L3 Build: LOC 5.5" Sandhawk

I started the tip to tip today, and was able to get one section completed. I was aiming for two, but I could not get the garage warm enough to cure the epoxy in a timely manner, and I am not sure our cats would leave the rocket alone if I brought it inside the house. But I started off by giving the surfaces of the fins a quick sanding, as well as the fillets, to rough them up a bit. I then cut out 4 squares of 4oz fiberglass cloth and set 3 of them aside for later use. After laying the cloth down on the section, I lifted one fin section back and painted epoxy on the fin, fillet, and body tube. I then laid the cloth back down, and repeated for the other side. Once the cloth was laying down on both sides, I worked any wrinkles out with a spatula, and applied more epoxy as needed to any dry areas. Once I was happy with how it was all laying down, I applied a layer of porous teflon release onto the glass, and smoothed it out again, using a paper towel to soak up any excess epoxy. Since the ambient temperature of my garage was 55 degrees, I borrowed a small space heater from my father in law, and set it up directly next to the fins, and turned it onto 80 degrees. The fins reached a nice temperature of 70 degrees on the far end, and 85 on the near end. Even with that, it still took about five hours to reach the leather stage, when I removed the release film and trimmed the excess glass off. A few areas weren't quite ready yet, and left strands, but I will go back and clean those up later. So far, I am pleased with my first venture into tip to tip fiberglassing. This first section has no wrinkles, voids, or air bubbles, and will require minimal work to finish.


I ended up trashing this first piece of cloth, as I could not get it to lay right when wet with epoxy. I ended up using a square that I cut and later trimmed.

I like to coat the surface with epoxy first. Next lay down the cloth then apply the top coat of epoxy.
Another trick is to use 777 spray adhesive the surface.

Another trick is to use masking tape (I prefer blue or green for this) and to mark the forward edge of the area I am going to tip to tip, for example just ahead of the leading edge where it meets the airframe (covering the length between both fin leading edges). Then wetting out the fin and airframe (one half of tip to tip area) I apply the cloth to the wet area and dab it into position with a brush, then I wet out the second half and lay the cloth over it and finish wet out of both halves. After reaching the leather stage it is super easy to trim the excess from the fin edges with a sharp razor blade (good ole Stanley utility knives work great), for the area under the tape I trim the FG along the edge of the tape and peel off the extra glass that is not needed. Learned some of these techniques watching Tfish's tip to tip tutorial video, especially the tape trick.

Kris,
I like the way you changed the nosecone eyebolt. In answer to your online posed question the forged bold should be just fine. Like you I prefer a u-bolt, but it would be more of a challenge to fit it on there.
If you ever seriously have a question for your TAPs be sure and call or write. We could easily miss it in the build thread.

Steve Shannon said:

Kris,
I like the way you changed the nosecone eyebolt. In answer to your online posed question the forged bold should be just fine. Like you I prefer a u-bolt, but it would be more of a challenge to fit it on there.
If you ever seriously have a question for your TAPs be sure and call or write. We could easily miss it in the build thread.

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Of course. Although now I am seriously considering not using the bay for the tracker, since I realized the only way to turn it on would be during prep of the rocket at my tables. I am not too sure I like that in case I run into any delays or so forth, and the battery runs down. I am now seriously considering placing it on my altimeter sled with the altimeters, as I have plenty of room, and I currently use that configuration on my ARCAS and Aerobee builds with no issues what so ever. If I do make this change, I will remove the nose sled from the coverplate, install a U bolt, and epoxy the coverplate in place with the screws installed for added strength.

Moving on, today I did the second section of the tip to tip. This one went smoother than the first, albeit with colder temperatures. The little space heater worked great, though, but not great enough to allow me to get more than one section done.


I propped the airframe up in the cradle to allow a more even flow of the hot air from the heater over the fiberglass.


The completed section. I still need to do a little clean up sanding on the edges, but this second section looks much better than the first.

The second section usually is better than the first...[emoji14]

Finally got around to laying down the final section of tip to tip yesterday. This morning, I went out and had a chance to briefly sand down the edges before leaving for work. After an interesting day at work in the snow (a somewhat rare event here in the Puget Sound region), I came home and looked over all four sections closely. Each one has a few imperfection and cosmetic flaws, but those are nothing that hinders functionality, and will easily clean up. Over all, I am pleased with how it turned out, and in fact I am already planning on doing tip to tip on a later build this year (Thor!). Next steps on the fins will be the detailed finishing, and then moving onto the avionics bay while I wait for warmer weather to get this beast outside and start the finishing process.

