Competitor 4 First Flight: CTI J1520 Vmax

The Competitor 4 had its first flight on 7-19-14 in Potter NY at the URRG picnic launch. It was a perfect flight to 2792.5 feet, when averaged between both altimeters. Top speed was about 315 mph, and the rocket pulled about 24 Gs (not measured) during the boost. I used my new Mobius HD camera duct taped to the side of the rocket for an onboard video, and my phone for a short ground video.

GROUND VIDEO
ONBOARD VIDEO

Above is a screenshot of the data from SL100 Altimeter. It is interesting to note that the main fired at 700 feet like it was supposed to, and the rocket fell to about 400 feet before it slowed down to its descent rate of about 20 feet per second. It takes a fairly long time for the deployment bag setup to fully deploy. However, it was a perfectly smooth and gentle deployment, and unlike Positive Ascent, the nose cone and pilot chute got out of the way instantly, eliminating the possibility of a fly through of the main.

The weather was not very good. It was drizzling most of the day, including at the time of launch. Fortunately the rocket stayed in sight and didn't get very wet (except for the parachute...more on that later).

I started by packing the drogue and main recovery systems for a ground ejection test to verify adequate black powder quantities. It turned out that 2 grams of powder for the drogue and 3 grams for the main (with two 4-40 shear pins in the nose) was about perfect, and that's what I flew with. The drogue charge ended up seeming slightly too powerful in the air as the forward section pulled the shock cord tight fairly violently. However, the thanks to the shear pins the nose cone (and main parachute) stayed in place.

I had a small electrical issue with the backup electronics. I couldn't get the altimeter to turn on once we were at the pad ready for flight. I took the rocket down and took it apart to inspect. Using a volt meter, I was able to determine that the battery was plenty good and providing the correct voltage. I also verified that the switch was creating continuity properly. By removing the wires that run from the battery holder to the altimeter power port, I was able to find that the voltage was near zero at the ends of the wires. However, each wire individually had proper (near zero) resistance when measured. This led me to assume there was an intermittent connection in one of the two wires that I still have not been able to reproduce.

To temporarily fix the issue so I could still fly with backup electronics, I zip tied a separate 9 volt battery to one of the threaded rods, and crudely twisted and taped wires together to attach to the power port of the altimeter. The worst case scenario is that a wire could have come loose and the SL100 altimeter should still do its job just fine.

When we got to the pad the second time, I was sure everything would be fine now, but it wasn't. Unbelievably, the same exact issue - the HA45k altimeter would not turn on. I very nearly decided to just fly without backup electronics, but Jim Livingston (thanks Jim) told me it's not worth the risk. So again, we took the rocket down (to the dismay of a dozen or more spectators who had been waiting to see a "big" rocket fly), took the electronics bay apart, and tested and inspected. This time, I realized pretty quickly that I made a serious and seriously simple mistake. I had forgotten to check polarity of the battery that I just rigged into the rocket. Sure enough it was backwards, and the altimeter is smart enough to protect itself from reversed polarity. After swapping the polarity, we were off to the pad for the third time. This time everything turned on as expected and we were finally able to walk back to the flight line.

Following are pictures from the launch. Many thanks to Sab Okazaki for troubleshooting help, and for many of the great action shots, and thanks to Jim Livingston and Ben Rothstein for assistance during the launch.

One of the two trips back from the pad to investigate electronics issues.

An interesting shot just after burnout. It is unusual to see a rocket this close in a photo with no smoke or flame visible. Since the Vmax motor was so fast, burnout occurred at about 100 feet. The rocket is still moving at over 300 mph in this shot which is why the tracking smoke is not visible.

Descending with the new 24" X-form drogue parachute from Top Flight Recovery.

Successful main deployment. Both the main rocket (under main parachute) and the nose cone and deployment bag (descending under the 24" pilot chute) are visible.

The main parachute landed in the irrigation ditch. It took a good amount of force to lift it out of the water as it had scooped up a bunch of water. I'm lucky it wasn't much closer or the electronics bay would have landed in the water.

Carrying the rocket and wet parachute back.

Competitor 4 Is Nearly Ready to Launch

The rocket is basically ready for launch hopefully this Saturday (7-19-14). I have the J1520 Vmax motor purchased and assembled for its first flight. It will be an aggressively fast accelerating launch, but only about 2500 feet in altitude.

I have done a lot of work on the recovery systems since the last update, and I do not have pictures at this time. Due to the higher weight of the rocket than I anticipated, I purchased a 70" Top Flight parachute for the main. I also purchased new chute protectors, a new 24" pilot chute, and a new 24" X form drogue chute. I realized that the technique for deployment of the main that I showed in my last post was extremely risky because it would allow the main to begin to open with the nose cone and pilot chute above it, in a position to fly through it. That being said, I will simply be "free bagging" the nose cone on the first flight which means I will have 2 pieces to recover. I have also prepared a 3 gram main charge for a ground test and a 2 gram drogue charge to ground test the ejections before the first flight.

Below is the additional progress (with pictures) since the last update.

