Engine hesitation?

Skip Miller said:
fixed that for you. The molecules themselves do not change size.

-Skip
Click to expand...

If the molecules are farther apart, what's between them? Vacuum?

No, they swell just as any other molecule.
 
Tom-D said:
If the molecules are farther apart, what's between them? Vacuum?

No, they swell just as any other molecule.
Click to expand...
The molecules themselves don't change size but the density of molecules does. Here's a good explanation.

http://www.grc.nasa.gov/WWW/k-12/airplane/fluden.html

For solids, the density of a single element or compound remains fairly constant because the molecules are bound to one another. For example, if you found a pure gold nugget on the earth or you found a pure gold nugget on the moon, the measured density would be nearly the same. But for gases, the density can vary over a wide range because the molecules are free to move. Air at the surface of the earth has a very different density than air 50 kilometers above the earth. An interactive simulator allows you to study how air density varies with altitude.
Click to expand...
 
Everskyward said:
The molecules themselves don't change size but the density of molecules does. Here's a good explanation.

http://www.grc.nasa.gov/WWW/k-12/airplane/fluden.html
Click to expand...

So, if they farther apart, what goes between them?

The molecules of a gas are not attached to each other, They are free to float in the mass, and cam readily mix with other gasses. and a gas will expand and contract at a greater rate than any other matter.

But the space between each molecule must be filled with some thing, So if the molecule of a gas doesn't expand, how does the gas get larger?

1 CC of O2 will weigh less at 100 degrees than one weighed at -40.

That means we have less O2 to burn at 100 degrees than we do at - 40. thus as the temp rises we go rich because the fuel transfer will be the same, unless the pressure changes.

Remember O2 is the only gas supporting combustion in the cylinder, all other gasses in the mix, simply get heated,

Pressure effects density and heat effects density but pressure effects the carb fuel transfer at two places, at the same rate, so pressure does not effect the fuel transfer as much as the heat will.

Also the fuel expands with heat too, as your reference pointed out, but it will not expand at the rate a gas will. so, there is a unbalance there too.
 
Quote from your reference.

" . Air at the surface of the earth has a very different density than air 50 kilometers above the earth. An interactive simulator allows you to study how air density varies with altitude. ""

That speaks to only a pressure difference.

and DA is a reference to HEAT AND PRESSURE.
 
From http://www.grc.nasa.gov/WWW/k-12/airplane/pressure.html

we read:


[FONT=Arial, Helvetica, sans-serif]Molecular Definition of Pressure[/FONT]
[FONT=Arial, Helvetica, sans-serif]From the kinetic theory of gases, a gas is composed of a large number of molecules that are very small relative to the distance between molecules. The molecules of a gas are in constant, random motion and frequently collide with each other and with the walls of any container. The molecules possess the physical properties of mass, momentum, and energy. The momentum of a single molecule is the product of its mass and velocity, while the kinetic energy is one half the mass times the square of the velocity. As the gas molecules collide with the walls of a container, as shown on the left of the figure, the molecules impart momentum to the walls, producing a force perpendicular to the wall. The sum of the forces of all the molecules striking the wall divided by the area of the wall is defined to be the pressure. The pressure of a gas is then a measure of the average linear momentum of the moving molecules of a gas. The pressure acts perpendicular (normal) to the wall; the tangential (shear) component of the force is related to the viscosity of the gas.
[/FONT]


Air molecules generate pressure by colliding with each other, not by molecular expansion. When molecules get cold they move less and generate less pressure. All molecular activity stops at absolute zero.


Reading about quantum mechanics will blow the minds of most of us. The deeper the scientists get into the structure of the atom, the more bizarre it gets. We used to talk about the orbits of electrons about the nucleus, but they tell us now that electrons don't orbit; we don't know what they do. Atom-smashing and analyzing equipment seems to indicate that all these particles are nothing but little packets of energy; they're not matter at all, and the desk my computer sits on is nothing but these tiny bits of energy separated by relatively enormous spaces, similar to the distances between the sun, planets, and the rest of the universe. It's not the solidity of the desk that supports my computer but the force fields between subatomic particles, atom, and molecules. Yes, Tom, it's mostly space between molecules.


