The fact that it is two flat surfaces was a surprise to most rotor enthusists. Until the author of the Modern UFO, Kenneth Sams (see below), 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...
It is a shame, they fly great, look cool, and well liked by the general public. These UFOs are also very much stronger than the meat tray rotor above using a fibreglass frame instead of the fragle styrofoam plastic, but then also heavier too, requiring a medium to strong wind.``Flying Toys'', by Kenneth Sams Milner Craft Series, Sally Milner Publishing (UK) ISBN 1-86351-038-9
STOP PRESS 24 Feburary 1999 :- A patent for a rotor kite very simular to the modern UFO (not quite the same) was brought to my attension. You can see this (and other related kite patents) on the IBM Patent Server US Patent 5,598,988. Enjoy. The Sams UFO is also available in US Patent 4,779,825.
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. and then remove all the excess ripstop
a mm or so from the sewn seam. The Double sided tape is vital to prevent the
ripstop sliping around the spar as it would if it was just a ordinary spar
I must say however that the mylar `silver' foil rotors, are much more visiable from certian angles in sunlight. The flashes generated by this rotating `beacon' in the sky is visible for miles around, even more so than the `giant' inflatable kites at over 20 km.
They are built from two ovals, created using 1.2 meter long 2mm diameter fibreglass rods, to form hoops. The original plan by Sams used 1 meter circumference hoops, but I find 1.2 meters better, and 1.3 geting too `flexiable'. I then squash the circular hoops into ovals using some scotch tape, one hoop 1/2 cm thiner than the other. The tape can be removed after the kite has been is covered, though that could be difficult with mylar foil.
The cover is a very light weight sail. Ripstop or mylar being prefered though other `no streach' covers is also posiable. Do not bother with plastic as it streatchs too much and the fibreglass hoop is likely to break due to un-equal streach. The cover is then double-sided taped directly to the fibreglass hoop.
After the two oval hoops are covered, a slit is cut in the `ear' oval (the slightly wider one) along the shortest diameter. To the thiner `wing' oval a `axil' is taped accross the center of the longest side so that it pokes out the both sides of the oval by about 4 cm. The `wing' is then inserted into the slit of the `ear' and the two ovals taped together along all four corners of the joint.
When I use ripstop, I just cover the `wing' as above, (sewn for extra strength), but using two seperate overlaping pieces for the `ear' oval so the `wing' can slide between the two halfs and sewn down the join.
The bridle to be attached to middle of three washers (fiberglass washers from the local hardware) at each end of the axil. The washers are kept loosly on the axil by short lengths of plastic tubing, which is also used to keep the washers well away from the rotating wing of the kite. The flying line is then attached to the middle point of the bridle where a loop has been tied. The kite should then be able to rotate freely at teh end of the flying line and bridle.
Once the kite is spinning the ear will never fold flat as centrigugal forces keeps it out. The elastic, in the book plan, I found was just not needed and its removal, cut of the kite down the weight of the kite and increased the speed at which it rotates.
Weight in UFO's is critical. My first prototype were rather heavy though very solidly constucted. It worked but needed a gale to fly. Yes these kite love medium to strong winds. But the lighter the kite the lighter the wind it will fly in, and the higher it will fly.
As such a very light twisted nylon line is better than a heavy dacron line. Also as nylon is streachy, all the better as the kite must be able to streach and release the flying line.
The Original Plan and the few UFO commercial models, use a fibreglass axil, but in high winds this I have found to be far too springy. The kite would bend, hold a moment, bend, hold a moment, etc... The springy axil just stopped the kite working well in high winds.
Experiments with dowel found it too brittle and thick, and does not form a good bearing for the bridle lines. But Carbon fibre tubing with its very stiff nature was perfect! Remember any spring in the kite should be in the flying line, NOT in the axil of the kite.
(Top view) __--+ ____,---==__ O ____,--' --+ ------------===____ __--+ `---==__ O --+Note that the two UFO's are not the same disance from the fork in the bridle line. This ensures that they do not interfer with each other. A swival 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 draged around the sky until the folded ear opens out and the second one starts to spin, climbing to join the first.
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 a long line with individual UFOs attached to shorter lines off the main line.
__--+ __--+ __--+ _,--==__ O _,--==__ O _,--==__ O _,-' --+ _,-' --+ _,-' --+ __--+ ---+------------------+-------------------+-------------------------==__ O --+Note the bridle prevents any chance of the UFO's tangling with the next bridle fork. With swivels just before each split and at the UFO attachment, line twisting is at a minimim.
Each UFO can still move about independantly in response to wind turbulance, 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 UFOs support it.