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why does estes alpha have holes in the fins?

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gjxj

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I'm helping my son build his first rocket for cub scouts which is an Estes alpha.
This is a curiosity really, but the pre-cut balsa fins have maybe 1mm clean drilled holes near the root in the upper third of the fin.
Do they serve some purpose?

PS I'm actually returning to the hobby after 40 years. "In my day" you actually used a knife to cut out the fins ..I certainly never drilled holes in them.
 

Tonimus

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Looking at the instructions, I believe it is only to identify the root edge.
 

gjxj

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They are not shown at all in the instructions I have, but that does make sense. Thanks.

Sorry i didn't think to take a pic until they were half filled with glue. Note just one in each fin.

20170928_220913-x.jpg
 

qquake2k

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I drill holes in the fin tabs of plywood fins to "pin" them for cutting and sanding. But I doubt if that's what these holes are for. I too remember when you had to cut your own balsa fins for kits. Then they came out with die cut, and finally laser cut. Modern technology, but sometimes I think they make things too easy.

010.jpg
 

Gary Byrum

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"In my day" you actually used a knife to cut out the fins.
I'm predominately a scratch builder, (LPR & MPR) And I still cut my own fins. Laser cut and plastic fin cans are just not craftsman's like in my opinion. Besides, when I clone an OOP model, it's usually an upscale and I always have to craft those.
 

GlenP

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Other than that little hole on the root edge, there is no mention of the balsa grain direction in the instruction sheet, or the importance of the grain being aligned parallel with the leading edge, unless I missed it somewhere.

Alpha designer Bill Simon himself made a special point of this at the Alpha building workshop last weekend held at the Museum of Flight in commemoration of the kit's 50th anniversary, using the cracks in the vertical wood beams in the room of the historical Boeing Red Barn to illustrate his point. :)
 

gjxj

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My paper instructions are similar to that, but do not show the holes. Mystery solved. I guess they upgraded the instruction sheet and we got an old one.
Mine also do not have the warning about "not" rounding the root.

there is no mention of the balsa grain direction in the instruction sheet
The fins are pre cut (properly oriented with the grain). No need for a knife, in fact they had already come loose from the sheet before we opened the packaging.
 

shreadvector

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The 'holes' were originally dimples and not through holes and may have first appeared in the Alpha II. Older instructions that used more words explained that they were to identify the root edge. This aid was added because many, many, many builders would glue the wrong edge to the body tube and the fins would then crack on the grain lines.
 

Flyfalcons

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Now if we could just find out why the new version wants you to overhang the motor mount tube by something like 3/8" (I rebelled on that one).
 

shreadvector

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Do you mean hang out the back of the main body tube? If so, that could be for a couple of reasons:

The Alpha is horribly short and a terrible first rocket since it does not have decent room for both the proper amount of wadding and the recovery system. By having the motor mount tube move back a bit, it gives you just a wee bit more room inside.

The fins sweep back and some beginners have a hard time getting their fingers around the spent motor to remove it after flight. Sure, the new style motor hook had the big finger tap, but you still need to grip the motor and pull it back out.

Did they add a thrust ring to prevent the motor mount tube from tearing at the top and the hook from sliding back and forth? (Answer is "NO" - I looked at the current instructions.....)

Now if we could just find out why the new version wants you to overhang the motor mount tube by something like 3/8" (I rebelled on that one).
 

rharshberger

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Now if we could just find out why the new version wants you to overhang the motor mount tube by something like 3/8" (I rebelled on that one).
What Shread said, plus I ditch motor hooks and instead friction fit, then a wrap of tape as insurance which is hard to do if the motor tube is flush.
 

GlenP

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...The fins are pre cut (properly oriented with the grain)...
But they are not yet glued to the body. Some other beginner kits, like the Viking, have paper/fiberboard fins which can be glued to the body on any edge. The balsa fins must be glued on their root edge, thus the hole/dot reference marker. Occasionally, a creative scout might attempt to glue the leading edge to the body because it might look cool, but the fin would easily break off on a grain line in that situation.
 

BEC

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As others have noted, the holes are the laser-cut successors to the dimples that appeared in the die-cut fins (yes, first in Alpha IIs and when die-cut fins came to “regular” Alphas about 1980) to denote which is the root edge. I have seen many an Alpha with fins glued on in other ways so I made a quite a point about it last Saturday when we were building Alphas at the Museum of Flight (the workshop Glen alluded to above).

I also agree that the current instructions say nothing about this. In fact I ADDED a dot on all the illustrations I pulled from the online version of the instructions for the Keynote presentation I used to lead the MoF build effort. In looking back, I find the explicit mention of the dimple/dot went away literally decades ago. The last to even show the dot (no words about why it’s there) were in the in the very early 1990s. The fins were die-cut then.

As for the motor mount aft overhang - that was introduced in the 2011 revision of the instructions. I have asked everyone at Estes who might know and no one knows why it was done. When I mentioned this over on YORF a few months ago someone speculated it was to do away with the interference between the motor hook and the main body that happens when you install/remove a motor - the main body tube has to deform in order for one to get the hook out of the way enough to get the motor out. But that situation has existed since the finger-tab motor hooks were introduced to the Alpha (about 1993!). So if that’s why - waiting nearly 20 years to fix it seems odd. It’s a good thing the Alpha is nice and stable since that’s moving mass the wrong way.