Dan
 
Tom-D said:
DA is a reference to HEAT AND PRESSURE.
Click to expand...
Right, and here from the FAA Glider Flying Handbook is an explanation of the effect of heat on density altitude.

attachment.php


The molecules get farther apart, they don't expand.
 

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Physical chemistry course was more than twenty years ago for me and I'm going from memory here, but isn't the temperature of a gas an indication or measure of the velocity of the molecules?

As to molecules expanding, well maybe only slightly. If the gas is hot enough to glow then obviously electrons are changing orbitals and emitting photons. I think that's right anyway...
 
Clark1961 said:
As to molecules expanding, well maybe only slightly. If the gas is hot enough to glow then obviously electrons are changing orbitals and emitting photons. I think that's right anyway...
Click to expand...
If the gas is hot enough to glow I don't think I want to be flying through it.... :eek:
 
Everskyward said:
Right, and here from the FAA Glider Flying Handbook is an explanation of the effect of heat on density altitude.

attachment.php


The molecules get farther apart, they don't expand.
Click to expand...

That theory is a false, because it will not enplane how the molecules move apart with out something filling the gap.

But in effect,both theories produce less O2 in the cylinder, resulting in a richer mixture.

My contention is that heat has a greater effect on mixture than atmospheric pressure. Simply because we are only dealing with 14.7 PSI (ISD) at MSL, and that pressure effects both the bowl vent and the venturi in the same manner. thus as you climb, the pressure at both places is the same, but heat will cause less O2 to enter the cylinder and cause a richer mixture.

Temperature being the same during the climb (not a reality) the loss of horse power will be due to the loss of manifold pressure.

Temperature rising across a flight at the same altitude, HQ remaining the same (not a reality) will cause the mixture to go richer.
 
Dan Thomas said:
From http://www.grc.nasa.gov/WWW/k-12/airplane/pressure.html

we read:


[FONT=Arial, Helvetica, sans-serif]Molecular Definition of Pressure[/FONT]
[FONT=Arial, Helvetica, sans-serif]From the kinetic theory of gases, a gas is composed of a large number of molecules that are very small relative to the distance between molecules. The molecules of a gas are in constant, random motion and frequently collide with each other and with the walls of any container. The molecules possess the physical properties of mass, momentum, and energy. The momentum of a single molecule is the product of its mass and velocity, while the kinetic energy is one half the mass times the square of the velocity. As the gas molecules collide with the walls of a container, as shown on the left of the figure, the molecules impart momentum to the walls, producing a force perpendicular to the wall. The sum of the forces of all the molecules striking the wall divided by the area of the wall is defined to be the pressure. The pressure of a gas is then a measure of the average linear momentum of the moving molecules of a gas. The pressure acts perpendicular (normal) to the wall; the tangential (shear) component of the force is related to the viscosity of the gas.
[/FONT]


Air molecules generate pressure by colliding with each other, not by molecular expansion. When molecules get cold they move less and generate less pressure. All molecular activity stops at absolute zero.


Reading about quantum mechanics will blow the minds of most of us. The deeper the scientists get into the structure of the atom, the more bizarre it gets. We used to talk about the orbits of electrons about the nucleus, but they tell us now that electrons don't orbit; we don't know what they do. Atom-smashing and analyzing equipment seems to indicate that all these particles are nothing but little packets of energy; they're not matter at all, and the desk my computer sits on is nothing but these tiny bits of energy separated by relatively enormous spaces, similar to the distances between the sun, planets, and the rest of the universe. It's not the solidity of the desk that supports my computer but the force fields between subatomic particles, atom, and molecules. Yes, Tom, it's mostly space between molecules.


Dan
Click to expand...

