7.5" - 6" Terrier Sandhawk

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Fins attach at 2 points. Inside the airframe it's bolts & nylon lock nuts through the vertical spars. Really this is so solid I doubt the external ones add much but they don't hurt. Outside, it's short bolts and low profile nylon lock nuts through the fins (not yet installed - finishing that up later today) and vertical bolts down into the tee nuts in the spars. Very solid. It better be, the 1st flight will be on an 11,000ns N4000 :)

Wow, exceptional work Jerry. The Sandhawk was one my favorite rockets growing up although I never managed to build one. I'm adding it to the queue....
 
Finally it's done!!! Yay !!! Well, the top half at least :) I'll get cracking on the finishing up the booster after the upcoming URRF launch this weekend. Luckily it's somewhat well on already.

shawk001.jpg
 
Awesome!!
icon14.png
 
Wow, using all the new capabilities at once... you couldn't fit an N in the old Sandhawk ;)

Great video and flights!

Is that an almost pressure/drag sep that I see on the on-board? How fast was it going?!
 
Last edited:
Sweet flight! @1:38 it started to get a little scary. Looks like you might need a vent hole in the lower section.
 
My wife and I were recovering a rocket in the field to the right of where the Astrobee landed. As you can tell from the video, the booster was flipped over. The thing sounded EXACTLY like a moose. I stopped and was like "WTF is that?"
 
Hahaha - yea, the old Shawk (I still have the fin can) was a 75mm mount. Without extending the lower section I can jam in a 54" 98mm like Mitch Guess's Astrobee (this was the smaller 11k ns 98)

Yes, it was attempting to drag separate which is a little ironic given that no matter what I tried I never could get the old 2 stage to do that. I'll be using a sep charge via RC on the new one, it just looks cool, those few moments of coast.....

Max speed was 1060fps, pulled 19gs, 9,900'. Rolled a bit more that I'd expected but that happens when you go faster....


Wow, using all the new capabilities at once... you couldn't fit an N in the old Sandhawk ;)

Great video and flights!

Is that an almost pressure/drag sep that I see on the on-board? How fast was it going?!
 
The Smoke propellant was a new (to me) formula that I'd had concerns about due to excessive porosity - the mix was a problem before curatives. Anyway I rolled the dice, and oh well....It can be repaired though, after I finish the new Terrier booster I'll get to it - it was a great test platform.

Off-topic but what happened to that poor Nike Smoke?
 
Resuming work on the Terrier booster, I actually cut these fin blanks back in March. They're 3/8 BB ply which will have CNC cut foam added for the diamond airfoil then vacuum bagged with carbon and a glass veil. They need notches 1st though so that necessitated building the internal structure so the notches could be aligned. Done this a few times now, it's getting a little easier. Spars are poplar, nice stuff to work with.

P1030014.jpg

P1030017.jpg

P1030023.jpg

shawk-3-2014a-00011.jpg

shawk-3-2014a-00013.jpg

shawk-3-2014a-00015.jpg
 
Cut some squares, 1/2" BB, and proceeded to cut notches for the spars. The notches themselves are easy to size, you just move the stop block over in small increments until the width matches the spars. The tricky bit is getting the center UNCUT portion to match the width of whatever fin material you're using. I haven't yet figured out a good way to do this, and this time I left it slightly large so the fins would be an easier slip fit. A little too large, the fins will need a bit of gaffers tape as shims as will become apparent later.

P1030021.jpg

P1030025.jpg

P1030027.jpg

P1030029.jpg

P1030032.jpg
 
Dry fit the pieces and it looked good, so I used some leftover cutouts as cauls to clamp it up while gluing. Just some thin CA wicked into the joints is all, it's incredibly strong. The black stuff is gaffers tape used as a temporary shim for the pilot-bearing bit. This will make the tube slot width exactly match the plywood fin. Theoretically....

P1030035.jpg

P1030037.jpg

P1030039.jpg

P1030041.jpg
 
Slotting box and a piloted bit on the router make perfect but incomplete slots, just a couple minutes to finish these though.

P1030053.jpg

P1030054.jpg

P1030056.jpg
 
Probably not really necessary but I wanted to lighten these fin cores a bit so I hacked out some material with a jig saw. Saved just 40 grams per fin, so not sure it was worth the effort.

