I'm trying to "clone" the North Coast Rocketry Hobgoblin, an upscale version that NCR did of the old Estes Goblin. I have some pictures that I found of the Hobgoblin on the Internet, along with a page of an old NCR catalog which gives the basic specs for the Hobgoblin: 8" diameter, 60" high, 1/4" ply fins...
I tried measuring the fins in the pictures, but because the pics aren't "straight on", the dimensions didn't seem right; the fins I made seem out of proportion to the rest of the rocket.
Well, I would, except that I can't find any info on the fin dimensions of the original Goblin either! So, even using the body dimensions of the original, I'm back to "eyeballing" it...
Here are the fin dimensions for the *original* Goblin, based on BT-55 (1.325" diameter), so multiply by the appropriate factor for your upscale BT size:
No problem! Hey, it occurred to me after posting those measurements, that re-creating the pattern without the angles is a little more problematic than with angles (I didn't have a protractor, just my calipers).
Well, there's lots more than two pictures. For some reason they don't always show up in Google searches. I went through some of them and ensured that they have better keywords. One of these days Google will pick them up.
IAE, this picture is one of my favorites. I use it as one of my screen-saver shots:
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There's a lot of motors I could put in it, but in reality once a rocket goes out of sight I lose interest, so I prefer smaller motors. I've flown it on lots of different I's; my favorite is probably the I-211. I flew it once years ago on a J-350, but that was before the current certification regime, and I've never bothered to recertify L2.
This rocket actually survived a lawn-dart on it's first launch (12 years ago.) The standard BP load in all AP motors is insufficient to pressurize the body and eject the nose, which in my younger days I didn't know. So it went up and came right down again. It hit close enough that we could all see it. You may not realize it, but stressed fiberglass will act as a spring, just before is shatters into a zillion pieces. The rocket literally bounced three feet back into the air when hit. The top three inches of the body had to be cut away, and the nose had to be replaced, but it has flown again many times since them. (Matt designed tough rockets! Too bad Estes tanked 'em.)
Unfortunately this was before Tom took as many pictures as he does now, and before Zia had a website, so there's no pictures on the 'net. Still, I could send you a piece of the nose if you'd like. We still find them when walking out that direction to recover rockets.
The moral of this story, boys and girls, it to always ground test your ejection charges before launching a new rocket. Of course, we all know that, and do it every time, don't we. ;)
Yeah, the two I have show you with the Hobgoblin (one holding it & another standing next to it on a launcher).
Good news for me...according to the dimensions you gave me, I'm only off a little bit on the sweep of the fins I "eyeballed" the dimensions of.
I was hoping to use high "I"/low "J" motors for the first few flights, but my version may be too heavy; I reinforced the body with fiberglass, and made it a 3 motor cluster (1 - 3" & 2 - 38mm motor mounts) and it's at 14.5 lbs without motor, chute, or paint.According to the NCR catalog, their version should be about 9 lbs empty. Rocksim says mine should go about 2000' on a J800, so I may try that first.
After the first few flights, I intend to fly it on my experimental (excuse me, "research") motors. I have a nice J700 sorbitol motor that should be fine, if it does well on the J800.
alt.binaries - are we still in the stone age? I'm just suggesting, why not show pictures where they may be seen.and admired. and replyed to. rather than the model rocket picture boneyard of very few visitors.
Oh, my mistake. I thought you were referring me to a forum that had something related to the Hobgoblin specifically.
You're right; alt.binaries is a "holdover" from the past, but I thought that's where most people were still posting pix that were referred to here. I'm going to post the pic on the "Oregon Rocketry" pictures page; I'll let you know when that's done.
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