Turns at low IAS

[old man emu]

2 hours ago, Thruster88 said:

I am guessing

Why the hell should I answer whether a guess is right or not? You've given no reasons why you come to your guessed value, not have you set the conditions for when the observation of the reading was made. If you slam the throttle lever to the wall, does you plane immediately try to sit on its bum?

 

2 hours ago, APenNameAndThatA said:

if he aircraft was flying nose down 30 degrees, steadily, what would the AOA meter say the AOA was?

I'm glad that you said "steadily", which implies uniform motion. Everything should be in equilibrium. Also you say "nose down", so I take it that your reference line is the longitudinal axis of the aircraft. That's nice and clear. However, you don't say if the aircraft is flying steadily earthwards at an angle of 30 degrees or is trying to fly "parallel" to the earth's surface with the nose 30 degrees down. I am going to answer for the first case.

 

If you followed my installation instructions the longitudinal axis of the spirit level would be at +4 degrees to the aircraft's longitudinal axis. Since the AoA is the angle between the chord line and the direction of airflow with reference to the longitudinal axis of the aircraft, and the chord line doesn't know up from down, then the ball or bubble would be at +4 degrees. The ball or bubble is travelling down the slope at the same velocity as the rest of the aircraft.

[APenNameAndThatA]

Okay. If you hold a spirit level at 30 degrees (same as the aircraft) and move it at 30 degrees (same as the aircraft) what does it say? 

[jackc]

I gave up long ago, too hard for me.  I simply obey the laws of flight and gravity......

[old man emu]

I've just read through this thread from the start. It has drifted more than Pangea, so I've decided this:

 

That's Golden Advice, which I will happily accept.

[aro]

18 hours ago, old man emu said:

For your benefit I know I should have listed all the things that would alter that trajectory from the theoretical, but there are other readers here.

It's not nitpicking to point out that aeroplanes have wings and as a result the trajectory is nothing like ballistic - even when stalled. Some aircraft have lost their wings in flight - they will follow a ballistic trajectory. You might think the difference between aircraft with and without wings is a nitpick, I do not.

 

18 hours ago, old man emu said:

I had to use trigonometry as a basic tool. Admittedly, it was at the simple end of the spectrum, but so is the basic physics of flight.

Physics of flight are not as simple as you seem to think.

 

18 hours ago, old man emu said:

Most physicists will say that, in relation to the planet, the acceleration due to gravity is a vector directed towards the centre of the planet. Since the aircraft and the planet are as one with respect to astronomic bodies, one can discount the effects of the gravitational forces exerted by those bodies.

I said relative to the aircraft. In a climb, the centre of the planet is towards the rear of the aircraft - and  gravity slows you down. In a descent, the planet and gravity is towards the front, and causes you to speed up. In a 30 degree banked turn it is out to the side. The gravity vector moves around relative to the aircraft.

 

18 hours ago, old man emu said:

Inertia, is a property of an object by which it opposes any Force to put it in motion or, if it is moving, to accelerate it by changing the magnitude or direction of its velocity. Inertia is a passive property and does not enable a body to do anything except oppose forces. A moving body keeps moving not because of its inertia but only because of the absence of a force to slow it down, change its course, or speed it up. In that case, the object has zero inertia. If the object is subjected to the Force of gravity, then it attains inertia. If you take the case of an object motionless on a surface, then it also has no inertia because the force of gravity is mathematically negated by the resistance of the surface to further movement of the object.

 

This is fundamentally wrong. An object with mass does not have zero inertia. Mass (kg) can be described as a measurement of inertia.

 

If you push your car and it is hard to get it moving, that is inertia. As you keep pushing, it gains momentum. When you stop pushing and it keeps moving that is inertia. When it hits the car in front and they end up travelling locked together at 1/2 the speed, that is momentum.

 

Momentum is a quantity that can change and be transferred from one object to another. Inertia does not change.

Edited March 8, 2021 by aro

[old man emu]

2 hours ago, aro said:

It's not nitpicking to point out that aeroplanes have wings and as a result the trajectory is nothing like ballistic

It's nit-picking when aro ignores the rider I put on my statement that if an aircraft was travelling on a straight path, neither climbing nor descending and that the excess of the Thrust force over all Drag forces in allowing the aircraft to maintain a constant airspeed, then in theory it would descend in a ballistic trajectory BUT in practice an aircraft will not follow the ballistic trajectory because there are sources of other forces, such as indeed Lift generated by the wing and drag from a stopped propeller adding to the inherent drag of the aircraft.

