what the heck is lift?

[buttman]

I have always been under the impression that lift is the product of
airspeed and angle of attack, and that lift is the measure of upward
force acting on the plane at a given time. For instance, if you are
doing slow flight, your wings are producing the same amount of life
that you would be if you were cruising, GIVEN that you did not lose or
gain any altitude during the maneuver.

My instructor, which is a very knowledgable guy tried telling me that
lift has nothing to do with airspeed. He said that lift is directly and
soley related to AOA and AOA only. So if you are doing slow flight, you
are producing more life than you are when you're cruising. I overheard
a ATP guy who flies King Air's say that this huge 20 ton military plane
he used to fly would fly approaches at 110 knots, and I heard him say
"It is able to do this because it producing so much lift", which I took
as him defining lift as my instructor does.

So whats the deal here? Are we just thinking of two diffrent concepts?

[Peter Duniho]

"buttman" > wrote in message
ups.com...
> [...]
> So whats the deal here? Are we just thinking of two diffrent concepts?

Your instructor is wrong, and should not be instructing.

In straight and level flight, lift equals weight. Unless your weight
changes, lift does not change, regardless of airspeed. What *can* change is
the lift coefficient, which is determined by the angle of attack. But lift
itself remains static.

Pete

[Peter Wendell]

buttman wrote:
> I have always been under the impression that lift is the product of
> airspeed and angle of attack, and that lift is the measure of upward
> force acting on the plane at a given time. For instance, if you are
> doing slow flight, your wings are producing the same amount of life
> that you would be if you were cruising, GIVEN that you did not lose or
> gain any altitude during the maneuver.
>
> My instructor, which is a very knowledgable guy tried telling me that
> lift has nothing to do with airspeed. He said that lift is directly and
> soley related to AOA and AOA only. So if you are doing slow flight, you
> are producing more life than you are when you're cruising. I overheard
> a ATP guy who flies King Air's say that this huge 20 ton military plane
> he used to fly would fly approaches at 110 knots, and I heard him say
> "It is able to do this because it producing so much lift", which I took
> as him defining lift as my instructor does.
>
> So whats the deal here? Are we just thinking of two diffrent concepts?
>


Good question,

In its most basic form, the amount of lift is determined by how many air
molecules are being deflected by the lifting surfaces, what angle they
are being deflected at, and how fast they are being deflected. We can
mostly ignore the low pressure over the wing stuff, since that is, a.
relatively minor, and b. is also a product of how many molecules are
flowing over the wing and how fast they are flowing.

Obviously, the faster the wing, or rotor, is moving through the air, the
more molecules it will be encountering and accelerating downward in a
given period of time. It is also obvious that the greater the AOA, the
steeper the angle of deflection and the greater the number of molecules
being deflected.

Therefore lift is a product of the airspeed of the lifting surface and
it's angle of attack.

Drag is another issue altogether.

[Roger Long]

Lift in a fully developed spin or steady sinking mush is also exactly
the same as in level flight.

--

Roger Long

[Gone Flyin'. -----==0==-----]

Lift is created by the differing pressures between the upper and lower
surfaces of the wing coupled together with AOA.

Wings generally tend to have a curved suface. The upper surface has a
greater arc or curvature than the lower surface. As the air flows across the
surfaces of the wing, the upper surface air is forced to move faster than
the lower surface air thus causing a pressure difference between the two
surfaces.
The pressure difference coupled together AOA is what causes lift.
On the question of wether the wing is 'pushed' or 'sucked' into the air, as
far as I am aware the jury is still out on that point. Personally I
subscribe to the view that it's probably a bit of both.

As for air density, that is another point. as you will be aware that air
desity decreases with altitude i.e the higher you go the molecules are less
densly packed which is why any wing has a maximum service ceiling, i.e the
point at which it won't generate any more lift. It's also worth noting that
VNE decreases with altitude.

Glider pilot.

-|-
-----===()===-----

[Thomas Borchert]

Gone,

> Lift is created by the differing pressures between the upper and lower
> surfaces of the wing coupled together with AOA.

I'd say it's the other way around: Lift creates the pressure differential.

>
> Wings generally tend to have a curved suface. The upper surface has a
> greater arc or curvature than the lower surface. As the air flows across the
> surfaces of the wing, the upper surface air is forced to move faster than
> the lower surface air thus causing a pressure difference between the two
> surfaces.

Forced by what? And how does your "theory" explain inverted flight? I don't
buy it.

BTW, this has been beaten to death in countless aviation newsgroup
discussions. I once thought like you, because I was taught that way. It's
still a bad theory. I suggest googling. Keywords might be: lift, flight,
Bernoulli, Newton.

--
Thomas Borchert (EDDH)

[Brien K. Meehan]

buttman wrote:
> He said that lift is directly and
> soley related to AOA and AOA only. So if you are doing slow flight, you
> are producing more life than you are when you're cruising.

So, if follows that if I stand my airplane on its tail, sitting on the
ground with an airspeed of zero, it's producing the maximum amount of
lift possible.

[Jimbob]

On Fri, 09 Sep 2005 11:12:36 GMT, "Roger Long" >
wrote:

>Lift in a fully developed spin or steady sinking mush is also exactly
>the same as in level flight.


Hmm. If lift was equal to weight in level flight the forces are
equal, thus no change in height.

How do you reconcile this with a mush or spin? Height is changing,
thus left is less than weight.



Jim

http://www.unconventional-wisdom.org

[buttman]

Gone Flyin'. -----==0==----- wrote:
> It's also worth noting that
> VNE decreases with altitude.


Actually, it's not. the true airspeed at which VNE occurs is greater as
altitude increases, but the calibrated aurspeed (VNE is defined as a
calibrated airspeed) remains the same regardless of altitude.

[buttman]

Thats what I told him. This guy is an amazing instructor. He's an MEI
and a CFII with a ton of CFI and CFII singoffs. I was just wondering if
we were thinking of two different concepts. My definition of lift being
different than his...

[Gone Flyin'. -----==0==-----]

don't take may word for ask NASA...

http://www.grc.nasa.gov/WWW/K-12/airplane/factors.html

[Brian]

Generally speaking lift = AOA * Airspeed.

Except when accerlating or decelerating up or down (i.e Beginning or
ending a climb or descent) the lift = weight of the airplane. Check out
the 1st few pages of any physic book to verify this. Another way of
thinking about it is that the tension on an elevator (Building elevator
not an airplane elevator) cable always equals the weight of the
elevator and occupants even if the elevator is moving. It changes only
as the elevator accelerates or decelerates.

so since the lift seldom changes the only other 2 variables are AOA
and Airspeed. If you slow down you must increase the AOA to maintain
lift. If you decrease the AOA you must increase airspeed to maintain
lift.

