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There are some beautiful images of the Qu8k rocket launch on this web page and I show a few below. There's a video (below) and the PDF Qu8k Final By Derek Deville, November 27, 2011

The stainless steel point of this rocket's nosecone appears to be quite sharp and replaceable, which made me wonder just how pointy does a rocket need to be?

Would a 1cm radius rounded nosecone tip perform significantly different than this sharply pointed tip for a rocket like this? What about for a larger, heavy orbital rocket; do they need to be sharp as well?

Qu8k rocket

Click below for full size

Qu8k rocket Qu8k rocket

Qu8k rocket Qu8k rocket

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    $\begingroup$ There would be some difference - but mostly at the very end of the flight: ddeville.com/images/Rocket/Qu8k/IMG_7305.JPG $\endgroup$ – asdfex May 19 at 9:43
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    $\begingroup$ I seem to recall that someone (Max Faget?) discovered through wind tunnel testing that sharper noses tended to melt at hypersonic speeds. $\endgroup$ – DrSheldon May 19 at 14:53
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    $\begingroup$ Related question about aerospike noses on ICBMs: space.stackexchange.com/q/35523/6944 $\endgroup$ – Organic Marble May 19 at 15:42
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    $\begingroup$ @uhoh sorry, just saw that; of course! I honestly thought it would be posted to you as a suggested edit, didn't mean to step on toes! (Deleting now irrelevant discussion). $\endgroup$ – Magic Octopus Urn May 22 at 16:15
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    $\begingroup$ @uhoh I added 2-3 more questions into the tag too, and tried to add a meta excerpt. I'm under 4,000 though so the excerpt I wrote needs peer-reviewed. Sorry again about all this, I just wanted to try my hand at helping out on the site meta :). $\endgroup$ – Magic Octopus Urn May 22 at 17:08
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As rockets get larger, the importance of drag relative to mass decreases (drag runs generally proportional to cross section and surface area while mass runs generally proportional to volume). Hence big rockets tend to have less pointy payload fairings, which provide more useful volume by mass, as Hobbes' answer shows.

Qu8k was a small rocket developed with the sole goal of reaching 100,000 feet (30km) altitude under the Carmack Micro Prize rules; it was designed over a weekend and took some departures from normal amateur rocketry conventions in the name of reducing drag:

Most pads require use of a launch lug or rail guide. These protruding parts on a rocket create lots of drag. By removing these parts, simulations showed I was able to increase peak altitude by over 10,000 feet. The desire to keep drag low and have full control over when the pad would be setup and available for launch drove me to make my own launch tower.

The Wikipedia nose cone design article that Hobbes links mentions that conic tips are often chosen for ease of manufacture over more complex shapes, and this was probably the driving factor for Qu8k. This chart from that page shows that cones are actually poor performers in the transonic regime. Qu8k reached its top speed of around mach 2.8 at only 17,000 feet (5km), meaning that it spends a lot of time in dense air at speeds where a conic nose is not ideal:

enter image description here

Comparison of drag characteristics of various nose cone shapes in the transonic to low-mach regions. Rankings are: superior (1), good (2), fair (3), inferior (4).

So presumably the tradeoff here was that Deville knew he could fabricate a conic nose cone, and his simulations said it would go to 100,000 feet, so that's the route he took; I imagine that with more time and effort he could have made a very slightly smaller rocket with a Haack/von Kármán nose and reached the target altitude, but in rocket development it's very rare that you're ever optimizing for only one factor.

The chart doesn't show the performance of spherical-tip conics separately from pure conics, but I suspect that a 1cm radius tip would have been an insignificant difference on this rocket: a little more time in the shop grinding the tip down, and a little less likely to accidentally puncture something while being handled, and still capable of breaking 100,000 feet.

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  • $\begingroup$ This is a really interesting answer, thanks! $\endgroup$ – uhoh May 19 at 20:36
  • $\begingroup$ Do you have any information about the source / raw data shown in this graph? There is no reference given in Wikipedia. E.g. the "half parabolic" is very close to a cone, but has a rating of 2 vs. 4, which is hard to understand. $\endgroup$ – asdfex May 20 at 10:58
  • $\begingroup$ @asdfex No, I don’t, but it’s probably findable. $\endgroup$ – Russell Borogove May 20 at 15:28
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Blunted noses, especially in the case of the Shuttle Orbiter, are a thermal consideration as well. To put it simply, when a vehicle travels at supersonic speeds, there is a shockwave produced by the nose “because the air wouldn’t otherwise get out of the way fast enough”. This wave produces a large component of total drag, especially at hypersonic (Mach > 5) speeds. Having a more slender, smooth airframe mitigates this drag.

Much of the energy of air particles impacting this shockwave is turned to heat, which ionizes the gas and produces the “flames” seen around reentering vehicles. With a slender, pointed nose, the shockwave isn’t as immediately intense so it sticks closer to the airframe, especially at the tip. The heat at the center of the shockwave is very intense, enough to melt or weaken most materials known to man.

To avoid the tip melting, the nose can be made blunt. A blunt tip produces an immediately stronger shockwave, which is pushed out further from the nose. While this increases total drag, there is a weight and heat savings from not having to insulate/dissipate the heat at the nose tip.

There is a trade-off here that must be evaluated design by design to decide what tip structure and material is best.

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  • $\begingroup$ The shuttle stack had a very sharp tip. You seem to be mostly talking about entry considerations. $\endgroup$ – Organic Marble Oct 3 at 3:31
  • $\begingroup$ @OrganicMarble yes, I meant the Orbiter’s nose. Edited. $\endgroup$ – CourageousPotato Oct 3 at 3:33
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Orbital rockets generally don't have such sharp noses. Here's an Ariane 5 as an example:

enter image description here

You can see there's a large radius on the tip. Eyeballing from a scale model I have handy, I'd say that radius is about 0.5 m.

The Falcon 9 fairing has a large radius too:

enter image description here

The Apollo LAS had a sphere embedded in the tip.

The nose design with the lowest drag seems to be the Haack/von Karman design, which uses a rounded tip.

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  • $\begingroup$ As rockets get larger, the importance of drag relative to mass decreases (drag runs generally proportional to cross section and surface area while mass runs generally proportional to volume). Hence big rockets tend to have less pointy payload fairings, which provde more useful volume by mass. $\endgroup$ – Russell Borogove May 19 at 15:13
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As a counterexample to some statements in the other answers....the actual extreme tip of the shuttle stack was surprisingly sharp....

enter image description here

(personal photo)

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    $\begingroup$ Do you know if the needle on the tip of the ET had a primarily aerodynamic function, or if it served some other purpose? My guess would be en.wikipedia.org/wiki/Drag-reducing_aerospike $\endgroup$ – Russell Borogove Oct 3 at 3:49
  • $\begingroup$ With that provocative photo I feel you are trolling me in the best possible way! I'll get to it later today ;-) $\endgroup$ – uhoh Oct 3 at 3:49
  • $\begingroup$ @RussellBorogove I'll post a question asking further about it in several hours, but if you're interested please feel free to ask first! I think an explanation could require a separate answer. $\endgroup$ – uhoh Oct 3 at 3:51
  • $\begingroup$ It served several purposes! I'll wait for the question though. $\endgroup$ – Organic Marble Oct 3 at 3:57

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