Estes Alpha laser-cut fins

[ZoomieG]

Anyone know why current Alpha fins have a hole near the root edge? (Pic attached for reference) I seem to remember reading somewhere on this forum or the other one that it was added when the switch was made from die-cut to laser cut, but I haven't seen any other laser cut fins with this marker.

Additionally, do they need to be filled? Or are they small enough that sanding sealer/primer/paint will make them disappear?

Thanks,
zG

 

[user 35280]

Anyone know why current Alpha fins have a hole near the root edge? (Pic attached for reference) I seem to remember reading somewhere on this forum or the other one that it was added when the switch was made from die-cut to laser cut, but I haven't seen any other laser cut fins with this marker.

Additionally, do they need to be filled? Or are they small enough that sanding sealer/primer/paint will make them disappear?

Thanks,
zG

Get these from Rocketry Works and you can choose between balsa and basswood, also you can choose the original pre-2003 style or modern post-2003 style.
https://www.rocketryworks.com/alpha-fin-upgrade-2-mm-basswood-plywood-set-of-3/

 

[Rex R]

I believe that the hole is an aid to Not gluing the fin in the wrong attitude. The filet should cover the hole nicely.

 

[BEC]

The reference to the holes in the Alpha in the instructions have been gone since — well at least a couple of decades....so they no longer serve the "this is the root edge!" purpose of the die-imprinted dots on the die-cut fins. But that's what they were originally there for — to let folks know which edge is the root.

It would take a big fillet to cover them, but filling them before paint would be appropriate. If you're heavy-handed enough with your finish, they might get filled with that .

The Rocketry Works fins, post 2003, match the current laser-cut ones' shape exactly, but don't have that hole. The pre-2003 versions match the SP-25 template and later die cut Alpha shape (the original shape). I have checked the Rocketry Works fins against SP-25 (the original Alpha sheet that included the fin template back when you had to cut your own out before the die cut ones appeared in the early 1980s).

Rex probably has nightmares about SP-25...but that's another Alpha fin story ...

 

[kuririn]

Termites.



Another classic example of keeping the tradition and losing the explanation why.
But yeah, root chord marker.

 

[Rex R]

Rather than reopening that can of worms.. I would suggest that folks Google 'sp-25 fin template’, thread (all 4 pages). Thankfully that discussion remained civil.

 

[Rex R]

I note that jimze roçket plans has the sp-25 template for the astron alpha, evidently some in the past five years they updated the site.

 

[kuririn]

I note that jimze roçket plans has the sp-25 template for the astron alpha, evidently some in the past five years they updated the site.

He updated a few months ago.
Wondering what you mean by "can of worms" and "thankfully that discussion remained civil"
Like this one hasn't?

 

[Rex R]

That post had more than 120 posts from people arguing whether I had the real thing. It got a bit heated..
Hence the suggestion to look it up.

 

[kuririn]

Got it.
We aren't going down that rabbit hole.

 

[Rob Campbell]

Some of the older Estes kits, like the Astron Cobra had the builder drill a small hole near the root of one fin for a static line, which was part of the recovery harness. I suspect this was to protect the very large fins during landing as the rocket would land fins up.

 

[kuririn]

Problem is that the hole is there with no explanation in the instructions.
Can be confusing for new builders.
Same thing with the hole on a centering ring for the new 1/100 Saturn 1B:
Saturn 1B - Small hole in ring? | The Rocketry Forum
I checked the instructions at JimZ's:
Alpha K-25 had fins traced from a template. Of course, no hole.
Alpha 1225 had pre cut fins with a hole. No explanation in the instructions for that hole.
Was there an interim Alpha with an explanation for the hole in the instructions? IDK.
For the OP, just put a dab of CWF or putty in the hole and sand smooth. Done.

 

[BEC]

Since the thread that I alluded to as a sort of inside "joke" to Rex and then Rex suggested here to "look it up" I've done LOTS of Alpha evolution research via online digging and acquiring lots of Alpha kits mostly on eBay.

The dimple indicating the root edge appeared when the fins went from trace-and-cut-out-them-out-yourself to die cut with instructions 82925 revision C, circa 1980. This would be after the first fifteen years of the Alpha's existence. The 1980 catalog is the first to mention the Alpha's fins were die cut. At this time the Alpha still had a balsa BNC-50K nose cone, and this was a couple of years before the appearance of the big "Alpha" decal and the fin flashes (in red and black) which came in 1982.

The latest instructions I can find that have any mention of the root edge marker (at that time a still a dimple in the die cut fins) was 82925 revision G, which was the same one that showed the option of having an Alpha III-type nose cone as well as a blow-molded plastic nose cone. These instructions were in kits from the early 1990s.