The Rate of Climb indicator directly show excess or Power in a climb or
insufficent power (to maintain alt) in a descent.
Movement of the Rate of climb needle (decreasing or increasing) shows
changes in the amount of lift generated.
A G Meter will directly show the amount of lift being Generated. i.e.
2G = 2x gross weight of the airplane is being generated.

Hope that helps a little

Brian
CFIIG/ASEL

[Jimbob]

On Fri, 09 Sep 2005 14:29:18 +0200, Thomas Borchert
> wrote:

>> Wings generally tend to have a curved suface. The upper surface has a
>> greater arc or curvature than the lower surface. As the air flows across the
>> surfaces of the wing, the upper surface air is forced to move faster than
>> the lower surface air thus causing a pressure difference between the two
>> surfaces.
>
>Forced by what? And how does your "theory" explain inverted flight? I don't
>buy it.
>
>BTW, this has been beaten to death in countless aviation newsgroup
>discussions. I once thought like you, because I was taught that way. It's
>still a bad theory. I suggest googling. Keywords might be: lift, flight,
>Bernoulli, Newton.


He is describing the traditional airfoil theory which is correct. It
is the most efficient method as it produces lift with minimal drag.
That's what most people are taught.

There is another mode that is related to the force of the air
impacting on the bottom of the wing at high AOA producing lift as
well. Think of your control surfaces. Your rudder control surface is
symmetric, yet it produces horizontial components of force. IIRC, the
Jeppesen books cover high AOA effects as well.

Inverted flight is accomplished by the second of the two effects.
They have to fly at a higher AOA relative to normal flight to
compensate for the airfoil effect. Some aerobatic planes have
symmetric airfoils for this reason.

As AOA increases, the deflection takes more of a role. At stall, the
deflection is suffcient for the airfoil effect to be interfered with
and ceases. Thus a large component of left is lost. You drop. You
still have some lift, but it is not sufficient to keep you airborne.





Jim

http://www.unconventional-wisdom.org

[Thomas Borchert]

Jimbob,

> He is describing the traditional airfoil theory which is correct.
>

Uhm, no.

--
Thomas Borchert (EDDH)

[Thomas Borchert]

Gone,

> don't take may word for ask NASA...
>

I do. Sentences no.2 and 3:

"An aerodynamic, curved airfoil will turn a flow. But so will a simple
flat plate, if it is inclined to the flow."

That's a direct contradiction to what you said. Also, see:

http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html

Nothing about curvature, nothing about pressure. My point exactly.

--
Thomas Borchert (EDDH)

[Thomas Borchert]

Buttman,

> This guy is an amazing instructor.
>

Apparently.

--
Thomas Borchert (EDDH)

[Dudley Henriques]

"T o d d P a t t i s t" > wrote in message
...
> Jimbob > wrote:
>
>>He is describing the traditional airfoil theory which is correct. It
>>is the most efficient method as it produces lift with minimal drag.
>>That's what most people are taught.
>>
>>There is another mode that is related to the force of the air
>>impacting on the bottom of the wing at high AOA producing lift as
>>well.
>
> You make it sound like there are two effects, one that
> applies in some cases and one that applies in other cases.
> The reality is that both descriptions apply in all cases.
> They are alternative descriptions of the same thing, and
> both "explain" the effect 100%
>
>>Inverted flight is accomplished by the second of the two effects.
>
> No, both descriptions (often referred to as the Bernoulli
> and Newton descriptions) are 100% correct and either can be
> used.
>
>
>

Not AGAIN!!!!!!!!!
:-)))))))))))))))))))))))))))))))))))))))))))))))))) ))))))))))))))))))))))

Dudley

[Gone Flyin'. -----==0==-----]

> > He is describing the traditional airfoil theory which is correct.
> >
>
> Uhm, no.


Oh uhm, YES!

[Hilton]

Roger Long wrote:
> Lift in a fully developed spin or steady sinking mush is also exactly
> the same as in level flight.

Not even close!

Hilton

[Greg Copeland]

On Fri, 09 Sep 2005 13:57:30 +0000, Jimbob wrote:

[snip]

> There is another mode that is related to the force of the air
> impacting on the bottom of the wing at high AOA producing lift as
> well. Think of your control surfaces. Your rudder control surface is
> symmetric, yet it produces horizontial components of force. IIRC, the
> Jeppesen books cover high AOA effects as well.

Isn't this the theory behind lifting bodies (aka, Space Shuttle) and why
many low wing planes tend to generate some minor amount of lift across the
fuslage area, in between the root coords?

[snip]

[[email protected]]

buttman wrote:
>
> So whats the deal here? Are we just thinking of two diffrent concepts?

Nonsense. Don't listen to what any of these people are saying here.
Lift is produced by the action of millions of tiny gnomes standing on
each other's shoulders. The thing is they're not too strong so you have
to keep moving because each gnome can only hold you up for a brief
instant and pass you on to the next one. Larger wings allow you to
spread the load out over more gnomes, thus creating more "lift." Spins
happen when you move the controls the wrong way and scare the gnomes.
Some people don't accept this because they can't see the gnomes, well,
you can't see air particles either. Even the Ph.D. guys can't explain
it, but any fool can see that planes fly. Gnomes!

-cwk.

[Margy]

Jimbob wrote:
> On Fri, 09 Sep 2005 14:29:18 +0200, Thomas Borchert
> > wrote:
>
>
>>>Wings generally tend to have a curved suface. The upper surface has a
>>>greater arc or curvature than the lower surface. As the air flows across the
>>>surfaces of the wing, the upper surface air is forced to move faster than
>>>the lower surface air thus causing a pressure difference between the two
>>>surfaces.
>>
>>Forced by what? And how does your "theory" explain inverted flight? I don't
>>buy

Forced by limiting the space through which the fluid must flow. Think
of your garden hose. If you put your thumb over the end and constrict
the space the water flows faster through the opening. As the speed
increases the pressure decreases, air moves from high pressure to low
pressure and the wing of the airplane is in the way of this movement so
it is lifted up with the high pressure air. This also explains wing tip
vortices and why for a given configuration a higher aspect ratio wing
will produce more lift than a lower aspect ration wing.

Inverted flight and equal camber wings use AOA to create the air
pressure differential.

