Parabolic Drag

[RockyMtnMT]

Steve,
Simply put, the link you shared is describing the relationship between lift and drag for an airfoil over a range of angles of attack; the relationship is parabolic. That is, as angle of attack goes up from zero, lift increased faster than drag for a short time, then drag starts to increase much more quickly than lift. Instead of plotting lift against angle of attack and then drag against angle of attack, they plotted lift and drag (coefficients) against one another, which is much less intuitive to follow.

Try it for yourself if you like: put your open hand out the window of your car while driving, and hold it flat. You feel a little bit of drag and no lift. Now start rotating your thumb upwards relative to your pinkie finger. At first you start to feel your hand want to rise (lift), with only a little more force backwards (drag). By the time you get your palm facing into the wind, your hand is producing only drag, with no lift. The relationship of lift to drag you just felt is parabolic - once you rotated your hand too far, it slowly stopped producing more lift and rapidly started producing more drag.

Hope that made sense and helps. While drag is obviously important to bullets, we generally are not trying to produce lift, so this topic may not be especially relevant to your goals as a bullet maker...

Thank you sir. The reason that I posed the question was because another member here stated that parabolic drag was induced by mono bullets due to their lower material density. I had never heard of such a thing and when I asked for clarification in the thread I was being told that I was out of line, for lack of better terms, so I started this thread to see if there was even such a thing. I now know that it has nothing to do with bullets let alone what they are made of. I posted the correction, and that went about as well as asking for clarification.

Appreciate the help.

 

[dfanonymous]

G

Thank you sir. The reason that I posed the question was because another member here stated that parabolic drag was induced by mono bullets due to their lower material density. I had never heard of such a thing and when I asked for clarification in the thread I was being told that I was out of line, for lack of better terms, so I started this thread to see if there was even such a thing. I now know that it has nothing to do with bullets let alone what they are made of. I posted the correction, and that went about as well as asking for clarification.

Appreciate the help.

Well actually while I'm not a aircraft engineer, parabolic drag polar helps in modeling. A lot of time that modeling maybe in something like airfoil dynamics…during initial designing. So if lift is in question, there is some material relevance in that regard.

However, to beat a dead horse, we aren't concerning ourselves with lift with regards to bullets.

People who may come from that side of the aircraft world might be trying to build a bridge where it shouldn't be.

 

[VTbluegrass]

Arguing two different drags(not they/them drags) but physical drags. Hammer bullet design reduces bearing surface drag created by contact with the barrel which is very simple physics and I doubt Mr. Steve was thinking about air drag once it leaves the barrel; with the obvious exception proven design features such a boat tail and and fairly pointy front end. At ballistic speeds especially after facing deformation by rifling it would take a hell of a lot of research to determine PDR grooves impact on air drag/lift. Which again I doubt was their purpose based on Steve's responses.

 

[DWier]

I like them quite a bit. Tonight was 15 year, but every one is delicious. I was gifted a 18 year, but haven't worked up the nerve to open it yet. The 10 & 12 year are the sweet spot for price/drinkability. If you like a rye Old Fashioned the 6 year Piggyback is great. they are very smooth rye whiskeys with good notes and not just overly spicy.

 

[DWier]

When you open the 18yr let us know how it is. I haven't worked up the courage to pay that much. Kind of like Barry Crockett Leagacy. Absolute heaven in Irish Whiskey but I didn't pay for it.

 

[Greyfox]

I'll take a crack at it. My simplistic interpretation of parabolic drag as it effects a bullet in flight, is perhaps best explained in a picture depicting parabolic drag. This holds true for projectiles whether a bullet, baseball, arrow, etc.
The bullet in flight will travel in a parabolic shape, parabolic "drag" occurs after the bullet reaches the apex(highest point in the trajectory), changing the paranoiac curve(back-side) of the falling bullet. This shape is present with all trajectories,
In addition to gravity, the factors effecting forward and falling motion of the bullet on the back of the curve are, velocity, air resistance/drag force, shape, surface area of the projectile(bullet), and angle. IMO, using "our" lingo, we capture much(or all) of this with the bullets ballistic coefficient(BC). The external effects are compensated for with our ballistic calculators/drop charts.

