7.5" Modular Booster / upscale Estes SM-3 Seahawk - FINISHED!

[SMR]

L2300G (KBA Animal-compatible) fits in there.

Interesting how there is only a single K on the list, and L's take only a few spots.

Thanks. I figured I'd miss at least a couple. There are a disproportionate number of bigger motors due to some duplications in average thrust (I400 & J400, I500 & J500, I600 & J600, J800 & L800, etc...). Whenever I had a choice, I usually went with the higher impulse motor. ('cause its a gift and I'm sure she'd want to get me the best one.)

 

[SMR]

Strakes are all on, good time for a photo op. The sustainer is 1" shy of hitting the 9' ceiling. Still too cold to do any outside work (sanding and painting), so going to finish up the few things I can do inside (avionics, Aero Packs) and hope for an early spring.

 

[patelldp]

This build thread is great! I am in awe of your meticulous building...you get every little detail right. Careful planning and great execution, I'm impressed!

 

[daveyfire]

Strakes are all on, good time for a photo op..

Sather that is GORGEOUS... Wow! I can't wait to see it in person

 

[Eat, sleep, and Fly]

Sather that is GORGEOUS... Wow! I can't wait to see it in person

+1! Any chance of onboard video?

 

[SMR]

Still too cold to do any outside work (sanding and painting), ... and hope for an early spring.

Finally, a few warm days without rain. A little Super-Fil to eliminate the seam, and a quick coat of primer on the interstage coupler. Then the sun went down. Moving back inside, I finished the ISC bulkheads - the upper has a couple of blastcaps for stage separation charges, the lower gets a single U-bolt to connect to the booster's recovery harness.

 

[SMR]

+1! Any chance of onboard video?

Absolutely. I really enjoyed the video from your 2-stage Dark Star at Thunderstruck, especially the staging and sustainer ignition sequence. My plan is to fly an aft-facing camera on the sustainer and a forward-facing camera on the booster. At Midwest Power 11.

 

[sodmeister]

Very good to see you back at it Sather !

You are the second person who mentions Super Fil ,I shall have to try that one day.

Cheers


Paul T

 

[SMR]

Sather, you have so many HPR projects going @ approximately the same size--if I did that I know I'd end up gluing the wrong parts together some how, some where :eyepop:

Well, Tim called this one, absolutely spot on. In addition to losing track of specific parts, I sometimes also forget where I am and/or what I'm doing. A few months ago, I epoxied the interstage coupler together. Then I lost the sheet of paper where I had the measurements of where the centering rings were. This was important, as to avoid relying solely on epoxy to carry the load of the upper stage (the band of the ISC sitting on the upper tube of the booster) during launch, I planned on thru-screwing the band into the physical structure of the ISC. Luckily, I took pictures of it, and was able to reconstruct the measurements. So, the ISC is marked and ready to be drilled for these screws, as well as access holes for the avionics it contains.

Speaking of avionics, I have been collecting the components for and will start assembling some specific sleds unique to this project. The av bay within the ISC uses G-switched timers to initiate staging separation. The av bay in the sustainer contains two sleds, pictured here to deconflict hardware to ensure they will both fit. One has a Tiltometer to control airstarting the sustainer's motor. The other has redundant altimeters to manage the sustainer's dual deploy recovery.

 

[SMR]

You are the second person who mentions Super Fil, I shall have to try that one day.

Not an independent discovery, I must admit. I first saw it used in Tim D's "Hope-N-Pray" build thread. It works great. My fiberglassing skills are pretty bad, so I use a LOT of it...

 

[SMR]

Slow but steady progress on smaller details. I originally planned on using a stock Polecat 7.5" bulkhead for the booster's avionics bay. This is a very nicely designed disk of 3/8" plywood with a routered edge around the perimeter, basically a one-piece bulkhead with it's own integral shoulder. I use this on my 7.5" Patriot in the same configuration, i.e. the av bay built in to the motor section of the rocket instead of separating at apogee with the payload bay, and controlling the main deployment via Defy Gravity Tether. The bulkhead takes both opening shocks... the drogue at apogee and the main nearer the ground.