All mention of (and even illustration of) the root edge "dot" disappeared at the beginning of the Beta series packaging circa 1993.

So, the root indicator dimple or dot had a documented purpose from ~1980 to ~1993. So, ten years later, when the fins were changed to laser cut (and the shape slightly tweaked) the no-longer-referred-to "dot" or dimple in the fin root became a laser cut hole....but nothing in the kit's documentation tells you why it is there. This situation remains to this day — twenty-eight years later.

There have been quite a few detail configuration changes in the nearly 56 years the Alpha has been in production. Every component has been altered in some way at least once. But then, it's been in production for 56 years now....that's a long run.

 

[kuririn]

You would think that instead of a hole that needs filling they could do just a laser tic mark or arrow, right?
Witness my just recently completed Rocketship Games Micro Hawkeye, with laser marks for the root chord:

 

[BEC]

Agreed, that's what should be done.....but as I noted, there's been no mention of the marker (dimple or hole) in the instructions for about 28 years now, and the laser-cut fins with the useless hole have been made that way now for ~18 years. I suspect changing the laser cut files in China and updating the instructions, including two or three views in the current artwork, are not a priority. It certainly could be done...

But as you noted, it's a "Another classic example of keeping the tradition and losing the explanation why."

 

[ZoomieG]

Thank you everyone for the wealth of information!

@Rex R , thanks for the point-out to that thread. I had read some threads regarding the changes to Alpha nose cones and fins over time, but somehow missed that one.

Strangely, it does seem that pattern SP-25 has non-parallel root and tip edges. This made me curious, so I broke open a pre-beta Alpha kit I bought recently. It's apparently an early 90's kit, as it has the fat ogive plastic nose cone shaped like the balsa original, but has red and blue decals. It's die-cut fins (with a root edge dot) seem to match SP-25. The modern kit I have with laser-cut fins does not match SP-25, and has parallel root and tips, with about 1/16" less overall span. The modern Alpha fins also very closely match the shape of current Alpha III fins.

As noted by several here, the holes mark the root edge of the fin. Do any other kits have this feature? One is left to wonder why with the Alpha, even if the instructions no longer mention it, Estes felt it necessary to mark the root edge. Why wasn't this done for any other kit?

 

[Rex R]

I wouldn't swear to it but, I seem to recall a goonie bird or two with markings on the die crushed fins. I imagine that Estes had a number reports and requests for replacement fins .

 

[BEC]

Thank you everyone for the wealth of information!

@Rex R , thanks for the point-out to that thread. I had read some threads regarding the changes to Alpha nose cones and fins over time, but somehow missed that one.

Strangely, it does seem that pattern SP-25 has non-parallel root and tip edges. This made me curious, so I broke open a pre-beta Alpha kit I bought recently. It's apparently an early 90's kit, as it has the fat ogive plastic nose cone shaped like the balsa original, but has red and blue decals. It's die-cut fins (with a root edge dot) seem to match SP-25. The modern kit I have with laser-cut fins does not match SP-25, and has parallel root and tips, with about 1/16" less overall span. The modern Alpha fins also very closely match the shape of current Alpha III fins.

You have corroborated what I knew. Until the laser-cut fins, the fin shape was unchanged. Remember that Bill Simon created it on his kitchen table in 1965 and drew what he liked to see (with an eye toward good stability) as the Alpha was originally conceived to be a beginner's kit. It was the first with a quick change engine mount (via the steel hook) and the first with the tri-fold shock cord mount as well. There was never any requirement that the tip edge be parallel to the root...the tiny performance penalty (if any) was not a consideration. Bill Simon wanted something that looked nice...and it did.

The Alpha III (which itself turned 50 years old this year) has been much more the same over its run than the Alpha. Really, externally, it has never really changed in 50 years outside of color choices.

As noted by several here, the holes mark the root edge of the fin. Do any other kits have this feature? One is left to wonder why with the Alpha, even if the instructions no longer mention it, Estes felt it necessary to mark the root edge. Why wasn't this done for any other kit?

I expect it was an attempt to have fewer Alphas built looking like Centuri Astro-1s, which is what you get if you put the fins on with the trailing edge as the root and the tip as the leading edge. I've seen a number of Alphas done that way, and my grandson managed to build one with the leading edge as the root. That one was unstable on a C.

There were a number of things that were done for the educational Alpha (Alpha II) that were intended to make it easier to build for beginners, and I think the dot at the root was just one of them. The die cut fins and the first plastic nose cone were also first on the Alpha II before the regular Alpha. Of course the Alpha II as a separate product is long gone.....