Propeller Efficiency

Hi All,

I was thinking today about the fluid dynamics surrounding a propeller
as it moves in a circular motion.

It seems that, no matter what the blade angle, there would be a
significant amount of energy lost simply by turning the fluid. IOW,
even if there were no drag at any point on the aircraft, only a
fraction of the engine power would result in forward movement of the
aircraft. The remaining power would be lost in turning fluid in in a
vortex in the vicinity of the propeller.

Does anyone have any idea of the ratio between thrust power and churn
power?

TIA,

-Le Chaud Lapin-

Start here


http://books.google.com/books?id=BKU...Z2GDBjeo&hl=en


On Apr 13, 9:40*pm, Le Chaud Lapin wrote:
Hi All,

I was thinking today about the fluid dynamics surrounding a propeller
as it moves in a circular motion.

It seems that, no matter what the blade angle, there would be a
significant amount of energy lost simply by turning the fluid. IOW,
even if there were no drag at any point on the aircraft, only a
fraction of the engine power would result in forward movement of the
aircraft. *The remaining power would be lost in turning fluid in in a
vortex in the vicinity of the propeller.

Does anyone have any idea of the ratio between thrust power and churn
power?

TIA,

-Le Chaud Lapin-

On Apr 14, 1:40*pm, Le Chaud Lapin wrote:
Hi All,

I was thinking today about the fluid dynamics surrounding a propeller
as it moves in a circular motion.

It seems that, no matter what the blade angle, there would be a
significant amount of energy lost simply by turning the fluid. IOW,
even if there were no drag at any point on the aircraft, only a
fraction of the engine power would result in forward movement of the
aircraft. *The remaining power would be lost in turning fluid in in a
vortex in the vicinity of the propeller.

Does anyone have any idea of the ratio between thrust power and churn
power?

Less than 80%. Look in Wiki for discussion of losses.

Cheers

Le Chaud Lapin wrote:
Does anyone have any idea of the ratio between thrust power and churn
power?

There are literally hundreds of books on propellor efficiency - some
exceedingly inexpensive. There are probably dozens of web sites you would
find by a simple google search of "propeller efficiency". A newsgroup on
piloting is really the last place to ask - once one has done their own bit
of research and come up empty. What resources did you use that you couldn't
find an answer?

(Anyway, try he

http://www.allstar.fiu.edu/AERO/BA-Background.htm
)

On Apr 14, 12:58*am, Jim Logajan wrote:
Le Chaud Lapin wrote:

Does anyone have any idea of the ratio between thrust power and churn
power?

There are literally hundreds of books on propellor efficiency - some
exceedingly inexpensive. There are probably dozens of web sites you would
find by a simple google search of "propeller efficiency". A newsgroup on
piloting is really the last place to ask - once one has done their own bit
of research and come up empty. What resources did you use that you couldn't
find an answer?

None. Didn't think to look, but it does indeed say 80% on the
Wikipedia page.

http://en.wikipedia.org/wiki/Propeller

(Anyway, try he

http://www.allstar.fiu.edu/AERO/BA-Background.htm
)

All repsonses gave very good suggestions. I was suprised that the
ebook that Tina linked to had such detailed theoretical information
about flying in 1920. I guess I have seen one too many videos of
"slapping pancake" contraptions.

Also, another reason for the laziness is that I am knee-deep in a
research project, so for weeks I have been trying to abstain from
thinking about flying, as I can only think about one hard subject at
once to be productive, but over past week it's been hard to resist.

As I am still learning to fly, I have come across many articles about
flying cars. Yes, I know, it's the honey-pot for crack-pots in
aviation, but it seems that there are a lot of people interested in
having such a contraption, and not just people like Moller.

So during my breaks at lunch, I have been thinking about flying
vehicles, what they might look like, given obvious constraints (should
not kill the children if prop accidentally starts), and so that's how
I started thinking about prop efficiency.

I also started thinking about balance, how there is not very much
variation on component distribution in GA aircraft. They all follow
the same basic model: wings are placed to counteract very heavy
components (engine) and cause turning. Elements on empannage used for
elevation and normalizing centripetal force toward center of
curvature. Yes, this is all obvious by opening any book on flying, but
when you start thinking about actually designing an aircraft, it
*really* becomes obvious. I am beginning to wonder if there are
alternative models that would reduce length of aircraft
significantly. The existing model is tried and true, but there is no
law that say that the component distribution must be as it is now.

I think though, to get away from tried-and-true, if there is any value
in doing so, would require the designer to acknowledge the great
benefit that computerized control would bring. And I don't mean
Stealth, which is an obvious example. It might happen that the so-
called flying car would be best served by breaking away from the
current model and going with something that is a bit more distributed,
with computers effect what the pilot implicitly specifies via fly-by-
wire controls.

Needless to say, this is an *extremely* exciting field. Wish I had
more time to think about these things.

