Propellors vs Rotors

GET BACK IN THERE! 'YA DAMN WORMS!

Yea, rotor wash is real. I've been in it... under an AS Puma slow
orbiting just over wet pine trees, 100 ft. from a Bell 412, 212, 214,
206, 222, Boelkow 105C, AS AStar, AS Twinstar, Hughes 500C getting out
of a Bell 206-B3, Robinsin R44, Bell 206-L1, and numerous other
encounters that I can't quite remember over the years. My Dad was a
helicopter A&P.

Yea, a significant portion of the air surrounding a hovering helicopter
is moved downward, just as fixed-wing props throw back a pretty good
blast. So I guess it is possible that fixed wings do deflect some air
downward, though I've never felt it while flying hang-gliders. And
that's still not what makes wings work. Its one of the things that
makes them less efficient.

Wilbur Wright struggled with this very issue for months while
attempting to develop his propeller theory. And Wilbur's theory is that
propellers are not "screws", no or they fans. They're airfoils and not
rotating "aero planes". Not that you can't propel a plane or SkyCar
with a ducted fan, but thats reaction-thrust from my understanding. A
propeller is a wing traveling in a corkscrew path through air. Some of
the energy consumed by the prop makes lift and pulls the aircraft
forward. Some of the energy consumed by the prop pulls the air
backward. Developing a prop that puts enough energy into pulling the
plane forward and not just swishing the air around is the trick. Its
kinda like trying to turn a bolt with a wrench in space. Your arm can
turn the wrench in reference to you, or it can turn you in reference to
the wrench. In reality, space arms and propellers are pretty good at
doing some of both.

Wilbur and Orville used the largest props that would fit on their
airframe. In 1903 those were 8' 6" each and turned between 300 and 350
rpm depending on how hot the engine was. At an average of 8.56hp (the
engine only made 11.78hp for a few seconds dead cold), the twin props
produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
Not bad on the first try.

Getting back to the original issue, here's another experiment. Hold a
peice of paper vertically. Grasp its lower edge with your thumb and
forefinger. Now let the paper drape over your wrist so that the free
edge hangs down and away from you. Now blow along the upper surface of
the paper. DO NOT let any part of your breath blow under the paper. See
what happens. Hmmmmmmm. What's holding that paper up? All of the air
that it, the sheet of paper, is throwing downward, all on its own,
because it instinctually "knows" that this is the correct behavior for
good little sheets of paper that get blown on? Hold your other hand
under the paper as you blow. Any air moving downward? And what's the
paper doing? Hmmm?

BTW, addressing my previous statement about AOA, some planes can
definately climb nose-down in upright flight. Amazing, but the B-52 is
one of them. I was reminded of this 2 days ago while watching the
Hitler Channel. Looks goofier than hell.

The original Wright 16" wind tunnel did not survive history. However,
the original balances and test airfoils did and are currently at the
Franklin Institute in Philly. Orville stored them in a box for years
and almost threw them out once. Thanks for shaking that box Orv. There
are numerous reproduction wind tunnels in museums. I'm planning to
build one myself. Nick Engler had blueprints for one on his website
http://first-to-fly.com/Adventure/Wo..._and_drift.htm

Harry "rotor-ramp-rat" Frey

Hi Harry,

wright1902glider wrote:
GET BACK IN THERE! 'YA DAMN WORMS!

;-)

The original Wright 16" wind tunnel did not survive history. However,
the original balances and test airfoils did and are currently at the
Franklin Institute in Philly. Orville stored them in a box for years
and almost threw them out once. Thanks for shaking that box Orv. There
are numerous reproduction wind tunnels in museums. I'm planning to
build one myself. Nick Engler had blueprints for one on his website
http://first-to-fly.com/Adventure/Wo..._and_drift.htm

Harry "rotor-ramp-rat" Frey

I misunderstood what I was seeing at the Air Force museum. You
are correct that it is a 3/4 scale replica constructed under Orville
Wright's guidance sometime before WWII.

http://www.centennialofflight.gov/wb...ind-tunnel.pdf

This link also refers to the balances and experiments you are talking
about.

Thanks for correcting me.

BTW, I think that the discussion about the way wings work
is fascinating although slightly off the original topic.

IIRC the diplacement of the air molecules around a wing can be
conclusively demonstrated by multiple smoke streams in a wind
tunnel, or by mutiple dye streams in a water tank. I remember
such demonstrations in the lab back at good ole Wichita State
U.

