Whitcomb Area Rule.

[OttoVonMog]

I have question for Mr. Litz-- why are large caliber monolithic bullets designed using the Whitcomb Area Rule? It seems to me it would solve two issues: the bearing surface problem and the cross section drag problem that occurs as you increase the surface area and volume of an object traveling through a fluid.

What are your thoughts on this idea?

 

[Bryan Litz Ballistics]

Because bullets don't have wings.

https://en.m.wikipedia.org/wiki/Area_rule

The Whitcomb area rule is about minimizing overall cross sectional area by minimizing fuselage cross section where the wings are.

There used to be some bullets called something like wasp waist but they didn't stand the test of time, no genuine benefit for bullets. Probably because bullets don't have wings.

Take care,
Bryan

 

[OttoVonMog]

Because bullets don't have wings.

https://en.m.wikipedia.org/wiki/Area_rule

The Whitcomb area rule is about minimizing overall cross sectional area by minimizing fuselage cross section where the wings are.

There used to be some bullets called something like wasp waist but they didn't stand the test of time, no genuine benefit for bullets. Probably because bullets don't have wings.

Take care,
Bryan

Yes, I do realize that most bullets with exceptions that are fin-stablized sabots lack any wing-fulseage joint. However, as you design a large monolithic bullet, you get a very large cross section due to the increased bearing surface. It seems to me that you might see some advantages in your bullet design if you employ a design that follows the Whitcomb area rule. Now, I have no empirical evidence to support my idea. I just have a sense that in bullets larger than .375 in diameter with lengths approaching maximum length to diameter ratio for stabilization-- you might see an advantage in this design.

 

[243Mendoza]

The idea behind area rule is to minimize the CHANGE in cross-sectional area along the axis of flow: when you have wings, there is a sudden change in cross-sectional area and therefore an increase in drag and narrowing the fuselage will minimize this change. A bullet has a change an area but that is inevitable since a blunt nose will increase drag much more than a gentle increase in area. Also this effect is only effective in the transonic region of flight.

 

[OttoVonMog]

The idea behind area rule is to minimize the CHANGE in cross-sectional area along the axis of flow: when you have wings, there is a sudden change in cross-sectional area and therefore an increase in drag and narrowing the fuselage will minimize this change. A bullet has a change an area but that is inevitable since a blunt nose will increase drag much more than a gentle increase in area. Also this effect is only effective in the transonic region of flight.

Remember Monolithic bullets need driving bands to reduce the friction in the barrel. These will change the bullets cross-section and thus cause more drag-- especially at transonic flight. Which is exactly where you want to improve the large monolithic's performance if you want absolute accuracy and maximum range.

 

[Keith Glasscock]

I'd suggest that you lathe turn some samples and give it a test. No harm in trying it.

 

[243Mendoza]

The idea behind area rule is to minimize the CHANGE in cross-sectional area along the axis of flow: when you have wings, there is a sudden change in cross-sectional area and therefore an increase in drag and narrowing the fuselage will minimize this change. A bullet has a change an area but that is inevitable since a blunt nose will increase drag much more than a gentle increase in area. Also this effect is only effective in the transonic region of flight.

Remember Monolithic bullets need driving bands to reduce the friction in the barrel. These will change the bullets cross-section and thus cause more drag-- especially at transonic flight. Which is exactly where you want to improve the large monolithic's performance if you want absolute accuracy and maximum range.

a bullet is an axisymmetric body so area rule will not work other than having gentle area changes.

 

[JarheadAZ]

Aerodynamics can only be relevant once the bullet emerges from the muzzle, and unless the firearm has a smooth bore, the bullet cross section has already been distorted by the engraved rifling grooves, which is seldom uniform from bullet to bullet, from rifle to rifle.

While it may be difficult to quantify this uniformity from instance to instance, it should be possible to generalize that this is a factor in generating dispersion. If one factors in the idea that the bullet's effective BC is in constant flux along the trajectory, and that the the RPM/FPS relationship must have a bearing on instantaneous effective BC value, the art of prediction becomes less and less reliable.

I think that what I'm getting to here is the admonition that calculation can only work effectively in an environment where all the significant variables can be quantified.

I believe we have yet to reach that day.

But I also believe that we can approach the problem from the pragmatic end of the equation, as in "I do this, and that happens..."; with the caveat that direct numerical results may not be attainable, but that each individual variable can be assessed, one at a time, and that the resulting trend can become a learned value.

One observation re: Whitcomb is that for pragmatic reasons, while area rule fuselages were once the vogue, they are no longer.

One reason is that the rule resulted in a minimized fuselage cross section at precisely the point where structural rigidity was most necessary. This cost additional weight in the structure and nullified the efficiencies that the rule was supposed to be enhancing. Any way you slice it; additional weight requires additional lift, and lift is always directly related to drag.

Greg

 

[Mozella]

....... snip............
One observation re: Whitcomb is that for pragmatic reasons, while area rule fuselages were once the vogue, they are no longer.

........... snip..........

While the classic "Coke bottle" fuselage shape of many fighters from the 50's and 60's is no longer in vogue, I can assure you that aerodynamicists still pay very close attention to minimizing wave drag at transonic speeds, both in high performance combat aircraft and modern airliners. The pinched waist is obviously a disadvantage in an airliner, but Mr. Whitcomb is not forgotten.

For example, take a look at the trailing edge any modern airliner wing. You'll see large flap-track fairings which are sometimes larger than necessary simply to house the complicated flap track associated with gigantic Fowler flaps. These fairings smooth the abrupt reduction in cross section at the aft edge of the wing and in fact were a prominent add-on feature of the Convaier 990 which had speed and fuel burn problems at high subsonic mach numbers until those large "shock fairings" were added to the trailing edge of the wing.

You may have to look closer at modern fighters to spot similar structures, but designers are very careful when it comes to shaping the aft end of the cockpit, the position of various ECM pods, and the shape of other fairings housing a variety of components, all of which are considered in the plot of length vs area. Mother Nature hasn't changed and while very powerful engines can partially mask the need for every ounce of drag reduction, clever designers still know all about Mr. Whitcomb.

Of course, bullets and golf balls are things quite different from aircraft and putting a "wasp waist" on either of those objects will prove to less than successful.

 

[243Mendoza]

The boat tail on a bullet can be seen as an area-rule effect as it make the transition to the flat base less abrupt.