Rockymtn/Mt….I would speculate that the comment made about your bullet effecting parabolic drag was inferring that your bullet design, right or wrong, perhaps could have been better expressed by saying that it didn't have as high a BC as whatever he was using.

 

[WahooYahoo]

Um... am I oversimplifying this?
The drive bands are the "parabolic" part, they're radiused (from parabola).
The "drag reduction" happens in the bore. Thus parabolic drag reduction ...

In mathematics, a parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits several superficially different mathematical descriptions, which can all be proved to define exactly the same curves. One description of a parabola involves a point and a line. Wikipedia

No Whistlepig involved, sadly.

 

[Northkill]

Eh, I'm pretty sure the "drag" has something going with the vapor trail. Steve's got that patented.

 

[Hugnot]

New stuff for me but here goes:

Different things make for bullet drag like bullet shape, bullet attitude, & skin friction. As the bullet plows thru air in a parabolic trajectory the attitude of the bullet will change affecting drag & skin friction. This is sort of like what happens with airfoils being affected with variables like lift, angle of attack as shown on graphs looking like a parabola. Driving bands & anular grooves might reduce drag by reducing skin friction causing turbulent air flow but changes of bullet attitude could negate the effect of the driving bands or anular grooves that were previously effective before bullet attitude change. The changing drag effect of the driving bands or anular grooves would also affect the shape of the parabolic graph curve.

I sort of think the parabolic stuff is hooked into the parabolic drag graph shape instead of the parabolic flight path.

 

[Mikecr]

I've seen in the past where claims(and patent claims) were made, I believe from Lost River Ballistics, crediting bullet lift from upward attitude bias in flight. This, supposedly resulting from solid bullet bands. All of this has been thoroughly debunked though.
Bullets do not fly, they fall the whole way(from any given path) per local gravity. They fall point forward, dead into vector.
The only lift (+or-) with bullets results from spin drift against wind.

It seems like airplane people, and even rocket people don't really get this, as their perspectives center on propelled objects. Not purely falling objects, that happen to be spinning really fast. Well, unless there is a Mach 4 glider that spins at 300,000rpm. Hadn't thought of that

 

[Hugnot]

From Hornady 4DOF Program:

"Spin Drift, Drift Due to the Yaw of Repose

As a projectile flies down range, the trajectory is curved in the vertical plane by the action of gravity. The trajectory curvature in the vertical plane, combined with the gyroscopic moment arising from the projectile spin and inertia, make the projectile nose point slightly up relative to the velocity vector of the bullet. The projectile nose pointing up relative to its velocity vector, combined with the trajectory curvature induces an angular rate on the projectile. If the bullet spin is in the "right hand" sense (spin axis aligned with your thumb, the direction of rotation aligned with your fingers), the projectile angular momentum makes the bullet point nose right relative to its velocity vector. The projectile nose pointing slightly to the right causes higher pressure on the left side of the projectile. This pressure differential left to right makes the bullet "drift" to the right for right hand twist barrels. The drift is known as the "drift due to the yaw of repose" or "spin drift". The drift due to yaw of repose depends on the ballistic drop of the bullet, the twist of the barrel, and the inertial and aerodynamic characteristics of the projectile."

Would this attitude change in bullet point direction away from the relative velocity vector increase during bullet flight "induces an angular rate on the projectile" & "ballistic drop of the bullet" & if so would the effects of anular grooves that might be reducing skin friction be changed ? This is assuming dead air - no wind.

Skin friction is a drag component.

Hopefully, some math guy might step in & explain Reynolds Numbers & boundary stuff.

Edit - If it moves thru the air it's subject to drag & if the attitude changes the drag changes.

