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.
Anyone have the fin dimensions for this rocket?
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:
Root edge 2.059"
Leading edge 2.583"
Outer edge 1.496"
Trailing edge 1.832"
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).
There is a template here:
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
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. ;)
Mark E. Hamilton
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
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.
On Thu, 30 Mar 2006 18:46:34 -0700, Mark Hamilton
Well, for anyone following this thread...
I finished the Hobgoblin clone, and I've posted a picture of it on
On Fri, 31 Mar 2006 11:15:39 -0800, email@example.com wrote:
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.
but it's your dime, nice rocket
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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