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You just defined force yourself, with the qualifier "when unopposed". "When unopposed" is the important bit. F = m.a BUT F is the vector sum of all forces acting on the mass. We can only calculate a force using F= m.a if there is only one force, or all other forces are known. It is very common e.g. for there to be 2 forces perfectly opposed, and therefore acceleration is zero, net force is zero, but significant and measurable force is being applied. An example is standing on a set of scales. The scales measure a force, but there is no change in velocity. If I use a spring compressor and apply a force of 2000 newtons and compress a spring by 50cm, I have applied a force. I have done work, as evidenced by the energy stored in the spring. Where is the mass? Where is the acceleration? We know the value of F, but there are no values for m or a to use in the equation. If the compressor suddenly breaks, we will have mass (the spring and parts of the compressor) and acceleration. F = m.a suddenly applies. Force is the potential to accelerate a mass when unopposed (as you said in your first definition) which is why the units of measurement incorporate mass and acceleration. It does not mean that you can't have force without acceleration - which is what defining force as F = m.a implies: if a = 0, F = 0. To repeat myself, to apply F = m.a, F must be the sum of all forces. The equation doesn't tell you the value of any specific force if there is more than one.

We do not agree. That is an equation about acceleration. You can have a force where acceleration is zero. If you push a box of bricks across the floor at a constant speed, you are exerting a force to overcome friction. You can measure the work done as force x the distance you moved the box. Acceleration (once the box is moving at a constant speed) is zero, but you have a force that must be used if you want to calculate e.g. work and power. Likewise, when an aircraft is straight and level at a constant speed (i.e. no acceleration) we do not say that there is no force acting on the aircraft. If we add all the forces we get zero net force, true, but that does not help us define force. You do like complex explanations. That doesn't really answer "what is a kilogram?", it answers how much is a kilogram. Previously there was a lump of stuff with a mass of exactly 1 kg for comparison, but the problem is any physical object can gain or lose mass to the environment. So that is the answer they came up with for how do you define a kilogram without using something that can physically vary. For our purposes, the mass of 1 litre of water, or the mass of a reference object of 1 kg is almost certainly sufficient. A kilogram is the measurement of mass: how much "matter" is in an object. Effectively a measure of how many protons, neutrons etc. it contains in it's atoms. (Can we ignore relativity please!) Kilogram-weight is a measure of force - the amount of force exerted by gravity on a mass of 1kg on earth. We want to measure kilograms (mass), but scales measure force. Calibrating them in kilogram-weight and calling it kilograms is convenient. We could measure newtons and divide by 9.8, that would be less convenient.

That diagram is a turn not a roll. The force vectors are totally different. Nor is is a diagram of the result where the AOA remains unchanged.

This video shows some interesting instruction on rolls: The whole video is worth watching, but there is discussion on the slow roll at 17:18 and hesitation rolls at 24:30. The description of the hesitation roll is that it is the same as the slow roll, but with the hesitation added. This really dispels the idea that the pilot rolls the aircraft and then corrects the flight path. It is simultaneous aileron, elevator and rudder inputs.

I said lift required was infinite for a turn with 90 degrees of bank. Of course you are right. Lift required trends to infinity as you approach 90 degrees, but at 90 degrees you need to divide by zero: infinity is not the answer, there is no valid answer.

Maybe if you post the answers instead we will have more luck trying to work out the question you want to ask. You introduced the question with a video, that suggests that you are intending to post a question that relates to real aircraft behaviour. Incidentally, the video includes real time G readings which actually show us the lift the wing is producing at each point. Not surprisingly they differ from the "perfect" roll I described. There are limits to how perfectly a pilot can fly, and also limits to what an aircraft is capable of.

That is true if the aircraft is instantaneously rotated around an axis perfectly aligned with the airflow. But it's not real life. In real life, even at maximum roll rate it takes time to go from 0 to 45 degrees. It also depends on the skill of the pilot, but lets assume the pilot can fly the roll perfectly. As the pilot begins the roll the lift vector is pointed to the side, which would begin to turn the aircraft. To prevent the turn, opposite rudder is required and the aircraft is in uncoordinated flight. At 45 degrees, the wing provides half the lift, and the side force on the fuselage due to uncoordinated flight provides the other half. The wing and fuselage produce equal and opposite sideways forces which means the aircraft does not turn. The wing is providing half the vertical lift at a 45 degree angle. That requires less total lift than supporting the whole aircraft at zero degrees bank. To fly it perfectly, the rudder needs to be increased and AOA of the wing decreased as the aircraft rolls from 0 to 45 degrees. That is for a 45 degree coordinated turn, not a roll. A turn is totally different to a roll. In a turn, lift required increases as bank angle increases. In a roll, lift from the wing decreases as bank angle increases. At 90 degrees angle of bank in a roll (knife edge flight) the lift required from the wing is zero. At 90 degrees angle of bank in a turn the lift required from the wing is infinite i.e. a coordinated 90 degree banked turn is impossible.

