Hi PierreB,

My experience is limited to flying a Sharp Rotor kite. Besides end discs, it required a very large central disc to make it reasonably stable. Many toy rotary kites do the same thing. So a heavier than air Magnus cylinder would presumably need the same kind of stabilizer.

However, there are additional ways to stabilize a rotary kite, and they have not all been explored. For a Magnus cylinder, pendulum stability could be achieved by mounting the motor well below the cylinder and then connecting them with a thin belt or rope drive. Another approach is to use 2 cylinders end to end and at a vertical angle to each other to create dihedral (which is used by airplanes to prevent side-slip. Or a single cylinder might be contracted to be slimmer in the middle; that could work because the lift from the top is larger than the lift from the bottom, so it is the equivalent of using dihedral.

But the form of stability depends upon what you want to do with the kite in terms of maneuvering it.

Another approach is to use two cylinders end to end, each with its own small motor. Then increase or decrease the lift separately to keep the overall kite stable and to maneuver it. That might be done automatically using some sort of level or gyroscope inside of the kite.

End discs don’t have to be solid and heavy. They could be fabric discs stiffened by a light hoop. Or, the discs could be stiffened by centrifugal force by sewing a light chain inside of the circumference of the fabric disc.

Just a reminder: If an air inflated balloon is black, it can absorb heat from the sun and expand its internal air so as to make it lighter than air. No helium required. Here is an interesting fact to put in the back of your mind:

If the rotating cylinder is made buoyant by solar heating, it will retain its heat unusually well. That is because its rotation produces a centrifugal force on its internal air. That causes the colder air, which is heavier, to be forced toward the circumference of the cylinder, while the hotter air, which is lighter, is forced  to the middle of the cylinder. So if the ends of the cylinder have some foam insulation, the solar cylinder should hold its heat rather well and continue to be buoyant longer than expected as the sun goes down. It would help if the heat from the spin motor were kept inside of the kite. In theory at least, it might be possible to build a solar heated cylinder kite that stayed buoyant all night long. At night, some heat usually radiates from the surface of the ground.

PeterS

Hi Tallak,

Dihedral is used to prevent sideslip. The direction of the relative wind changes during sideslip. The relative wind shifts toward the side of the sideslip. It changes differently for the two sides of a wing with dihedral since the two sides are at a different angle to the relative wind. So it doesn’t matter if the wings are conventional or rotating cylinders. Dihedral works for both to prevent sideslip.

I demonstrated that back in the 1970’s with a free-flying, gliding toy that auto-rotated. It rotated on its span-wise axis like a Magnus effect cylinder. It also had dihedral. The dihedral increased its stability noticeably. It was thicker at the ends than in the middle, which gave the top positive dihedral and gave the bottom negative dihedral. Since the top produces more lift than the bottom, the result was increased stability. I tested it against rotary wings with the same average thickness so as to rule out the effect of pendulum stability.

See https://patents.google.com/patent/US4051622A/en?q=Peter&q=A.&q=Sharp&q=flying+toy&oq=Peter+A.+Sharp+flying+toy 

Magnus effect cylinders can be constructed with dihedral by joining two paper cups bottom-to-bottom, and then adding end discs. The dihedral will improve their stability as compared to a constant-diameter cylinder with end discs.

So using two cylinders mounted at an angle to create dihedral, should produce increased stability. The increase should be larger than for a single cylinder that has dihedral. If you doubt that, you might wish to test it to find out.

Actually, the test has already been done. There is a toy, red, plastic airplane kite that uses spinning S rotors for the wings. They are given dihedral to increase the stability of the kite. The spinning S rotors are similar enough to spinning cylinders to draw a conclusion. The conclusion is that Magnus effect wings with dihedral will increase stability.

If you believe that that evidence is not convincing, I encourage you to demonstrate that the conclusion is false.

PeterS

Hi Tallek,

“..., i was thinking more traditional dihedral with two separate rotating axes with a dihedral angle at the center of the wing.” Yes, I realize that. Just to be clear, I did address that option in my response to you.

Thanks for asking about the flying toy. Whamo (hula hoop, etc.) almost produced it but they felt that competitors would sell the Donaldson rotor kite as a free-flight toy, even though it is unstable, to take advantage of Whamo’s publicity for the “Weirdwing” (the name I used for the patented toy). The patent is expired and anyone is free to sell the toy.

I make mine out of card-stock (business card) paper, and I made one using vacuum forming around a mold, plus internal foam braces. It flew quite well. I’m retired now and have no desire to build another business.

I will eventually make a video showing how it works. Basically, if you investigate the “Tumblewing”, you can see essentially how it works. It utilizes the Kramer effect for lift, instead of the Magnus effect, when auto-rotating. The difference is that the Weirdwing is more stable and has twice the lift-to-drag ratio as the Tumblewing. It’s fun to throw a Weirdwing underhand, with back spin, by throwing it straight up. It does a forward loop and comes back to you so that you can catch it. The same can be done with a paper Donaldson rotor, but it is a bit more difficult to throw due to its lower stability.

I have previously discussed the technology on this website, so you might be able to find that previous discussion. That discussion includes the 3-sided Sharp Rotor which may have some potential as a kite.

PeterS

Hi PierreB,

https://www.youtube.com/watch?v=2JzdERxpzes  

I wonder if a solar balloon skin could be made to act like a one-way mirror (similar to some window coatings) that let infrared radiation to pass through in one direction but not the other. If so, then that combined with “spin-insulation” might be sufficient to keep a solar balloon aloft at night. Very hard to do, but very useful if it could be done.

How might a spinning balloon stabilize itself due to its internal air mass rotating? Specifically, how will it prevent side-slip?

PeterS