 

[dfanonymous]

From Hornady 4DOF Program:

"Spin Drift, Drift Due to the Yaw of Repose

As a projectile flies down range, the trajectory is curved in the vertical plane by the action of gravity. The trajectory curvature in the vertical plane, combined with the gyroscopic moment arising from the projectile spin and inertia, make the projectile nose point slightly up relative to the velocity vector of the bullet. The projectile nose pointing up relative to its velocity vector, combined with the trajectory curvature induces an angular rate on the projectile. If the bullet spin is in the "right hand" sense (spin axis aligned with your thumb, the direction of rotation aligned with your fingers), the projectile angular momentum makes the bullet point nose right relative to its velocity vector. The projectile nose pointing slightly to the right causes higher pressure on the left side of the projectile. This pressure differential left to right makes the bullet "drift" to the right for right hand twist barrels. The drift is known as the "drift due to the yaw of repose" or "spin drift". The drift due to yaw of repose depends on the ballistic drop of the bullet, the twist of the barrel, and the inertial and aerodynamic characteristics of the projectile."

Would this attitude change in bullet point direction away from the relative velocity vector increase during bullet flight "induces an angular rate on the projectile" & "ballistic drop of the bullet" & if so would the effects of anular grooves that might be reducing skin friction be changed ? This is assuming dead air - no wind.

Skin friction is a drag component.

Hopefully, some math guy might step in & explain Reynolds Numbers & boundary stuff.

You can probably still find Jim who wrote this over on snipershide. https://www.researchgate.net/publication/327582502_Calculating_Yaw_of_Repose_and_Spin_Drift

 

[Bob Wright]

RockyMtnMT

www.longrangehunting.com

For bullet shape we use ogive "arcs", tangent secant and hybrid, in Bergers world of bullet shapes, as well as other bullets I presume.
Parabola shapes are not related to bullet shapes although they look quite similar.
Parabolic "groove" in the Hammer, only Steve can answer how the math worked out there.
Realistically, these 3 shapes are not related such as "parabolic drag" which seems to be a misdirection in terminology.
Below are examples of ogive and parabola shapes. Also where "parabolic trajectory on a chart" is influenced by drag and gravity
I didn't hit the whiskey but I stayed at a Holiday Inn once.

 

[Hugnot]

From Hornady 4DOF Program:

"Spin Drift, Drift Due to the Yaw of Repose

As a projectile flies down range, the trajectory is curved in the vertical plane by the action of gravity. The trajectory curvature in the vertical plane, combined with the gyroscopic moment arising from the projectile spin and inertia, make the projectile nose point slightly up relative to the velocity vector of the bullet. The projectile nose pointing up relative to its velocity vector, combined with the trajectory curvature induces an angular rate on the projectile. If the bullet spin is in the "right hand" sense (spin axis aligned with your thumb, the direction of rotation aligned with your fingers), the projectile angular momentum makes the bullet point nose right relative to its velocity vector. The projectile nose pointing slightly to the right causes higher pressure on the left side of the projectile. This pressure differential left to right makes the bullet "drift" to the right for right hand twist barrels. The drift is known as the "drift due to the yaw of repose" or "spin drift". The drift due to yaw of repose depends on the ballistic drop of the bullet, the twist of the barrel, and the inertial and aerodynamic characteristics of the projectile."

Would this attitude change in bullet point direction away from the relative velocity vector increase during bullet flight "induces an angular rate on the projectile" & "ballistic drop of the bullet" & if so would the effects of anular grooves that might be reducing skin friction be changed ? This is assuming dead air - no wind.

Skin friction is a drag component.

Hopefully, some math guy might step in & explain Reynolds Numbers & boundary stuff.

Edit - If it moves thru the air it's subject to drag & if the attitude changes the drag changes.

Thinking about the differences between airfoils having parabolic drag descriptions & bullets. Airfoils or wings on an airplane having a means of propulsion. Bullets, wingless, no lift component, subject to continual deceleration. Do parabolic shaped graphs describe drag on each? For wings would decreasing speed or shape of the airdfoil reduce drag or turbulent flow? For bullets, would constant deceleration reduce the drag caused by gyroscopic precession (angular momentum?) causing the bullet to fly more point forward. Would bullet skin friction be less as any skin friction reducing effect of anular grooves would be improved as bullet attitude changed?