# Blunt noses subsonic drag - why a complete ellipse?

At subsonic speeds, blunt noses - both fuselage and airfoil - are good for two reasons:

1. the need to maintain attached flow at varying angles of attack.
2. it has less surface area for the volume, reducing skin friction.

TOP: 0 AoA/Cruise | BOTTOM: extreme AoA, 20-30degrees, takeoff/landing

If the airflow had to flow over a ridge/point in scenario 2, instead of the smooth curve, flow separation would be more likely.

But things don't seem to add up.

Firstly, it's not like most airplanes - particularly airliners - fly at AoA beyond 20-30 degrees. At least not without high-lift devices. Am I correct? But on the rounded nose, there are surfaces smoothly curving all the way from 90 degrees! This seems to me like a useless increase in cruise drag.

Secondly, why push a blunt face ahead of you just to increase the volume a little, whem you can use a curve terminating at a point/ridge, as will be demonstrated below? If the surface area to volume ratio becomes so important, we can just sacrifice the fineness ratio and still have less drag, as the new nose creates less drag, right?

Would limiting the curvature to the max AoA limit for the aircraft, then terminating at a point, as in the image below, not keep the flow attached throughout the expected AoA range, while producing less drag? At the maximum AoA, the flow over the top of the shape encounters no "ridge" or "point", as it is parallel to the half-angle at the nose.

TOP: less drag is created at cruise | BOTTOM: Flow remains attached at extreme AoA conditions.

What am I missing about the sharp nose? How and how much does it hurt performance? Why, after all this seemingly shown in the question, is it - aside from the radar - that big planes have round noses?

In short: I am claiming that an elliptical nose tipped with a triangle or cone of 20-30 degrees half-angle should be better than a pure ellipse for subsonic aircraft. Why am I wrong?

• Does this answer your question? Why/when is the blunt nose better? May 4 '20 at 9:28
• No it doesn't. I came here after reading it. May 4 '20 at 9:29
• A ridge on the leading edge is a terrible idea for subsonic flight. That's how icing kills airplanes.
– JZYL
May 4 '20 at 15:47

What you are missing is suction on that round nose which adds some thrust.

Granted, around that stagnation point there is a pressure region which also acts on a forward-facing surface, thus creating drag. But that region is small. Thanks to the curvature of the elliptic nose shape, air accelerates quickly out of this high pressure region. In order to follow the curved surface, the pressure has to fall below ambient on a still somewhat forward-facing area so the air is actively pulling the nose forward. No such suction can be expected on the straight contour of a pointed, cone-shaped nose.

The plot below only shows an airfoil, but flow around an elliptic nose is quite similar.

CPV plot from XFOIL, showing local pressure as arrows. Suction is pointing out, pressure into the contour. Length denotes difference to ambient pressure.

• what does that diagram show - pressure or pressure gradient? May 4 '20 at 16:47
• @ABJX Pressure. Suction is pointing out, pressure into the contour. Length denotes difference to ambient pressure. May 4 '20 at 19:34
• wow........negative pressure even at the bottom...... May 5 '20 at 7:31
• what's that drooped nose-like thing at the nose? May 5 '20 at 7:31
• @ABJX: That is just a bunch of arrow tips. They scale with arrow length (would be hard to do otherwise). The airfoil has a regular contour. And yes, suction at the bottom from the displacement effect is completely normal at lower angles of attack. May 5 '20 at 13:33

There is a stagnation point at the nose, where the airflow separates around it. As the aircraft attitude changes, it reduces drag if this stagnation point can move. Technically the explanation for this is a problem of three-dimensional flow, which is difficult to analyze. Intuitively the air "wants" to flow the most efficient way and fixing the stagnation point prevents that. There is an increase of pressure on the side of the point facing the incoming flow; the air has to turn harder to avoid it on that side, and that increases the local pressure. This is also destabilizing, so tail surfaces have to be larger. A round nose allows the stagnation point to move, in turn letting the air find the lowest-drag route.

Also, extending the nose uses more material, which increases skin drag, weight and cost.

Having said all that, these effects are small to trivial and many planes have had pointed noses - or pointed prop spinners - and not suffered unduly.

• but why does the stagnation point have to move to reduce high AoA drag? besides, the extension can be used to store things, and surely the pointed shape reduces pressure drag. May 4 '20 at 11:59
• OK, I have added a bit more detail. May 4 '20 at 12:28
• Right. In your answer itself it says that some planes have had pointed noses without hurt. And now that I sort of get what you're saying with the stagnation point moving, it would still appear that the drag reduction at angle would not be significant. Also, what about airfoils? This also I was asking. Thanks for the answer though :) May 4 '20 at 15:10
• Wait I just noticed: "There is a stagnation point at the nose, where the airflow separates around it" why is the airflow separating, especially since the flow over the low-pressure side is not turned at all over the sharp nosepoint in the high-AoA scenario shown above? May 4 '20 at 15:12
• The airflow separates around it, not from it. There is a difference. May 4 '20 at 16:23