Backwash Causes Lift?
Le Chaud Lapin
Student pilot here, self-teaching using the Jeppensen Private Pilot
Kit after taking ground school. :D
I read in the book that combustion "creates" energy, which is
technically not true, but I decided to ignore it since the pictures
are sooo pretty.
Now, in Chapter 3, section about airfoils, it actually says:
"In addition to the lowered pressure, a downward-backward flow of air
also is generated from the top surface of the wing. The reaction to
this downwash results in an upward force on the wing which demnstrates
Newtons' third law of motion. This action/reaction principle also is
apparent as the airstream strikes the lwoer surface of the wing when
inclinded at a small angle (the angle of attack) to its direction of
motion. The air is forced downward and therefore causes an upward
reaction resulting in positive lift."
IMHO, the latter part of this paragraph is correct, but the former
part is wrong.
Obviously, any air above the wing can only result in a force downward
on top of the wing. The only force causing the plane to want to move
upward comes from beneath the wing. The effect of any air above the
wing is to cause rarefication above the wing, resulting in lower
pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That
"reaction" coming from downward movement of air seems just plain silly
to me.
I am also inclined to take issue with the explanations of Bernouilli's
Principle which I see often in the literature, but that's a different
subject. [Note, I don't doubt Bernouilli's Principle, I just think
there is more to it than the way it is being described in context of
flying.]
-Le Chaud Lapin-
Dan Luke
"Le Chaud Lapin" wrote:
> Obviously, any air above the wing can only result in a force downward
> on top of the wing. The only force causing the plane to want to move
> upward comes from beneath the wing. The effect of any air above the
> wing is to cause rarefication above the wing, resulting in lower
> pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That
> "reaction" coming from downward movement of air seems just plain silly
> to me.
Then why does the wing stall and cease lifting when flow separates from the
upper surface?
--
Dan
T-182T at BFM
Dudley Henriques
Please don't take this the wrong way but I'm sure you would have passed
me up as a potential flight instructor.
:-))))
--
Dudley Henriques
Le Chaud Lapin
Because the situation of rarefication no longer exists during a stall,
or is significantly abated.
When plane is on the ramp, pressure above and below the wing are
equivalent.
When plane is flying certain critical speed, there is, IMO, pinching
that occurs at the leading edge of wing. This area of high pressure
results in a tendency for air to flow away from that pressure point in
all directions.
1. Flowing forward is not an option - that would make pressure
situation worse.
2. Flowing backward, toward the empennage, is not an option. The
leading edge of wing is there.
3. Flowing upward is possible, since above-the-pressure-point pressure
is less than that induced at pressure point.
4. Flowing backward is possible, since below-the-pressure-point
pressure is less than that induced at pressure point.
But here is the catch. If you take an umbrella, open it, find a friend
with extremely long arms, and ask him to yank the umbrella toward his
torso in one, quick, abrupt motion, he will feel a force immediately.
The umbrella might even invert if the impulse is strong enough.
[Sidenote: In the 1970's, I convinced small children that they could
fly if they jumped of 7ft brick wall with umbrella. Very amusing to
see their faces when they hit ground going just about as fast as they
would have without umbrella.] The force that is felt is due to
pressure building under the curved part of umbrella. But even if the
pressure did not build from compression, a force would still be felt,
becaue the force that was equalizing the pressure under the curved
part will have been removed.
And now the $1,000,000 point:
The air on the "outside" of the umbrella does *NOT* instantaneously
fill the void that is created by yanking the umbrella. A finite
amount of time is required for such air to rush in. If the unbrella
is pulled at even a low speed, the net effect can be felt. Pull it
fast enough, and it will invert or snap.
This is, IMO, a more illustrative way of looking at aerodynamics above
the wing than the canned Bernouilli speech.
1. The pinchage creates pressure.
2. A void is created over the wing, provided that plane is moving fast
enough that air high above win cannot rush in.
3. Air at back of wing participates in futile effort to fill the void.
But the most important thing is the pinchage. That pinching results
in high net speed of air molecules backward. Any air above wing that
tries to rush in and fill void is bombarded backward before it can
"touch" the upper surface of wing. I speculated that, if this point a
view were correct, gliders should have short chords with very long
spans, which, of course, is true.
About stalling:
When the angle of attack is too great, the pinchage is still present,
and depending on the shape of the leading edge, the backward flow is
still pressent, but not at the right angle relative to wing, and
certainly not flowing backward enough to stop the onrush of air coming
from above at back of wing. In the air comes, rushing in, and
pressure builds on top of wing.
But there is an ace in hole. Some books say that a plane will stall
if AOA is above critical angle. I do not think this is quite true. It
would seem that, worst-case-scenario, the dynamics above the wing
become royal mess at huge AOA. However, that mess will be less than
static pressure, and there will still be compression beneath the wing.
So if thrust is great enough, airplane should be able to do whatever
it wants.
-Le Chaud Lapin-
Bertie the Bunyip
news:1191379054.6...@y42g2000hsy.googlegroups.com:
Nope, it's not the same at all.
>
> 1. The pinchage creates pressure.
> 2. A void is created over the wing, provided that plane is moving fast
> enough that air high above win cannot rush in.
> 3. Air at back of wing participates in futile effort to fill the void.
>
> But the most important thing is the pinchage. That pinching results
> in high net speed of air molecules backward. Any air above wing that
> tries to rush in and fill void is bombarded backward before it can
> "touch" the upper surface of wing. I speculated that, if this point a
> view were correct, gliders should have short chords with very long
> spans, which, of course, is true.
>
> About stalling:
>
> When the angle of attack is too great, the pinchage is still present,
> and depending on the shape of the leading edge, the backward flow is
> still pressent, but not at the right angle relative to wing, and
> certainly not flowing backward enough to stop the onrush of air coming
> from above at back of wing. In the air comes, rushing in, and
> pressure builds on top of wing.
>
> But there is an ace in hole. Some books say that a plane will stall
> if AOA is above critical angle. I do not think this is quite true.
It's precisely true since th ecritical angle is defined by the stall.
Bertie
Bertie the Bunyip
qqoYJ_anZ2d...@rcn.net:
I nominate Anthony!
Bertie
george
> "In addition to the lowered pressure, a downward-backward flow of air
> also is generated from the top surface of the wing. The reaction to
> this downwash results in an upward force on the wing which demnstrates
> Newtons' third law of motion. This action/reaction principle also is
> apparent as the airstream strikes the lwoer surface of the wing when
> inclinded at a small angle (the angle of attack) to its direction of
> motion. The air is forced downward and therefore causes an upward
> reaction resulting in positive lift."
I blame the lift pixies myself
Le Chaud Lapin
> > But there is an ace in hole. Some books say that a plane will stall
> > if AOA is above critical angle. I do not think this is quite true.
>
> It's precisely true since th ecritical angle is defined by the stall.
What is the definition of a stall anyway?
I'm saying that, if you take a plane with certain critical angle,
throw away engine, put on an engine that can generate 10x the thrust,
the plane should still fly, even if you exceed critical angle.
These books imply that the critical angle is angle at with bad things
happen above the wing, and because of that, the plane will fall. I'm
saying that, you can have all the bad things happen above the wing and
still be able to keep the plane aloft due to compression that occurs
beneath the wing.
Of course, I have only been doing this officially 7 weeks, so I might
be wrong. ;)
-Le Chaud Lapin-
Le Chaud Lapin
LOL.
This flying business is a bit too fascinating. I'm having trouble
concentrating on my day job. In no other hobby has the opportunity
arisen to apply essentially everything technical I have ever learned.
Physics, chemistry, mathematics, electronics, computation...it's all
there.
-Le Chaud Lapin-
Le Chaud Lapin
> > Please don't take this the wrong way but I'm sure you would have
> passed
> > me up as a potential flight instructor.
> >:-))))
>
> I nominate Anthony!
Heh.
I knew going into ground school that the focus would be flying, not
aero/astro, so I was not disappointed with the course. By rushing us,
the instructor gave us a broad overview of what we should know. This
has been hugely beneficial for my learning.
Makes going through it again, slowly, with physics book nearby very
pleasurable.