 

If, in an attempt to appease the nit-pickers, I add riders, then it should be courteous of the nit-pickers to also read and understand the riders.

2 hours ago, aro said:

This is fundamentally wrong.

 aro is referring to my statement that an object moving with a constant velocity - and velocity can have a value of zero - has no inertia. This comes from Newton's First law, since an object will only react to the imposition of an external force. Inertia is resistance to external forces that want to result in an alteration to current rate of movement. In the case of an object moving at a constant velocity, one would be quite correct that the object possesses potential  inertia due to its mass. It's not until an external force acts on the object that acquires inertia.

 

So I say to aro, "Prove it! With references".

 

DAMN and BLAST!  I ignored the advice.

[aro]

1 hour ago, old man emu said:

It's nit-picking when aro ignores the rider I put on my statement that if an aircraft was travelling on a straight path, neither climbing nor descending and that the excess of the Thrust force over all Drag forces in allowing the aircraft to maintain a constant airspeed, then in theory it would descend in a ballistic trajectory

The flight path is so different from a ballistic trajectory that it is unreasonable to describe it as ballistic, no matter what riders you apply. It's the difference between an aircraft and a cannonball.

 

1 hour ago, old man emu said:

aro is referring to my statement that an object moving with a constant velocity - and velocity can have a value of zero - has no inertia. This comes from Newton's First law, since an object will only react to the imposition of an external force. Inertia is resistance to external forces that want to result in an alteration to current rate of movement. In the case of an object moving at a constant velocity, one would be quite correct that the object possesses potential  inertia due to its mass. It's not until an external force acts on the object that acquires inertia.

 

So I say to aro, "Prove it! With references".

See Q1 answers c, d, e, f, g, i here:

 

https://www.physicsclassroom.com/reviews/Newtons-Laws/Newtons-Laws-Review-Answers-1

 

• Mass is a measure of an object's inertia.
• Any object with mass has inertia.
• Mass is a measure of an object's inertia. Objects with greater mass have a greater inertia; objects with less mass have less inertia.
• The speed of an object has no impact upon the amount of inertia that it has. Inertia has to do with mass alone.
• Inertia (or mass) has nothing to do with gravity or lack of gravity. In a location where g is close to 0 m/s/s, an object loses its weight. Yet it still maintains the same amount of inertia as usual.
• inertia is unaffected by alterations in the gravitational environment. An alteration in the g value effects the weight of an object but not the mass or inertia of the object.

[facthunter]

Mass is the amount of "stuff" in an object. Weight is the force a gravitational system  imposes on the considered object.  The gravitational pull  reacts to the masses of the objects and the distance they are apart. Very distant objects have little PULL. The Moon at 240,000 miles causes earth tidal effect. 

  A body with velocity relative to some datum has momentum. Mass x speed .

  IF the whole thing was happening in a vacuum there'd be no lift or drag and it would behave ballistically. In the  earth gravitation effect the acceleration is 32 ft /sec/sec. Acceleration is the time rate of change of velocity. .Nev

Edited March 9, 2021 by facthunter

[APenNameAndThatA]

17 hours ago, APenNameAndThatA said:

Okay. If you hold a spirit level at 30 degrees (same as the aircraft) and move it at 30 degrees (same as the aircraft) what does it say? 

OME?

 

[old man emu]

Inertia

Meaning: lack of activity or interest, or unwillingness to make an effort to do anything

 

Etymology: 1713, "that property of matter by virtue of which it retains its state of rest or of uniform rectilinear motion so long as no foreign cause changes that state" [Century Dictionary], introduced as a term in physics 17c. by German astronomer and physician Johann Kepler (1571-1630) as a special sense of Latin inertia "unskillfulness, ignorance; inactivity, idleness," from iners (genitive inertis) "unskilled; inactive". Also sometimes vis inertia "force of inertia." Used in 1687 by Newton, writing in Modern Latin. The classical Latin sense of "apathy, passiveness, inactivity" is attested in English from 1822.

 

4 hours ago, aro said:

Mass is a measure of an object's inertia.

Mass is a factor in determining an object's inertia, which is the result of a force accelerating the mass. One must measure the magnitude of the applied force as well as the acceleration that force causes in order to determine the mass of the object, since F=ma, by rearrangement

F/a = m.

