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  #11  
Old 08-06-2020, 02:25 PM
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ghrocketman ghrocketman is offline
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There NEVER was a "plastic cone" version of the K-27/1227 Honest John.
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  #12  
Old 08-06-2020, 07:37 PM
Jack Hydrazine Jack Hydrazine is offline
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Quote:
Originally Posted by BEC
I did some digging but for some reason I can't come up with my reissue Estes Goblin with the plastic nose cone. Here are my original Goblin (which was built but unfinished for over 30 years) and one built from the Semroc repro kit which was released just after eRockets bought Semroc. Nose cone closeup is in the same order - original BNC-55AO on left, Semroc interpretation on the right.


I can definitely see a slight difference. One that stands out is the radius of the tip of the nose cone. I may go ahead and design that AO as well as the AO I have designed and just published to Thingiverse.

Thanks so much for taking the time out to do that for me! It's greatly appreciated!
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  #13  
Old 08-21-2023, 12:06 AM
SolarYellow SolarYellow is offline
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Quote:
Originally Posted by BEC
I did some digging but for some reason I can't come up with my reissue Estes Goblin with the plastic nose cone. Here are my original Goblin (which was built but unfinished for over 30 years) and one built from the Semroc repro kit which was released just after eRockets bought Semroc. Nose cone closeup is in the same order - original BNC-55AO on left, Semroc interpretation on the right.


I'm wondering if anyone can put together a comparison of the Semroc repro cone vs. the Estes wood BNC-55AO that was used on the Phoenix Bird and Sky Warrior, possibly others I haven't identified yet.

This is the Sky Warrior parts layout. Cone looks a little more like the PNC-55AO in the recently discontinued Goblin kit than the Semroc cone in Bernard's photo does, I think.

https://www.acsupplyco.com/image/ca...rts-800x800.jpg
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  #14  
Old 08-24-2023, 01:16 PM
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Arogen Arogen is offline
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I thought the Goblin used the same nosecone as the Der Red Max. How different are they?
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  #15  
Old 08-24-2023, 01:57 PM
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LeeR LeeR is offline
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Quote:
Originally Posted by Arogen
I thought the Goblin used the same nosecone as the Der Red Max. How different are they?


Goblin is BT-55, DRM is BT-60. The shape is very similar.
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  #16  
Old 08-24-2023, 03:23 PM
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Arogen Arogen is offline
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Quote:
Originally Posted by LeeR
Goblin is BT-55, DRM is BT-60. The shape is very similar.


Then here you go:
https://www.printables.com/model/39...5-bt-20-bt-50-b
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  #17  
Old 08-24-2023, 08:02 PM
SolarYellow SolarYellow is offline
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Quote:
Originally Posted by LeeR
Goblin is BT-55, DRM is BT-60. The shape is very similar.


True. A BT-60 Goblin could use a DRM cone and be a lot closer than many "clones" that are marketed under the Goblin name. But it's not a true upscale. I have precisely reverse engineered the PNC-55AO Goblin cone in Autocad, but have only done the DBRM, not the DRM. It's on my list, though. Once that's done, I might post up a comparison of the PNC-55AO, PNC-56, PNC-60AH, and DBRM. Who knows, I might have a MDRM cone by then. Of course, I would scale them to a common OD to provide a more meaningful comparison.
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  #18  
Old 08-24-2023, 10:12 PM
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astronwolf astronwolf is offline
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Quote:
Originally Posted by Arogen

There is no comparison between the PNC-60AH and PNC-55AO there. Nothing to see at your site.
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  #19  
Old 09-26-2023, 11:40 AM
SolarYellow SolarYellow is offline
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Quote:
Originally Posted by SolarYellow
I'm wondering if anyone can put together a comparison of the Semroc repro cone vs. the Estes wood BNC-55AO that was used on the Phoenix Bird and Sky Warrior, possibly others I haven't identified yet.