I'm really enjoying following your build! Great attention to detail! Another great thread to learn from!

Decided I had to get the partially completed project out into the snow for a couple of photos today. 9"s of the white stuff is rare in the Seattle area!

Not much work has been accomplished on the Sandhawk due to a combination of weather and being sick, but today I decided I should start seriously looking at updating the weight estimates of this project. So I weighed the build so far, which is basically complete except for primer and paint. I was actually surprised at what I saw! The booster section, by far the heaviest single component, weighs 179.5oz, the electronics bay weighs 50.05oz (minus the charge wells and wiring), and the payload section and nosecone weighs 100.4oz. All together, I am looking at right around 21 pounds without primer, paint, or recovery gear. So I think my weight estimation of 35lbs is going to be pretty close.

Based on what I saw with the preliminary weights, I decided to go ahead and order my main parachute, a Rocketman 14ft. This should see a 35lb rocket descend at a nice 15fps, or a 40lb one at around 16.5fps. I also ordered a deployment bag and a set of RocketJunkies charge wells at the same time.

Been slowly doing some more work on the build over the past several days. Last week, the drogue, a SkyAngle Cert 3 Drogue arrived from Wildman.


And I started to fill/prime the airframe sections. After testing out Bondo and another brand of filler that I cant remember the name of at the moment, I decided to go in a somewhat old school direction, and use Kilz as a combination filler/primer. Over the course of two days, I applied three heavy coats to the payload section, then let it sit for three days to fully cure.


Then yesterday, I broke out some 80 and 120 grit sand paper and spent the better part of an hour sanding away on the tube. It has a nearly perfectly smooth finish now as a result. As mentioned in the previous post, the payload section and nosecone together weighed 100oz before this. After sanding, they weigh 104oz, so I am very pleased with the results.

After discussing the location of my tracker with my TAPs, they expressed concern about my idea of placing it in with my altimeters, which I was considering in case I couldn't come up with a solution for a power switch for the unit. I remembered that I had ordered several screw switches from MissileWorks, and I pulled them out. A couple of standoffs, a drill and 4-40 tap, and I had a solution.


The wire is only temporarily installed. I will solder it to the switch permanently later. I can now fully install the tracker in the nosecone, then right before I install the nose on the rocket, use a screwdriver to arm the unit. I also drilled a few holes to use as a battery mounting location.





Then today, I decided it was time to install the thrust plate. I temporarily installed it, and drilled three #10 holes in the spacer blocks, removed the plate, and tapped the holes for 10-32 screws. I then mixed up a batch of JB Weld and applied it to the mating surfaces on the airframe and in the screw holes before installing the plate. I then installed the three screws, using the JB weld as a thread locker.





Next step is to fill/prime the booster section, and then finish the altimeter bay.

very nice!

I know that opinions on thrust plates greatly differ, but boy I like them.

Theory said:

very nice!

I know that opinions on thrust plates greatly differ, but boy I like them.

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What are the down opinions of them? I just installed on my L3 project, hadn't considered negatives.

roytyson said:

What are the down opinions of them? I just installed on my L3 project, hadn't considered negatives.

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Weight in the wrong end. I have two sitting at home, never used. One was for my L3 rocket. 8" diameter nd 98mm mmt. The thrust plate is a full pound. I also bought one for my PML 1/2 Scale patriot. 7.5" dia and 98mm mmt. Also darn near a pound. I still may use the 7.5X98 plate since that tube is phenolic. But the 8" rocket is fiberglass, so no need.

jd2cylman said:

Weight in the wrong end. I have two sitting at home, never used. One was for my L3 rocket. 8" diameter nd 98mm mmt. The thrust plate is a full pound. I also bought one for my PML 1/2 Scale patriot. 7.5" dia and 98mm mmt. Also darn near a pound. I still may use the 7.5X98 plate since that tube is phenolic. But the 8" rocket is fiberglass, so no need.

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I can see that. Mine is a 4" with 75mm motor. so it is not much more than a ring with mostly holes.

Not much progress has been made the past few days. After sanding the base coat of filler/primer to the upper airframe, I applied a layer of Rustoleum filling primer, and after letting it cure, I gave it another sanding. There are still a few areas where the weave can be seen, but I think it adds character, and won’t be too noticeable once the top coat is on.

I’m the mean time, I’ve also been working on applying the filler/primer to the booster section. The next step with that will be to let it fully cure then sand, and apply a layer of the rusto primer.

