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SolarYellow said:
Extremely unlikely that it's exactly elliptical. Most generally "bulbous and rounded" nose cones aren't. The archetype "elliptical" nose cone was the Ranger/Big Bertha, and it was actually a more or less spherically blunted ogive of small fineness ratio, as far as I can tell. Today's plastic replacement that was tooled for the goonies is not really elliptical, as far as I can tell.

I've seen various photos of the Mini Bertha NC and it doesn't look really elliptical. However, they are always of the finished part, after someone has sanded it. With the small size, it's really easy for someone to change the profile just getting it smooth and trying to even everything out by hand.

There are at lease several old kits from the balsa era where the manufacturer's marketing photos show a rounded NC tip, but then you see a vintage bagged kit and the NC that's provided was very much closer to a pointed tip. So someone rounded the tip by hand in finishing the demo/display sample.

FWIW, I'd be pretty astonished if any COTS nose cones prior to the common use of CNC machinery (Carl/Semroc) were actually elliptical within any reasonable tolerance.
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Interesting. That would (to a small degree) invalidate the results of hundreds of science fair projects.
 
Not necessarily. If they tested a bulbous and rounded shape against several other shapes, and their results showed the bulbous and rounded shape to be the best, then those are their results. However, if they used a commercially-manufactured nose cone, it may well be the case that their "elliptical" shape wasn't actually an elliptical profile, just sort of ellips-y.

As a practical matter, the difference between an elliptical and a spherically blunted ogive nose cone of equal overall fineness ratio is utterly splitting hairs at speeds below about Mach 0.75. I haven't seen any science projects looking at that difference. The basis for saying elliptical is best, if you trace it back all the way, is a series of tests done in a water tunnel in about 1947, looking at what would be the best nose shape for torpedoes. They just happened to choose elliptical as one of the shapes to test, and it was better than anything other shape they happened to choose to test. That in no way implies it's the best possible. (By the way, the reports on those tests never calculated a CD. I presume that the chart of CDs in Hoerner, which was then repeated in TIAMR and later in Stine, was generated by someone - likely Hoerner or an assistant - re-analyzing the data published in the water test report.) It may well be the case that alternative shapes could outperform elliptical up to around Mach 0.75-0.8, at which point the Von Karman shape would likely take over by its minimization of pressure drag through the transonic region.

My earlier request for photos of the Mini Bertha NC before it's sanded was based on an interest in accurately reproducing the shape that was actually shipped by Estes, rather than simply assuming it to be an elliptical shape.
 
SolarYellow said:
Not necessarily. If they tested a bulbous and rounded shape against several other shapes, and their results showed the bulbous and rounded shape to be the best, then those are their results. However, if they used a commercially-manufactured nose cone, it may well be the case that their "elliptical" shape wasn't actually an elliptical profile, just sort of ellips-y.
Click to expand...
Well, that was my point. If the project write-up says they tested several shapes, including elliptical, but they actually tested some other shape, then the project is, to a small degree, invalid. They'll have shown that the bulbous mystery shape is better than the others tested. I am most certainly splitting hairs.
My earlier request for photos of the Mini Bertha NC before it's sanded was based on an interest in accurately reproducing the shape that was actually shipped by Estes, rather than simply assuming it to be an elliptical shape.
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Yes, I understood. I'll be interested to see what you find.
 
Stock orders. Looks like the Estes Tazz, Interceptor, Cosmic Interceptor, MAV and Mini HoJo are going to be off the Estes kit list. A couple of others as well (I don’t have the list in front of me).

Avoided the temptation to stock up Leapers… 😆

Nice big order to Custom Rocket Company for parts. Have to clean up for some kit runs.
 
Plugging away at the Nuclear Crowbar build. Yesterday I started the fin ring fillets. Once they are complete, it's a bit of sanding and then a final coat of filler primer. Then a coat of Createx Autoborn Sealer. And then on to the color spray. I did get my colors mapped out; I figured a rocket with the word 'nuclear' in it should look MIL.
 

