Nose Cone Preference

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Gary Byrum said:
I found a chart which shows the different shapes including both tangent and secant ogives. It appears to me that the tangent has more girth near the base of the nose cone. Although I don't really see much difference between the secant and the VK or the Haack.

View attachment 152760
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Von Karman nosecones are slightly "fuller" near the tips than ogives, and are skinnier toward the back. The aft section never goes quite parallel to the body tube.

Also, that "better <-> worse" is a blatant overgeneralization. At really high Mach numbers, conical nosecones are better. Subsonic, length matters more than the shape.
 
Zeroignite said:
Question: if elliptical nosecones have less drag when subsonic (as I've seen claimed in a few places), why are ogives the most commonly seen/produced nose shape? Is it simply aesthetics?
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If you are talking about ogives used on model rockets, that is largely a matter of style preference (unless it is a scale model of something with an ogive)

If you are talking about a "real" rocket/missile (like an AMRAAM), that nose shape is often used for a radome because it is mathematically simple enough for the radar guys to easily program corrections so the radar can "see" through it with minimal distortion.
 
GregGleason said:
The differences are subtle:

View attachment 152790Greg
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powderburner said:
If you are talking about ogives used on model rockets, that is largely a matter of style preference (unless it is a scale model of something with an ogive)
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Yes, they are subtle. I can hardly see what the deal is in model rocketry unless altitudes are a focal point.
And yes, a lot of rocket models use the ogive nose cone because...well let's face it, it's a sharp look on a rocket. I'm all about design and not so focused on altitudes and such. That's why the ogive is my choice when it comes to designing models with a look. They gotta pass the stability factor also.
 
Zeroignite said:
Question: if elliptical nosecones have less drag when subsonic (as I've seen claimed in a few places), why are ogives the most commonly seen/produced nose shape? Is it simply aesthetics?
Ogives aren't optimal at transsonic/supersonic either, where I'd expect to see von Karman noses.

...also, what are good places to find plastic von Karman nosecones?
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Supersonic nose cones make it look like a supersonic rocket even if it's not. Unfortunately the really supersonic cones -- 7:1 von Karman etc. -- tend to be for rockets (or with kits) that are more actually supersonic, or at least are lower diameter and a bit heavy, to handle big thrust and acceleration and which coast half of forever, e.g. Wildman rockets.

Conical is also good if it's even longer and more pointy. Also I have 2 rockets that use them well for a particular look, one is mostly nose cone. That's enough of those and if/when I do another rocket it will be ogive of some kind on a long rocket.
 
GregGleason said:
There is some discussion on high-performance rifle bullets related to the use of the VK profile. Apparently, at least a few long range bullets spend a lot of time in the transonic region.

My guess is the bullet below utilizes a VK shape:

View attachment 152875

from: https://forum.lutzmoeller.net/10,3-mm/Bilder/408/408-MSG-dyn-Druck-900-ms.png

Greg
Click to expand...
https://forum.lutzmoeller.net/index.html is a very good website on bullet design and low drag ballistics. When looking at bullet (or rocket) performance, low drag rather than higher initial velocity, is more important for longest range (or altitude). The total drag is the sum of the nose, body and aft end drag coefficients, and all long range projectiles employ an aft end boat-tail which can reduce aft end dray by up to 80% in some velocity ranges.

The website is in German but Google Translate does a good job translating it into English.

Bob
 
GregGleason said:
There is some discussion on high-performance rifle bullets related to the use of the VK profile. Apparently, at least a few long range bullets spend a lot of time in the transonic region.

My guess is the bullet below utilizes a VK shape:

View attachment 152875

from: https://forum.lutzmoeller.net/10,3-mm/Bilder/408/408-MSG-dyn-Druck-900-ms.png

Greg
Click to expand...

That holder shape influences the reading of the bullet due to the streamlineing that is not present on the actual travel. The holder rod should be of only the minimum diameter to stop flex or vibration. Base drag is nearly non-existant and the actual shockwave pattern is grossly disturbed and distorted. Seeing the wave transitions from body to boat tail then boat tail to flat base are missing and makes the whole photo session a waste of time. The photo leaves out incredibly important parts of a bullet(or rocket) flight. Rockets can have the added benefit of base bleed smoke filling in the vacuum but not much, it takes a larger volume of smoke than a delay element is made to make.


Based on that theory then a 7.62 tracer bullet should exhibit better ballistics than a solid round but I think the ever changing weight throws that off. One thing I do know is the flattest shooting bullet there is is a 7mm in 165 grain Spitzer boat tail hollow point. The vast majority of long range target shooters use this bullet for 1000-2000 yard shots. It's easy to spend over $5000 for one of these custom guns, you can't carry one to shoot off-hand, bench rest only :)

I went to the Lutz Moeller site, very informative. They are a high performance bullet manufacturer. I've only used Speer/CCI but if I was still reloading I'd be looking at their product.
 