This is the Sky Warrior parts layout. Cone looks a little more like the PNC-55AO in the recently discontinued Goblin kit than the Semroc cone in Bernard's photo does, I think.

https://www.acsupplyco.com/image/ca...rts-800x800.jpg


I got to do that comparison this morning, thanks to BEC's willingness to part with an early balsa-cone Phoenix Bird kit. I recently purchased the Semroc cone from eRockets. I have some blow-molded PNC-55AO cones on hand as well.

The current Semroc cone has a kind of flat on the tip and a significantly larger blunting radius than either of the Estes cones. It will take a significant amount of hand work to make it the tip reasonably spherical, and then it will be a case of "no two the same," because everybody will do it a little differently. Just like in the good ol' days of die-crushed fin sheets.

The balsa Estes cone is very narrow in the forward half, with sides straighter, closer to conical, than the PNC. Holding the balsa cone in front of the PNC, I estimate it's missing about half a mm per side, maybe a little more, of "belly." Doesn't sound like much, but the visual effect is significant. The Estes balsa tip is more spherical than the Semroc cone and the tip diameter is close enough for balsa to the PNC tip diameter.

I figured out awhile back that the balsa cones back in the day were all over the place. Just in the instruction sheet posted in JimZ https://www.spacemodeling.org/jimz/k-55.htm, the shape of the cone on the finished rocket photographed for the front panel of the instructions and face card is noticeably fuller than the shape of the raw cone photographed in the parts layout in the instructions. The latter has a smaller tip diameter and appears more nearly ogive behind the spherical blunting than the finished rocket's cone.

Visually, to me, the blow-molded PNC-55AO is closest in shape to the parts layout cone, of the four examples discussed here. However, whereas the parts layout cone visually appears to be closer to a single-radius ogive, the PNC actually has three different radii joined together, giving it a visually distinctive shape that I happen to like. Maybe I just imprinted on it due to messing with it first.

I think the current Semroc cone would come closest to the JimZ face card shape and could actually get pretty darn close if finished with that in mind.

I haven't tried to do a detailed comparison to BEC's matchup photo posted earlier in this thread.

The big takeaway for me is that, while all PNC-55AO cones presumably came out of the same mold and therefore differ only by the variation inherent in that process, there isn't "one" Goblin BNC-55AO shape. Or rather, the variation inherent in the production process of the balsa cones is great enough that there isn't "one" Goblin BNC-55AO shape. Of the available options, pick what you like, and what will make you smile the most when you build and fly it.

I do kinda still have an issue with companies issuing "clones" using cones that were never intended to even be similar to the Goblin shape, however. An ogive cone with substantially different fineness ratio and minimal blunting of the tip is trying about as hard as Private Pyle tried to get over the obstacle.

Besides a raging case of OCD, the inspiration for this investigation was the idea that I want to build a "traditional" Goblin with a balsa cone. So I wanted to figure out what was the best way forward. I thought it would likely be the Estes PB cone, but now I'm thinking I might just work the Semroc cone into matching the face card at JimZ as best I can. That will at least give me the traditional balsa cone experience.

Quoting myself to save typing and bring more of my Goblin NC content together in this thread:

Quote:
Originally Posted by SolarYellow
True. A BT-60 Goblin could use a DRM cone and be a lot closer than many "clones" that are marketed under the Goblin name. But it's not a true upscale. I have precisely reverse engineered the PNC-55AO Goblin cone in Autocad, but have only done the DBRM, not the DRM. It's on my list, though. Once that's done, I might post up a comparison of the PNC-55AO, PNC-56, PNC-60AH, and DBRM. Who knows, I might have a MDRM cone by then. Of course, I would scale them to a common OD to provide a more meaningful comparison.


Quote:
Originally Posted by SolarYellow
I just measured a Der Red Max cone, PNC-60AH, from an unopened DRM kit purchased this year. It turns out that the end of the straight at the base, where it actually starts to taper, is close enough to call it 14mm from the base. Which gives the tapered part of the cone the exact same fineness ratio, to three significant figures, as the Goblin. Just have to paint the bottom 9/16" of the cone airframe color to have it look perfect, and tolerate the split being a little more visible because it's not in a color transition as discussed a few posts above.

I have no idea why upscaling Goblins to BT-60 and/or 38mm MMT using DRM cones isn't a thing, because it should be.
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