What are spikes on aircraft nose cones for?

[Gordon Fecyk]

I've seen and used an antenna as a substitute spike at the end of aircraft noses in KSP when designing for Ferram Aerospace. Aside from the somewhat cheaty way of avoiding cockpit overheating on re-entry in game, what are these spikes used for on real aircraft?

The classic example is the Bell X-1. Strangely, that Wikipedia article doesn't explain the purpose of those spikes on the nose and wings.

I barely remember a History Channel show or some documentary that explained the sharp point was good for subsonic flight and then the rounded nose was better for supersonic flight, and this combination design was a compromise.

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[Wjolcz]

Are we talking about intake cones or these antennae things? Becose if the first one they are for slowing down the intake air and if the second one it's most likely for air speed measurements.

[Gaarst]

It's a drag-reducing aerospike. When going supersonic, you have a shock forming at the tip of your plane; if you plane has a slightly blunt nose it creates large amounts of pressure and turbulent flow, ie: drag. The spike creates a shock that is detached from the nose, thus it is not in contact with the nose of the plane and reduces supersonic drag.

Wikipedia does have an article on this.

Edit: if you want to go further, Wikipedia also has nice articles on nose cone design and wave drag (the drag created by shockwaves I mentioned above).

 

Edit2: apparently I'm an idiot. See the post below for an actual answer.

Edited January 16, 2017 by Gaarst

[p1t1o]

8 minutes ago, Gaarst said:

It's a drag-reducing aerospike. When going supersonic, you have a shock forming at the tip of your plane; if you plane has a slightly blunt nose it creates large amounts of pressure and turbulent flow, ie: drag. The spike creates a shock that is detached from the nose, thus it is not in contact with the nose of the plane and reduces supersonic drag.

Wikipedia does have an article on this.

Edit: if you want to go further, Wikipedia also has nice articles on nose cone design and wave drag (the drag created by shockwaves I mentioned above).

Im pretty sure this is not the case. Although drag reducing aerospikes are a real thing, aircraft designed to be supersonic tend to be designed with sharp noses in the first place. A sharp body will produce a shockwave that is in contact with the nose. A blunt nose in the supersonic regime will produce a shockwave at a standoff. Stood-off shockwaves produce more drag. However at subsonic speeds this is not an issue and in fact a blunt nose will produce less drag in this regime.

Hence airliners have blunt noses and Concorde had a sharp one. Its also the reason that reentry capsules are blunt - increase drag (allows more speed to bleed off in upper atmosphere, reducing heatshield requirements) and stand-off the shockwave (again reduces the thermal impulse on the capsule) whereas nuclear warhead RVs are sharp - reduced drag for maximum speed reentry.

If you are thinking about why the Trident nuclear missile uses an aerospike (just about the only example I can think of without google) instead of a sharp nose, it is because when the aerospike is retracted the missile juuuuuust about fits in the launch tube - its so that they can get a bigger missile in a smaller tube and still have good supersonic performance.

The "antenna" that you often see on an aircraft nose cone is (most often) a pitot-static probe, used to calculate airspeed amongst other things.

https://en.wikipedia.org/wiki/Pitot_tube

https://en.wikipedia.org/wiki/Pitot-static_system

Sometimes these can appear as small, side-mounted probes.

Test or research aircraft may have other instrumentation attached to the nose (as it is a good place to sample airflow undisturbed by the rest of the aircraft).

 

 

[Nibb31]

They are pitot tubes for airspeed sensors and are commonly used on experimental aircraft and prototypes

[Gordon Fecyk]

Hm, so you want a sharper nose on supersonic aircraft, but not one of these spikes except for instrumentation. Probably why the Bell X-1 had them.

That would also explain why the nose cone design article didn't mention them. The spike would sharpen a blunter nose though, as with the Trident missile. Kind-of a compromise between good supersonic performance and package size.

I'll take KSP questions related to this back to the FAR Spacecraft Exchange thread.

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[Nibb31]

2 hours ago, Gordon Fecyk said:

Hm, so you want a sharper nose on supersonic aircraft, but not one of these spikes except for instrumentation. Probably why the Bell X-1 had them.

The Bell X-1 was a very primitive supersonic aircraft. At the time, very little was known about supersonic aerodynamics, which explains why it didn't even have swept wings.

The Trident aerospike design dates back to the 70s.

 

Edited January 16, 2017 by Nibb31

[Racescort666]

7 hours ago, p1t1o said:

The "antenna" that you often see on an aircraft nose cone is (most often) a pitot-static probe, used to calculate airspeed amongst other things.

https://en.wikipedia.org/wiki/Pitot_tube

https://en.wikipedia.org/wiki/Pitot-static_system

Sometimes these can appear as small, side-mounted probes.

Test or research aircraft may have other instrumentation attached to the nose (as it is a good place to sample airflow undisturbed by the rest of the aircraft).

On experimental aircraft they usually do more than just pitot pressure. They will also have AOA and side slip as well. Sorry about the tiny pictures, I couldn't find very many good ones.