Nose cone considerations, questions, and frustrations.

[Senior Space Cadet]

First, let me say that I've been thinking about what I want out of my rockets and rocketry. On launch day, what turns my crank is seeing a rocket, I designed and built, go fast, high, and straight. I don't care how big and cool looking my rocket is, if it only goes up 100 ft. or flies erratically, I'm disappointed. And I want my rockets to be inexpensive to fly and easy to prep for launch. I'm thinking of sticking to, mostly, 18mm motors and 24mm and 33mm body tubes. You can do quite a lot with that.
So, back to nose cones.
I'm pretty sure that I want an ellipsoid nose cone for low power rockets.
At least one article, I read, seemed to indicate that I wanted a 5 to 1 length to base diameter ratio.
So, maybe, if I were designing and making my own nose cones I'd make an ellipsoid with the 5 to 1 ratio.
Thing is, I don't make my own nose cones. And, except for one possible exception, an ellipsoid, 5 to 1 nose cone doesn't exist in the marketplace.
The closest thing I can buy is a balsa nose cone from Balsa Machining, and one really nice 41.6mm plastic nose cone from Estes.
As a nose cone material, balsa has advantages and disadvantages. Personally, I'd prefer a fairly solid plastic.
In plastic you can get any shape you want, as long as it's ogive. Other choices are pretty limited.
Ogive is pretty far down the list of most efficient shapes.
So, one question might be: which is better, a 5 to 1 ogive or a 3 to 1 of a better shape, such as ellipsoid or parabolic?
Or is this in the nit-picking or who cares category?

 

[dhbarr]

At anything below Mach ~0.8 ( 600mph ) they all perform somewhat similarly. Yes, a long elliptical might be optimal, but ( to me ) those extra few percent of performance aren't usually worth it.

Note that the space modeling competitors -do- find this sort of thing worthwhile, with hand-rolled everything, etc.

 

[OverTheTop]

Openrocket is you friend here. You can try different shaped noses on the same rocket, keeping the launch mass the same and see what difference there is in altitude out of the simulations. This is one of the primary uses of simulations, comparing different forms to get a feel for how much each change is "worth". As dhbarr said, if you are below transonic there will not be much difference between all the traditional shapes. Haack or von-Karman will probably get you quite good results, but there other shapes that perform similarly.

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

 

[XrayLizard]

aha! hah whats better is to buy a small wood or metal lathe! and make them
it would be an investment in yourself and for the future

 

[lakeroadster]

aha! hah whats better is to buy a small wood or metal lathe! and make them
it would be an investment in yourself and for the future

Plus then you can make transitions, centering rings and a plethora of other projects.

 

[XrayLizard]

Nice work !
Sometimes a good lathe at a very good price will show up on Craigslist

 

[Senior Space Cadet]

aha! hah whats better is to buy a small wood or metal lathe! and make them
it would be an investment in yourself and for the future

It would be nice. If I got good with it, there is no limit to what I could do rocket wise.
I'm guessing they aren't cheap, but I'll look into it. Let's see, sports car or lathe, hmmm.

 

[OverTheTop]

If you are looking at lathes get a metal one. You can do wood on a metal lathe but nit vice versa.

Sports car is way more expensive than a small lathe. Get both.

 

[Senior Space Cadet]

At anything below Mach ~0.8 ( 600mph ) they all perform somewhat similarly. Yes, a long elliptical might be optimal, but ( to me ) those extra few percent of performance aren't usually worth it.

Note that the space modeling competitors -do- find this sort of thing worthwhile, with hand-rolled everything, etc.

I need to get that Johnny Rocket gadget. I'm working on an 18mm minimum diameter rocket that I'll power with a C12, if not a D16. Probably pretty fast, but maybe not Mach 0.8. But I'm working on the Dave theory. A little bit here and a little bit there, adds up to a lot. Just got some plastic parabolic nose cones that might be better than the ogive. Nearing Mach one, I'm not sure what would be better, long ogive, parabolic, or ellipsoid?

 

[GlenP]

Those are great questions, look to airplane noses for some reference geometries that can inspire choice of model rocket noses that fly in similar flight regime. Granted they make different trade offs for windows and pilot visibility, but generally the lower speed fuel efficient transport passenger plane has a fairly short rounded nose compared to an F-16 fighter, or the X-15. Transonic and supersonic noses get pointy to reduce the compression wave drag. Slower speed noses tend to reduce the total surface area to reduce skin friction drag.

Fineness ratios observed for the high speed pointy noses tend to reach the point of diminishing returns for reducing the wave drag at the expense of added skin friction, ie you can reduce wave drag more with a longer nose, but eventually you end up adding more skin friction drag and weight than you saved.

Welcome to rocketry! This is the fun stuff.

 

[lakeroadster]

It would be nice. If I got good with it, there is no limit to what I could do rocket wise.
I'm guessing they aren't cheap, but I'll look into it. Let's see, sports car or lathe, hmmm.

A $200 dollar sports car? Must be a Triumph?

 

[Amsterdam]

Harbor freight bench top lathe

ive had this since December 2018 It works great, I must admit I find myself using my bench top drill press more often for turning,

Harbor freight bench top drill press

before I got theses tools I carved by hand, it’s not hard Especially with soft woods or foam insulation, just make sure you get enough blanks to practice with (balsa and especially foam are cheap by even the most frugal standards)
if you must have hollow plastic parts look into how scale plane builders make canopy’s and spinners, most of these builders do all of their work by hand.

