vintage astron alpha fin pattern

To add to this discussion, it should also be noted even though everyone is discussing the analysis through an empirical process, the oldest precedent with actual known dimensions rather than drawing would be the Alpha description on 'page 42' of Estes tech bulletin TR-11 which uses those fin dimensions for Aerodynamic drag analysis. Copyright 1970.( see YORF site for PDF file) FYI. I would always use those numbers before any other info ( such as scan distorted imaging of publishing reproductions), but I'm an Architect. I think SP-25 is for reference only due to lack of dimensions. Estes published those dimensions so I have to go with it for that reason as well.

I have in fact printed out the pdf (both of them) and compared the print outs to the kit supplied pattern...they were identical. so Raygun, which fin pattern would you use to clone; a Ranger/big bertha/apogee eh ?
Rex

Rex R said:

I have in fact printed out the pdf (both of them) and compared the print outs to the kit supplied pattern...they were identical. so Raygun, which fin pattern would you use to clone; a Ranger/big bertha/apogee eh ?
Rex

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I did this too, and it comes very close but not exact, there was suspected distortion in the scan, so no one really knows for certain due to capture reproductions through raster files (optical imaging error) and mechanical print errors. It does however confirm that the numerical floating point linear dimensions were used when drafted, not by angular dimensions for sure, as that would have necessitated integer values imperceptible with mechanical drafting tools of the day. As a bit of advice, never trust the graphic when you have the dims. They are secondary reference. If you don't have dims, then that another story.. field examples would need to be required, but then that could be argued as: 'as- manufactured examples' vs. 'as designed'--Manufacturing deviation of die- cuts . I dont know if this answers the Ranger/Big bertha question as I am unfamiliar with it. If i consider myself a STEM person, I go with certainty of known quantities. These just happen to be published by the manufacturer, in this case. I would consider the The Alpha (see Fig. 76), in tech. pub. TR-11 as design specifications. EDIT: For the Big Bertha or any plan for that era, when you can't find dims, at least you can become familiar with the drafting convention of the company designers through other projects, as a tip. You can be surprised what that will turn up, if not dead on numbers are not available. That's all anyone can hope for, if everyone is no longer around to confirm.

I think we've officially gone around the bend here .

After all, we are talking about the dimensions of fins for which the fabrication process is: cut out the card stock template from SP-25. Trace around that onto the balsa stock with a pen or pencil (or if you're clever, the pinholes at the corners method). Then cut out with a handheld knife. Again if you're clever you used a straightedge of some kind to help guide the knife. Then - after you get three parts that aren't identical in shape you stack them together and sand until they match (or until you decide it's close enough).

For parts made that way, relying on dimensions in TR-11 (and creating your own template with which to do this process) is "within tolerances" at best .

As with many things, including buildings, I am sure, "as drawn" and "as built" don't match precisely....

While it is true that there are "practical" considerations and that real-world balsa fins can easily depart from the idealized starting point, it is also true that Raygun's proposed baseline definition kinda has to be held as the authoritative reference point. That's just the way it works with rocket science.

Well.... maybe so....but looking at TR-11 which was published 10 years after the Alpha first appeared, one has to wonder where the dimensions called out came from. The diagram which calls out those dimensions also shows an ogive nose cone with a radiused tip, which does not correspond to any variant of the K-25/1225 Alpha up through the currently available ones. The indicated dimension from tip to the joint with the body tube is called out as 2.75 inches in that illustration, which is longer than any Alpha cone I know of from the original BNC-50K through the current blow molded Alpha cone, or the blunted (but shorter) ogive used on the Alpha III/IV.

So if the nose cone is wrong, why should I trust the fin dimensions and see them as definitive?

Gone round the bend? Guilty......

Second picture is of the models built for the test program described in the 55-page report.

BEC said:

Well.... maybe so....but looking at TR-11 which was published 10 years after the Alpha first appeared, one has to wonder where the dimensions called out came from. The diagram which calls out those dimensions also shows an ogive nose cone with a radiused tip, which does not correspond to any variant of the K-25/1225 Alpha up through the currently available ones. The indicated dimension from tip to the joint with the body tube is called out as 2.75 inches in that illustration, which is longer than any Alpha cone I know of from the original BNC-50K through the current blow molded Alpha cone, or the blunted (but shorter) ogive used on the Alpha III/IV.

So if the nose cone is wrong, why should I trust the fin dimensions and see them as definitive?




Gone round the bend? Guilty......

Second picture is of the models built for the test program described in the 55-page report.