I've only got one such photo available right now, and it is on page
141 of "Fluid Mechanics" 5th edition by Ray Binder. It shows a
symmetric airfoil at approximately 20 degrees AOA. In the photo
_all_ of the smoke streams (e.g. both the ones above the airfoil
and the ones below) that are disturbed by the airfoil end up
lower than they started out. This shows that a symmetric
airfoil at positive AOA pushes the air below it down, and _also_
pulls the air above it down. The net result is a slight downward
displacement of a _lot_ of air including air that is ~2x the chord
away from the airfoil.

I'll try to see if I can find similar photos on the web because I
think it will enliven this discussion to the general benefit of all
the participants (including me).

Don W.

wright1902glider wrote:

GET BACK IN THERE! 'YA DAMN WORMS!

Hi Harry,
snipped in places...


Wilbur and Orville used the largest props that would fit on their
airframe. In 1903 those were 8' 6" each and turned between 300 and 350
rpm depending on how hot the engine was. At an average of 8.56hp (the
engine only made 11.78hp for a few seconds dead cold), the twin props
produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
Not bad on the first try.

96 pounds of thrust from 11 horse?

What did that whole rig weigh?



what happens. Hmmmmmmm. What's holding that paper up? All of the air
that it, the sheet of paper, is throwing downward, all on its own,
because it instinctually "knows" that this is the correct behavior for
good little sheets of paper that get blown on? Hold your other hand
under the paper as you blow. Any air moving downward? And what's the
paper doing? Hmmm?

But you Cheated!

Very localized pressure field resulted above the paper, and so what?

You sped up the air above the paper by blowing it.
(cheater)



BTW, addressing my previous statement about AOA, some planes can
definately climb nose-down in upright flight. Amazing, but the B-52 is
one of them. I was reminded of this 2 days ago while watching the
Hitler Channel. Looks goofier than hell.

BIG Lift Fairies!

snipped in places...
--------------and snipped some more-----------


Wilbur and Orville used the largest props that would fit on their
airframe. In 1903 those were 8' 6" each and turned between 300 and 350
rpm depending on how hot the engine was. At an average of 8.56hp (the
engine only made 11.78hp for a few seconds dead cold), the twin props
produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
Not bad on the first try.

96 pounds of thrust from 11 horse?

Actually from the 8+ horsepower. Based on 1 horsepower = 1 pound of thrust
at 315 knots, the figure sounds like a reasonable static thrust value. The
thrust may have been a little less in flight.

What did that whole rig weigh?


I vaguely remember reading something like 600 pounds, plus the pilot of
course. Orville and Wilbur were both small and slight, so the gross weight
was probably only a little more than 700 pounds...

Peter Dohm wrote:

snipped in places...

--------------and snipped some more-----------

Wilbur and Orville used the largest props that would fit on their
airframe. In 1903 those were 8' 6" each and turned between 300 and 350
rpm depending on how hot the engine was. At an average of 8.56hp (the
engine only made 11.78hp for a few seconds dead cold), the twin props
produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
Not bad on the first try.

96 pounds of thrust from 11 horse?


Actually from the 8+ horsepower. Based on 1 horsepower = 1 pound of thrust
at 315 knots, the figure sounds like a reasonable static thrust value. The
thrust may have been a little less in flight.


What did that whole rig weigh?



I vaguely remember reading something like 600 pounds, plus the pilot of
course. Orville and Wilbur were both small and slight, so the gross weight
was probably only a little more than 700 pounds...



700 lbs / 96 thrust = .137 - which is a wee bit below the .20 rule of thumb.

Might consider catapult launch?

"Richard Lamb" wrote in message
link.net...
Peter Dohm wrote:

snipped in places...

--------------and snipped some more-----------

Wilbur and Orville used the largest props that would fit on their
airframe. In 1903 those were 8' 6" each and turned between 300 and 350
rpm depending on how hot the engine was. At an average of 8.56hp (the
engine only made 11.78hp for a few seconds dead cold), the twin props
produced an average of 96 lbs of thrust. or 11.22 lbs of thrust per hp.
Not bad on the first try.

96 pounds of thrust from 11 horse?


Actually from the 8+ horsepower. Based on 1 horsepower = 1 pound of
thrust
at 315 knots, the figure sounds like a reasonable static thrust value.
The
thrust may have been a little less in flight.


What did that whole rig weigh?



I vaguely remember reading something like 600 pounds, plus the pilot of
course. Orville and Wilbur were both small and slight, so the gross
weight
was probably only a little more than 700 pounds...



700 lbs / 96 thrust = .137 - which is a wee bit below the .20 rule of
thumb.

Might consider catapult launch?


In a way, they almost did--sending it down a greased slide....

Remember that they had nearly 12 HP when first started--which gave them a
decent start slightly down hill and into the wind. All in all, I agree that
the whole enterprise was a little crazy. I am glad they succeeded, and
further engine development must have followed quickly.