a wrote in
:

On Sep 7, 3:23*am, Bertie the Bunyip wrote:
a wrote
innews:b2735259-d892-4737-b243-0514e9cd3f84@5
9g2000hsb.googlegroups.com:



On Sep 6, 5:24*pm, Bertie the Bunyip wrote:
a wrote
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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
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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 tha
t
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.

Nah, just suspicious.


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.

Oh i don't see any change. Toothpicks have, by far, been the most common
props on lightplanes for years and not without good reason. I'm not
arguing that. But it depends on a lot of things. A lot of turboprops
have relatively wide chord scimitar props, for instance. My point was
really more directed towards the sentiment that efficiency shoud be
described in such narrow terms. Most people want an airplane to go from
A-B real fast and burn as little fuel as possible, but that doesn't mean
that it's nore efficient than an airplane that excelles in some other
way..



Bertie