That's the new error thinkers explanation of " PASCALS LAW SIMPLY STATED, IS: “PRESSURE IN AN ENCLOSED CONTAINER IS TRANSMITTED EQUALLY AND UNDIMINISHED TO ALL PARTS OF THE CONTAINER AND ACTS AT RIGHT ANGLES TO THE ENCLOSING WALLS.”

and if the pressure becomes unequal, the container will move in the opposite direction. (rocket engine)
 
Tom-D said:
That's the new error thinkers explanation of " PASCALS LAW SIMPLY STATED, IS: “PRESSURE IN AN ENCLOSED CONTAINER IS TRANSMITTED EQUALLY AND UNDIMINISHED TO ALL PARTS OF THE CONTAINER AND ACTS AT RIGHT ANGLES TO THE ENCLOSING WALLS.”

and if the pressure becomes unequal, the container will move in the opposite direction. (rocket engine)
Click to expand...

"Error thinkers"? All I know is that the guys who come up with this stuff have some really fancy, expensive machinery to test their theories and they publish what they find. I read what they find. I am in no position to challenge them and I don't think most of us at POA are either.

Yes, a rocket, or a balloon, or a jet engine all move forward because of differences in pressure.

Dan
 
Tom-D said:
If the molecules are farther apart, what's between them? Vacuum?
Click to expand...
Er, yes. If by vacuum you mean "nothing".

In the rarified levels of the uppermost atmosphere, O2 molecules (and the other atmospheric constituents) are not the size of the Astrodome. They are the size of O2 molecules...they're just very far apart from each other, with nothing but "space" or "vacuum" or "nothing" in-between them.

As you descend through the atmosphere, the molecules get closer together. They don't get smaller. At least, not in the sense that you're implying.
 
Tom-D said:
That theory is a false, because it will not enplane how the molecules move apart with out something filling the gap.
Click to expand...

Most of everything is nothing! Literally empty space. A vacuum. Just nothing.

http://education.jlab.org/qa/atomicstructure_10.html

What is between the Earth and the Sun? Not much. A few hydrogen nuclei every now and then, but otherwise its pretty much empty. Same thing between the molecules that make up air.

Air behaves as a mass because the molecules are moving in random directions and bounce off of each other. The more energy they have, the more force they impart to each other.

Trivia question: How fast do the molecules in the air move (on average)?
 
From memory, A&P school late 70s.

If it has a carb and it's not operator error, it could be the accelerator pump (little hydraulic piston inside the carb). Maybe a seal is leaking.

When you open a throttle, low press in the engine draws more air in. More air going through carb throat venturi sucks more fuel out of carb nozzle into engine. If you open it fast and there is no accrelerator pump, there is a lag until the additional fuel makes it into intake manifold.

When you move the throttle fwd fast, a good accelerator pump mechanically squirts a bit of fuel into the throttle body to compensate for the timing lag that occurs.
 
COFlyBoy said:
Most of everything is nothing! Literally empty space. A vacuum. Just nothing.

http://education.jlab.org/qa/atomicstructure_10.html

What is between the Earth and the Sun? Not much. A few hydrogen nuclei every now and then, but otherwise its pretty much empty. Same thing between the molecules that make up air.

Air behaves as a mass because the molecules are moving in random directions and bounce off of each other. The more energy they have, the more force they impart to each other.

Trivia question: How fast do the molecules in the air move (on average)?
Click to expand...

So, what we have is a perfect vacuum in a compressed gas.
 
Tom-D said:
So, what we have is a perfect vacuum in a compressed gas.
Click to expand...

Everything physical is mostly empty space. Space and vacuum are different. Vacuum is a lack of pressure; space is the "boundless, three-dimensional extent in which objects and events occur and have relative position and direction" (Wikipedia). The compressed gas does not have the properties of a vacuum, but there's lots of space in it.

Dan
 
Looks like I opened a can of worms hehe
 
Haha--very nice!
 
The engine does it quite often (Only during or right after application of power though, usually in the pattern) I'm thinking about just asking my A&P to take it around the patch and see what he thinks, jsut to give me some peace of mind
 
I'm still thinking it has to do with the high heat. It never did it in cooler temperatures, and the airplane has lived all of its life in Utah (Until I got it)
 
Tom-D said:
The accelerator pump in the carb is set too high, the engine is running full rich, and when the throttle is advanced the accelerator pump squirts more fuel into the intake and the engine goes way too rich for a moment.
Click to expand...


