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Old 10-06-2017, 12:18 PM
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blackshire blackshire is online now
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Default Estes Alpha "purists'" part (link)

Hello All,

While shopping online for 3D printed scale model rocket parts on the Aerobotix store page on the Shapeways website this morning (our own member "Raygun" is the founder of Aerobotix), I had a "Now I've seen *everything*!" moment... :-) Now:

There are Estes Alpha K-25 purists here on YORF, as the various threads about the changes to its decor scheme, fin planform, motor mount, and other features over the years show (which I say not in ridicule or condemnation, but in admiration!). Estes Alpha "purism" has been taken perhaps to its limit by Raygun, who has created a 3D printed plastic fin unit of the balsa-finned Alpha (see: http://www.shapeways.com/product/HV...tionId=43827433 [he also produces a 3D printed duplicate of its balsa nose cone]!) This part faithfully reproduces all of the attributes of the Alpha's tail assembly--and I mean *ALL* of them. He describes this ultimate fidelity to the original, which includes "printed-in" attributes that the kit builder was instructed to supply, thus:

"PRODUCT DESCRIPTION

"This is a reproduction of the fin plan introduced in the Estes kit K-25. Note this is the full classic swept tapered fin plan first described in pattern sheet SP-25 and definitively dimensioned in Estes Tech. pub. TR-11. I thought it would be fun to make a fin unit out of it, to get folks of the sanding business which is becoming less tolerable these days. What I maintain as charm is NOT having the 'fin tip-to-root taper' that I commonly use, but describe the fins as per the original kit instructions. They therefore have the sheet stock thickness look, and having a perfect symmetrical airfoil profile as instructed to shape according to those plans. I have even left out fillets, as the plans pre-date the technique. You can compare this fin unit to my other offering in the PFS-50 ( Alpha 3 )-style fin can that I also reproduce maintaining those classic, though slightly different swept delta lines as well. I hope the purists could appreciate these as much as I do. Enjoy!" *ALSO*:

If this ^isn't^ the Golden Age of model rocketry right now, then there's no such thing as gold! :-)
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http://www.lulu.com/product/cd/what...of-2%29/6126511
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Old 10-06-2017, 05:20 PM
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....except that the SP-25 shape was NOT "definitively dimensioned in Estes Tech. pub. TR-11". There was a long tedious thread on that exact subject over on that other forum, which ended abruptly when I showed Bill Simon, the designer of the Alpha, TR-11 and he basically told me "never heard of it". When I asked him what the definition was, he told me it was SP-25.

As most know, that was a printed pattern you had to transfer to the balsa and then cut for yourself was the official definition of the original Alpha fin shape. The dimensions in Dr. Gregorek's TR-11 are clearly taken from built examples and do not match the original pattern.

Subsequent to that whole discussion, I have had the opportunity to compare fin shapes among several different printings of SP-25, the die cut fins that followed, and the current laser-cut fins. The fin shape changed with the laser cut version, with a reduced span and slight change in the angle of the tip with respect to the root (they were not quite parallel initially).

So yes, I guess I'm a purist, at least from a lineage of the design point of view.

Note that the shape in the yellow handbook pages in some catalogs is not the same.

As soon as I saw that language in the description for those 3D printed parts I wondered if the vendor wasn't the architect (I think that what he said he was) with whom I was arguing in that TRF thread and who simply couldn't wrap his mind around a part being graphically defined or the idea that the bill of materials for knowing the cost of the kit would be, for the fins, a sheet of BFS-30 (which is what was in those kits, of course) rather than explicitly costing a dimensioned fin part. *sigh*
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Old 10-06-2017, 06:17 PM
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Quote:
Originally Posted by BEC
....except that the SP-25 shape was NOT "definitively dimensioned in Estes Tech. pub. TR-11". There was a long tedious thread on that exact subject over on that other forum, which ended abruptly when I showed Bill Simon, the designer of the Alpha, TR-11 and he basically told me "never heard of it". When I asked him what the definition was, he told me it was SP-25.

As most know, that was a printed pattern you had to transfer to the balsa and then cut for yourself was the official definition of the original Alpha fin shape. The dimensions in Dr. Gregorek's TR-11 are clearly taken from built examples and do not match the original pattern.

Subsequent to that whole discussion, I have had the opportunity to compare fin shapes among several different printings of SP-25, the die cut fins that followed, and the current laser-cut fins. The fin shape changed with the laser cut version, with a reduced span and slight change in the angle of the tip with respect to the root (they were not quite parallel initially).

So yes, I guess I'm a purist, at least from a lineage of the design point of view.

Note that the shape in the yellow handbook pages in some catalogs is not the same.

As soon as I saw that language in the description for those 3D printed parts I wondered if the vendor wasn't the architect (I think that what he said he was) with whom I was arguing in that TRF thread and who simply couldn't wrap his mind around a part being graphically defined or the idea that the bill of materials for knowing the cost of the kit would be, for the fins, a sheet of BFS-30 (which is what was in those kits, of course) rather than explicitly costing a dimensioned fin part. *sigh*
"You da man" (the authority, that is) regarding the Alpha and its evolution over the years; yes, I recall the fin planform in the yellow handbook insert in the late 1960s Estes catalogs. (The Astron Falcon, and not the Renger Sky Slash, was kitted for--at least partially--the same "bill of sale" reason, because it required less sheet balsa than the Sky Slash, so that cost consideration was--and may still be--a significant factor in the development of balsa-finned model rocket kits.) I apologize for causing an unpleasant past occurrence to come to mind again.
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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR
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Old 10-06-2017, 08:26 PM
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Jason,

No need to apologize. I kind of enjoy that sort of discussion, especially when I am able to go right to the source (Bill Simon in this case) and have him back my reasoning .

You referred to the fellow who has the 3D printed parts as "Raygun". I just relocated the thread on TRF I was thinking of and that was, in fact, the handle of the guy who was stuck on the idea that Larry Gregorek's measurements of built models that show up in TR-11 were "definitive". If you have nothing better to do, and you don't mind sullying your computer by going over there, here's that thread: http://www.rocketryforum.com/showth...ha-fin-pattern/

"Raygun" enters the discussion at post 61. He finally sort of admits defeat in the argument at post 113 after I took TR-11 and an SP-25 scan and asked Bill Simon, at NARCON in 2015, which he thought *defined* the fin shape.

I see that hasn't prevented him from claiming the TR-11 shape is definitive in his product description. To which I would say to all the other K-25 Alpha geeks out there "if you're looking for accuracy (as opposed to precision), buyer beware!"

I've since had the chance to get to know Bill Simon a little as we prepared for the recent 50th Anniversary of the Alpha affair at the Museum of Flight. I got to see some of his other design work when my wife and I spent a lovely afternoon and evening with Bill and his wife at their home a few weeks ago. I'm sure the original shape, drawn in 1965 as it turns out, was simply transferred to SP-25 by Gene Street and was reproduced from there in all the versions of SP-25 (including having it printed on the back of the yellow face cards in the 1970s) and the dies used to die cut Alpha (and Alpha II) fins during the period in which they were die cut.

Thanks for giving me an excuse to ramble a bit.....
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