The Impossibility of Flying Heavy Aircraft Without Training

Jose wrote:
Perhaps you are not familiar with nerf balls. Nerf balls are foam
rubber. When a cue ball hits a nerf ball (sufficiently large) nerf
ball it stops and the nerf ball just quivers a bit. The center of
mas quits moving. The kinetic energy of the cue ball has been
converted to heat. Energy is conserved, momentum is not.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.

But it will not move in a manner that conserves momentum.

--

FF

Not until after it passes the high point in the airfoil. Befor it
gets there, it is accelerated upwards.

Does the air split (top/bottom path) at the same level as it rejoins?
If the air splits at a higher altitude, then the air has to have a net
downward motion to get to the rejoin point.

When the air reaches the trailing edge it is back to where it started.

Is it? I think it's lower than when it started. It certainly is with
any appreciable AOA.

No, it is a way of looking at downrushing air that has never
contacted the wing.

It doesn't matter whether it contacts the wing or not. The contact is
by proxy (by contacting the other molecules of air that contact...the
wing.) You call it pressure. I agree. Pressure is ultimately
newtonian; I think we agree there too.

It's a floor wax. It's a dessert topping.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.
But it will not move in a manner that conserves momentum.

Yes it will. What will not be conserved is macroscopic kinetic energy.

Make the room bigger. Make it an infinite room. At what point does
the fan continue to put momentum into the air mass continuously, and
not just during start up?

At the point when it's an infinite room. The bigger the room, the
longer it takes for a pressure equilibrium to occur. If we deal with
the earth's atmosphere and a propeller, the propeller pushes air back,
which alters the rotational momentum of the earth, in a manner equal
(and opposite) to the amount of rotational (around the earth's center)
momentum the airplane acquires. This could potentially happen until the
earth is spinning godawful fast (faster than the propeller could
handle). In practice we'll get tired of arguing before that.

So, are you saying that in the presence of the Earth there is no
net change in the momentum of the basketballs being thrown by the
dribbler and also no net change in momentum of the air molecules
accelerated by the wing?

Averaged over all basketballs and all air molecules, yes, because the
earth acts as a momentum transfer point.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

In article om,
wrote:

Jose wrote:
Perhaps you are not familiar with nerf balls. Nerf balls are foam
rubber. When a cue ball hits a nerf ball (sufficiently large) nerf
ball it stops and the nerf ball just quivers a bit. The center of
mas quits moving. The kinetic energy of the cue ball has been
converted to heat. Energy is conserved, momentum is not.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.

But it will not move in a manner that conserves momentum.

You really need to study basic physics...

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

Alan Baker wrote:
In article om,
wrote:

Jose wrote:
Perhaps you are not familiar with nerf balls. Nerf balls are foam
rubber. When a cue ball hits a nerf ball (sufficiently large) nerf
ball it stops and the nerf ball just quivers a bit. The center of
mas quits moving. The kinetic energy of the cue ball has been
converted to heat. Energy is conserved, momentum is not.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.

But it will not move in a manner that conserves momentum.

You really need to study basic physics...


Doh!

You'd never guess it but I did get A's in freshman Physics.

Of course I had that bass akwards. Energy can change from
kinetic to gravitatonal potential to heat etc. An elastic collision
is one in which kinetic energy is conserved. In an inelastic collison
some kinetic energy is converted to another form, typically heat.
Momentum is always conserved, as you noted earlier.

--

FF

Jose wrote:
Not until after it passes the high point in the airfoil. Befor it
gets there, it is accelerated upwards.

Does the air split (top/bottom path) at the same level as it rejoins?
If the air splits at a higher altitude, then the air has to have a net
downward motion to get to the rejoin point.

Agreed. Clearly this happens with high AOA.


When the air reaches the trailing edge it is back to where it started.

Is it? I think it's lower than when it started. It certainly is with
any appreciable AOA.

Are there any airfoils that produce lift at an AOA at or below zero?


No, it is a way of looking at downrushing air that has never
contacted the wing.