-Le Chaud Lapin-
Mxsmanic
> Obviously, any air above the wing can only result in a force downward
> on top of the wing. The only force causing the plane to want to move
> upward comes from beneath the wing. The effect of any air above the
> wing is to cause rarefication above the wing, resulting in lower
> pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That
> "reaction" coming from downward movement of air seems just plain silly
> to me.
Lift is a reaction to the force required to push air downward behind the wing
(downwash). How the air gets pushed downward is not very important. The wing
twists air into a downwash as it passes through it, leaving a swath of air
moving gently downward behind it. The force required to do this engenders an
equal and opposite force that is lift. Lift accelerates the wing upward,
counteracting gravity. The wing accelerates a large mass of air downward.
> I am also inclined to take issue with the explanations of Bernouilli's
> Principle which I see often in the literature, but that's a different
> subject. [Note, I don't doubt Bernouilli's Principle, I just think
> there is more to it than the way it is being described in context of
> flying.]
There are a lot of different ways to examine and describe the aerodynamics of
lift. It boils down to accelerating one mass (a mass of air) downward, which
engenders another acceleration of another mass (the wing, and anything to
which it is attached) upward. Any flat surface moving relative to the air
with a positive angle of attack below the stall angle will generate lift.
Mxsmanic
> Then why does the wing stall and cease lifting when flow separates from the
> upper surface?
Because it is no longer accelerating air efficiently downward.
Mxsmanic
> However, that mess will be less than
> static pressure, and there will still be compression beneath the wing.
> So if thrust is great enough, airplane should be able to do whatever
> it wants.
Pressure beneath the wing is not what lifts the aircraft. It's the twisting
acceleration of air above the wing downward that results in lift.
Mxsmanic
> What is the definition of a stall anyway?
An abrupt loss of lift.
> I'm saying that, if you take a plane with certain critical angle,
> throw away engine, put on an engine that can generate 10x the thrust,
> the plane should still fly, even if you exceed critical angle.
No, the thrust of the engine doesn't matter, unless the engine itself is
supporting the weight of the aircraft with thrust (possible in a few fighter
aircraft). A wing above the critical angle will stall at any speed.
> These books imply that the critical angle is angle at with bad things
> happen above the wing, and because of that, the plane will fall.
Yes, true.
> I'm saying that, you can have all the bad things happen above the wing and
> still be able to keep the plane aloft due to compression that occurs
> beneath the wing.
The wing is not supported by compression. It is supported by the displacement
of a mass (of air) downward. If this displacement ceases to take place, lift
disappears. A stalled wing does not divert air downward, so it doesn't
generate lift.
Bertie the Bunyip
news:l886g3hj3eulpinen...@4ax.com:
This should be entertaining.
Bertie
Bertie the Bunyip
news:4686g39uiopo7ria0...@4ax.com:
No, it isn't, fjukkktard.
Unless the rules of physics have changed.
Bertie
Bertie the Bunyip
Tina
Bertie the Bunyip
@o80g2000hse.googlegroups.com:
> It is clearly time to revisit airplanes taking off on tredmills.
>
>
>
Do tell. Must have been before my time here.
Bertie
Matt Whiting
It doesn't cease lifting. It doesn't lift as hard, and not hard enough
to support the airplane, but the force doesn't magically go away.
Matt
gpaleo
Ο "Le Chaud Lapin" <jaibu...@gmail.com> έγραψε στο μήνυμα
news:1191376626.6...@22g2000hsm.googlegroups.com...
>
> Hi,
>
> Student pilot here, self-teaching using the Jeppensen Private Pilot
> Kit after taking ground school. :D
>> there is more to it than the way it is being described in context of
> flying.]
>
> -Le Chaud Lapin-
Hot Bunny ??????????????
ROTFLMAO
BDS
> Le Chaud Lapin writes:
>
> > What is the definition of a stall anyway?
>
> An abrupt loss of lift.
Son, for someone who continually chastises the pilots here for their lack of
knowledge, you sure can come up with some doozies yourself!
BDS
Dudley Henriques
Nah.....Anthony has offered many times to teach me about aerodynamics
and flying but so far at least I've cleverly managed to avoid that
enlightening experience.
:-))
--
Dudley Henriques
Tina
waiting for a unified field theory, or maybe a proposed standard of
care for depression.
I had a thought for what would be the longest thread ever in this
newsgroup -- "The collected corrections of Mx statements". Bertie
could be its editor, he has a deft and gentle way of pointing out
errors.
Tina
You would do well to think in terms of differential pressure. If one
can by some means cause the pressure on the upper surface of the wing
to be 1 psi less than the pressure on the lower surface, there would
be an upward force on the wing of the order of 144 pounds per square
foot (my physics training, a million years ago, was in english units).
You might also want to think carefully about airfoil shapes, since
wings can provide lift when flying inverted. Any theory that does not
support inverted flight is obviously flawed.
But the neat thing to do is to hold your hand out of a moving car's
window, and feel the impact pressure on its surfaces as you tilt it in
the airstream. It's not that the hand is being "sucked" up, you don't
feel suction on the top surface, you feel push on the bottom one. Any
theory you develop had better be consistant with those observations.
Someone with more time than I have might like to start with the fact
that air weighs about .08 pounds per square foot near sea level, and
crack some numbers to show how that deflecting that mass can result in
lift even if the lifting surface has some funny shapes.
Le Chaud Lapin
> You might also want to think carefully about airfoil shapes, since
> wings can provide lift when flying inverted. Any theory that does not
> support inverted flight is obviously flawed.
Actually I did because every book I read about flying skimped on the
subject. I'm going to hop over to MIT's OpenCourseWare later this
week and download their most basic course on aero/astro. Benoulli's
principle is toss around as if it were facecloth, but I'm getting the
feeling that no one is really doing the physics.
> But the neat thing to do is to hold your hand out of a moving car's
> window, and feel the impact pressure on its surfaces as you tilt it in
> the airstream. It's not that the hand is being "sucked" up, you don't
> feel suction on the top surface, you feel push on the bottom one. Any
> theory you develop had better be consistant with those observations.
> Someone with more time than I have might like to start with the fact
> that air weighs about .08 pounds per square foot near sea level, and
> crack some numbers to show how that deflecting that mass can result in
> lift even if the lifting surface has some funny shapes.- Hide quoted text -
Yes it is. In fact, I was having this discussion with someone who
claimed that it *was* Benoulli's principle only. I made the following
diagram to try to illustrate my point. View in fixed width
| inverted |
| table |
|--------------------|
|--------------------|
| upright |
| table |
The Bernoulli people often describe air flowing above the a table
being faster than air below a table, and therefore, pressure is
reduced. Hmmm... what happens if the horizontal velocities above and
below a table are both essentially 0?
If you place an inverted table on top of an upright table so that the
table tops are mated, then have a machine, with a tremendous amount of
force, on the order of 14.4lbs/in^2 of force, yank the inverted table
upward, in one quick jerk, I contend that the lower table will be
strongly inclined to follow by jumping updward, obviously due to
pressure beneath it. So any type of rarefication on one side of a
doubly-pressurized surface that is free to move in direction that is
perpendicular to the surface, will, indeed, move, if pressure is
reduced.
And this is why, I am pretty sure, that if I were to search the web,
one would find people who are fanatical about the leading edges of
wings, in the most minute detail, because it is not simply the length
of the top of the wing that matters, but the amount of pinching, and
the distribution of air as it flows backward from the pressure point.
IMO, that pinching results in displacement of the air above to make it
effective go backwares, causing rarefication.
-Le Chaud Lapin-
Dudley Henriques
I love Bertie's personal rendition of Occam's Razor to Anthony's long
extended posts where he "explains" everything in intimate and minute detail.
"Nope"!
--
Dudley Henriques
Dan_Thom...@yahoo.com
> Actually I did because every book I read about flying skimped on the
> subject. I'm going to hop over to MIT's OpenCourseWare later this
> week and download their most basic course on aero/astro. Benoulli's
> principle is toss around as if it were facecloth, but I'm getting the
> feeling that no one is really doing the physics.
