OT: Who invented the airfoil?

Clay <clay@claysturner.com> wrote:
(snip)

> The curious thing about Bernoulli's formula is you don't see
> acceleration explicitly written in it. It does however have pressure
> (force per area) and Newton gave us via his 2nd law -> force = d/dt
> (momentum) which most 1st year students learn as simply F=ma. So with
> a physics viewpoint I see both being there since I know that Bernoulli
> can't violate Newton's laws of motion. So using Bernoulli's
> formulation without explicitly using Newton's laws is okay since they
> are buried in there anyway. Although your sewer pipe example is easy
> to understand in terms of accerated mass (acceration due to turning a
> corner). 

Reminds me of a Feynman problem related to a bent arm sprinkler.
There is a common sprinkler design that rotates due to, as you
say, fluid turning the corner.  Someone asked Feynman about the
case where fluid was going in (instead of out), and still going
around the corner.   The test Feynman did was to put a similar
shape inside a water filled bottle, and presurize the bottle.
(Reminder that he was a theoretical physicist, though most often
not so bad doing experiments.)  Anyway, at some point the bottle
exploded from being pressurized, but it seems that it doesn't
rotate with water going in and around the corner.

> To apply Bernoulli's formula to the bent pipe problem is
> going to take more math to see how the radially dependent velocities
> results in radially dependent pressures thus yielding a net force on
> the pipe.
 
(snip)

-- glen

On Dec 13, 5:31&#4294967295;pm, glen herrmannsfeldt <g...@ugcs.caltech.edu> wrote:

  ...

> Reminds me of a Feynman problem related to a bent arm sprinkler.
> There is a common sprinkler design that rotates due to, as you
> say, fluid turning the corner. &#4294967295;Someone asked Feynman about the
> case where fluid was going in (instead of out), and still going
> around the corner. &#4294967295; The test Feynman did was to put a similar
> shape inside a water filled bottle, and presurize the bottle.
> (Reminder that he was a theoretical physicist, though most often
> not so bad doing experiments.) &#4294967295;Anyway, at some point the bottle
> exploded from being pressurized, but it seems that it doesn't
> rotate with water going in and around the corner.

  ...

The bend in the arm isn't necessary to make the sprinkler spin. The
torque comes from the water's not emerging radially, and the bend
spreads the pattern. The sprinkle'sr not rotating when external
pressure forced the water in isn't related to reaction effects.
Internal water pressure lifts the rotor against the upper bearing.
Thar's the one with low friction. External pressure jams the rotor
against the lower bearing, which isn't designed to allow free motion.
Reaction forces are reversible; friction forces are not.

Jerry

On Dec 13, 7:00&#4294967295;pm, Jerry Avins <j...@ieee.org> wrote:
> On Dec 13, 10:51&#4294967295;am, maury <maury...@core.com> wrote:
>
>
>
> > On Nov 26, 12:08&#4294967295;am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > On Nov 25, 6:32&#4294967295;pm, eric.jacob...@ieee.org (Eric Jacobsen) wrote:
>
> > > > On Wed, 24 Nov 2010 21:08:42 -0800 (PST), Rune Allnor
>
> > > > <all...@tele.ntnu.no> wrote:
> > > > >Hi all.
>
> > > > >This is one of those questions that just popped into my mind
> > > > >last night: Who invented / discovered the airfoil? Like in aviation
> > > > >history.
>
> > > > >I know the Montgolfiers discovered the balloon, the Wright did
> > > > >the first powered flight and so on, but who was the first to
> > > > >describe the airforil as a component for 'heavier-than-air' flight?
>
> > > > >Lilienthal used devices very similar to what we today would call
> > > > >hang gliders a couple of decades before the Wrights got their
> > > > >flyer together. I have seen claims that one of Lilienthal's main
> > > > >contributions to aviation history was that he published a very
> > > > >detailed description of the flight charactersitics of the airfoil
> > > > >glider,
> > > > >a description that turned out to be essential for e.g. the Wrights
> > > > >to be able to build an actualair plane.
>
> > > > >But describing the airfoil charactersitics is one thing - who
> > > > >*invented* the airfoil? Was it ol'e Otto himself? Or somebody else?
>
> > > > >Rune
>
> > > > Birds have had them for a long time. &#4294967295; Some flying reptiles before
> > > > that.
>
> > > > IIRC DaVinci did a bunch of sketches of bird wings and had various
> > > > illustrated ideas about flying machines.
>
> > > > I don't know if it's an "invention" if you just copy or adapt it off a
> > > > bird.
>
> > > Of course. But the question that popped into my head the other
> > > day was who first described the airfoil as a viable method for
> > > human aviation. Leonardo drew / fantasized about the thing, but
> > > did not verify that it actually worked.
>
> > > I suppose I'll settle for Lilienthal.
>
> > > Rune- Hide quoted text -
>
> > > - Show quoted text -
>
> > Rune,
> > When we teach aviation here in the States, we attribute the
> > mathematicall analysis/synthesis of the airfoil to Bournoulli's work
> > with restricted fluid flow. By taking a cross-section (length wise) of
> > Bournoulli's restricted tube, you have an airfoil. The venturi tube,
> > used to generate a vaccum on early aircraft, is also based on this
> > principal.
>
> While the Bernoulli explanation of an airfoil is correct locally,
> accepting it as a complete explanation obscures the more general truth
> that an airfoil provides lift by imparting downward momentum to the
> fluid it passes through. The shape of a wing is material only for its
> efficiency -- read "lift-to-drag ratio." Glenn Curtis correctly
> observed that given an engine of sufficient power, he could fly a
> kitchen table. Naive application of the Bernoulli Principle to an
> airfoil doesn't make obvious that the pressure over the top of a wing
> being less than the pressure under it implies that air leaving the
> wing is accelerated downward. To put it differently, airfoils provide
> lift for the same reason that non-metallic sewer lines need anchor
> blocks wherever they turn corners.
>
> Jerry