The booster for the Seahawk is quite a bit heavier, however, as I used bigger fins, heavier glass cloth, and internal structure to manage the added weight of the sustainer during boost. Failure of that bulkhead would be significant, so I needed to beef it up. I started by filling the pre-drilled holes for the Polecat supplied eye-bolt, and enlarging the center hole to fit a jig I use to turn bulkheads on a disk sander (photo #1). I then removed the wood extending beyond the existing lip, turning the one-piece stepped bulkhead into a coupler-only bulkhead (photo #2). I also turned a piece of G-10 (leftover from the sustainer's fins created back in Post #56) to be the body tube bulkhead (photo #3). I personally prefer glass bulkheads on the ejection charge side (easier to clean up), with wood on the inside (thicker to give better seal). Filled the remaining holes, epoxied them together and added hardware (photo #4). Finished with a larger U-bolt and a set of Blast Cap ejection charge canisters (photo #5).

 

[SMR]

The staging avionics bay sits in the lower half of the ISC assembly, with the upper half devoted to holding the separation charges and the sustainer itself. This creates a little problem, that the internal functions don't necessarily line up well with the external shape. I normally use POPO switches on my sleds, operated by inserting a dowel thru holes in the av bay's band. Most of the ISC is buried (in the respectively joined rocket body tubes) or sloped (the 7.5" to 5.5" transition). There is a small section of band on the ISC, however, and putting the two access holes for POPO switches low on the band (photo #1) and the switches high on the sled (photo #2) will allow them to line up. Just like the bulkhead of the booster, the exposed side of the ISC's forward av bay bulkhead is G-10 (photo #3, for easier clean-up), while the inside is plywood (photo #4). This photo also shows how close the switches can be to the top. I'll have about 1/4" of adjustment to ensure the switches line up with the access holes.

 

[SMR]

Back to the rocket itself, I have put this next step off as long as possible IAW my "Problem Shock" theory*. I normally leave off the aft ring, allowing me access to the interior of the fin can to add fillets and foam. Due to the recessed aft ring, that was not possible on the sustainer. And the corresponding small fin tangs make it even more essential to have a solid assembly. So, this will be my first ever injected fillet. I am using medicine syringes from Target (photo #1). Drilling a 13/64" hole between each pair of fins (photo #2) allows the needle to fit snugly. I injected West Systems epoxy with a bit of chopped carbon fiber into the cavity. The mixture was thin enough to run down and pool against the upper side of the ring. Putting a small tilt on the rocket keeps the pool butted up against the inside of the body tube into a reasonable fillet (photo #3). I'll have to re-orient the rocket and make multiple pours to complete all internal fillets... both sides of each ring, each side of the fin tang to motor tube, and each side of each fin to body tube. I am also considering using this technique to foam the fin can, before eventually filling the holes and painting the sustainer.


* - I took credit for this observation in August 2011 in my recycling container odd-roc build thread. If the idea ever becomes commercial, I should get some serious royalties. In his 1970 book, Alvin Toffler defined "future shock" as a personal perception of "too much change in too short a period of time". The accelerated rate of technological and social change leaves people disconnected and suffering from stress and disorientation. Here is the connection to rocketry. When you build a kit, the directions are laid out in a logical order, basically engineered for ease of assembly. In scratch-building, however, as you run into problems, they get deferred. Eventually, when all the fun, easy to do stuff is finished, all you have left are the problems and they pile up in front of you like a giant wall. With a deadline, it could become "too many problems in too short a period of time".

 

[Eat, sleep, and Fly]

Back to the rocket itself, I have put this next step off as long as possible IAW my "Problem Shock" theory*. I normally leave off the aft ring, allowing me access to the interior of the fin can to add fillets and foam. Due to the recessed aft ring, that was not possible on the sustainer. And the corresponding small fin tangs make it even more essential to have a solid assembly. So, this will be my first ever injected fillet. I am using medicine syringes from Target (photo #1). Drilling a 13/64" hole between each pair of fins (photo #2) allows the needle to fit snugly. I injected West Systems epoxy with a bit of chopped carbon fiber into the cavity. The mixture was thin enough to run down and pool against the upper side of the ring. Putting a small tilt on the rocket keeps the pool butted up against the inside of the body tube into a reasonable fillet (photo #3). I'll have to re-orient the rocket and make multiple pours to complete all internal fillets... both sides of each ring, each side of the fin tang to motor tube, and each side of each fin to body tube. I am also considering using this technique to foam the fin can, before eventually filling the holes and painting the sustainer.


