"Best" Nose Cone Shapes? =advanced=

I found the attached (zipped .doc) file to be a very interesting read. According to this, the conical nose is not the best for Mach busters, and not even close. Anybody got pointers to data that shows otherwise?

This
https://myweb.cableone.net/cjcrowell/VCPMAIN.htm
is where it came from.

I've seen similar data online somewhere. Try googling the references, or ask on the arocket email list, I think that's where I originally followed the link from.

Here's the data I was thinking of. As I thought, it's one of the references in the doc you posted: https://naca.larc.nasa.gov/reports/1958/naca-report-1386/

I'll see if I can dig up more info for or against later when I have some time, but for now I think the explanation is similar to one I've offered in related threads. Specifically: multiple weak shocks is better than one strong one. First a little review: oblique shocks are weaker than normal (i.e., 90 degrees relative to the flow) shocks. So, from a trans/supersonic perspective, worst case would be a blunt nose (cylinder) which would create a big, strong normal shock. Better would be a cone that would create a single oblique shock. Bestest (as my 4 year old daughter would say) would be a curving surface (not just *any* curving surface, mind you, but one that was designed to minimize shock strength - i.e., von Karman) that creates multiple weak oblique shocks. Witness the different types of jet inlets: Internal compression using a single normal shock is worst. External compression using an external oblique shock is better. And mixed compression using a series of oblique shock waves is bestest.

Here's a reference: https://aerodyn.org/Drag/super-drag.html

Here's another point (not to be confused with the point of a cone): One reason you see cones on older trans/supersonic designs is that they are much easier to analyze. Nice straight lines with only one or two angle changes are a supersonic aerodynamicist's dream when all you have is a slide rule and pocket protector. For a *much* more theoretical discussion (one of those that is more equations than words), I'd refer you to one of my old textbooks (a classic): "Elements of Gasdynamics" by Liepmann & Roshko. Chapter 9 (of my edition anyway) is Bodies of Revolution - Slender Body Theory, and it gets into all the mathematical nastiness. You'll quickly see why '50s era aerodynamicists would have stopped at section 9-9 "Solution for a Cone", and not bothered much with section 9-12 "Slender Body Drag" which gets into von Karman's general formula.

From what I have read Von Kaarman shapes are best for their volume while cones are best for their surface area. I've rarely seen sounding rockets with Von Kaarman nc. I guess they are too had to manufacture and relatively insignificant because sounding rockets do fly so high where the atmosphere is thinner and therefore there is less drag. I have heard of VK nc being filled with avionics because they do give a large internal volume for relatively low drag.

Originally posted by illini
Here's another point (not to be confused with the point of a cone): One reason you see cones on older trans/supersonic designs is that they are much easier to analyze. Nice straight lines with only one or two angle changes are a supersonic aerodynamicist's dream when all you have is a slide rule and pocket protector.

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And I believe that's a crux of a problem with rocketry today. Our "best" is often the "best they could do at the time", and that time was quite a while ago. Combining this "should be built like" with our tendency towards "should look like" copying of rockets we know to be real rockets, and a lot of what we do is the same as we've done for 40+ years.

A lot of our research we follow is internal and so reviewed only by people who "know" the old things, and often aren't as qualified scientifically as the people doing the research itself. They get high marks for doing good research, not for producing what others independently determine to be the real best result. Many of them go on to become professionals, but in reality based on doing good research, which does not have anything to do with producing the real best result. Nor should it. We have fail as well as succeed in order find the edges of the envelope. But our legacy is information which is good, but we mistakenly accept as best.

Originally posted by DynaSoar
And I believe that's a crux of a problem with rocketry today. Our "best" is often the "best they could do at the time", and that time was quite a while ago. Combining this "should be built like" with our tendency towards "should look like" copying of rockets we know to be real rockets, and a lot of what we do is the same as we've done for 40+ years.

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I certainly saw that trend in the "big" solid rocket motor company where I worked as well. The philosophy there was "build 'em and burn 'em". In fact, they could have made that the company motto...maybe even the stock ticker symbol (BEBE). Every motor design was based on what worked previously. Engineering was nothing more than prior experience. Do a few test firings and if it doesn't blow up then you call it a success...at least until people start dying due to your mistakes. Most of my work was when problems occurred and then they actually had to figure out what went wrong...not that they actually cared about the *real* answer so much as the one that would make things *nice* with the customer. Not that I'm bitter or anything...

As for your second point, have you read Thomas Kuhn's "The Structure of Scientific Revolutions"? Good read. You'd agree with much of it.

Originally posted by illini
I certainly saw that trend in the "big" solid rocket motor company where I worked as well. The philosophy there was "build 'em and burn 'em". In fact, they could have made that the company motto...maybe even the stock ticker symbol (BEBE). Every motor design was based on what worked previously. Engineering was nothing more than prior experience. Do a few test firings and if it doesn't blow up then you call it a success...at least until people start dying due to your mistakes. Most of my work was when problems occurred and then they actually had to figure out what went wrong...not that they actually cared about the *real* answer so much as the one that would make things *nice* with the customer. Not that I'm bitter or anything...