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Gary Byrum said:
WOW! I was cruising through my old threads this evening and forgot that you posted this. I'm going to turn one of these on my lathe and build a design around it. It's about time for another BT 80 rocket anyway.
Click to expand...


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?
 
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?
Click to expand...

I just got an order including a BT80 G3 cone. The list of nosecones keeps getting shorter but they still have some in every size including some I didn't know were out there, BT4 anyone?
 
dave carver said:
I just got an order including a BT80 G3 cone. The list of nosecones keeps getting shorter but they still have some in every size including some I didn't know were out there, BT4 anyone?
Click to expand...

Very nice.I'm a sucker for an ogive NC.(damn spell checker doesn't like ogive)

Regarding it's availability, I am unsure, which is why I would turn this one regardless, I guess it's, because I can.
 
The nose cone that was used in the Iris sounding rocket. A 1/10 scale version was the Semroc BC-1180. https://www.semroc.com/Store/Scripts/prodView.asp?idproduct=2002

iris.jpg
 
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Also BNC-50BD, the nose cone that Estes used in the EAC Firecat. I'm not a designer; I just like these shapes.

est0821@.gif
 
dave carver said:
That comes from the "numbered" list? I have a hard time figuring out the code and with no photo makes it hard to know what you're looking at.

Might take some time to try and figure it out, there's a lot of cones left on that list...
Click to expand...
The link in my post should take you right to that n.c.'s (deci-scale Iris) product page.

Semroc apparent no longer has any BNC-50BDs, unfortunately.
 
I went with ogives exclusively when I got into the hobby, but have since swung toward conical more and more. There's a very no-nonsense look to them in my opinion.
 
For a competition bird, I go with parabolic cone.

We had a guy who questioned every aspect of an ELD model for a state-level TARC-style event. He told me that based on what he saw in the Handbook, rounded shapes were better. He failed to read the pressure drag coefficients correctly.
 
I like Conicals, like on my Crossfire and Black Brant II, but my favorites would have to be any of the Cones that I have to make a "Paper Hat" for.
 
Winston said:
VKs and x^1/2 shapes should be more common based upon their performance. I wonder why they aren't.
Click to expand...

I've always wondered this myself. Seems like an odd thing that Ogive cones are so dominant.
 
wfcook said:
I've always wondered this myself. Seems like an odd thing that Ogive cones are so dominant.
Click to expand...

It's prolly more about the look than it is performance. The ogive is indeed a smart looking nose, maybe not the best in performance, but they are more readily available. Haack and VK's not so. The bottom line, to me, is really how a nose cone is of smaller importance than the fins. As a designer, I am more focused on stability than hi powered performance, and lets face it, if your rocket flies exponentially, does it matter what kind of nose cone it has? You might get more altitude using the Haacks and VK's, but, is that what's all about? I say no. I like knowing I made a good decision choosing an adequate nose cone, and proper fins to achieve a stable flight. And that it looks awesome to me.

I did of course turn 4 nose cones that I gave as a gift to LW for his Bday. Both were based on Haack & VK shapes. I'm challenging his crafting ability....if you will. I hope he creates a design he can use them in.
 
Gary Byrum said:
It's prolly more about the look than it is performance. The ogive is indeed a smart looking nose, maybe not the best in performance, but they are more readily available. Haack and VK's not so.
Click to expand...
I don't think there's that much difference in appearance and I really like the 3D look of a 5:1 VK I just created in Rocksim, visually indistinguishable from a tangent ogive, at least to me. Since there's no "ugly" factor involved with the more efficient nose cones and even though most flights are below 0.8 Mach where the differences between shapes are not relevant, as long as they're making injection molds, they might as well make them for the most efficient shapes at all velocities. However, since the molds have already been made, they'd have to wear out the currently used ones for that situation to change. Anyway, who knows, any nose cone that's listed as an "ogive" and looks like a tangent ogive might potentially be a VK already. Only the manufacturer might know.
 
Winston said:
I don't think there's that much difference in appearance and I really like the 3D look of a 5:1 VK I just created in Rocksim, visually indistinguishable from a tangent ogive, at least to me. Since there's no "ugly" factor involved with the more efficient nose cones and even though most flights are below 0.8 Mach where the differences between shapes are not relevant, as long as they're making injection molds, they might as well make them for the most efficient shapes at all velocities. However, since the molds have already been made, they'd have to wear out the currently used ones for that situation to change. Anyway, who knows, any nose cone that's listed as an "ogive" and looks like a tangent ogive might potentially be a VK already. Only the manufacturer might know.
Click to expand...

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

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