when an airplane is flying how does the speed increase or decrease?

Question

when an airplane is flying how does the speed increase or decrease? does it work on the newtron's 3rd law?

Answer 1

There are a lot of good answers here, Yes - both 1.increasing the throttle and 2. lowering the nose should increase airspeed,
but I think your question was subtley asking how low flying affects airspeed.

I think what you are alluding to is what is called "ground effect". When an airplane or helicopter is low enough (1/2 to 1 wingspan or less for an airplane or 1/2 rotor diameter for a helicopter),
ground effect produces more lift. You are able to have higher acceleration and airspeed as less energy is required for "lift". That is because the hard or liquid surface is pushing back at you, better than a volume of air can.

An aircraft's top speed is actually likely to occur at a higher altitude where the air is thinner, but acceleration in ground effect, is greater than acceleration in level flight at 500 feet. Optimum altitudes are different for each airplane and found in the POH, which is like an owners manual, for each airplane, and are ususally thousands of feet above sea level.

As an aside, pilots have to be careful of getting overconfident with the effects of ground effect in high altitude flying, as airplanes will become airbourne at slower speeds than they will need to keep from wingstall once they get out of ground effect. Big Bear Airport, in California, at 6748 ft. / 2056.8 m, is a prime example http://www.bigbearcityairport.com/ . On a hot day the air is very thing and pilots can take off and then climb a bit into a stall and end up landing in the lake. Talk about soggy sandwiches!

Hovercraft rely on ground effect and could not normally fly higher. The Russians had huge planes that would only fly in ground effect above the water in the Caspian Sea http://en.wikipedia.org/wiki/Ekranoplan . I know of one experienced pilot that was ferrying a small twin engine airplane from Hawaii to California. When one engine went out, he descended to about 5 meters and flew on one engine the rest of the way, sometimes getting a little ocean spray.

P.S. Yes, Newton's law is valid for this. F = ma
There are four forces operating on an aircraft:
Lift, Drag, Gravity, Thrust.
In ground effect, there is more lift because for every action, there is an equal and opposite reaction and pushing on the ground - which can't move, gets more direct reaction than pushing on air particles that can move AND
2. The drag is less out higher altitudes, because of thinner air, there is less friction, so higher altitudes can be optimal.

Unfortunately the engine performs less well, unless it's turbo charged or a jet, so at some point there will be an optimum altitude for speed.

Answer 2

two parts , indicated airspeed and ground speed.

first part: indicated airspeed; speed is increased or decreased by adding or subtracting power. Interestingly even if we have an infinite amount of power available the drag of the aircraft structure will limit the airspeed that can be achieved; this will also be variable in the altitude that full power can be maintained. another limiting factor here is the structural strength of the airframe.

second part: ground speed, this will take into account tail wind or headwind components. A wind component will not add any airframe stress and is free speed in the aircraft's movement over the surface. An aircraft operating at it's maximum altitude that will allow the engine to still develop full power will be in a thinner atmosphere of air allowing the plane to attain a higher airspeed. The indicated airspeed will need to be corrected for temperature and pressure altitude to determine what the actual airspeed is.

This all assumes level flight; diving the aircraft will achieve more speed to the point that the aircraft's maximum structural speed is reached.

It all made the engineers start thinking Hmmmmm......retractable gear.......flush riviets.......winglets........controlable pitch prop......

Honestly....if you had to sit in the cockpit and dissect the principles of flight and laws of physics; you aren't going to be flying the airplane. The key is understand the design; be familiar with the aircraft and fly it by the numbers.

Answer 3

Yes it works on Newton's third law: every action has an equal and opposite reaction.

But what causes that action in the first place?

That is where we go to Newton's second law: The acceleration of an object is directly proportional to the force applied to it and inversely proportional to the mass of the object.

A = F/M

Acceleration is increasing speed, so we need a force. Rewriting the equation we get F = ma or force equals the mass of the object times the acceleration of the object.

So we need to accelerate something if we are going to accelerate out aircraft (action, reaction).

