Nose Cone Preference

wfcook said:

I've always wondered this myself. Seems like an odd thing that Ogive cones are so dominant.

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On the "real" rockets and missiles in the past, nose cone shapes were selected for specific reasons. I doubt that very many were ever designed because someone thought they looked cool. I could believe that some nose cones were chosen because somebody had a pile of them left over from a previous project....

Ogives are mathematically simple to describe; this can make a difference when drawing/defining the nose cone parts, whether built in-house or supplied by vendors. For this same reason, simple conical nose cones were used extensively and were even less expensive to build.

Ogives provide reasonably good aero characteristics. Yes, other shapes may be better in some speed regimes but generally only by a few percent, none of the other shapes will be "twice" as good or anything like that.

Ogive radomes on guided missiles must also provide certain RF signal propagation effects for the radar sets inside to be able to function with decent sensor range. The ogive shape offered acceptably low levels of signal loss, and was commonly used on air-to-air missiles. (Sort of the same compatibility reasons that spherical nose shapes are often used to cover IR guidance systems.)

And other reasons: the missile may have flown at low enough velocities that drag was relatively low and fancier shapes were not extremely necessary, the missile may have needed the volume inside the nose fairing to contain a specific payload shape, or more mathematically exotic nose shapes had not yet been invented. Or, others....

When the "big" missiles use these nose cone shapes, they tend to show up in our scale and semi-scale models. From there it's a small step to general use in other model rocketry.

CarVac said:

I don't think there are any plastic von Karman nosecones except for the 54mm Space Cowboy.

I like loooooooong nosecones, no matter the shape. Bare Necessities had 7.2:1 plain conical and it was awesome.

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HEY! Watch that language...this is a family website! ( LOL!)

Tangent Ogive, Elliptical , and VK are all flexible enough to give me a wide range of design choices. Anything that looks like it's going fast while it is still sitting on the pad looks good to me.

Some of you know, I turn nose cones that aren't readily available, like for clones and upscale jobs. I will have to say that THIS, is one of my finest turn jobs for a cone I couldn't find, but had the stock for. Truth be known, the stock I had was undersized and I had to laminate the block with some leftover cuts, but I still impressed myself that it was perfect (by my standards). This was a joy moment for me because it was an upscale with a two stage advantage.

CarVac said:

VKs are very different looking in real life. Much less pointy and not tangent at the back.

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The shaded 3D view of a 5:1 VK in Rocksim and Openrocket looks fine to me. From another post in this thread:

https://www.rocketryforum.com/attachment.php?attachmentid=152760&d=1383782659

powderburner said:

Yes, other shapes may be better in some speed regimes but generally only by a few percent, none of the other shapes will be "twice" as good or anything like that.

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All shapes perform virtually the same at subsonic speeds where most of our rockets, even HPR ones, fly. At transonic and above, the differences are much more than a few percent. However, you are correct on the not as much as twice bit:

https://www.everyspec.com/NASA/NASA-General/NACA-RM-I53K17_46178/

Cones are easiest for scratch builds....plus Madonna likes them.

swatkat said:

Cones are easiest for scratch builds....plus Madonna likes them.

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Sure, but I'm not talking about custom builds. My point is, if numerically controlled methods are used to create the molds for HPR nose cones, as I suspect they are, and the aerodynamically best nose cone shapes aren't unattractive or present some molding process issue due to their shape which I wouldn't expect since they're so close to other nose cone shapes, the best performing nose cone shapes at all velocities, sub, trans, and supersonic should be the standard. In other words, unless you're after some unusual nose cone shape for appearance or scale use, VK and x^1/2 should be the standard shapes used when creating nose cone molds. Only when a rocket goes trans or supersonic would there be an advantage, but since the more aerodynamic shapes at those velocities are just as good as the other less optimal shapes at the more typical subsonic velocities, why not make them the standard?

EDIT: and any HPR kit manufacturer who makes a kit capable of trans and/or supersonic flight could brag about supplying a VK or x^1/2 nose cone.

