Originally Posted by FlexibleResponse
Now consider a ballistic bullet fired in a straight line through a multitude of wind velocity changes. When the bullet experiences a headwind or a tail wind change, does the IAS of the bullet remain fairly constant or does the groundspeed remained constant?
Neither. In target shooting, it's all about ballistic coefficient vs velocity - and nothing to do with mass.
Once fired, a projectile's BC (and longitudinal axis stability, which affects BC) - otherwise known as its drag profile - will determine how quickly its velocity and kinetic energy are lost, as its mass remains constant.
A headwind will cause the projectile to strike the target lower, as it has more air mass to cover, more time to reach the target, more time for drag and gravity to act. A tailwind will move the point of impact up. A crosswind will move the POI to the side and down, as it increases the distance the projectile must cover. In all scenarios, the groundspeed differs in relation to nil-wind conditions.
Compare two projectiles of equal mass and velocity, but high and low BC ("pointy" versus "blunt" bullets). The more aerodynamic projectile is less affected by wind (in all conditions), and it's POI does not shift as much . . . which, as you can see, has nothing to do with mass.
Neither does gravity, for that matter - if a feather were as aerodynamic as a bomb, they would both fall at the same speed.
Where I think some are getting confused with mass and inertia is in relation to
changing constants.
Why is a turn into downwind at low level a potential hazard? Because of the wind-direction. No, not the direction of the constant air mass, but the direction of any gusts or other changes in wind velocity (vectors) which are more likely to happen close to the ground due to friction and other variables, and are generally (but not always) in line with the prevailing wind direction.
If you are turning into a constant tailwind at a constant airspeed, and that wind suddenly gusts, your airspeed will instantly decay in direct proportion to the suddenly increasing tailwind component (vector). This is where mass (inertia) affects how long it takes for airspeed to recover and stabilise.
An aircraft in a constant air mass will not suddenly change direction in relation to the earth if that air mass suddenly changes direction. It takes time for the aircraft to accelerate, decelerate or otherwise change direction in line with the new constant (vector) due to its inertia (which has
everything to do with mass).
This is basic aerodynamics that we learned in PPL. Maybe we should all read some Bob Tait?
Bob Tait's Aviation Theory School - Wind Shear - Bob Tait's Aviation Theory School Forums