Margy
>>
>>BTW, this has been beaten to death in countless aviation newsgroup
>>discussions. I once thought like you, because I was taught that way. It's
>>still a bad theory. I suggest googling. Keywords might be: lift, flight,
>>Bernoulli, Newton.
>
>
>
> He is describing the traditional airfoil theory which is correct. It
> is the most efficient method as it produces lift with minimal drag.
> That's what most people are taught.
>
> There is another mode that is related to the force of the air
> impacting on the bottom of the wing at high AOA producing lift as
> well. Think of your control surfaces. Your rudder control surface is
> symmetric, yet it produces horizontial components of force. IIRC, the
> Jeppesen books cover high AOA effects as well.
>
> Inverted flight is accomplished by the second of the two effects.
> They have to fly at a higher AOA relative to normal flight to
> compensate for the airfoil effect. Some aerobatic planes have
> symmetric airfoils for this reason.
>
> As AOA increases, the deflection takes more of a role. At stall, the
> deflection is suffcient for the airfoil effect to be interfered with
> and ceases. Thus a large component of left is lost. You drop. You
> still have some lift, but it is not sufficient to keep you airborne.
>
>
>
>
>
> Jim
>
> http://www.unconventional-wisdom.org

[Peter Duniho]

"Hilton" > wrote in message
. net...
> Roger Long wrote:
>> Lift in a fully developed spin or steady sinking mush is also exactly
>> the same as in level flight.
>
> Not even close!

He's quite close. See Todd' post.

I wrote "straight and level flight" simply because that was the scenario
being discussed in the original post. But any unaccelerated flight means
lift equals weight, and that includes the "fully developed spin" and "steady
sinking mush" Roger described.

Pete

[George Patterson]

Roger Long wrote:
> Lift in a fully developed spin or steady sinking mush is also exactly
> the same as in level flight.

Not according to the Jepp Private Pilot's Manual.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

[George Patterson]

buttman wrote:
>
> My instructor, which is a very knowledgable guy tried telling me that
> lift has nothing to do with airspeed. He said that lift is directly and
> soley related to AOA and AOA only. So if you are doing slow flight, you
> are producing more life than you are when you're cruising.

No. From the Jeppesen Sanderson "Private Pilot Manual" -- "Lift can be increased
in two ways; by increasing the forward speed of the airplane or by increasing
the angle of attack."

And elsewhere -- "When an aircraft is in straight and level flight, .... lift
equals weight ..."

So, you have no more lift when you are cruising level than if you're in level
slow flight.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

[Peter Duniho]

"George Patterson" > wrote in message
news:_8kUe.739$626.593@trndny08...
> Roger Long wrote:
>> Lift in a fully developed spin or steady sinking mush is also exactly the
>> same as in level flight.
>
> Not according to the Jepp Private Pilot's Manual.

Are you relying on the part of that manual that you quoted elsewhere?

You'll note that the quote you provided does not include the word "only".
It's incorrect to infer from the statement that lift equals weight in
straight and level flight, that when not straight and level lift does not
equal weight.

The statement you quoted is not inconsistent with Roger's post.

Pete

[john smith]

> Forced by limiting the space through which the fluid must flow. Think
> of your garden hose. If you put your thumb over the end and constrict
> the space the water flows faster through the opening. As the speed
> increases the pressure decreases, air moves from high pressure to low
> pressure and the wing of the airplane is in the way of this movement so
> it is lifted up with the high pressure air. This also explains wing tip
> vortices and why for a given configuration a higher aspect ratio wing
> will produce more lift than a lower aspect ration wing.

PV=nRT

[Larry Dighera]

On Fri, 9 Sep 2005 10:51:23 -0700, "Peter Duniho"
> wrote in
>::

>But any unaccelerated flight means
>lift equals weight, and that includes the "fully developed spin" and "steady
>sinking mush"

Isn't there acceleration in a sinking mush? If the aircraft is
descending, does lift equal weight?

[Hilton]

Peter wrote:
> Hilton wrote:
> > Roger Long wrote:
> >> Lift in a fully developed spin or steady sinking mush is also exactly
> >> the same as in level flight.
> >
> > Not even close!
>
> He's quite close. See Todd' post.
>
> I wrote "straight and level flight" simply because that was the scenario
> being discussed in the original post. But any unaccelerated flight means
> lift equals weight, and that includes the "fully developed spin" and
"steady
> sinking mush" Roger described.

Todd's reply to this clearly shows why Roger's statement is wrong. A large
percentage of the upward force in a spin is drag. The extreme case is a
parachutist coming straight down in one of those old round parachutes. In
this case, the 'aircraft' has zero lift and DRAG == WEIGHT.

Lift, drag, and thrust can be pointed in any direction; the only constant is
weight which always points towards the center of the earth.

Hilton

[Klein]

On Fri, 09 Sep 2005 10:59:00 -0400, T o d d P a t t i s t
> wrote:

>"Brian" > wrote:
>
>>Generally speaking lift = AOA * Airspeed.
>
>Not quite. Generally speaking lift is proportional to AOA *
>(Airspeed squared).
>
>>Except when accerlating or decelerating up or down (i.e Beginning or
>>ending a climb or descent) the lift = weight of the airplane.
>
>This is close and is often a reasonable approximation, so
>I'm not really disagreeing, just expanding. However, lift
>is actually defined as a force perpendicular to the flight
>path, so in climbs, some weight is supported by thrust, and
>in descents, some weight is supported by drag. Lift is
>slightly reduced in both cases.

In a somewhat more extreme example, when I pull my 400 hp Sukhoi into
a nearly vertical attitude, the rate of climb decreases to essentially
zero, i.e., the airplane hovers. In this case, the wings are
providing essentially no lift and the airplane is being supported by
almost totally by thrust. Actually, you should imagine Sean Tucker
doing this as I don't do it all that well. ;-)

Klein

[George Patterson]

Peter Duniho wrote:
>
> Are you relying on the part of that manual that you quoted elsewhere?

No. In a spin, at least one wing is at least partially stalled. According to
Jepp, this "results in a loss of lift in the area of the wing where it is taking
place."

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

[Stefan]

Peter Duniho wrote:

> I wrote "straight and level flight" simply because that was the scenario
> being discussed in the original post. But any unaccelerated flight means
> lift equals weight, and that includes the "fully developed spin" and "steady
> sinking mush" Roger described.

It depends on how you define "lift". If every upward pointing force is
lift, you're correct. If however you make a difference between, hmmm,
let's call it "true" lift created by the airfoil and drag that's just
incidentally pointing upwards, then you're not.

Stefan

[Stefan]

Klein wrote:

> In a somewhat more extreme example, when I pull my 400 hp Sukhoi into
> a nearly vertical attitude, the rate of climb decreases to essentially
> zero, i.e., the airplane hovers. In this case, the wings are
> providing essentially no lift and the airplane is being supported by
> almost totally by thrust.

In this situation, you might call that trust lift produced by the
propellor blades.

Stefan

[Stefan]

George Patterson wrote:

> Not according to the Jepp Private Pilot's Manual.

Which is the authoritative physics textbook ;-)

Stefan

[Matt Whiting]

Peter Duniho wrote:

> "buttman" > wrote in message
> ups.com...
>
>>[...]
>>So whats the deal here? Are we just thinking of two diffrent concepts?
>
>
> Your instructor is wrong, and should not be instructing.
>
> In straight and level flight, lift equals weight. Unless your weight
> changes, lift does not change, regardless of airspeed. What *can* change is
> the lift coefficient, which is determined by the angle of attack. But lift
> itself remains static.