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When there is authorship of who owns it, you have to acknowledge it as their own, they being Estes. When they are dimensioned, its not arbitrary. Like I said never go with a graphic, when you have dims. So don't go with the cone, (An inconsistant graphic with no dims ) but do go with the fins ( dimensions), simple.

So... what came first? The dimensions or the drawings?

I'd suspect dimensions were taken from drawings.

foamy said:

So... what came first? The dimensions or the drawings?

I'd suspect dimensions were taken from drawings.

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I suspect your suspicions are correct.

TR-11 has a 1970 copyright notice on the second page....so it came some years after the drawings (both the SP-25 and the catalog insert versions).

BEC said:

TR-11 has a 1970 copyright notice on the second page....so it came some years after the drawings (both the SP-25 and the catalog insert versions).

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Actually, it doesn't matter when it was published. It could have been published yesterday by Estes, as an after-the fact, through rummaging through their own historical archives, theoretically. The manufacturers specifications supersede all other graphical image, which is easily corrupted. Having data that is reliable within 100 percent accuracy is why designs are dimensioned; no interpretation needed, required, and definitely not desired in a legal sense when the drawing is a construction contract. That's nice to have for archive data, as they (Estes) are the authority of properties of their own designs. That is first hand quantifiable data, appearing for the first time for tech publishing purposes, and there has been no official change since that time (to my knowledge anyway) or one that has yet to appear as archive record to supersede it in turn.

Has anyone noticed yet that the fin tip in the SP-25 scan is not parallel to the root ( by about a degree)? There is no mention of that in the dimensioning of the fin. That should give one a clue that nothing is arbitrary, and yet a single degree is suspicious as a non-design, imaging error perhaps from of a distortion through low quality scan ( the error could have even come from Estes in-house, and consequently printed, and then later copied in error in perpetuity ). That is pure speculation as one can never know for sure. I believe those great designers at Estes drafted better than that. This is why you go by specs. when available. It is not open to interpretation.

All of this assumes that the dimensions in TR-11 ARE in fact specifications and not measurements taken from built examples. My expectation is that they are the latter and that no dimensioned specifications exist. ?Rather, the definition of those fins, if one can say such a thing exists at all, is graphical.

The dimensions in the report are used for the purpose of calculating the wetted area and other parameters of the fin shape for drag estimation. It is certainly possible that, even if the author of the report had noticed that the tip is not perfectly parallel to the root (and that that is a feature of the original, not scanned SP-25 template) that he ignored that so as to simplify those calculations.

I assume it as data that is specified to describe the design of the Alpha (as per the title of fig. 76). Why would you disseminate anything but the data published? Your 'expectation' is speculative as you know, and yet you build upon it with more. Its lacks basis just like my earlier example, it cannot be supported by facts that we know. We only know dimensions of the fin plan, and that they were published by Estes.

*sigh*

One more time, then I am done with this. The K-25 Astron Alpha was designed by Bill Simon and first appeared in the 1967 catalog. Kits produced at that time included the SP-25 template sheet to give builders a pattern from which to cut out fins (I remember this - I built one back then - I just wish I still had the SP-25). The yellow page catalog insert "Model Rocketry Technical Manual" which contains a small scale drawing of the Alpha showing all the components and a full size fin pattern which is slightly different than that on SP-25 kit pattern sheet, first appeared in the 1970 catalog. The Alpha illustration and pattern appears on page 58 of that catalog.

In the 1971 catalog, Technical Report TR-11, "Aerodynamic Drag of Model Rockets", by Dr. Gerald M. Gregorek, who was at the time an Aerodynamics Professor at Ohio State University (see https://www.star-tech-inc.com/bios/drgeraldmgregorek.html) and was published "As a service to its customers" by Estes Industries first became available. In this extensive paper Dr. Gregorek uses the Alpha as an illustrative case for a drag analysis and a flight test program. As part of documenting that analysis and test program he includes a simplified layout of the Alpha's design with several external features omitted and the nose cone shape shown incorrectly in a figure titled "The Design of the Astron Alpha". In that figure he does happen to list some dimensions for the fins for use in the subsequent drag buildup.

Yet somehow, because they are numbers, not pictures, you contend that they are specifications for the design of the Alpha, when it is clear from the context in which they appear that they are illustrative only. And the basis for elevating this illustration to the status of product definition is that Estes Industries (rather than, say, Ohio State University) happened to be the publisher of the paper. So you assume, therefore, that Bill Simon was asked to check those dimensions or that they somehow were otherwise verified and approved as definitive by him or someone else at the company at the time and were intended to supersede the graphical definitions (ether one of them) of the Alpha's fin design then available to anyone with a current Estes catalog or a K-25 kit.

