On Sep 7, 3:23*am, Bertie the Bunyip wrote:
a wrote :



On Sep 6, 5:24*pm, Bertie the Bunyip wrote:
a wrote
innews:3bdcc9b5-67cc-4c34-a7a2-41e2a744b82d@z
72g2000hsb.googlegroups.com:

On Sep 6, 5:41*am, Bertie the Bunyip wrote:
a wrote
innews:14d9aabc-33a9-4fdf-9ca5-78e407249a02@7
9g2000hsk.googlegroups.com:

On Sep 6, 3:51*am, Bertie the Bunyip wrote:
a wrote in
news:e5fb9dcd-6bd8-42e3-9a50-f6370d188424
@x35g2000hsb.googlegroups.com:

On Sep 5, 6:46*pm, Leviterande Leviterande.
wrote:
Now woludnt a shorter prop with a bigger chord(and q-tips)
move more a
ir
and thus creating equal thrust as a longer propeller with
thinner chor
d?

when I tried the patented fan it was pretty quiet *however.

How did you try the patented fan?

AS for longer chords? Probably not. Think of the *most
efficien
t
wing
s
for airplanes -- the ones that provide the best lift/drag.
They are long and slender. The same principles hold for
props. You can be sure if wide chords were better they'd be
showing up on experimental aircraft, and they are not.

They do actually, and they can be very efficient indeed.

http://www.youtube.com/watch?v=Nxz1UF67EQI

There's also been the Dyke Delta, and the facetmobile, of
course.

Bertie

I don't think you'd find these as 'efficient' as conventionally
shaped aircraft, else we'd be seeing competition gliders shaped
this way. Those airplane shapes would have very light wing
loading of course, but huge wetted areas -- think drag.

Yeah, I understand al of that, but the word efficient is one that
is often bandied as some sort of standard, but is just as
misunderstood.

While I know you mean aerodynamic efficiency in it's purest form,
the mission is the yardstick by which you must measure the success
of an airplane. Gliders are good at what they do, but they're as
much a compromise as any other type of airplane. Low aspect ration
machines have a few enormous advantages, not the least of which is
a huge speed range and relatively low drag at low alpha. Span
loading is more relevant than area loading in many ways and
application, depending on what you're trying to get the wing to do
at any given momen, and a low span loading, as in a glider, has to
be paid for with *drag just like any other aerodynamic benifit.
Simply put, the longer the span, the more air you're moving
around. Now, for some applications, this is more efficient, since
by agitating a greater volume air in a less agressive fashion than
a little air, you may, and may is the operative word here, create
less drag in your flight situation.

. As for using that concept for prop blade shape, , where
efficiency is defined in the conventional engineering sense as
power out divided by power in, long and thin blades seem to win
over short and fat.

Depends on the application and what you're asking the blade to do.
Length brings its own problem here again, but in spades, since tip
speeds, particulalry at high cruise speeds, becomes a problem.
There simply are no pat answers in aerodynamics. "Monoplanes are
more efficient than biplanes" for instnace, is an oft touted
example. Simply not true in every aspect. It depends on what
you're asking the airplane to do. Of course, particualrexamples
may be plucked from the air to prove almost any POV here. You
could look at two types of aircraft and compare their performance
with a single yardstick, such as fuel burn, but that doesn't make
one more efficient than another as whole. just on fuel burn. If
the fuel efficient one can't get out of the 800 foot strip it's
parked in and the other one can, then the one that can is the more
efficient machine for it's mission. That's not to say some
airplanes aren't just plain inefficient, but it is a bit
ridiculous to say that just because there's a popular mission and
most airplanes tend to gel in that corner of design that those
types of aircraft are ultimatley the most efficient things in the
sky.

Bertie

The mission that seems best served by short span broad chord
propellers seems to be in the marinas -- long and thin are not
popular there. Even that may be changing, you may have seen a
satellite view of an Ohio class submarine with its screw exposed
recently (the navy goofed, those things are usually shrouded when
they would be otherwise exposed) *and it looked like something that
belonged on an airplane.

Well, my main drive has short span long chord blades. So do most high
bypass fan jets...

Bertie

early on I mentioned relatively low speed GA airplanes, and for sure
recognize the difference fan jets provide. I'm sure you recognize that
the high bypass stuff you drive is a different animal, and really not
unlike the ducted fan with lots of hardware overhead I also
mentioned.

Get thy tongue from thy cheek! Your digression was from Anthony's
manual.

Not really. In fact I wondered if you might be an anthony sock for a
bit!
I just have a bee in my bonnet about emprical statements!
You're not wrong about high aspect ration wings, but you're not
completely right either. You're not going to win a soaring competition
with an airplane with a 1-1 aspect ratio doesn't mean youcan't make it
do something quite respectable.
That Arup had some remarkable performance figures. They were far from
just being a curiosity in the thirties when they were built. They got a
lot of attention in the aviation press and the performance was
remarkable. I have some of them somewhere but just going from memory the
small engined ones, I think it had a 75 HP LeBlond on it, had a speed
range of something like 30-120 MPH. They have some serious drag issues
at low speeds, of course, but this can be turned to advantage, giving a
steep approach so desirable in stol ops.
This is the reason the Navy were interested in the Flying Flapjack
airplanes in the mid 40s. Potentially good carrier airplanes with a very
high cruise speed.

Bertie


If you associate me with Mx your judgment is seriously impaired. Keep
an eye on that, and if the manifestations continue seek some
professional help before it's too late.

I seriously doubt the form factors those airplanes suggest for props
would lead to any improvement in propeller efficiency, using the
classical (energy out over energy in) definition. If they did,
hanging one on a C152, C172, or a P140 would improve things like rate
of climb or service ceiling or fuel economy (my Mooney gets about 18
mpg) by about the the same percentage as increased efficiency. There
would be a nice market for such an improvement. My prediction is we'll
continue to see only narrow chord blades in front of us for the next
15 years.