Slight addition ... lift remains static in unaccelerated flight.

Matt

[Peter Duniho]

"T o d d P a t t i s t" > wrote in message
...
> Pete, in your reply above, you did the same thing Roger did,
> (and what I often do too,) you equated the vertical
> component of aerodynamic force to "lift."

I made the assumption that when I wrote "See Todd's post" people would. You
clarified that quite well there, and I didn't see any reason to try to use a
finer brush than what started the thread.

The real issue here is whether lift changes according to airspeed. The
generic idea of lift (as in, the force that keeps airplanes aloft) versus
the specific physics definition of lift is inconsequential in that context,
and not one I feel is worth nitpicking over.

If you'll note, I also wrote "He's quite close". Had his definition of lift
been correct, he would have been exactly correct. Again, referencing your
post explains the minute detail where he was incorrect, and I didn't feel a
need to delve more deeply.

Frankly, I think this might be one of the reasons so many pilots don't
understand lift. As soon as the discussion turns technical, many people
want to make sure every last detail is just perfectly right. But in
reality, one can gain a very useful and practical understanding of lift
without ever knowing that lift is perpendicular to relative wind. Jumping
right into the minutiae of relative wind, vertical components, etc. just
makes some people's eyes glaze over, and they don't learn anything at all,
not even that lift is relatively constant over all unaccelerated flight,
regardless of airspeed.

Pete

[Peter Duniho]

"Hilton" > wrote in message
ink.net...
> Todd's reply to this clearly shows why Roger's statement is wrong.

No, it doesn't. See my reply to Todd and Stefan's reply here to understand
what we are all talking about.

[Peter Duniho]

"George Patterson" > wrote in message
news:bWkUe.743$626.107@trndny08...
> No. In a spin, at least one wing is at least partially stalled. According
> to Jepp, this "results in a loss of lift in the area of the wing where it
> is
> taking place."

That still does not contradict Roger's post.

IMHO, by "lift" Roger clearly meant "the force acting against gravity".
This is a fairly common (though not aerodynamically correct) definition of
"lift", and in fact is the one the Jepp training book uses (assuming it
hasn't changed much in the 15 years since I used it). That is, they have
the classic "lift, weight, thrust, drag" picture with the two pairs of
opposing arrows.

If Roger had meant by "lift", the "aerodynamic force created by the wing as
a result of relative wind" (or something similar), then he would have been
incorrect. But given that that definition makes his post incorrect, and
given that there's another widely accepted definition that does not, it
seems fair to give him the benefit of the doubt and assume he was using the
definition that's consistent with his post.

Now, granted, this *is* Usenet after all, and everyone seems to think it's
their job to point out why everyone else is wrong. So maybe I'm all wet in
my thinking. But that's my thinking, nonetheless.

Pete

[Peter Duniho]

"Stefan" > wrote in message
...
> In this situation, you might call that trust lift produced by the
> propellor blades.

You might. But then you get into trouble in straight and level flight when
those propeller blades are still producing that lift. Then the total lift
greatly exceeds the airplane's weight. :)

Pete

[Jimbob]

On Fri, 09 Sep 2005 10:51:57 -0400, T o d d P a t t i s t
> wrote:

>Jimbob > wrote:
>
>>He is describing the traditional airfoil theory which is correct. It
>>is the most efficient method as it produces lift with minimal drag.
>>That's what most people are taught.
>>
>>There is another mode that is related to the force of the air
>>impacting on the bottom of the wing at high AOA producing lift as
>>well.
>
>You make it sound like there are two effects, one that
>applies in some cases and one that applies in other cases.
>The reality is that both descriptions apply in all cases.
>They are alternative descriptions of the same thing, and
>both "explain" the effect 100%
>

You are correct. Both are consequences of Bernoulli.

However, I am trying to explain it to people that may not be versed in
the the conservation of energy in fluids, conservation of momentum and
Newton's #3.

Sometimes it helps to view it from bernoulli some times form Newton.
To the layman, they they don't care. They just have a simple question
they want answered.




Jim

http://www.unconventional-wisdom.org

[Jimbob]

On Fri, 09 Sep 2005 10:47:52 -0400, T o d d P a t t i s t
> wrote:

>
>A change in height is not an indication that the vertical
>component of the total aerodynamic force is less or more
>than weight. Only an accelerating change in height
>indicates an imbalance in forces. Constant climbs, constant
>descents, fully developed spins, etc. all have the vertical
>component equal to weight.
>


Sorry, I wrote before I thought. I meant "no change in acceleration"
and didn't catch that he had stated "Steady sinking" and "fully
developed"

He's right. I'll go crawl away now...


Jim

http://www.unconventional-wisdom.org

[Dudley Henriques]

"T o d d P a t t i s t" > wrote in message
...
> "Dudley Henriques" <dhenriques@noware .net> wrote:
>
>>> both descriptions (often referred to as the Bernoulli
>>> and Newton descriptions) are 100% correct
>>
>>Not AGAIN!!!!!!!!!
>>Dudley
>
> Now Dudley, you don't say that to every new student who
> tries to steer with the yoke while taxiing, do you? OMG,
> not another student who's got it wrong -when will it ever
> end!
>
> Similarly, there is an endless supply of people who haven't
> yet figured out what "lift" is. It will never ever stop.
> The best we can do is to do a better job of teaching it at
> the pilot level (the quality of instruction on this is
> abysmal), and a better job of answering the questions that
> arise. :-)

Just an attempt at a small bit of "inside" humor here...obviously misguided.
Dudley Henriques

[Hilton]

Peter Duniho wrote:
> Hilton wrote:
> > Todd's reply to this clearly shows why Roger's statement is wrong.
>
> No, it doesn't. See my reply to Todd and Stefan's reply here to
understand
> what we are all talking about.

You wrote "Had his definition of lift been correct, he would have been
exactly correct." Ummm, OK. But lift is well-defined and it is not
defined as the force that opposes weight. So, you can redefine whatever you
want, doesn't make it right.

Hilton

[Peter Duniho]

"Hilton" > wrote in message
ink.net...
> You wrote "Had his definition of lift been correct, he would have been
> exactly correct." Ummm, OK. But lift is well-defined

Actually, part of the problem is that "lift" is poorly defined. It means
different things in different contexts.

> and it is not
> defined as the force that opposes weight.

Actually, most basic aviation texts written for pilots DO define lift as
"the force that opposes weight". You should not be faulted for having never
read one; after all, the texts certainly gloss over many important facts,
and it's not necessary to have studied one to become a pilot. But many
pilots DO use them as a reference, and they DO define lift in exactly the
way you seem to think they do not.