Lemme see: People have been building flying machines since the late
1800's, about 125 years now, and none of them have been interested
enough in the phenomenon of lift to do the physics? How old are you,
anyway? Many of the contributors here have been flying much longer
than you have likely been alive and have studied this in detail, and
some of them might even have doctorates in the subject. The subject of
lift has been beaten to death on this forum and if you Googled it
you'd find some good information.
Both Newton and Bernoulli are correct. Even inside a pipe the
static pressure drops as velocity increases. That's why your bottom
table jumps as you yank off the top one: you accelerated an airflow.
And in generating lift there's a displacement of air. Can't escape
that at all.
The stagnation point on a leading edge isn't right at the front.
It's slightly below the wing, and as AOA increases it moves back
underneath quite a bit. It's not all intuitive, you see, and that
intuitive understanding of some of this stuff is where people get all
messed up and think they have the answers that have escaped all the
other experts all these years. We run into this attitude rather
frequently in the flight training industry. It tends to make the
student unteachable.
Dan
Bertie the Bunyip
Be a bit like letting a jackhammer operator do your teeth, that.
Bertie
Bertie the Bunyip
@g4g2000hsf.googlegroups.com:
He's an idiot, what else does one need to know?
Bertie
Bertie the Bunyip
news:1191420953.4...@w3g2000hsg.googlegroups.com:
> On Oct 3, 8:39 am, Tina <tbaker27...@gmail.com> wrote:
>> You might also want to think carefully about airfoil shapes, since
>> wings can provide lift when flying inverted. Any theory that does
>> not support inverted flight is obviously flawed.
>
> Actually I did because every book I read about flying skimped on the
> subject. I'm going to hop over to MIT's OpenCourseWare later this
> week and download their most basic course on aero/astro. Benoulli's
> principle is toss around as if it were facecloth, but I'm getting the
> feeling that no one is really doing the physics.
Well, NASA have and they wholeheartedly support Bernoulli , as do an
Airbus engineeer and a Boeing Engineer of my acquantence. NASA used to
have a whole web page debunking the Bernoulli deniers, but it sems to be
gone now.
It's pretty simple in how it relates to how the airplane flies from one
standpoint and complex from another, but at the end of the day it's how
your knowledge makes the airplane perfomr that counts, and the only
thing tha's going to teach you that is flying an airplane guided by a
good instructor.
If you try to understand it at a molecular level, you've got a problem,
as nobody really undertands lift completely (Here's anthony's chance to
go all creationist on us now)
That all sounds fairly sound, but it's too esoteric to relate to
handling an airplane well.
Don't forget, handling, and it's handling that is the aim of the
knowledge you seek, is primarily a right hand brain operation. If you
try to fly with too much of the left included, you are going to fly like
a chicken on crack.
Bertie
>
>
>
Le Chaud Lapin
> Both Newton and Bernoulli are correct. Even inside a pipe the
> static pressure drops as velocity increases. That's why your bottom
> table jumps as you yank off the top one: you accelerated an airflow.
> And in generating lift there's a displacement of air. Can't escape
> that at all.
It is the removal of air from above the table that causes the lift.
If a person sucks on a straw, thus removing air from the inside of the
straw, the fluid rises into the straw from the container do to the air/
fluid system outside the straw. This is the same phenomenon that is
occurring in my table scenario. In fact, I could enclose the entire
table scenario inside a tube, and cause the bottom table to rise up
off the ground. This has nothing to do with the velocity or
acceleration of air.
> The stagnation point on a leading edge isn't right at the front.
> It's slightly below the wing, and as AOA increases it moves back
> underneath quite a bit. It's not all intuitive, you see, and that
> intuitive understanding of some of this stuff is where people get all
> messed up and think they have the answers that have escaped all the
> other experts all these years. We run into this attitude rather
> frequently in the flight training industry. It tends to make the
> student unteachable.
I do rely on intuition to figure things out, but most importantly, I'd
rather actually understand, than except shallow explanations.
I never attempted to contradict either Bernoulii or Newton. What I
keep saying is that I have seen too many situations where someone will
rattle of "Bernoulli's Principle" and not really understand it
themselves.
For example, as I mentioned earlier, I am reading Jeppesens Private
Pilot manual, and there are clearly errors in concept the manual
(energy being created by engine, for example), even though Jeppensen
probably has access to as many Ph.D. laureates as they want.
-Le Chaud Lapin-
Bertie the Bunyip
news:13g5u96...@news.supernews.com:
>
> "Le Chaud Lapin" wrote:
>
>> Obviously, any air above the wing can only result in a force downward
>> on top of the wing. The only force causing the plane to want to move
>> upward comes from beneath the wing. The effect of any air above the
>> wing is to cause rarefication above the wing, resulting in lower
>> pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That
>> "reaction" coming from downward movement of air seems just plain
>> silly to me.
>
>
> Then why does the wing stall and cease lifting when flow separates
> from the upper surface?
>
>
Actually, that's not the definition of the stall, seperation occurs just
after the stall with most airfoil/planform combinations and in most
flight situations, ordinarily. Some wings will have seperation at the
stall, but I've never flown one.
The defintion is an abrupt loss of lift when the critical angle is
reached. Seperation usually occurs immidiatly after (*but not always,
for instance, deltas will continue to have smooth flow way below he
point they will actually keep flying) This is not to be confused with
the back siide of the drag curve, BTW.
Having said all hat, there are some reputable design texts that define
stall as the point at which the bubble breaks down and buffet occurs and
as far as I know, this doesn't disturb engineers (of which I am not one,
BTW, so take this all with a large grain of salt) any more than a "po-
tay-to, po-tah-to" argument would.
Bottom line is you're interested in keeping your airplane from going
down and the point at which the wing ceases to do what you would like it
to do is the point at which you're most interested.
Make sense? If it does I must not have explained it well.
Bertie
Kloudy via AviationKB.com
>like a chicken on crack.
>
>Bertie
Funny...I suspect you know what that looks like. ; )
--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums.aspx/aviation/200710/1
Bertie the Bunyip
Yes, well, you obviously need to write a good old fashioned, angry,
frothng at the mouth letter to Jeppeson. I'm sure Elry will be suitably
rattled.
Bertie
Bertie the Bunyip
> Bertie the Bunyip wrote:
>
>>like a chicken on crack.
>>
>>Bertie
>
> Funny...I suspect you know what that looks like. ; )
>
Nah,I just have a good imagination.
Though if oyu send me some crack I do have some chickens I could try it on.
Bertie
ji...@specsol.spam.sux.com
I think the main issue is that it doesn't require a Phd in physics to
fly an airplane and the explanations of lift, stall, drag, etc.
for pilots tend to be highly simplified, and rightfully so.
A full explanation that would satisfy a physisicist would likely
cause exterme eye glaze in the average pilot.
If one want's that level of insight, I would suggest they go read
a good aerodynamics text and not expect to find it in a couple of
paragraphs in a USENET posting.
--
Jim Pennino
Remove .spam.sux to reply.
Le Chaud Lapin
> "Kloudy via AviationKB.com" <u33403@uwe> wrote innews:79253d6018083@uwe:
>
>
> Nah,I just have a good imagination.
> Though if oyu send me some crack I do have some chickens I could try it on.
>
> Bertie
:))))!
-Le Chaud Lapin-
Le Chaud Lapin
>
> > Actually I did because every book I read about flying skimped on the
> > subject. I'm going to hop over to MIT's OpenCourseWare later this
> > week and download their most basic course on aero/astro. Benoulli's
> > principle is toss around as if it were facecloth, but I'm getting the
> > feeling that no one is really doing the physics.
>
> Lemme see: People have been building flying machines since the late
> 1800's, about 125 years now, and none of them have been interested
> enough in the phenomenon of lift to do the physics? How old are you,
> anyway? Many of the contributors here have been flying much longer
> than you have likely been alive and have studied this in detail, and
> some of them might even have doctorates in the subject. The subject of
> lift has been beaten to death on this forum and if you Googled it
> you'd find some good information.