-Le Chaud Lapin-

Jim, have you forgotten?

Le Chaud Lapin is a MX sock puppet, or so most think.

Makes sense, why he could not find something that has several hundred hit,
with a simple search.
--
Jim in NC

Le Chaud Lapin wrote:
As I am still learning to fly, I have come across many articles about
flying cars. Yes, I know, it's the honey-pot for crack-pots in
aviation, but it seems that there are a lot of people interested in
having such a contraption, and not just people like Moller.

If you haven't already located it, the following website has a fairly
lengthy list (93 designs as of today) of past and present attempts to build
"flying cars":

http://www.roadabletimes.com/

The number of ideas and variations (and actual occasional flying
prototypes) that have been tried should keep you occupied for a while.

(Check its link on Resources and Research, including the one on "Can We
Eliminate The Propeller On Roadable Aircraft?":

http://www.roadabletimes.com/roadable_experimenter.html

Which takes you to:

http://www.fanwing.com/

wherein you can find videos of experimental RC models in flight. Look ma -
no prop!)

"Morgans" wrote:
Jim, have you forgotten?

Le Chaud Lapin is a MX sock puppet, or so most think.

I recognize "Le Chaud Lapin" from previous threads. I also recall that he
eventually stated it was a mistake to have posted a question on
aerodynamics to a discussion group having to do with piloting. I'm sure he
remembers his own writing.

On Apr 14, 9:32*pm, Jim Logajan wrote:
Le Chaud Lapin wrote:

As I am still learning to fly, I have come across many articles about
flying cars. Yes, I know, it's the honey-pot for crack-pots in
aviation, but it seems that there are a lot of people interested in
having such a contraption, and not just people like Moller.

If you haven't already located it, the following website has a fairly
lengthy list (93 designs as of today) of past and present attempts to build
"flying cars":

http://www.roadabletimes.com/

The number of ideas and variations (and actual occasional flying
prototypes) that have been tried should keep you occupied for a while.

(Check its link on Resources and Research, including the one on "Can We
Eliminate The Propeller On Roadable Aircraft?":

http://www.roadabletimes.com/roadable_experimenter.html

Hah!

That's actually the second link on my list of quick-access links on my
Internet Explorer. I visit maybe 2 times a week on average just to
see what's new. I offered to "face-lift" the web site as a fan, but
author did not reply.

Which takes you to:

http://www.fanwing.com/

wherein you can find videos of experimental RC models in flight. Look ma -
no prop!)

Illuminating indeed.

I have some thoughts about a new kind a propulsion system that would
also elminate the danger of the propeller. A one-passenger vehicle of
my design would fit in a small, US parking space (non-folding wings
included). My guess is that the propeller efficiency of this design
would be better than that of a conventional prop, but since I am just
starting out, I have to wait until I finish my current research find
out.

I did notice that a lot of designs on that site derives directly from
the expression "flying car". Many of the designers simply take a car
and add wings, a prop.

The people over at http://www.terrafugia.com have a nice-looking
vehicle, but I remember reading somewhere that even they, several MIT
aero/astro graduates, were "not going to pursue a super-radical design
because the software control was simply not there yet."

I'd be inclined to move toward more computer control.

-Le Chaud Lapin-

On Apr 13, 8:20 pm, WingFlaps wrote:

Does anyone have any idea of the ratio between thrust power and churn
power?

Less than 80%. Look in Wiki for discussion of losses.

Wiki isn't so accurate. The figure for max efficiency is in the
range of 85 to 87%, depending on AOA and a bunch of other stuff. The
Wright Brother's propeller on their Flyer had an efficiency of 83%
because they understood that it was a rotating airfoil rather than
some sort of paddlewheel.
For prop math, see this: http://www.epi-eng.com/propeller_tec..._propeller.htm

Sure, the air will swirl around some as it leaves the prop. It
has to, since there is no such thing as a drag-free propeller. But
it's manageable. Anyone who thinks he can design a better propeller or
airplane or anything else is well advised to do his research first so
as to avoid spending vast sums of money making the same mistakes
dozens of other guys have already made. If the OP, who is a PPL
student and has been known to "know better than the experts" in the
past, wishes to design and build himself a phenomenally new and
successful airplane or flying car, he'll have a pretty hard time doing
it. There are hundreds, maybe thousands worldwide, of aeronautical
engineers who know the limits of the physics and materials involved
and they are often employed at very good salaries by huge aircraft
manufacturers who wish to save even a few percent on fuel consumption,
drag, safety risks and other costs just to give themselves a
perceptible advantage over the competition. Any large improvement at
this point is going to require some new technologies that don't exist
yet. Better to spend the time discovering those new technologies.
There are many garages and barns and landfills full of pointless
efforts at designing a new airplane. Most successful new designs are
variations on the same old theme we've had for a long time now.

Dan