> So, you can redefine whatever you want, doesn't make it right.

I'm not the one doing the "redefinition". The word "lift" is simply not a
technical term. You can get closer by using the phrase "aerodynamic lift",
but ultimately you simply need to know in what context you're using the
word.

Pete

[George Patterson]

Hilton wrote:
>
> But lift is well-defined and it is not
> defined as the force that opposes weight.

That's the way Jeppesen describes it.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

[Gone Flyin']

>
> Nothing about curvature, nothing about pressure. My point exactly.

OK check this out...

http://scienceworld.wolfram.com/physics/BernoulliEffect.html

I think this makes my point.

G

[Dudley Henriques]

"Hilton" > wrote in message
ink.net...
> Peter Duniho wrote:
>> Hilton wrote:
>> > Todd's reply to this clearly shows why Roger's statement is wrong.
>>
>> No, it doesn't. See my reply to Todd and Stefan's reply here to
> understand
>> what we are all talking about.
>
> You wrote "Had his definition of lift been correct, he would have been
> exactly correct." Ummm, OK. But lift is well-defined and it is not
> defined as the force that opposes weight. So, you can redefine whatever
> you
> want, doesn't make it right.
>
> Hilton

I would tend to agree with you on this point, but with a caveat.
Unfortunately for many student pilots searching for information on lift,
many of the data sources in use at the student pilot level present subjects
like lift improperly in my opinion anyway.
Rather than state a definition of lift, the "definition" actually passes
that stage and presents what lift DOES! It's a fine point, but it is worthy
of note for the more "scientific minds" among us :-)
I've always STARTED an explanation of lift by presenting it initially as the
aerodynamic force that opposes the relative wind, NOT the force that opposes
gravity or weight. (That comes later :-)))
Again, it's a fine point, and there are many ways to discuss definition, and
if nothing else, what you are discussing here with others on the group helps
demonstrate why the subject of lift is so misunderstood by the student pilot
community. (Not your fault BTW :-)
I think I've spent more time discussing lift with students through the years
than any other single aspect of flight. Part of the reason for that is the
confusion caused by the community's seeming insistence on presenting lift in
a non standard written form.
Dudley Henriques

[Ash Wyllie]

buttman opined

>I have always been under the impression that lift is the product of
>airspeed and angle of attack, and that lift is the measure of upward
>force acting on the plane at a given time. For instance, if you are
>doing slow flight, your wings are producing the same amount of life
>that you would be if you were cruising, GIVEN that you did not lose or
>gain any altitude during the maneuver.

>My instructor, which is a very knowledgable guy tried telling me that
>lift has nothing to do with airspeed. He said that lift is directly and
>soley related to AOA and AOA only. So if you are doing slow flight, you
>are producing more life than you are when you're cruising. I overheard
>a ATP guy who flies King Air's say that this huge 20 ton military plane
>he used to fly would fly approaches at 110 knots, and I heard him say
>"It is able to do this because it producing so much lift", which I took
>as him defining lift as my instructor does.

>So whats the deal here? Are we just thinking of two diffrent concepts?

Lift = Cl(AOA) * Area * V^2


-ash
Cthulhu in 2005!
Why wait for nature?

[Roger Long]

The distinction is really a thought convenience to help us talk about
what is going on and not a real physical difference. Lift is really
drag directed upwards.

--

Roger Long

[Roger Long]

Stall is not loss of lift but loss of stability in the airstream.
Stability is the ability to reach a steady state. A fully stalled
wing will develop just as much lift as an unstalled one but will seek
an angle of attack that will result in a steady state by sinking
faster. This makes most aircraft head nose first for the ground which
feels like loss of lift.

For a more complete explanation:

http://www.avweb.com/news/airman/184307-1.html

--

Roger Long

[[email protected]]

T o d d P a t t i s t wrote:

> >I'd say it's the other way around: Lift creates the pressure differential.
>
> The pressure differential is caused by the motion of the air
> as the wing moves through the air.

Well how will that work. The air on top is set into motion as a result
of the wing pulling on it and the air on bottom is set into motion as a
result of the wing pushing on it. How can the motion of the air on the
top and bottom of the wing cause a pressure differential? It can't.
The pressure differentials are actually caused by the wing pulling and
pushing on the air and the air pushing and pulling back. Low pressure
does very little to generate lift directly. Example. A ball will
suspend in an upward airflow from an air hose. This causes the not to
bright people at the NASA web sight to jump to the large and mostly
inaccurate conclusion that it is sucked in to the low pressure flow or
pushed into it by the higher atmospheric pressure. This is disproved
by the fact other shaped object do not seem to be sucked into the flow
at all.


The shape of the wing,
> particularly, the upper surface, strongly affects the motion
> of the air and thereby strongly affects the amount of lift
> and drag produced.
>


The shape of the wing (the top or bottom) strongly affects the
direction of the motion of influenced air. Thereby strongly affecting
the amount of lift produced. Example One of the airfoil shapes that
generates the most lift at zero degrees angle of attack is the under
cambered. It uses shape on top and bottom to divert the low-pressure
air.

[gregg]

Dudley Henriques wrote:

>
> "Hilton" > wrote in message
> ink.net...
>> Peter Duniho wrote:
>>> Hilton wrote:
>>> > Todd's reply to this clearly shows why Roger's statement is wrong.
>>>
>>> No, it doesn't. See my reply to Todd and Stefan's reply here to
>> understand
>>> what we are all talking about.
>>
>> You wrote "Had his definition of lift been correct, he would have been
>> exactly correct." Ummm, OK. But lift is well-defined and it is not
>> defined as the force that opposes weight. So, you can redefine whatever
>> you
>> want, doesn't make it right.
>>
>> Hilton
>

> I've always STARTED an explanation of lift by presenting it initially as
> the aerodynamic force that opposes the relative wind, NOT the force that
> opposes gravity or weight. (That comes later :-)))
> Dudley Henriques

Lift opposes the Relative Wind?

How does lift (and I assume you are talking wing lift here since you mention
gravity/weight) *oppose* the relative wind?

What do you mean when you use the word "oppose"?

Or were you speaking of prop lift?

