Level 1 Build Thread - name pending

[Clusterphiliac]

Not really sure what to say as an introduction, but here's my Level 1 Certification build. As a bit of personal background, I've been building rockets since I was twelve, but now I'm finally making the leap to high power. I'm a college sophomore, building this with my school's rocketry club.

The rocket, like most cert builds, is a fairly standard 3FNC. It's 3" diameter and 54.5" tall (not counting about 3/8" of overhanging motor retainer), with a 38mm motor mount. The thing was first designed several years ago, but has gone through a few iterations before I actually ordered parts.

The design - not every component shown.

The airframe and motor mount are standard LOC cardboard tubing, but the coupler is blue tube, which should be a bit stiffer. The fins, bulkheads, and main centering rings are 1/4" plywood, and some minor components are 1/8".

Now, this rocket has a few unusual features. First, the avionics bay is built into the nose cone, and is a "sledless" design. There are three small bays: a pair of 29mm bays sized to accomodate a Raven 3 in a Featherweight 29mm Avbay kit, and a longer BT-60 sized bay in the front for any radio, GPS, or acoustic tracking devices that might be installed. It is dual-deploy; the apogee charge ejects the parachute and nose cone, and the main charge is located in an Archetype Rocketry Cable Cutter. In flight, the airframe never actually separates in the middle; the upper airframe is connected with Apogee's removable rivets. Technically it isn't zipper-proof, but the only part that could ever zipper is the upper airframe, which is very easy to replace.

Now, on to the build.

The first major part I put together is the avionics bay. As previously mentioned there are two altimeter bays (allowing for an upgrade to redundant altimeters), and a tracker/everything else bay. The tubes are just plain old thin-walled "Estes Grade" cardboard. The rings are 1/8" plywood, with the rear ring actually being two rings - one fitting the airframe, one fitting the nose cone shoulder - sandwiched together. The whole thing attaches to the nose cone with a pair of 1/4-20 threaded rods. A 6-32 machine screw and washer fit into a threaded standoff (bottom of the image), holding the altimeters in place.

Meanwhile, here's the motor mount. 9" of LOC 38mm MMT tube with 1/4" plywood centering rings. The rings are in contact with the ends of the fin tabs, providing a very strong assembly. The rear CR is unattached; it goes in later to allow for internal fillets on the fins. The three holes in it are for threaded 6-32 standoffs. As with the altimeter bays, screws and washers are used for motor retention.

Here's the coupler, with a third 1/8" centering ring glued to the aft end. This only comes into play if the motor case is more than 15" long (a Cesaroni 6G or 6GXL), and provides a little bit of extra insurance that the motor stays straight.

This bulkhead (consisting of two 1/4" pieces sandwiched together) goes in the other end of the coupler. It has holes for a short loop of kevlar that I can attach a quick link to. This is only attached AFTER the motor mount and coupler are in the rocket, and the 1/8" has been test-fitted with a motor case and sanded as necessary.

The lower airframe tube is slotted for fins.

This is the avbay mounting ring, a 1/4" ring that gets epoxied into the piece of LOC coupler which serves as a nose cone shoulder and stays there. Two weld nuts epoxied in hold the mentioned 1/4-20 threaded rods that keep the avbay in place.

Here's what that looks like assembled. Note that the nose cone is a plastic one. The shoulder is chopped off and this piece of coupler is epoxied in.

The avbay, test-fit in the shoulder.

And, back at the booster section, the motor mount is epoxied in - but only the front ring. The rear CR was put in place to keep things aligned, but not attached to either the MMT or the airframe. It is removed once the epoxy sets. Off-camera, the coupler has been added as well.

Next, the fins are attached.

Here's the front end of the avbay. This is a foam plug that prevents whatever is in the tracker bay from coming loose and rattling around inside the nose cone. It's held in place by a pair of 6-32 nylon screws, but the threads don't actually do anything. In the background is another of my rockets, Development Hell. Named because it took FOREVER to finish; the fin assembly provides a clue as to why.

 

[Clusterphiliac]

So, you may have noticed a lack of pictures of the coupler actually glued into the nose cone.

This is because, as it turns out, I am a complete idiot and I managed to glue the avbay into the coupler-nose cone assembly. It took over an hour with a dremel to cut the nose cone and shoulder - which where completely unsalvageable - away from the avionics bay. Note: this is still a more than a month ago. I had to order a new nose cone and coupler. In the meantime...

Internal fin fillets were added, followed by external ones. These are epoxy, thickened with tiny glass beads. As it turned out, on the first pass I used too many glass beads, and it was impossible to spread smoothly enough. So, a batch of slightly thinner epoxy was used to fill in the resulting "pits" in the fillets.

The rear centering ring is added, along with the motor retention standoffs.

The bulkhead is finally epoxied in, and the loop of kevlar shock cord is added, along with a quick link. Also note the holes in the coupler for rivets.

Here's a shot of the nose cone with the avionics bay inserted (about time!). I thought I took more pictures than this. Note the addition of another loop of shock cord to the avbay, as well as two aluminum ejection charge holders. These are both for the drogue/apogee charges, there's just space for a backup.

Here's the Featherweight avbay kit assembled, with a nifty addition. This isn't mentioned in the instruction manual, but the active bulkhead has a pair of tiny pieces of metal on the outside labelled "3rd" and "4th." I've soldered on a pair of alligator clips, which should allow me to use all four of the Raven's pyro outputs, allowing backup charges. This avbay will be used in other rockets as well.

