Talk:Aircraft flight mechanics
|WikiProject Aviation||(Rated Start-class)|
|WikiProject Physics / Fluid Dynamics||(Rated Start-class, Mid-importance)|
Under the "Airplane Control and Movement" paragraph, who is this Andrew Davis who is alleged to be "the creator of the first real airplane"?
No if anything flight controls should be merged with this, while this is hardly complete, the dynamics of flight is a more fundamental subject than flight controls. What I mean is flight controls could be a sub topic of the Aircraft flight mechanics main topic.Pubuman 21:37, 8 August 2006 (UTC)
- I agree. Dynamics of Flight is broader than Flight Controls. Jonathon Barton 03:01, 23 October 2007 (UTC)
Also...what's the deal with the bottom section, claiming that the most common explanation (like, the one they teach you in Flight School) of "How Things Fly" is false, yet, not offering a single documented example of HOW it's false, or even what the alternative explanation of what the physics of flight really are. Jonathon Barton 03:01, 23 October 2007 (UTC)
- This article has a lot of problems, including this one. That section really doesn't belong in this article. If you're seeking an explanation as to the content of that section, checkout lift (force), and specifically the Equal transit-time fallacy. As to the article, if I have some time this weekend, I'll try to fix it up some. User:!jimtalk contribs 08:31, 9 November 2007 (UTC)
The two paragraphs under Aerodynamics cover the equal-transit time theory. This has no relevance to Aircraft flight mechanics and I believe it should be deleted.
The equal-transit time theory already has extensive coverage in at least three places:
- Equal transit-time
- Misunderstandings about the generation of lift
- List of works with the equal transit-time fallacy
Straight and Level Flight of Aircraft
In straight and level flight, lift is approximately equal to weight. In addition, if the aircraft is not accelerating, thrust is approximately equal to drag.
This becomes less true as angle of attack increases.
In straight, climbing flight, thrust exceeds drag, and lift is less than weight. At first, this seems incorrect because if an aircraft is climbing it seems lift must exceed weight. When an aircraft is climbing at constant speed it is its thrust that enables it to climb and gain extra potential energy. Lift acts perpendicular to the velocity vector so lift is unable to alter the aircraft's potential energy or kinetic energy. This can be seen by considering an aerobatic aircraft in straight vertical flight - one that is climbing straight upwards (or descending straight downwards.) Vertical flight requires no lift! When flying straight upwards the aircraft can reach zero airspeed before falling earthwards - the wing is generating no lift and so does not stall.
In straight, descending flight thrust is less than drag, and lift is less than weight. In turning flight, lift exceeds weight and produces a load factor greater than one, determined by the aircraft's angle of bank.
In straight, climbing flight, thrust exceeds drag, and lift is less than weight
This is not necessarily true. Lift could be greater than weight. You don't know without doing the calculations. Nor do you know the relationship between thrust and drag. You could be decelerating, in which case thrust might exceed drag. You could, for example, accelerate to a high speed and cut the engine power back. You'd then be decelerating, thrust would be less than drag, but your velocity could be high enough that your lift was greater than your weight, and you'd be in straight, climbing flight.
so lift is unable to alter the aircraft's potential energy
This is not correct. The vertical component of lift alters the aircraft's potential energy, as do gravity and the vertical components of thrust and drag. Similarly, lift alters the aircraft's kinetic energy because it provides acceleration perpindicular to the plane of the wings. In a climb, this generally enhances the vertical component of thrust and reduces the horizontal component of thrust, thus altering the net kinetic energy change resulting from the forces acting on the aircraft. Also, the wing can generate lift in vertical flight, so long as there is airflow over the wing. There seems to be some confusion here between lift as defined aerodynamically and lift meaning something like "force acting perpendicular to the earth and away from it."
In straight descending flight thrust is less than drag, and lift is less than weight
If thrust were less than drag, the plane would stop flying and fall out of the air (eventually), as the only way to maintain sufficient flying airspeed is to descend. It's not clear what "straight" means here -- but it seems to be "level," implying the plane's longitudinal axis is parallel to the ground. Another meaning would be "not turning." In level, descending flight, lift is less than weight, but you know nothing about the relationship between thrust and drag. You could be accelerating and descending, so long as the lift was not greater than the weight. Lift does not always act perpendicular to the ground and thrust does not always act parallel to it. So, each will likely have components both perpendicular to and parallel to the ground.
In turning flight, lift exceeds weight and produces a load factor greater than one, determined by the aircraft's angle of bank.
Lift does not necessarily exceed weight in a turn. An airplane could fly in a circle with lift less than weight, particularly if it had a very powerful engine. The turning force required in a circle is proportional to the square of the aircraft's velocity divided by the radius of the circle, so it is possible to turn in a large circle using very little force, particularly if the aircraft has a low stall speed and is flying slowly. If the engine can provide a lot of vertical force through thrust, very little lift is required. This is how air-to-air missiles generally work. They get little or no lift from their wings (which they usually don't have)and bodies, but rely on high thrust-to-weight to keep the missile in the air and control it (with the aid of fins). So, for example, a heavy missile like a Sidewinder can turn even though its weight far exceeds the lift provided by its wings and body. Having said all that, the statement is probably correct for most light private planes in most reasonable flight profiles. It's just not true generally. Even at that, the load factor is determined primarily by the aircraft's speed (velocity) and the position of the horizontal stabiliser (turn radius), not the bank angle. As said above, the acceleration is the square of the velocity divided by the radius of the turn. If you doubt that, just think about a "turn" where you have no bank angle, but accelerate (by adding power) and pull back on the stick. You'll feel flattened into your seat by the same inertia that you'd feel in a banked turn (plus a gravity component). If you now think of that, but put in a 30-degree bank, you'll have a banked turn. The only thing that will change is the direction of the forces that your body feels because your body position will have changed relative to gravity.
- Hi NZAero. Some of your observations are correct because the article made statements based on unaccelerated flight (constant airspeed) but without making that clear. I have amended the offending statements to make it clear that the statement is based on unaccelerated flight.
- You wrote that it isn't clear what straight flight means. Straight flight is flight in a straight line. (That could be level flight, climbing flight, descending flight, or even vertical flight, but the essential characteristic is that it is flight in a straight line.) The opposite of straight flight is turning flight. Flight at constant altitude is level flight.
- You wrote that if thrust were less than drag the plane would stop flying and eventually fall out of the air. Consider a glider. It has no engine and therefore never has any thrust, but gliders don't stop flying and don't fall out of the air. Because gliders have no thrust they can't fly level at constant airspeed or climb at constant airspeed in a stationary atmosphere. Gliders can fly level and climb, all at constant airspeed, if the atmosphere is rising such as occurs in thermals, lee waves, and up the sides of mountains, hills and ridges. Dolphin51 (talk) 11:59, 19 September 2009 (UTC)