Semroc - PSC Infinity

PSC Infinity is a neat two stage cluster that Semroc offers. Loaded up with two motors in the booster, and two in the sustainer this rocket should really go. The kit was normal Semroc quality, and easy to build. I used Duplicolor High Fill Primer to fill the spirals and wood grain. I had to go with a military type finish since it is way to humid to use anything else. Overall a nice result, can't wait to give it a try.

Definitely an interesting kit. Just make sure that both boosters light on the pad. During the last flight of my PSC Infinity, only one booster lit on the pad, but somehow all four motor were burnt when the rocket was recovered. The unlit booster was ignited from the front end. I have not used any extra tape on the booster motors other than the cellophane tape on the booster-upper stage motor joint.

mwtoelle said:

Definitely an interesting kit. Just make sure that both boosters light on the pad. During the last flight of my PSC Infinity, only one booster lit on the pad, but somehow all four motor were burnt when the rocket was recovered. The unlit booster was ignited from the front end. I have not used any extra tape on the booster motors other than the cellophane tape on the booster-upper stage motor joint.

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Yow, that had to be an ... ummm... 'interesting' flight profile for the booster stage. Heck, for the whole rocket!!

:y::y::y:


Just guessing, things would have to have gone something like this (assuming C6-0/C6-7 motor combo -- fractional-second times are only guesstimates):

Elapsed time 0.00: Motor 1A ignites, 1B does not.

Elapsed time 1.68: Motor 1A burnout/blow-through

Elapsed time 1.683: Motor 2A ignition, stages separate, exhaust flame of 2A directed against top of booster stage

Elapsed time 1.7: Motor 1B ignites at top end when exhaust flame of 2A enters

Elapsed time 1.73: Undirected "reverse thrust" flames from top end of 1B directed against tail end of sustainer stage (separation distance at this point is still only a couple feet)

Elapsed time 1.75: Motor 2B ignites when undirected 'reverse exhaust' from 1B enters its nozzle

Elapsed time 1.9: Motors 1B and 2B reach max thrust. Sustainer now separating rapidly from booster. Booster stage continues wild pinwheel flight with Motor 1B burning "in reverse" with huge thrust (due to full-surface ignition of fuel grain).

Elapsed time 3.4: Motors 1B and 2B burn out. Rocket coasts to ejection at approximately 10.4 seconds ET.

Actually, I used a B6-0 (*2)/ B6-6 (*2) combo on that flight. So, the booster staged a bit lower and flame could be seen coming out the front of the lower stage. One of the booster motors was pulled about one inch forward when the booster was recovered. The interstage area on both stages was a bit scorched. People who think kevlar is fire proof have another thing coming when it burns through and comes loose. YMMV. Other than the damage shown in the pictures, there was no other damage to my rocket, and the upper stage descended normally on parachute. It is nice to see someone else build this rocket.

oh, OK, substituting B's for C's would only change the elapsed-time figures on my sequence above, but still the basic sequence of what happened had to be pretty much like that.

As I speculated it looks like both stages were under the direct blast of an exhaust flame for a fraction of a second.


Just as a final thought I suppose using B's in the lower stage probably increased the chances of this crazy ignition sequence actually happening -- if you had C's in the first stage, first-stage burnout would take place at a higher airspeed, probably making it more likely the booster stage would be kicked into a tumble before this "sequential ignition" could actually take place.

The booster would need bigger fins to tumble. It actually had a streamer that attached to the piece of kevlar in the booster. I am actually glad that I used the B6 motors in the booster. The rocket was at less than a 45 degree angle to the horizon when it staged. If I had used C6s in the booster, there is a good chance of a power prang occurring, which would have destroyed the upper stage. I am not fond of lawn darts, but I really, really hate power prangs.

I have one of these. I got it for a SS in July gift about 2 years ago IIRC.

Haven't had a chance to fly it yet but looking forward to it.

I'll more than likely go with 2 B6-0's in the booster and 2 A8-5's in the sustainer for the maiden flight.

That is what I used for the first flight of my PSC Infinity. That combo will result in a fairly low and slow flight. The really important thing is to make sure that both motors light on the pad. I would use Quest Q2G2 igniters if you have them. I used Estes igniters on the dramatic flight that I described earlier.

That's a really cool kit! I have a Loadstar II, and it's the only 2 stage rocket I've built/flown. A 2 cluster motor boosted rocket is really cool....I may have to add one to my fleet.

I fly a lot of clusters, and since switch to the Q2G2 igniters when they were released I've had no failures. Best LP igniters by far.

Here's mine in flight from a CMASS launch last year. Pictures courtesy of Jim Flis. I was very nervous about flying the 2 to 2 clustered staging arrangement, but it flew beautifully on a B6-0 to B6-6 combination. I was very careful to use the old cellophane tape method of staging, which has always worked for me. The only negative was the streamer in the booster didn't deploy and was rather toasty after the flight. I'll try putting it between the sustainer motors next time.

Great pictures!

A PSC Infinity would be an awesome bird to shoot keychain videos from.

Boosterdude said:

snip... I had to go with a military type finish since it is way to humid to use anything else. Overall a nice result, can't wait to give it a try.

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Really nice build and paint scheme. Tough look'in.

I was unaware (I don't know why) that the PSC Infinity was a cluster. That puts a whole new spin on it.

Agree about the nice paint scheme and built. I have a keychain camera and plan on using it with this rocket.