Installing Rail Buttons

The rail buttons are the guides that the rocket slides onto the launch pad with. There are 2 standard sizes: 1" (called 1010) and 1.5" (called 1515) rails. Since this rocket is small enough for 1" rails, but may eventually fly on M motors (and launch pads for M motors generally have the bigger rail), I decided to make the rail buttons removable so I can accommodate either size. That way, I can fly it at the minimum "safe" distance away for any motor.

I mounted the two lower rail buttons on the forward and aft centering rings of the motor mount. This meant that I had to do some tricky aligning to ensure that the holes in the body tube were in the exact spots that coincide with the hex nuts epoxied in place to take the rail button hardware. I may use a third rail button. If I do, it will be attached to the electronics bay, which is how I did it in Positive Ascent.

I used a card between the fins to mark the exact center. Then ran a string to the very tip of the nose cone. By eyeballing down the length of the rocket, I could easily set the string so it was exactly straight. This is what I used as my reference to mark the locations for the two rail buttons.

The tape is marking where the centering ring is, and the nut was used to locate where to drill the hole through the body tube. By allowing the drill to go beyond the body tube to nick the motor mount tube, I was able to mark exactly where to tack glue the hex nut on the centering rings.

The forward rail button tack glued in place with the 8-32 hardware sticking out to adjust the angle of the nut to ensure it's square. I used a piece of straw between the nut and motor tube to seal the threads and space behind it from epoxy.

I built up a tape barrier around the nut. I used this space to fill with epoxy, which I had mixed with milled fiberglass for strength.

This is the forward rail button mount, complete with the large chunk of epoxy to keep it solid.

Same process for the aft rail button mount.

Completed aft rail button mount.

Everything lines up beautifully. Here are the 1515 rail buttons installed.

Here are the 1010 rail buttons installed. It takes less than a minute to change them.

Motor Mount/ Fin Can

I finished up the fin can assembly. This required completing all of the JB Weld fillets and finishing the shock cord mount.

All the gray is the JB Weld fillets.

The shock cord mount is finished. I saturated the knot and trailer with 5 minute epoxy. Note the electrical tape wrapped around the shock cord where it lies against the end of the motor mount tube. This will prevent the sharp edges of the fiberglass tube from slowly wearing the Kevlar strands.

Fin Can Installation

To install the fin can into the body tube, I had to ensure the JB Weld and epoxy had good surfaces to bond to. This meant a combination of 100 grit sandpaper and using the end of a needle file to scrape and sand all areas inside the body tube, on the outside of the motor tube.

The sanded internal fillet and future fillet locations.

The three centering ring locations, and the areas along the fin slots, all roughed up.

I used a band of tape and many rubber bands to hold the aft portion of the body tube against the aft centering ring.

Verifying that the JB Weld hasn't leaked past the centering ring.

Looking into the forward end of the body tube. You can see that the JB Weld did a good job of filling in the space on top of the centering ring. Hopefully, enough bonded to the body tube as well.

Electronics Sled

I thought I had finished the electronics sled, but I decided it couldn't hurt to add some reinforcement, especially for potentially ridiculous G loads. The J1520 for the first flight will actually pull over 20Gs, which is kind of a lot for a rocket of this size, but I'm confident it can take it and much more.

Since the two rotary switches are armed through small holes in the airframe tube , it was very awkward trying to line the screwdriver up with them. I made some simple (not so elegant) cones from index cards to guide the screwdriver to the switch. It works really well.

Showing one switch with the cone, one without.

Both cones glued in place.

The custom (end ground down some) screwdriver for arming the altimeters.

I added a foam block and epoxied the power wires to it. This will ensure that the wires can't pull out from the altimeters during acceleration.

Two foam blocks on the back of the board. These run from the switches, through the board, to the switch terminals on the altimeters. Again, these blocks are to reduce stress on the wires and switches during acceleration. The orange block is the 9 volt batteries taped in. Since this picture was taken I have also added a zip tie around the forward end of the batteries for extra security.

Internal Fillets

To create the internal fin/ body tube joints, I masked the area of interest on the outside of the rocket, then drilled holes at about the middle of the fin length through the tube. I made small funnels out of card stock and poured about 1 ounce of West Systems epoxy into each hole. I did either side of one fin at a time. Once all the epoxy was in place, I taped over the holes and set the rocket so the epoxy would run and settle into the intended joint areas.

External Fillets

To create the external fin fillets, I masked off the area and poured 1/2 ounce of West Systems epoxy into each joint. I leveled the rocket to allow 2 fillets at a time to form into the correct spots. This technique gives very nice fillets except for the ends, where the epoxy forms flat "walls" against the tape that will have to be ground away with a Dremel tool.

Aft end of a fillet taped off.

Forward end of a fillet taped off.

Both fillets ready for epoxy.

Epoxy is poured into each fillet.

Body Tube Slots

I used JB Quick Weld to fill in the slots at the end of the airframe tube. I'm not sure if they are strong enough, but they are purely cosmetic anyway.

I notched each slot in several spots with a file to provide more surface area for the JB Weld to bond to. You can see the saw tooth shape of these notches.

Motor Retainer

I mounted the 75mm Slimline motor retainer. I used regular cure JB Weld for this step.