The fact that it is two flat surfaces was a surprise to most rotor enthusiast. Until the author of the Modern UFO, Kenneth Sams, started experimenting it was thought the main wing had to be an 'S' shape to ensure that it would rotate.
Unfortunately the basic UFO plan came from a book called "Flying Toys" and as such I can't publish the plans. Here however is the book reference...
"Flying Toys", by Kenneth Sams Milner Craft Series, Sally Milner Publishing (UK) ISBN 1-86351-038-9
It is a shame about the copyright, they fly great, look cool, and well liked by the general public. These UFO's are also very much stronger than the meat tray rotor, using a covered fibreglass frame instead of the fragile styrofoam meattrays.
The book recommends using a mylar cover, I have however had success with light
ripstop. What I do is (same as for mylar) double sided tape to the oval
fibreglass hoops, but then I sew around the edges using a 'side' or 'zipper'
foot on the sewing machine. Then remove all the excess ripstop a mm or so from
the sewn seam. The double sided tape is vital to prevent the ripstop slipping
around the spar as it would if it was just a ordinary spar pocket, eventually
making the spar break.
I must say however that the mylar 'silver' foil rotors, are much more visible from certain angles in sunlight. The flashes generated by this rotating 'beacon' in the sky are visible for miles, even more so than the 'giant' inflatable kites at a distance of 20 km or more. The silver or aluminised mylar is also supposed to be highly radar visible.
WARNING: Aluminised mylar is conductive of electricity. Because of this commercial sale of kites made from this material is banned in the USA as kites of have shorted out powerlines and transformers. These incidences were usally the result of larger kites, often using the mylar for long tails. Even so I suggest you be very carful and keep them completely away from any electrical equipment, which you should be doing anyway.
Modern UFO Patents
Now the original book "Flying Toys" is out of print, and you need to be very
lucky to get a copy, or to find one in a library to borrow (or photocopy).
However I was recently told that many rotor patents are now available online
the latest (at time or writing) being US Patent 5,598,988.
Well this isn't exactly the same as the books version, though it is pretty close. After a bit more searching I found US Patent 4,779,825, The Sams UFO Patent.
There was also second UFO design, in the same SAMS patent, which I found VERY
interesting! A Ringed UFO!
After building a prototype I found this design to work very well. However I built it with the same bridle mechanism as a 'normal' modern UFO, instead of the 'bridle ring' shown in the diagram of the patent. My reasons for removal was that the extra weight is just not needed, or warranted, and I am not convinced it would even work with the tension it would need to transfer, between flying line and the wing axil.
This design I found is more difficult to get started from the ground (hand launch is recommended). It is much easier to build due to a less complex ear/wing attachment (just tie the two spars together at two points).
My own ringed UFO's uses 3 hoops made from 2mm fibreglass (instead of the 2).
The wing oval is 120cm (which is the normal size I use in my UFO's). The
ring uses two hoops, an inner 95cm, and outer 136cm. The oval main wing is
squashed before covering (as for a normal UFO) so the short axis just fits
inside the inner circle of the 'ear' ring (Pun is not intensional! groan! :-).
A commercial version of the Ringed UFO, made from ripstop and using special
plastic molded bits and bobs, is now being manufactured by Prism Kite Technology.
This kite flies very well, and as it is very light weight will fly in a very
light wind, while still handling a strong gusty wind.
Two UFO's flying from the same line is a great idea. If one UFO decided to
wander, the second UFO tends to support the first until it can right itself and
climb into the sky.
(Top view) __--+ ____,---==__ O ____,--' --+ ------------===____ __--+ `---==__ O --+Note that the two UFO's are not the same distance from the fork in the bridle line. This ensures that they do not interfere with each other. A swivel at the fork and individual UFO bridle points will remove any twisting up of the kite line.
For launching you only need to launch one UFO the other will be pulled up and dragged around the sky until the folded ear opens out and the second one starts to spin, climbing to join the first.
Today I tend to use a forked line with a UFO (preferably an ringed UFO) on the short line and a mini-circoflexi (ringed kite) on the longer line. The circoflex ring tends to fly slightly higher and above the UFO. People have asked me of the arrangement "How are they connected, I can't see any spars between the two?".
Longer UFO trains can be created but only one method has so far proved practical for three or more UFO's attached to one line. This involves using a 'forked line'. That is long line with individual UFO's attached to shorter lines off from the main line.
__--+ __--+ __--+ _,--==__ O _,--==__ O _,--==__ O _,-' --+ _,-' --+ _,-' --+ __--+ ---+------------------+-------------------+-------------------------==__ O --+Note the line lengths is such that it is impossible for the UFO's to tangling with the next one in sequence. With swivels just before each split and at the UFO attachment, line twisting is also kept to a minimum.
Each UFO can still move about independently in response to wind turbulence, and they are far enough from the main line so that they will rarely hit it though if they do they will right themselves quickly while the other UFO's support it.
Looking up the line it looks like a flock of UFO's all flying is a group.
Watch out though as any other kite or kite lines contacting this arrangement will most likely result in the biggest tangle you can imagine.