Hippocket forum

the end results you want are not expensive pipe dreams, you could make any low-mid power nose cone, any boat tail, ogive body, literally anything, by hand If you honestly try.

 

[bmonagle]

In my (MUCH) younger days (Late 60s) I turned many balsa nose cones and transitions using using my father's metal cased 1/4 inch non-variable speed drill. With a little ingenuity and work, just about anything can be fabricated

 

[Kelly]

I'm not going to talk anyone out of buying a lathe, but at this size, you should also consider a 3D printer. You can get near-perfect cones of any shape imaginable at the push of a button.

 

[XrayLizard]

The jet lathe above is one fantastic deal
I would taken it immediately

 

[Jeff Lassahn]

I'm also frustrated with the selection of off-the-shelf noses. Balsa Machining seems to be the best selection out there. And we may just have to make our peace with balsa as a nose material because the setup costs of making a good plastic nose are high enough that the selection in plastic is always going to be more limited.

To answer your actual question, yest it's kind of nitpicking. Particularly since an "ogive" nose in a small size will sometimes have a rounded tip instead of coming to a true point. Which makes it act more like an elliptical.

At low power rocket speeds the difference between a really good nose and a kind of good nose is going to be a few percent of the total drag on the rocket. Surface finish matters more. Fin shape matters more. Base drag matters more. Launch lug drag matters more.

The difference in drag force between an 18mm diameter rocket and a 24mm rocket is almost 2 to 1. So if you're optimizing for drag, make your rocket minimum diameter. That's bigger bang for the buck than optimizing nose and fin shapes.

But since you ask, I think the answer to which is better is "no one knows".
The optimum for length to diameter ratio depends on the relationship between friction drag and form drag. Form drag goes up roughly as the square of the velocity while friction drag goes up slower more like the first power. So the best choice is highly speed dependent.
It's also dependent on things that change friction drag, like surface finish, how turbulent the boundary layer is, and a host of other stuff that's really hard to estimate.

You also can't simulate this stuff with a computer. Programs like Rocksim and OpenRocket do not have a sophisticated enough model of drag forces to give a useful answer to questions like this. It's possible _nobody_ has sophisticated enough computer models of drag to give reliable answers to these questions. Maybe somebody like Boeing or Airbus has really fancy CFD code that can help them get the last few percent of fuel efficiency from their nose shapes, but I wouldn't be surprised if event the big guys have to do experimental testing.

 

[dhbarr]

I need to get that Johnny Rocket gadget. I'm working on an 18mm minimum diameter rocket that I'll power with a C12, if not a D16. Probably pretty fast, but maybe not Mach 0.8. But I'm working on the Dave theory. A little bit here and a little bit there, adds up to a lot. Just got some plastic parabolic nose cones that might be better than the ogive. Nearing Mach one, I'm not sure what would be better, long ogive, parabolic, or ellipsoid?

https://en.wikipedia.org/wiki/Nose_cone_design#Influence_of_the_general_shapeand
https://en.wikipedia.org/wiki/Nose_cone_design#Influence_of_the_fineness_ratiosummarize pretty well, or for more detail
https://www.offwegorocketry.com/userfiles/file/Nose Cone & Fin Optimization.pdfbut the tl;dr is there's a reason so many kits come with 5:1 Von Karman

 

[n27sb]

A $200 dollar sports car? Must be a Triumph?

Some of us have one. Would not sell for $200

 

[John Kemker]

A $200 dollar sports car? Must be a Triumph?

Complete with original Lucas wiring!

Q: Why do the British drink warm beer?

A: Lucas makes refrigeration, also.

 

[Cape Byron]

Complete with original Lucas wiring!

Q: Why do the British drink warm beer?

A: Lucas makes refrigeration, also.

Oh yeah. I had a Triumph Dolomite Sprint, 2 litre 127BHP 4 cylinder 16 valve SOHC with electric Laycock overdrive.

Great performance and handling. Electrics by Joseph Lucas, the Prince of Darkness'.

 

[tsmith1315]

Some of us have one.

Wow. I didn't see that coming when I opened the pics! Seriously interesting. Lots of questions some to mind.
But, what will you do for the British sports car sound? I don't think I could shift gears without it!

 

[n27sb]

Wow. I didn't see that coming when I opened the pics! Seriously interesting. Lots of questions some to mind.
But, what will you do for the British sports car sound? I don't think I could shift gears without it!

PM Sent so not to distract.

 

[lakeroadster]

Some of us have one. Would not sell for $200

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Nice... and a fair bit away from OEM! Pretty quick?

Wow. I didn't see that coming when I opened the pics! Seriously interesting. Lots of questions some to mind.
But, what will you do for the British sports car sound? I don't think I could shift gears without it!

It has a tachometer... but a tachometer with shift light would be better.

 

[prfesser]

I've made more than a few nose cones using a drill press. So far the largest has been 2" x 10" long. For rigidity, instead of a wood dowel I drill a 3/8" or 1/2" hole for an aluminum rod and glue it in place with epoxy. When finished, a piece of copper or brass tubing slightly larger than the rod has notches cut in the end, and is used to cut the rod free, by hand. The hole where the rod was is then filled with epoxy + microballoons, or a dowel whittled from scrap balsa is epoxied in place.

Best -- Terry

 

[XrayLizard]

with electric Laycock overdrive.

That’s what she said !