Here Is Why Some Airplanes Have Rounded Tips Instead Of A Pointed One


A Boeing passenger aircraft (Image: Pinterest)
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If you do not go into the details of aerodynamic design, you would think that an airplane will fly the fastest, tearing through the air with high efficiency only with a pointed nose. Despite this, most passenger airplanes are made with blunt round noses instead of a sharp one, and we see the sharp tips mostly in the fighter planes. Wouldn’t a pointy nose on an airplane account for less drag and more efficiency?

Tomahawk subsonic cruise missile (Image: Aerospaceweb.org)

Drag is a mechanical force caused by the interaction of a solid body with a fluid. In case of an airplane, all parts of it contribute to drag from its nose and wings to its engines, acting in opposite direction to the motion of the airplane. Drag is affected significantly by the shape of the solid body moving through the fluid, and a sharp design is not necessarily the best choice in all cases. The three most important types of drag are skin drag (due to friction), form drag (due to shape), and wave drag (relevant at supersonic speeds).

Aerodynamic forces (Image: Wikipedia)

Design of any kind of vehicle is never perfection. A lot of compromises go into airplane design, and the design parameters vary from plane to plane according to requirements. The shape and aerodynamic requirements of a fighter jet can be poles apart from those of a passenger plane.

When an aircraft is moving at subsonic speeds, the deciding factors are the skin and form drag, and a blunt or round nose causes much less drag than a pointed nose would. It may sound counter intuitive, but since a blunt nose has a surface area much smaller than that of a pointed one, it contributes to lesser skin drag. When the airplane moves, the pressure field around it extends forward along with it. The suction area on the side of the fuselage or the wing will begin to suck on the air molecules before they reach the vehicle and the rounded nose will allow the flow from many angles, thus the drag is much lower.

A Boeing passenger aircraft (Image: Pinterest)

Since passenger aircraft cruise at speeds much smaller than that of sound (with the exception of Concorde that did have a sharp nose), they deliver good performance with their rounded blunt noses. Below are the drag coefficients for some common shapes, that shows that a rounded end has a drag coefficient much smaller than that of a sharp or a conical one.

Source: Automotive

When an aircraft begins to cruise at transonic and supersonic speeds, factors other than surface drag come into play. At such higher speeds, the air does not know of the approaching airplane, and once it comes in contact, it causes a sudden change of direction called shock. This shock results in wave drag which can be brought down by making the shock very weak. A smaller change in direction means weaker shock and that can be obtained best by a sharp and pointy tip.

Lockheed Martin F-22 Raptor (Image: F-16.net)

The Lockheed SR-71 Blackbird was one of the best fighter jets of the US airforce that cruised at Mach 3+ speeds. The cone on the Blackbird is made symmetrical to the oncoming flow and angled downward, so the flow is pressed sideways by the aircraft.

Lockheed SR-71A Blackbird (Image: National Museum of the USAF)

When the aircraft is designed to move out of the atmosphere at hypersonic speeds (Mach 5 and above) and return, a blunt nose is a better option to consider due to aerodynamic heating limitations. There is no need to minimize the drag for a re-entry vehicle. So a round tip is preferred as it produces more drag and higher heat loads but spreads this heat over a larger area that keeps the peak loads lower. Space shuttles are thus designed with blunt noses.

North American X-15 hyper sonic rocket powered aircraft (Image: AviationCV.com)

So, yes slender and sharp tips are good for supersonic aircraft but one size does not fit all, and any craft cruising at subsonic speeds are preferably designed with rounded tips.

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