7.5" - 6" Terrier Sandhawk
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Now the fun part - shaping the root to tip taper. At least balsa is fairly easy to sand. I used my trusty random orbital sander to remove the bulk then spent some time with a bar sander. They needed varying amounts of Bondo, but are finally ready for the top reinforcements. At this stage it's amazing how stiff and light they are. Pretty cool.
dixontj93060
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Nice job on the fins!
Gerald Taylor shared an excellent DVD instructional set by his friend competition sailplane wing builder Phil Barnes. Really interesting stuff and naturally much is adaptable for rockets.
One thing Phil does to beef up certain wing leading edges is to give it a strip of hybrid kevlar/fiberglass fabric on a bias which he makes in the shop. The bias cut makes it easy to conform around many shapes and it puts a lot of material on the leading edge. Taking this idea for my fin leading edges, I cut some mylar, taped on some lightweight glass, repeated with some Kevlar and following his instruction, 3M-77'd them together and removed the tape. As you can see I forgot to reverse one of the mylars, but no worry, there's more than enough material here to cut the strips I need.
One thing Phil does to beef up certain wing leading edges is to give it a strip of hybrid kevlar/fiberglass fabric on a bias which he makes in the shop. The bias cut makes it easy to conform around many shapes and it puts a lot of material on the leading edge. Taking this idea for my fin leading edges, I cut some mylar, taped on some lightweight glass, repeated with some Kevlar and following his instruction, 3M-77'd them together and removed the tape. As you can see I forgot to reverse one of the mylars, but no worry, there's more than enough material here to cut the strips I need.
Phil's wings are usually partially painted during the bagging process, I decided to try this with the 1st fin to see how it would turn out. Here's my mylar painting setup, a perfect day to paint too. I used Rustoleum from Home Depot, Phil uses Krylon because that's what his store has. The painted mylars are placed on the bench and overlaid with sone light, tight weave glass, secured on one side to keep it from moving. Phil does this so he can squeegee excess epoxy which I didn't do.
Once the glass is wet out I added the carbon, cut to the size of the mylar and tricky now because the epoxy is beginning to get tacky. It tends to want to roll up with the roller as you wet it. I also rolled some epoxy onto the fin, then cut the glass and mated the mylars to the fin making a big sandwich, secured with a couple pieces of tape.
This assembly is placed inside a pre-cut breather/release piece, then slid into the bag. Here's my oven - 1" foam, duct taped together, and an oil-filled space heater. I can get 120 with a fairly low setting. According to Phil, this isn't for post-cure, but simply to cut the time necessary under vacuum.
This assembly is placed inside a pre-cut breather/release piece, then slid into the bag. Here's my oven - 1" foam, duct taped together, and an oil-filled space heater. I can get 120 with a fairly low setting. According to Phil, this isn't for post-cure, but simply to cut the time necessary under vacuum.
The result was interesting. Some of the paint stuck to the mylar leaving a finish in need of some work. Perhaps insufficient waxing of the mylar, but since the edges need finishing anyway I'm not concerned. The rest of the fin and leading edges came out great - with the mylar cut to just cover the LE, a fairly sharp line was created and the LE bevel is nicely defined. All in all a very interesting technique, thank you Gerald & Phil. For the remaining fins I'll forego the pre-painting and do a normal prime/paint routine. They emerge from the mylar very smooth so this should be pretty easy.
Thanks for asking Mike. With a fair number of gigs, lots of nice fall cycling weather and oh yeah, work, the build schedule took a bit of a hit 
I do want it ready for the NERRF launch in June tho, so please stay tuned, updates will be posted as segments are completed. Happy New Year!
I do want it ready for the NERRF launch in June tho, so please stay tuned, updates will be posted as segments are completed. Happy New Year!
Finally, a day's mostly uninterrupted work, except for the occasional distraction of the Godfather marathon. Here are the sustainer spars and soon-to-be centering rings getting sized and notched. Using a stop block on 1 side to cut notches in the squares which will be rings guarantees the resultant fin slots will be at 90 deg. Started cleanup on the fins for this procedure.
David Reese just asked how accurate the Jasper circle jigs are. Here's one of the 75mm-98mm adapter rings inserted, the fit is excellent for this purpose. As it happens my Jasper 200 (larger) jig cuts slightly smaller than indicated and the 400 (smaller) jig cuts slightly larger. Between the two I can usually get what I need without too much adjusting
Drilling holes in one side of the spars for fin bolts. When everything's fitted and glued up I'll use these as pilot holes to go through the fin and out the other spar. Checking the depth of the fin slot - theoretically, the fin rear and middle slot should contact the rings while the front is about 1/8" proud to allow for the body tube.
This is woodworking pornography. I can't wait until I grow up and can have nice things like a garage and a router
I used a slower/stronger epoxy on the aft ring since it won't have allthread and will retain the motor. I then hit all the joints with thin CA. I doubt this part can be removed without total destruction. Fins fit great and the unit rests evenly on all 4 tips. Nice.
Going old-school and using flexible phenolic from Red Arrow Hobbies. This is my favorite stuff to glass, it takes epoxy well, is not brittle, is light and holds up well to repeated abuse. My Terrier-Smoke is still going strong after 50+ M flights, so I'm confident it'll do the job. But I'm hoping that statement doesn't come back to bite me
Opted to do the slotting now since the slot box was sized for different tubing and so is a bit tight. The flush trim router bit has a pilot bearing which rides on the spars, makes a nice smooth cut. Corners need to be squared though, and after glassing I'll complete the job by tapering the front to match the fin LE bevel and running out the rears (fin assembly slides in)
Opted to do the slotting now since the slot box was sized for different tubing and so is a bit tight. The flush trim router bit has a pilot bearing which rides on the spars, makes a nice smooth cut. Corners need to be squared though, and after glassing I'll complete the job by tapering the front to match the fin LE bevel and running out the rears (fin assembly slides in)
I made a couple end caps using some 1" foam scraps leftover from the low-temp oven (Jasper jig to the rescue again). They're wrapped in teflon tape, which is an idea borrowed from John Coker, thanks John. The tube supports are discs inside but the end caps provide a runoff area for the glass which in theory should help the adhesion of the fg to the tube ends. Making these in 3/4" plywood instead of foam would eliminate the need for the internal discs, but as I'd already cut those I figured I'd use 'em and see how the foam did.
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