Run that bit about the non-metallic sewer lines past me again, would
you? ... :-)

On Dec 14, 5:16&#4294967295;am, Chris Bore <chris.b...@gmail.com> wrote:

  ...

> Run that bit about the non-metallic sewer lines past me again, would
> you? ... :-)

Flow through an elbow in a pipe puts tension in both the entering and
leaving arms. Most metallic pipe (and pipe intended to operate under
pressure) can withstand this tension, but sewer pipe isn't
pressurized, and concrete has relatively little tensile strength.
Moreover, the joints are simply gasketed or caulked. Without heavy
concrete structures at the turns to buttress the reaction forces, the
pipes might break or come apart at high flows.

Jerry

On Dec 14, 8:54&#4294967295;am, Jerry Avins <j...@ieee.org> wrote:
> On Dec 14, 5:16&#4294967295;am, Chris Bore <chris.b...@gmail.com> wrote:
>
> &#4294967295; ...
>
> > Run that bit about the non-metallic sewer lines past me again, would
> > you? ... :-)
>
> Flow through an elbow in a pipe puts tension in both the entering and
> leaving arms. Most metallic pipe (and pipe intended to operate under
> pressure) can withstand this tension, but sewer pipe isn't
> pressurized, and concrete has relatively little tensile strength.
> Moreover, the joints are simply gasketed or caulked. Without heavy
> concrete structures at the turns to buttress the reaction forces, the
> pipes might break or come apart at high flows.

I can explain that more didactically. Imagine a tall box, closed on
the bottom, with a hole in the bottom of each vertical side. (The area
of the hole is much larger than what is left laterally.) A pipe fitted
into one hole supplies water. A piston in the facing hole prevents
flow in that direction, so the water comes out the two sides (and may
climb the box if the pipe is full). It is easy to understand the force
on the piston. It is the rate at which the momentum of the incoming
water is diverted. (There is no net sideways momentum because of the
counterflowing output, hence no net sideways force.) Now add a second
piston to one of those side holes. All the water flows out of the hole
opposite it, so it exerts the same force as the first piston. In a
real pipe, the "pistons" are part of the elbow fitting which is in
turn restrained by being fastened to the pipe. When the calculated
load approaches the tensile strength of the pipe (or joint), it
becomes necessary to relieve the forces by the buttressing the
"pistons" from the outside. Ancient structures reveal that Roman
aqueduct builders were aware of this effect, even though it is
doubtful that they understood it theoretically.

Jerry

On Dec 14, 1:54&#4294967295;pm, Jerry Avins <j...@ieee.org> wrote:
> On Dec 14, 5:16&#4294967295;am, Chris Bore <chris.b...@gmail.com> wrote:
>
> &#4294967295; ...
>
> > Run that bit about the non-metallic sewer lines past me again, would
> > you? ... :-)
>
> Flow through an elbow in a pipe puts tension in both the entering and
> leaving arms. Most metallic pipe (and pipe intended to operate under
> pressure) can withstand this tension, but sewer pipe isn't
> pressurized, and concrete has relatively little tensile strength.
> Moreover, the joints are simply gasketed or caulked. Without heavy
> concrete structures at the turns to buttress the reaction forces, the
> pipes might break or come apart at high flows.
>
> Jerry

Cool. Is this related to the shape of manhole covers?

On Dec 15, 4:03&#4294967295;am, Chris Bore <chris.b...@gmail.com> wrote:
> On Dec 14, 1:54&#4294967295;pm, Jerry Avins <j...@ieee.org> wrote:

  ...

> Cool. Is this related to the shape of manhole covers?