--
Saville

Replicas of 15th-19th century nautical navigational instruments:

http://home.comcast.net/~saville/backstaffhome.html

Restoration of my 82 year old Herreshoff S-Boat sailboat:

http://home.comcast.net/~saville/SBOATrestore.htm

Steambending FAQ with photos:

http://home.comcast.net/~saville/Steambend.htm

[Dudley Henriques]

"gregg" > wrote in message
...
> Dudley Henriques wrote:
>
>>
>> "Hilton" > wrote in message
>> ink.net...
>>> Peter Duniho wrote:
>>>> Hilton wrote:
>>>> > Todd's reply to this clearly shows why Roger's statement is wrong.
>>>>
>>>> No, it doesn't. See my reply to Todd and Stefan's reply here to
>>> understand
>>>> what we are all talking about.
>>>
>>> You wrote "Had his definition of lift been correct, he would have been
>>> exactly correct." Ummm, OK. But lift is well-defined and it is not
>>> defined as the force that opposes weight. So, you can redefine whatever
>>> you
>>> want, doesn't make it right.
>>>
>>> Hilton
>>
>
>> I've always STARTED an explanation of lift by presenting it initially as
>> the aerodynamic force that opposes the relative wind, NOT the force that
>> opposes gravity or weight. (That comes later :-)))
>> Dudley Henriques
>
> Lift opposes the Relative Wind?

This should read "Lift is the component of aerodynamic force perpendicular
to the relative wind.", and not "opposes". My error in presentation.
DH

[Hilton]

Dudley,

As usual, excellent post - I totally agree.

Hilton

[Hilton]

Roger Long wrote:
> The distinction is really a thought convenience to help us talk about
> what is going on and not a real physical difference. Lift is really
> drag directed upwards.

I have absolutely no idea what you mean. I have never seen lift described
as "drag directed upwards". Please explain.

Hilton

[Hilton]

Peter,
> Todd wrote:
> > Pete, in your reply above, you did the same thing Roger did,
> > (and what I often do too,) you equated the vertical
> > component of aerodynamic force to "lift."
[zap]
> The real issue here is whether lift changes according to airspeed. The
> generic idea of lift (as in, the force that keeps airplanes aloft) versus
> the specific physics definition of lift is inconsequential in that
context,
> and not one I feel is worth nitpicking over.

It is *exactly* worth discussing and it is not nitpicking. Lift as DEFINED
is completely different to the force pointing upwards and there are many
examples where they all completely different; some example: spins, steep
turns, a plane climbing vertically, a flat spin, the F-18 slow pass...

OK, quick question: how much 'lift' (your definition) is an aircraft
producing in a 45 degree bank? Equal to the weight? If so, why does my
stall speed increase? Nitpicking? Well this nitpicking kills a lot of
pilots including very experienced ones.

How would you explain to a pilot that even though lift equals weight in a
steep turn (your definition), the stall speed increases?

Hilton

[Peter Duniho]

"Hilton" > wrote in message
k.net...
> It is *exactly* worth discussing and it is not nitpicking.

Not in this context. Still, you have demonstrated you are happy to continue
to do so, so please...knock yourself out.

[[email protected]]

The hardest thing about teaching someone about lift and drag in trying
to unlearn them the misconceptions they have already learned. The Nasa.
Gov web pages are a poster boy for this misconception. They define lift
and drag and thrust with narrow-minded characterizations that do not
differentiate one from the other. Example lift is THE force that
supports the aircraft in flight. Drag opposes the forward motion of an
aircraft thru the air. Thrust causes the forward motion of the
aircraft. They exclusively refer to drag as resistance force when the
major use of lift in aeronautics is to resist gravity. How stupid do
they think people are?

I am a member in model airplane club whose members are made up mostly
by retired pilots (commercial and private). I make it a point to ask
any pilot I meet what is the difference between lift and drag and I
have never Got a correct answer except for I don't know.

I hate it when some one says it's just a matter of semantics. Words
are useless without meaning and the words that have simple and accurate
definitions are the most useful. Glider pilots look for lift when they
fly their craft. But the upward aerodynamic force they are looking for
to accelerate their craft upward as a result of this lift is called
drag.
I like to discuss aerodynamics with people of authority. Please do not
think I am picking on you because I think you are one of the smarter
people in this group. I find it hard to argue with you because I agree
with so much of what you say. I sound like I am on a soap box don't
I?

[private]

"Dudley Henriques" <dhenriques@noware .net> wrote in message
hlink.net...
snip
> This should read "Lift is the component of aerodynamic force perpendicular
> to the relative wind.", and not "opposes". My error in presentation.
> DH

Hello Dudley,

Nicely stated,

Are we not really looking at two different concepts of lift here?

A - The aerodynamic resultant reaction of an airfoil pulling air downward.

B - The flight physics teaching concept that an aircraft (in unaccelerated
flight) must generate a force (lift, thrust ,drag) that balances its
(apparent) weight.

ISTM that A is the description of the dynamics of motion through a fluid
and B is the description of the dynamics of motion of a mass. The fact
that the mass is moving through a fluid makes it a complex problem that is
straining our definitions, and perhaps is more of a problem of conceptual
semantics.


In regards to "not AGAIN", here in Canada we have an ongoing debate on
Quebec nationalism/referendum that we wags refer to as the "neverendum".

regards,

[private]

"Ash Wyllie" > wrote in message
...
snip
> Lift = Cl(AOA) * Area * V^2
snip

I believe this is more correctly stated as

Lift = Cl(AOA and some other stuff including shape) * Area * P/2 * V^2

[Bob Fry]

>>>>> "private" == private > writes:

private> A - The aerodynamic resultant reaction of an airfoil
private> pulling air downward.

private> B - The flight physics teaching concept that an aircraft
private> (in unaccelerated flight) must generate a force (lift,
private> thrust ,drag) that balances its (apparent) weight.

The problem with restricting your example to unaccelerated flight is
that the resulting definition of lift will almost surely be incorrect,
by not being general. Imagine for example an airplane in a
continuously positive-g loop. Neither definition A or B are valid,
yet lift from the wing always occurs.

[RK Henry]

On Sat, 10 Sep 2005 20:48:51 -0700, Bob Fry >
wrote:

>>>>>> "private" == private > writes:
>
> private> A - The aerodynamic resultant reaction of an airfoil
> private> pulling air downward.
>
> private> B - The flight physics teaching concept that an aircraft
> private> (in unaccelerated flight) must generate a force (lift,
> private> thrust ,drag) that balances its (apparent) weight.
>
>The problem with restricting your example to unaccelerated flight is
>that the resulting definition of lift will almost surely be incorrect,
>by not being general. Imagine for example an airplane in a
>continuously positive-g loop. Neither definition A or B are valid,
>yet lift from the wing always occurs.

So what do we call the aerodynamic force on the horizontal tail that
forces the back of the airplane downward to keep the airplane from
diving into the ground? If it were acting upward we'd easily refer to
it as lift, but it acts downward. Is that lift?

Of course this same force is upward when it's on an airplane with a
canard. I guess that then it qualifies as lift.

What about the aerodynamic force on the vertical tail/rudder that
controls yaw? It's acting sideways. And what about the aerodynamic
force created by the propeller, which is a wing after all?

