Cross posted here and at that other forum. So far zero replies there.

Figured this is the best section of the forum, since it's about specific historical model rockets.

Semroc Balsa Nose Cone ST-13 2.7" Bezier SEM-BC-1327
https://www.erockets.biz/semroc-bal...er-sem-bc-1327/

I understand this nose cone is a balsa "clone" of the shape used on the original Enerjet Nike-Ram and the earliest appearances of the 1340 sounding rocket. It is described as a "Bezier" curve. I'm assuming that means it's some kind of Bezier curve rotated about a central axis. I'd like to generate this geometry accurately for 3D printing upscales and downscales, as well as generating a part directly that has a shoulder of the correct diameter to work with LT-125 tubing. Also, with erockets discontinuing the ST-13 tubing, it's hard to imagine them keeping this NC in stock. Other than just buying one or two and measuring them, does anyone have access to the mathematical (Bezier points, etc.) details that defined the shape originally? Or a dimensioned drawing of the original?

Noted that AeroTech is re-releasing the Enerjet Nike-Ram this year on 35mm Quest tubing. That's cool and I may buy one if the nose cone looks right*, but it doesn't help with cloning the 1340 or up- and downscales.

*Gary has said that it will likely use an existing Quest nose cone, not an accurate replica of the original, so jury is out on whether I'll like it enough to build it.

I have an EnerJet Nike-Ram with the plastic nose cone. I took a picture of it and traced over it in CAD. The attached pdf shows the points used to create a spline that I revolved to make the cone. It is pretty close to the photo (I scaled it using the shoulder length/diameter and base diameter to get proper dimensions).

Finally, I created an stl file for printing, but I'm not sure of the settings to get a good printable file, so YMMV with that one.

Attached Thumbnails

 

Attached Files

	NikeRamNose.PDF (92.4 KB, 22 views)
	NikeRamNose.STL (682.6 KB, 8 views)

__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here

Awesome, thanks!

It's interesting that it's 1.36 for the base OD, the ST-13 tubing that other information says the Nike-Ram was made with is supposed to be 1.34 inches.

Well, I was measuring over paint so you might subtract a little for that. The shoulder was not painted. My actual measurement of the base (over paint) was 1.357 in one direction and 1.362 in the other (90 deg apart). I used the average of 1.3595 in the CAD model and rounded to 1.36 in the table.

EDIT: and I feel a bump between the body tube and base of the nose on my model.

__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here

Thanks for the additional detail.

While Centuri parts were for the most part very 'precision' in their fit, some of the plastic nose cones were a bit oversized at their interface with their respective tube size. In particular, the PNC-74 and the PNC-76 both really require sanding around the lower part of the cone (not the shoulder) to avoid having that 'bump' at the nosecone/bodytube interface once the nosecone is socketted into place. Other plastic nosecones, such as the PNC-132 being discussed in this thread, may have varying degrees of the same issue.

Earl

__________________
Earl L. Cagle, Jr.
NAR# 29523
TRA# 962
SAM# 73
Owner/Producer
Point 39 Productions

Rocket-Brained Since 1970

That's really too bad. I can see using existing T-35 tubing, since it's darn close, but at least give it the right NC! Who wants to print up a bunch of those 3D cones?

__________________
Paul
If we weren't all crazy, we would go insane - Jimmy Buffett
NAR #87246 www.wooshrocketry.org

This is such an important nose cone for Enerjet/Centuri for both historical and cloning purposes, yes? From the introduction of the ST-13 tube (1965 catalog?), it was THE choice for ST-13 until the 4.3" came along (1975 Rocket Times?). First as BNC-132, then later as PNC-132. I rely heavily on the ancient catalogs for the chronology, but I am seeing the first appearance in 1971? Just in time for Enerjet, Nike Ram and the 1340 perhaps?

I have often wondered when that great 1340 brochure/spec sheet that we all use was produced, since it features the newer 4.3" nose cone so prominently - as well as the earlier 2.7" 132. Perhaps the 4.3" was created and used initially just for the 1340? While sold separately for a few years, I have it's first use on a commercially available model in the Phoenix Bird (1977?). So most (all?) of the classic ST-13 model kits up to that time (Taurus, Space Shuttle, etc.) would have used the old 132 either in balsa or plastic form.

I could have sworn that I have an Estes Cyclone (1983 Centuri parts elimination vehicle) kit somewhere, most likely acquired for its inclusion of the PNC-132, but I can't find it at the moment.

I've disparaged the 2023 Nike Ram parts choices already, so won't belabor it. I try to always see a bright side to any new release, even if it feels like an opportunity to do it right was sadly missed. And we'd have had a source for the correct Enerjet/Centuri body tube and nose cone for years going forward. I plan to make my Nike Ram clone with ST-13 (or BT-56) and the balsa BNC-132, though I may get the 2023 Aerotech version too, as a whole different rocket. Am homage to the original, at least.

Please correct me if I am getting any of this chronology significantly wrong!

The longer PNC for the 1340 was a specific nosecone for that kit, as that kit used a 'heavy walled' tubing. Same OD as ST-13 but much thicker. That was the only kit that used that particular nosecone as far as I know.

Later, Centuri did introduce another PNC for the normal ST-13 tubing that looked just like the 1340 cone, just as long, but was for the much thinner ST-13 tubing. And I think you are right: it's first use was for the Phoenix Bird....no wait, it's first use was for the UFO Invader kit (Super Kit) which were introduced in late '75, early '76. But, the Phoenix Bird was next in latter '76.

That particular PNC (UFO Invader and Phoenix Bird) was typically sold (and I think manufactured/molded with) an ST-13 plastic coupler. The 1340 also had a plastic coupler, but, like the nosecone for the 1340 mentioned above, it was for thick walled tubing also with only a 1/10 inch exposed section between the tubes, whereas the coupler for the UFO Invader and Phoenix Bird had a larger exposed section...maybe about a half inch.

Earl


Earl

__________________
Earl L. Cagle, Jr.
NAR# 29523
TRA# 962
SAM# 73
Owner/Producer
Point 39 Productions

Rocket-Brained Since 1970

Do you have a stockpile of ST-13 somewhere? All that's left at erockets is short chunks that would need multiple couplers to glue together into a rocket.




Can you confirm that the Centuri ST-13 cone is the same one still available in a four-pack, color black, as an Estes PNC-56?