* - I took credit for this observation in August 2011 in my recycling container odd-roc build thread. If the idea ever becomes commercial, I should get some serious royalties. In his 1970 book, Alvin Toffler defined "future shock" as a personal perception of "too much change in too short a period of time". The accelerated rate of technological and social change leaves people disconnected and suffering from stress and disorientation. Here is the connection to rocketry. When you build a kit, the directions are laid out in a logical order, basically engineered for ease of assembly. In scratch-building, however, as you run into problems, they get deferred. Eventually, when all the fun, easy to do stuff is finished, all you have left are the problems and they pile up in front of you like a giant wall. With a deadline, it could become "too many problems in too short a period of time".

I have to ask, What made you decide to inject the fillets into the center of the fins, instead of injecting right next to the root edge of the fin? It seems to me that injecting into the center would just waste epoxy coating the motor mount, plus then you have to fill a hole, versus covering it with a fillet.

 

[SMR]

I have to ask, What made you decide to inject the fillets into the center of the fins, instead of injecting right next to the root edge of the fin? It seems to me that injecting into the center would just waste epoxy coating the motor mount, plus then you have to fill a hole, versus covering it with a fillet.

This is the first time I've done it, so no real good reason. Always open to new ideas, here was my logic. We'll see if it turns out to be flawed...

(a) I am trying to minimize the number of holes drilled into the airframe, and I am hoping one hole will be enough for each cavity I'm filleting. Putting it in the center made it roughly equidistant from each of the six fillets that I'm adding, (top of one ring, bottom of adjacent ring, fin tang to motor tube on each side, fin tang to body tube on each side), which minimizes the distance the epoxy has to drip. Part of the technique is finding the "just right" pressure to squeeze the syringe, so it doesn't squirt against the outside of the motor tube or dribble against the inside of the body tube. You'll notice I started with the fillet closest to the hole, as I experiment with this technique. With chopped carbon fiber added, the epoxy turns black and shows up very well through the green fiberglass*. So far I haven't had much, if any, adhere to the sidewalls.

(b) I thought about putting three holes along the fin tang as previously shown in other builds, but that would be 6 holes per cavity, which I believe would be excessive for the small tangs. And I'm still considering injecting foam as a last step in the fin can. With the body horizontal, one hole per cavity (at the top) will be easier to manage than 6 holes per cavity (near the bottom). I'm okay with filling a few holes. I'll just inject some thicker epoxy and orient the tube so the epoxy settles back over the hole and makes a plug.

(c) While putting the holes near the tang does make it easy to cover them with the external fillets, it would require leaving the external fillets until AFTER the internals. I always finish the external fillets BEFORE starting the internals. Otherwise, runny epoxy will find a way to ooze out any gaps between the fin and the slot, making a mess of your fins. I intentionally kept the epoxy / carbon fiber sludge runny, so I wouldn't lose much adhering to vertical surfaces as it seeks the correct (low) spot, and it would flow well left and right once reaching it.

As with most projects, there are many different ways to do things. Not claiming this is better than anyone else's technique, just that (so far) it works for me.

* This is why I prefer conventional "green" (translucent) fiberglass and NOT the black (opaque) tubing.

 

[sodmeister]

Sather ,

When you mentioned "Future Shock" and your/its connection to rocketry ,more so as it pertains to certain scratch build projects ,I sat at my computer and gazed at it, mouth slightly agape.......

I then realized how I could so relate to this and how I have a "special" gift for deferment ,and often looking at my Great Wall of China before me !

Take care


Paul t

 

[SMR]

I then realized how I could so relate to this and how I have a "special" gift for deferment ,and often looking at my Great Wall of China before me !

If I was a better planner, I would be a better builder. But alas, I am a championship procrastinator, so most of my problems are of my own doing.

Just like in my golf game.

:smile:

Sather

 

[SMR]

This is the part of the build I had been putting off most fervently. As mentioned previously, I prefer to fillet and foam the fin can with the aft ring off to provide access to the interior. This was not possible on the Seahawk sustainer due to the submerged coupler of the ISC. The recessed ring also required shortening the fin tang to a length of only 3 1/2”, vs the 10” root chord of the fin. Therefore, needing good internal fillets and foam was even more important. Here is the progress to date.