RK Henry

[Hilton]

RK Henry wrote:
> Bob wrote:
>
> >The problem with restricting your example to unaccelerated flight is
> >that the resulting definition of lift will almost surely be incorrect,
> >by not being general. Imagine for example an airplane in a
> >continuously positive-g loop. Neither definition A or B are valid,
> >yet lift from the wing always occurs.

Correct, the whole lift opposes weight description focuses on a very narrow
case (or set of cases). It is not general at all; in fact, it falls apart
when the airplane turns! (Try explain why stall speed increases when lift
stays the same).

IMHO: Those who think of lift as the 'upward' force(s) have simplified the
problem too much and this sets up a whole host of inconsistencies.


> So what do we call the aerodynamic force on the horizontal tail that
> forces the back of the airplane downward to keep the airplane from
> diving into the ground? If it were acting upward we'd easily refer to
> it as lift, but it acts downward. Is that lift?

Yes, it is lift. Perhaps 'we' should have called it "push" instead of
"lift", but then some would have said that is really should be called
"pull". :) Seriously, just as "stall" is a badly chosen word (since 99% of
the world population think when a plane stalls, its engine has stopped),
"lift" is also badly chosen. Think of it as the "push" or "pull" force.


> Of course this same force is upward when it's on an airplane with a
> canard. I guess that then it qualifies as lift.

Same thing really - their primary objective is to induce a nose-up pitching
moment to oppose the wing's pitching moment. To answer your quesion, yes,
this is also lift.


> What about the aerodynamic force on the vertical tail/rudder that
> controls yaw? It's acting sideways.

Lift.


> And what about the aerodynamic
> force created by the propeller, which is a wing after all?

Lift.

Hilton

[Peter Duniho]

"Hilton" > wrote in message
k.net...
> Correct, the whole lift opposes weight description focuses on a very
> narrow
> case (or set of cases). It is not general at all; in fact, it falls apart
> when the airplane turns!

A turn is not "unaccelerated flight", which was the condition specifically
restricting this entire discussion.

> IMHO: Those who think of lift as the 'upward' force(s) have simplified the
> problem too much and this sets up a whole host of inconsistencies.

In unaccelerated flight, it is an entirely appropriate simplification for
the introduction of the subject. It is certainly FAR more correct than what
the original poster's instructor claimed.

Pete

[Montblack]

("Margy" wrote)
[snip]
> Forced by limiting the space through which the fluid must flow. Think of
> your garden hose. If you put your thumb over the end and constrict the
> space the water flows faster through the opening. As the speed increases
> the pressure decreases, air moves from high pressure to low pressure and
> the wing of the airplane is in the way of this movement so it is lifted up
> with the high pressure air.


Garden hose + thumb:
"As the speed increases the pressure decreases..." part throws me. As the
flow increase?

C'mon over here and explain it again please. Yes, yes. Of course I'll keep
the hose kinked --- almost in range. <hehehe>


Montblack

[Bob Fry]

>>>>> "PD" == Peter Duniho > writes:
PD> "Hilton" > wrote in message
>> IMHO: Those who think of lift as the 'upward' force(s) have
>> simplified the problem too much and this sets up a whole host
>> of inconsistencies.

PD> In unaccelerated flight, it is an entirely appropriate
PD> simplification for the introduction of the subject. It is
PD> certainly FAR more correct than what the original poster's
PD> instructor claimed.

An unaccelerated flight example is fine for the first introduction to
aerodynamic forces. The problem is if one doesn't move beyond it. It
sounds like the instructor in the OP has done that, never engaging in
any thought experiments at the boundaries of the example to explore
the limits of his knowledge. That, and no high school physics.

Once I taught an aviation class to a couple of Boy Scouts. I started
with the typical airplane in level flight and the 4 forces of flight,
weight, lift, drag, thrust. All well and good, nothing hard about
that! For homework I asked them to consider now a glider: "it's still
has weight, so it must product lift, right? And moving through the
air, it experiences drag, so there must be thrust, right? But from
where? A glider has no engine!"

[Brian]

Admittedly I did simplify it a bit.

Brian

[Brian]

In a somewhat more extreme example, when I pull my 400 hp Sukhoi into
a nearly vertical attitude, the rate of climb decreases to essentially
zero, i.e., the airplane hovers. In this case, the wings are
providing essentially no lift and the airplane is being supported by
almost totally by thrust. Actually, you should imagine Sean Tucker
doing this as I don't do it all that well. ;-)


Still the same Principle, Your just transfering your lift from the
Fixed wing the Rotating Wing (the Propeller)

Brian

[[email protected]]

> > But the upward aerodynamic force they are looking for
> >to accelerate their craft upward as a result of this lift is called
> >drag.
>
> Not really.

Yea really. The upward acceleration of the flying glider in a thermal
entry is caused 100 percent by the component of the relative airflow
caused by the thermal. It requires a force to accelerate the glider
upward as a result of the thermal. Lets see what aerodynamic force is
most accurately defined as the aerodynamic force that is in the
direction of the relative airflow that caused it? That's right drag.
Any lift from an upward airflow will be horizontal. That will be why
the increased lift points more horizontal.

It is true that angle of attack goes up causing more lift but as far as
accelerating the glider upward this extra lift is negated by the fact
that the direction of this lift moves farther away from the upward
direction. This additional lift comes with additional drag and so does
the additional wind speed as a result of the thermal. And the direction
of this drag is more in the upward direction as a result of the
thermal. The thermal not only changes the direction of the relative
airflow it increases its speed. A fact that you conveniently left out.
Don't dem thar velocity vectors have magnitudes?

Now hear is another clue. When drag causes the acceleration of an
object the faster that object goes the less drag it generates until it
reaches the speed of the air and generates no drag, like the horizontal
flight of a balloon. This is because the more the object moves with the
wind the less motion between the object and the air. This is why the
flight stabilizes to a steady climb at the original constant speed in
the rising air. When lift causes the acceleration of an object it has
similar dynamics as the flying glider in a thermal entry. If the
glider accelerated upward as a result of the aerodynamic force lift it
would also affect the relative airflow by changing its speed and
direction. You never said any thing about this influence in your
analysis.