I want to be clear. I did not me to say "no one" is doing the
physics. Obviously there are aero/astro scientists all over the
world. What I mean to say is that there seems to be a lot of *pilots*
who are using Bernoulli's principle somewhat carelessly, IMO. Some of
these people are CFI's. Please don't ask me to name individuals, but
I know with certainty that there are at least 2 living, breathing
CFI's who do not understand where 29.92 Hg comes from, or does not
understand it well enough to make it make sense to a student. The
might have understood it at one point, but they don't now. I know
because I asked them. My feelings about teaching is that if you are
not very certain about something, you do more damage than talking
about it. Of course, this leads to the conundrum of having to explain
to a student why a plane stays in the air without providing erroneous
information. If I were a CFI, I would simply say that the aerodynamics
result in pressure below plane is sufficient to counteract pressure
above planes for force of gravity. If they wanted to know more, I'd
direct them to book on aerodynamics.
Can you fly without understanding many of these things? Certainly.
But personally, I would feel a lot better in a cockpit if I did. The
more I know, the more confident I am, and if something goes wrong, the
added perspective will allow me to quickly eliminate those things
which I am certain is not root of problem. This reminds me of
incident about year ago when I was fixing a neighbor's car, and
another neighbor kindly ask me if we needed to borrow jumper cables,
even though she had heard the engine turn over with no problem many
times. Someone who understands how automobile works would have known
that it is highly unlikely that there was problem with battery with
such robust cranking. [Turned out to be fuel line].
-Le Chaud Lapin-
Mxsmanic
> Lemme see: People have been building flying machines since the late
> 1800's, about 125 years now, and none of them have been interested
> enough in the phenomenon of lift to do the physics?
The physics seems simpler than it is, and the explanation of the physics
depends hugely on one's frame of reference.
However, the practical reality is simple: an airfoil with an angle of attack
greater than zero and less than the critical (stall) angle will produce lift.
This is completely reliable, and it's all a pilot needs to know (although,
oddly enough, many pilots don't know this).
> Many of the contributors here have been flying much longer
> than you have likely been alive and have studied this in detail, and
> some of them might even have doctorates in the subject.
See above.
> We run into this attitude rather
> frequently in the flight training industry. It tends to make the
> student unteachable.
Students only need to know about the angle of attack, if theory is required.
Or you can simply teach them by rote, which is even easier albeit somewhat
less safe.
Le Chaud Lapin
> static pressure drops as velocity increases. That's why your bottom
> table jumps as you yank off the top one: you accelerated an airflow.
> And in generating lift there's a displacement of air. Can't escape
> that at all.
Also, if you don't mind, I would like to understand what you mean
here.
It's not clear to me.
-Le Chaud Lapin-
Mxsmanic
> For example, as I mentioned earlier, I am reading Jeppesens Private
> Pilot manual, and there are clearly errors in concept the manual
> (energy being created by engine, for example), even though Jeppensen
> probably has access to as many Ph.D. laureates as they want.
Describe the errors in a letter and send it to them. Good technical
publishers are always willing to accept corrections.
Bertie the Bunyip
That's not enough either.
you need to know how and why lift varies throughot the flight envelope,
but after th ebook learning, it's mostly intuitive and the intuition
comes from experience.
Bertie
Bertie the Bunyip
news:a7i7g35rgjpjfiu46...@4ax.com:
You have no idea what you are talking about.
You don't fly and you never will, mercifully.
Bertie
Bertie the Bunyip
Couldn't be clearer and it's really all you need to know.
Go out and fly now. If you ask any more questions I'l just hand you over to
Anthony from now on.
Tough love.
Bertie
Le Chaud Lapin
I don't think actually flying an airplane will explain the
aerodynamics of lift any more than driving a car will help with
understanding of rack-and-pinion. Yes, there will be an an intuition
that will develop, but that's going to happen anyway, and that would
have happened even if I were a 16-year-old sitting in pilot's seat.
Doesn't mean that 16-year-old is going to understand aerodynamics.
Let's face it. A large pecentage of people walking this planet think
there is a "suction" force. I was watching the History Channel one
day, and the narrator actually used that term - a "suction" force, and
he did not mean the force that is on the other side of the barrier
where the "suction" force was being applied. I've also seen countless
erroneous explantions on the same channel about electronics which I do
know about. Typically the narrator will say voltage when he meant
current, or energy when he meant power.
I'm more of a mind-over-matter type. I'll get my license and fly
around and develop the intuition that you mention, certainly, but
that's not enough.
-Le Chaud Lapin-
Bertie the Bunyip
> On Oct 3, 12:05 pm, Bertie the Bunyip <S...@rt.1> wrote:
>> Le Chaud Lapin <jaibudu...@gmail.com> wrote
>> innews:1191430563.1...@w3g2000hsg.googlegroups.com:
>>
>> > On Oct 3, 10:34 am, Dan_Thomas_nos...@yahoo.com wrote:
>> >> Both Newton and Bernoulli are correct. Even inside a pipe
>> >> the
>> >> static pressure drops as velocity increases. That's why your
>> >> bottom table jumps as you yank off the top one: you accelerated an
>> >> airflow. And in generating lift there's a displacement of air.
>> >> Can't escape that at all.
>>
>> > Also, if you don't mind, I would like to understand what you mean
>> > here.
>>
>> > It's not clear to me.
>>
>> Couldn't be clearer and it's really all you need to know.
>>
>> Go out and fly now. If you ask any more questions I'l just hand you
>> over to Anthony from now on.
>
> I don't think actually flying an airplane will explain the
> aerodynamics of lift any more than driving a car will help with
> understanding of rack-and-pinion.
Well, then you're a lost cause.
Ask Anthony and be damned, then
Bertie
Dan_Thom...@yahoo.com
See http://www.petester.com/html/bachap02.html or
Google yourself using terms like static, dynamic pressures, kinetic
energy, converging or diverging ducts, net energy, and so on. If we
have gas flow in a pipe, and if we had a static gauge and a dynamic
pressure gauge (airspeed), we would see the static pressure fall as
the airspeed rose. If the no-movement static pressure was 29.92" hg,
the dynamic pressure would be zero. As the speed comes up to, say,
10" hg on the dynamic, the static will fall 10" to 19.92. There is no
free lunch. The static and dynamic always add up to the same figure as
speed increases or decreases, unless there is further energy input as
in a turbine combustion section.
As I said, it's not intuitive. Converging and diverging ducts
do different things than you'd expect, but we know they work because
the turbine engine uses their principles, and wouldn't work without
them.
Dan
Le Chaud Lapin
> On Oct 3, 10:56 am, Le Chaud Lapin <jaibudu...@gmail.com> wrote:
>
> > On Oct 3, 10:34 am, Dan_Thomas_nos...@yahoo.com wrote:
>
> > > Both Newton and Bernoulli are correct. Even inside a pipe the
> > > static pressure drops as velocity increases. That's why your bottom
> > > table jumps as you yank off the top one: you accelerated an airflow.
> > > And in generating lift there's a displacement of air. Can't escape
> > > that at all.
>
> > Also, if you don't mind, I would like to understand what you mean
> > here.
>
> > It's not clear to me.
[explanation of Bernoulli's principle clipped].
I did not mean that I did not understand Bernoulli's principle.
What I am saying is that I do not believe that the bottom table jumps
because of airflow acceleration. In fact, if I were to use tables
with circular faces, and put the entire apparatus in a giant
cylindrical tube, and pull up on the top table, assuming that the very
bottom of the tube were open-ended, the bottom table would follow the
top table upward, no matter how fast any air inside the tube were
moving. I could move the top table one molecular diameter every
10,000,000 years, and after the top table has moved, say, 0.5 meters,
the bottom table will follow. This assumes, of course, that the
appartus is airtight, that no air from outside the tube can squeeze in
between the walls of table and tube to fill the void that was created.
There are 14.7 lbs per square inch of pressure pressing upward against
the underside of the bottom table. The yanking of the top table
creates a vacuum between the two faces of the table. The lack of
pressure on the top of the bottom table leaves nothing to counteract
the pressure pressing upward on the underside of the bottom table.
Then the only thing holding the bottom table on the floor is gravity.