[grin]

Jerry

On Dec 14, 12:25&#4294967295;pm, Jerry Avins <j...@ieee.org> wrote:
> On Dec 14, 8:54&#4294967295;am, Jerry Avins <j...@ieee.org> wrote:
>
> > On Dec 14, 5:16&#4294967295;am, Chris Bore <chris.b...@gmail.com> wrote:
>
> > &#4294967295; ...
>
> > > Run that bit about the non-metallic sewer lines past me again, would
> > > you? ... :-)
>
> > Flow through an elbow in a pipe puts tension in both the entering and
> > leaving arms. Most metallic pipe (and pipe intended to operate under
> > pressure) can withstand this tension, but sewer pipe isn't
> > pressurized, and concrete has relatively little tensile strength.
> > Moreover, the joints are simply gasketed or caulked. Without heavy
> > concrete structures at the turns to buttress the reaction forces, the
> > pipes might break or come apart at high flows.
>
> I can explain that more didactically. Imagine a tall box, closed on
> the bottom, with a hole in the bottom of each vertical side. (The area
> of the hole is much larger than what is left laterally.) A pipe fitted
> into one hole supplies water. A piston in the facing hole prevents
> flow in that direction, so the water comes out the two sides (and may
> climb the box if the pipe is full). It is easy to understand the force
> on the piston. It is the rate at which the momentum of the incoming
> water is diverted. (There is no net sideways momentum because of the
> counterflowing output, hence no net sideways force.) Now add a second
> piston to one of those side holes. All the water flows out of the hole
> opposite it, so it exerts the same force as the first piston. In a
> real pipe, the "pistons" are part of the elbow fitting which is in
> turn restrained by being fastened to the pipe. When the calculated
> load approaches the tensile strength of the pipe (or joint), it
> becomes necessary to relieve the forces by the buttressing the
> "pistons" from the outside. Ancient structures reveal that Roman
> aqueduct builders were aware of this effect, even though it is
> doubtful that they understood it theoretically.
>
> Jerry

The Romans figured out quite a few neat engineering tricks. I'm sure
it was mostly through the school of hard knocks though. Plus I'm sure
the guys who failed likely ended up being part of the show at the
colosseum.

When they built domes, they placed heavy stone rings around their
bases which effectively kept the stone domes all in compression. Since
as you know stone is weak in terms of tension. And they were great
fans of arches which work the same way.

And we see a lot of flying buttresses in medieval structures. The
historical record shows a few large failures while the learning
process was underway.

Clay

On Dec 15, 11:17&#4294967295;am, Clay <c...@claysturner.com> wrote:

  ...

> And we see a lot of flying buttresses in medieval structures. The
> historical record shows a few large failures while the learning
> process was underway.

One of the neatest features of Medieval churchs is the spires that
surmount the in-wall buttresses. Their purpose isn't decorative. A
masonry pier whose load falls outside the central ninth -- central
third each way -- will separate at the joints. When the intended load
can't be properly placed, adding weight in the right place relocates
the force.

Jerry

On Thursday, November 25, 2010 at 4:08:42 PM UTC+11, Rune Allnor wrote:
> Hi all.
>=20
> This is one of those questions that just popped into my mind
> last night: Who invented / discovered the airfoil? Like in aviation
> history.
>=20
> I know the Montgolfiers discovered the balloon, the Wright did
> the first powered flight and so on, but who was the first to
> describe the airforil as a component for 'heavier-than-air' flight?
>=20
> Lilienthal used devices very similar to what we today would call
> hang gliders a couple of decades before the Wrights got their
> flyer together. I have seen claims that one of Lilienthal's main
> contributions to aviation history was that he published a very
> detailed description of the flight charactersitics of the airfoil
> glider,
> a description that turned out to be essential for e.g. the Wrights
> to be able to build an actualair plane.
>=20
> But describing the airfoil charactersitics is one thing - who
> *invented* the airfoil? Was it ol'e Otto himself? Or somebody else?
>=20
> Rune

Cayley and others realised that cambered surfaces produced lift, which was =
experimentally proven in a steam wind tunnel by Horatio Phillips in the 188=
0's.

Lawrence Hargrave invented the aerofoil (particularly the thick leading edg=
e) via a series of experiments in the 1880's and 1890's.

Hargrave also invented the box-kite (bi-plane wing), powered flight (via co=
mpressed air engine) and rotary engine, however with insufficient power to =
weight for long term (sustained flight). see - https://en.wikipedia.org/wik=
i/Lawrence_Hargrave

Hargrave's contributions to aviation and priority were acknowledge in Franc=
e but not by the Wrights who had access to Hargrave's work which he distrib=
uted freely for the benefit of mankind.=20

The Wright's contributions were a light-weight engine enabling sustained fl=
ight and warped wings for roll-control which proved impractical. Practical =
control surfaces (elevator and rudder) were already invented by Lilienthal =
and others and roll-control only required independent elevator motion for e=
ach wing.