Before entering rising air, a glider's wing
> sees a relative wind pointed slightly upward. It's pointed
> straight back up the angle of the glidepath. The lift
> vector is perpendicular to this, so it angles slightly
> forward. As the glider enters rising air, the relative
> wind turns and now angles more steeply upwards as the
> upwardly pointed vector of rising air is added to the
> previous vector of relative wind from the glide. If the
> glider's attitude is unchanged, the changing relative wind
> increases the AOA and the corresponding lift vector, and
> that lift vector tilts forward.
>
> The drag vector also increases and tilts upwards. Most of
> the additional force that initially accelerates the glider
> upwards comes from the increased lift vector. A smaller
> component comes from the more upwardly tilted drag vector.
>
> As the flight stabilizes to a steady climb at the original
> constant speed in the rising air, the lift and drag vectors
> will return to the same magnitudes and angles as before
> relative to the ground. The glider will be in the same
> attitude relative to the ground. The drag will be the same
> (same magnitude, same direction), the lift will be the same
> and the vectors of lift and drag will add up to produce a
> vertical aerodynamic force that exactly opposes the downward
> force of gravity. The glider will continue in unaccelerated
> flight and the only difference will be that the glider is
> now in a steady unaccelerated climb instead of a steady
> unaccelerated descent.
>
>
> Do not spin this aircraft. If the aircraft does enter a spin it will return to earth without further attention on the part of the aeronaut.
>
> (first handbook issued with the Curtis-Wright flyer)

[cjcampbell]

buttman wrote:

>
> My instructor, which is a very knowledgable guy tried telling me that
> lift has nothing to do with airspeed. He said that lift is directly and
> soley related to AOA and AOA only.

Uh-huh. So if you use a crane to lift up the nose of a 747 sitting on
the ramp, your instructor believes it will be generating the same
amount of lift as it would at that AOA and 400 knots. Detach the crane
and the 747 will just stay there in a nose up attitude without any
visible means of support. Or maybe your instructor has a poor
understanding of lift.

Lift is actually a mathematical formula: L = 1/2 air density * velocity
squared * area of the wing * coefficient of lift for that wing. Your
instructor should know that; it is on both the commercial and flight
instructor written exams.

You generally can't do much about the air density, but you usually can
change your velocity and the coefficient of lift. The coefficient of
lift for most wings increases with AOA, peaking at the critical AOA and
dropping off sharply at higher AOA after that. Some flaps and other
devices (variable geometry wngs come to mind) can change the area of
the wing and/or its coefficient of lift. Also, "the area of the wing"
is not quite right; it really is a reference area which might have
little to do with the actual wing size. A helicopter, for example, uses
a reference area equal to the entire disk, not just the blades. The
same rule applies to propellers. The reference area on a fixed wing
plane includes the area through the fuselage, as if the wing was all
one piece.

You can use either sq. feet or sq. meters (or, heck, sq. rods if you
want to) for the reference area; it all works out as long as you use
the same type of units all through the calculation, including air
density.

[Ross Richardson]

http://www.allstar.fiu.edu/aero/airflylvl3.htm


Regards, Ross
C-172F 180HP
KSWI


buttman wrote:
> I have always been under the impression that lift is the product of
> airspeed and angle of attack, and that lift is the measure of upward
> force acting on the plane at a given time. For instance, if you are
> doing slow flight, your wings are producing the same amount of life
> that you would be if you were cruising, GIVEN that you did not lose or
> gain any altitude during the maneuver.
>
> My instructor, which is a very knowledgable guy tried telling me that
> lift has nothing to do with airspeed. He said that lift is directly and
> soley related to AOA and AOA only. So if you are doing slow flight, you
> are producing more life than you are when you're cruising. I overheard
> a ATP guy who flies King Air's say that this huge 20 ton military plane
> he used to fly would fly approaches at 110 knots, and I heard him say
> "It is able to do this because it producing so much lift", which I took
> as him defining lift as my instructor does.
>
> So whats the deal here? Are we just thinking of two diffrent concepts?
>

[[email protected]]

> I don't follow the point you are trying to make here. The
> increased lift does affect the RW. As the glider
> accelerates upwards, it begins to match the upward motion of
> the air, changing the RW back to the previous RW. I
> attribute the upward acceleration mostly to the increased
> lift and only partly to the increased drag. You claim that
> the vertical component of lift is unchanged.
>issued with the Curtis-Wright flyer)

When the motion of an object is caused by lift it will never reduce the
relative airflow that initially caused that motion it will increase the
speed and change the direction of it. This is why wind powered vehicles
can move faster than the wind they are powered by. When the motion of
an object is caused by drag the faster it moves the less drag it
generates because the less relative airflow it generates. It is
impossible for the increased lift to do anything but increase the
relative airflow if that object is allowed to move as a result of it
(lift). If the glider accelerates upward and relative airflow decreases
the only aerodynamic force that can cause that is drag. You claim that
the increased lift does affect the RW but it actually will affect it
the complete opposite way that you say it does if the upward
acceleration were due to lift.

Lets say you are holding a propeller in the wind. The relative airflow
caused by the wind causes the propeller to tend to rotate. If the
propeller were to be allowed to rotate as a result of this lift the
relative airflow now influencing the prop is still all of the wind plus
the relative airflow caused by its motion. The relative airflow is
made up by the actual motion of the air (Wind) plus the motion of the
propeller thru the wind. Objects that move as a result of drag don't
move thru the air they move with the air.

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T o d d P a t t i s t wrote:
> wrote:
>
> >When the motion of an object is caused by lift it will never reduce the
> >relative airflow that initially caused that motion it will increase the
> >speed and change the direction of it.
>
> You're making the same argument here that you made before -
> you are separating the vector components of the new RW into
> two parts, the original RW and the new vector component of
> RW comprising a vertical RW due to rising air. Then you
> ignore the original component and make arguments about the
> other component in isolation. It's obviously true that if
> there were no wind other than the vertically rising air,
> then all the aircraft vertical acceleration would be due to
> drag from that rising air. That's not what's happening
> though.

There is no wind other than the vertically rising air, the rest of the
relative airflow is caused by the motion of the glider thru the still
air. The difference between the two is that to move thru the air you
must over come drag and to remain still in moving air you must overcome
drag. This makes them easy to separate. The glider uses inertia to
overcome drag from the lift (a meteorological term for rising air). I
did not use the term vertical acceleration I said upward acceleration
witch did not include the gliders downward deceleration from the
thermal. I believe that when the gliders downward motion stops it is
slightly less influenced by the downward motion thru the air.
You said after the flight stabilizes to a steady climb at the original
constant speed in the rising air The glider will continue in
unaccelerated flight and the only difference will be that the glider
is now in a steady unaccelerated climb instead of a steady
unaccelerated descent. Here is another difference. The lift and drag go
from resisting downward motion to causing upward motion among other
things.

> The validity of your argument depends on the ability to
> separate the RW into two non-orthogonal vector components
> and attribute lift and drag separately to each, then add up
> the lift and drag from each component. That's what's wrong.
> You can't treat your vector components independently, as you
> are doing.

So my argument is not valid due to the many and obvious shortcoming of
mathematical formula. You cannot explain it mathematically so it's
not true or does not exist or even more absurd metrological lift causes
vertical aerodynamic lift. This does not make what I said true but sure
is a good sign that it is. Save the math to balance your checkbook not
to distort actual occurrences in the real world. This is not rocket
science you simply have to apply a little common sense and logic. You
know I am wrong but you do not know why.