A very dim lightbulb, but.
I can see where some of the confusion is coming from. When Richard mentioned inertia, I saw where I am having trouble communicating my thoughts.
Going out on a limb here by not waiting for Richard's response to my question:
I was not clear in stating that (in my opinion) the bullet experiences increased drag to to the increased airspeed, BUT NOT FOR THE ENTIRE TRIP DOWN THE GLIDE PATH.
I believe Richard is going to tell me that increase in airspeed (and therefore increased drag) only happens for a very finite and very, very, very short period of time.
Once the inertia of the bullet (which is the same whether or not there is a head or tail wind) overrcomes the force exerted by the increased drag, the bullet reacts the same as it would if there were no head or tail wind.
I agree completely with the above statement. I knew it going in, but was unable to communicate it clearly.
Once the momentum of the bullet in a headwind reaches the momentum it would have had if there were no headwind, drag is EXACTLY the same.
An airplane analogy would be: For a brief period of time when an airplane lifts off the ground in a headwind (at that moment when the wheels first leave the ground), there is increased drag. Once the airplane is stable in flight, the plane never feels the headwind again.
The same would be true with the bullet. It would only take a few miliseconds to overcome increased drag, but that increase in drag is there nonetheless and this is what affects flighttime.
I am sorry if I inferred that I thought there was increased drag all the way to the target. That was never my intention.
Any, hey. If I'm wrong, I can eat crow with the best of them. As I said earlier, I am a STUDENT of the rifle. I am always will to learn something else.
Lisa
And Lisa, here it is (written before I read your post):
What is causing the confusion in my statements and in interpreting others, is that I have not been taking into account the inertia of the bullet.
Inertia is the property of an object which opposes a change in velocity. It is proportional to the objects weight.
When a force, such as drag, acts on an object, how fast it decelerates (slows down) in a headwind, or speeds up (accelerates) in a tail wind, is very dependent on the objects inertia.
Wind shear is a rapid change in the winds velocity. How much force the wind shear exerts on an object is a function of the objects weight, and how much and how fast the wind velocity changed. A light object is not affected by wind shear as much as a heavy object, because a light object has less inertia than the heavy object.
As a bullet leaves the muzzle and proceeds down range it may encounter all sorts of different wind shears (headwind, tailwind, cross wind, updraft downdraft, boil, etc.). These different winds can be steady or gusty.
Assuming there is no wind, the bullet is strictly creating its’ own wind. This wind, or flow of air, is in a direction opposite to the bullets flight and creates a drag proportional to the square of the bullets speed. The bullet slows down due to the force of the drag (F=MA) and takes a certain amount of time to reach the target. During this time, gravity acts to cause bullet drop.
To answer Lisa’s question, a bullet leaving the muzzle into a 100 mph headwind, will immediately experience a large wind shear (an abrupt increase of 100 mph in the wind speed acting on the bullets surface). Because of the bullet’s inertia it cannot immediately slow down. Therefore there is an increase in drag relative to what it would be without the 100 mph headwind. In this case headwind causes an increase in drag.
However, this increase in drag only lasts long enough for the bullet to lose 100 mph in velocity relative to what the speed would have been if there was no headwind. As soon as that happens, the headwind is no longer causing an increase in drag force over and above what it would have been without the headwind.
A light bullet (30 grain 22LR) will lose that 100mph very rapidly as compared to a 300 grain (.338 Lapua Magnum) heavy bullet. This is due to a ten fold difference in the inertia of the two different bullets. The heavy bullet is “bucking” the wind better than the light bullet.
I have no idea, nor does probably anyone else, how quickly the 22 will lose the 100 mph. Maybe it is within the first 10 feet, or maybe it takes all the way to the target. In any event the 300 grain bullet will take a whole lot longer.
The same event will occur if the bullet leaves the muzzle with no headwind or tailwind but encounters a change in wind on its’ way to the target.
Drag does not cause a bullet to drop, gravity does. Drag causes a bullet to take longer to reach the target so gravity has a longer time to act on the bullet.
The statement that drag increases in a headwind, or decreases in a tailwind, is only correct for a wind shear situation (an abrupt change in wind velocity). How much the drag will change due to the wind shear is proportional to how much the wind changed, how fast it changed, and how much the bullet weighs. Very complex, to say the least, as is the flight of the bullet.
From a purely academic standpoint, a very light body, encountering a very small change in wind speed, can change its’ ground speed fast enough to not feel a noticeable increase in drag.
I stand corrected in being wrong to view this question as a bullet already immersed in a headwind (academic environment) without having considered how it got there (real world). In the first case there is no increase in drag, in the real world there is due to wind shear and the bullets inertia.
Ray, I still don’t like the flat out statement made in the book you quoted. A clarification by the authors would have been in order. They should at least address the large difference in drag increase due to the variables of wind velocity amount and rate of change, and bullet weight
Lisa, I hope I answered your question.
Here is the real world:
At the 600 yard range yesterday, the wind was all over the place, doing every dance imaginable. My .260, with a 142 grain bullet, smoked everyone else because they were trying to chase the wind changes with their 22’s and 6mm’s and I was just holding dead on the X and shot a F Class 194-4X (20 shot string). Inertia wins every time.
Richard
What can I say. Richard is right and McDonald & Almgren are wrong.