Gary Byrum said:

It's choices like this which inspired me to buy a lathe. There are also very few nose cones for BT 70 tubes and I have turned quite a few BNC 70 AH noses for a number of builds. Many times when I've done upscale builds I often find the perfect NC doesn't exist. And I usually wont settle for a close facsimile. Nose cones for my upscale Constellation, 2 stage Der Red Max, Starship Excalibur, Gyroc, Arapahoe F are all upscale and noses had to be turned. Including a great many of my own designs and OOP clones. And for anyone that has ever turned a conical nose on a lathe, you prolly found it much harder to turn than an elliptical nose.

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Try Python Rocketry excellent custom cones. Any shape including odd cones 5.5" to 20" diameter, up to 90" long.

GDJ said:

Yeah I do that sometimes too.
On the subject of this nose cone, the Semroc link is still active. Is Semroc still alive and kicking? Would it be possible to still buy this nose cone and other parts?

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Sheryl is still selling down inventory. I think she is going through inventory and occasionally finding things that she thought she was out of. And who knows? Maybe there's some new production of some kits (again to sell down her inventory of parts).

Ravenex said:

Try Python Rocketry excellent custom cones. Any shape including odd cones 5.5" to 20" diameter, up to 90" long.

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Thanks, but why would I have someone else make it when I can do it myself? I'd just draw (trace & scale) a pattern like your "Python" guy has posted on his site, turn that into a template and print it off. Wha-lah! All done in Autocad. And no doubt, I could do it for way less expense.

I apologize I misread your post, I thought you said these type of cones make you consider getting a lathe, not that you already had one. If you can make them yourself that awesome.

Winston said:

Sure, but I'm not talking about custom builds. My point is, if numerically controlled methods are used to create the molds for HPR nose cones, as I suspect they are, and the aerodynamically best nose cone shapes aren't unattractive or present some molding process issue due to their shape which I wouldn't expect since they're so close to other nose cone shapes, the best performing nose cone shapes at all velocities, sub, trans, and supersonic should be the standard. In other words, unless you're after some unusual nose cone shape for appearance or scale use, VK and x^1/2 should be the standard shapes used when creating nose cone molds. Only when a rocket goes trans or supersonic would there be an advantage, but since the more aerodynamic shapes at those velocities are just as good as the other less optimal shapes at the more typical subsonic velocities, why not make them the standard?

EDIT: and any HPR kit manufacturer who makes a kit capable of trans and/or supersonic flight could brag about supplying a VK or x^1/2 nose cone.

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Any HPR kit manufacturer who makes performance-oriented kits should offer 7:1 VK with them instead of piddling 5:1.

CarVac said:

Any HPR kit manufacturer who makes performance-oriented kits should offer 7:1 VK with them instead of piddling 5:1.

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Nope, according to the literature, there is very minimal advantage to anything over 5:1.

Winston said:

Nope, according to the literature, there is very minimal advantage to anything over 5:1.

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There is no advantage when you leave the body tube the same length, but when it means you can fit more in the nose and remove more of the body tube then it yields advantages.

CarVac said:

There is no advantage when you leave the body tube the same length, but when it means you can fit more in the nose and remove more of the body tube then it yields advantages.

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"At supersonic speeds, the fineness ratio has a significant effect on nose cone wave drag, particularly at low ratios; but there is very little additional gain for ratios increasing beyond 5:1. As the fineness ratio increases, the wetted area, and thus the skin friction component of drag, is also going to increase. Therefore the minimum drag fineness ratio is ultimately going to be a tradeoff between the decreasing wave drag and increasing friction drag."

And, if you look at the graphs, this goes for transonic, too.

Winston said:

"At supersonic speeds, the fineness ratio has a significant effect on nose cone wave drag, particularly at low ratios; but there is very little additional gain for ratios increasing beyond 5:1. As the fineness ratio increases, the wetted area, and thus the skin friction component of drag, is also going to increase. Therefore the minimum drag fineness ratio is ultimately going to be a tradeoff between the decreasing wave drag and increasing friction drag."

And, if you look at the graphs, this goes for transonic, too.

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The total wetted area will decrease when you shorten the body tube in order to keep total vehicle length (or even volume) constant.

The nose cone is not the whole vehicle.