The avionics bay is on hold until my charge wells arrive, and at that point, I can complete the layout of where everything will be arranged on the bulkheads.

Came home from work today to a box from Ky and Buddy at Rocketman sittin on my front porch. My 14ft main chute and deployment bag, as well as my Rocketjunkie charge wells arrived!





After unboxing the last reaming items needed for the cert flight except for the motor and casing, I decided to take advantage of the good weather and sand the filler/primer on the booster sections. After a good 45 minute work out, I applied a layer of Rustoleum primer, and will give it another sanding soon. Again, not all of the weave is covered, but I kind of like it. Back in the 50's through 70's, sounding rockets were often hastily painted prior to flight, many times with just brushes and rollers. so the fact that my finish job is will not be perfect kind of makes sense in a way! And I certainly am not going for performance here!



I then proceeded to layout the bulkheads for the ebay. I had previously taken the stock LOC plywood bulkheads and doubled them up with G10 bulkheads from Madcow and epoxied them together and installed ubolts. Now, with the charges wells finally on hand, I found the best places to install them, and install the terminal blocks.



The charge wells are big, capable of holding up to 8grams of black powder each, even though they will never see that much. Using a black powder and shear pin calculator, I calculated out that only 2 grams should be needed to separate the drogue section using 4 4-40 shear pins, and 4 grams for the main with 4 pins as well. Ground testing will of course be conducted to confirm these values.

The deployment charges sound about right as they are almost exactly the sames as what I used on my Cherokee-D, which is similar in size to your Sandhawk.

That calculator has been spot on for my previous builds, so I have no reason to doubt it. Those charge wells are overkill, but they only make 3 or 8gram wells, so I figured I might as well go larger with them. I can always replace them later for use on a future bigger project (and yes, I have plans already... next year!)

I was able to get the electronics sled wired up this evening. To prevent me from hooking up the charges incorrectly, I used opposite JST connectors on each plate. For example, for the drogue charges, the main altimeter, in this case the MissileWorks RRC3 Extreme is hard wired to a male JST pigtail, while the backup, the Perfectflite, is using a female JST pigtail. The same was done for the main chute charges.



The back side of the sled is a mess of wiring that I still need to clean up, but it will be much neater soon.



Next up, I need to seal up the holes and wire pass throughs on the bulkheads, then figure out my switch mounting. Once that is done, I will probably be ready for the ejection testing.

Coming along nicely Kris.

Enjoying your thread.

Came home from work today and discovered that my project as well has caught the red plaque, Rich...





I was going to leave the finish as is, but I decided to apply a thin coat of Bondo to fill in the remains. Tomorrow I will give it a good sanding then a final coat of primer. I still need to finish with a thin coat of Bondo around the fins, but other than that, it is looking good!

Too bad about the Red Plague Kris, and those two rockets haven't even met yet...

rharshberger said:

Too bad about the Red Plague Kris, and those two rockets haven't even met yet...

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Oh, they will meet... and soon!

Spent some more time working on the build today. I will admit, the final finish will not be up to the standards of many, and will be rough in some areas, such as around the fins, but it will still look great from 15 feet away. And plus, this rocket is by no means a high performance flyer... I’m not building it with speed and altitude in mind! Sure, if I spend many hours with a sanding block working on it, I can get near perfection, but that’s not what I’m after here.



Here is the rocket, fully primed. I still need to make provisions for my electronics switches, and layout where the payload section will bolt to the electronics bay, as well as layout locations for shear pins. That is all up next. Once those are all done, it will be time to perform the ejection testing. Then I will be able to move on to final paint!

It will be ready before you know it! I wish our snow would go away like yours....

rharshberger said:

It will be ready before you know it! I wish our snow would go away like yours....

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Yes it will be! If the forecast looked better next weekend, and If I wasn't making a whirlwind trip to Detroit Friday, I would try to make it on Saturday... Oh well! The Sandhawk will make her debut at the May TCR launch!

Next weekend is not looking good for a TCR launch the unseasonably cold weather and fairly deep snow still on the field would make launch and recovery a pain, there are areas where the snow drifts are still over 2' deep though the majority of the areas are under 1' now. Thursday the temps are supposed to come up above freezing through the next weekend so April will probably be our first launch for this year.

Check out the Boosted Bertha on page 38, interesting. And the new Double Ringer and SA-2061
Sasha scalelike missle, there was also a Black Brandt and another re-release.