#21
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Aahh, OK. I have never seen that particular item before. Mark \\.
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Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
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#22
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And then there was the fin adjusting band, up above the shroud. Perhaps this was kept loose while the brackets were being adjusted, and then tightened down to anchor and stabilize the upper part of the fin? Speaking of the fins, you had mentioned that these were hard to draw in SolidWorks, but they are also really hard to model in the real world. Along with the brackets, this part of the construction has kept me scratching my head for almost a year and a half. The hollow built-up method, using styrene for the skin, that is outlined in the NARTS pack would probably work well for a model of, say, BT-60 size, and you could use a stronger material to make the skin in large models, but I feel that my 2" model is stuck in no-man's land between these two scale ranges. It's too large to use styrene, and too small to use something tougher and thicker. The problem is that not only does the Sandhawk fin have a symmetrical knife-edge bevel on the leading edge, it also tapers in thickness from the root edge out to the tip edge. The fins on the real Sandhawks were quite thin to to begin with (only 1.017" thick at the root), so when you try to scale them down... Well, you run into an issue with material - finding something that is the right thickness, that can be tapered and beveled, and yet will have sufficient strength. Also, because the root edges will be pretty thin, there may not be enough surface area on them to bond well to the surface of the airframe, so you are looking at TTW construction. For my 1/6 (approx.) scale Sandhawk, the 7.125" root edge of the fins need to be 0.17" thick (a little less than 3/16ths of an inch), and then they need to taper down to 0.086" (slightly over 2mm) thick at the tip edge, which is approx. 3.3" away! I have tentatively come up with a plan to use a lamination of alternating layers of two different types of wood with two different thicknesses, with a sculpted knife-edge bevel. If that doesn't prove to be strong enough, then it is back to the drawing board (no pun intended). You have to see my prototype to appreciate how really thin these scale fins are. Mark \\.
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Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
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#23
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That's them.....scum bags.....
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Don NAR 53455 "Carpe Diem" |
#24
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Mark those fins will be tough to make! Will plywood work? What are you flying this on? I built a semi-scale using 2" plotter paper core tube, but opted to make constant-thickness fins from balsa, covered w/ 110# card stock to form the sharp leading edge. A coat of CA made them pretty strong, but I am flying on an "F".
I dug out a Thiokol brochure on the Sandhawk motor (TE-M-473) and scanned it into a pdf. I had to de-res a little to fit the size limit on this forum. I think I see now why the fin shroud is split, to fit over the motor nozzle (see pg 2). The bell of the nozzle forms that metal ring at the base of the rocket. |
#25
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I've been following this thread with a keen eye; I have the vintage Estes Sandia Sandhawk
(Kit # K-51) still "in-the-bag" I've been wanting to build (if I can ever get to it). The links to the scale data will help considerably. Thanks again and keep up the great dialog.
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Dave, NAR # 21853 SR. |
#26
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This bird is deceptive...it looks fairly simple as a 4FN model, but that fin shroud/bracket assembly and the antennas can drive you nuts, not to mention the fin planform as Mark has already pointed out. It has always been one of my favorites. I have two vintage Estes kits from the 70s...one I built several years ago and didn't do it justice. The other is in the bag (but opened).
I look forward to you posting pictures of your Sandhawk if/when you build it -- I always enjoy seeing your models here and over at the NSF forum! |
#27
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Are you saying the Estes K-51 kit is fairly difficult to assemble? It's suppose to be a Skill Level - 2 build (at least, that's what the catalogs say). I'll have to go find it (the kit) in my stash in the several large boxes I have and maybe pull the instructions out and study it. I was thinking it (the Sandhawk) would be somewhat similar to the re-released D - Region Tomahawk (which I also have, but haven't assembled yet).
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Dave, NAR # 21853 SR. |
#28
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The unresolved question is whether the resulting fin will be stiff enough. This is one of the ideas that I had for constructing the fins, anyway. The attached photos are of a stack of the unlaminated layers for one of the fins, before they are bonded together and before the Bondo is added. This is the "prototype" that I mentioned before. The stack includes the top "skin" layer, but only the part that covers the flat part of the fin. The first photo is a shot of the root edge, the second is a shot of the tip edge, and the third is a shot of the overall fin. In the second shot, the layers aren't too tightly held together. If I were to get them tighter, the clamps that I would need to put on would block the camera's view of the edge. The root edge of the fin is a little over 7" long, and the chord is approx. 3-5/16". What is missing from this prototype is the TTW tab on the root edge; I forgot to add it when I traced and cut out the layers. Mark \\.
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Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
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#29
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No, no! Sorry thats what I get for posting at midnight--the 51 yr old brain wants to be in bed by 10:30 No the Estes model is pretty straight forward, with a lot of great detailing molded-in. I did not install the antennas, because I figured they would break off after the first flight. Somewhere I had read (perhaps Model Rocketry magazine?) someone suggested replacing the plastic antennas with music wire--I was lazy. There were some blemishes in the plastic parts, especially the nose cone that I had to fill in with Testors putty. But the K-51 is a great kit and is really impressive-- here is a shot of mine at lift off. When I wrote the above, I was thinking of scratch built models. Last edited by rocketguy101 : 02-14-2010 at 02:53 PM. |
#30
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Nice lift off picture! That's what I like about the Sandhawk; the colors really make it standout.
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Dave, NAR # 21853 SR. |
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