
Hmm sounds like a @Vimana89 challenge. You up for it?
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Vimana89
Legendary member
Possibly, If I knew exactly what was wanted. Do you want a round wing like the Nutball, a ring wing with space in the middle like the Thor ship? That would be up to the OP. As far as a plane that spins like a frisbee...maybe you could flat spin a twin engine, non-dihedral Nutball as a trick, but not just fly all over like that. That's some next level stuff right there.
Piotrsko
Legendary member
No, no spin. Just a circle the biggest you can get out of a square of foam board, maybe even the thicker elmers/staples. Since I still consider you to be the king of low aspect, I kinda figured you had the answer on which series of options would increase the likelihood of success. I could hang one on my trusty slow stick but I don't do social media, it's hard to post demonstration stuff here.
Vimana89
Legendary member
A slow stick with a round wing is a nice idea, I've thought of it before, but this sounds more like a tailless idea. The biggest you can get a perfect circle in one sheet of foam is about 19-20", which is FT's standard Nutball size. I happen to have a fan with a stand that big around that can be traced. At that size the wing is structurally strong with no air foil, just like the FT Nutball. The difference would be, a straight up disk like a frisbee has no dihedrals, so for this, the goal would be a flat Nutball with elevons, possibly 4ch with rudder also. I have some spare time between ordering my Charlie kit and new parts to do a random scratch build. This would be a quick possibility.
Piotrsko
Legendary member
So it sounds definitely do-able. Probably just 1 sheet. Since flat wings just yaw, there is no need for anything like a controlled rudder, 3 ch bank and yank should be enough. I'm envisioning this the round equivalent to a large square sheet flying, but simpler, possibly with the heavy bits on the underside for added stability.
Vimana89
Legendary member
It would work without the rudder, but the rudder adds more control and stability in high alpha, plus the possibility of flat spins and flat turns on a single engine build with a flat wing. 🤔It is an extra channel though.
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Do you have two a or f pack motors? That would actually be really fun!
Vimana89
Legendary member
I only have basically a spare F pack motor free at the moment. I have to order some more parts! I have no experience setting up twin engines yet, but a twin engine Nutball would be cool!
Hmmm, I’m tempted... So you like the nutball?
Vimana89
Legendary member
Oh yeah. To be honest I haven't flown a stock, basic Nutball for a long time, and when I tried it early on I wasn't a good pilot or builder, and didn't have much success with it, but still liked it. I have had a lot of success with a tailed version of the Nutball I made, plus the Floating Kidney, which is basically an oblong Nutball. If I flew a stock RET Nutball now I'm sure it would be awesome, it's a great plane. I have no experience with non-dihedral elevon models of round wing planes though.
Vimana89
Legendary member
Not 100% sure how it would behave, I haven't built or flown a twin engine anything or a flat Nutball. Only planes with a rudder I've flown have dihedral and won't yaw very flat since roll and yaw are so coupled. Ideally a flat wing would yaw flat with the rudder, and with hard throws might do a flat spin. I could definitely see it doing flat spins as a twin engine.