Assuming that the table is a typical table of typical weight and size,
one is guranteed that the impulse net pressure of 14.7lbs / in^2 is
enough to overcome gravity and lift the bottom table off the floor.
Note that this really has nothing to do with Bernoulli's principle or
dynamic pressures.
If it is still not clear, put the assembly in a tube again, anchor the
bottom table with a tie wire so it cannot move upward, and using a
hydraulic jack, pull the top table upward, then stop, wait a minute,
have a Coke (sipping with a straw of course), then take cutters and
snap the wire holding the bottom table to the floor.
At the precise moment that the wire is snapped, there is no movement
of anthing at all. There is no Bernoulli action.
The bottom table will rush up toward the top table, even slamming
against it quite hard if the coefficient of sliding friction between
table-side and tube wall is low enough.
-Le Chaud Lapin-
Just go look it up!
>On Oct 3, 1:57 pm, Le Chaud Lapin <jaibudu...@gmail.com> wrote:
>
>> "In addition to the lowered pressure, a downward-backward flow of air
>> also is generated from the top surface of the wing. The reaction to
>> this downwash results in an upward force on the wing which demnstrates
>> Newtons' third law of motion. This action/reaction principle also is
>> apparent as the airstream strikes the lwoer surface of the wing when
>> inclinded at a small angle (the angle of attack) to its direction of
>> motion. The air is forced downward and therefore causes an upward
>> reaction resulting in positive lift."
>
>
>I blame the lift pixies myself
I thought it was how the airflow goes through the splaps?
Kloudy via AviationKB.com
>Though if oyu send me some crack I do have some chickens I could try it on.
>
>Bertie
Chicken you have, eh?
I want to be clear. I did not me to say "no one" is doing the
physics. Obviously there are chickens all over the
world. What I mean to say is that there seems to be a lot of farm fowl
who are using Bernoulli's principle somewhat carelessly, IMO. Some of
these roasters are CFI's (Chicken Food Items). Please don't ask me to name
individuals (Rhode Island Reds, Faverolles) but I know with certainty that
there are at least 2 living, breathing
guinea hens who do not understand where 29.92 Hg comes from, or does not
understand it well enough to make it make sense to other livestock. They
might have understood it at one point, but they don't now. I know
because I asked them and ate them.
My feelings about teaching is that if you are
not very certain about something, you do more damage than talking
about it. Of course, this leads to the conundrum of having to explain
to chickens why a sparrow stays in the air without providing erroneous
information. If I were a delicious farm fowl, I would simply say that the
marinade's
result in pressure below skin is sufficient to counteract pressure
above breast meat for force of gravity.
If they wanted to know more, I'd direct them to book on preparing delicious
poultry.
I don't think actually roasting a bird will explain the thermodynamic
contraction of proteins any more than braising a cow will help with
understanding of BBQ rack of ribs. Yes, there will be an an intuition
that will develop, but that's going to happen anyway, and that would
have happened even if I were a 16-year-old sitting in a restaurant.
Doesn't mean that 16-year-old is going to understand food science.
Let's face it. A large pecentage of people walking this planet think
there is a "poultry" force. I was watching the History Channel one
day, and the narrator actually used that term - a "poultry" force, and
he did not mean the force that is on the other side of the grill
where the "poultry" force was being applied. I've also seen countless
erroneous explantions on the same channel about bovine slaughter methods,
which I do
know about. Typically the narrator will say captured bolt when he meant
head-whacker, or ZAPPO! when he meant lethal humane execution.
I'm more of a mind-over-muncher type. I'll get my bib on and nibble
around and develop the intuition that you mention, certainly, but
that's not enough.
sorry, this all was seeming a bit tedious to me.
--
Message posted via http://www.aviationkb.com
Morgans
"Le Chaud Lapin" <> wrote in message
> I'm saying that, if you take a plane with certain critical angle,
> throw away engine, put on an engine that can generate 10x the thrust,
> the plane should still fly, even if you exceed critical angle.
>
> These books imply that the critical angle is angle at with bad things
> happen above the wing, and because of that, the plane will fall. I'm
> saying that, you can have all the bad things happen above the wing and
> still be able to keep the plane aloft due to compression that occurs
> beneath the wing.
>
> Of course, I have only been doing this officially 7 weeks, so I might
> be wrong. ;)
You are.
With a stronger engine, the wing would still be stalled. You would be
flying on the thrust of the engine.
Disruption of the flow on the top side of the wing is what defines a stall.
The wing would create only a fraction of the list that it would, unstalled.
--
Jim in NC
Le Chaud Lapin
>
> sorry, this all was seeming a bit tedious to me.
ROFL!!!!
-Le Chaud Lapin-
Bertie the Bunyip
Thus the pile of "thank you for your input" letters.
Froootloop.
Bertie
Bertie the Bunyip
Whoowh!
Zero point energy!
In my own kitchen!
I can tell the electric company to fuck off now.
Bertie
Bertie the Bunyip
Ah, a cluelessness vaguely remiscent of someone else I may have seen
around here.
Bertie
Morgans
"Bertie the Bunyip" <Sn@rt.1> wrote
>
> He's an idiot, what else does one need to know?
And yet so many can not resist posting replies to his posts, either with
corrections or witty zingers.
I'm starting to think that they are the bigger losers.
What we have lost is a good newsgroup. Why can't everyone see that when
they reply, he wins. And wins and wins.....
Folks, I'll say it _again_.
The ONLY way to get rid of a know-nothing, know-it-all, obnoxious troll, is
to IGNORE him. ALL of him. EVERY time, not just when you feel like it.
I thought we were turning a corner a couple days ago, with very few replies
to him being posted. Guess again.
Sigh.
--
Jim in NC
John Godwin
news:1191446106....@k79g2000hse.googlegroups.com:
> Ah, a cluelessness vaguely remiscent of someone else I may have seen
> around here.
>
> Bertie
I wonder if Mx is really Bobo in sheep's clothing.
--
Morgans
>> It is clearly time to revisit airplanes taking off on tredmills.
I have to agree. ANYTHING would be better than hearing the resident idiot
troll's blithering.
It goes something like this.
An airplane is about to takeoff on a runway, that is really a treadmill; a
very expensive treadmill.
The treadmill senses the airplane's speed, and matches the aircraft's speed,
with speed increases of its own.
Can the airplane takeoff? Why or why not?
--
Jim in NC
Mxsmanic
> Also, if you don't mind, I would like to understand what you mean
> here.
You can only push the wing upward if something else is pushed downward. Thus,
the wing generates lift only to the extent that it diverts a substantial mass
(of air) downward. No downwash, no lift.
Bertie the Bunyip
> "Mxsmanic" <mxsma...@gmail.com> wrote
>
> > Le Chaud Lapin writes:
>
>
> > An abrupt loss of lift.
>
> Son, for someone who continually chastises the pilots here for their lack of
> knowledge, you sure can come up with some doozies yourself!
>
Actually, it's correct, but only because he read it off wickepedia or
something.
It's not like he'd actually ever DO a stall.
Bertie
Bertie the Bunyip
> Dan Luke writes:
> > Then why does the wing stall and cease lifting when flow separates from the
> > upper surface?
>
> Because it is no longer accelerating air efficiently downward.
Wrong again, fjukktard.
Bertei
Bertie the Bunyip
Nope.
Wrong again, fjukkwit.
Of course, it doesn't matter sionc eyou will never fly and your
sockpuppet there won't either.
Bertie
Bertie the Bunyip
> Bertie the Bunyip <bertie_the_bun...@hotmail.com> wrote innews:1191446106....@k79g2000hse.googlegroups.com:
>
> > Ah, a cluelessness vaguely remiscent of someone else I may have seen
> > around here.
>
> > Bertie
>
> I wonder if Mx is really Bobo in sheep's clothing.
>
Nah. just as k00ky, different style.
Anthony needs something a little different from Bobo and Bertie will
provide..
BTW, if you feel the urge to harass bobo, you can still find him in
alt.security .alar,s, where he still causes just as much trouble as he
ever did. I pop in and pull his chain every once in a while.
Bertie
Bertie
Le Chaud Lapin
wrote:
> Whoowh!
