I wonder how significant a disadvantage duct drag winds up being,
considering most aircraft (tractors) blow the down the fuselage, which
has to have more drag than any sensible duct design. Do you think we
could make money/cancel the drag loss using stators downstream of the
fan like in a turbine, to recover the thrust in the rotating component?
That could even things up for the duct a bit, as the rotational velocity
imparted by a prop is significant, wasted energy.
Excellent thread, Gordon. Another thought I have that may give the duct
idea an edge is what happens in larger applications. The trouble with
competing with a conventional prop on a skinny Cozy / Imp airframe, is
that the flat plate drag is so low to start with, the weight/drag
penalty of adding a reasonable diameter tube more than cancels the
benefit. If we mentally pull the engine nacelles off the wings of a
twin, making a bigger fuselage, buying some cabin width / fuel / cargo
capacity with it flat-plate wise, and the diameter of the fan in the
embedded duct can be almost the diameter of the fuselage with no added
penalty, we can get around the thrust / drag penalty of a small diameter
tube because volume increases exponentially with circumference. Throw in
some more fan blades to absorb the extra horsepower, bump it to a
four-rotor in the 7-800+ HP range, my guesstimatation says the seat /
payload cost per mile starts to look pretty good--especially considering
this puts you up in the flight levels with the jets as Gordon has noted.
Double the horsepower of a Skymaster with what--nine more inches in
length, zero more in diameter at the price I just saw for two additional
rotors?
Maybe stretches the budget for a homebuilt, but not by 2X. The same
basic build time for more than twice the airplane, what if I find a
partner or two and time share it like a flying club.
While I'm having fun with this--Paul, what would it take to shut down a
couple of rotors at cruise, way simpler than that Cadillac V-8--some
kind of clutch and redundant fuel / ignition? Would the fuel flow
numbers improve enough to make it worth the hassle? This could be
worthwhile to consider when you add in the thought that this almost
gives us a twin engine in a single installation.
Donald Willard Garrett
See
http://www.rotaryeng.net/RX8.html
Paul Lamar
---------------------------
Why not just simply link 2 engines together ? Using the right linking &
clutching/declutching
system you can get exactly what you are talking about, without getting
into special design
in the engines, the 2 engines together would be longer but it should be
simpler to create.
You may wind-up with a slight weight penalty, compared to doing it in a
single engine,
however if the engine/s are all alloy then it should not be too much.
This is not a new idea
and has been used before in things such as generator/s. Thanks to
computer technology
the ability to control this is much better than it would have been in
the past.
Regards David
David, you may be right. What intrigues me here is the apparent
modularity of the rotary, that they are stackable like pancakes.
Couldn't the declutching you mention just as easily happen as another
module in the stack? This isn't actually an engine redesign if the
pancake analogy is valid, it's a matter of the location of the clutch.
Either way, it stops short of being fully redundant without concentric
shafts, but the only remaining vulnerabilities are seizure / prop / PSRU
failure. If we were talking about co-shafting pistons I'd say forget
about it, but--correct me if my thinking is incomplete here--seizure
failures modes with rotaries seem like an easy swap for all the ways to
die with one good engine in a conventional twin. With all the money
invested over the years to get an extra engine on board, this might be
worth gnawing on a bit, separate or stacked.
_______________________________
Matt, I read what you wrote, and even if you're right on every point you
raise re ducts, I don't think it's productive to shoot holes in a
brainstorming process. Keep in mind, the stats are that most of the time
someone invents something cool, it's usually completely different from
what he (or she) set out to do. As a community of both pilots and
inventor / builders, I recommend leaving plenty of room for silly ideas
to play out, since most really good ideas (including aviation) sound
ridiculous at first. Even if you're up to your eyeballs sorting
something like an ignition problem out, it will pay out in the long run
to just tune it out, rather than trying to squelch it:
This is not some pet peeve. The amount of talent and experience on tap
just in this mailing list, rivals or exceeds the leverage historically
available to kings and nations for getting useful things done--if it can
be focused productively. The problem is, successfully doing that turns
out to have more in common with growing flowers and herding cats than
anything you can engineer or put on a flowchart. Laugh if you want, but
if you watched your Google investment six or seven years ago being spent
on stuffed animals, rollerblading in the halls and playing video games
on company time, you'd be laughing all the way to wherever you wanted to
go, in your Learjet.
Not to pick on anyone--this is investment incentive: there are a million
forums and chat rooms out there where we can go to step on someone or
get stepped on, where do you find someone willing to get in his plane,
fly over and help you fix yours, or save you from some bright idea you
had, that would've killed you or cost you a bunch. I know this is a load
of touchy-feely crap, but it's PROFITABLE touchy-feely crap!
Donald Willard Garrett
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