An AOA indicator that according to the expert you quote "can’t tell AoA" doesn't work.

APenNameAndThatA pointed it out and how many posts did you spend arguing? I knew what you meant and it didn't seem worth worrying about.

Rather than bringing other planets into it, maybe you should re-read what you wrote. You made a simple unit conversion error - switching from kg to newtons without a conversion. 3 newtons should have been 30 newtons, rounding 9.81 to 10.

Someone might have been looking for a higher level of proof than OME declaring himself correct. I think you have misunderstood what Mr Munn wrote - selectively picking out bits that support you. From your post of his reply: We can and do derive AOA much more accurately and reliably from the airspeed indicator. A stopped clock is also correct for a given set of parameters, but like the spirit level AOA you need enough additional references to know when that is that the original reading becomes redundant. That is correct. It displays attitude not AOA, but only in one axis and only in unaccelerated flight. The attitude indicator shows the same and more information more reliably e.g. it isn't affected by acceleration.

There's a chance to earn $500 for your favorite charity then. (The offer only applies once i.e. the first person)

You attack and insult people who disagree with you, but will only stand behind your posts with angry words. Never mind, my offer still stands. If you find someone with a degree in physics or aeronautical engineering who will publicly say you are more correct in the instances where I have disagreed, not only can you point to it and say I was wrong but you will earn $500 for your favorite charity. That is how confident I am in my information - I will put up $500 to zero to back it. (I have taken a copy of the thread for the purposes of the offer, in case moderators decide to moderate.)

I am becoming more confident I was right earlier: 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?

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

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.

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.

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

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. 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.

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

Two things are glaringly missing: Physics, and aerodynamics past PPL level. I don't see any more qualifications than many other posters to the site. The traffic accident reconstruction is interesting, it maybe explains some of the errors e.g. the reference to ballistic trajectories. A car that leaves the ground in an accident will follow a ballistic trajectory. A ballistic trajectory in an aircraft is unusual e.g. the Vomit Comet, some aerobatics perhaps, or floating dog videos. A stalled aircraft will not follow a ballistic trajectory. Nor will an aircraft when you reduce power. Most of OME's errors are year 11 physics and BAK level stuff. Your Dynon, Garmin etc. EFIS has all that information. They can't use it to generate AOA information. They require additional information e.g. pressure sensors at an angle to the airflow for AOA. More advanced systems use a vane on the outside of the aircraft, i.e. direct reading of AOA.

OK... lets say we climb an aircraft at 60 knots with an angle of climb of 5 degrees. Then we reduce power to descend at an angle of 5 degrees at the same 60 knots. The airspeed is the same. The angle of attack must therefore be the same. What do you expect your indicator to show? I would expect it to show a change of 10 degrees, where the correct indication would be a change of zero.

There's the problem. It won't work in a descent, which is an important part of circuit work. If the reading is totally different in a climb and in a descent at the same AOA, it is not an AOA indicator. You need to measure AOA in relation to the aircraft. But the spirit level reading is influenced by both gravity and the acceleration of the aircraft. Gravity moves around relative to the aircraft as the attitude changes. A spirit level is in principle the same mechanism as your inner ear. We know that the inner ear is unreliable and subject to illusions due to acceleration etc. Your proposed AOA indicator suffers the same problems.

Because that is the most efficient angle of attack for cruise flight. Straight and level is not an angle of attack. The point is climbing and descending is not a result of more or less left. When climbing, lift is less than in straight and level flight. It will descend. It is hopefully not a ballistic trajectory. The actual behaviour is typically adjusted by modifying the thrust line of the engine in the design/testing phase. Climb comes from excess power. Best climb speed is maximum excess power. Descent comes from insufficient power. So your aerodynamics is basically PPL? Why do you think that prevents people questioning your information?

I would say it's about 95% standard mechanics, 5% major errors or misunderstandings. An example from the previously linked Social Australia post (where we can't comment) : In fact, inertia is mass. An object has the same inertia with or without gravity. Assuming the force is lifting the object against gravity (it is not centripetal force unless the object is travelling in a circle), the object will move when the tension exceeds the force of gravity. How fast it accelerates depends on the inertia (mass) of the object and how much the tension exceeds the force of gravity, i.e. the net force.