How to Make a Von karman Nose

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Mohamed

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is it possible to make a VK cone by myself ? Any ideas how to manufacturing it ?
 

Bat-mite

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What material? Solid or hollow? What size? For a model rocket, you could use balsa and turn it on a small lathe. Others use rings of foam for the shape, then cover with fiberglass cloth. All of this requires knowledge of machining and CAD.
 

Igotnothing

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Ahem - CAD is optional.

- Signed: Guys (and gals) who made things before CAD
 

REK

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Sketch out the curve, build with foam, cut with hotwire, cover with fiberglass.

I think John Coker had a video on it.

something like https://www.youtube.com/watch?v=5mUKQ7CUd8I , in which he does a transition
You can also find this method a lot in the Australian Rocketry Forums. They do it all the time for their scratch built projects.


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OverTheTop

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Ahem - CAD is optional.

- Signed: Guys (and gals) who made things before CAD
Ah. Those were the days. No CAD, no internet. Such simple times. Thank goodness for progress. I am so glad we have CAD and internet now :)

Having said that, I have been known to regress to methods from earlier times when I need to get a job done without a learning curve. Whatever gets you where you need to go is OK. Use the resources and capabilities you have available. YMMV.
 

Pointy_end_up

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If you have Matlab, Solidworks, and a 3d printer you can go to this website; https://www.instructables.com/id/Design-a-Rocket-Nose-Cone-with-Software/ Be sure to double check the matlab output as I remember having to modify the code a little.

I've used that process to successfully fabricate a LV-HAACK nosecone.

If you don't have a lot of fancy software and printers, then there is a wikipedia page; https://en.wikipedia.org/wiki/Nose_cone_design that has all of the formulas. You can take that, stick it into excel, plot the curve, print it to scale, cut it out and now you have the profile to carve a foam mold to like what is outlined in the Jon Coker video discussed earlier.

20170630_165226.jpg
 

Viking

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...
If you don't have a lot of fancy software and printers, then there is a wikipedia page; https://en.wikipedia.org/wiki/Nose_cone_design that has all of the formulas. You can take that, stick it into excel, plot the curve, print it to scale, cut it out and now you have the profile to carve a foam mold to like what is outlined in the Jon Coker video discussed earlier.
There's already an excellent excel spreadsheet for that:
https://www.rimworld.com/nassarocketry/fabrication/nosecones/spreadsheet.html
 
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Mohamed

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I've used that process to successfully fabricate a LV-HAACK nosecone.

If you don't have a lot of fancy software and printers, then there is a wikipedia page; https://en.wikipedia.org/wiki/Nose_cone_design that has all of the formulas. You can take that, stick it into excel, plot the curve, print it to scale, cut it out and now you have the profile to carve a foam mold to like what is outlined in the Jon Coker video discussed earlier.
what's better for 4'' D and 20 Length >>> make a mold use a wood plug and layup fiberglass fiber inside it , OR use a Foam as shape with fiber cloth
 

Incongruent

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Are you going to be putting anything (electronics, nose weight, laundry, etc.) into the nose cone?
Can you fill and sand a block of wood repeatedly for excessive periods of time without going insane or acquire a cone of the proper profile?

If Yes to both, the former option will work.
If Yes to the first only, you can dissolve the foam with acetone.
If Yes to the second only, it doesn't matter


Oh, and did you mean four foot diameter or four inch diameter?
 

Incongruent

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Someone shared a video above which does it by sanding an array of styrofoam blocks glued to a guide down to shape on a lathe, but if you don't have the equipment, you can approximate the shape with a hot wire jig shown in here and then sand it to shape (or create a better design/ improve the current one).

To sand it, mask the nose cone profile to prevent sanding the jig (replace the tape periodically), then use a sanding block to smooth out the cone and get close to the shape.

Calculate the thickness of the fiberglass you will use and factor that into the nose cone profile in the jig.


Can you tell us your experience with rocketry so we can describe the processes according to your skill level?
 

fyrwrxz

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Depends, how big is the parachute for recovery?
LOL! Maybe it depends on motor size? That would help define the thickness of the tube which in turn would help with the shoulder thickness/step which could dictate the material to start with? Somehow the mass of the nosecone relates to the size of the chute. Or are we figuring internal volume? Solid or hollow? Hmmmm-expiring minds need to know.........
 

RCgothic

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Making a von karman profile is more difficult than a more analytic profile. If you have to approximate it and then smooth, that's going to be more draggy than an ideal surface?

How perfect does the real nose cone approximation have to be before it's worth just going with a profile you can easily jig, like a tangent ogive?
 

OverTheTop

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I think the VK is the ultimate, but there are other Newtonian solutions that can be made that are quite close in performance (0.02% IIRC). Not sure of the amount of difference between VK and tangent ogives.

If it were me I would aim for the VK profile (lots of information around, and easier than figuring out how to apply Newtonian physics in a solver). If it is not perfect it will probably be quite acceptable.

I am happy to be corrected if there is somebody that knows aerodynamics better than me.
 

dhbarr

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VK is optimal trans-mach, which is important for most of our flights.

My rough understanding is the power series is superior in the m2/3 range, which is typically of less concern to your average flyer.
 

Mohamed

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some replies made me more confused. let's say the problem in VK is to make the perfect shape of Mould ,
but what about the tangent ogives notice that mach number around .9 ?

 

Binder Design

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Fusion 360 has a good CAD/CAM package. Molds/plugs are no problem. Export g-code to CNC or just send the file over to your favorite slicer for 3D printing. Cake.

2.6 Von Karman final v15.jpg
 

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