On Mon, 07 Mar 2005 05:27:57 GMT, "Colin W Kingsbury"
wrote in
et::


"Larry Dighera" wrote in message
.. .
On Sat, 05 Mar 2005 17:26:33 GMT, "Colin W Kingsbury"
wrote in
. net::

Sure, it might fly, but who wants a machine with the fuel burn of an old
Lear (at low altitude), the maintenance costs of a big Sikorsky, and the
payload of a 172?

It's a start. It portends the future. It's going to need development
and refinement, but I believe these vectored thrust machines will
eventually be successful in achieving flight and eventually public
acceptance.

It seems to me that vectored-thrust aircraft face a couple of fundamental
challenges that will not be easily overcome.

First, you have the poor efficiency of turbines at low speed.

Because the engine(s) of vectored-thrust machines must provide thrust,
as they do in conventional aircraft, as well as providing lift, they
will never achieve the same economy and efficiency as fixed wing
aircraft. I have no idea if turbine or turbofan engines are the best
choice for these newly conceived machines; perhaps more efficient
diesel or electrical* power plants will be found more efficient in
this role.

The ducted fan
approach will improve this somewhat but if you look at the V-22, it has HUGE
propellers, more like mini chopper blades. The V-22 may be intended to spend
more time in hover than a Mollermobile, but I'll side with the machine
that's being flown seriously over the eternal prototype.

If the Wrights had had the same attitude, we'd still be floating
around in lighter than air vehicles. :-)

Second, the powertain complexity is considerable. You need at least 4
nozzles for control, and 2 engines cross-linked to drive the blowers.

Power train complexity could be eliminated with a system of ducts.
The Harrier manages with two nozzles.

I'm not a MechE but that sounds like a lot of transmission hardware to manage.

Nor am I, but the answer may be to eliminate the transmission hardware
all together such as independent electric motors powering ducted fans
or a single engine with high pressure airflow ducted to (rather than
generated at) exit nozzles. Clearly, it's going to take a visionary,
creative force able to think outside-the-box to be the enabler for
this technology.

What's that statistic I've read about the ratio of shop hours to flight
hours for helicopters? This would be much worse.

My gut feeling is that the vectored-thrust machine, once refined, will
probably require slightly more maintenance than a rotary wing.

And let's not even get into the control systems. These things would seem to
demand pretty sophisticated fly-by-wire and that's going to cost serious
money to design and certify, made all the worse by the fact that someone's
got to be first.

I don't see the control system as being that difficult a hurdle.
After all, the Harrier is able to hover with only two nozzles.

While fly-by-wire is a new and sophisticated concept for General
Aviation, it's been in use for decades on the F-16 and Airbus
equipment. As you are no doubt aware, Lockheed intentionally designed
the F-16 to be dynamically unstable to facilitate enhanced
maneuverability. Then flight stability was artificially programmed
into the computerized control system. A similar scheme would be
necessary for the machines we are discussing. So while the control
system will require research and development, it isn't like it needs
to be invented; it already exists.

Remember the Starship? FAA conservatism has more than a
little to do with why the plane became an albatross, though it also paved
the way for planes like the Premier.

The Starship** was designed to compete with conventional aluminum
aircraft in conducting the same missions those aircraft already had a
history of accomplishing reliably. The Starship was a rather
unconventional canard design constructed of relatively unproven
composite materials. If you were tasked with acquiring aircraft to
generate income, would you choose aircraft of known and proven
materials and capability, or risk your career/corporation on a new
design for which there existed limited repair facilities and mission
accomplishment data? Radically new aircraft must have adequate time
to prove themselves superior to succeed.

Again, the V-22 is the best precedent we have to go on here, and the
evidence is pretty bad. Twenty-some billion spent as I recall and the things
are still nowhere close to deployment. Heck, by that standard the 70 million
or so Moller has spent seems like a pretty good investment.

I see the V-22 as being many times larger and heavier than the
prototype vehicles we are discussing. Perhaps, of those designs
currently existent, a Harrier most closely approaches a reasonable
comparison vehicle. But the Harrier has wings and is capable of
speeds in excess of those likely to be achieved by the machines we are
discussing, so it's nowhere near an exact precedent.

Still, I don't see any of these guys solving or even coming close on any of
these fundamental problems. Remember the old engineering saying: 90% done, only
90% to go. Software has become fantastically cheap largely because consumers
have been willing to put up with 90% done. Aerospace does not enjoy this
advantage.

It is disappointing indeed that there has been such limited success to
date with these designs. Part of the problem is convincing those with
the ability to fund such projects that there is a viable market for
them by virtue of the unique missions they are capable of
accomplishing. Because existing designs are capable of fulfilling
most missions, there is little impetus to venture the requisite
funding for their development. They look like a good thing, but they
don't really do much more than existing aircraft are capable of.

In the end, it's going to take an inspired genius like Bert Rutan to
pave the way for their development. So far that talent has not
emerged.

There are many technologies that stubbornly refuse to yield to our desire to
make them workable. Fusion power, for one.

Personally, I have little doubt that small vectored-thrust aircraft
are possible, unlike the prospect of contained fusion reactions.

In aircraft, the real area to watch (imho) is pulse-detonatation engines, which
if they ever become commercially viable would give us the "Orient Express" planes
that take you to Tokyo in a few hours. But Pratt and GE have been working on these
for some years, and expect to be working on them for many more, and cannot tell
you how close they are to getting it right.

Pulse Detonation Rocket Engines*** are throttle controlled rocket
engines that have an economical advantage over conventional rocket
motors by not requiring an expensive turbopump to overcome the
pressure in the combustion chamber to introduce fuel and oxidizer.
Indeed rocket power technology may be the future of airline travel.
But it must successfully prove itself as economically advantageous,
mission enhancing, and safe before it will begin to supplant the
current entrenched technology. Because turbine engines are unable to
operated in the vacuum of space, pulse detonation technology must only
prove it is superior to conventional rocket technology to be deployed
there. I see the use of pulse detonation engines being used in space
missions long before an attempt is made to use them for airline
transportation.

As much as I'd like my Jetsons car, I doubt I shall be seeing one anytime soon.

That statement reveals the true appeal of the machines we are
discussing. They are futuristic dream machines that possess a certain
visceral appeal. Science fiction writers dangle them as bait in front
of quixotic aviators and the public as they did in The Fifth
Element****. Although these machines fail to solve real world
missions any better than the current technology, I believe they will
eventually be developed as an expression of that playful part of the
human spirit that craves the sheer joy of exuberant freedom of
personal flight.


*
http://www.halfbakery.com/idea/Highe...ectric_20Motor


** http://www.aviatorservices.com/starship_history_1.htm


***
http://www.msfc.nasa.gov/NEWSROOM/as...e_detonate.pdf


**** http://www.imdb.com/title/tt0119116

See them fly he
http://videodetective.com/home.asp?PublishedID=7001