And finally, here's everything put together. Off-camera, most of the recovery system has been put together, vent holes for both altimeter bays have been drilled, and shear pin holes have been drilled as well. The recovery system should be ready for ground testing in under a week. The only real "structural" thing left to do is gluing rail guides (the club 3D printed a bunch of surface-mount rail guides) onto the lower airframe. Other than that, it's mostly sanding, filling in tube spirals, and painting.

 

[Rex R]

Hi, welcome to the forum. looks good...I think, hard to tell from the photos. while I enjoy pics as much as the next person. it is easier to grasp what the whole picture is when they are somewhat smaller say, 1200 x 800. please, if you insist on the large image format, use jpeg file format some of us are still on dial up, even dsl takes a long time to down load enormous pictures. thanks
Rex

 

[grouch]

Love the choice of materials. So tired of the glass rockets lately. Good job so far man! Good luck with the flight.

 

[dward]

It isn't immediately clear to me how you will seal up the two small av bays. They seem to be open next to the charge wells. I suspect there is a bulkhead not shown, but I don't know why the charge wells wouldn't be on that. Looking very nice so far.

 

[Clusterphiliac]

The featherweight avbay kit's active bulkhead seals the altimeter off from any ejection gases. I guess it's a little confusing without pictures: I'll post a photo with the altimeter in place as soon as possible.

Unfortunately, the bulkhead doesn't have space for a charge holder once the alligator clips for outputs 3 and 4 are installed, so the charges are located on the aft bulkhead of the main avbay assembly.

 

[crazyed]

Looking great so far !!

 

[Clusterphiliac]

Hey all! It's been a while.

To make a long story short, I finished the rocket, and came up with a name for it: Derecho (a type of storm notable for very strong straight-line winds).

Here it is with the paint on (linked since it's a big image).
https://imgur.com/pdxpBKM

After that, it sat around for a few months before I had an opportunity to fly, at Tripoli Colorado's Hartsel site - this is as far as I know the highest high-power launch site in the country, at 8800 feet ASL.

Here's a "before" picture at the site (linked since it's a big image).
https://imgur.com/pdxpBKM

The launch itself took place on a CTI H225WT with the ejection charge removed, with dual deployment using a Raven 3. The apogee charge, using 1.2 grams of 4F BP, separated the nose cone and pulled out the parachute. At 1000 feet, a cable cutter released the chute bundle and allowed full deployment.

The cert was successful, and the flight looked picture-perfect, but I still have a few mistakes to learn from.

What went right:

• The motor, including removed ejection charge, worked flawlessly (no Hibachi effect from the delay grain). In fact, it came up to pressure instantaneously when the button was pressed, causing me to fail to catch the entire boost on video because I wasn't expecting the rocket to launch so soon.
• The recovery system was also nearly perfect, with the rocket separating cleanly and in the right place at apogee, and full chute deployment 1-2 seconds after the cable cutter fired. No damage was sustained to the recovery system, and the drag of the nose cone and reefed chute was enough to keep the airframe from coming in ballistic and pulling it down.

What went wrong:

• The "sledless" avbay design using drop-in altimeter subassemblies is a sound concept, but the Featherweight avbay kits are really designed to be used in minimum diameter rockets. The assembly was less stiff than I'd have liked, and the magnetic switch was an absolute pain to deal with - it took several minutes of futzing to turn the altimeter on. I plan on keeping the basic concept, but building my own altimeter and battery mounting system, hopefully getting rid of the threaded rods and nuts, using a screw switch instead of the magnet, using a proper terminal block instead of the nuts and alligator clips, and maybe even installing a built-in battery charger.
• The cable cutter did blunt the aluminum piston a bit. I plan on upgrading to a steel one in the near future.
• I learned that while surface-gluing rail buttons to a 2 foot long rocket that weighs under 2 lbs on the pad is okay, when you try it with a nearly 3 lb, 54" long rocket, it is not. The first time I put it on the rail, both rail buttons ripped off. The rocket was repaired thanks to some borrowed superglue, and it flew fine, but at some point (quite likely after landing - see below) the aft rail button ripped off again and was clinging to the rocket by a strip of peeled-up cardboard. I plan to fix this by drilling holes in the tube, injecting some epoxy, screwing the rail buttons into the wet epoxy, and letting it cure.
• The wad of duct tape I wrapped around part of the shock cord as an anti-zipper device came loose during the flight and slid a couple inches up the cord. It didn't zipper, but I'd still like to have some insurance for unusually violent deployments.
• After the rocket landed, the wind picked up and it went windsurfing for what I'd guess was several hundred feet until the shock cord snagged on a piece of vegetation and stopped it. I didn't see this happen, so I was searching the area where I saw the rocket land for quite a while until someone pointed out the bright orange parachute flapping in the breeze. Fortunately, there was little damage from being dragged apart from a little scuffed paint and the previously mentioned aft rail guide.
• It came down a little fast on a 36" chute at 8800 feet (somewhere around 25-30 fps instead of the simulated 15-20). I may use a 48" for flights with larger motors, as well as mostly flying at around 5000 feet.

Max altitude was 2700 feet (a little lower than the simulated 2900 feet, but temperature may have affected this), with a top speed of 480 MPH. The first is a personal record, but the second might have been beaten by an 18mm MD rocket I flew several years ago.

 

[REK]

Haha Derecho is the spanish word for straight. Good one and good work on the rocket and congrats on the flights.

 

[KenRico]

Solid flight and insightful analysis .

3 inches in diameter..you may be able to put together a sled with additional small altimeter like a eGGtimer Quark or a Stratologger CF for redundancy. Double the wiring..double the fun !

Whats next for you?

Kenny