P1030066.jpg

P1030072.jpg

P1030074.jpg
 
I contacted Coby at flyingfoam.com for some contoured fin halves after deciding not to go the all-wood route or making and learning how to use a hot wire cutter. Maybe next time. EPS foam isn't impact resistant but it was fairly cheap compared to the other options and it'll get a carbon/glass treatment which hopefully will help. Just have to try and not smash the fins into things :) 3M-77 spray adhesive works well here.

P1030060.jpg

P1030062.jpg

P1030076.jpg

P1030077.jpg

P1030084.jpg
 
Coby had some difficulty getting the edges to zero thickness so left a little meat on. After pondering how to deal with this I decided the easiest way would be to add some balsa strips then sand down to retain a smooth bevel. That worked pretty well - both the balsa and foam are extremely easy to sand and shape.

P1030085.jpg

P1030088.jpg

P1030089.jpg
 
Did a little experiment on a scrap of this foam, Foodsaver'd with the carbon/glass layup I'm planning. Not great - this foam has lots of little holes which show through AND it's still fairly easy to ding. Next time I'll acquire samples PRIOR to any work if I'm unsure. I ordered some 1/64" birch ply from Balsa USA to skin these which is more work than I'd planned but the result should be a durable and good looking fin set.
 
While waiting on the ply I turned to the booster transition section. I like to use as little epoxy possible to make things modular but there isn't a good way to do that so the center 6" section gets glued in. The rod assembly is removable for replacement if needed, and gets held in and prevented from rotating by 2 tee nuts. The bulkhead at the base will get further support and transfer of weight by a coupler which will meet with the one coming up from the lower section, transferring loads all the way down.

P1030095.jpg

P1030097.jpg

P1030098.jpg

P1030102.jpg

P1030103.jpg
 
I contacted Coby at flyingfoam.com for some contoured fin halves after deciding not to go the all-wood route or making and learning how to use a hot wire cutter. Maybe next time. EPS foam isn't impact resistant but it was fairly cheap compared to the other options and it'll get a carbon/glass treatment which hopefully will help. Just have to try and not smash the fins into things :) 3M-77 spray adhesive works well here.


Just a quick comment: white beaded foam is only good up to ~7" Hg reliably. If you vac-bag your fins, just keep that in mind.

Looks awesome, and Coby does good work. I got some free-flight C-RG wings from him a couple weeks ago.
 
Thanks for the tip Brian. For better or worse I've opted to sheet these with 1/64" ply. And FWIW, the Foodsaver didn't crush the sample but I have no idea what pressure it applied. Interestingly, I saw on TV the other day that a variant of EPS foam is used in road building...

https://www.geofoam.org/road-construction.asp
 
Working on the shroud, I figured if I used enough supports and a heavier card stock I could pass on foaming the gaps as I'd done before. I stacked up 3/32" plywood and used a circular saw blade on the table saw to cut the 36 little triangles.

P1030106.jpg

P1030109.jpg

P1030111.jpg

P1030112.jpg

P1030117.jpg
 
I tried firing up old VCP to make a shroud template but apparently it doesn't run on Windows 7 or 8. I found a workaround on payloadbay.com which generates a template. The caveat here was it wouldn't print full-size across multiple 8.5x11 pages so I printed a few copies of a section of the shroud and taped them together, then transferred to some heavy poster board stock from Michaels. Scotch 77 spray adhesive on the triangles and shroud worked well, securely gluing the stock to the frame. No need to foam, this is pretty good.

Taking a step from a sail plane builders technique, I made a composite fiberglass wrap by lightly misting spray adhesive onto some 6oz glass and laying on some 3.25oz tight weave cloth. This makes it super east to handle and cut with no frayed edges. Nice!

P1030116.jpg

P1030118.jpg

P1030120.jpg

P1030124.jpg

P1030128.jpg
 
This 1/64" birch ply is very nice stuff to work with. I stacked the 8 sheets for a rough cut and adjusted each quarter panel with a utility knife and some sandpaper. I'm using some slow setting epoxy to bond these to the cores with a bit of 15 minute down the center and across the top to hold it while it's being handled. Good tip Gerald! As Brian and Gerald pointed out, this foam is delicate and easily deforms under too much vacuum. I briefly pulled a little hard on the 1st one which was enough to partially dent a portion before I got it under control at 5" Hg. That'll be the flat black one :)

P1030132.jpg

P1030133.jpg

P1030134.jpg

P1030136.jpg

P1030139.jpg
 
Back
Top