 

4 hours ago, aro said:

Any object with mass has inertia.

Any object with mass can exhibit inertia - resistance to acceleration - as a result of the Force applied. It has no inertia until the Force is applied.

 

4 hours ago, aro said:

Mass is a measure of an object's inertia. Objects with greater mass have a greater inertia; objects with less mass have less inertia.

The second sentence is true. Relative to the magnitude of the acceleration achieved. The Force required to accelerate a brick from 0 m/s to 5 m/s is a lot more that the Force required to accelerate a pebble from zero  to 5 m/s.

 

4 hours ago, aro said:

The speed of an object has no impact upon the amount of inertia that it has. Inertia has to do with mass alone.

That's true if an object is moving at a constant velocity where there is no acceleration (v2 - v1)/t. If the velocity changes, there is acceleration, and the only way to change the acceleration is to apply an external force.

 

4 hours ago, aro said:

• inertia (or mass) has nothing to do with gravity or lack of gravity. In a location where g is close to 0 m/s/s, an object loses its weight. Yet it still maintains the same amount of inertia as usual.

Best recognise the correct term, acceleration due to gravitational attraction or "Force of gravity", but we'll shorten it to "gravity". The Force of gravity is an external force that accelerates an object. It is true that with our concept of "weight" if the acceleration due to gravity is zero the value we call "weight" is also zero, despite the presence of mass.  If there is no external force applied to the mass, the mass cannot exert an equal and opposite force (Newton's Third Law). The object has potential to have inertia, but at that time has none. 

 

Compare it to a cup. If the cup is empty, it has the potential to accept liquid. Fill it with water and the cup's potential to hold water is satisfied.

4 hours ago, aro said:

inertia is unaffected by alterations in the gravitational environment. An alteration in the g value effects the weight of an object but not the mass or inertia of the object.

Yes. if the value of the acceleration due to gravitational attraction changes, the value we call "weight" will change. The mass of the object will not change. However, the magnitude of the force required to accelerate the mass by the same amount will differ between the locations where the gravitational attraction differs. We know this from observations of astronauts on the Moon.

 

4 hours ago, aro said:

The flight path is so different from a ballistic trajectory that it is unreasonable to describe it as ballistic, no matter what riders you apply. It's the difference between an aircraft and a cannonball.

When you started to learn Maths in Primary School, did you start at 1 + 1 + 2, or did you go immediately to the square roots of negative numbers? Because that's what you've done by not considering the riders. You've gone from the simple to the complex without accepting that the simple is a starting point.

 

I started with the simplest case where no other factors affecting the motion of the aircraft. Then I said that the simplest case would not be exhibited by an airplane because of a multitude of factors, one of which you identified as being the lift produced by the wings. One thing the cannon ball and the aircraft have in common is the retarding force of of the collisions with particles of air. Another thing is that both objects would cause the formation of vortices, which we know are retarding forces.

[jackc]

Maybe it’s time to start another forum dedicated to the complexities and debate on these subjects?

[aro]

7 minutes ago, old man emu said:

If there is no external force applied to the mass, the mass cannot exert an equal and opposite force (Newton's Third Law). The object has potential to have inertia, but at that time has none. 

You asked for a reference, but did you actually read it? You are rejecting the definitions from physics and substituting your own.

[old man emu]

11 minutes ago, jackc said:

Maybe it’s time to start another forum dedicated to the complexities and debate on these subjects?

What a fine idea, and one that if put into practice would please many here for whom this has become boring. What if I start a thread in the Science section of the sister site?

[aro]

17 minutes ago, old man emu said:

I started with the simplest case where no other factors affecting the motion of the aircraft. Then I said that the simplest case would not be exhibited by an airplane because of a multitude of factors, one of which you identified as being the lift produced by the wings

By that argument my car follows a ballistic trajectory when I drive over the Westgate Bridge, if you ignore the influence of the road surface holding it up. It makes no sense to ignore the lift from the wings.

[old man emu]

9 minutes ago, aro said:

You asked for a reference, but did you actually read it? You are rejecting the definitions from physics and substituting your own.

I'm not substituting my own definitions. I was simply expanding on what you quoted. I have had a look at that reference.

 

From that reference -

Question (d) All objects have inertia.

Answer . (d) True - Bet money on this one. Any object with mass has inertia. (Any object without mass is not an object, but something else like a wave.)