Rolling the rocket around in various orientations made it possible to fillet (one at a time) the internals using eight holes, four between ring #1 and #2, and four between ring #2 and #3. The volume between rings #1 and #2 was further partitioned by the fin tangs, requiring one hole in each quadrant between fins. There are no obstructions around the perimeter of the motor tube in the space between rings #2 and #3, so I could have used less than four holes in this area. Photo #1 shows the results of injection fillets on the 1515 button side of he sustainer. The chopped carbon fiber mixed in the otherwise clear epoxy allows it to show well through the translucent fiberglass body tube, even more so when backlight as in Photo #2.

Injection foaming turned out, thankfully, to be only slightly more difficult than injection fillets. The biggest challenge to contend with is time compression. While you have many minutes to work with epoxy, your foam working time will be in seconds. I layed everything out in advance… pre-measured Part A and B of foam, a 35cc syringe (with a home-made adapter, so the big hypo would fit in the existing hole), popsicle stick for mixing, paper towels, masked off body tube. (That looks like a lot of foam and a really big syringe, but I was doing 2 rockets at a time to minimize wasting syringes. Each quadrant was done individually, so I used four syringes total.) Wearing latex gloves, start mixing and counting. I found I could get a good mix in about 30 seconds, pour it into the syringe and inject, pour another syringe full and inject, and then the foam would kick off and I could no longer refill the syringe. The Seahawks fin can cavity is a much smaller volume then the other rocket I was doing, so it really just took a little squirt. The foam fills the space and then starts coming out the hole like a little volcano. I kept the popsicle stick handy and squeegeed off the excess as it appeared. When it was fully cured, peel off the masking tape. The proper expansion of the foam also shows up quite nicely though the fiberglass. Yet to do is fill the hole with an epoxy plug.

 

[SMR]

Some progress with the on-board electronics. The timer sled of the interstage coupler has two MiniTimer 4's to initiate staging charges, (as a backup to drag separation.) The first step was to mount the POPO switches oriented to ensure access through the rocket wall. Next is to build the battery box. (I prefer a physical structure to contain the batteries, as one coming loose can really beat up a circuit board.) This board must fit in a 4" coupler tube, so it needed beveled sides to fit inside the curve of the bay. I also finally got around to putting color-coded wires through the avionics bulkheads of the booster and sustainer. The aft bulkhead of the sustainer's bay has extra terminals for the airstart igniters.

 

[SMR]

After all the fillets and foaming were done, it was time to fill those access holes through the body tube. This was best accomplished upside down, working overhead. Sort of like changing one's oil on a lift, the easiest way I found to do it was to raise the rocket high enough to have access under it. One of my PVC stands reached (just barely) across the aisle between the tables of our train layout (my other hobby). I then filled a hypo needle with JB Weld and injected the holes. Quickly and carefully removing the syringe and taping over the hole, the epoxy flowed back to fill the opening flush with the body surface. A little light sanding and voila - plugged holes! Notice the epoxy flowed back over the inside of the tube in open areas to make a larger surface (photo #4), making a strong plug. In areas with foam, I undercut the foam a little with a drill to make a cone shape for the epoxy to fill, for the same purpose (photo #5).

 

[SMR]

Happy Fourth of July to all. I spent most of the day doing yard work, but snuck in a little time to wet sand and prime the sustainer. Rustoleum "Self Etching Primer" goes on easily, covers well, and if you believe the can, adheres well to fiberglass. It also is a nice flat olive drab color, which would be nice on an Honest John or similar. Now off to watch some fireworks!

 

[patelldp]

This looks incredible! Cannot wait to see a launch report.

 

[SMR]

This looks incredible! Cannot wait to see a launch report.

Thanks, Dan. Looking like a definite go for Midwest Power 11, 2-4 Nov 2013 in Princeton, IL. Any chance you'll make the drive this year?

 

[patelldp]

Thanks, Dan. Looking like a definite go for Midwest Power 11, 2-4 Nov 2013 in Princeton, IL. Any chance you'll make the drive this year?

Absolutely zero chance. I really wish I could, though! I will have to live vicariously through the forum.

