Project
626 Flight and Catastrophic Failure Inhibitor (CFI) static tests

Post-flight Analysis

• This flight marks the 34th consecutive successful firing of a J300 engine without failure. For me, that's a huge accomplishment. The vehicle for this flight differed slightly from the 605 flight vehicle in that the nosecone length was reduced by half and 2" was removed from the upper body assembly. These two changes had a noticeable positive effect on the stability of the vehicle.
• 25' nylon webbing was used for the parachute rigging instead of bungee cord however the ejection charge failed to actuate causing the rocket to crash.
• There was a fantastic 6' tail coming out the end of the rocket. I have no idea where that came from. A 3/4" smoke tracer element was fed in the center of the four engines but I can't see it producing that kind of flame since it was made from Kno3 and sugar itself. Also, later in the flight, the smoke tracer can be seen blowing out the aft end of the rocket as it's falling back to the ground.
• Four J300 engines were used in this flight producing a total impulse of 4800 Newton seconds.
• The rocket was recovered about 1/2 mile downrange. It was on fire, so any analysis of why the delay element didn't work or where the flame tail came from will have to wait for the next launch.
• This flight from launch to impact was 6 seconds shorter than the 605 flight. Not having the wreckage makes it difficult to determine what the difference was. One possibility is that the fin section vent holes on this rocket were a good deal smaller than the 605 flight. It's also possible that it's burning ABS coming out the back due to elevated temperatures in the fin section because of the smaller vent holes.
• Also tested was the new Catastrophic Failure Inhibitor (CFI) device which needs some more work since both the test exploded. The thinking behind the CFI was to produce a device that would allow the case bonded fuel to crack and expand along predetermined fault lines which would be inhibited from burning. A piece of matt board was used for this test as the CFI. The matt board would stick to either side of the fault and inhibit the burn. There were holes in the matt board along it's length and this proved to be a problem. The holes pulled air down into the hot fuel and created more surface area for the fuel to burn.
• More tests will be done in the future with the CFI because I believe it's a valid way to increase the size of case bonded propellants.
• Alberto Gassol from Mexico came up to watch the launch. Alberto has done extensive work with various types of engines including sugar. His page on ceramic nozzle construction for PVC engines can be found here.

Construction

• 6" ABS.
• Four J300 engines.
• Matt board / balsa wood fins.
• Plaster gauze nosecone filled with two part marine foam
• 7' plastic parachute 2 mil thick with 8 lanyards and a 25' x 3/4" nylon webbing strap.
• 33.5 lbs. total take off weight.

Pros

• Stability is perfect.
• Rocket gets good altitude on four J300 engines.
• Having the engines in the center of the rocket reduces the CG shift throughout flight.
• Plenty of space in the nosecone for future video payloads.
• Easy to construct and inexpensive, close to 5000' for $80 isn't bad.

Cons

• Smoke tracer did not work as expected.
• An electronic timer may be better than the chemical delay element for the parachute.

Pictures

Video

• Flight 01
• Static 01 with new CFI
• Static 02 with new CFI

Drawings

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