Ye Olde Rocket Forum

Go Back   Ye Olde Rocket Forum > The Doctor is In! > Ask the Doctor
User Name
Password
Auctions Register FAQ Members List Calendar Today's Posts Search Mark Forums Read


Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 12-14-2008, 04:16 PM
Mark II's Avatar
Mark II Mark II is offline
Forest Sprite
 
Join Date: Dec 2006
Location: Back Up in the Woods
Posts: 3,657
Default

Quote:
Originally Posted by rocketguy101

Aahh, OK. I have never seen that particular item before.

Mark \\.
__________________
Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
+09281962-TAK-08272007+
SAM # 0011
Reply With Quote
  #22  
Old 12-14-2008, 05:12 PM
Mark II's Avatar
Mark II Mark II is offline
Forest Sprite
 
Join Date: Dec 2006
Location: Back Up in the Woods
Posts: 3,657
Default

Quote:
Originally Posted by rocketguy101
That is what it looks like to me. I think the fin brackets fit onto the flats, with the boss (the round "knob" sticking out of the bottom of the bracket) going into the center hole of the flat area. The slotted holes in the fin bracket allow for adjustment of the fin angle to either add spin or to make up for manufacturing tolerances. After all the bolts are tightened down the fin is good to go!

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 \\.
__________________
Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
+09281962-TAK-08272007+
SAM # 0011
Reply With Quote
  #23  
Old 12-14-2008, 08:16 PM
barone's Avatar
barone barone is offline
Master Modeler
 
Join Date: Apr 2005
Location: Bartlett, TN
Posts: 3,352
Send a message via Yahoo to barone
Default

Quote:
Originally Posted by rocketguy101

That's them.....scum bags.....
__________________
Don
NAR 53455
"Carpe Diem"
Reply With Quote
  #24  
Old 12-15-2008, 10:42 PM
rocketguy101's Avatar
rocketguy101 rocketguy101 is offline
frustrated aero
 
Join Date: Sep 2006
Location: Duncan, OK
Posts: 827
Default

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.
Attached Files
File Type: pdf ThiokolSandhawkBrochure2.pdf (314.3 KB, 114 views)
__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here
Reply With Quote
  #25  
Old 12-15-2008, 10:56 PM
dwmzmm's Avatar
dwmzmm dwmzmm is offline
Master Modeler
 
Join Date: Apr 2005
Location: Katy, TX
Posts: 2,345
Default

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.
__________________
Dave, NAR # 21853 SR.
Reply With Quote
  #26  
Old 12-15-2008, 11:24 PM
rocketguy101's Avatar
rocketguy101 rocketguy101 is offline
frustrated aero
 
Join Date: Sep 2006
Location: Duncan, OK
Posts: 827
Default

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!
__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here
Reply With Quote
  #27  
Old 12-15-2008, 11:40 PM
dwmzmm's Avatar
dwmzmm dwmzmm is offline
Master Modeler
 
Join Date: Apr 2005
Location: Katy, TX
Posts: 2,345
Default

Quote:
Originally Posted by rocketguy101
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!


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).
__________________
Dave, NAR # 21853 SR.
Reply With Quote
  #28  
Old 12-16-2008, 12:26 AM
Mark II's Avatar
Mark II Mark II is offline
Forest Sprite
 
Join Date: Dec 2006
Location: Back Up in the Woods
Posts: 3,657
Default

Quote:
Originally Posted by rocketguy101
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.


  • A 1/64" plywood core layer, in the shape of the whole fin,
  • sandwiched between two layers of 1/16" basswood, in the shape of the fin, minus the knife-edge.
  • each piece of the basswood layer is sanded, on its upper side, in a smooth slope from 1/16" at the root edge to 0.5mm at the tip edge.
  • the flat, unsanded side of each basswood layer is epoxied to opposite sides of the core layer. The portion of the core layer that will be under the knife-edge bevel is left uncovered.
  • Bondo is applied to the uncovered core over the knife-edge layer on one side and is scraped and sanded to match the desired bevel for that side. When the Bondo on the first side has cured, the fin is flipped over and the process is repeated on the other side.
  • a skin consisting of another layer of 1/64" plywood is bonded to the top layer on both sides of the fin. A piece corresponding to the outline of the fin minus the bevel is bonded on each side first, and then another piece to cover the bevel is bonded onto each side. The inner edges of the bevel pieces are themselves beveled where they will meet at the leading edge of the fin so that they maintain a sharp edge when they are bonded together. Aeropoxy 6209 will be used for the bonding, and the lamination will be subjected to constant pressure (firm, but not crushing) until the epoxy cures. The Aeropoxy will be used in order to give the laminated layers the strongest bond that I can reasonably accomplish.
The total lamination will be 11/64" thick at the root edge, or 0.171875", close enough to the target thickness of 0.17". At the tip edge, it will consist of the three layers of 1/64" plywood (the core plus the two top skins), combined with the half-millimeter edges of the two basswood layers. The sum of 3/64" plus 1mm equals 0.086245", close enough to the target thickness of 0.086".

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 \\.
Attached Thumbnails
Click image for larger version

Name:  DSCF0632-compressed.JPG
Views: 66
Size:  140.2 KB  Click image for larger version

Name:  DSCF0634-compressed.JPG
Views: 65
Size:  110.0 KB  Click image for larger version

Name:  DSCF0636-compressed.JPG
Views: 72
Size:  140.4 KB  
__________________
Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
+09281962-TAK-08272007+
SAM # 0011
Reply With Quote
  #29  
Old 12-16-2008, 08:42 AM
rocketguy101's Avatar
rocketguy101 rocketguy101 is offline
frustrated aero
 
Join Date: Sep 2006
Location: Duncan, OK
Posts: 827
Default

Quote:
Originally Posted by dwmzmm
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).

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.

Attached Thumbnails
Click image for larger version

Name:  SandhawkFly.jpg
Views: 63
Size:  38.1 KB  
__________________
David Stribling
NAR 18402 SR
But it is rocket science!
Get yer Barrowmans here

Last edited by rocketguy101 : 02-14-2010 at 02:53 PM.
Reply With Quote
  #30  
Old 12-16-2008, 09:17 AM
dwmzmm's Avatar
dwmzmm dwmzmm is offline
Master Modeler
 
Join Date: Apr 2005
Location: Katy, TX
Posts: 2,345
Default

Quote:
Originally Posted by rocketguy101
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.



Nice lift off picture! That's what I like about the Sandhawk; the colors really make it standout.
__________________
Dave, NAR # 21853 SR.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump



All times are GMT -5. The time now is 11:55 PM.


Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Ye Olde Rocket Shoppe © 1998-2024