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I found that the cross-sectional shape of some jet airliners' nose is not perfectly a circle. For example the Boeing 737 aircraft: Boeing 737 nose
(source: aeroprints.com via Wikimedia Commons, CC BY-SA 3.0)

Look at the frame (below cockpit window) that draws the nose cross sectional shape of the B737, it is not perfectly a circle, but a little rectangular shape. While on the A320, the nose cross-sectional shape is nearly a perfect circle.

What is the difference between these two? Does it have to do with the instruments built in the nose? Which design creates less drag? How does the change in nose cross-sectional shape affect the aerodynamic properties?

(plus the B737 nose is more pointy than the A320's, the A320 and almost all Airbus planes have a blunt nose compared to Boeing aircraft)

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Two reasons… One, airliner fuselages are not usually circular, and actually not a smooth oval. They tend to be a compound vertically-elongated oblong shape. Most Boeings, for instance, tend to be the compounding of two radii, one for the bottom half and one for the top half.

But the top of the nose have to also be “flattened” down to where the windshields start. Modern transport and military aircraft, like cars, have windshields that don’t simply follow the contour of the body, but are more “vertical”, effectively “cutting into” what would otherwise be a smooth line from nosed to roof.

So the nose cone shape is a vertical oval, that is then flattened across the top to create a place for the windshield, unlike something like the nose of a B-29 bomber.

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In addition to the above answers or to simplify you'd want a pointy nose so that you can easily and smoothly cut through the on coming air because air itself has mass. Thus, reduces drag. Another thing is that having such a shape at the nose also helps to streamline the Radome since it's surface structure and the shape plays a vital role in terms of optimizing its performance.

It must be understood that static electricity has the tendency to concentrate at points that have the greatest curvature. Thus, having certain points on the aircraft that fits this description such as the wings and nose tip helps to install statics wicks at or near those locations instead of having a dozen of those every where on the aircraft.

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  • $\begingroup$ What a confusion: "a pointy nose can easily and smoothly cut through the on coming air" this is true at supersonic speeds, not at the subsonic speeds typical of a jetliner where the tail should be pointy... "static electricity has the tendency to concentrate at points that have the greatest curvature" the smallest curvature you mean, that's why static discharges are niddle-like... $\endgroup$
    – sophit
    Jun 25 at 7:05
  • $\begingroup$ Neither at subsonic nor at supersonic speeds you'd still need have a pointy nose or have it tapped to create such a curvature shape in order to reduce drag which will be caused by the relative air. Why i stated having such points or places where the curvature is the greatest helps to place static wicks at or near those points where the negative charges tend to concentrate than installing it at various places where the degree of curvature is smaller. Yes, the virtual fin is a directional component that aids the plane to stay firm as it flies through the air. $\endgroup$
    – Ludwig T
    Jun 25 at 7:35
  • $\begingroup$ At supersonic speed you do need a pointy nose to get an oblique shock wave attached to the nose. Unless the aircraft is a reentry vehicle and then a detached shock wave is better to slow it down: in that case the forward part of the vehicle should be curved. At subsonic speeds the back of the aircraft is much more important than the nose to reduce drag. $\endgroup$
    – sophit
    Jun 25 at 8:05
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    $\begingroup$ @LudwigT: no problem, we're all here to learn something new. A radome has normally no structural properties (if not to sustain itself). It is not made of metal since it covers and protect the weather radar so it has to be transparent at the electromagnetic waves at which the radar works. This answer gives a very nice point of view related to this topic. $\endgroup$
    – sophit
    Jun 25 at 16:40
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    $\begingroup$ Maybe this answer and this answer will help to answer your question about nose shapes. $\endgroup$
    – Peter Kämpf
    Jun 25 at 18:48

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