> Zero point energy!
>
Surely, you must be joking. The exposition I wrote above is nothing
more than high school physics.
Where do you see me implying zero point energy?
I know my physics. Do you? There is no "zero point" energy.
Plain and simple:
If a person sucks on a straw, the reason the fluid rises has *NOTHING*
to do with Bernoull's principle. It has to do with the balance in
force being eliminated. In particular, the air in the straw is
removed, so the 14.4lbs/square in will lift the fluid in the straw.
This should be familiar to you, since you are a pilot. Where do you
think 29.92 Hg comes from? It comes from the height that a column of
mercury will rise in a complete rarefied tube in STP, which just
happens to be 29.92.
Both you and Mxmanic are wrong.
-Le Chaud Lapin-
Kloudy via AviationKB.com
>
>Both you and Mxmanic are wrong.
>
>-Le Chaud Lapin-
ooooo.....wait for it.....here it comes....
Dan_Thom...@yahoo.com
> If a person sucks on a straw, the reason the fluid rises has *NOTHING*
> to do with Bernoull's principle. It has to do with the balance in
> force being eliminated. In particular, the air in the straw is
> removed, so the 14.4lbs/square in will lift the fluid in the straw.
So, if it has nothing to do with Bernoulli, what has it to do
with lift? With tables and straws and the like we're talking static,
not dynamic pressures. The airplane uses dynamic AND static
pressures.
In cruise flight (low AOA), I would expect a reduced pressure
on the bottom of the wing, though not as low as on the top. The
velocity of air across the bottom will drop its pressure, there, too.
Air has mass. Anytime you try to push it out of the way,
there will be some reaction. Newton says so. We know this as drag.
But we also know it as lift reaction. A flat plate flying
through the air at some tiny angle of attack doesn't have much faster
air over the top than the bottom, if any difference at all, yet it
will generate plenty of lift. Try this on, if you want to think
outside the box: The airfoil we know is just that: a foil (device to
deceive) to trick the air into flowing over it without breaking up at
much higher angles of attack than a flat plate would let us. So the
leading edge has to have some radius so the air can get around the
corner from the natural stagnation point under the LE at high AOA, and
that curve must gradually taper off toward the rear or the now-
disturbed air would want to separate and turbulate, and if it did that
it would then slow down dramatically, pressure would rise and lift
would decrease. But, happily, Newton is still at work underneath so
the airplane falls, but not as if the wings fell off. We're still
moving forward and the wing is still shoving air out of the way
downward, so lift is still generated.
Dan
Morgans
<jimp wrote
> I think the main issue is that it doesn't require a Phd in physics to
> fly an airplane and the explanations of lift, stall, drag, etc.
> for pilots tend to be highly simplified, and rightfully so.
>
> A full explanation that would satisfy a physisicist would likely
> cause exterme eye glaze in the average pilot.
>
> If one want's that level of insight, I would suggest they go read
> a good aerodynamics text and not expect to find it in a couple of
> paragraphs in a USENET posting.
Exactly.
To learn to fly, it is important to understand aerodynamics to the point of
knowing what you can do to mess them up, and what you can do to fix things.
Only the most basic understanding of the subject is needed to achieve these
goals.
--
Jim in NC
Morgans
"Morgans" <> wrote
>
> It goes something like this.
>
> An airplane is about to takeoff on a runway, that is really a treadmill; a
> very expensive treadmill.
>
> The treadmill senses the airplane's speed, and matches the aircraft's
> speed, with speed increases of its own.
>
> Can the airplane takeoff? Why or why not?
I forgot one important qualifier of the treadmill's operation.
It goes in the opposite direction of the intended direction of travel for
the airplane.
--
Jim in NC
Le Chaud Lapin
> So, if it has nothing to do with Bernoulli, what has it to do
> with lift?
You can have lift of an object with no Bernoulli. It's simple vector
addition.
> With tables and straws and the like we're talking static,
> not dynamic pressures. The airplane uses dynamic AND static
> pressures.
Right.
> In cruise flight (low AOA), I would expect a reduced pressure
> on the bottom of the wing, though not as low as on the top. The
> velocity of air across the bottom will drop its pressure, there, too.
Right. The AOA matters here. Angle the wing up any significant amount,
and over-pressure will build under the wing.
> Air has mass. Anytime you try to push it out of the way,
> there will be some reaction. Newton says so. We know this as drag.
Hmm...ok, sure. I wouldn't call that drag necessarily. That's like
saying that a hydraulic piston assembly has drag. I more prefer to
think of drag as laminar fricitional forces of the fluid. Pushing out
of way implies that plane doing the pushing is perpendicular to the
direction in which pushing is being done (which is true at leading
edge of wing). But I guess this is acceptable.
> But we also know it as lift reaction. A flat plate flying
> through the air at some tiny angle of attack doesn't have much faster
> air over the top than the bottom, if any difference at all, yet it
> will generate plenty of lift. Try this on, if you want to think
> outside the box:
Thinking outside the box is what lead me to refuse to accept hand-
waving explanations of aerodynamics from CFI's.
> The airfoil we know is just that: a foil (device to
> deceive) to trick the air into flowing over it without breaking up at
> much higher angles of attack than a flat plate would let us. So the
> leading edge has to have some radius so the air can get around the
> corner from the natural stagnation point under the LE at high AOA, and
> that curve must gradually taper off toward the rear or the now-
> disturbed air would want to separate and turbulate, and if it did that
> it would then slow down dramatically, pressure would rise and lift
> would decrease. But, happily, Newton is still at work underneath so
> the airplane falls, but not as if the wings fell off. We're still
> moving forward and the wing is still shoving air out of the way
> downward, so lift is still generated.
Yes this is true, but the explanation in the Jeppensen book is wrong.
it defines downwash:
downwash: - "the downward deflection of the airstream as it passes
over the wing and past the trailing edge"
It goes on to say:
"According to Bernoulli's principle, the increase in speed of air on
top of an airfoil profdues a drop in pressure and this lowered
pressure is a component of lift."
Ok, we really know that the lift results from what's under the wing no
longer being balanced out, but I won't nit-pick this explanation.
Next paragraph it says:
"In addtion to the lowered pressure, a downwar-backward flow of air is
also generated from the top surface of the wing. The reaction to this
downwash results in an upward force on the wing which demnstrates
Newton's third law of motion."
This is plane false. That is *NOT* what Newton said. Newton did not
say you could take any action and willy-nilly find what you think is
the reaction, and say, "Hey, this looks good, let's use this."
Newtons law, in fact, is better stated as reciprocity of force, IMO.
This says that, if you take two objects, one apply force to the other,
the other, by reciprocity, must appy an opposite force against the
first.
Newton's law, conbine with F=ma, also yields the notion of
conservation of momentum.
But getting back to Jeppensen, the downwash, if they mean what's
happening on the top surface of the wing, is *not* contributing to
lift. Note that they say "results in", but don't explain how. This
seems to be typical of books of flight dynamics.
I'd like to point something else out regarding Bernouilli's principle.
I haven't tried, but I suspect that I could build a contraption that
consists of surface where the velocity of air above the surface is
much higher than that below, but the pressure above the surface is
higher.
-Le Chaud Lapin-
Crash Lander
news:ZcWdnUxKYOBHO57a...@rcn.net...
> Tina wrote:
>> Then there's the Mx medical advice column, physics advice -- I'm
>> waiting for a unified field theory, or maybe a proposed standard of
>> care for depression.
>>
>> I had a thought for what would be the longest thread ever in this
>> newsgroup -- "The collected corrections of Mx statements". Bertie
>> could be its editor, he has a deft and gentle way of pointing out
>> errors.
>>
>>
>
> I love Bertie's personal rendition of Occam's Razor to Anthony's long
> extended posts where he "explains" everything in intimate and minute
> detail.
>
> "Nope"!
>
>
> --
> Dudley Henriques
I'd like to see what his thoughts are on String Theory.
LOL.
Crash Lander
--
Straight and Level Down Under.
http://www.straightandleveldownunder.net/
Dudley Henriques
I'm sure he'd most likely say that twine was better :-))
--
Dudley Henriques
Le Chaud Lapin
Tricky question. I will take a stab at it.