CarVac said:

The total wetted area will decrease when you shorten the body tube in order to keep total vehicle length (or even volume) constant.

The nose cone is not the whole vehicle.

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While that may be true, a vendor is more likely to sell 5:1 VK's (which look extraordinarily cool, IMHO) than 7:1 VK's.

And really, if we are going to "go there" for all out performance, then the likelihood may be great that the designer/builder will just one-off the NC himself to get it exactly how he wants it.

Greg

GregGleason said:

While that may be true, a vendor is more likely to sell 5:1 VK's (which look extraordinarily cool, IMHO) than 7:1 VK's.

And really, if we are going to "go there" for all out performance, then the likelihood may be great that the designer/builder will just one-off the NC himself to get it exactly how he wants it.

Greg

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Once again, it's not a matter of even wanting to "go there," it's just a case of "if the nose cone isn't more difficult or expensive to manufacture nor unattractive, why not generically use the most efficient shape?" On the fineness ratio, there may be molding issues for plastic nose cones with greater fineness rations since the longest polypropylene 4" diameter ogive nose cone I know of is the Mad Cow one which is 4:1. And remember that I'm taking about mass-produced plastic nose cones here, not about custom or fiberglass stuff.

Winston said:

Once again, it's not a matter of even wanting to "go there," it's just a case of "if the nose cone isn't more difficult or expensive to manufacture nor unattractive, why not generically use the most efficient shape?" On the fineness ratio, there may be molding issues for plastic nose cones with greater fineness rations since the longest polypropylene 4" diameter ogive nose cone I know of is the Mad Cow one which is 4:1. And remember that I'm taking about mass-produced plastic nose cones here, not about custom or fiberglass stuff.

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I agree and it is logical in a "perfect world".

I have no idea what all of the factors are in the decision for a nose cone shape for a given vendor, but my guess is that NC performance is lower down on the list. It may or may not matter to him. He just wants as much of his product flying off the shelf as he can.

Greg

GregGleason said:

I agree and it is logical in a "perfect world".

I have no idea what all of the factors are in the decision for a nose cone shape for a given vendor, but my guess is that NC performance is lower down on the list. It may or may not matter to him. He just wants as much of his product flying off the shelf as he can.

Greg

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I agree, it's just the way it currently is. I'm just suggesting that IF and when current nose cone molds wear out, replace them with VK or x^1/2 shapes. Given the relatively tiny numbers of nose cones produced compared to other plastic things made in molds, there might be a very, very long wait for molds to wear out. OR, a manufacturer might choose to go to the expense of making a VK or x^1/2 mold so they can use it as a kit marketing advantage for HPR kits that are capable of safe trans and/or low-supersonic flight. This will mostly appeal to those after personal altitude records, so it won't be a huge marketing advantage and, from what I've read, making molds is very expensive.

MarkH said:

I'd assume it cost more to make a long 6:1 or 7:1 VK nosecone than a 4:1 ogive for example, just because of material costs with the extra length. A short VK shape in a 4:1 probably doesn't offer much benefit. So I wouldn't expect manufacturers to standardize on long 6 or 7:1 VK shapes, because most probably don't care enough about altitude to pay extra for it.

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At transonic and supersonic velocities, equivalent fineness ratio ogive vs VK or x^1/2 should have significantly different performance. At those velocities, even a 4:1 VK or x^1/2 should do better than a 4:1 ogive.

Here's a fantastic document I just found. I'll be trying to find the referenced documents on-line and read them because I don't see supporting evidence in the charts/graphs they show for their definitive statement that a 5:1 fineness ratio is absolutely critical. It's more like "optimal" since there appear to be rapidly diminishing returns for anything finer:

https://tripolimn.org/files/Nose Cone & Fin Optimization January 2011.pdf

And "paying extra" for a VK or x^1/2 shape won't be necessary if, as I've said, molds for those shapes are made when the old ogive (or whatever) molds wear out or someone who's making a new mold anyway simply uses one of those more optimal shapes for their design as they should. For a 4:1 VK or x^1/2, the material costs wouldn't be significantly different from a 4:1 ogive (or whatever).