As for your second point, have you read Thomas Kuhn's "The Structure of Scientific Revolutions"? Good read. You'd agree with much of it.

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Read it? I taught it.

Before we ever got to the history or the systems part of "Systems and History", my students had to learn the difference between "Science" and real science (including real scientists). They read Kuhn, and then Collins & Pinch's "The Golem".

I live by Kuhn. Being ahead of the Kuhn curve in psychology was a problem for me. I was applying analyses from radio astronomy and stuff to EEG. My bosses semed impressed and liked to show me off to the other P.I.'s but they wouldn't help me put out any papers becuase they couldn't understand what I was talking about. The people who were turning down my papers at the journals were trying to say what was wrong with them, but they didn't understand it either.

That pretty much explains my ornery attitude towards a lot of rocketry. I doubt everything, and experts most of all. Anybody who's ever going to be righter than they were in their day has to do that.

Originally posted by DynaSoar
Read it? I taught it.

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Ah HAH!!! I suspected you were a Kuhnian! It really *is* amazing how right he was. I got out of the aerospace biz in part because I couldn't believe how stupid the "experts" were. It was absolutely impossible to do anything new there. Build 'em and burn 'em. Don't bother to think. Don't ask questions. Just build 'em and burn 'em...

Even in my new line of work (if the last 11 years could be called "new") I still run into those issues regularly. Leading edge stuff that changes the paradigm gets trivial funding, but if you want to improve an existing system by a few percent, why then the R&D agencies can't wait to shove millions in your direction. Given the options, I'd rather accept the trivial funding and break new ground than accept millions to reinvent the wheel.

Originally posted by illini
Here's another point (not to be confused with the point of a cone): One reason you see cones on older trans/supersonic designs is that they are much easier to analyze. Nice straight lines with only one or two angle changes are a supersonic aerodynamicist's dream when all you have is a slide rule and pocket protector....

Click to expand...

They're also much easier to make. The MASA Planet newsletter ran a series on turning nose cones several years ago, and the authors presented superimposed plots of the various shapes. There isn't much difference--If you're not careful with a balsa nose cone, you could sand away the differences !

[Those drawings are here: https://www.mn-rocketry.net/masa/planet/masa_Vol6-1.pdf, and subsequent issues have two articles on how to turn the nosecones themselves.]

FWIW,

--tc

Originally posted by Ted Cochran
They're also much easier to make.

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Exactly right. That's what you call a two-fer. Easier to analyze AND easier to make. Shazam!

Originally posted by illini
As for your second point, have you read Thomas Kuhn's "The Structure of Scientific Revolutions"? Good read. You'd agree with much of it.

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This was a History course at Ohio State that was full of Engineers. I actually have went back and read the book a couple of times for reference. I wrote my paper about the revolution in fluid dynamics, great father/son battle.

The 29mm nose cone for the Apogee Aspire is a Von Karman design--the originals were balsa--Tim is now selling plastic versions.

If you want to make a career out of pushing the envelope, I suggest writing for a magazine, ideally as a regular columnist. Once you prove yourself as someone who can write reliably month after month, you often have an amazing amount of freedom to push new ideas and concepts.

Voltaire, Dictionnaire Philosophique

The best is the enemy of the good. I can just see the scientist walking into the engineer's office with the grand plans for the best nose cone ever. The engineers smile politely and say they'll get right on it. A few back of the envelope calculations later they decide it will cost three times as much and delay the project for months while showing only a modest improvement over a cone.

It comes down to economics--better designs are only better if the end result justifies the added expense--time, money, accuracy, whatever.

Definitely venturing into "Coffee House" territory here (may have to move my own post ), but I remember this cartoon that showed four different engineers' drafts of the the same airplane design. The aerodynamicist envisioned a sleek, contoured design. The propulsion guy - a huge honkin' engine inside a basic airplane. Stability and control - massive control surfaces. Structures - I-beams welded together in the basic shape of an airplane.

Its more than economics. Any *real* engineering is always a compromise of multiple competing requirements. However, where I draw the line between engineering and stupidity is this: Good engineers understand the physics and math leading to the optimal solution to meet a subset of the requirements, then compromise from there in order to meet all requirements. Stupidity is when designs are not questioned, based more on past designs than current requirements, and/or are the result of a vote (what I call "engineering by democracy" - an all too common practice).

Originally posted by illini
Definitely venturing into "Coffee House" territory here (may have to move my own post ), but I remember this cartoon that showed four different engineers' drafts of the the same airplane design. The aerodynamicist envisioned a sleek, contoured design. The propulsion guy - a huge honkin' engine inside a basic airplane. Stability and control - massive control surfaces. Structures - I-beams welded together in the basic shape of an airplane.