You said "sense the airplanes speed". Relative to what?
Assuming no friction between wheels and treadmill, the prop of the
plane will cause the airplane to move in the wind. The speed
"sensing" of the airplane by the treadmill does not really make sense
and less you mean that the treadmill senses relative to the wind.
If the treadmill senses that the plane has a relative wind speed of
Vpw, and starts moving in the opposite direction, and the relative
speed of wind against treadwill were nil before all this started, then
the treadmill will only cause the wheels to turn twice as fast as they
would have if the treadmill had not been moving. In this case, the
speed of the plane relative to the treadmill will simply be twice the
speed of the plane relative to the win, in opposite direction, of
course. The plane will take off.
If you mean to imply that there is some way for the treadmill to sense
the speed of the plane relative to the treadmill, then adjust the
speed of treadmill accordingly, of course, that won't work, as it is a
circuitous proposition.
-Le Chaud Lapin-
BDS
"Bertie the Bunyip" <bertie_t...@hotmail.com>...
> On 3 Oct, 13:27, "BDS" <skyh...@hotmail.com> wrote:
> > "Mxsmanic" <mxsma...@gmail.com> wrote
> >
> > > Le Chaud Lapin writes:
> >
> > > > What is the definition of a stall anyway?
> >
> > > An abrupt loss of lift.
> >
> > Son, for someone who continually chastises the pilots here for their
lack of
> > knowledge, you sure can come up with some doozies yourself!
> >
>
> Actually, it's correct, but only because he read it off wickepedia or
> something.
Here's my take on it - a stall occurs at the angle of attack where the
coefficient of lift stops increasing with angle of attack and begins to
decrease. It continues to decrease beyond this point as angle of attack is
increased further. It is not necessarily an abrupt change - most lift
versus angle of attack curves that I've seen do not have a drastic (abrupt)
drop beyond the peak.
BDS
Bertie the Bunyip
Yes, sorry, you´re right and that´s more accurate. i mistakenly
assumed that you were adfvocating the buffet definition.
Bertie
Bertie the Bunyip
Le Chaud Lapin wrote:
> On Oct 3, 4:14 pm, Bertie the Bunyip <bertie_the_bun...@hotmail.com>
> wrote:
> > Whoowh!
> > Zero point energy!
> >
>
> Surely, you must be joking. The exposition I wrote above is nothing
> more than high school physics.
>
> Where do you see me implying zero point energy?
>
> I know my physics. Do you? There is no "zero point" energy.
Actually, there is. Not theory anymore, proven in a lab..
You´re proving to be quite the plaything.
>
> Plain and simple:
>
> If a person sucks on a straw, the reason the fluid rises has *NOTHING*
> to do with Bernoull's principle. It has to do with the balance in
> force being eliminated. In particular, the air in the straw is
> removed, so the 14.4lbs/square in will lift the fluid in the straw.
>
> This should be familiar to you, since you are a pilot. Where do you
> think 29.92 Hg comes from? It comes from the height that a column of
> mercury will rise in a complete rarefied tube in STP, which just
> happens to be 29.92.
>
> Both you and Mxmanic are wrong.
>
Maybe, but I can fly.
Bertie
Tina
had come from its passage over the upper surface of the airfoil, then
there had been an acceleration provided to that air -- acceleration in
this case being conventionally defined as the second time derivative
of position.
Now, if the air is accelerated downward, and it has mass, it means
there had been a force applied. The local prime mover is of course the
wing, so it must experience an upward force. Maybe you have a
different idea as to on what that equal and opposite force is
operating on -- I'd be interested in hearing about that.
There are a number of basic principles in operation here, be careful
not to paint yourself into too tight a corner unless you are quite
expert.
I am not claiming skill in this area -- physics was a minor a long
time ago -- but I remember some of the basics.
Bertie the Bunyip
It´s the main reason I´m here.
Bertie
Bertie the Bunyip
It´s the main reason I´m here.
Bertie
Bertie the Bunyip
It´s the main reason I´m here.
Bertie
Dudley Henriques
The main thing about all this is that both Bernoulli and Newton are
complete explanations of lift and will stand alone. In fact they are
both explanations of the same thing really as they occur simultainously
as lift is being created.
The big rub about Bernoulli is that for years Ole' Daniel was raped by
text books stating several totally false applications of Bernoulli as
fact. The equal transit theory for example, often stated as an
explanation for Bernoulli is totally incorrect.
The real truth of it is that neither Newton or Bernoulli were dealing
with lift at all in their respective work that explains lift.
My fondest hope is that someday, pilots will collectively get it
together enough to realize that Bernoulli and Newton are not in
competition with each other and never have been.
Personally though.....I like my old friend Mary Shafer's explanation for
lift that blames it on the "lift demons". :-)
DH
--
Dudley Henriques
Dudley Henriques
This is a good explanation.
--
Dudley Henriques
Tina
lift pixies. If you call them demons they may take you high and then
let go.
Newton warned us that for every fairy there is an equal and opposite
demon.
I would be interested in having the OP tell us how to derive
conservation of momentum from F=MA though.
Jim Logajan
> Personally though.....I like my old friend Mary Shafer's explanation for
> lift that blames it on the "lift demons". :-)
No science like lift demons is ever the work of just one person. See for
example the collection titled:
"The Emerging Science of Lift Demons":
at this site:
Le Chaud Lapin
> In fact, if there is a downward component of the air's velocity that
> had come from its passage over the upper surface of the airfoil, then
> there had been an acceleration provided to that air -- acceleration in
> this case being conventionally defined as the second time derivative
> of position.
The acceleration is indeed downward. If God declared that all air
molecules in the universe must remain still for the sake of USENET
explication, and the wing move forward, and you took a snapshot of
that picture, there would be a vacuum created above the wing. It would
be quite large (not laminar). The floor of this vacuum would be the
wing itself. The ceiling would be the underside of an air mass above
the entire wing, ready to move downward to fill the void. Now if God
said, "Let molecules move!", the air mass above would, indeed, push
downward. But they would not be allow to go completely downward.
Molecules accelerated from the leading edge of the wing would fly
backward, colliding with those coming from above, and the net-effect
would be a stream.
> Now, if the air is accelerated downward, and it has mass, it means
> there had been a force applied. The local prime mover is of course the
> wing, so it must experience an upward force. Maybe you have a
> different idea as to on what that equal and opposite force is
> operating on -- I'd be interested in hearing about that.
The force is coming from the air mass above the wing, the air mass
that would be right above the vacuum created if no molecules were
allowed to move. That airmass pushes downward, toward the void. This
has nothing to do with the wing, except that the wing created the
void, and also created high-pressure area at tip of wing causing
acceleration of air backwards.
> There are a number of basic principles in operation here, be careful
> not to paint yourself into too tight a corner unless you are quite
> expert.
> I am not claiming skill in this area -- physics was a minor a long
> time ago -- but I remember some of the basics.
I am not an expert either, but I know enough to know that the
explanations I am reading in books are, at best, misleading. Some of
them are plain wrong. Note: going to start a new thread so we can get
to the bottom of this.
And yes, I am certain. :)
-Le Chaud Lapin-
Dan_Thom...@yahoo.com
> The main thing about all this is that both Bernoulli and Newton are
> complete explanations of lift and will stand alone. In fact they are
> both explanations of the same thing really as they occur simultanously
> as lift is being created.
> The big rub about Bernoulli is that for years Ole' Daniel was raped by
> text books stating several totally false applications of Bernoulli as
> fact. The equal transit theory for example, often stated as an
> explanation for Bernoulli is totally incorrect.
Exactly. The equal-transit theory isn't correct. The air
over the top actually reaches the trailing edge *before* the bottom's
flow. Intuitive thinking would have it arriving later because the
distance is greater.