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ac2fv said:
Plugging away at the Nuclear Crowbar build. Yesterday I started the fin ring fillets. Once they are complete, it's a bit of sanding and then a final coat of filler primer. Then a coat of Createx Autoborn Sealer. And then on to the color spray. I did get my colors mapped out; I figured a rocket with the word 'nuclear' in it should look MIL.
Click to expand...
Will it have a nuclear hazard symbol?
1709916131715.png
 
SolarYellow said:
Not necessarily. If they tested a bulbous and rounded shape against several other shapes, and their results showed the bulbous and rounded shape to be the best, then those are their results. However, if they used a commercially-manufactured nose cone, it may well be the case that their "elliptical" shape wasn't actually an elliptical profile, just sort of ellips-y.

As a practical matter, the difference between an elliptical and a spherically blunted ogive nose cone of equal overall fineness ratio is utterly splitting hairs at speeds below about Mach 0.75. I haven't seen any science projects looking at that difference. The basis for saying elliptical is best, if you trace it back all the way, is a series of tests done in a water tunnel in about 1947, looking at what would be the best nose shape for torpedoes. They just happened to choose elliptical as one of the shapes to test, and it was better than anything other shape they happened to choose to test. That in no way implies it's the best possible. (By the way, the reports on those tests never calculated a CD. I presume that the chart of CDs in Hoerner, which was then repeated in TIAMR and later in Stine, was generated by someone - likely Hoerner or an assistant - re-analyzing the data published in the water test report.) It may well be the case that alternative shapes could outperform elliptical up to around Mach 0.75-0.8, at which point the Von Karman shape would likely take over by its minimization of pressure drag through the transonic region.

My earlier request for photos of the Mini Bertha NC before it's sanded was based on an interest in accurately reproducing the shape that was actually shipped by Estes, rather than simply assuming it to be an elliptical shape.
Click to expand...
Do you still need a photo of the Mini Bertha nose cone. Just got a kit this week and am building it now but I haven't touched the nose cone yet. It's listed as a BVC-20L, BMS sells them.
 
Jeff Curtis said:
Do you still need a photo of the Mini Bertha nose cone. Just got a kit this week and am building it now but I haven't touched the nose cone yet. It's listed as a BVC-20L, BMS sells them.
Click to expand...

I'd love to see a photo of a nose cone from an original kit, with a good view of the profile before it's been sanded.
 
jqavins said:
Well, that was my point. If the project write-up says they tested several shapes, including elliptical, but they actually tested some other shape, then the project is, to a small degree, invalid. They'll have shown that the bulbous mystery shape is better than the others tested. I am most certainly splitting hairs.

Yes, I understood. I'll be interested to see what you find.
Click to expand...
In my experience with various CAD programs and reference images, the Bertha nosecones are not elliptical (agreeing with previous comments). Best result I got was ogive + sphere (spherically blunted ogive - again agreeing with what was said) but ultimately just traced the outline to create a Bertha NC shape. True ellipsoid was more pointy than the Bertha NC (looking at both virtual CAD designs as well as physical 3D prints).

https://www.rocketryforum.com/threa...not-a-default-one-anyway.174269/#post-2309575
 
Went to Hog Heaven in Sturbridge, MA and too advantage of a sale there. Got a pack of D12-5s, D12-3s, and two packs of A8-3s, as well as more 30 minute epoxy.

I also picked up the two sets of chutes for my 5.5" LOC Bullet. One set will be for when it flys at Amesbury with CMASS and the other set will be for LDRS.
 
Primed and sanded the BT for my Big Bertha.

Sent my DRM and Swift for their maiden flights. The DRM went beautifully on a B6-4, nice and low which suited the park I was launching from. The swift vanished from sight on a 1/2A4-2T, a short while later noticed the ejection charge and then spent 20min trying to find it. Eventually found it fins up right at the edge of the field I was flying in. Second flight much smoother, even recovered the spent engine.1000000757.jpg1000000758.jpg
 
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