Its more than economics. Any *real* engineering is always a compromise of multiple competing requirements. However, where I draw the line between engineering and stupidity is this: Good engineers understand the physics and math leading to the optimal solution to meet a subset of the requirements, then compromise from there in order to meet all requirements. Stupidity is when designs are not questioned, based more on past designs than current requirements, and/or are the result of a vote (what I call "engineering by democracy" - an all too common practice).

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I'll be starting a new rant in the forum so we'll have someplace to attack a more objective topic. So, as a last thought: one of the 4 most productive spin offs from the space program from Mercury through Apollo was systems analysis programs. In a highly complex system, optimization is an enormous problem, and results can pop out from completely non-intuitive combinations. It wasn't until 20 years later that complex dynamic systems became a field on its own with a dedicated research center and a set of general guiding principles. Seems to be a fairly valid line of research. As far as I know it's the only field to derive and predict a natural constant prior to its discovery.

Originally posted by DynaSoar
In a highly complex system, optimization is an enormous problem, and results can pop out from completely non-intuitive combinations. It wasn't until 20 years later that complex dynamic systems became a field on its own with a dedicated research center and a set of general guiding principles. Seems to be a fairly valid line of research. As far as I know it's the only field to derive and predict a natural constant prior to its discovery.

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Preachin' to the choir! Complex systems of systems analysis is what my company does. One of my areas of expertise now (since abandoning the aerospace world) is developing and applying evolutionary computation methods (e.g., genetic algorithms) for the solution of complex problems.

Originally posted by Ted Cochran
They're also much easier to make. The MASA Planet newsletter ran a series on turning nose cones several years ago, and the authors presented superimposed plots of the various shapes. There isn't much difference--If you're not careful with a balsa nose cone, you could sand away the differences !

[Those drawings are here: https://www.mn-rocketry.net/masa/planet/masa_Vol6-1.pdf, and subsequent issues have two articles on how to turn the nosecones themselves.]

FWIW,

--tc

Click to expand...

I'm getting a 404 on that link.
But I found it on the web site.

Ah, comma after PDF
should be period.

Originally posted by illini
Preachin' to the choir! Complex systems of systems analysis is what my company does. One of my areas of expertise now (since abandoning the aerospace world) is developing and applying evolutionary computation methods (e.g., genetic algorithms) for the solution of complex problems.

Click to expand...

The best summer of my life was spent playing with such things at Santa Fe. I learned more about signal analysis there than in all the years before or since, and it wasn't even presented as signal analysis, just time series. One of my 'breakthrough' EEG analysis techniques was published in the same month as the same technique applied to fossil data in order to refute catastrophe theory as the basis of punctuated equilibrium. We both picked it (recurrence plot analysis) from there. Unfortunately for both of us, the major players in our fields couldn't accept it because they couldn't understand it.

One of BT's chief scientists was there at the time learning GA and applying it to network switching. They got some major patents out of that. Engineers are a lot more likely to accept what works than scientists are. Favoring the practical over the theoretical, I assume.

Originally posted by DynaSoar
Engineers are a lot more likely to accept what works than scientists are. Favoring the practical over the theoretical, I assume.

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Well...as I said, funding tends to be light for this stuff. Most of my work is to apply these fancy techniques to the military domain and related. Folks are as skeptical there as anywhere since this is new ground for them. But at the end of the day I'm betting they'll come around once they see what we're enabling them to do. Believers are still few and far between.

Originally posted by DynaSoar


Ah, comma after PDF
should be period.

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My bad for trying to embed a link in a grammatical sentence

I have the spreadsheet around here somewhere that did those drawings if anyone is interested.

--tc

Originally posted by Ted Cochran
My bad for trying to embed a link in a grammatical sentence

I have the spreadsheet around here somewhere that did those drawings if anyone is interested.

--tc

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Please do.

.xls is a valid type for attaching here.

Might also consider submitting it to EMRR's 'tools' section.

Originally posted by DynaSoar
Read it? I taught it.

I live by Kuhn.

That pretty much explains my ornery attitude towards a lot of rocketry. I doubt everything, and experts most of all. Anybody who's ever going to be righter than they were in their day has to do that.

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I strongly agree.

Jerry

Originally posted by DynaSoar
I found the attached (zipped .doc) file to be a very interesting read. According to this, the conical nose is not the best for Mach busters, and not even close. Anybody got pointers to data that shows otherwise?

This
https://myweb.cableone.net/cjcrowell/VCPMAIN.htm
is where it came from.

Click to expand...

Back in the old mid 70s, we mod rockers were told to use a parabolic cone for transonic and just nearly supersonic designs.

We were taught that the conicle design was best for superduper sonic speeds.

I forget what they were but always just reconed it was about mach 2 or better that the cone worked best.