I don’t quite agree with Fred that the Alpha is “horribly short” but it certainly doesn’t have much spare room. I have flown a PerfectFlite FireFly in a couple of Alphas and it requires that I fold the ‘chute in thirds to get the altimeter in. The one I fly most that way has a Semroc 12 inch ‘chute in it, which is made of nice thin pliable material (like the Estes ‘chutes back when the Alpha was designed) and that one doesn’t mind being folded that small. Without the altimeter, folding the ‘chute in half seems to be fine - as was evidenced by no recovery failures (save for an untied-at-the-nose-cone shock cord) among the Alphas we built last Saturday at the Museum of Flight which were flown the next day.

Added: interesting that Fred links back to a scan I made for K’Tesh awhile back. That is revision D of the instructions which mark the introduction of the Alpha logo/livery similar to what we still see today. The dot in the illustrations was last seen in revision G, which was the version for the kits that had either a blow-molded plastic nose cone or an Alpha III cone, which were in the 1989-1992 catalogs. Die cut fins appeared in revision C, for whatever that’s worth.
 

GlenP

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DSC_7081.jpg
this particular one had not been glued yet, the fins were just pre-assembled and held in place with the jig
 

BEC

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Yes, I remember remarking to him that that was a variation I hadn’t seen before. Usually they ones that are done incorrectly have the trailing edges glued to the body (turning the tip into the new leading edge and making the Alpha look like a slight downscale of the Centuri Astro-1), not the leading edges as this one is in the guide. That one (and all of them) ultimately got them on the right way around.

Interesting shot of Bill Simon and Chris Nutter (camera) chatting.
 

Trident

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I'm predominately a scratch builder, (LPR & MPR) And I still cut my own fins. Laser cut and plastic fin cans are just not craftsman's like in my opinion. Besides, when I clone an OOP model, it's usually an upscale and I always have to craft those.
I'm building an upscale Astron Cobra now, and cutting the basswood fins by hand. Would be pretty easy if they had no tabs, but I want them to anchor to the space between motor tubes (my upscale is 4 motors so the 4 fins can all have identical tabs.)

I finished my upscaled Orbital Transport and entered it in the upscale competition at NSL this year. I actually started it about 10 years ago. After cutting all those parts by hand, most of them being basswood, I was so tired of working on it that it took a competition to motivate me to fill, prime, and paint the rocket and its glider :)
 

Gary Byrum

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I'm building an upscale Astron Cobra now, and cutting the basswood fins by hand. Would be pretty easy if they had no tabs, but I want them to anchor to the space between motor tubes (my upscale is 4 motors so the 4 fins can all have identical tabs.)

I finished my upscaled Orbital Transport and entered it in the upscale competition at NSL this year. I actually started it about 10 years ago. After cutting all those parts by hand, most of them being basswood, I was so tired of working on it that it took a competition to motivate me to fill, prime, and paint the rocket and its glider :)
I have an upscale Astron Cobra as well. 3 - 24mm in a BT 70 airframe. D's are about all I'll use in it with those surface mount balsa fins. Flies like a champ though.

Cobra Cropped.jpg
 

BEC

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Here is one of the little displays I made for the Alpha 50th affair. This one is showing the evolution of the fins.

IMG_8279.jpg
 

gna

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Did they add a thrust ring to prevent the motor mount tube from tearing at the top and the hook from sliding back and forth? (Answer is "NO" - I looked at the current instructions.....)
My first rocket as an adult was an Alpha. Last summer I was flying it, and the motor tube had torn and the motor slid forward, pinching the motor tube and making it off center so the rocket went awry:

[video]https://youtu.be/5aWdwpOKvHY[/video]
[video=youtube;5aWdwpOKvHY]https://youtu.be/5aWdwpOKvHY[/video]
 

gjxj

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wow.. any advice on how to avoid that? Maybe a zip tie around the top of the tube.
 

gna

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wow.. any advice on how to avoid that? Maybe a zip tie around the top of the tube.
I made an engine block/thrust ring by cutting a small section out of an used motor, and used a dowel to insert it from above. All good again.
 

Trident

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I have an upscale Astron Cobra as well. 3 - 24mm in a BT 70 airframe. D's are about all I'll use in it with those surface mount balsa fins. Flies like a champ though.
Gary, is your Cobra red and white, or red and silver? I haven't finished my upscale yet but I have no idea what color scheme I'll use. I may just go with a classic scheme from one of the old catalogs.

My standard Cobra had its maiden flight in August. I flew it on B6-4s. I could not believe the altitude. I was going to fly it a second time on C6-5s but ran out of time. I'll use four D12s on the upscale and it should be pretty impressive. My build is not overly beefed up. I used standard body tubes. The fins are heavier since I used basswood but otherwise it's reasonably light.
 

Gary Byrum

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Gary, is your Cobra red and white, or red and silver?
I think it was Duplicolor Dark Cherry Met, some silver vinyl I bought at HL and cut by hand, then trimmed in black stripes. I wasn't interested in the classic looks for this one. Too plain Jane. My color scheme isn't all that, but I like it better than the catalog look.
 
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