I don't buy that. If you want to, go ahead.

Added: I couldn't resist this - taken from a Launch Magazine interview with Bill Simon HERE. Here's what he had to say about designing the Alpha "The Alpha went together on my kitchen table one night to get Vern off my back because he had been insisting that we needed a new beginner&#8217;s model." <sarcasm>Clearly he was obsessed about contractual dimensions.</sarcasm>

The SP-25 scans aid informally to support the case of those dimensions, but I wouldn't I agree with you that it is the other way around and that they supersede the dimensions on the basis of being publicly released earlier than the dimensions. When you put your name on something such as Estes had done, and there is no other drawn dimensioned plans anywhere else that conflict with it, I will accept as the design data of the Alpha as submitted by Estes R&D department. I only go by information that is supported. I don't follow intent from because that lacks relevancy with what we actually know through the artifacts. Estes owns it for publishing it. Hey don't get me wrong I like conjecture as much as the next person ( because its fun), and the forum is good for the magic of storytelling (much like the interview piece), to be sure, but I make a distinctions between known facts and what could be 'X'. FWIW, I don't actually disagree with you on me assuming me reading them as specifications for the Alpha design. I do accept them in that fashion. Estes must have had dimensions to make a bill of materials to release the kit and put a unit price tag. The R& D provided us with dimensional data from their department and published it in TR-11.

75 posts on the Alpha fin shape... give it to'em Mick.

[video=youtube;jp_jEryyND8]https://www.youtube.com/watch?v=jp_jEryyND8[/video]

Raygun said:

Estes must have had dimensions to make a bill of materials to release the kit. How else could they calculate the the unit sale price?

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Sure they did. One piece of BFS-30 fin stock. That is a 3x9 inch sheet of 3/32 inch thick balsa from which the person building the model was expected to cut his own fins (using the aforementioned template as a guide). I can post an image of the bill of materials from the kit instructions if I must. I have my original set here next to the computer.

samb: I should give that a listen.

I wondered about all the fuss some 4 years ago . if you don't like a particular fin shape, then don't use it. model the bird at a younger/older version of the model. sp-25 could be called version one, Raygun's fav might be version 2 etc.
Rex

Rex R said:

I wondered about all the fuss some 4 years ago . if you don't like a particular fin shape, then don't use it. model the bird at a younger/older version of the model. sp-25 could be called version one, Raygun's fav might be version 2 etc.
Rex

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V.1 will have more tip vortex problems than V.2 just so ya know! :wink:

my understanding is that tip vortexes occur a 'high' angles of attack...since I like to fly mine on A8-3s I'm not going to worry about it much .
Rex

Sure they did. One piece of BFS-30 fin stock. That is a 3x9 inch sheet of 3/32 inch thick balsa from which the person building the model was expected to cut his own fins (using the aforementioned template as a guide). I can post an image of the bill of materials from the kit instructions if I must. I have my original set here next to the computer.

I guess my point is they had to have scale for it to fit into a certain package size so they mist have dimensioned it somehwere., you cant have designs without knowing quanitities and try to sell. Cant have a buisness otherwise. why wasn't it 4 x10 which maybe cheaper. these are these are things one has to evaluate for product design. there must have been decided upon dimensions for the plans before it left the drawing board. The main point of all this being : Why would I assume they had spent billable time giving different dimensions for a publication they may see little in return for other than the benefit of its readers ( but i think they charged a little for it, I think).

pretty sure they checked (eyeball) to see if one could get 3 fins from a 3" x 9" sheet of balsa .
Rex

'pretty sure' sounds very speculative to say the least..

tip vortex in the sense it will be larger due to increased drag by the canted/ curved tip edge not parallel in the sp-25 scan. Its draggier and will slow rocket.

well it was 1967, balsa was a lot cheaper than making a die crusher. all the precut fins need the precision to reduce the cost of the cutters.
Rex

It's true but you still need to calculate all aspects of production which in some cases requires number and measurements, usually done with aide of slide rulers and and drafting tables. rounding doesn't work for linear board feet of material to be ordered on a large industrial scale run without project sales figues and other variables helping in the equation. Its all about the math ( and the money!)

Rex R said:

I wondered about all the fuss some 4 years ago . if you don't like a particular fin shape, then don't use it. model the bird at a younger/older version of the model. sp-25 could be called version one, Raygun's fav might be version 2 etc.