Yep, at a 5100'DA you need to lean to run well at any phase of operation. It was probably barely running to begin with and as soon as it got the fuel boost from the accelerator pump it went so rich it couldn't burn it and had to clear some fuel first, hence the hesitation.
 
Tom-D said:
That theory is a false, because it will not enplane how the molecules move apart with out something filling the gap.

But in effect,both theories produce less O2 in the cylinder, resulting in a richer mixture.

My contention is that heat has a greater effect on mixture than atmospheric pressure. Simply because we are only dealing with 14.7 PSI (ISD) at MSL, and that pressure effects both the bowl vent and the venturi in the same manner. thus as you climb, the pressure at both places is the same, but heat will cause less O2 to enter the cylinder and cause a richer mixture.

Temperature being the same during the climb (not a reality) the loss of horse power will be due to the loss of manifold pressure.

Temperature rising across a flight at the same altitude, HQ remaining the same (not a reality) will cause the mixture to go richer.
Click to expand...

Nothing need "fill" the gap, and doesn't, that is why the density goes down, because there is less per molecule. When heated the molecules are more energetic bouncing further off each other. You can have a vacuum between molecules, in fact, that is pretty much the condition once you leave the atmosphere. The higher you go the greater the distance between molecules due to decreasing pressure. The hotter you go the greater the distance due to more energy.
 
DavidWhite said:
I'm still thinking it has to do with the high heat. It never did it in cooler temperatures, and the airplane has lived all of its life in Utah (Until I got it)
Click to expand...

There is a definite likelihood that temperature is what caused your problem.
 
kontiki said:
From memory, A&P school late 70s.

If it has a carb and it's not operator error, it could be the accelerator pump (little hydraulic piston inside the carb). Maybe a seal is leaking.

When you open a throttle, low press in the engine draws more air in. More air going through carb throat venturi sucks more fuel out of carb nozzle into engine. If you open it fast and there is no accrelerator pump, there is a lag until the additional fuel makes it into intake manifold.

When you move the throttle fwd fast, a good accelerator pump mechanically squirts a bit of fuel into the throttle body to compensate for the timing lag that occurs.
Click to expand...

Or it could be going too rich, with the same result.
 
Henning said:
Nothing need "fill" the gap, and doesn't, that is why the density goes down, because there is less per molecule. When heated the molecules are more energetic bouncing further off each other. You can have a vacuum between molecules, in fact, that is pretty much the condition once you leave the atmosphere. The higher you go the greater the distance between molecules due to decreasing pressure. The hotter you go the greater the distance due to more energy.
Click to expand...

No matter which theory you subscribe to, both will produce the same result.
 
DavidWhite said:
The engine does it quite often (Only during or right after application of power though, usually in the pattern) I'm thinking about just asking my A&P to take it around the patch and see what he thinks, jsut to give me some peace of mind
Click to expand...

That consistency of behavior indicates a bad accelerator pump on the carb. We get high DAs here in the summer but we don't get hesitation like that due to temp or altitude.

There are two little check-valve balls in the pump, and one might be stuck. If one has a broken spring it can allow the induction air to suck extra fuel at high power settings, causing roughness, and it will also delay the closing of the valve and affect pump operation. The pump plunger has a rubber cup on it that can shrink, crack or split. The pump on many carbs is operated by a tiny pushrod from a bellcrank on the throttle shaft, and the cotter pin retaining the rod can wear out and let the rod fall out.

Is there any hesitation if you open the throttle rapidly on takeoff? Not a good habit to do that, but a good diagnostic tool.

Dan
 
Tom-D said:
That theory is a false, because it will not enplane how the molecules move apart with out something filling the gap.
Click to expand...

The molecules are more widely spaced due to movement of the molecules. Molecules move (for lack of a better term, they vibrate) when hot. In fact, the vibration of the molecules is the *definition* of heat.
The definition of absolute zero temperature is when molecules stop moving.

The movement causes space between the molecules, hence less density.
The size of a molecule does *not* change.
When molecules are vibrating less, the spacing becomes less, and the material becomes more dense.

As for the question of what's between them, the answer is energy. It's the same thing that's between the nucleus and the electrons in their orbit.
 
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