Russian rockets look like this:

Russian rocket designs

They flare them out at the bottom. With their newest rocket, the Proton, the flared shape is gone but the boosters still have caps that angle in towards the main rocket so the shapes fuse together. American rockets look like this:

American rocket designs

The boosters look like mini-rockets, with their own nose cones, stages are straight, not flared out. The Chinese do the same. Europe takes the Russian approach with Ariane.

Why the different approach in booster design?

  • $\begingroup$ You didn't include Proton or Angara. The Sputnik/Soyuz was designed in the 1950's. And compare with European Ariane 5. $\endgroup$ – LocalFluff Jan 31 '15 at 23:10
  • $\begingroup$ @LocalFluff Hm, i searched for images of Russian rockets and got stuff that didn't include the Proton. My bad... I guess that makes this more into a historical inquiry, which isn't so interesting. I did notice the Ariane is sort of a fusion of the two approaches, which the Proton is as well. I will ponder possible edits to make this more accurate and hopefully still interesting. Is the difference in the two approaches to aerodynamics significantly different, i guess it boils down to that. $\endgroup$ – kim holder Feb 1 '15 at 0:59
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    $\begingroup$ It's interesting as it is, hoping for nice writeups in answers. This is actually "heritage" from the cold war era, coming from the fact that Americans were way ahead in nuclear weapons miniaturization and solid fuels (JPL) than Soviets were. Earliest US ICMBs (e.g. Atlas missile) actually weren't that sleek either, but they soon became in Minutemen and Titan II. Soviets needed quite a bit longer to get to that point, from R-7 to Dnepr/Satan. That later proved advantageous to Soviets and later Ukrainians and Russians, but that's another story. :) $\endgroup$ – TildalWave Feb 1 '15 at 1:21
  • $\begingroup$ Interesting related (from the propellants perspective) lecture for those with 90 minutes to kill: Putting the 'P' in 'JPL'--The Past, Present, and Future of Propulsion at the Jet Propulsion Laboratory. If you can find them, BBC also made some pretty good spaceflight history documentaries discussing cold war era and Soviet space program, e.g. BBC Space Race (4 part series) and BBC Cosmonauts - How Russia Won the Space Race. There's of course also books. $\endgroup$ – TildalWave Feb 1 '15 at 4:26
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    $\begingroup$ Ariane 5 and Proton use cylindrical boosters, only the nose profile is pointed inward like the Atlas V. $\endgroup$ – Hobbes Feb 1 '15 at 10:33

The Soyuz uses conical boosters because there's an aerodynamic advantage.
According to The Red Rockets' Glare:

Engineers gravitated to a conical shape primarily because of the aerodynamic advantages ...but also for 3 other reasons: the large size of the engines at the tail end, the possibility of imparting additional thrust to the central sustainer by the shape of the booster, and the opportunity of decreasing wall thickness.

Another source claims:

But it turned out that the conical-shaped boosters of the Soyuz are an advantage for the aerodynamics, especially the gap between the boosters has an effect of a “negative” wing.

At first glance a cone wouldn't appear to have an advantage: drag depends mostly on frontal area, and a cone has a larger frontal area than a cylinder of the same volume.
But a cylinder of this diameter would be half as long as the conical booster, giving a short, stubby shape that is less efficient than a long, thin cylinder.

And there's a more subtle effect going on here, one specific to having 4 boosters close to each other. Rockets with 2 boosters wouldn't benefit from this effect.

The other conical rocket is the N-1. In this case, there's no aerodynamic advantage. The rocket's shape is due to limitations of manufacturing technology: a spherical tank was easier to manufacture than a cylindrical one, so they used spheres. But they needed two spheres of different diameters to get the fuel:oxidiser ratio correct, so they ended up with conical stages.
According to Foothold in the Heavens: The Seventies, the Soviets were unable to produce cylindrical tanks that were part of the rocket's load-bearing structure: they couldn't manufacture aluminium plate that was thick enough for the job. So they had to separate the rocket's skin from the tank. They chose to use a spherical tank instead of having two cylinders inside one another, to minimize contact between the tank and the outer skin.

From the website linked to the book N-1 for the Moon and Mars:
N-1 diagram

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    $\begingroup$ You're right about the drag, but precisely because of the drag, a conical flare-out at the bottom of an otherwise cylindrical shape can improve stability, by moving the center of aero pressure backwards. That may be one of the "aerodynamic advantages" alluded to. $\endgroup$ – Russell Borogove Feb 1 '15 at 20:22
  • $\begingroup$ are you sure that "spherical tank was easier to manufacture" ? I would say that spherical tank is more effective ( better volume-to-surface ratio and homogenous distribution of mechanical stress ) which allows to make it lighter for the same volume, but that it is more technologically complicated to produce. I would say that advantage of cylindrical bodies - especially if all stages has the same diameter - is that you can use more common parts like in mass production. $\endgroup$ – Prokop Hapala Feb 2 '15 at 12:50
  • $\begingroup$ @Prokop: I've amended my answer. In a rocket, a spherical tank creates a lot of unused space around it; a cylinder can consist entirely of tankage. A cylinder that contains 2 spheres is larger for the same tankage volume, and contains more metal because you can't use the tank wall as the outer skin of the stage. $\endgroup$ – Hobbes Feb 2 '15 at 15:28
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    $\begingroup$ That N-1 cutaway drawing is amazing. Never seen that before. $\endgroup$ – Organic Marble Dec 22 '16 at 16:41

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