Propellers and jet engines accelerate air. Since air is much lighter than our aircraft we must accelerate a lot of air to a high velocity. Propellers take a large mass of air and accelerate it a relatively small amount while jet engines take a small amount of air and give it a large acceleration. This is the action.

The reaction is the aircraft speeds up proportionally to how much force (thrust) is pushing it forward. Well, almost.

Drag is air resisting the aircraft movement. It increases the faster the aircraft goes until it balances the thrust force.

So to speed up, we make sure our thrust is greater than drag. To slow down, we can reduce our thrust to be less than drag.

Gravity also exerts a force on the aircraft (equal to the mass of the aircraft times the acceleration due to gravity). If we climb, gravity will aid the drag in slowing the aircraft down. If we descend, it will aid the thrust in speeding the aircraft up.

Answer 4

Airplanes fly thanks to their wings. The wings are long and flat, and they are tilted slightly upwards—that is, the front edge (the edge that faces forwards into the wind) of the wing is a little bit higher than the rear edge. When a wing is tilted like this, air passing over the top of the wing speeds up, and air beneath it slows down. This causes the air to twist downwards as it leaves the rear edge of the wing. Thus, the wing effectively pulls air above it downwards, creating an invisible swath of air that drifts downwards behind the airplane after it has passed. The wing has to exert considerable force on the air in order to pull it downwards like this. The air is actually quite heavy, so it resists being pulled downwards, and it tries to push the wing upwards instead. Thanks to that, the wing is able to fly. It pulls air down, and the air pushes it up. The math and physics that describe the details of this are complicated, but that's the basic idea. There are a lot of misconceptions about how airplanes fly, even among some pilots. It's not a question of pressure, or air meeting behind the wing, or things like that. It's purely a question of Newton's Third Law of Motion: when the wings pull air down, the air pushes the wings up. For every action, there's a reaction. No air moving down means no wing going up. But as long as the wing is tilted slightly upwards, it will produce lift. The shape of the wing isn't very important, either—a wing is usually more curved on top to reduce air resistance and improve some of its flying characteristics, but it doesn't have to be curved to produce lift. Even a barn door will produce lift if you push it forwards through the air and tilt it upwards a bit. Try holding a wooden board like that in a strong wind, and you'll feel it trying to move upwards.

Answer 5

there are two things to consider when dealing with the speed of the aircraft: drag and thrust. now the thrust is the foward motion which is created by the planes jet engines. the drag is the force acting opposite the thrust (towards the back of the plane)

so in order for the plane to increase speed, the thrust should exceed the drag. and yes it does work on newtons 3rd law of motion. (well the jet engine does, the air is 'pushed' out the back of the engine.)

Answer 6

A couple of different ways. Primarily, you add thrust, which overcomes drag, and increases speed. Also, you can trade altitude for airspeed, but this only works over limited distances (until you run out of altitude).
Newton's Third Law applies to lift, not necessarily to speed, although efficiency of lift allows greater speed increases by reducing drag

Answer 7

The most effective way to change speeds in a plane is by raising or lowering the nose. (large and practically instantaneous response). Changes in power act only VERY slowly to change speed.

It relys on Newton's 3rd law in that by raising or lowering the nose, you are applying a (thrust or drag) force equal to the weight of the plane times the sine of the angle of climb or descent. The weight of the average plane at cruise is about 15 times the drag, so it doesn't take a real big angle to get a lot of force in the longitudinal direction.

Answer 8

When a plane is flying in a straight level you push the throttle forward to increase the engine rpm to speed up and the opposite to slow down

Answer 9

there are several ways to increase or decrease an aircraft speed, one is to simply increase or decrease the engine power, two, you can take the nose a little bit up to create some drag to decrease the speed, and third you can go along with the wind direction to increase your speed or go against the wind direction to decrease the speed

Answer 10

Partially newtons 3rd law, but Also Brenulli's Principle. It needs to increase to combat the gravitational pull. Engine Specs will increase the speed, coupled with the pressure of the flight level.