 

[SMR]

Absolutely zero chance. I really wish I could, though! I will have to live vicariously through the forum.

We'll take some good pictures and hopefully a video or two.

 

[SMR]

Today was a B-E-A-U-T-I-F-U-L day. Took a lot of stuff outside for sanding, fill, priming, and final paint. During the pauses between, I assembled the full stack of Seahawk... booster, ISC, and sustainer. Bear in mind each component is in different stages of paint, nothing final and no decals yet, but everything fit (and it didn't blow over.)

 

[Eat, sleep, and Fly]

Today was a B-E-A-U-T-I-F-U-L day. Took a lot of stuff outside for sanding, fill, priming, and final paint. During the pauses between, I assembled the full stack of Seahawk... booster, ISC, and sustainer. Bear in mind each component is in different stages of paint, nothing final and no decals yet, but everything fit (and it didn't blow over.)

:jaw::shock::roll::wave::clap:

Wow! I didn't get any idea of the scale of this until I saw the bucket next to it.

On it's own, is the booster stable? in other words, after the separation charge(s) fire, will the booster fly stable, or tumble? On the onboard video of my darkstar, the booster tumbled to the side instantly, which may have been a part of the failure. In addition the altimeter fired both apogee charges and the cable-cutter's charge (due to the sudden increased pressure). I still have no clue why the altimeter bay got blown out of the ISC, however a lack of venting may have been a part of the issue.

 

[SMR]

On it's own, is the booster stable? in other words, after the separation charge(s) fire, will the booster fly stable, or tumble?

Rocsim shows the booster stable on its own. The ISC is heavy (helps Cg) and the fins are substantial (helps Cp). The two things that I can think of that might affect that are the staging separation charge and the open throat of the ISC after staging. The sustainer will have flying airspeed at the staging event, so I believe the movement of the sustainer up the coupler will be in the correct direction without significant yaw/pitch. I don't know if Rocsim accounts for the open coupler after staging, though. This adds surface area forward of the Cg, which would be a destabilizing contribution.

 

[SMR]

On it's own, is the booster stable?

Some minor details completed. Added a button and through-screwed the ISC band to mechanically connect with internal structure. Put the booster's buttons back on, which had been off during sanding. And added the 98mm Aero Pack, recycled from the retirement of the 12" modular booster. (motor is assembled here as my plan is to fly the booster alone in primer at Eat Cheese or Fly this weekend. It will have a different top, not the ISC, as it is the planned carrier of my secret payload for Kelly's Challenge.)

 

[SMR]

We successfully flew the booster at "Eat Cheese or Fly" in Wisconsin this past weekend. A big shout out thanks to my friends at WOOSH for all the help to and from the field. My first three event deployment, and everything functioned as scheduled. Of course, it took a full day and a half to prep. (You know you are a slow prepper when the guy with the microphone starts heckling you. Thanks, Tim!) On top of the 7.5" Seahawk booster I had added a standard 7.5" diameter avionics bay with another 48" length of body tube, which in turn was topped by an adapter ring and the "secret payload" capsule. I had to make the rocket tall enough so the 12" wide adapter sat above the 8' tall 1515 rail on the away pad, or I would have had to raise the stand-off to do so. 2 MAWD altimeters were in each of the two avionics bays. She was flown on an L3150 (CTI 98-2G Vmax) motor to a planned 1,800' apogee. I was initially concerned about the stability in this launch configuration, as the adapter ring has a lot of surface area forward of the Cg. A cardboard cutout would therefore show the Cp roughly amidship. But with those big fins, Rocksim promised me 2.2 calibers of stability which turned out to be reasonably accurate. It arced over slightly into the 10 knot crosswind with no roll whatsoever. Straight boost and coast to an actual apogee of 1,652', at which point the two halves opened in the middle. This allowed me to test-recover the Seahawk booster in it's planned flight configuration via Defy Gravity Tether. An 84" Giant Leap drogue brought both sections down to 700', where the booster's 168" main Spherachute (in a Giant Leap kevlar deployment bag) was released. With the booster clear, a second Tether released the capsule at 500' to recover on it's own. All pieces were recovered unscathed within a 100' circle in tall grass and reeds. 2 stage flight is a go for MWP.