It doesn't matter whether it contacts the wing or not. The contact is
by proxy (by contacting the other molecules of air that contact...the
wing.) You call it pressure. I agree. Pressure is ultimately
newtonian; I think we agree there too.

But the pressure that supplies the lift is in the air below the wing
whereas it is the air above the wing that washes down.You're
attributing lift to the wrong air.

If he air above the wing washed sideways, and not down at all
you'd still get lift as the thumbtack, notecard and soda straw
demonstrates. No downwash from the notecard.




It's a floor wax. It's a dessert topping.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.
But it will not move in a manner that conserves momentum.

Yes it will. What will not be conserved is macroscopic kinetic energy.

Right. My mistake.

...

So, are you saying that in the presence of the Earth there is no
net change in the momentm of the basketballs being thrown by the
dribbler and also no net change in momentum of the air molecules
accelerated by the wing?

Averaged over all basketballs and all air molecules, yes, because the
earth acts as a momentum transfer point.


--


FF

I'll tell ya what.
I do admire it.

This is the nicest pair of debaters on the planet!

Polite.
Considerate.
Seeem to take time to read, and understand(!) what somebody wrote.
Patiently explaining their own position.
No yellin.
No screamin.
No ugly name callin.

Archie and Jughead ponder quantum pressure fluctuations.

I do love it so...

Are there any airfoils that produce lift at an AOA at or below zero?

Depends how AOA is defined (I don't know the precise definition). But
if we define it as the angle between the line from split to rejoin
point, and the direction of travel (or relative wind), then I think not.

But the pressure that supplies the lift is in the air below the wing
whereas it is the air above the wing that washes down. You're
attributing lift to the wrong air.

It doesn't matter. The molecules collide all over the place and
momentum is moved around (but never lost).

If he air above the wing washed sideways, and not down at all
you'd still get lift as the thumbtack, notecard and soda straw
demonstrates. No downwash from the notecard.

Describe the notecard setup better and I will do the experiment, and
then tell you what I think.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

On Sat, 4 Mar 2006 10:14:36 -0700, "Matt Barrow"
wrote:


"Dallas" wrote in message
ink.net...

"cjcampbell"
Actually, he is not. Not in the US, anyway. There is no one by the name
of Sagadevan currently holding a pilot certificate of any kind in the
US

Here he is:
http://www.warpaintofthegods.com/wp/about.cfm

WOW!! What a fruticake!!

Too bad that, or those, mind altering experiences didn't give him a
grasp of rationality and reality.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Jose wrote:
Are there any airfoils that produce lift at an AOA at or below zero?

Depends how AOA is defined (I don't know the precise definition). But
if we define it as the angle between the line from split to rejoin
point, and the direction of travel (or relative wind), then I think not.

ISTR that AOA is defined relative to the chord.


But the pressure that supplies the lift is in the air below the wing
whereas it is the air above the wing that washes down. You're
attributing lift to the wrong air.

It doesn't matter. The molecules collide all over the place and
momentum is moved around (but never lost).

Of course it matters. It is the undisturbed molecules (or minimally
disturbed molecules) under the wing that push up on the wing.

The air flowing over the top of the wing cannot push UP on the
wing.


If he air above the wing washed sideways, and not down at all
you'd still get lift as the thumbtack, notecard and soda straw
demonstrates. No downwash from the notecard.

Describe the notecard setup better and I will do the experiment, and
then tell you what I think.


Take 3 x 5 index card or a similar light small card like a playing
card and push a thumbtack through the center.

Leave the thumbtack in and set the card on a table point up.

Put a soda straw, standing on end over the point of the tack.

Blow through the straw and while blowing lift the straw
straight up.

--

FF

wrote:

A fluid can transmit force without flow in the conventional sense.
That is the basis for hydraulics.

I guess it depends on what you mean by "conventional sense."

Nothing can transmit a force without some deflection. Some molecules in
the fluid have to move in order to generate a force and typically
movement of a fluid, however minute, is flow.


Matt