 

Let's skip that bit in the brackets. We won't go into quantum physics.

We have to accept that zero, nothing, nada are acceptable answers in physics. If no Force acts on an object, then F = ma becomes 0 = ma. That's not illogical. It simply means that if no force is applied to a mass, then it will not accelerate (change velocity). The calculated inertia of the object is zero. That doesn't mean that the object cannot obey Newton's Third Law. It just means that there is no external force present for the mass to resist the application of the Force.

[aro]

2 minutes ago, old man emu said:

The calculated inertia of the object is zero.

Inertia isn't a calculated value. Also from that reference:

 

Mass is a measure of an object's inertia.

Inertia has to do with mass alone.

[old man emu]

13 minutes ago, aro said:

By that argument my car follows a ballistic trajectory when I drive over the Westgate Bridge, if you ignore the influence of the road surface holding it up. It makes no sense to ignore the lift from the wings.

It makes no sense to try to explain things to people who have not the mental capacity to contemplate what has been said. 

 

Mea culpa. Mea culpa, Mea maxima culpa. I ignored a multitude of factors that would alter the theoretical ballistic trajectory in real life when I started off with the simplest case. 

[pmccarthy]

This thread is like a Road Runner cartoon.  Both sides think they understand physics, but haven't grasped cartoon physics.

[old man emu]

9 minutes ago, aro said:

Inertia isn't a calculated value. Also from that reference:

 

Mass is a measure of an object's inertia.

Inertia has to do with mass alone.

Inertia is a property of matter. According to Newton's Law of Inertia, an object at rest tends to stay at rest unless acted upon by a force. Likewise, an object in motion tends to remain at that velocity unless acted upon by some force.

 

The concept of an inertial force comes from Newton's Laws of Motion, which can be stated as:

I. Every object in a state of uniform motion—including being stationary—tends to remain in that state of motion unless an external force is applied to it (Law of Inertia).

II. The relationship between an object's mass m, its acceleration a, and the applied or external force F is: F = ma.

III. If a force is applied to an object, there is an apparent equal and opposite reaction or resistance (Action-Reaction Law).

 

That equal and opposite reaction is called the inertial force. It is a factious or pseudo force equal to −F = ma. 

An inertial force resists a change in velocity of an object and equal to and in the opposite direction of an applied force, as well as a resistive force. What that means is that there is no such thing as a unidirectional force or a force that acts on only one object. There must always be two objects involved, acting on each other. One object acts on the other, while the second resists the action of the first.

https://www.school-for-champions.com/science/force_inertial.htm#.YEcUk2gza70

[old man emu]

2 minutes ago, pmccarthy said:

This thread is like a Road Runner cartoon.  Both sides think they understand physics, but haven't grasped cartoon physics.

There's got to be a Physics book here somewhere!

[aro]

15 minutes ago, old man emu said:

That equal and opposite reaction is called the inertial force. It is a factious or pseudo force

Inertial isn't a force, and using pseudo forces or fictional forces to try to define inertia is not helpful.

[old man emu]

The fictitious force F is due to an object's inertia when the reference frame does not move inertially, and thus begins to accelerate relative to the free object.  The fictitious force thus does not arise from any physical interaction between two objects, but rather from the acceleration a of the non-inertial reference frame itself, which from the viewpoint of the frame now appears to be an acceleration of the object instead, requiring a "force" to make this happen.

 

This sounds like double-Dutch, and just as hard to visualise. See if this helps http://cseligman.com/text/physics/fictitious.htm

[aro]

I am becoming more confident I was right earlier:

 

On 07/03/2021 at 6:35 PM, aro said:

I have a growing suspicion that OME is trolling us with deliberately false theories. If so the joke is on us I guess. But it is a bit unfair to student pilots who might be trying to learn this stuff, and unfair to the owner of the site who is trying to create a useful resource.

 

All I can say is that if you want to rely on OME's posts for exams etc, get a second opinion from someone qualified first.

 

In fact that's not a bad idea - how about a challenge?

 

If someone can find a person with a degree in Aerospace or Aeronautical Engineering or Physics who is prepared to be publicly identified and say that based on their knowledge and qualifications, OME is more correct than I am where I have disagreed with him here, I will donate $500 to a charity of their choice.

 

OME: how confident are you about your posts? Are you prepared to take the opposite side?

[old man emu]

Piss off

[Jabiru7252]

Oh dear.....☹️