"B2431" wrote in message
...
From: (


SNIP

proved
how complicated things really were. The downward ducted fan
concept has
been tried several times and not one vehicle had the performance to
justify
proceeding to an operational prototype.


The results of the tests were as follows:

http://www.autobahn.mb.ca/~billzuk/F...aucer%202.html
"The results of the testing revealed a stability problem and
degraded
performance due to turbo-rotor tolerances. Before modifications
could
be achieved, funding ran out with the final flight test program
completed in March 1961. With the problems that the contractor was
facing in the wake of the cancellation of its premier fighter
program,
the Avro Arrow by the Canadian government, Avro was unable to
continue
the project. "

OK so the engineering problem of turbo tollerances is corrected ( a
cinch for todays wide bodied cowling manufacturers I expect ) and
the
stability problems are solved by a gyroscoep based "Fly By Wire"
stability augmentation system.
( an FBW system like this is an of the shelf cinch today )

Why wouldn't it work now?


From what I can see this system should work. An efficient VTOL
device
needs large volumes of slow moving air. A helicopter achieves this
with a rotor. A "saucer" like this can do so by sucking in air at
the
top and distributing it to a lip at the edge of the saucer where
the
high velocity air is converted to low velocity by inducing an
airflow.

However that is not how the Avro machine worked. See:

http://www.laesieworks.com/ifo/lib/avro-graph02.html

If you poke around the web you will find all kinds duct being used
to hover.
You will even find a few that can transition from vertical to
horizontal
flight. The closest to being practical I can recall was in the 1960s
Boeing
produced on with four ducts mounted on winglets.

Dan, U. S. Air Force, retired

There are a number of ducted fan concepts. The Piasaki flying Jeeps
worked and had advantages but were fuel hogs that had trouble landing
on uneven ground and there were concerns that they were dangerous in
gusty conditions.
http://www.faqs.org/docs/air/avplatfm.html#m4

It seems to me that the Israeli guy (built the prototype in his
apartment and had to knok down the wall to get it out) has adressed
most of the shortcommings of these Piasaki aerial platforms.
http://www.urbanaero.com/Urban_Main.htm

Many VTOL and ducted fan concepts are documented on
http://www.vstol.org/ The 'wheel of misfortune' is interesting and
the Boeing project you refer to is I think the Bell X22A but there
were others such as the Bell model 65 ATV

In reference to the Avro canada saucer:
http://www.faqs.org/docs/air/avplatfm.html#m4

"A wind-tunnel test model and a flying prototype were built. The test
model was sent to the NASA Ames Center in California for wind-tunnel
tests. First tethered flight of the flying prototype was at Malton on
29 September 1959, followed by the first untethered flight on 5
December 1959. Although Frost and his staff recognized that the
Avrocar was inherently unstable and had incorporated an
electromechanical stabilization system, it wasn't up to the job, and
once the Avrocar picked itself up to above chest height and got out of
ground effect, it bobbled around drunkenly.

An improved stabilization system was considered, but Avro was in chaos
due to the cancellation of the "CF-105 Arrow" interceptor program. The
chaos filtered down to the Avrocar program, and the US backers of the
program lost interest. The program was axed in December 1961. Whether
it would have ever flown right remains an open question. "

The "Electromechanical" stabalisation sytem was surely no more than a
single gyroscope and some microswitches mounted on the gimballs to
opperate shutters in the air-stream. A 3 axis multi-input
multi-output non linear or state space controller was probably needed
to achieve rock steady stabillity and that needs to be put together by
specialist control theorotecians.