Nick, If nothing else you have made me do some study... Good thing I have a couple of days off.
You said..
The aircraft is immersed in a fluid, and as long as its conditions are not changed with respect to that fluid, it will perform identically regardless of its direction in that fluid.
Now if Velocity is a vector quantity which refers to "the rate at which an object changes its position." The air has one velocity and the aircraft has another eg. air- 50 knots from the north aircraft-100 knots(gps) to the north... differential 150knots relative(airspeed) & if
Acceleration is a vector quantity which is defined as "the rate at which an object changes its velocity." The aircraft turns and tracks south the difference in relative motion is now 50 knots so at least 1 of 2 things must happen, either the airspeed reduces or the aircraft accelerates to 200 knots(GPS).
Back to Newtons first law
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Therefore if the airspeed stays constant and the thrust stays constant the acceleration of the aircraft would come from an unbalanced force which must be the reduction of Air Resistance Force.
Newtons second law
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
Air Resistance Force
Fair
The air resistance is a special type of frictional force which acts upon objects as they travel through the air. Like all frictional forces, the force of air resistance always opposes the motion of the object. This force will frequently be neglected due to its negligible magnitude. It is most noticeable for objects which travel at high speeds (e.g., a skydiver or a downhill skier) or for objects with large surface areas.
Flingwing If as you say
it doesn't matter what the speed of the air is. The helicopter (or bird, or balloon) will not know or be affected by the speed of the airmass. Airspeed is airspeed - if you fly 50 KT airspeed surrounded by a 50 KT southbound airmass, the helicopter will not handle, respond, or perform any differently than if the airmass was not moving.
Why is inertia only important if the velocity of the air changes... surely if ANYTHING changes you have changed the relative velocity between the aircraft and the air.
you also say
Airspeed is airspeed - if you fly 50 KT airspeed surrounded by a 50 KT southbound airmass, the helicopter will not handle, respond, or perform any differently than if the airmass was not moving.
And you are right... but that is not ALL we are talking about we are talking about going from travelling 50 kt in one direction to travelling 50 kt in the other direction. Assuming that aircraft performance, lift or aerodynamics are not affected by compass heading it makes no difference to the laws of physics whether you encounter a tailwind of 50 kt by turning the aircraft or by turning the wind (windshear) accept for the time spent in the turn.
Last edited by overpitched; 25th Feb 2004 at 10:13.