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More than likely, there is not much chance that we will ever recover all the original dimensions from these early models. If they were ever recorded in the first place. (versus some designer cutting out a shape freehand and choosing a fin planform that "looks good")

And as long as we have one or two (or three) early fins documented, as in the pattern sheets, we have something good enough to start from when we need to make copies.

The potential problem is when we (1) start with one drawing, put on paper that changes size when the humidity and temperature change, (2) make a copy of that drawing either by computer printer (with all associated optical/mechanical distortions) or by Xerox copy (again, with all associated optical/mechanical distortions), (3) re-publish our own distorted fin in a magazine or in a rocksim file, including our own size errors, and call it "same as the original" (4) use that non-original source to re-draw a new fin pattern, (5) lay the pattern on fin stock and draw "around" it to mark new fins, (6) etc etc etc. We end up with compounded dimensional errors. And this doesn't even touch on the probability that the original designer at Estes probably handed off the plan to an illustrator for the newsletter, who did the best he could but inevitably introduced his own dimensional errors before we ever even saw the design.

That is why, whenever possible, I go with dimensions. I try to find the most authoritative source I can for the measurements. If I can't find numbers I will use a picture, but I also realize the potential pitfalls of that approach.

Sometimes it's best to let sleeping dogs lie.

I said I was done....but I guess I'm not. I clearly have gone 'round the bend with this.

Raygun said:

I guess my point is they had to have scale for it to fit into a certain package size so they mist have dimensioned it somehwere., you cant have designs without knowing quanitities and try to sell. Cant have a buisness otherwise. why wasn't it 4 x10 which maybe cheaper. these are these are things one has to evaluate for product design. there must have been decided upon dimensions for the plans before it left the drawing board.

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Have you ever bought balsa wood? Three inch wide by 36 inch long sheets have been a standard size for as long as I can remember (over 50 years). Estes fin stock sizes were portions of standard sheets - hence 3x9 - you get four of them out of one standard sheet. I have never seen, in 50+ years that I've been going to hobby stores or buying balsa mail order, four-inch wide balsa being less expensive. That's crazy talk.

As for having to measure - with dimensions - to see if the fins will fit - why? Just lay the graphic representation on the balsa and see as any modeler can/would do (though in this case that would've been quite unnecessary as it is obvious by inspection). The sheets were stock sizes - grab one out of stock and just do a trial. No rulers required then or now. Of course these days it would be a CAD drawing....which is great for driving a laser cutter but certainly not needed to give guidance to a person cutting parts out by hand or seeing how many Alpha fins can be cut out of a stock size sheet of wood when there is so much excess as to make the question silly.

The main point of all this being : Why would I assume they had spent billable time giving different dimensions for a publication they may see little in return for other than the benefit of its readers ( but i think they charged a little for it, I think).

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Yes, why would you? It was written by a college professor - and was probably offered to Estes (the company) to see if they were interested. Even if they commissioned it, I really don't see why they would have wanted or needed to verify the numbers we're arguing about to see if they were correct or close enough. That wasn't the point of the 56-page publication in which they happen to appear. Considering this all happened after Estes Industries was sold to Damon, the people paying the bills (if they paid Dr. Gregorek at all) wouldn't have cared. They wouldn't have given him dimensions - he had twelve models built, nine of which had the original fin planform, that he could measure himself.

So again, you can choose to believe those dimensions are specifications. I do not. I believe them to be simply illustrations made for the purposes of the paper. In a way it's too bad they're not much further off from the SP-25 or the catalog Handbook insert than they are. Then it would be more obvious what is going on here. One thing is obvious to me: since the dimension called out for the tip chord is less than that in either of the two graphic sources (including one for which I have an original physical example in a 1970 catalog), the measurements were taken after the stack sanding matching process. It certainly represents a real-world dimension for an Alpha built according to the instructions in the kit. But that does not make that dimension the definition of the tip chord of the original design. Bill Simon's original drawing/sketch/whatever was used to create SP-25 in 1966 IS.

I need to build another Alpha the old fashioned way (hand cut fins) as penance for this whole thing . Also, this whole thing reminds me of my "accuracy vs. precision" lesson for Jr. High students. I contend the dimensions in TR-11 are precise, but not necessarily accurate (as well as NOT being the authoritative source for the design).

If I can remember (hopefully not, but if I do) when I see Vern Estes at NARCON I can ask him about all this. He'll probably just laugh at me - deservedly.

I hope I'm really done with this now.....

Go Berni... Go!!!