Our OP should see the diagrams here:
http://www.av8n.com/how/htm/airfoils.html
This one shows the pressure distribution over the typical cambered
airfoil:
http://www.kemi.fi/kk019065/calculators/ClarkY.jpg
Note that there's pressure acting on the bottom. Where would
that come from, if not Newton? And note that Bernoulli runs out of
steam on the top near the trailing edge, and the pressure actually
goes above ambient there. I see this on the wing of my Jodel in
flight. It's a low wing, fabric covered, and the pressures are easily
visible by the way the fabric is pressed down or pulled up between the
ribs. Over about the last third of the chord, the fabric is pushed
below the ribs as the pressure there goes quite positive, while ahead
of that it's pulled up.
Look at that leading edge. Lots of lift over the first bit,
right where we'd expect a lot of drag (positive pressure) instead.
Not at all what you'd expect intuitively, is it? And that's
where the uninformed get into trouble: by using "experience' gained
from other, vastly different things, or from reasoning based on
inadequate information.
After all the years of reading this stuff and seeing wind-
tunnel demos and graphs and all such, I know there's an awful lot of
information out there on the generation of lift. Most of it is
available on the 'net. The strangest thing is the newbie who starts to
argue with his textbooks, very publicly (as on a newsgroup) without
Googling it for himself first. He knows better, he's sure.
Dan
Dudley Henriques
> Mr Dudley sir, those are not lift demons, those are lift fairies or
> lift pixies. If you call them demons they may take you high and then
> let go.
>
> Newton warned us that for every fairy there is an equal and opposite
> demon.
Well.....as they say.....everything is relative; :-)))
I'm sitting here wondering if I could actually survive explaining
fairies and pixies at the bar at next reunion of the Naval Test Pilot
School :-))
With fighter pilots, you have to be REAL careful with the words you
throw out there, especially after a few rounds of "attitude adjustment".
Knew a guy once who got to his first fighter assignment and hadn't had
the honor of having a call sign given to him. To make an impression on
the squadron, on his first day of duty assignment he showed up at the
ready room with a tray full of the best damn muffins any of the guys had
ever tasted. His wife had baked them.
From that day on through his retirement, poor Ed was known as "Muffin".
Ya just have to pity a guy who flies formation with "Viper", "Ironman",
"and "Snake" with a callsign like "Muffin". He did get at least a
partial break. Most of the guys called him "Muff".
DH
--
Dudley Henriques
Tina
been there and done that.This particular writer, if she chooses to
analyse physics problems, tends to use the Newtonion approximations as
first principles. The good news is my profession doesn't demand those
skills often. I would, however, be interested, as I mentioned earlier,
how you derive conservation of mV from Newton's force/acceleration
relationship. I think you made that claim earlier in this thread.
Dudley Henriques
I remember the lift demon stories from years ago. In fact, I believe the
origins go back to WW2 in my memory anyway.
I just liked the Mary put it together. :-)
--
Dudley Henriques
TheSmokingGnu
> The ONLY way to get rid of a know-nothing, know-it-all, obnoxious troll, is
> to IGNORE him. ALL of him. EVERY time, not just when you feel like it.
Hush up and grab some popcorn with me n' Bertie. They're just announcing
the second act! :D
TheSmokingGnu
TheSmokingGnu
> Crash Lander wrote:
>> I'd like to see what his thoughts are on String Theory.
>> LOL.
>
>
What, and discount the obvious implications that Duct Tape has on modern
thinking?
TheSmokingGnu
Morgans
"Bertie the Bunyip" <> wrote
It愀 the main reason I惴 here.
Remind me again. What is the main reason you're here?
Why do you feel the need to answer his posts?
--
Jim in NC
TheSmokingGnu
> You can have lift of an object with no Bernoulli. It's simple vector
> addition.
1. You are talking about nature's abhorrence of a vacuum.
2. Vacuum abhorrence is not lift.
3. Airplanes do not generate lift as a result of vacuum abhorrence.
----------
Conclusion: you are not talking about how aircraft generate lift.
QED.
TheSmokingGnu
Dudley Henriques
Ah, duct tape!! Where would aviation be without it ?
--
Dudley Henriques
Le Chaud Lapin
> After all the years of reading this stuff and seeing wind-
> tunnel demos and graphs and all such, I know there's an awful lot of
> information out there on the generation of lift. Most of it is
> available on the 'net. The strangest thing is the newbie who starts to
> argue with his textbooks, very publicly (as on a newsgroup) without
> Googling it for himself first. He knows better, he's sure.
What's strange is CFI'S (two of them) who did not know how to explain
VOR to an electrial engineer (me), who, after reading the discription
of how it works, could probably make after reading the technical
specs.
What's strange is one of the recognized leaders in flight training
materials using words like "energy" when they mean "power". I might
be a newbie to flying, but I'm not a newbie to physics.
-Le Chaud Lapin-
Le Chaud Lapin
Yes, I am. It's a combination of many things taking place at once.
Vacuum generation by the forward motion of the wing is one of them.
> QED.
-LCL-
Le Chaud Lapin
Hmm...I was afraid you would say that.
A non-hand-waving explanation would too close to the quantum, and
so...it's a bit much to discuss, at least right now. I've posted more
messages in this thread in small period of time than I have ever for
any other topic, in the history of using USENET, or...as one might
say, dN/dt >> 0, where N is number of messages.
-Le Chaud Lapin-
TheSmokingGnu
> Yes, I am. It's a combination of many things taking place at once.
> Vacuum generation by the forward motion of the wing is one of them.
Then why do wings generate lift at negative AOA? Surely the immense
vacuum pressures generated would immediately pull any flying craft
desperately into the Earth the moment the wing crossed that threshold
(say, in a descent).
My goodness, it's a good thing you got on here to tell us all this;
imagine all those airliners going overhead that have been doing it wrong
all this time, actually descending to a destination. They ought very
well to know that they could never do such a thing because the vacuum
pressures won't allow it!
TheSmokingGnu
Dan_Thom...@yahoo.com
> > Yes, I am. It's a combination of many things taking place at once.
> > Vacuum generation by the forward motion of the wing is one of them.
And the other is the displacement of air downward.
> Then why do wings generate lift at negative AOA? Surely the immense
> vacuum pressures generated would immediately pull any flying craft
> desperately into the Earth the moment the wing crossed that threshold
> (say, in a descent).
Must be careful not to mix attitude up with angle of attack. The
path of the wing's chord line through the air determines AOA. If the
airplane is pointed downward a bit so that the chord line is down 2°
with respect to the horizon, and the descent path of the airplane is
3°, the AOA is still 1°. An airplane in a steep climb, with its nose
up 20°, does not have a 20° AOA. Its flight path is upward at maybe
10° so that its AOA is only 10°.
Some wings (thick, heavily cambered wings) will generate lift
at up to -4° AOA. The bottom surface of the wing is not the chord
line; that's the line between the leading and trailing edges. The
bottom surface might be angled downward even more in level flight. the
old Champ was a good example: the bottom surface was angled quite
visibly down in level cruise flight, but the chord line was still at a
positive degree or two.
Admittedly there are instructors who don't understand this
stuff well at all and think they know more than they do. I'm still
learning 34 years after starting to fly. I'm old enough now to realize
how little I knew when I thought I knew it all, and to know that I'll
now never have a good handle on it all. Too little time and too many
other responsibilities. But private pilots need to have the basics,
because that's all they have time for and because they'll kill
themselves without them. I'm appalled when I see a pilot do a low-and-
over and yank back hard for the vertical zoom. They have no idea how
close they come to an accelerated stall doing that. Those that manage
to get the stall don't live to avoid the same mistake again, and the
accident report gives a bland, uninteresting and uninformative "pilot
lost control in the climb after the low pass." They don't give the
real reason: the pilot did not understand AOA, never did, and thought
he was safe because the airplane's speed was well above the stall
speed.
Dan
Don Tuite
rotating propeller on a stationary plane says that a propeller merely
sucks an airplane through the sky. But people get into a tizzy if one
mentions Newton's third law wrt a wing. Bernoulli and Newton are not
alternatives; they are both universally and simultaneously the same
thing.
It's like those ladder-against-the- wall problems in Statics. The
forces don't change, but depending on what you're calculating,
sometimes you choose one reference point for your moments, sometimes
another.
Conservation of Energy: it's not just a good idea, it's the Law.
Don